All-solid-state batteries incorporating lithium metal anode have the potential to address the energy density issues of conventional lithium-ion batteries that use flammable organic liquid electrolytes and low-capacity carbonaceous anodes. However, they suffer from high lithium ion transfer resistance, mainly due to the instability of the solid electrolytes against lithium metal, limiting their use in practical cells. Here, we report a complex hydride lithium superionic conductor, 0.7Li(CB
9
H
10
)–0.3Li(CB
11
H
12
), with excellent stability against lithium metal and a high conductivity of 6.7 × 10
−3
S cm
−1
at 25 °C. This complex hydride exhibits stable lithium plating/stripping reaction with negligible interfacial resistance (<1 Ω cm
2
) at 0.2 mA cm
−2
, enabling all-solid-state lithium-sulfur batteries with high energy density (>2500 Wh kg
−1
) at a high current density of 5016 mA g
−1
. The present study opens up an unexplored research area in the field of solid electrolyte materials, contributing to the development of high-energy-density batteries.
Magnesium borohydride ammonia borane, Mg-(BH 4 ) 2 (NH 3 BH 3 ) 2 , was electrochemically investigated. Impedance measurements of the mechanochemically synthesized Mg-(BH 4 ) 2 (NH 3 BH 3 ) 2 exhibited an ionic conductivity of 1.3 × 10 −5 S cm −1 at 30 °C. Electrochemical cells fabricated with Mg-(BH 4 ) 2 (NH 3 BH 3 ) 2 as the solid electrolyte demonstrated reversible Mg migration through the material, indicating its potential for use as a Mg ionic conductor in all-solid-state Mg-ion batteries.
Crystal structure determination is essential for characterizing materials and their properties, and can be facilitated by various tools and indicators. For instance, the Goldschmidt tolerance factor (T) for perovskite compounds is acknowledged for evaluating crystal structures in terms of the ionic packing. However, its applicability is limited to perovskite compounds. Here, we report on extending the applicability of T to ionic compounds with arbitrary ionic arrangements and compositions. By focussing on the occupancy of constituent spherical ions in the crystal structure, we define the ionic filling fraction (IFF), which is obtained from the volumes of crystal structure and constituent ions. Ionic compounds, including perovskites, are arranged linearly by the IFF, providing consistent results with T. The linearity guides towards finding suitable unit cell and composition, thus tackling the main obstacle for determining new crystal structures. We demonstrate the utility of the IFF by solving the structure of three hydrides with new crystal structures.
closo-type complex hydrides contain large cage-type
complex polyanions in their crystal structures and thus can exhibit
superior ion-conducting properties (e.g., Li and Na). However, the
unique structures of complex polyanions have made it challenging to
modify crystal structures, making systematic control of ion conductivity
difficult. Here, we report an atom deficiency approach to enhance
lithium-ion conductivity of complex hydrides. We find that lithium
and hydrogen could be simultaneously extracted from Li2B12H12 by applying a small external energy,
enabling the formation of atom deficiencies. These atom deficiencies
lead to an increase in carrier concentration, improving lithium-ion
conductivity by 3 orders of magnitude compared to that of a pristine
material. An all-solid-state TiS2/Li battery employing
atom-deficient Li2B12H12 as a solid
electrolyte exhibits superior battery performance during repeated
discharge–charge cycles. The current study suggests that the
atom deficiency can be a useful strategy to develop high ion-conducting
complex hydride solid electrolytes.
Recent results of energetic ion driven MHD instabilities observed in the
heliotron/torsatron devices Compact Helical System (CHS) and Large Helical
Device (LHD) are presented. Alfvén eigenmodes (AEs)
and fishbone-like burst modes (FBs) destabilized by energetic ions were observed in
NBI heated plasmas of CHS. The AEs are toroidicity induced Alfvén eigenmodes (TAEs)
and global Alfvén eigenmodes (GAEs), where the identified toroidal mode numbers
are n = 1 and 2 for TAEs and n = 0 for GAEs. The frequencies of the FBs are less than,
at most, half of the minimum TAE gap frequency and do not exhibit the obvious density
dependence related to Alfvén velocity. The modes have characteristic features of the
energetic particle modes or the resonant TAEs excited by circulating energetic beam
ions produced by NBI. Bursting amplitude modulation is observed in TAEs as well as in
FBs. Rapid frequency chirping is observed in each burst, by a factor of 2-6 in FBs
and about 25% in TAEs. In several shots, the power spectrum of the TAEs is split into
multiple peaks having the same toroidal mode number through non-linear evolution of
TAEs. A pulsed increase in energetic ion loss towards the wall is induced by m = 3/n = 2
FBs, but so far not by m = 2/n = 1 FBs, TAEs and GAEs, where m is the poloidal mode
number. This research has been extended to LHD plasmas heated by neutral hydrogen beams
with about 130 keV energy. Similar to CHS, TAEs and FBs were observed in relatively low
density plasmas at low toroidal magnetic field (Bt = 1.5 T).
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