Annealing Modulation Defect Chemistry toward High-Performance Sodium-Layered Cathodes.

Layered sodium transition-metal oxides generally encounter severe capacity decay and inferior rate performance during cycling, especially at a high state of charge. Herein, defect concentration is rationally modulated to explore the impact on electrochemical behavior in NaNi1/3Fe1/3Mn1/3O2 layered oxides. Bulk vacancies are increased through annealing in an oxygen-rich atmosphere, demonstrated by electron paramagnetic resonance measurement. It is found that the cathode with enriched oxygen vacancies exhibits significantly enhanced reversibility of redox reactions with a higher initial Coulombic efficiency of 90.0%. Furthermore, the reduced volume variations during the initial charge/discharge process are also confirmed by in situ X-ray diffraction. As a result, the oxygen-vacancy-rich cathode shows great cycling stability and superior rate performances. Also, full cells deliver a specific capacity of approximately 145.2 mAh g-1 at 0.5 C, with a high capacity retention of 78.3% after 100 cycles. This work presents a viable strategy for designing Na+ intercalated cathodes with a high-energy density.

Manipulating Local Chemistry and Coherent Structures for High-Rate and Long-Life Sodium-Ion Battery Cathodes.

Layered sodium transition-metal (TM) oxides generally suffer from severe capacity decay and poor rate performance during cycling, especially at a high state of charge (SoC). Herein, an insight into failure mechanisms within high-voltage layered cathodes is unveiled, while a two-in-one tactic of charge localization and coherent structures is devised to improve structural integrity and Na+ transport kinetics, elucidated by density functional theory calculations. Elevated Jahn-Teller [Mn3+O6] concentration on the particle surface during sodiation, coupled with intense interlayer repulsion and adverse oxygen instability, leads to irreversible damage to the near-surface structure, as demonstrated by X-ray absorption spectroscopy and in situ characterization techniques. It is further validated that the structural skeleton is substantially strengthened through the electronic structure modulation surrounding oxygen. Furthermore, optimized Na+ diffusion is effectively attainable via regulating intergrown structures, successfully achieved by the Zn2+ inducer. Greatly, good redox reversibility with an initial Coulombic efficiency of 92.6%, impressive rate capability (86.5 mAh g-1 with 70.4% retention at 10C), and enhanced cycling stability (71.6% retention after 300 cycles at 5C) are exhibited in the P2/O3 biphasic cathode. It is believed that a profound comprehension of layered oxides will herald fresh perspectives to develop high-voltage cathode materials for sodium-ion batteries.

Aluminum ion chemistry of Na4Fe3(PO4)2(P2O7) for all-climate full Na-ion battery.

Na4Fe3(PO4)2(P2O7) (NFPP) is currently drawing increased attention as a sodium-ion batteries (SIBs) cathode due to the cost-effective and NASICON-type structure features. Owing to the sluggish electron and Na+ conductivities, however, its real implementation is impeded by the grievous capacity decay and inferior rate capability. Herein, multivalent cation substituted microporous Na3.9Fe2.9Al0.1(PO4)2(P2O7) (NFAPP) with wide operation-temperature is elaborately designed through regulating structure/interface coupled electron/ion transport. Greatly, the derived Na vacancy and charge rearrangement induced by trivalent Al3+ substitution lower the ions diffusion barriers, thereby endowing faster electron transport and Na+ mobility. More importantly, the existing Al-O-P bonds strengthen the local environment and alleviate the volume vibration during (de)sodiation, enabling highly reversible valence variation and structural evolution. As a result, remarkable cyclability (over 10,000 loops), ultrafast rate capability (200 C), and exceptional all-climate stability (-40-60 °C) in half/full cells are demonstrated. Given this, the rational work might provide an actionable strategy to promote the electrochemical property of NFPP, thus unveiling the great application prospect of sodium iron mixed phosphate materials.

Difluoroethylene Carbonate as an Electrolyte Additive for Engineering the Electrolyte-Electrode Interphase of Lithium Metal Batteries.

Difluoroethylene carbonate (DFEC) featuring abundant fluorine atoms has been proposed as a multifunctional electrolyte additive to boost the stability of the electrolyte-electrode interphase of lithium metal batteries. Thus, introducing the DFEC additive enables a high capacity retention rate of the Li||NCM811 full cell (up to 75% after 200 cycles) at 4.5 V high voltage.

High-Entropy Na-Deficient Layered Oxides for Sodium-Ion Batteries.

Sodium layered oxides always suffer from sluggish kinetics and deleterious phase transformations at deep-desodiation state (i.e., >4.0 V) in O3 structure, incurring inferior rate capability and grievous capacity degradation. To tackle these handicaps, here, a configurational entropy tuning protocol through manipulating the stoichiometric ratios of inactive cations is proposed to elaborately design Na-deficient, O3-type NaxTmO2 cathodes. It is found that the electrons surrounding the oxygen of the TmO6 octahedron are rearranged by the introduction of MnO6 and TiO6 octahedra in Na-deficient O3-type Na0.83Li0.1Ni0.25Co0.2Mn0.15Ti0.15Sn0.15O2-δ (MTS15) with expanded O-Na-O slab spacing, giving enhanced Na+ diffusion kinetics and structural stability, as disclosed by theoretical calculations and electrochemical measurements. Concomitantly, the entropy effect contributes to the improved reversibility of Co redox and phase-transition behaviors between O3 and P3, as clearly revealed by ex situ synchrotron X-ray absorption spectra and in situ X-ray diffraction. Notably, the prepared entropy-tuned MTS15 cathode exhibits impressive rate capability (76.7% capacity retention at 10 C), cycling stability (87.2% capacity retention after 200 cycles) with a reversible capacity of 109.4 mAh g-1, good full-cell performance (84.3% capacity retention after 100 cycles), and exceptional air stability. This work provides an idea for how to design high-entropy sodium layered oxides for high-power density storage systems.

Multiscale Crystal Field Effect for High-Performance Ultrahigh-Ni Layered Cathode.

Further popularization of ultrahigh-Ni layered cathodes for high-energy lithium-ion batteries (LIBs) is hampered by their grievous structural and interfacial degeneration upon cycling. Herein, by leveraging the strong electronegativity and low solubility properties of Sb element, a multifunctional modification that couples atomic/microstructural reconstruction with interfacial shielding is well designed to improve the LiNi0.94Co0.04Al0.02O2 (NCA) cathode by combining Sb5+ doping and Li7SbO6 coating. Notably, a robust O framework is established by regulating local O coordination owing to the incorporation of a strong Sb-O covalence bond, leading to the inhibited lattice O evolution at high voltage, as revealed by synchrotron X-ray absorption spectroscopy. Moreover, the radially aligned primary particles with (003) crystallographic texture and refined/elongated sizes are achieved by the pinning of Sb on grain boundaries and are confirmed by scanning transmission electron microscopy, resulting in the fast Li+ diffusion and mitigated particle cracking. Additionally, in situ construction of the Li7SbO6 ionic conductive layer on grain boundaries can effectively boost interfacial stability and Li+ kinetics. As a result, the optimal Sb-modified NCA delivers a high capacity retention of 94.6% after 200 cycles at 1 C and a good rate capacity of 183.9 mAh g-1 at 10 C, which is expected to be applied to next-generation advanced LIBs.

Advanced NASICON-Type Na4Fe3(PO4)2(P2O7) Cathode for High-Performance Na+/Li+ Batteries.

Na4Fe3(PO4)2(P2O7) (NFPP) is an attractive candidate for Na+ batteries (SIBs) and Li+ batteries (LIBs). However, the real implementation of NFPP has been critically restrained by the inferior intrinsic electronic conductivity. Herein, in situ carbon-coated mesoporous NFPP, obtained via freeze drying and heat treatment, demonstrates highly reversible insertion/extraction of Na+/Li+. Mechanically, the electronic transmission and structural stabilities of NFPP are significantly enhanced by the graphitized carbon coating layer. Chemically, the porous nanosized structure shortens Na+/Li+ diffusion paths and increases the contact area between the electrolyte and NFPP, ultimately rendering fast ion diffusion. Greatly, long-lasting cyclability (88.5% capacity retention for over 5000 cycles), decent thermal stability at 60 °C, and impressive electrochemical performances are demonstrated in LIBs. The insertion/extraction mechanisms of NFPP in both SIBs and LIBs are systematically investigated, confirming its small volume expansion and high reversibility. The superior electrochemical performances and the insertion/extraction mechanism investigation confirm the feasibility of utilizing NFPP as a cathode material for Na+/Li+ batteries.

A Universal Molten Salt Method for Direct Upcycling of Spent Ni-rich Cathode towards Single-crystalline Li-rich Cathode.

With ever-increasing pursuit for high-value output in recycling spent lithium-ion batteries (LIBs), traditional recycling methods of cathodes tend to be obsolete because of the complicated procedures. Herein, we first upcycle spent polycrystal LiNi0.88 Co0.095 Al0.025 O2 (S-NCA) to high value-added single-crystalline and Li-rich cathode materials through a simple but feasible LiOH-Na2 SO4 eutectic molten salt strategy. The in situ X-ray diffraction technique and a series of paratactic experiments record the evolution process of upcycling and prove that excessive Li occupies the transition metal (TM) layers. Beneficial from the single-crystalline and Li-rich nature, the regenerated NCA (R-NCA) exhibits remarkably enhanced electrochemical performances in terms of long-term cyclability, high-rate performance and low polarization. This approach can also be successfully extended to other cathode materials e.g., LiNix Coy Mnz O2 (NCM) and mixed spent NCAs with varied degree of Li loss.

Electrochemically Engineering a Single-Crystal Nickel-Rich Layered Cathode.

Nickel-rich layered electrode material has been attracting significant attention owing to its high specific capacity as a cathode for lithium-ion batteries. Generally, the high-nickel ternary precursors obtained by traditional coprecipitation methods are micron-scale. In this work, the submicrometer single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM) cathode is efficiently prepared by electrochemically anodic oxidation followed by a molten-salt-assisted reaction without the need of extreme alkaline environments and complex processes. More importantly, when prepared under optimal voltage (10 V), single-crystal NCM exhibits a moderate particle size (∼250 nm) and strong metal-oxygen bonds due to reasonable and balanced crystal nucleation/growth rate, which are conducive to greatly enhancing the Li+ diffusion kinetics and structure stability. Given that a good discharge capacity of 205.7 mAh g-1 at 0.1 C (1 C = 200 mAh g-1) and a superior capacity retention of 87.7% after 180 cycles at 1 C are obtained based on the NCM electrode, this strategy is effective and flexible for developing a submicrometer single-crystal nickel-rich layered cathode. Besides, it can be adopted to elevate the performance and utilization of nickel-rich cathode materials.

Cationic-potential tuned biphasic layered cathodes for stable desodiation/sodiation.

Sodium layered oxides generally suffer from deep-desodiation instability in P2 structure and sluggish kinetics in O3 structure. It will be great to design P2/O3 biphasic materials that bring the complementary merits of both structures. However, such exploration is hindered by the ambiguous mechanism of material formation. Herein, supported by theoretical simulations and various spectroscopies, we prove that P2/O3 biphasic structures essentially originate from the internal heterogeneity of cationic potential, which can be realized by constraining the temperature-driven ion diffusion during solid-state reactions. Consequently, P2/O3 biphasic Na0.7Ni0.2Cu0.1Fe0.2Mn0.5O2-δ with well-designed quaternary composition is successfully obtained, exhibiting much-improved rate capabilities (62 mAh g-1 at 2.4 A g-1) and cycling stabilities (84% capacity retention after 500 cycles) than its single-phase analogues. Furthermore, synchrotron-based diffraction and X-ray absorption spectroscopy are employed to unravel the underlying sodium-storage mechanism of the P2/O3 biphasic structure. This work presents new insights toward the rational design of advanced layered cathodes for sodium-ion batteries.

Structure/Interface Coupling Effect for High-Voltage LiCoO2 Cathodes.

LiCoO2 (LCO) is widely applied in today's rechargeable battery markets for consumer electronic devices. However, LCO operations at high voltage are hindered by accelerated structure degradation and electrode/electrolyte interface decomposition. To overcome these challenges, co-modified LCO (defined as CB-Mg-LCO) that couples pillar structures with interface shielding are successfully synthesized for achieving high-energy-density and structurally stable cathode material. Benefitting from the "Mg-pillar" effect, irreversible phase transitions are significantly suppressed and highly reversible Li+ shuttling is enabled. Interestingly, bonding effects between the interfacial lattice oxygen of CB-Mg-LCO and amorphous Cox By coating layer are found to elevate the formation energy of oxygen vacancies, thereby considerably mitigating lattice oxygen loss and inhibiting irreversible phase transformation. Meanwhile, interface shielding effects are also beneficial for mitigating parasitic electrode/electrolyte reactions, subsequent Co dissolution, and ultimately enable a robust electrode/electrolyte interface. As a result, the as-designed CB-Mg-LCO cathode achieves a high capacity and excellent cycle stability with 94.6% capacity retention at an extremely high cut-off voltage of 4.6 V. These findings provide new insights for cathode material modification methods, which serves to guide future cathode material design.

Hierarchical CoO/MnCo2O4.5 nanorod arrays on flexible carbon cloth as high-performance anode materials for lithium-ion batteries.

A facile synthetic route is presented to fabricate highly ordered three-dimensional hierarchical CoO/MnCo2O4.5 nanorod arrays on carbon cloth (CC) as a high performance anode material for lithium ion batteries (LIBs). Inheriting the merits from the CC substrate and the special hierarchical architecture, as well as the interfacial and synergistic effects between CoO nanorods and MnCo2O4.5 nanosheets, the as-prepared product exhibits outstanding electrochemical performance in terms of high reversible capacity, cycling stability, and rate capability. Electrochemical characterization depicts that the hierarchical CoO/MnCo2O4.5 nanorod electrode can retain a high reversible capacity of about 1183 mA h g-1 at 200 mA-1 for the second cycle and a high rate capacity of 657 mA h g-1 at 1000 mA-1. After 120 cycles, a reversible capacity of 1030 mA h g-1 at 200 mA-1 can be maintained without obvious decay. These results demonstrate that the hierarchical CoO/MnCo2O4.5 nanorod array on CC is a promising candidate as an anode material for LIBs with superior properties.