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.
In contrast to conventional ceramic
ionic conductors relying on
bulk ionic transport, making use of interfaces such as grain boundary
and surface may provide various new possibilities to develop novel
ionic conductors. Here we demonstrate that nanograined structures
of yttria-doped zirconia (YSZ), of which the bulk property involves
negligible proton solubility or conductivity, are endowed with appreciable
proton conductivity via interfacial hydrated layers. A combination
of nanopowder synthesis and ultra high-pressure compaction (4 GPa)
at room temperature enables us to fabricate the nanograined specimens.
The material thus prepared can retain an appreciable amount of protons
and water within the grain-boundary or “internal surface”,
resulting in a hierarchical structure of hydroxyl groups and water
molecules with different thermal stability and thereby mobility. The
physicochemical properties of those protonic species have been investigated
by means of in situ FT-IR, 1H MAS NMR, and thermal desorption
spectroscopy. At lower temperatures, proton conductivity prevails
over normally observed oxide ion conductivity, which is facilitated
by interplay of those protonic species at the interfaces. The present
study provides a new prospect for developing proton-conducting materials
which are based on “surface protonics” of nanograined
oxides.
High quality
Li3PO4
thin films have been prepared by pulsed laser deposition (PLD) as a solid electrolyte for thin-film batteries. The structure, composition, ionic conductivity, and electrochemical stability of the
Li3PO4
thin films have been characterized. The
Li3PO4
film exhibits a single lithium-ion conductor with an ionic conductivity of
4.0×10−7Scm−1
at
25°C
and an activation energy of 0.58 eV. The
Li3PO4
film is electrochemically stable in the potential range from 0 to 4.7 V vs
Li/Li+
. All-solid-state thin-film batteries,
Li/Li3PO4/LiCoO2
, have been fabricated by using PLD-grown
Li3PO4
thin film. The thin-film battery shows excellent intercalation property and stability for long-term cycling in the potential range from 3.0 to 4.4 V.
Understanding and improving the behavior of interfaces is essential to the development of safer and high performance Li-based batteries regardless of their range of applications. Indirect methods such as impedance spectroscopy or direct methods such as the live in situ observation of batteries cycled within a scanning electron microscope (in situ SEM) are used to determine the interface microstructure/composition evolution upon cycling. These methods are used to establish a direct link between interface properties and batteries performance; they also enable us to spot local interface defects that are crucial to the development of 2D solid-state microbattery, for instance. Indeed, this technology is of interest in powering the new generation of microelectromechanical systems (MEMS). Here, we demonstrate the first ex situ TEM observation of “nanobatteries” obtained by cross-sectioning a microbattery using focus ion beam (FIB) in a dual beam SEM. Then, TEM analyses between pristine, cycled, and faulted all solid-state LiCoO2/solid electrolyte/SnO Li-ion batteries have revealed drastic changes such as the presence, depending on the battery fabrication process, of both cavities within the solid electrolyte layers and low wetting points between the electrolyte and the negative electrode. Moreover, post-mortem TEM observations of cycled microbatteries have revealed a rapid deterioration of the interface upon cycling because of the migration of the chemical elements between stacked layers. Such findings are involved both in the improvement of the reliability of the 2D all solid-state battery assembling process and in the enhancement of their cycling performances. Such achievements constitute the technical platform for our future targets namely the development of live in situ TEM observation of “nanobatteries” cycled within the microscope.
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