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Abstract: In this work, a surface modified Nafion 212 membrane was fabricated by plasma etching in order to enhance the performance of a membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell. Single-cell performance of MEA at 0.7V was increased by about 19% with membrane that was etched for 10min compared to that with untreated Nafion 212 membrane. The MEA with membrane etched for 20min exhibited a current density of 1700mAcm−2 at 0.35V, which was 8% higher than that of MEA with untreated membrane (1580mAcm−2). The performances of MEAs containing etched membranes were affected by complex factors such as the thickness and surface morphology of the membrane related to etching time. The structural changes and electrochemical properties of the MEAs with etched membranes were characterized by field emission scanning electron microscopy, Fourier transform-infrared spectrometry, electrochemical impedance spectroscopy, and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Abstract: A solid solution of spinel (2/3)Li(Li1/3Ti5/3)O4–(1/3)Li(Ni1/2Ti3/2)O4 was prepared, and its structural/electrochemical properties were compared with Li(Li1/3Ti5/3)O4 to identify the effect of doping to the structural invariance of Li(Li1/3Ti5/3)O4. The solid solution retained the zero strain characteristic of Li(Li1/3Ti5/3)O4 during discharge/charge with an excellent cycle stability, while the rate capability was notably improved. However, a reversible broadening of the XRD peak was observed at the end of discharge, indicating some structural changes. XANES measurements showed that the oxidation state of Ti was +4 and that of Ni was +2 in the solid solution. [Copyright &y& Elsevier]

The continuous activation of electrolyte-derived surface layer contributes the abnormal high specific capacity and capacity increase of ordered mesoporous Co 3 O 4 anode material. [Display omitted] • The anomalous electrochemical phenomenon of ordered mesoporous Co 3 O 4 anode material. • The reversible conversion reaction for mesoporous Co 3 O 4 by low bond strength. • The significance of mesoporous structure on the electrolyte-derived surface layer. Nanostructured engineering is one of the strategies for optimizing transition metal oxides as anode materials in lithium-ion batteries. Among them, mesoporous structures have received significant attention due to their intrinsic properties which are related to porous structure. This structure provides short Li-ion diffusion pathways and acts as a buffer for volume changes during electrochemical reactions, affecting various electrochemical properties and performances. One of the intriguing aspects of the mesoporous structure effect is that it sometimes triggers a negative fading. Herein, we observed that ordered mesoporous Co 3 O 4 exhibits a higher reversible capacity and anomalous cycle behavior that capacity increases during cycling, known as a negative fading, compared to bulk Co 3 O 4. Moreover, the observed capacity is even higher than its theoretical capacity. Mesoporous Co 3 O 4 exhibits stable and more reversible conversion reactions, and even gradually activated electrolyte-derived surface layer formation/decomposition during cycling. Based on combined synchrotron-based X-ray analyses and electrochemical tests, we found the weaker Co-O and Co-Co bond strength in mesoporous material than those in the bulk material, gives rise to a more reversible conversion reaction during cycling. In addition, the distinctive structural properties of mesoporous leads to the further formation/decomposition of electrolyte-derived surface layer, resulting in the negative fading. [ABSTRACT FROM AUTHOR]

In Sodium-ion capacitors (SICs), employing high-capacity anodes based on alloying/conversion reactions can potentially alleviate the performance issues but are susceptible to rapid capacity fading due to consistent dissolution of the electrode surface by the electrolyte. Herein, we extend the "hybrid mixed electrolyte" strategy to ion capacitors for overcoming the rapid cycle decay issues in high-energy SICs: molybdenum disulphide (MoS 2 , MS) nanocrystals grown on carbon nitride (C 3 N 4 , CN), denoted as MS/CN, as anode exhibited remarkable performance in both sodium electrolyte and replaced with a hybrid mixed electrolyte comprising larger Na+ ions and smaller Li+ ions. Thus, constructed SICs exhibited a high energy density of 124 Wh Kg−1 with a mixed ion electrolyte, and low energy loss (71% retention after 40000 cycles) with a hybrid electrolyte (lower than conventional sodium-ion-based electrolyte: 37% retention after 15000 cycles). Systematic investigations, including X-ray photoelectron spectroscopy and electron probe microanalysis, revealed an advantageous formation of a stable interface for electrode and electrolyte. [Display omitted] • Sodium ion vs Mixed ion hybrid capacitor. • Stability more than two-fold (40000 cycles). • XPS and electron probe micro analysis (EPMA) mapping to unravel mechanism. • Schematic of S dissolution in presence of Na ion and mixed ion/hybrid. [ABSTRACT FROM AUTHOR]

Nanostructured materials for lithium-ion batteries (LIBs) have many advantages over bulk electrode materials, and therefore, such materials should be effectively utilized in next-generation batteries. Herein, we identify that the superior performances of mesoporous Mn 2 O 3 results from the different lithium storage behaviors of mesoporous and bulk Mn 2 O 3. X-ray absorption spectroscopy (XAS) and bond strength calculation show that mesoporous Mn 2 O 3 has a larger capacity than bulk Mn 2 O 3 owing to an additional oxidation of Mn2+ to a higher oxidation state during charging, as well as an additional reversible reaction during cycling because the weaker Mn–O bond strength of mesoporous Mn 2 O 3 requires much less strength to break or form atomic bonds during the electrochemical reactions. Furthermore, the combined results of X-ray photoelectron spectroscopy and soft XAS indicate that an additional lithium storage reaction through the reversible formation–decomposition of the electrolyte-derived surface layer occurs more in mesoporous Mn 2 O 3 than in bulk Mn 2 O 3. Consequently, the improvement in the lithium storage behavior of mesoporous Mn 2 O 3 due to the increasing specific surface area and decreasing particle size with the progression of cycles, also affects their cycle performances. This study provides a better understanding of the synergistic relationship between nanostructures and the electrochemical performances of anode materials for LIBs. • Comparison of lithium storage behaviors between mesoporous Mn 2 O 3 and bulk Mn 2 O 3. • Weaker Mn–O bond strength of mesoporous Mn 2 O 3 causes further oxidation reaction. • Capacity due to the electrolyte-derived surface layer is larger in mesoporous Mn 2 O 3. • Structural changes after cycling affect the cycle performance of mesoporous Mn 2 O 3. [ABSTRACT FROM AUTHOR]

Lithium-ion hybrid capacitors (LICs) take the advantage of simultaneous high energy – power output, and become increasingly important for next generation applications. Developing a high performing LICs with high energy-power-cycle combination remains a significant challenge due to low capacity intercalation electrodes, and kinetically sluggish alloying type electrodes. A strategy employing fast pseudocapacitive lithium ion storage in high-capacity alloying type anode, rather than a bulk storage, can output kinetically superior LICs with high energy even at high power conditions. Herein, we demonstrate a highly interconnected 3-dimensional (3D) SiO 2 nanospheres embedded Nitrogen-doped carbon shell with fast lithium ion storage kinetics as high performing anode for LICs. As a result, LIC with a high energy (139 Wh kg−1), high power density (42 kW kg−1), and super stability (20,000 cycles) is obtained, outperforming previously studied alloying type metal oxide and sulfide anodes. A flexible LICs is further demonstrated which shows good stability under different bending conditions. The current research promotes the practical utilization of earth-abundant material as a high capacity and high rate electrode for the next-generation flexible and wearable devices. Flexible Quasi-Solid-State Lithium-Ion Capacitors Employing Amorphous SiO 2 Nanospheres Encapsulated in Nitrogen-Doped Carbon Shell as a High Energy Anode. Image 1 • Highly interconnected 3D SiO 2 nanospheres embedded Nitrogen-doped carbon shell. • SiO 2 exhibits pseudocapacitive effect to enable a fast charge storage process. • The Li-ion capacitor delivers high energy (139 Wh kg−1) and power (42 kW kg−1). • Flexible Li-ion capacitor has stability at different bending conditions. [ABSTRACT FROM AUTHOR]

• The Na 3 V 2 (PO 4) 2 F 3 with reduced-graphene oxide composite calcined at 650 ℃ exhibited excellent cycling and rate capability. • Using carboxymethyl cellulose binder and dimethyldiglycol electrolyte in Na 3 V 2 (PO 4) 2 F 3 improved electrochemical performance. • Full cell test with Na 3 V 2 (PO 4) 3 anode delivers stable discharge capacity at 2 C rate. Sodium-ion batteries have gained an intense attention as a promising alternate for Li-ion batteries due to their low cost, and abundant availability. To meet high energy density requirements, developing a high voltage cathode with ultra-long cycle life is of great importance. Na 3 V 2 (PO 4) 2 F 3 (NVPF) features a high working voltage, fast sodium-ion diffusion channels, and small volume change during the cycling process. However, the practical performance of NVPF cathode is currently hindered by poor Na+ ion diffusion at high voltage, low cycle life, and limited rate behavior. Herein, we evaluate the effect of synthesis conditions in sol–gel technique, binders (PVDF, PAI and CMC), and electrolytes (ether, and ester based solvents) to overcome the diffusion limitation in high voltage NVPF cathode. Benefiting from the synergistic effect of CMC binder, and DEGME electrolyte, and reduced graphene oxide composite, NVPF effectively overcome the potential barrier during Na+ ion insertion/extraction at high voltage. NVPF with CMC binder and DEGDME electrolyte displayed a high Na+ ion diffusion kinetics, low cell resistance, and delivered an excellent electrochemical performance. NVPF delivered a high coulombic efficiency (92%), long cycle life (10,000 cycles), and an excellent rate performance (50 C), outperforming the conventional PVDF binder, and carbonate based electrolytes. Furthermore, the full-cell constructed by NVPF cathode, and Na 3 V 2 (PO 4) 3 anode delivered an capacity retention. The current study provides new insights for overcoming the kinetic barrier during sodium ion storage in high voltage cathode that could direct the research development towards high energy sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Ni-rich layered oxide cathodes with Ni content above 80% have considerable potential for Li rechargeable batteries due to their high capacity and low cost. However, what with stability issues, inferior cycle performance and thermal instability, studies are still underway to improve their performance. Herein, Al-doped Ni-rich (LiNi 0. 80 Co 0. 15 Mn 0. 05 O 2) cathode is investigated to stabilize structural, electrochemical, and thermal properties. Compared to undoped one, Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO 6 interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Furthermore, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction. Therefore, this study provides structural aspects of Al-doping effects on the stabilization of layered cathode materials for the high energy density of rechargeable batteries. • Al-doping in Ni-rich cathodes alleviates abrupt lattice changes during cycling. • Al-doped NCM maintains wider LiO 6 interslab thickness at highly charged states. • The rigid structural integrity of Al-doped NCM enhances electrochemical properties. • Al-doping improves the thermal stability of Ni-rich layered cathodes. [ABSTRACT FROM AUTHOR]

Anode materials storing large-scale lithium ions gradually decrease electrochemical performance due to severe volume changes during cycling. Therefore, there is an urgent need to develop anode materials with high electrochemical capacity and durability, without deterioration arising due to the volume changes during the electrochemical processes. To date, mesoporous materials have received attention as anode materials due to their ability to mitigate volume expansion, offer a short pathway for Li + transport, and exhibit anomalous high capacity. However, the nano-frameworks of transition metal oxide collapse during conversion reactions, demanding an improvement in nano-framework structure stability. In this study, ordered mesoporous nickel manganese oxide (m-NMO) is designed as an anode material with a highly durable nanostructure. Interestingly, m-NMO showed better cycle performance and higher electrochemical capacity than those of nickel oxide and manganese oxide. Operando small-angle X-ray scattering and ex situ transmission electron microscopic results confirmed that the binary m-NMO sustained a highly durable nanostructure upon cycling, unlike the single metal oxide electrodes where the mesostructures collapsed. Ex situ X-ray absorption spectroscopy proved that nickel and manganese showed different electrochemical reaction voltages, and thus undergoes sequential conversion reactions. As a result, both elements can act as complementary nano-propping buffers to maintain stable mesostructure., (© 2024 Wiley‐VCH GmbH.)

In this study, the one-dimensional (1D) material V 2 Se 9 was successfully synthesized using a colloidal method with VO(acac) 2 and Se powder as precursors in a 1-octadecene solvent. The obtained colloidally synthesized V 2 Se 9 (C-V 2 Se 9 ) has an ultrathin nanobelt shape and a 4.5 times higher surface area compared with the bulk V 2 Se 9 , which is synthesized in a solid-state reaction as previously reported. In addition, all surfaces of C-V 2 Se 9 are exposed to Se atoms, which is advantageous for storing Li through the conversion reaction into the Li 2 Se phase. Herein, the electrochemical performance of the C-V 2 Se 9 anode material is evaluated; thus, the novelty of C-V 2 Se 9 as a Se-rich 1D anode material is verified. The C-V 2 Se 9 electrode exhibits a reversible capacity of 893.21 mA h g -1 and a Coulombic efficiency of 97.82% at the 100th cycle and excellent structural stability. Compared with the bulk V 2 Se 9 electrode, the outstanding electrochemical performance of C-V 2 Se 9 is attributed to its ultrathin nanobelt shape, high surface area, shorter Li diffusion length, and more electrochemically active sites. This work indicates the great potential of the Se-rich 1D material, C-V 2 Se 9 , as a post-transition metal dichalcogenide material for high-performance LIBs.

All-solid-state lithium batteries have been developed to secure safety by substituting a flammable liquid electrolyte with a non-flammable solid electrolyte. However, owing to the nature of solids, interfacial issues between cathode materials and solid electrolytes, including chemical incompatibility, electrochemo-mechanical behavior, and physical contact, pose significant challenges for commercialization. Herein, critical factors for understanding the performance of all-solid-state batteries in terms of solid interfaces and non-zero lattice strains are identified through a strategic approach. The initial battery capacity can be increased via surface coating and electrode-fabrication methods; however, the increased lattice strain causes significant stress to the solid interface, which degrades the battery cycle life. However, this seesaw effect can be alleviated using a more compacted electrode microstructure between the solid electrolyte and oxide cathode materials. The compact solid interfaces contribute to low charge-transfer resistance and a homogeneous reaction between particles, thereby leading to improved electrochemical performance. These findings demonstrate, for the first time, a correlation between the uniformity of the electrode microstructure and electrochemical performance through the investigation of the reaction homogeneity among particles. Additionally, this study furthers the understanding of the relationship between electrochemical performance, non-zero lattice strain, and solid interfaces., (© 2023 Wiley-VCH GmbH.)

Campanula carpatica is an ornamental flowering plant belonging to the family Campanulaceae. The complete chloroplast genome of C. carpatica was obtained using Illumina HiSeq X and Oxford Nanopore (Nanopore GridION) platforms. The chloroplast genome exhibited a typical circular structure with a total length of 169,341 bp, comprising a large single-copy region of 102,323 bp, a small single-copy region of 7744 bp, and a pair of inverted repeats (IRa/IRb) of 29,637 bp each. Out of a total 120 genes, 76 were protein-coding genes, 36 were transfer RNA genes, and eight were ribosomal RNA genes. The genomic characteristics of C. carpatica are similar to those of other Campanula species in terms of repetitive sequences, sequence divergence, and contraction/expansion events in the inverted repeat regions. A phylogenetic analysis of 63 shared genes in 16 plant species revealed that Campanula zangezura is the closest relative of C. carpatica . Phylogenetic analysis indicated that C. carpatica was within the Campanula clade, and C. pallida occupied the outermost position of that clade.

Although Li- and Mn-rich layered oxides are attractive cathode materials possessing high energy densities, they have not been commercialized owing to voltage decay, low rate capability, poor capacity retention, and high irreversible capacity in the first cycle. To circumvent these issues, we propose a Li 1.2 Ni 0.13 Co 0.13 Mn 0.53 Nb 0.01 O 2 (Nb-LNCM) cathode material, wherein Nb doping strengthens the transition metal oxide (TM-O) bond and alleviates the anisotropic lattice distortion while stabilizing the layered structure. During long-term cycling, maintaining a wider LiO 6 interslab thickness in Nb-LNCM creates a favorable Li + diffusion path, which improves the rate capability. Moreover, Nb doping can decrease oxygen loss, suppress the phase transition from layered to spinel and rock-salt structures, and relieve structural degradation. Nb doping results in less capacity contributions of Mn and Co and more reversible Ni and O redox reactions compared to pristine Li 1.2 Ni 0.133 Co 0.133 Mn 0.533 O 2 (LNCM), which significantly mitigates the voltage decay (Δ0.289 and Δ0.516 V for Nb-LNCM and LNCM, respectively) and ensures stable capacity retention (82.7 and 70.3% for Nb-LNCM and LNCM, respectively) during the initial 100 cycles. Our study demonstrates that Nb doping is an effective and practical strategy to enhance the structural and electrochemical integrity of Li- and Mn-rich layered oxides. This promotes the development of stable cathode materials for high-energy-density lithium-ion batteries.

Iron oxide anode materials for rechargeable lithium-ion batteries have garnered extensive attention because of their inexpensiveness, safety, and high theoretical capacity. Nanostructured iron oxide anodes often undergo negative fading, that is, unconventional capacity increase, which results in a capacity increasing upon cycling. However, the detailed mechanism of negative fading still remains unclear, and there is no consensus on the provenance. Herein, we comprehensively investigate the negative fading of iron oxide anodes with a highly ordered mesoporous structure by utilizing advanced synchrotron-based analysis. Electrochemical and structural analyses identified that the negative fading originates from an optimization of the electrolyte-derived surface layer, and the thus formed layer significantly contributes to the structural stability of the nanostructured electrode materials, as well as their cycle stability. This work provides an insight into understanding the origin of negative fading and its influence on nanostructured anode materials.

In this study, four different MnO 2 polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion-based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low-crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion-based materials. Thus, differences in the ion storage behaviors among various MnO 2 polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO 2 polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel-phased MnO 2 formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel-type λ-MnO 2 delivers the highest reversible capacity of ≈1270 mAh g -1 . The structural similarity between the cycled and pristine states of λ-MnO 2 induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high-performance materials for next-generation rechargeable batteries., (© 2021 Wiley-VCH GmbH.)

Sodium-ion batteries (SIBs) have become increasingly important as next-generation energy storage systems for application in large-scale energy storage. It is very crucial to develop an eco-friendly and green SIB technique with superior performance for sustainable future use. Replacing the conventional inorganic electrode materials with green and safe organic electrodes will be a promising approach. However, the poor electrochemical kinetics, unstable electrode-electrolyte interface, high solubility of the electrodes in the electrolyte, and large amount of conductive carbon present great challenges for organic SIBs. In this study, the issues of organic electrodes are addressed through atomic-level manipulation of these organic molecules using a series of ultrathin (Å-level) metal oxide coatings (Al 2 O 3 , ZnO, and TiO 2 ). Uniform and precise coatings on the perylene-3,4,9,10-tetracarboxylicacid dianhydride by gas-phase atomic layer deposition technique shows a stable interphase, enhanced electrochemical kinetics (71C, 10 A g -1 ), and excellent stability (89%-500 cycles) compared to conventional organic electrode (70%-200 cycles). Further studies reveal that the chemical stability of the metal oxide coating layer plays a critical role in influencing the redox behavior, and improving kinetics of organic electrodes. This study opens a new avenue for developing high-energy organic SIBs with performance equivalent to inorganic counterparts., (© 2020 Wiley-VCH GmbH.)

To meet the growing demand for global electrical energy storage, high-energy-density electrode materials are required for Li-ion batteries. To overcome the limit of the theoretical energy density in conventional electrode materials based solely on the transition metal redox reaction, the oxygen redox reaction in electrode materials has become an essential component because it can further increase the energy density by providing additional available electrons. However, the increase in the contribution of the oxygen redox reaction in a material is still limited due to the lack of understanding its controlled parameters. Here, it is first proposed that Li-transition metals (TMs) inter-diffusion between the phases in Li-rich materials can be a key parameter for controlling the oxygen redox reaction in Li-rich materials. The resulting Li-rich materials can achieve fully exploited oxygen redox reaction and thereby can deliver the highest reversible capacity leading to the highest energy density, ≈1100 Wh kg -1 among Co-free Li-rich materials. The strategy of controlling Li/transition metals (TMs) inter-diffusion between the phases in Li-rich materials will provide feasible way for further achieving high-energy-density electrode materials via enhancing the oxygen redox reaction for high-performance Li-ion batteries., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lithium-sulfur batteries are attractive candidates for next generation high energy applications, but more research works are needed to overcome their current challenges, namely: (a) the poor electronic conductivity of sulfur, and (b) the dissolution and migration of long-chain polysulfides. Inspired by eco-friendly and bio-derived materials, we synthesized highly porous carbon from cinnamon sticks. The bio-carbon had an ultra-high surface area and large pore volume, which serves the dual functions of making sulfur particles highly conductive and acting as a polysulfide reservoir. Sulfur was predominantly impregnated into pores of the carbon, and the inter-connected hierarchical pore structure facilitated a faster ionic transport. The strong carbon framework maintained structural integrity upon volume expansion, and the unoccupied pores served as polysulfide trapping sites, thereby retaining the polysulfide within the cathode and preventing sulfur loss. These mechanisms contributed to the superior performance of the lithium-sulfur cell, which delivered a discharge capacity of 1020 mAh g -1 at a 0.2C rate. Furthermore, the cell exhibited improved kinetics, with an excellent cycling stability for 150 cycles with a very low capacity decay of 0.10% per cycle. This strategy of combining all types of pores (micro, meso and macro) with a high pore volume and ultra-high surface area had a synergistic effect on improving the performance of the sulfur cathode.

The ever-growing demand for high-energy lithium-ion batteries in portable electronics and electric vehicles has triggered intensive research efforts over the past decade. An efficient strategy to boost the energy and power density of lithium-ion batteries is to increase the Ni content in the cathode materials. However, a higher Ni content in the cathode materials gives rise to safety issues. Herein, thermal expansion and oxygen vacancies are proposed as new critical factors that affect the thermal stability of charged Ni-rich cathode materials based on a systematic synchrotron-based X-ray study of Li 0.33 Ni 0.5+ x Co 0.2 Mn 0.3- x O 2 ( x = 0, 0.1, 0.2) cathode materials during a heating process. Charged cathode materials with higher Ni contents show larger thermal expansion, which accelerates transition metal migration to the Li layers. Oxygen vacancies are formed and accumulate mainly around Ni ions until the layered-to-spinel phase transition begins. The oxygen vacancies also facilitate transition metal migration to the Li layers. Thermal expansion and the presence of oxygen vacancies decrease the energy barrier for cation migration and facilitate the phase transitions in charged cathode materials during the heating process. These results provide valuable guidance for developing new cathode materials with improved safety characteristics., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.)

Layered-layered composite (xLi 2 MnO 3 ·(1 -x) LiMO 2 , M = Mn, Ni, Co, and Fe) cathode materials have attracted much attention as cathodes for high energy density lithium ion batteries. However, these materials are structurally unstable resulting from complicated phase transformation mechanisms during cycling. Additionally, the complex structural characteristics and structural stability of these materials largely depend on their preparation methods. Studying the correlation between multiscale structural properties and preparation methods is important in the development of layered-layered composite cathode materials. In this work, 0.5Li 2 MnO 3 ·0.5LiCoO 2 composite materials were prepared with different heating and cooling rates with a maximum temperature of 600 °C. The structural properties of the 0.5Li 2 MnO 3 ·0.5LiMO 2 composite materials were investigated using combined in situ X-ray absorption spectroscopy (XAS), in situ X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high resolution transmission electron microscopy (HRTEM) techniques. Heating and cooling rates have no significant effect on either the crystal or local atomic structures of the prepared samples. However, the microstructure was critically important for its impact on electrochemical properties.

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.)

The anionic redox chemistries of layered cathode materials have been in focus recently due to an intriguing phenomenon that cannot be described by the number of electrons of transition metal ions. However, even though several studies have investigated the anionic redox chemistry of layered materials in terms of the charge compensation, the relationship between the origin of the structural behavior and anionic redox chemistry in layered materials remains poorly understood. In addition, a simultaneous redox process of transition metal ions could occur through the d bands interaction. Here, it is demonstrated that the anionic redox chemistry is associated with the anisotropic structural behavior of the layered cathode materials albeit without providing additional capacities exceeding the theoretical values. These findings will provide a foundation of a new chapter in the understanding of the properties of materials., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Beyond a traditional view that metal nanoparticles formed upon electrochemical reaction are inactive against lithium, recently their electrochemical participations are manifested and elucidated as catalytic and interfacial effects. Here, ruthenium metal composed of ≈5 nm nanoparticles is prepared and the pure ruthenium as a lithium-ion battery anode for complete understanding on anomalous lithium storage reaction mechanism is designed. In particular, the pure metal electrode is intended for eliminating the electrochemical reaction-derived Li 2 O phase accompanied by catalytic Li 2 O decomposition and the interfacial lithium storage at Ru/Li 2 O phase boundary, and thereby focusing on the ruthenium itself in exploring its electrochemical reactivity. Intriguingly, unusual lithium storage not involving redox reactions with electron transfer but leading to lattice expansion is identified in the ruthenium electrode. Size-dependent charge redistribution at surface enables additional lithium adsorption to occur on the inactive but more environmentally sensitive nanoparticles, providing innovative insight into dynamic electrode environments in rechargeable lithium chemistry., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recently, we synthesized a one-dimensional (1D) structure of V 2 Se 9 . The 1D V 2 Se 9 resembles another 1D material, Nb 2 Se 9 , which is expected to have a direct band gap. To determine the potential applications of this material, we calculated the band structures of 1D and bulk V 2 Se 9 using density functional theory by varying the number of chains and comparing their band structures and electronic properties with those of Nb 2 Se 9 . The results showed that a small number of V 2 Se 9 chains have a direct band gap, whereas bulk V 2 Se 9 possesses an indirect band gap, like Nb 2 Se 9 . We expect that V 2 Se 9 nanowires with diameters less than ∼20 Å would have direct band gaps. This indirect-to-direct band gap transition could lead to potential optoelectronic applications for this 1D material because materials with direct band gaps can absorb photons without being disturbed by phonons., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

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 conventional view of conversion reaction is based on the reversibility, returning to an initial material structure through reverse reaction at each cycle in cycle life, which impedes the complete understanding on a working mechanism upon a progression of cycles in conversion-reaction-based battery electrodes. Herein, a series of tin-doped ferrites (Fe 3- x Sn x O 4 , x = 0-0.36) are prepared and applied to a lithium-ion battery anode. By achieving the ideal reoxidation into SnO 2 , the Fe 2.76 Sn 0.24 O 4 composite anchored on reduced graphene oxide shows a high reversible capacity of 1428 mAh g -1 at 200 mA g -1 after 100 cycles, which is the best performance of Sn-based anode materials so far. Significantly, a newly formed γ-FeOOH phase after 100 cycles is identified from topological features through synchrotron X-ray absorption spectroscopy with electronic and atomic structural information, suggesting the phase transformation from magnetite to lepidocrocite upon cycling. Contrary to the conventional view, our work suggests a variable working mechanism in an iron-based composite with the dynamic phases from iron oxide to iron oxyhydroxide in the battery cycle life, based on the reactivity of metal nanoparticles formed during reaction toward the solid electrolyte interface layer.

High theoretical capacity and low-cost copper sulfide (Cu x S)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (Na x S) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous Cu x S with a large surface area embedded in the MOF-derived carbon network (Cu x S-C) through a two-step process of sulfurization and carbonization via H 2 S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu 1.8 S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu 1.8 S-C/C core/shell anode materials than that of pure Cu 1.8 S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu 1.8 S-C to accommodate the volume variation of the Cu 1.8 S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of Na x S into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu 1.8 S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Lithium rich layered oxide xLi 2 MnO 3 ∙(1-x)LiMO 2 (M = Mn, Co, Ni, etc.) materials are promising cathode materials for next generation lithium ion batteries. However, the understanding of their electrochemical kinetic behaviors is limited. In this work, the phase separation behaviors and electrochemical kinetics of 0.5Li 2 MnO 3 ∙0.5LiCoO 2 materials with various Li 2 MnO 3 domain sizes were studied. Despite having similar morphological, crystal and local atomic structures, materials with various Li 2 MnO 3 domain sizes exhibited different phase separation behavior resulting in disparate lithium ion transport kinetics. For the first few cycles, the 0.5Li 2 MnO 3 ∙0.5LiCoO 2 material with a small Li 2 MnO 3 domain size had higher lithium ion diffusion coefficients due to shorter diffusion path lengths. However, after extended cycles, the 0.5Li 2 MnO 3 ∙0.5LiCoO 2 material with larger Li 2 MnO 3 domain size showed higher lithium ion diffusion coefficients, since the larger Li 2 MnO 3 domain size could retard structural transitions. This leads to fewer structural rearrangements, reduced structural disorders and defects, which allows better lithium ion mobility in the material.

Nanostructured materials make a considerable impact on the performance of lithium-storage characteristics in terms of the energy density, power density, and cycle life. Direct experimental observation, by a comparison of controlled nanostructural uniformity of electrode materials, reveals that the lithium-storage behaviors of mesoporous MoO 2 and CuO electrodes are linearly correlated with their nanostructural uniformity. Reversible capacities of mesoporous MoO 2 and CuO electrodes with well-developed nanostructures (1569 mA h g -1 for MoO 2 and 1029 mA h g -1 for CuO) exceed their theoretical capacity based on the conversion reaction (838 mA h g -1 for MoO 2 and 674 mA h g -1 for CuO). Given that exact understanding of the origin of the additional capacity is essential in maximizing the energy density of electrode material, this work may help to gain some insights into the development of high energy-density lithium-storage materials for next-generation lithium rechargeable batteries., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biomass-derived carbon, as a low-cost material source, is an attractive choice to prepare carbon materials, thus providing an alternative to by-product and waste management. Herein, we report the preparation of carbon from hemp stem as a biomass precursor through a simple, low-cost, and environment-friendly method with using steam as the activating agent. The hemp-derived carbon with a hierarchically porous structure and a partial graphitization in amorphous domains was developed, and for the first time, it was applied as an anode material for lithium-ion battery. Natural hemp itself delivers a reversible capacity of 190 mA h g -1 at a rate of 300 mA g -1 after 100 cycles. Ball-milling of hemp-derived carbon is further designed to control the physical properties, and consequently, the capacity of milled hemp increases to 300 mA h g -1 along with excellent rate capability of 210 mA h g -1 even at 1.5 A g -1 . The milled hemp with increased graphitization and well-developed meso-porosity is advantageous for lithium diffusion, thus enhancing electrochemical performance via both diffusion-controlled intercalation/deintercalation and surface-limited adsorption/desorption. This study not only demonstrates the application of hemp-derived carbon in energy storage devices, but also guides a desirable structural design for lithium storage and transport., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

It is widely accepted that solid electrolyte interphase (SEI) layer of carbonaceous material is formed by irreversible decomposition reaction of an electrolyte, and acts as a passivation layer to prevent further decomposition of the electrolyte, ensuring reliable operation of a Li-ion battery. On the other hand, recent studies have reported that some transition metal oxide anode materials undergo reversible decomposition of an organic electrolyte during cycling, which is completely different from carbonaceous anode materials. In this work, we revisit the electrochemical reaction of an electrolyte that produces SEI layer on the surface of carbonaceous anode materials using soft X-ray absorption spectroscopy. We discover that the reversible formation and decomposition of SEI layer are also able to occur on the carbonaceous materials in both Li- and Na-ion battery systems. These new findings on the unexpected behavior of SEI in the carbonaceous anode materials revealed by soft X-ray absorption spectroscopy would be highly helpful in more comprehensive understanding of the interfacial chemistry of carbonaceous anode materials in Li- and Na-ion batteries.

Li-rich layered oxide has been known to possess high specific capacity beyond the theoretical value from both charge compensation in transition metal and oxygen in the redox reaction. Although it could achieve higher reversible capacity due to the oxygen anion participating in electrochemical reaction, however, its use in energy storage systems has been limited. The reason is the irreversible oxygen reaction that occurs during the initial charge cycle, resulting in structural instability due to oxygen evolution and phase transition. To suppress the initial irreversible oxygen reaction, we introduced the surface-modified Li[Li 0.2 Ni 0.16 Mn 0.56 Co 0.08 ]O 2 prepared by carbon coating (carbonization process), which was verified to have reduced oxygen reaction during the initial charge cycle. The electrochemical performance is improved by the synergic effects of the oxygen-deficient layer and carbon coating layer formed on the surface of particles. The sample with suitable carbon coating exhibited the highest structural stability, resulting in reduced capacity fading and voltage decay, which are attributed to the mitigated layered-to-spinel-like phase transition during prolonged cycling. The control over the oxygen reaction of Li 2 MnO 3 by surface modification affects the activation reaction above 4.4 V in the initial charge cycle and structure changes during prolonged cycling. X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses as well as electrochemical performance measurement were used to identify the correlation between reduced oxygen activity and structural changes.

Current lithium ion battery technology is tied in with conventional reaction mechanisms such as insertion, conversion, and alloying reactions even though most future applications like EVs demand much higher energy densities than current ones. Exploring the exceptional reaction mechanism and related electrode materials can be critical for pushing current battery technology to a next level. Here, we introduce an exceptional reaction with a Co(OH) 2 material which exhibits an initial charge capacity of 1112 mAh g -1 , about twice its theoretical value based on known conventional conversion reaction, and retains its first cycle capacity after 30 cycles. The combined results of synchrotron X-ray diffraction and X-ray absorption spectroscopy indicate that nanosized Co metal particles and LiOH are generated by conversion reaction at high voltages, and Co x H y , Li 2 O, and LiH are subsequently formed by hydride reaction between Co metal, LiOH, and other lithium species at low voltages, resulting in a anomalously high capacity beyond the theoretical capacity of Co(OH) 2 . This is further corroborated by AIMD simulations, localized STEM, and XPS. These findings will provide not only further understanding of exceptional lithium storage of recent nanostructured materials but also valuable guidance to develop advanced electrode materials with high energy density for next-generation batteries.

The design of active, stable, and cost-effective electrocatalysts for the H 2 evolution reaction (HER) in alkaline conditions is important for electrochemical systems such as the chloro-alkaline process and H 2 production. Here we report catalysts comprising Pt on Ni single crystalline spines (Pt/Ni-SP) with high activity and stability for HER in alkaline solution with proposed mechanism. The Pt/Ni-SP catalysts are prepared by dispersing platinum nanoparticles (1.7-3.1 nm) on the single-crystalline spines (Ni-SP) of Ni urchin-like particles. The size and coverage of Pt nanoparticles on Ni-SP are increased with increases in the Pt loading amount. X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy are performed to observe the structure of the Pt/Ni-SP catalyst. The catalysts achieve the mass activity of 1.11 A mg -1 (Pt) , comparing favorably to Pt/C catalysts with the mass activity of 0.33 A mg -1 (Pt) at 0.05 V overpotential. The Tafel slope of the Pt/Ni-SP catalyst is approximately 30 mV dec -1 , similar to that of Pt, while Pt/Ni-SP is very stable in alkaline solution, like Ni. The synergistic effect of Pt/Ni-SP is ascribed to H spillover from Pt to Ni.

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.

A three dimensional vanadium pentoxide/reduced graphene oxide/carbon nanotube (3D V2O5/RGO/CNT) composite is synthesized by microwave-assisted hydrothermal method. The combination of 2D RGO and 1D CNT establishes continuous 3D conductive network, and most notably, the 1D CNT is designed to form hierarchically porous structure by penetrating into V2O5 microsphere assembly constituted of numerous V2O5 nanoparticles. The highly porous V2O5 microsphere enhances electrolyte contact and shortens Li(+) diffusion path as a consequence of its developed surface area and mesoporosity. The successive phase transformations of 3D V2O5/RGO/CNT from α-phase to ε-, δ-, γ-, and ω-phase and its structural reversibility upon Li(+) intercalation/de-intercalation are investigated by in situ XRD analysis, and the electronic and local structure reversibility around vanadium atom in 3D V2O5/RGO/CNT is observed by in situ XANES analysis. The 3D V2O5/RGO/CNT achieves a high capacity of 220 mAh g(-1) at 1 C after 80 cycles and an excellent rate capability of 100 mAh g(-1) even at a considerably high rate of 20 C. The porous 3D V2O5/RGO/CNT structure not only provides facile Li(+) diffusion into bulk but contributes to surface Li(+) storage as well, which enables the design of 3D V2O5/RGO/CNT composite to become a promising cathode architecture for high performance LIBs.

Developing electrode materials with high-energy densities is important for the development of lithium-ion batteries. Here, we demonstrate a mesoporous molybdenum dioxide material with abnormal lithium-storage sites, which exhibits a discharge capacity of 1,814 mAh g(-1) for the first cycle, more than twice its theoretical value, and maintains its initial capacity after 50 cycles. Contrary to previous reports, we find that a mechanism for the high and reversible lithium-storage capacity of the mesoporous molybdenum dioxide electrode is not based on a conversion reaction. Insight into the electrochemical results, obtained by in situ X-ray absorption, scanning transmission electron microscopy analysis combined with electron energy loss spectroscopy and computational modelling indicates that the nanoscale pore engineering of this transition metal oxide enables an unexpected electrochemical mass storage reaction mechanism, and may provide a strategy for the design of cation storage materials for battery systems.

The structural changes and electrochemical behavior of RuO2 are investigated by using in situ XRD, X-ray absorption spectroscopy, and electrochemical techniques to understand the electrochemical reaction mechanism of this metal oxide anode material. Intermediate phase-assisted transformation of RuO2 to LiRuO2 takes place at the start of discharge. Upon further lithiation, LiRuO2 formed by intercalation decomposes to nanosized Ru metal and Li2 O by a conversion reaction. A reversible capacity in addition to its theoretical capacity is observed on discharging below 0.5 V during which no redox activity involving Ru is observed. TEM, X-ray photoelectron spectroscopy, and the galvanostatic intermittent titration technique are used to probe this additional capacity. The results show that the additional capacity is a result of Li storage in the grain boundary between nanosized Ru metal and Li2 O. Findings of this study provide a better understanding of the quantitative share of capacity by a unique combination of intercalation, conversion, and interfacial Li storage in a RuO2 anode., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

To monitor dynamic volume changes of electrode materials during electrochemical lithium storage and removal process is of utmost importance for developing high performance lithium storage materials. We herein report an in operando probing of mesoscopic structural changes in ordered mesoporous electrode materials during cycling with synchrotron-based small angel X-ray scattering (SAXS) technique. In operando SAXS studies combined with electrochemical and other physical characterizations straightforwardly show how porous electrode materials underwent volume changes during the whole process of charge and discharge, with respect to their own reaction mechanism with lithium. This comprehensive information on the pore dynamics as well as volume changes of the electrode materials will not only be critical in further understanding of lithium ion storage reaction mechanism of materials, but also enable the innovative design of high performance nanostructured materials for next generation batteries.

Tracking thermally induced reactions has always been challenging for electrode materials of electrochemical battery systems. Traditionally, a variety of calorimetric techniques and in situ XRD at elevated temperatures has been used to evaluate the thermal stability of electrode materials. These techniques are capable of providing variations in heat capacity, mass and average bulk composition of materials only. Herein, we report investigation of thermal characteristics of Li0.33Ni0.8Co0.15Al0.05O2 by using in situ soft XAS measurements in combination with XRD. Fluorescence yield and partial electron yield measurements are used simultaneously to obtain element selective surface and bulk information. Fluorescence yield measurements reveal no energy change of the absorption peak and thus no valence state change in the bulk. However, electron yield measurements indicate that NiO-type rock salt structure is formed at the surface at temperatures above 200°C while no evidence for a surface reaction near Co sites in investigated temperature range is found. These results clearly show that in situ soft XAS can give a unique understanding of the role of each element in the structural transformation under thermal abuse offering a useful guidance in developing new battery system with improved safety performance.

Herein, we explore the capacity degradation of dilithium rhodizonate salt (Li2C6O6) in lithium rechargeable batteries based on detailed investigations of the lithium de/insertion mechanism in Li2C6O6 using both electrochemical and structural ex situ analyses combined with first-principles calculations. The experimental observations indicate that the LixC6O6 electrode undergoes multiple two-phase reactions in the composition range of 2 ≤ x ≤ 6; however, the transformations in the range 2 ≤ x ≤ 4 involve a major morphological change that eventually leads to particle exfoliation and the isolation of active material. Through first-principles analysis of LixC6O6 during de/lithiation, it was revealed that particle exfoliation is closely related to the crystal structural changes with lithium deinsertion from C6O6 interlayers of the LixC6O6. Among the lithium ions found at various sites, the extraction of lithium from C6O6 interlayers at 2 ≤ x ≤ 4 decreases the binding force between the C6O6 layers, promoting the exfoliation of C6O6 layers and pulverization at the electrode, which degrades capacity retention.

The phase control of spinel LiNi0.5 Mn1.5 O4 was achieved through surface treatment that led to an enhancement of its electrochemical properties. Li(+) diffusion inside spinel LiNi0.5 Mn1.5 O4 could be promoted by modifying the surface structure of LiNi0.5 Mn1.5 O4 through phosphidation into a disordered phase (Fd3m) that allows facile Li(+) transport. Phosphidated LiNi0.5 Mn1.5 O4 showed a significantly enhanced electrochemical performance, even at high rates exceeding 10 C, demonstrating that the improved kinetics (related to the amount of Mn(3+) ) can render LiNi0.5 Mn1.5 O4 competitive as a high-power cathode material for electric vehicles and hybrid electric vehicles., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Surface decoration strategy for one-dimensional nanostructures will improve their electrical, optical, mechanical, and electrochemical performances dramatically. Heterogeneous growth/deposition on surfaces, however, may create undesired junction interfaces in the system. Here we report a procedure during which amorphous titania nanotubes are readily self-branched with crystalline titanate nanorods at room temperature. The starting amorphous titania nanotubes were prepared by low-temperature atomic layer deposition combined with the template-directed approach. We routinely observed the self-branching phenomenon of crystalline titanate nanorods with a few nanometers in diameter onto the surfaces of the amorphous titania nanotubes in mild alkali solutions. The resulting structures were analyzed by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy. The reactivity of the hierarchical titania nanotube arrays was observed to be improved as a Li secondary battery electrode. Upon complete consumption of the amorphous body of titania nanotubes, in addition, titanate nanosheets/layers consisting of single TiO(2) layers with unit-cell thickness were obtained, elucidating the formation mechanism of layered titanate materials by alkali treatment.

In situ hard X-ray absorption spectroscopy (XAS) at metal K-edges and soft XAS at O K-edge and metal L-edges have been carried out during the first charging process for the layered Li1-xCo1/3Ni1/3Mn1/3O2 cathode material. The metal K-edge XANES results show that the major charge compensation at the metal site during Li-ion deintercalation is achieved by the oxidation of Ni2+ ions, while the manganese ions and the cobalt ions remain mostly unchanged in the Mn4+ and Co3+ state. These conclusions are in good agreement with the results of the metal K-edge EXAFS data. Metal L-edge XAS results at different charge states in both the FY and PEY modes show that, unlike Mn and Co ions, Ni ions at the surface are oxidized to Ni3+ during charge, whereas Ni ions in the bulk are further oxidized to Ni4+ during charge. From the observation of O K-edge XAS results, we can conclude that a large portion of the charge compensation during Li-ion deintercalation is achieved in the oxygen site. By comparison to our earlier results on the Li1-xNi0.5Mn0.5O2 system, we attribute the active participation of oxygen in the redox process in Li1-xCo1/3Ni1/3Mn1/3O2 to be related to the presence of Co in this system.