The growing need to store an increasing amount of renewable energy in a sustainable way has rekindled interest for sodium-ion battery technology, owing to the natural abundance of sodium. Presently, sodium-ion batteries based on Na3V2(PO4)2F3/C are the subject of intense research focused on improving the energy density by harnessing the third sodium, which has so far been reported to be electrochemically inaccessible. Here, we are able to trigger the activity of the third sodium electrochemically via the formation of a disordered NaxV2(PO4)2F3 phase of tetragonal symmetry (I4/mmm space group). This phase can reversibly uptake 3 sodium ions per formula unit over the 1 to 4.8 V voltage range, with the last one being re-inserted at 1.6 V vs Na+/Na0. We track the sodium-driven structural/charge compensation mechanism associated to the new phase and find that it remains disordered on cycling while its average vanadium oxidation state varies from 3 to 4.5. Full sodium-ion cells based on this phase as positive electrode and carbon as negative electrode show a 10–20% increase in the overall energy density.

Although layered lithium nickel‐rich oxides have become the state‐of‐the‐art cathode materials for lithium‐ion batteries in electric vehicle (EV) applications, they can suffer from rapid performance failure—particularly when operated under conditions of stress (temperature, high voltage)‐the underlying mechanisms of which are not fully understood. This essay aims to connect electrochemical performance with changes in structure during cycling. First, structural properties of LiNiO2 are compared to the substituted Ni‐rich compounds NMCs (LiNixMnyCo1−x−yO2) and NCAs (LiNixCoyAl1−x−yO2). Particular emphasis is placed on decoupling intrinsic behavior and extrinsic “two‐phase” reactions observed during initial cycles, as well as after extensive cycling for NMC and NCA cathodes. The need to revisit the various high‐voltage structural changes that occur in LiNiO2 with modern characterization tools is highlighted to aid the understanding of the accelerated degradation for Ni‐rich cathodes at high voltages.

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.

Key to advancing lithium-ion battery technology, and in particular fast charging capabilities, is our ability to follow and understand the dynamic processes occurring in operating materials under realistic conditions, in real time, and on the nano-to mesoscale. Currently, operando imaging of lithium-ion dynamics requires sophisticated synchrotron X-ray or electron microscopy techniques, which do not lend themselves to high-throughput material screening. This limits rapid and rational materials improvements. Here we introduce a simple lab-based, optical interferometric scattering microscope to resolve nanoscopic lithium-ion dynamics in battery materials and apply it to follow the repeated cycling of the archetypical cathode material LixCoO2. The method allows us to visualise directly the insulator-metal, solid solution and lithium ordering phase transitions in this material. We determine rates of lithium insertion and removal at the single-particle level and identify different mechanisms that occur on charge vs. discharge. Finally, we capture the dynamic formation of domain boundaries between different crystal orientations associated with the monoclinic lattice distortion at around Li0.5CoO2. The high throughput nature of our methodology allows many particles to be sampled across the entire electrode and, moving forward, will enable exploration of the role of dislocations, morphologies and cycling rate on battery degradation. The generality of our imaging concept means that it can be applied to study any battery electrode, and more broadly, systems where the transport of ions is associated with electronic or structural changes, including nanoionic films, ionic conducting polymers, photocatalytic materials and memristors.Lithium-ion batteries have emerged as the frontrunner technology to achieve highpower, intermediate-scale energy storage, with a broad range of applications including electric

Sodium ion batteries (NIBs) are one of the versatile technologies for low cost rechargeable batteries. O3-type layered sodium transition metal oxides (NaMO2, M = transition metal ions) are one of the most promising positive electrode materials, capacity-wise. However, the use of O3 phases is limited due to their low redox voltage and associated multiple phase transitions which are detrimental for long cycling. Herein, we proposed a simple strategy to successfully combat these issues. It consists in the introduction of a larger, non-transition metal ion Sn 4+ in NaMO2 to prepare a series of NaNi0.5Mn0.5-ySnyO2 (y=0-0.5) compositions with attractive electrochemical performances, namely for y=0.5, which shows a single phase transition from O3  P3 at the very end of the oxidation process. Na-ion NaNi0.5Sn0.5O2/C coin cells are shown to deliver an average cell voltage of 3.1 V with an excellent capacity retention as compared to an average step-wise voltage of ~2.8 V and limited capacity retention for the pure NaNi0.5Mn0.5O2 phase. This study potentially shows the way to manipulate the O3 NaMO2 for facilitating their practical use in NIBs.

Disordered rocksalt compounds showing both anionic and cationic redox are being extensively studied for their very high energy storage capacity. While the Mn-based disordered rocksalt compounds show decent energy efficiency, it is drastically lower in the Ni-based materials due to different voltage hysteresis, 0.5 V and 2 V, respectively. To understand the origin of this difference, we herein report the design of two model compounds Li 1.3 Ni 0.27 Ta0. 43 O 2 and Li 1.3 Mn 0.4 Ta 0.3 O 2 and study their charge compensation mechanism through the uptake and removal of Li via an arsenal of analytical techniques. We show that different voltage hysteresis with Ni or Mn substitution is due to differences in the way anionic redox proceeds. We rationalized such a finding by DFT calculations and propose this drastic difference to be nested in the smaller charge transfer band gap of the Ni-based compounds compared to the Mn ones. Altogether these findings provide vital guidelines for designing high capacity disordered rocksalt cathode materials based on anionic redox activity for next generation of Li-ion batteries.

Multiple electrochemical processes are involved at the catalyst/electrolyte interface during the oxygen evolution reaction (OER). With the purpose of elucidating the complexity of surface dynamics upon OER, we systematically studied two Ni-based crystalline oxides (LaNiO3-δ and La2Li0.5Ni0.5O4) and compared them with the

Searching for novel high-capacity electrode materials combining cationic and anionic redox processes is an ever-growing activity within the field of Li-ion batteries. In this respect, we report on the exploration of the Li 3 Ru y Nb 1−y O 4 (0 ≤ y ≤ 1) system with an O/M ratio of 4 to maximize the number of oxygen lone pairs, responsible for the anionic redox. We show that this system presents a very rich crystal chemistry with the existence of four structural types, which derive from the rocksalt structure but differ in their cationic arrangement, creating either zigzag, helical, jagged chains or clusters. From an electrochemical standpoint, these compounds are active on reduction via a classical cationic insertion process. The oxidation process is more complex, because of the instability of the delithiated phase. Our results promote the use of the rich Li 3 MO 4 family as a viable platform for a better understanding of the relationships between structure and anionic redox activity.