Monodisperse MgH2 nanoparticles with homogeneous distribution and a high loading percent are developed through hydrogenation-induced self-assembly under the structure-directing role of graphene. Graphene acts not only as a structural support, but also as a space barrier to prevent the growth of MgH2 nanoparticles and as a thermally conductive pathway, leading to outstanding performance.

In search of new electrode materials for lithium-ion batteries, metal phosphides that exhibit desirable properties such as high theoretical capacity, moderate discharge plateau, and relatively low polarization recently have attracted a great deal of attention as anode materials. However, the large volume changes and thus resulting collapse of electrode structure during long-term cycling are still challenges for metal-phosphide-based anodes. Here we report an electrode design strategy to solve these problems. The key to this strategy is to confine the electroactive nanoparticles into flexible conductive hosts (like carbon materials) and meanwhile maintain a monodispersed nature of the electroactive particles within the hosts. Monodispersed carbon-coated cubic NiP nanoparticles anchored on carbon nanotubes (NiP@C-CNTs) as a proof-of-concept were designed and synthesized. Excellent cyclability (more than 1000 cycles) and capacity retention (high capacities of 816 mAh g after 1200 cycles at 1300 mA g and 654.5 mAh g after 1500 cycles at 5000 mA g) are characterized, which is among the best performance of the NiP anodes and even most of the phosphide-based anodes reported so far. The impressive performance is attributed to the superior structure stability and the enhanced reaction kinetics incurred by our design. Furthermore, a full cell consisting of a NiP@C-CNTs anode and a LiFePO cathode is investigated. It delivers an average discharge capacity of 827 mAh g based on the mass of the NiP anode and exhibits a capacity retention of 80.7% over 200 cycles, with an average output of ∼2.32 V. As a proof-of-concept, these results demonstrate the effectiveness of our strategy on improving the electrode performance. We believe that this strategy for construction of high-performance anodes can be extended to other phase-transformation-type materials, which suffer a large volume change upon lithium insertion/extraction.

Zn(BH 4) 2 •2NH 3 , a new ammine metal borohydride, has been synthesized via simply ball-milling a mixture of ZnCl 2 •2NH 3 /2LiBH 4. Structure analysis shows that the subsequent complex has a monoclinic structure with unit-cell parameters of a = 6.392(4) Å, b = 8.417(6) Å, c = 6.388(4) Å and β = 92.407(4) ° and space group P2 1 , in which Zn atoms coordinate with two BH 4 groups and two NH 3 groups. The interatomic distances reported herein show that Zn-H bonding in Zn(BH 4) 2 •2NH 3 is shorter than Ca-H bonds in Ca(BH 4) 2 •2NH 3 and Mg-H in Mg(BH 4) 2 •2NH 3. This reduced bond contact leads to an increase in the ionic character of H. This study is able to show a good correlation between the reduced M-H distance and enhanced dehydrogenation behavior of the hydride material. Dehydrogenation results showed that this novel compound is able to release 8.9 wt. % hydrogen below 115 °C within 10 min without concomitant release of undesirable gases such as ammonia and/or boranes, thereby demonstrating the potential of Zn(BH 4) 2 •2NH 3 to be used as a solid hydrogen storage material.

A new ammine dual-cation borohydride, LiMg(BH(4))(3)(NH(3))(2), has been successfully synthesized simply by ball-milling of Mg(BH(4))(2) and LiBH(4)·NH(3). Structure analysis of the synthesized LiMg(BH(4))(3)(NH(3))(2) revealed that it crystallized in the space group P6(3) (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three-dimensional architecture is built up through corner-connecting BH(4) units. Strong N-H···H-B dihydrogen bonds exist between the NH(3) and BH(4) units, enabling LiMg(BH(4))(3)(NH(3))(2) to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH(4))(3)(NH(3))(2)/LiBH(4) composite is able to release over 8 wt% hydrogen below 200 °C, which is comparable to that released by Mg(BH(4))(3)(NH(3))(2). More importantly, it was found that release of the byproduct NH(3) in this system can be completely suppressed by adjusting the ratio of Mg(BH(4))(2) and LiBH(4)·NH(3). This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.