The Enhanced Propertity Of LiBH₄Complex And [NH₂BH₃]^-Ionic Clusters Influence On The Properties Of The Hydrogen Storage Materials

In this paper, first-principles density-functional theory were used to calculate several fundamental physical properties of Li3M(BH4)4(M=Na, K, Mg, Ca), including Lattice constant, the density of states and charge density. Detialedly, The properties of Li1-xMxBH4(M=Na, K) doped with x=0,0.25,0.5,0.75,1were analysed. Furthermore, the difference of structure properties between1×1×2super Li4K4B8H32doped with x=0.5and double cation borohydride LiK(BH4)2were compared. How the electronic structure、bonding properties and thermodynamic stability affect the hydrogen storage were explored. Furthermore, the most important properties of K2Mg(NH2BH3)4, including lattice constant, the density of states, charge density and enthalpy, have been researched and discussed.The calculational data identify many valuable microstructural and provide predicting information about how to choose the doping element.The main conclusions of this paper are as follows:1. Doping with Na, K, Mg and Ca leads to unstable structure of LiBH4. The structure stability of Li0.75M0.25BH4(M=Mg, Ca) formed by replacing Liwith (M=Mg, Ca) is easy to form stable intermediate MgB2and CaB6in reaction process.2. Li4K4B8H32(1×1×2) and LiK(BH4)2show extraodinary similar properties in electronic structure, charge density and thermodynamics, whereas the structure of LiK(BH4)2is more compact than that of Li4B8H32.3. Independent radical of NH3exists in Ca(BH4)2·NH3and Ca(BH4)2-2NH3compounds, while does not exist in Ca(NH2BH3)2, which has the least formation enthalpy absolute value and the B, N and H atoms exist in the form of atomic groups. This indicates that Ca(NH2BH3)2has lower thermodynamic stability and hydrogen desorption temperature than Ca(BH4)2-NH3and Ca(BH4)2·2NH3compounds have, which suggest that it is more suitable for hydrogen storage.4. K2Mg(NH2BH3)4and Na2Mg(NH2BH3)4compounds have similar crystal structure and electronic structure. Compared with K2Mg(NH2BH3)4, Na2Mg(NH2BH3)4has less formation enthalpy absolute value and lighter density, which means more conductive to hydrogen desorbing and more convenient to carry. So Na2Mg(NH2BH3)4is more suitable for hydrogen storage material.