Ezhiylmurugan Rangasamy

An Iodide-Based Li7P2S8I Superionic Conductor

In an example of stability from instability, a Li(7)P(2)S(8)I solid-state Li-ion conductor derived from β-Li(3)PS(4) and LiI demonstrates electrochemical stability up to 10 V vs Li/Li(+). The oxidation instability of I is subverted via its incorporation into the coordinated structure. The inclusion of I also creates stability with the metallic Li anode while simultaneously enhancing the interfacial kinetics and ionic conductivity. Low-temperature membrane processability enables facile fabrication of dense membranes, making this conductor suitable for industrial adoption.

Excellent stability of a lithium-ion-conducting solid electrolyte upon reversible Li+/H+ exchange in aqueous solutions

Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long-term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li7 La3 Zr2 O12 garnet as a Li-stable solid electrolyte. The material underwent a Li(+) /H(+) exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li(+) /H(+) exchange was reversed without any structural change. These observations suggest that cubic Li7 La3 Zr2 O12 is a promising candidate for the separator in aqueous lithium batteries.

Synthesis of nano-scale fast ion conducting cubic Li7La3Zr2O12

A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol-gel chemistry was developed to prepare solid metal-oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 ° C. Sol-gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0.4 mS cm(-1) at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol-gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO.

Pushing the Theoretical Limit of Li-CFx Batteries: A Tale of Bifunctional Electrolyte

In a typical battery, the inert electrolyte functions solely as the ionic conductor without contribution to the cell capacity. Here we demonstrate that the most energy-dense Li-CF(x) battery delivers a capacity exceeding the theoretical maximum of CF(x) with a solid electrolyte of Li3PS4 (LPS) that has dual functions: as the inert electrolyte at the anode and the active component at the cathode. Such a bifunctional electrolyte reconciles both inert and active characteristics through a synergistic discharge mechanism of CF(x) and LPS. The synergy at the cathode is through LiF, the discharge product of CF(x), which activates the electrochemical discharge of LPS at a close electrochemical potential of CF(x). Therefore, the solid-state Li-CF(x) batteries output 126.6% energy beyond their theoretic limits without compromising the stability of the cell voltage. The additional energy comes from the electrochemical discharge of LPS, the inert electrolyte. This bifunctional electrolyte revolutionizes the concept of conventional batteries and opens a new avenue for the design of batteries with unprecedented energy density.

High conducting oxide--sulfide composite lithium superionic conductor

A solid electrolyte for a lithium-sulfur battery includes particles of a lithium ion conducting oxide composition embedded within a lithium ion conducting sulfide composition. The lithium ion conducting oxide composition can be Li7La3Zr2O12 (LLZO). The lithium ion conducting sulfide composition can be β-Li3PS4 (LPS). A lithium ion battery and a method of making a solid electrolyte for a lithium ion battery are also disclosed.

A high-conduction Ge substituted Li3AsS4 solid electrolyte with exceptional low activation energy

Lithium-ion conducting solid electrolytes show potential to enable high-energy-density secondary batteries and offer distinctive safety features as an advantage over traditional liquid electrolytes. Achieving the combination of high ionic conductivity, low activation energy, and outstanding electrochemical stability in crystalline solid electrolytes is a challenge for the synthesis of novel solid electrolytes. Herein we report an exceptionally low activation energy (Ea) and high room temperature superionic conductivity via facile aliovalent substitution of Li3AsS4 by Ge, which increased the conductivity by two orders of magnitude as compared with the parent compound. The composition Li3.334Ge0.334As0.666S4 has a high ionic conductivity of 1.12 mS cm−1 at 27 °C. Local Li+ hopping in this material is accompanied by a distinctive low activation energy Ea of 0.17 eV, being the lowest of Li+ solid conductors. Furthermore, this study demonstrates the efficacy of surface passivation of solid electrolyte to achieve compatibility with metallic lithium electrodes.

A study of suppressed formation of low-conductivity phases in doped Li7La3Zr2O12 garnets by in situ neutron diffraction

Doped Li7La3Zr2O12 garnets, oxide-based solids with good Li+ conductivity and compatibility, show great potential as leading electrolyte material candidates for all-solid-state lithium ion batteries. However, the conductive bulk usually suffers from the presence of secondary phases and the transition towards a low-conductivity tetragonal phase during synthesis. Dopants are designed to stabilize the high-conductive cubic phase and suppress the formation of the low-conductivity phases. In situ neutron diffraction enables a direct observation of the doping effects by monitoring the phase evolutions during garnet synthesis. It reveals the reaction mechanism involving the temporary presence of intermediate phases. The off-stoichiometry due to the liquid Li2CO3 evaporation leads to the residual of the low-conductivity intermediate phase in the as-synthesized bulk. Appropriate doping of an active element may alter the component of the intermediate phases and promote the completion of the reaction. While the dopants aid to stabilize most of the cubic phase, a small amount of tetragonal phase tends to form under a diffusion process. The in situ observations provide the guideline of process optimization to suppress the formation of unwanted low-conductivity phases.