Improving solid-state hydriding and dehydriding properties of the LiBH4 plus MgH2 system with the addition of Mn and V dopants

The hydriding process of the 2LiH + MgB₂ mixture is controlled by outward diffusion of Mg and inward diffusion of Li and H within MgB₂ crystals to form LiBH₄. This study explores the feasibility of using transition metal dopants, such as Mn and V, to enhance the diffusion rate and thus the hydriding kinetics. It is found that Mn can indeed enhance the hydriding kinetics of the 2LiH + MgB₂ mixture, while V does not. The major factor in enhancing the diffusion rate and thus the hydriding kinetics is related to the dopant's ability to induce the lattice distortion of MgB₂ crystals. This study demonstrates that the kinetics of the diffusion controlled solid-state hydriding process can be improved by doping if the dopant is properly selected.     

Effect of gas back pressure on hydrogen storage properties and crystal structures of Li2Mg(NH)2

The ternary imide Li₂Mg(NH)₂ is considered to be one of the most promising on-board hydrogen storage materials due to its high reversible hydrogen capacity of 5.86 wt%, favorable thermodynamic properties and good cycling stability. In this work, Li₂Mg(NH)₂ was synthesized by dynamically dehydrogenating a mixture of Mg(NH₂)₂–2LiH up to 280 °C under different gas (Ar and H₂) and pressures (0–9.0 bar). The crystal structure of Li₂Mg(NH)₂ was found to depend on the gas back pressure in the dehydrogenation process. The crystal structure of Li₂Mg(NH)₂ and the dehydrogenation/rehydrogenation properties of the Mg(NH₂)₂–2LiH system strongly depend on the gas back pressure in the dehydrogenation process due to the effect of the pressure on the dehydrogenation kinetics. This study provides a new approach for improving the hydrogen storage properties of the amide–hydride systems.     

Hydrogen release from a mixture of NaBH4 and Mg(OH)2

Hydrogen generating reaction between sodium borohydride, NaBH₄, and magnesium hydroxide, Mg(OH)₂ (brucite), was studied. Reaction rate was found to depend on the degree of reactants homogenization and/or their particle size. Kinetic of the reaction was studied in isothermal approach in the temperature range of 240–360 °C. It is shown that the reaction obeys 2D diffusion mechanism and its activation energy is 155.9 kJ/mol. Powder XRD analysis and Raman spectroscopy reveal that mechanically activated mixture of NaBH₄ and Mg(OH)₂ reacts yielding MgO as the only crystalline phase in the temperature range of 240–318 °C. At higher temperatures a new crystalline tetragonal phase of as yet undetermined composition is developed.     

Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode

Li₂FeSiO₄/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li₂FeSiO₄/C cathode were investigated. The XRD patterns of the Li₂FeSiO₄/C samples indicate that all the samples are of good crystallinity, and a little Fe₃O₄ impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750 °C. The Li₂FeSiO₄/C sample synthesized at 650 °C has good electrochemical performances with an initial discharge capacity of 144.9 mAh g⁻¹ and the discharge capacity remains 136.5 mAh g⁻¹ after 10 cycles. The performance of Li₂FeSiO₄/C cathode is further improved by modification of Ni substitution. The Li₂Fe_0.9Ni_0.1SiO₄/C composite cathode has an initial discharge capacity of 160.1 mAh g⁻¹, and the discharge capacity remains 153.9 mAh g⁻¹ after 10 cycles. The diffusion coefficient of lithium in Li₂FeSiO₄/C is 1.38 × 10⁻¹² cm² s⁻¹ while that in Li₂Fe_0.9Ni_0.1SiO₄/C reaches 3.34 × 10⁻¹² cm² s⁻¹.     

Basic molten salt process—A new route for synthesis of nanocrystalline Li4Ti5O12-TiO2 anode material for Li-ion batteries using eutectic mixture of LiNO3-LiOH-Li2O2

A nanocrystalline Li₄Ti₅O₁₂-TiO₂ duplex phase has been synthesized by a simple basic molten salt process (BMSP) using an eutectic mixture of LiNO₃-LiOH-Li₂O₂ at 400-500 °C. The microstructure and morphology of the Li₄Ti₅O₁₂-TiO₂ product are characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sample prepared by heat-treating at 300 °C for 3 h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li₄Ti₅O₁₂; with heat treatment at 400 °C for 3 h (S-2), there is a duplex crystallite size (fine < 10 nm, and coarse > 20 nm) of Li₄Ti₅O₁₂-TiO₂; at 500 °C for 3 h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size ∼15-30 nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193 mAh g⁻¹ at 0.2 C, 168 mAh g⁻¹ at 0.5 C, 146 mAh g⁻¹ at 1 C, 135 mAh g⁻¹ at 2 C, and 117 mAh g⁻¹ at 5 C. After 100 cycles, the discharge capacity is 138 mAh g⁻¹ at 1 C with a capacity retention of 95%. The S-2 sample yields the best electrochemical performance in terms of charge-discharge capacity and rate capability compared with other samples. Its superior electrochemical performance can be mainly attributed to the duplex crystallite structure, composed of fine (<10 nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li₄Ti₅O₁₂ and the anatase TiO₂.     

The reactions in LiBH4-NaNH2 hydrogen storage system

Stepwise reactions were observed in the ball milling and heating process of the LiBH₄-NaNH₂ system by means of X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR). During the ball milling process, two concurrent reactions take place in the mixture: 3LiBH₄ + 4NaNH₂ → Li₃Na(NH₂)₄ + 3NaBH₄ and LiBH₄ + NaNH₂ → LiNH₂ + NaBH₄. The heating process from 50 °C to 400 °C is mainly the concurrent reactions of Li₃Na(NH₂)₄ + 3LiBH₄ → 2Li₃BN₂ + NaBH₄ + 8H₂ and 2LiNH₂ + LiBH₄ → Li₃BN₂H₈ → Li₃BN₂ + 4H₂, where the intermediate phases Li₃Na(NH₂)₄ and LiNH₂ serve as the reagents to decompose LiBH₄. The merged equations for the mechanochemical and the heating reactions below 400 °C can be denoted as 3LiBH₄ + 2NaNH₂ → Li₃BN₂ + 2NaBH₄ + 4H₂. The maximum dehydrogenation capacity in closed system below 400 °C is 5.1 wt.% H₂, which agrees well with the theoretical capacity (5.5 wt.% H₂) of the merged equation and thus demonstrates the suggested pathway. The subsequent step consists of the decompositions of NaBH₄ and Li₃Na(NH₂)₄ within the temperature range of 400 °C-600 °C. The apparent activation energies of the two steps are 114.8 and 123.5 kJ/mol, respectively. They are all lower than that of our previously obtained bulk LiBH₄.     

Structural changes and thermal stability of charged LiNi1/3Co1/3Mn1/3O2 cathode material for Li-ion batteries studied by time-resolved XRD

Structural changes and their relationship with thermal stability of charged Li_0.33Ni_1/3Co_1/3Mn_1/3O₂ cathode samples have been studied using time-resolved X-ray diffraction (TR-XRD) in a wide temperature from 25 to 600 °C with and without the presence of electrolyte in comparison with Li_0.27Ni_0.8Co_0.15Al_0.05O₂ cathodes. Unique phase transition behavior during heating is found for the Li_0.33Ni_1/3Co_1/3Mn_1/3O₂ cathode samples: when no electrolyte is present, the initial layered structure changes first to a LiM₂O₄-type spinel, and then to a M₃O₄-type spinel and remains in this structure up to 600 °C. For the Li_0.33Ni_1/3Co_1/3Mn_1/3O₂ cathode sample with electrolyte, additional phase transition from the M₃O₄-type spinel to the MO-type rock salt phase takes place from about 400 to 441 °C together with the formation of metallic phase at about 460 °C. The major difference between this type of phase transitions and that for Li_0.27Ni_0.8Co_0.15Al_0.05O₂ in the presence of electrolyte is the delayed phase transition from the spinel-type to the rock salt-type phase by stretching the temperature range of spinel phases from about 20 to 140 °C. This unique behavior is considered as the key factor of the better thermal stability of the Li_1−xNi_1/3Co_1/3Mn_1/3O₂ cathode materials.     

Li4Ti5O12/Sn composite anodes for lithium-ion batteries: Synthesis and electrochemical performance

Li₄Ti₅O₁₂/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li₄Ti₅O₁₂ matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li₄Ti₅O₁₂/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge-discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li₄Ti₅O₁₂ at a calcination of 500 °C, due to the steric effect of Li₄Ti₅O₁₂ and chemical interaction between Li₄Ti₅O₁₂ and tin oxide. The experimental results indicate that Li₄Ti₅O₁₂/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g⁻¹ is maintained after 50 cycles at 100 mA g⁻¹ current density, which is still higher than 195 mAh g⁻¹ for the pure Li₄Ti₅O₁₂ after the same charge/discharge cycles. It suggests Li₄Ti₅O₁₂/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.     

Lithium diffusion in Li4Ti5O12 at high temperatures

Synthesis of the spinel lithium titanate Li₄Ti₅O₁₂ by an alkoxide-free sol-gel method is described. This method yields highly pure and crystalline Li₄Ti₅O₁₂ samples at relatively low temperature (850 °C) and via short thermal treatment (2 h). ⁶Li magic angle spinning nuclear magnetic resonance (MAS NMR) measurements on these samples were carried out at high magnetic field (21.1 T) and over a wide temperature range (295-680 K). The temperature dependence of the chemical shifts and integral intensities of the three ⁶Li resonances demonstrates the migration of lithium ions from the tetrahedral 8a to the octahedral 16c sites and the progressive phase transition from a spinel to a defective NaCl-type structure. This defective structure has an increased number of vacancies at the 8a site, which facilitate lithium diffusion through 16c → 8a → 16c pathways, hence providing an explanation for the reported increase in conductivity at high temperatures. Molecular dynamics simulations of the spinel oxides Li_4+xTi₅O₁₂, with 0 ≤ x ≤ 3, were also performed with a potential shell model in the temperature range 300-700 K. The simulations support the conclusions drawn from the NMR measurements and show a significant timescale separation between lithium diffusion through 8a and 16c sites and that out of the 16d sites.     

Effects of Fe2P and Li3PO4 additives on the cycling performance of LiFePO4/C composite cathode materials

In this study, a solution method was employed to synthesize LiFePO₄-based powders with Li₃PO₄ and Fe₂P additives. The composition, crystalline structure, and morphology of the synthesized powders were investigated by using ICP-OES, XRD, TEM, and SEM, respectively. The electrochemical properties of the powders were investigated with cyclic voltammetric and capacity retention studies. The capacity retention studies were carried out with LiFePO₄/Li cells and LiFePO₄/MCMB cells comprised LiFePO₄-based materials prepared at various temperatures from a stoichiometric precursor. Among all of the synthesized powders, the samples synthesized at 750 and 775 °C demonstrate the most promising cycling performance with C/10, C/5, C/2, and 1C rates. The sample synthesized at 775 °C shows initial discharge capacity of 155 mAh g⁻¹ at 30 °C with C/10 rate. From the results of the cycling performance of LiFePO₄/MCMB cells, it is found that 800 °C sample exhibited higher polarization growth rate than 700 °C sample, though it shows lower capacity fading rate than 700 °C sample. For Fe₂P containing samples, the diffusion coefficient of Li⁺ ion increases with increasing amount of Fe₂P, however, the sample synthesized at 900 °C shows much lower Li⁺ ion diffusion coefficient due to the hindrance of Fe₂P layer on the surface of LiFePO₄ particles.     

Structural and electrochemical properties of LiNi1/3Co1/3Mn1/3O2: Calcination temperature dependence

The structure of the layered LiNi_1/3Co_1/3Mn_1/3O₂ has been investigated by powder X-ray diffraction and electron diffraction, and the relationship of the calcination temperature with the crystal structure, morphology and electrochemical properties has been studied. All the unit cell parameters increase monotonically with increasing the calcination temperature. Some of the [00.1] zone electron diffraction patterns for the sample calcined at higher temperature than 1000 °C show extra spots indicating the 2 × 2 ordering in the basal triangular lattice. These results indicate that the high temperature calcination leads to the formation of vacancies in the transition metal layers with the spinel-like ordering. The calcination at higher temperature lowers the specific capacities and degrades the cycle performances, while the packing density of the powder is increased by the sintering. The optimum calcination temperature is 900 °C in order to obtain the electrochemically active and dense packed oxide particles. The decrease of Li composition leads to coprecipitation of the spinel-like second phase in the range of 0.742 ≤ x ≤ 0.884 for Li_xNi_1/3Co_1/3Mn_1/3O₂, when calcined at 900 °C. The Li-deficient samples show the worse electrochemical properties similarly to the stoichiometric samples calcined at high temperature. For the Li-excess samples, no impurity phase has been detected and their cycle performances are improved.     

Synthesis of pristine and carbon-coated Li4Ti5O12 and their low-temperature electrochemical performance

Pristine and carbon-coated Li₄Ti₅O₁₂ oxide electrodes are synthesized by a cellulose-assisted combustion technique with sucrose as organic carbon source and their low-temperature electrochemical performance as anodes for lithium-ion batteries are investigated. X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) are applied to characterize the phase structure, composition, and morphology of the composites. It is found that the sequence of sucrose addition has significant effect on the phase formation of Li₄Ti₅O₁₂. Carbon-coated Li₄Ti₅O₁₂ is successfully prepared by coating the pre-crystallized Li₄Ti₅O₁₂ phase with sucrose followed by thermal treatment. Electrochemical lithium insertion/extraction performance is evaluated by the galvanostatic charge/discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), from room temperature (25 °C) to −20 °C. The carbon-coated composite anode materials show improved lithium insertion/extraction capacity and electrode kinetics, especially at high rates and low temperature. Both of the two samples show fairly stable cycling performance at various temperatures, which is highly promising for practical applications in power sources of electric or electric-hybrid vehicles.     

Electrochemical activity of Li2FeTiO4 and Li2MnTiO4 as potential active materials for Li ion batteries: A comparison with Li2NiTiO4

We demonstrate, for the first time, a considerable electrochemical activity of two members of lithium transition element titanates: Li₂FeTiO₄ and Li₂MnTiO₄. Both materials consist of 10–20 nm particles embedded in a conductive carbon coating. We show that not the coating but the small particle size is decisive for materials’ activity. Li₂FeTiO₄ shows a stable reversible capacity of up to 123 mA hg⁻¹ at C/20 and 60 °C which is 83% of the theoretical value for exchange of 1 electron (148 mA hg⁻¹). Li₂MnTiO₄ could only be prepared in a nanosized form that contained about 30% of impurities. The capacity of the whole material (including impurities) is comparable to that of Li₂FeTiO₄ but the cycling stability is much poorer. In contrast to the Fe and Mn analogues, the third member of the titanate family, Li₂NiTiO₄, shows a good electrochemistry even when the particle size is much larger (about 100 nm). During initial cycles at C/10 and 60 °C, exchange of more than 1 electron per compound formula has been observed. The cycling stability at high temperatures, however, is poor.     

Formation of the high lithium ion conducting phase from mechanically milled amorphous Li2S-P2S5 system

The fast ionic conducting structure similar to thio-Lithium Super Ionic Conductor (LISICON) phase is synthesized in the Li₂S-P₂S₅ system. The Li₂S-P₂S₅ glass-ceramics with the composition of xLi₂S·(100−x)P₂S₅ (75 ≤ x ≤ 80) are prepared by the heat-treatment of mechanically milled amorphous sulfide powders. In the binary Li₂S-P₂S₅ system, 78.3Li₂S·21.7P₂S₅ glass ceramic prepared by mechanical milling and subsequent heat-treatment at 260 °C for 3 h shows the highest conductivity of 6.3 × 10⁻⁴ S cm⁻¹ at room temperature and the lowest activation energy for conduction of 30.5 kJ mol⁻¹. The enhancement of conductivity with increasing x up to 78.3 is probably caused by the introduction of interstitial lithium ions at the Li sites which affects the Li ion distribution. The prepared electrolyte exhibits the lithium ion transport number of almost unity and voltage stability of 5 V vs. Li at room temperature.     

A novel high temperature stable lithium salt (Li2B12F12) for lithium ion batteries

Basic properties and battery performances of the novel high temperature stable lithium salt (Li₂B₁₂F₁₂, Dilithium Dodecafluorododecaborate; Li₂DFB) were studied using a Mn-based cathode and anode composed of a hard carbon and graphite mixture. The effect of co-solvents (mainly linear carbonate in electrolyte formulation of PC/EC/co-solvent (5/30/65 vol% mixture)) on conductivity, viscosity, charge-discharge capacities, rate performance, temperature performance, cycle life and storage life at 60 °C was investigated. Conductivity of Li₂DFB electrolyte increased with reducing its viscosity by changing co-solvent and increasing the volume of the higher dielectric solvent. Li₂DFB electrolytes showed comparable discharge capacity and columbic efficiency against LiPF₆ electrolyte. Li₂DFB electrolytes improved the storage life and cycle life of a Mn-based cell at 60 °C.     

Li ion exchange in CeO2-TiO2 sol-gel layers studied by electrochemical quartz crystal microbalance

The paper reports first on the electrochemical behavior in liquid Li⁺ electrolytes of 200 nm thick single sol-gel (CeO₂)_0.81-TiO₂ electrochromic (EC) layers deposited by the dip-coating process. The electrolytes were solutions of 1 M LiClO₄ dissolved in dry propylene carbonate (PC) (containing 0.03 wt% of water) and wet PC containing up to 10 wt% of water, respectively. Then an electrochemical quartz crystal microbalance was used as a sensitive detector to analyze the mass changes occurring during the Li⁺ ion exchange processes. These electrochemical processes were studied for 370 nm thick double layers, deposited on gold-coated quartz crystal electrodes and sintered at 450 °C in air. The electrolytes were the same solutions with water content varying from 0.03 up to 3 wt% of water. The processes have been studied in the potential range from −2.0 to +1.0 V vs. Ag/AgClO₄ during 100 voltammetry cycles. The composition of the (CeO₂)_0.81-TiO₂ layers was found to change during the early cycles, mainly because of an irreversible Li⁺ intercalation. It was found, however, that the mass change observed during cycling is not due only to a pure Li⁺ ion exchange process but also involves the adsorption/desorption or exchange of other cations and anions contained in the electrolyte. These ions are Li⁺ and ClO₄⁻ in dry electrolyte and Li⁺, hydrated Li(H₂O)_n⁺ and ClO₄⁻ in wet electrolyte. The improvement of the reversibility of the intercalation and deintercalation processes as well as the faster kinetics observed in wet electrolytes are finally discussed in terms of a model in which the formation of hydrated Li⁺ ions takes an important role.     

Al-doped Li7La3Zr2O12 synthesized by a polymerized complex method

Li₇La₃Zr₂O₁₂ electrolytes doped with different amounts of Al (0, 0.2, 0.7, 1.2, and 2.5 wt.%) were prepared by a polymerized complex (Pechini) method. The influence of aluminum on the structure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscopy (SEM), and thermal dilatometry. It was found that even a small amount of Al (e.g. 0.2 wt.%) added to Li₇La₃Zr₂O₁₂ can greatly accelerate densification during the sintering process. SEM micrographs showed the existence of a liquid phase introduced by Al additions which led to the enhanced sintering rate. The addition of Al also stabilized the higher conductivity cubic form of Li₇La₃Zr₂O₁₂ rather than the less conductive tetragonal form. The combination of these two beneficial effects of Al enabled greatly reduced sintering times for preparation of highly conductive Li₇La₃Zr₂O₁₂ electrolyte. With optimal additions of Al (e.g. 1.2 wt.%), Li₇La₃Zr₂O₁₂ electrolyte sintered at 1200 °C for only 6 h showed an ionic conductivity of 2.0 × 10⁻⁴ S cm⁻¹ at room temperature.     

Synthesis, phase relation and electrical and electrochemical properties of ruthenium-substituted Li2MnO3 as a novel cathode material

Layered oxides, ruthenium-substituted Li₂MnO₃, were synthesized at 800 °C and 1200 °C. Their phase relation and electrical and electrochemical properties were investigated. Li₂Mn_1−xRu_xO₃ synthesized at 800 °C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 ≤ x ≤ 0.05, while Li₂Mn_1−xRu_xO₃ synthesized at 1200 °C formed two solid solutions in the whole composition range across a structural transition between x = 0.6 and 0.8. The electrical resistivity of Li₂Mn_1−xRu_xO₃ decreased with increasing ruthenium content. Li₂Mn_0.2Ru_0.8O₃ (x = 0.8) synthesized at 1200 °C showed the lowest resistivity of 5.7 × 10² Ω cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li₂Mn_0.4Ru_0.6O₃ (x = 0.6) exhibited a discharge capacity of 192 mAh g⁻¹ in the initial cycle and 169 mAh g⁻¹ in the tenth cycle with high and almost constant charge-discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li₂MnO₃ is quite effective to improve electrical conductivity and charge-discharge performance.     

Structural changes of bare and AlPO4-coated LixCoO2 (x = 0.24 and 0.1) upon thermal annealing ≥200°C

Structural changes of bare and AlPO₄-coated Li_xCoO₂ with a coating thickness of 20 and 200 nm are investigated at x = 0.24 and 0.1 after thermal annealing at 200, 300, and 400 °C using XRD and Co K-edge XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure). Both the bare and coated cathodes exhibit faster phase transformation into spinel phases at lower annealing temperatures as x in Li_xCoO₂ is decreased. Bare Li_xCoO₂ cathodes exhibit phase transitions from Li_xCo₂O₄ to Co₃O₄ spinel as the annealing temperature is increased and the x is value decreased, which suggests a possible reaction according to (1/2)Li_xCo₂O₄ → xLi₂CO₃ + (1/3)Co₃O₄ + (2/3)O₂. However, the coated cathodes sustain a Li_xCo₂O₄ phase even at 400 °C and x = 0.1. This indicates that the AlPO₄ coating layer suppresses the Li_xCo₂O₄ phase decomposition into Co₃O₄.     

Role of MgCo compound on the sorption properties of the Mg-Co milled mixtures

The influence of MgCo on the reaction paths during hydriding and dehydriding processes of Mg-Co mixtures was studied using a combined HP-DSC and XRD approach. Mg-Co mixtures with different compositions were mechanically milled under argon to prepare Mg-Co nanocomposites and then submitted to thermal treatment at 300 °C for 5 days to induce MgCo formation. The local Mg-Co composition in the milled and milled-heated samples determines the nature of the phases obtained after hydriding/dehydriding cycling. The formation of Mg₆Co₂H₁₁, Mg₂CoH₅ and MgH₂ hydrides occurs after the first hydriding stage of the 2Mg-Co and Mg-Co milled mixtures due to kinetic restrictions. On the contrary, Mg-Co milled-heated mixture exhibits the selective formation of Mg₂CoH₅ during first hydriding via two-step reaction. In the first one, MgCo disproportion to MgH₂ and Co takes place simultaneously with Mg hydriding (<200 °C). The second step involves MgCo hydriding to Mg₂CoH₅ through MgH₂ as intermediate phase (>200 °C). Dehydriding reaction is enhanced by dispersion of Co into Mg-matrix, which reduces more than 100 °C the hydrogen desorption temperature when compared with the Mg-Co milled sample without previous heating.