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This study provides the first data on the preparation of ammonium iron–manganese phosphates monohydrates, NH4Mn1–xFexPO4·H2O, with a dittmarite-type structure in the whole concentration range. The structure, Mn2+/Fe2+distribution over 2acrystallographic site, and morphology of the mixed dittmarite salts are assessed by means of powder X-ray diffraction, infrared spectroscopy, electron paramagnetic resonance spectroscopy, and scanning electron microscopy. The mixed dittmarite salts participate in reactions of ion exchange with Li+and Na+ions, and as a result lithium and sodium phospho-olivines, LiMn1–xFexPO4and NaMn1–xFexPO4, are formed at low temperature. The main advantage of this synthesis route is that the homogeneous Mn/Fe distribution in the metal-phosphate layers of the dittmarite structure is transmitted to the target olivine structure without any reorganization, thus providing phospho-olivines largely free of antisite defects. Despite the use of one and the same precursor, the morphology of the lithium and sodium phases differ remarkably. The electrochemical properties of LiMn0.8Fe0.2PO4and NaMn0.8Fe0.2PO4phospho-olivines are tested in model two electrode cells versus lithium anode and LiPF6-based electrolyte. It has been found that both phospho-olivines are able to intercalate alkali ions reversibly, which determines their potential for application as electrode materials for lithium and sodium ion batteries.

Hybrid Li–Na ion batteries (HLSIBs) have become attractive because they combine the high energy density of lithium-ion batteries with the safety and low cost of sodium-ion batteries. However, the performance of HLSIBs is still far from the desired. The present study aims to probe the function of electrodes and the electrolyte in model half and full hybrid Li–Na cells by combining experimental and computational methods. As a positive electrode, sodium-deficient nickel manganese oxide, Na2/3Ni1/2Mn1/2O2, with a three-layered structure is used, while spinel Li4Ti5O12serves as a negative electrode. Two types of conventional LiPF6- and NaPF6-based electrolyte solutions are used. The structure and surface changes in the oxide electrodes after cell cycling are monitored by ex situ transmission electron microscopy and X-ray photoelectron spectroscopy analyses. The competitive solvation/desolvation of Li+and Na+by ethylene carbonate (EC) molecules is modeled as binuclear heterocomplexes, Li+Na+(EC)n(1 ≤ n≤ 8), in the framework of density functional theory computations. The hybrid-ion cell operates by a dual intercalation of Li+and Na+in the oxide electrodes, which provokes after few cycles a generation of a mixed Li–Na electrolyte. In the mixed electrolyte, each Li+and Na+ion is solvated as much as possible without any competition between them. At the electrode–electrolyte interface, the competition between Li+and Na+ions leads to the formation of polynuclear cationic associates which are strongly coupled with electrolyte molecules. The desolvation of the latter is further complicated by the presence of surface-deposited F–ions, resulting in the accumulation of Li+and Na+ions at the surface of both the oxide electrodes. Based on the extracted correlations, an outlook of further steps for optimization of the HLSIBs performance is suggested.

Sodium-deficient nickel–manganese oxides with a layered type of structure are, nowadays, of great interest as electrode materials for both lithium- and sodium-ion batteries since they are able to intercalate lithium and sodium ions reversibly within a broad concentration range. Herein, we report new data on the effects of the particle sizes and of the electrolyte salt on the intercalation properties of Na2/3Ni0.5Mn0.5O2with a P3-type of structure. The morphology of layered Na2/3Ni0.5Mn0.5O2oxides has been varied by changing the type of the precursor used: from Na–Ni–Mn acetates to Na–Ni–Mn mixed nitrate acetates. The structure, particle dimensions, and particle size distribution of oxides have been determined by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light-scattering measurements, and X-ray photoelectron spectroscopy (XPS). The intercalation properties of Na2/3Ni0.5Mn0.5O2have been studied in model electrochemical cells versus Li metal as the anode. We used two kinds of lithium salts dissolved in organic solutions as the electrolytes: 1 M LiPF6in EC:DMC and 1 M LiBF4in EC:DMC. The mechanism of the lithium intercalation into Na2/3Ni0.5Mn0.5O2is discussed on the basis of ex situXRD, HRTEM, and X-ray photoelectron spectroscopy analyses. It has been discovered that the lithium salt in the electrolyte salt contributes to the mechanism of the electrochemical reaction, while particle dimensions determine the capacity stability during continuous cycling, as well as the surface reactivity of oxide electrodes.

This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellent cycling stability based on composites of a-Ni(OH)2 and activated carbon (AC). The a-phase, Ni(OH)2.0.3H2O, consists of charged Ni(OH)2-x layers, SO2-4 anions being intercalated in the interlayer spaces. The hydroxide has a mesoporous structure and contains nanometric primary particles bounded into micrometric aggregates. The supercapacitor performance of a-Ni(OH)2 mixed with AC is tested by galvanostatic experiments in KOH-LiOH electrolyte. The ratio between a-Ni(OH)2 and AC is varied in a whole concentration range: 0[?]x[?]100 wt.%. In comparison with the symmetrical supercapacitor, the composite electrodes containing a-Ni(OH)2 between 6 and 35 wt. % demonstrate higher and more stable discharge capacitance, as well as a higher effectiveness of charge-discharge process. a-Ni(OH)2 has a better cycling stability in comparison with the b-phase. The supercapacitor performance is discussed in terms of structure and morphology stability of a-Ni(OH)2 in alkaline electrolyte.

The development of lithium and sodium ion batteries without using lithium and sodium metal as anodes gives the impetus for elaboration of low-cost and environmentally friendly energy storage devices. In this contribution we demonstrate the design and construction of a new type of hybrid sodium–lithium ion cell by using unique electrode combination (Li4Ti5O12spinel as a negative electrode and layered Na3/4Co1/3Ni1/3Mn1/3O2as a positive electrode) and conventional lithium electrolyte (LiPF6salt dissolved in EC/DMC). The cell operates at an average potential of 2.35 V by delivering a reversible capacity of about 100 mAh/g. The mechanism of the electrochemical reaction in the full sodium–lithium ion cell is studied by means of postmortem analysis, as well as ex situX-ray diffraction analysis, HR-TEM, and electron paramagnetic resonance spectroscopy (EPR). The changes in the surface composition of electrodes are examined by ex situX-ray photoelectron spectroscopy (XPS).

Layered lithium transition metal oxides with optimized nickel–manganese content are nowadays of primary interest as electrode materials for lithium ion batteries, since they are able to deliver a high capacity at a low cost. Herein we report a new class of less expensive cathode materials, which comprise sodium-deficient cobalt–nickel–manganese oxides NaxCo1/3Ni1/3Mn1/3O2characterized with a layered structure and broad concentration range of sodium solubility. NaxCo1/3Ni1/3Mn1/3O2oxides are obtained by thermal decomposition of mixed acetate–oxalate precursors, followed by thermal annealing between 700 and 800 °C. In the concentration range of 0.33 < x≤ 0.75, NaxCo1/3Ni1/3Mn1/3O2oxides assume a layered structure with a three-layer stacking (i.e., P3 type of structure). Based on electron paramagnetic resonance spectroscopy operating in the X-band (9.4 GHz), it is found that the charge compensation of Na deficiency is achieved by preferential oxidation of Ni2+to Ni3+and Ni4+, while Co and Mn ions retain their oxidation state of 3+ and 4+ within the whole concentration range. The electrochemical performance of NaxCo1/3Ni1/3Mn1/3O2in model lithium cells is simply controlled by the amount of sodium content in the pristine compositions: a higher reversible capacity is achieved for sodium-rich oxides (i.e., 0.75 ≥ x≥ 0.67), while sodium-poor oxides (i.e., 0.38 ≤ x≤ 0.50) display a lower reversible capacity and improved cycling stability. The mechanism of the lithium intercalation into NaxCo1/3Ni1/3Mn1/3O2is discussed on the basis of ex situXRD, HRTEM, and X-ray photoelectron spectroscopy analyses.

To modify the morphology and electrochemical properties of the resulting titanium oxide layer, we have applied high-intensity ultrasonication during the potentiostatic anodization of metallic titanium, and the applied voltage and anodizing time has been changed. The influence of the imposed voltage, anodizing time, and ultrasonication on the nanotubes growth has been studied. Additional dissolution process takes place under ultrasonication, as is observed in the anodizing curves (current density vs time) that show values on the order of ca. 200 A/m2. After only 30 min of ultrasound-assisted anodization at 42 V, the resulting nanotubes length is ca. 4 μm and, in contrast, in the case of non ultrasound-assisted anodization, the length is only ca. 1 μm. Further prolonged anodization under ultrasound induced the complete dissolution of the titanium. After anodization at 60 V during 20 h (no ultrasounds), the observed length of the nanotubes is as long as ca. 45 μm. The nanotube TiO2aspect ratio has been tailored between 40 and 320. The obtained nanotubes of TiO2exhibit high areal capacity (up to ca. 2 mAh/cm2and stabilized around 0.3 to 0.5 mAh/cm2) and good cycling behavior in lithium batteries. A nonlinear relationship between the nanotubes length and the resulting capacity has been revealed.

Lithium–nickel manganese spinel, LiNi1/2Mn3/2O4, is capable to intercalate lithium reversible at a high voltage delivering a high specific energy when used as cathode material for lithium ion batteries. In this study, the effects of cationic order and particle size distribution on the lithium intercalation in high-voltage LiNi1/2Mn3/2O4spinel are examined by the application of diffraction and spectroscopic techniques. At 400 °C, nonstoichiometric LiNi1/2Mn3/2O4-δwith a disordered spinel structure and particle size distribution between between 10 and 20 nm is obtained. 7Li NMR with ultrafast spinning rates and electron paramagnetic resonance spectroscopy show that Ni2+, Mn3+, and Mn4+ions are nonuniformly distributed forming nanoscale domains with (Ni2+,Mn4+)-, (Ni2+,Mn4+,Mn3+)-, and (Mn3+,Mn4+) compositions, respectively, the entirely cubic spinel structure being preserved. By increasing the annealing temperature, the amount of Mn3+decreases, and Ni2+and Mn4+tend to set up a long-range order. The particles start to grow above 600 °C, reaching submicrometer dimensions at 800 °C. Acid treatment of ordered submicrometer LiNi1/2Mn3/2O4modifies the particle size distribution without change of the cationic distribution. Cationic Ni,Mn distribution affects the Li+extraction/insertion from/into LiNi1/2Mn3/2O4, while the particle size distribution has an impact on the rate capability and on the interaction with the electrolyte. After storing of the spinels in electrolyte solutions, the nanosized particles are covered with LiF/LixPFyOz/P2O5, while Ni,MnF2/LixPFycompounds are deposited on the surface of the submicrometer particles. Ordered LiNi1/2Mn3/2O4with a three-modal particle size distribution displays the best rate capability.

The structural properties of sodium manganates and iron substituted sodium manganates with compositions Na2/3Mn1-xFexO2 (x=0, 1/3 and 2/3) were studied by Raman spectroscopy. The Raman spectroscopy allows distinguishing between layered phases with orthorhombic (Cmcm space group) and hexagonal (P63/mmc space group) distortion. It has been found that the crystal structure and the composition of Na2/3MnO2 display a strong dependence on the history of the thermal treatment. The orthorhombic distorted modification is stabilized at high temperatures (1000 oC). At lower quenching temperature, there is a phase separation into an orthorhombic and a hexagonal modification, concomitant with an increase in the oxidation state of Mn. When Fe substitutes for Mn, the hexagonal modification is stabilized. In order to understand the origin of the Raman spectra of Na2/3Mn1-xFexO2, we have used Na2/3Co2/3Mn1/3O2 as a standard for hexagonal structure, where Co3+ and Mn4+ are statistically distributed in the transition metal layers.

Single phases of olivinetype LiCoPO4and LiNiPO4were synthesized by thermal treatment of homogeneous lithium–metal–phosphate–formate precursors obtained by freeze drying of aqueous solutions of the corresponding metal formates and LiH2PO4. The structure, thermal behavior, and morphology of the precursors were studied by IR spectroscopy, DTA, and SEM. Cobalt and nickel phosphate–formate precursors have a composition LiMHxPO4HCOOx·yH2O, where the formate and phosphate groups are mainly deprotonated. For the Co precursor the formate and phosphates ions are randomly coordinated to both Co and Li cations, whereas for the Ni precursor there is a preferential coordination of the formate and phosphate ions around the Ni2+and Li+ion, respectively. Thermal treatment of the precursors yields single phases of olivinetype LiCoPO4at 450 °C and LiNiPO4at 700 °C. Structural analysis evidences that both LiCoPO4and LiNiPO4have an ordered olivinetype structure without any Li to M disorder between the metal positions and lithium deficiency. The effect of the freezedried solution concentration and annealing temperature on the structure, crystallite size, and morphology of LiCoPO4and LiNiPO4has been discussed. The morphology of the cobalt and nickel phosphoolivines comprises isometric particles with mean sizes of 190 and 380 nm, respectively.

Highpressure modification of LiNiPO4with a Na2CrO4type structure was obtained at ambient pressure and low temperature from a mixed LiNi–phosphate–formate precursor, LiNiPO4HxHCOOx·yH2O where x 1.2 and y 2.5. The structural and thermal characterization of the precursor and the LiNiPO4compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4HxHCOOx·yH2O precursors between 450 and 650 °C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4type and the olivine type. It was established that the obtained Na2CrO4type LiNiPO4is a metastable phase, which completely transforms at 700 °C into the olivinetype phase. The enthalpy of the phase transition is ΔH= –43.40 kJ mol–1. The mechanism of formation of the two forms of LiNiPO4from the LiNi–phosphate–formate precursor is discussed.

We report on the behavior of nanometric (LiMNC) as a cathode material for Li-ion batteries in comparison with the same material with submicrometric particles. The LiMNC material was produced by a self-combustion reaction, and the particle size was controlled by the temperature and duration of the follow-up calcination step. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman spectroscopy, electron paramagnetic resonance, inductively coupled plasma, and atomic force microscopy were used in conjunction with standard electrochemical techniques (cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) for characterizing the electrode materials. The effect of cycling and aging at was also explored. Nanomaterials are much more reactive in standard electrolyte solutions than LiMNC with a submicrometric particle. They develop surface films that impede their electrochemical response, while their bulk structure remains stable during aging and cycling at elevated temperatures. The use of nanomaterials in Li-ion batteries is discussed.

The structural properties of sodium manganates and iron substituted sodium manganates with compositions Na2/3Mn1-xFexO2 (x=0, 1/3 and 2/3) were studied by Raman spectroscopy. The Raman spectroscopy allows distinguishing between layered phases with orthorhombic (Cmcm space group) and hexagonal (P63/mmc space group) distortion. It has been found that the crystal structure and the composition of Na2/3MnO2 display a strong dependence on the history of the thermal treatment. The orthorhombic distorted modification is stabilized at high temperatures (1000 oC). At lower quenching temperature, there is a phase separation into an orthorhombic and a hexagonal modification, concomitant with an increase in the oxidation state of Mn. When Fe substitutes for Mn, the hexagonal modification is stabilized. In order to understand the origin of the Raman spectra of Na2/3Mn1-xFexO2, we have used Na2/3Co2/3Mn1/3O2 as a standard for hexagonal structure, where Co3+ and Mn4+ are statistically distributed in the transition metal layers.

Nongraphitic carbon microbeads were prepared by hydrothermal treatment of a glucose aqueous solution at 180 °C. Impregnation of glucose-derived carbon microbeads with citric acid was used to control the microbeads' surface and electrochemical properties. The microspherical sample thus obtained exhibited a highly disordered nanocrystalline structure and a low BET surface area. The electrochemical performance of carbon microbeads was evaluated from discharge/charge experiments in lithium and sodium cells, as well as from electrochemical impedance spectroscopy measurements. The intercalation of Li and Na in surface-modified carbon microbeads was explored by EPR and NMR spectroscopy. It was shown that similar mechanisms operate for lithium and sodium insertion into disordered carbons. The observed Curie-like behavior and the change in intensity of the EPR signals as a function of cell voltage agreed well with lithium insertion into different sites of disordered carbon structures forming paramagnetic centers. Microspherical carbon samples with high reversible capacities in both Li and Na cells commonly exhibit low concentrations of paramagnetic centers.

Solid solutions in the α-LiGaO2–LiNiO2system were prepared over the whole concentration range under high pressure 3 GPa at 700 °C in oxygen-rich atmosphere. The structure of LiGayNi1−yO2solid solutions was characterized by XRD analysis, EPR and IR spectroscopy. It was found that Ga substitutes for Ni in the NiO2layer 3a site, while Li and O are in their normal positions 3b and 6c, respectively. The occupancy of Ni in the Li site is negligible for Ga-substituted oxides. The progressive replacement of Ni by Ga leads to an unusual concentration variation of the a-parameter: at 10 Ga additives, there is a contraction of the a-parameter together with the expansion of the c-parameter. The concentration variation of the a-parameter can be related to increased trigonal distortion of GayNi1−yO2layers upon Ga substitution. The electrochemical performance of LiGayNi1−xCox1−yO2solid solutions as a cathode material in lithium ion cells has been evaluated in potentiostatic experiments. During the first charge, there is an irreversible peak at about 4.7 V, which was compared with the electrochemical Li extraction from layered oxides characterized with a partial mixing of lithium and metal ions in the metal layers. After the first charge, a reversible electrochemical intercalation of Li is achieved. The effect of Ga on the potential of lithium extractioninsertion in LiGayNi1−xCox1−yO2was discussed.

Solid solutions in the α-LiGaO₂–LiNiO₂ system were prepared over the whole concentration range under high pressure (3 GPa) at 700 °C in oxygen-rich atmosphere. The structure of LiGa_yNi_1−yO₂ solid solutions was characterized by XRD analysis, EPR and IR spectroscopy. It was found that Ga substitutes for Ni in the NiO₂ layer (3a site), while Li and O are in their normal positions (3b and 6c, respectively). The occupancy of Ni in the Li site is negligible for Ga-substituted oxides. The progressive replacement of Ni by Ga leads to an unusual concentration variation of the a-parameter: at 10% Ga additives, there is a contraction of the a-parameter together with the expansion of the c-parameter. The concentration variation of the a-parameter can be related to increased trigonal distortion of Ga_yNi_1−yO₂ layers upon Ga substitution. The electrochemical performance of LiGa_y(Ni_1−xCo_x)_1−yO₂ solid solutions as a cathode material in lithium ion cells has been evaluated in potentiostatic experiments. During the first charge, there is an irreversible peak at about 4.7 V, which was compared with the electrochemical Li extraction from layered oxides characterized with a partial mixing of lithium and metal ions in the metal layers. After the first charge, a reversible electrochemical intercalation of Li is achieved. The effect of Ga on the potential of lithium extraction/insertion in LiGa_y(Ni_1−xCo_x)_1−yO₂ was discussed.

LiGa_yCo_1−yO₂ solid solutions with a layered crystal structure (0 ≤ y &lt; 0.75) were prepared under high-pressure (3 GPa) at 850 °C using a piston–cylinder type apparatus. This is in contrast to the solubility of Ga in the layered LiCoO₂ structure at atmospheric pressure, which is strongly limited, and reaches a maximum value of y = 0.1 at 700 °C. The structure of Ga substituted LiCoO₂ is characterized by XRD analysis and IR spectroscopy. It has been found that Ga substitutes for Co in the CoO₂ layer (3a site), while Li and O are in their normal positions (3b and 6c, respectively). The progressive replacement of Co by Ga leads to a linear increase in the mean M–O bond distance and to a smooth decrease in frequency of the main vibration of the Ga_yCo_1−yO₂ layer, thus indicating a random Co/Ga distribution. The electrochemical performance of LiGa_yCo_1−yO₂ as a cathode material in lithium ion cells has been evaluated in potentiostatic and galvanostatic experiments. The de-intercalation voltage of the LiGa_yCo_1−yO₂ solid solutions increases and the reversible capacity decreases with increasing gallium content.

EPR of Mn⁴⁺ has been used to specify the electronic structure and cation distribution in LiCoMnO₄ compositions that belong to high-potential electrode materials. To prepare single phase LiCoMnO₄, two synthesis techniques have been adopted: solid state reactions and a lactate precursor method. EPR of Mn⁴⁺ shows that diamagnetic Co³⁺ (low-spin configuration, S = 0) and paramagnetic Mn⁴⁺ (S = 3/2) account for the electronic structure of LiCoMnO₄. Analysis of the EPR line width in terms of dipole–dipole and exchange interactions allows one to estimate the mean number of paramagnetic neighbours of Mn⁴⁺. It has been demonstrated that the Co³⁺/Mn⁴⁺ distribution in 16d spinel sites is sensitive towards the cooling rates. For the high-temperature LiCoMnO₄ phase obtained by air quenching from 750°C, three paramagnetic Mn⁴⁺ and three diamagnetic Co³⁺ give rise to the local coordination of Mn⁴⁺, indicating a random Co/Mn distribution. For the low-temperature LiCoMnO₄ phases obtained by air quenching from 600 °C and by slow-cooling from 750 to 25 °C, the mean paramagnetic number of Mn⁴⁺ decreases from 3 to 2, which is interpreted in the framework of short-range Co³⁺/Mn⁴⁺ ordering. The Co³⁺/Mn⁴⁺ octahedral ordering process is developed within a small-scale range (approximately up to a distance of the third metal shell) and does not affect the cubic spinel symmetry of LiCoMnO₄.

A metal-organic precursor method was adopted for the preparation of lithium-manganese spinel oxides. EPR spectra of Mn2+ in solutions and in freeze-dried compositions, as well as IR and DSC of freeze-dried compositions, show that α-hydroxyorganic acids (such as lactic, malic and citric acids) chelate Mn2+via hydroxy and carboxylate groups. At 450 °C, thermal decomposition of Li-Mn-organic acid precursors with Li/Mn=1.05/1.95 leads to the formation of non-stoichiometric Li[LiyMn2–y–Δ□Δ]O4 spinels (0.03

This study provides new data on the fabrication of hybrid battery-supercapacitor with an excellent cycling stability based on composites of α-Ni(OH)2and activated carbon (AC). The α-phase, Ni(OH)2.0.3H2O, consists of charged Ni(OH)2-xlayers, SO2-4anions being intercalated in the interlayer spaces. The hydroxide has a mesoporous structure and contains nanometric primary particles bounded into micrometric aggregates. The supercapacitor performance of α-Ni(OH)2mixed with AC is tested by galvanostatic experiments in KOH-LiOH electrolyte. The ratio between α-Ni(OH)2and AC is varied in a whole concentration range: 0≤x≤100 wt.%. In comparison with the symmetrical supercapacitor, the composite electrodes containing α-Ni(OH)2between 6 and 35 wt. % demonstrate higher and more stable discharge capacitance, as well as a higher effectiveness of charge-discharge process. α-Ni(OH)2has a better cycling stability in comparison with the β-phase. The supercapacitor performance is discussed in terms of structure and morphology stability of α-Ni(OH)2in alkaline electrolyte.

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We report on the behavior of nanometric LiMn1/3Ni1/3Co1/3O2(LiMNC) as a cathode material for Li-ion batteries in comparison with the same material with submicrometric particles. The LiMNC material was produced by a self-combustion reaction, and the particle size was controlled by the temperature and duration of the follow-up calcination step. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman spectroscopy, electron paramagnetic resonance, inductively coupled plasma, and atomic force microscopy were used in conjunction with standard electrochemical techniques (cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) for characterizing the electrode materials. The effect of cycling and aging at 60°Cwas also explored. Nanomaterials are much more reactive in standard electrolyte solutions than LiMNC with a submicrometric particle. They develop surface films that impede their electrochemical response, while their bulk structure remains stable during aging and cycling at elevated temperatures. The use of nanomaterials in Li-ion batteries is discussed.

Hydrothermal activation was used to modify the lithium-insertion properties of graphitized carbon nanotubes. The resulting solids showed a net improvement in their performance as anodes for advanced lithium-ion batteries. The mechanism of the electrochemical reaction with lithium of the modified carbon nanotubes was studied by X-ray diffraction and a combined use of two powerful resonance spectroscopies: solid-state nuclear magnetic resonance and electron paramagnetic resonance. Lithium was first intercalated in the activated multiwalled nanotubes between graphene layers, forming n-stages. Interlayer expansion and misfit between curved layers caused fracture and exfoliation of the nanotubes with an irreversible loss of staging phenomena. The resulting solids displayed an improved capacity retention on successive cycles. The line shape of electron paramagnetic resonance and Knight shifts in nuclear magnetic resonance reveal the electronic changes induced by lithium incorporation-removal in activated nanotubes. These results suppose a new strategy to improve the electrochemical performance of graphitized carbon nanotubes.

We report on a rigorous comparative study of nano- and microparticles of LiMn1.5Ni0.5O4spinel as cathode materials for Li-ion batteries. The stability of these materials in LiPF6/alkyl carbonate solutions in temperatures up to 70°Cwas explored. Capacity, cycling, rate capabilities, and impedance behavior were also studied. The methods included X-ray diffraction, Raman, X-ray photelectron, Fourier transform infrared, and electron paramagnetic resonance spectroscopies, and electron microscopy, in conjunction with standard electrochemical techniques: voltammetry, chronopotentiometry, and impedance spectroscopy. These materials show an impressive stability in solutions at elevated temperature. The use of nanomaterials was advantageous for obtaining a better rate capability of LiMn1.5Ni0.5O4electrodes. LiMn1.5Ni0.5O4particles develop a unique surface chemistry in solutions that passivates and protects them from detrimental interactions with solution species at elevated temperatures.