Guifan Zeng’s research while affiliated with Xiamen University and other places

Developing sacrificial cathode prelithiation technology to compensate for irreversible lithium loss is crucial for enhancing the energy density of lithium‐ion batteries. Antifluorite Li‐rich Li 5 FeO 4 (LFO) is a promising prelithiation agent due to its high theoretical capacity (867 mAh g ⁻¹ ) and superior decomposition dynamic (<4.0 V vs. Li/Li ⁺ ). However, the oxygen evolution mechanism in LFO remains unclear, limiting its application as an ideal prelithiation agent. Herein, we systematically track the full lifecycle oxygen footprint in LFO lattice, electrolyte and solid electrolyte interface (SEI). We demonstrate the lattice mismatch induced by the quasi‐disorder rocksalt intermediate phase can activate the lattice oxygen oxidation promoting the dimerization to O 2 . Specifically, in contrast to the O─O dimers formed within typical anionic‐redox active cathodes, the oxidation of lattice oxygen in LFO generates O ⁻ stabilized in Li 6 ‐O configuration. Significantly, a pair of edge‐sharing Li 6 ‐O configurations transforms into a superoxo dimer, which further evolves into O 2 via a ligand‐to‐metal charge transfer process. Moreover, we demonstrate that nucleophilic intermediates threaten the stability of electrolytes and SEI. Leveraging the insights above, we offer comprehensive perspectives for the modification of ideal prelithiation agents.

Developing sacrificial cathode prelithiation technology to compensate for irreversible lithium loss is crucial for enhancing the energy density of lithium‐ion batteries. Antifluorite Li‐rich Li5FeO4 (LFO) is a promising prelithiation agent due to its high theoretical capacity (867 mAh g⁻¹) and superior decomposition dynamic (<4.0 V vs. Li/Li⁺). However, the oxygen evolution mechanism in LFO remains unclear, limiting its application as an ideal prelithiation agent. Herein, we systematically track the full lifecycle oxygen footprint in LFO lattice, electrolyte and solid electrolyte interface (SEI). We demonstrate the lattice mismatch induced by the quasi‐disorder rocksalt intermediate phase can activate the lattice oxygen oxidation promoting the dimerization to O2. Specifically, in contrast to the O─O dimers formed within typical anionic‐redox active cathodes, the oxidation of lattice oxygen in LFO generates O⁻ stabilized in Li6‐O configuration. Significantly, a pair of edge‐sharing Li6‐O configurations transforms into a superoxo dimer, which further evolves into O2 via a ligand‐to‐metal charge transfer process. Moreover, we demonstrate that nucleophilic intermediates threaten the stability of electrolytes and SEI. Leveraging the insights above, we offer comprehensive perspectives for the modification of ideal prelithiation agents.

Compensating for the irreversible loss of limited active sodium (Na) is crucial for enhancing the energy density of practical sodium‐ion batteries (SIBs) full‐cell, especially when employing hard carbon anode with initially lower coulombic efficiency. Introducing sacrificial cathode presodiation agents, particularly those that own potential anionic oxidation activity with a high theoretical capacity, can provide additional sodium sources for compensating Na loss. Herein, Ni atoms are precisely implanted at the Na sites within Na2O framework, obtaining a (Na0.89Ni0.05□0.06)2O (Ni–Na2O) presodiation agent. The synergistic interaction between Na vacancies and Ni catalyst effectively tunes the band structure, forming moderate Ni–O covalent bonds, activating the oxidation activity of oxygen anion, reducing the decomposition overpotential to 2.8 V (vs Na/Na⁺), and achieving a high presodiation capacity of 710 mAh/g≈Na2O (Na2O decomposition rate >80%). Incorporating currently‐modified presodiation agent with Na3V2(PO4)3 and Na2/3Ni2/3Mn1/3O2 cathodes, the energy density of corresponding Na‐ion full‐cells presents an essential improvement of 23.9% and 19.3%, respectively. Further, not limited to Ni–Na2O, the structure–function relationship between the anionic oxidation mechanism and electrode–electrolyte interface fabrication is revealed as a paradigm for the development of sacrificial cathode presodiation agent.

Sodium-ion batteries are among the most promising alternatives to lithium-based technologies for grid and other energy storage applications due to their cost benefits and sustainable resource supply. For the cathode—the component that largely determines the energy density of a sodium-ion battery cell—one major category of materials is P2-type layered oxides. Unfortunately, at high state-of-charge, such materials tend to undergo a phase transition with a very large volume change and consequent structural degradation during long-term cycling. Here we address this issue by introducing vacancies into the transition metal layer of P2-Na0.7Fe0.1Mn0.75□0.15O2 (‘□’ represents a vacancy). The transition metal vacancy serves to suppress migration of neighbouring Na ions and therefore maintain structural and thermal stability in Na-depleted states. Moreover, the specific Na−O−□ configuration triggers a reversible anionic redox reaction and boosts the energy density. As a result, the cathode design here enables pouch cells with energy densities of 170 Wh kg⁻¹ and 120 Wh kg⁻¹ that can operate for over 600 and 1,000 cycles, respectively. Our work not only suggests a feasible strategy for cathode design but also confirms the possibility of developing a battery chemistry that features a reduced need for critical raw materials.

In P2-type layered transition metal (TM) oxides, which are typical cathode materials for Na-ion batteries, the presence of Li within the TM layer could lead to the formation of specific Na–O–Li configurations that trigger additional oxygen redox at high charging voltages. However, the prismatic-type (P-type) to octahedral-type (O-type) phase transition and irreversible TM migration could be simultaneously aggravated in high state of charge, resulting in structural distortion. Here we demonstrate that excessive desodiation of P2-Na0.67Li0.1Fe0.37Mn0.53O2 (NLFMO) induces the formation of neighbouring O-type stacking faults with an intergrowth structure (that is, interlacing of O- and P-type layers), which leads to out-of-lattice Li migration and irreversible oxygen loss. We show that, by controlling the depth of charge to tailor the intergrowth structure, a P-type stacking state can be uniformly interspersed between the O-type stacking state, thereby avoiding neighbouring O-type stacking faults. Adjusting the O/P intergrowth structure leads to both reversible migration of Li/TM ions and reversible anionic redox in the NLFMO cathode. We thereby achieve a high-performance pouch cell (with an energy density of 165 W h kg⁻¹ based on the entire weight of the cell) with both cationic and anionic redox activities.

Developing sacrificial cathode pre‐lithiation technology to compensate for active lithium loss is vital for improving the energy density of lithium‐ion battery full‐cells. Li 2 CO 3 owns high theoretical specific capacity, superior air stability, but poor conductivity as an insulator, acting as a promising but challenging pre‐lithiation agent candidate. Herein, extracting a trace amount of Co from LiCoO 2 (LCO), we develop a lattice engineering through substituting Li sites with Co and inducing Li defects to obtain Co‐Li 2 CO 3 @LCO, in which both the bandgap and Li‐O bond strength have essentially declined. Benefiting from the synergistic effect of Li defects and bulk phase catalytic regulation of Co, the potential of Li 2 CO 3 deep decomposition significantly decreases from typical >4.7 V to ∼4.25 V versus Li/Li ⁺ , presenting >600 mAh/g compensation capacity. Impressively, coupling 5 wt% Co‐Li 2 CO 3 @LCO within NCM‐811 cathode, 235 Wh/kg pouch‐type full‐cell is achieved, performing 88% capacity retention after 1000 cycles. This article is protected by copyright. All rights reserved

Raising the charging cut‐off voltage of layered oxide cathodes can improve their energy density. However, it inevitably introduces instabilities regarding both bulk structure and surface/interface. Herein, exploiting the unique characteristics of high‐valance Nb ⁵⁺ element, we achieved a synchronous surface‐to‐bulk modified LiCoO 2 featuring Li 3 NbO 4 surface coating layer, Nb‐doped bulk, and the desired concentration gradient architecture through one‐step calcination. Such a multifunctional structure facilitates the construction of high‐quality cathode/electrolyte interface, enhances Li ⁺ diffusion, and restrains lattice‐O loss, Co migration and associated layer‐to‐spinel phase distortion. Therefore, a stable operation of Nb‐modified LiCoO 2 half‐cell is achieved at 4.6 V (90.9% capacity retention after 200 cycles). Long‐life 250 Wh/kg and 4.7 V‐class 550 Wh/kg pouch‐cells assembled with graphite and thin Li anodes are harvested (both beyond 87% after 1600 and 200 cycles). This multifunctional one‐step modification strategy establishes a technological paradigm to pave the way for high‐energy density and long‐life lithium‐ion cathode materials. This article is protected by copyright. All rights reserved

The high‐voltage induced undesirable surface passivation bilayer (cathode/electrolyte interface and cation‐densified surface phase) of LiCoO2 inevitably leads to battery degradation. Herein, a continual/uniform enamel‐like olivine layer on LiCoO2 surface is fabricated by employing a high‐speed mechanical fusion method . The enamel‐like layer suppresses interfacial side reactions by tuning EC dehydrogenation, contributing to an ultrathin and stable cathode/electrolyte interface. The strong bonding affinity between LiCoO2 and enamel‐like layer restrains both lattice oxygen loss and associated layered‐to‐spinel structural distortion. Moreover, the thermal stability of highly delithiated LiCoO2 is improved, as both the onset temperatures of layered‐to‐spinel transition and O2 evolution are simultaneously postponed. Stable operation of LiCoO2 at 4.6 V high‐voltage and 55 °C elevated temperature (both >85% capacity retention after 200 cycles) is achieved. This facile and scalable high‐speed solid‐phase coating strategy establishes a technical paradigm to enhance surface/interface stability of high‐energy‐density cathode candidates by constructing an ideal enamel‐like surface layer.