Room temperature operation of all-solid-state battery using a closo-type complex hydride solid electrolyte and a LiCoO_(2) cathode by interfacial modification

We report on an all-solid-state battery that employs a closo-type complex hydride solid electrolyte and a LiCoO2 cathode.Interfacial modification between the solid electrolyte and cathode with a LiNbO3 buffer layer enables reversible charge-discharge cycling with a cell voltage of 3.9V (vs.Li^+/Li) at room temperature.Electrochemical analyses clarify that the given modification effectively suppresses side reactions at the cathode/solid electrolyte interface.The interfacial resistance is lowered by ca.10 times with a 5 nm thick LiNbO3 buffer layer compared to that without a buffer layer,so that a discharge capacity of 109 mAh g^-1 is achieved.These results suggest that interfacial modification can be a viable approach to the development of high-voltage all-solid-state batteries using closo-type complex hydride solid electrolytes and oxide cathodes.

Characterization of Compositionally Complex Hydrides in a Metastable Refractory High-Entropy Alloy

Here,we study the hydride formation in a metastable Ti-33Zr-22Hf-11Ta(at.%)refractory high entropy alloy(RHEA).Deviating to non-equiatomic compositions of RHEAs promotes the formation of transformation-induced plasticity where the body-centered cubic phase transforms to hexagonal close-packed(HCP)phase.It is found that the phase transformation capability assists the hydride formation due to the low solubility of hydrogen within the HCP phase.In this study,hydrogen is charged via electrochemical polishing and the corresponding phase transformation is activated in the metastable RHEAs.The newly formed HCP phase interacts with hydrogen to form a face-centered cubic hydride verified by electron energy loss spectroscopy.This work provides a primary exploration of the formation of compositionally complex metal hydrides in the metastable RHEAs,which are potential candidates for future hydrogen storage material design.

Enhanced dehydrogenation performances and mechanism of LiBH_4/Mg_(17)Al_(12)-hydride composite

Mg17Al12-hydride （abbreviated as MAH） was selected as a destabilization agent to improve de/rehydrogenation properties of LiBH4. 58LiBH4＋Mg17Al12-hydride composite was prepared by ball-milling. It is found that the dehydrogenation of ball-milled LiBH4/MAH composite presents a two-step reaction for hydrogen release. The composite starts desorbing hydrogen at about 300 ℃ and yields 9.8%of hydrogen （mass fraction） below 500 ℃. By adding MAH, the dehydrogenation kinetics of LiBH4 is improved and the dehydrogenation temperature of LiBH4 is also lowered by 20 ℃. High rehydriding capacity of 8.3% was obtained for the dehydrogenated composite in the first cycle at 450 ℃. The XRD analysis shows the formation of MgB2 and AlB2 in the dehydrogenation process, which reduces the thermodynamics stability of LiBH4 system and is beneficial to the reversible hydrogen storage behaviors of LiBH4/MAH composite.

Formation mechanism of MgB_2 in 2LiBH_4+MgH_2 system for reversible hydrogen storage

The formation conditions of MgB2 in 2LiBH4 ＋ MgH2 system during dehydrogenation were investigated and its mechanism was discussed. The results show that direct decomposition of LiBH4 is suppressed under relative higher initial dehydrogenation pressure of 4.0×10^5 Pa, wherein LiBH4 reacts with Mg to yield MgB2, and 9.16% （mass fraction） hydrogen is released within 9.6 h at 450 ℃. However, under relatively lower initial dehydrogenation pressure of 1.0×10^2 Pa, LiBH4 decomposes independently instead of reacting with Mg, resulting in no formation of MgB2, and 7.91% hydrogen is desorbed within 5.2 h at 450 ℃. It is found that the dehydrogenation of 2LiBH4 ＋ MgH2 system proceeds more completely and more hydrogen desorption amount can be obtained within a definite time by forming MgB2. Furthermore, it is proposed that the formation process of MgB2 includes incubation period and nucleus growth process. Experimental results show that the formation process of MgB2, especially the incubation period, is promoted by increasing initial dehydrogenation pressure at constant temperature, and the incubation period is also influenced greatly by dehydrogenation temperature.

Microstructural analyses of all-solid-state Li–S batteries using LiBH4-based solid electrolyte for prolonged cycle performance

Complex hydride materials have been widely investigated as potential solid electrolytes because they have good compatibility with the lithium metal anodes used in all-solid-state batteries. However, the development of all-solid-state batteries utilizing complex hydrides has been difficult as these cells tend to have short cycle lives. This study investigated the capacity fading mechanism of all-solid-state lithium–sulfur(Li–S) batteries using Li4(BH4)3I solid electrolytes by analyzing the cathode microstructure. Crosssectional scanning electron microscopy observations after 100 discharge–charge cycles revealed crack formation in the Li4(BH4)3I electrolyte and an increased cathode thickness. Raman spectroscopy indicated that decomposition of the Li4(BH4)3I solid electrolyte occurred at a constant rate during the cycling tests.To combat these effects, the cycle life of Li–S batteries was improved by increasing the amount of solid electrolyte in the cathode.

Dehydrogenation characteristics of LiAlH4 improved by in-situ formed catalysts

The hydrogen storage properties and catalytic mechanism of FeCl-doped LiAlHwere investigated in minute details. LiAlH-2 mol% FeClsamples start to release hydrogen at 76 °C, which is 64 °C lower than that of as-received LiAlH. Isothermal desorption measurements show that the 2 mol% FeCl-doped sample releases 7.0 wt% of hydrogen within 17 min at 250 °C. At lower temperatures of 110 °C and 80 °C, the sample can release 4.4 wt% and 3 wt% of hydrogen, respectively. The apparent activation energy of LiAlH-2 mol% FeClsamples for R2 is 105.02 k J/mol, which is 67 k J/mol lower than that of pure LiAlH. The reaction between LiAlHand FeClduring ball milling was found by analyzing the X-ray diffraction results,and Fe-Al particles formed in-situ from the reaction act as the real catalyst for the dehydrogenation of LiAlH.

Extreme high reversible capacity with over 8.0 wt% and excellent hydrogen storage properties of MgH2 combined with LiBH4 and Li3AlH6

Magnesium hydride has attracted great attention because of its high theoretical capacity and outstanding reversibility, nevertheless, its practical applications have been restricted by the disadvantages of the sluggish kinetics and high thermodynamic stability. In this work, an unexpected high reversible hydrogen capacity over 8.0 wt% has been achieved from MgH2 metal hydride composited with small amounts of LiBH4 and Li3AlH6 complex hydrides, which begins to release hydrogen at 276 ℃ and then completely dehydrogenates at 360 ℃. The dehydrogenated MgH2+LiBH4/Li3AlH6 composite can fully reabsorb hydrogen below 300 ℃ with an excellent cycling stability. The composite exhibits a significant reduction of dehydrogenation activation energy from 279.7 kJ/mol(primitive MgH2) to 139.3 kJ/mol(MgH2+LiBH4/Li3AlH6),as well as a remarkable reduction of dehydrogenation enthalpy change from 75.1 k J/mol H2(primitive MgH2) to 62.8 kJ/mol H2(MgH2+LiBH4/Li3AlH6). The additives of LiBH4 and Li3AlH6 not only enhance the cycling hydrogen capacity, but also simultaneously improve the reversible de/rehydrogenation kinetics, as well as the dehydrogenation thermodynamics. This notable improvement on the hydrogen absorption/desorption behaviors of the MgH2+LiBH4/Li3AlH6 composite could be attributed to the dehydrogenated products including Li3Mg7, Mg17Al12 and MgAlB4, which play a key role on reducing the dehydrogenation activation energy and increasing diffusion rate of hydrogen. Meanwhile, the LiBH4 and Li3AlH6 effectively destabilize MgH2 with a remarkable reduction on dehydrogenation enthalpy change in terms of thermodynamics. In particular, the Li3Mg7, Mg17Al12 and MgAlB4 phases can reversibly transform into MgH2, Li3AlH6 and LiBH4 after rehydrogenation, which contribute to maintain a high cycling capacity.This constructing strategy can further promote the development of high reversible capacity Mg-based materials with suitable de/rehydrogenation properties.

Influence of lanthanon hydride catalysts on hydrogen storage properties of sodium alanates

NaAlH4 complex hydrides doped with lanthanon hydrides were prepared by hydrogenation of the ball-milled NaH/Al＋ xrnol.% RE-H composites （RE=La, Ce; x=2, 4, 6） using Nail and A1 powder as raw materials. The influence of lanthanon hydride catalysts on the hydriding and dehydriding behaviors of the as-synthesized composites were investigated. It was found that the com- posite doped with 2 mol.% LaH3.01 displayed the highest hydrogen absorption capacity of 4.78 wt.% mad desorption capacity of 4.66 wt.%, respectively. Moreover, the composite doped with 6 mol% CEH2.51 showed the best hydriding/dehydriding reaction kinetics. The proposed catalytic mechanism for reversible hydrogen storage properties of the composite was attributed to the presence of active LaH3.01 and CeH2.51 particles, which were scattering on the surface of Nail and A1 particles, acting as the catalytic active sites for hydrogen diffusion and playing an important catalytic role in the improved hydriding/dehydriding reaction.

Remarkably improved hydrogen storage properties of nanocrystalline TiO2-modified NaAlH4 and evolution of Ti- containing species during dehydrogenation/hydrogenation

Adding a small amount of nanocrystalline TiO2@C （TiO2 supported on nano- porous carbon） composite dramatically decreases the operating temperatures and improves the reaction kinetics for hydrogen storage in NaAlH4. The nano- crystalline TiO2@C composite synthesized at 900 ℃ （referred as TiO2@C-900） exhibits superior catalytic activity to other catalyst-containing samples. The onset dehydrogenation temperature of the TiO2@C-900-containing sample is lowered to 90 ℃; this is 65 ℃ lower than that of the pristine sample. The dehydrogenated sample is completely hydrogenated at 115 ℃ and 100 bar of hydrogen pressure with a hydrogen capacity of 4.5 wt.%. Structural analyses reveal that the Ti undergoes a reduction process of Ti^4＋→Ti^3＋→Ti^2＋→Ti during the ball milling and heating processes, and further converts to Ti hydrides or forms Ti-Al species after rehydrogenation. The catalytic activities of Ti-based catalytic species decrease in the order Al-Ti-species 〉 TiH0.71 〉 TiH2 〉 TiO2. This understanding guides further improvement in hydrogen storage properties of metal alanates using nanocrvstalline transition metal-based additives.

Synthesis of nanoscale CeAl4 and its high catalytic efficiency for hydrogen storage of sodium alanate

Nanoscale CeAl4 was directly synthesized by the thermal reaction between CeH2 and nano-aluminum at300℃.Then nano CeAl4-doped sodium alanate（NaAlH4）was synthesized by ball milling NaH/Al with 0.04CeAl4under hydrogen atmosphere at room temperature,and the catalytic efficiency of nanoscale CeAl4 for hydrogen storage of NaAlH4 was systematically investigated.It is shown that CeAl4 can effectively improve the dehydrogenation properties of sodium alanate system.The 0.04CeAl4-doped NaAlH4 system starts to release hydrogen below 80℃,completes dehydrogenation within 10 min at 170℃,and exhibits good cycling de/hydrogenation kinetics at relatively lower temperature（100-140℃）.Apparent activation energy of the dehydrogenation of NaAlH4 can be effectively reduced by addition of CeAl4,resulting in the decrease in desorption temperatures.Moreover,by analyzing the reaction kinetics of nano CeAl4-doped NaAlH4sample,both of the decomposition steps are conformed to a two-dimensional phase-boundary growth mechanism.The mechanistic investigations gained here can help to understand the de-/rehydrogenation behaviors of catalyzed complex metal hydride systems.

Development and Application of Hydrogen Storage

Hydrogen,as a secure,clean,efficient,and available energy source,will be successfully applied to reduce and eliminate greenhouse gas emissions.Hydrogen storage technology,which is one of the key challenges in developing hydrogen economy,will be solved through the unremitting efforts of scientists.The progress on hydrogen storage technology research and recent developments in hydrogen storage materials is reported.Commonly used storage methods,such as high-pressure gas or liquid,cannot satisfy future storage requirement.Hence,relatively advanced storage methods,such as the use of metal-organic framework hydrides and carbon materials,are being developed as promising alternatives.Combining chemical and physical hydrogen storage in certain materials has potential advantages among all storage methods.Intensive research has been conducted on metal hydrides to improve their electrochemical and gaseous hydrogen storage properties,including their hydrogen storage capacity,kinetics,cycle stability,pressure,and thermal response,which are dependent on the composition and structural feature of alloys.Efforts have been exerted on a group of magnesium-based hydrides,as promising candidates for competitive hydrogen storage,to decrease their desorption temperature and enhance their kinetics and cycle life.Further research is necessary to achieve the goal of practical application by adding an appropriate catalyst and through rapid quenching or ball milling.Improving the kinetics and cycle life of complex hydrides is also an important aspect for potential applications of hydrogen energy.