The increase in hydrogen back pressure unexpectedly enhances the overall dehydrogenation reaction rate of the 4LiBH(4) + YH(3) composite significantly. Also, argon back pressure has a similar influence on the composite. Gas back pressure seems to enhance the dehydrogenation reaction by kinetically suppressing the formation of the diborane by-product.
We report the direct observation of microstructural changes of LixSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion. Because lithiation‐induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high‐capacity Si anodes in lithium‐ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials.
This paper investigates dehydrogenation reaction behavior of the LiBH 4 −MgH 2 composite at 450 °C under various hydrogen and argon backpressure conditions. While the individual decompositions of LiBH 4 and MgH 2 simultaneously occur under 0.1 MPa H 2 , the dehydrogenation of MgH 2 into Mg first takes place and subsequent reaction between LiBH 4 and Mg into LiH and MgB 2 after an incubation period under 0.5 MPa H 2 . Under 1 MPa H 2 , enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H 2 is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H 2 . The formation of Li 2 B 12 H 12 as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H 2 , which effectively suppresses the formation of Li 2 B 12 H 12 . The overall dehydrogenation behavior under argon pressure conditions is similar to that at hydrogen pressure conditions, except that under 2 MPa Ar.
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