Deniz Wong

Oxygen redox chemistry offers a pathway to high energy density in sodium‐ion batteries but is often accompanied by irreversible molecular O ₂ formation, leading to voltage hysteresis and poor cycling stability. The origin of molecular O ₂ formation is commonly attributed to high‐voltage charging yet remains debatable. Here, we uncover an overlooked mechanism in P2‐type Na _0.67 MnO ₂ , where molecular O ₂ formation is decoupled from the conventional high‐voltage paradigm and instead originates from Jahn–Teller distortion during discharge. Combined experimental and computational results reveal that Jahn–Teller‐induced lattice distortion shortens O–O distances and enhances the O–O dimerization tendency, leading to irreversible oxygen redox and structural degradation. This finding establishes a previously unrecognized distortion‐mediated pathway governing oxygen redox. To address this issue, an Al/Si co‐doping strategy is developed to regulate the electronic structure and reinforce the lattice framework. The co‐doping suppresses Jahn–Teller distortion, stabilizes O 2p states, and weakens the tendency toward O–O dimerization, thereby inhibiting molecular O ₂ formation. Consequently, the optimized Na _0.67 Al _0.01 Si _0.01 Mn _0.99 O ₂ exhibits superior cycling performance, retaining 95% capacity after 100 cycles within 4.4–2.0 V and 90% after 500 cycles within 4.0–2.0 V. These findings provide a mechanistic framework for oxygen redox chemistry and offer a practical design strategy for stabilizing high‐voltage manganese‐based sodium‐ion batteries.

Benefiting from the anionic redox activity, lithium‐rich layered oxide cathodes exhibit high specific capacity, but the migration of transition metal (TM) can exacerbate vacancy clustering, resulting in domino‐like structural degradation. To stabilize the structure, the electrostatic pinning effect is precisely incorporated into the Li layer to mitigate the TM migration via strong electrostatic repulsion. Concurrently, this configuration effectively modulates the electronic distribution around the oxygen ligands, thereby stabilizing the oxygen redox. Furthermore, robust electrostatic interactions endow the material with the capability to adaptively adjust its interlayer spacing, thereby buffering the structural evolution of the layered framework during (de)lithiation processes. The modified cathode achieves an 89.1% capacity retention over 400 cycles in half‐cells and an impressive 96.2% over 1000 cycles in full cells. To further decouple the capacity‐stability trade‐off while concurrently enhancing both bulk and interfacial stability, we engineered a gradient shielding architecture. This design not only attains 219.8 mAh g ⁻¹ at 0.5C and delivers capacity retention of 90.8% after 400 cycles but also promotes the formation of a compact CEI at the near‐surface region, markedly improving interfacial stability under harsh conditions. This progressive structural engineering paradigm offers fresh insights into overcoming the intrinsic structural challenges of lithium‐rich cathode materials.

Nowadays, fast‐charging capability in battery materials is intensively pursued in both academia and industry, yet the crystallographic factors that fundamentally determine rapid Li ⁺ transport remain unclear. Here, we identify the theoretical structural capacity for collective Li ⁺ transport, defined by the availability of crystallographically accessible Li diffusion sites, as a decisive but previously underappreciated structural origin governing interfacial Li ⁺ transport, and introduce Li‐site density (ρ _Li‐site ) as a quantitative descriptor to guide surface architecture design for accelerated Li ⁺ migration. Guided by this principle, we construct a coherent and fluorinated 1T‐Li _{1 + x} CoO _{2 − y} F _y surface structure on LiCoO ₂ , which simultaneously preserves crystallographic compatibility with the O3 matrix and provides an exceptionally high ρ _Li‐site (∼48 sites·nm ⁻³ ), substantially exceeding those of commonly employed frameworks (≤ 31 sites·nm ⁻³ ). The modified cathode delivers unprecedented rate capability, achieving 183 and 175 mAh g ⁻¹ at 10C and 20C, respectively. In‐situ synchrotron x‐ray and neutron diffraction results further reveal that the 1T phase effectively suppressed O3 to H1‐3 phase transitions and stabilized oxygen frameworks, enabling outstanding cycling stability with 87% capacity retention after 500 cycles. This work establishes Li site density‐guided surface engineering as a general structural principle for simultaneously improving interfacial reaction kinetics and structural durability in high‐voltage layered oxide cathodes.

Nowadays, fast‐charging capability in battery materials is intensively pursued in both academia and industry, yet the crystallographic factors that fundamentally determine rapid Li ⁺ transport remain unclear. Here, we identify the theoretical structural capacity for collective Li ⁺ transport, defined by the availability of crystallographically accessible Li diffusion sites, as a decisive but previously underappreciated structural origin governing interfacial Li ⁺ transport, and introduce Li‐site density (ρ _Li‐site ) as a quantitative descriptor to guide surface architecture design for accelerated Li ⁺ migration. Guided by this principle, we construct a coherent and fluorinated 1T‐Li _{1 + x} CoO _{2 − y} F _y surface structure on LiCoO ₂ , which simultaneously preserves crystallographic compatibility with the O3 matrix and provides an exceptionally high ρ _Li‐site (∼48 sites·nm ⁻³ ), substantially exceeding those of commonly employed frameworks (≤ 31 sites·nm ⁻³ ). The modified cathode delivers unprecedented rate capability, achieving 183 and 175 mAh g ⁻¹ at 10C and 20C, respectively. In‐situ synchrotron x‐ray and neutron diffraction results further reveal that the 1T phase effectively suppressed O3 to H1‐3 phase transitions and stabilized oxygen frameworks, enabling outstanding cycling stability with 87% capacity retention after 500 cycles. This work establishes Li site density‐guided surface engineering as a general structural principle for simultaneously improving interfacial reaction kinetics and structural durability in high‐voltage layered oxide cathodes.

Li‐rich cathodes combining cationic/anionic redox have rejuvenated high‐energy batteries. However, their practical applications remain constrained by the inferior anion redox reversibility and stability. Herein, a facile electrochemical relaxation route was implemented for the first time in the initial charging process to tune the anion redox chemistry. It declares the electrochemical relaxation in the oxygen activation plateau of 4.6 V contributes to a lattice framework with reduced structural distortion and weakened O─O interactions. A back‐bonding π ‐bond is formed between Mn and the O─O dimer, strengthening the interactions between oxygen and Mn, mitigating structural degradation and local distortion during the electrochemical cycling. The relaxed material demonstrates a high capacity over 250 mAh g ⁻¹ and a high plateau voltage of 3.57 V with a negligible voltage decay (0.8%) after 100 cycles at 1C. This strategy presents a straightforward methodology for high‐voltage activation of O redox cathodes.

We investigate the Yb valence instabilities in the strongly correlated YbPd compound using resonant x-ray emission spectroscopy as a function of pressure across the charge-order (CO) transition. At a low temperature ( T = 30 K ) in the CO phase, the Yb 4 f valence remains nearly constant up to a pressure P L = 1.5 ± 0.2 GPa , and then increases gradually at higher pressures. In contrast, at room temperature in the normal phase, an anomalous decrease of the Yb 4 f valence is observed, without any accompanying structural phase transition. This behavior is corroborated by a systematic pressure-dependent decrease of the unit-cell volume. Based on a Birch-Murnaghan analysis, the compressibility indicates hardening of the lattice with applied pressure up to a distinct kink seen at P K = 1.6 ± 0.2 GPa . In contrast, for P > P K , the Yb 4 f valence saturates, and the compressibility reveals a counterintuitive pressure-induced softening. The results show a minimum in the compressibility of YbPd (with f 0 – f 1 hole-type mixed valence), reminiscent of the maximum in compressibility seen in the γ – α first-order isostructural phase transition in cerium (with f 0 – f 1 electron-type mixed valence).

High-voltage operation boosts the energy density of sodium layered oxides by activating oxygen redox, but the underlying degradation mechanisms remain controversial, hindering rational materials design. Here we demonstrate that the applied cycling current determines which degradation pathway dominates, thereby resolving this long-standing inconsistency. Using synchrotron-based X-ray probes, advanced microscopic characterizations and first-principle calculation on a compositionally controlled set of Sc-, Sc–Ti-, and Sc–Ti–B-doped O3-type oxides, it is revealed that low current preserves oxygen-redox participation and drives oxygen-loss-induced degradation, whereas high current suppresses oxygen redox and induces a transition to a structure-governed evolution pathway along simplified P3-type routes. This compositional set makes the current-dependent degradation behaviour experimentally distinguishable, allowing the oxygen-redox-driven and structure-governed modes to be clearly disentangled. These findings establish a unified current-governed mechanistic framework and provide guidance for designing durable high-voltage sodium-ion cathodes.

The high-voltage oxygen redox activity of Li-rich layered oxides enables additional capacity beyond conventional transition metal (TM) redox contributions and drives the development of positive electrode active materials in secondary Li-based batteries. However, Li-rich layered oxides often face voltage decay during battery operation. In particular, although Li-rich positive electrode active materials with a high nickel content demonstrate improved voltage stability, they suffer from poor discharge capacity. Here, via physicochemical and electrochemical measurements, we investigate the correlation between oxygen redox activity and superstructure units in Li-rich layered oxides, specifically the fractions of LiMn₆ and Ni⁴⁺-stabilized LiNiMn₅ within the TM layer. We prove that an excess of LiNiMn₅ hinders the extraction/insertion of lithium ions during Li metal coin cell charging/discharging, resulting in incomplete oxygen redox activity at a cell potential of about 3.3 V. We also demonstrate that lithium content adjustment could be a beneficial approach to tailor the superstructure units. Indeed, we report an improved oxygen redox reversibility for an optimized Li-rich layered oxide with fewer LiNiMn₅ units.

In P2‐type layered oxide cathodes, Na site‐regulation strategies are proposed to modulate the Na ⁺ distribution and structural stability. However, their impact on the oxygen redox reactions remains poorly understood. Herein, the incorporation of K ⁺ in the Na layer of Na _0.67 Ni _0.11 Cu _0.22 Mn _0.67 O ₂ is successfully applied. The effects of partial substitution of Na ⁺ with K ⁺ on electrochemical properties, structural stability, and oxygen redox reactions have been extensively studied. Improved Na ⁺ diffusion kinetics of the cathode is observed from galvanostatic intermittent titration technique (GITT) and rate performance. The valence states and local structural environment of the transition metals (TMs) are elucidated via operando synchrotron X‐ray absorption spectroscopy (XAS). It is revealed that the TMO ₂ slabs tend to be strengthened by K‐doping, which efficiently facilitates reversible local structural change. Operando X‐ray diffraction (XRD) further confirms more reversible phase changes during the charge/discharge for the cathode after K‐doping. Density functional theory (DFT) calculations suggest that oxygen redox reaction in Na _0.62 K _0.03 Ni _0.11 Cu _0.22 Mn _0.67 O ₂ cathode has been remarkably suppressed as the nonbonding O 2 p states shift down in the energy. This is further corroborated experimentally by resonant inelastic X‐ray scattering (RIXS) spectroscopy, ultimately proving the role of K ⁺ incorporated in the Na layer.