Approaching the limits of cationic and anionic electrochemical activity with the Li-rich layered rocksalt Li3IrO4

Abstract

Progress over the last two decades in positive electrode materials for Li-ion batteries has generated a variety of novel materials. The Li-rich rocksalt oxides Li 2 MO 3 (M = 3d/4d/5d transition metal) are especially promising, displaying capacities exceeding 300 mAh/g thanks to the participation of the oxygen non-bonding O(2p) orbitals in the redox process.Understanding the oxygen redox limitations and the role of O/M ratio is therefore crucial for the rational design of materials with improved electrochemical performances. Herein, we push oxygen redox to its limits with the discovery of a new Li 3 IrO 4 compound (O/M = 4) which can reversibly uptake and release 3.5 e-per transition metal; the highest capacity ever reported for any positive insertion electrode, via the cumulative activation of cationic and anionic redox processes. By quantitatively monitoring the oxidation process, we demonstrate the material instability against O 2 release upon removal of all Li. Accordingly; we find the fully-delithiated phase to undergo irreversible amorphization producing a new a-IrO 3 phase with a local structure made of threefold connected IrO 6 octahedra. Our results show that the O/M parameter delineates the boundary between the material's maximum capacity and its stability, hence providing valuable insights for further high capacity materials developments.

Manganese‐Based Na‐Rich Materials Boost Anionic Redox in High‐Performance Layered Cathodes for Sodium‐Ion Batteries

“…Recent research disclosed, the increasing of the Li(Na) content within layered structure materials can effectively influence the local atom coordination around oxygen atoms which could improve O redox upon cycling and lead to a higher capacity . As demonstrated by Tarascon and Ceder et al, increasing the Li(Na) ratio can shift the O 2p nonbonding band gradually up near the Fermi level.…”

Proton Ion Exchange Reaction in Li3IrO4: A Way to New H3+xIrO4 Phases Electrochemically Active in Both Aqueous and Nonaqueous Electrolytes

“…Single phase Li 3 IrO 4 powder was prepared by a previously described ceramic process, which consists in heating a stoichiometric mixture of Ir and Li 2 CO 3 in air at 950 °C for 24 h. [15] The resulting powder was stirred in a 0.1 m H 2 SO 4 solution and, after 1 h of stirring, the powder was recovered by centrifugation and washed with distilled water prior to its characterization. Comparative scanning electron microscopy (SEM) pictures of the pristine and recovered powders (Figure 1, inset) indicate the break-up of the initial 10-20 µm aggregates but no impact of the acid treatment on the 1-2 µm size primary particles.…”

A High‐Performance Primary Nanosheet Heterojunction Cathode Composed of Na0.44MnO2 Tunnels and Layered Na2Mn3O7 for Na‐Ion Batteries

“…The reversible oxygen‐redox for the Na‐deficient cathode results from the reaction between the nonbonding 2p orbitals of the oxygen atoms and the nearby Mn vacancies, which contribute two charge plateaus in the high voltage region . Compared with oxygen‐redox from a noble metal‐based cathode (Na 2 IrO 3 and Na 2 RuO 3 ), the low‐cost Na 2 Mn 3 O 7 cathode is much more attractive . However, capacity fading and a low coulombic efficiency (C.E.)…”

“…[20] Compared with oxygen-redoxf rom an oble metal-based cathode (Na 2 IrO 3 andN a 2 RuO 3 ), the lowcost Na 2 Mn 3 O 7 cathode is much more attractive. [24,25] However, capacityf ading and al ow coulombic efficiency (C.E.) during multiple cycles weres till found in theser eports.…”