Band Structure Engineering Promotes Anionic Redox Reversibility of Cobalt-Free Li-Rich Layered Oxides Cathodes.

Li-rich layered oxides cathodes (LLOs) have prevailed as the promising high-energy-density cathode materials due to their distinctive anionic redox chemistry. However, uncontrollable anionic redox process usually leads to structural deterioration and electrochemical degradation. Herein, a Mo/Cl co-doping strategy is proposed to regulate the relative position of energy band for modulating the anionic redox chemistry and strengthening the structural stability of Co-free Li1.16Mn0.56Ni0.28O2 cathodes. The incorporation of Mo with high d state orbit and Cl with low electronegativity can narrow the band energy gap between bonding and antibonding bands via increasing the filled lower-Hubbard band (LHB) and decreasing the non-bonding O 2p energy bands, promoting the anionic redox reversibility. In addition, strong covalent Mo─O and Mn─Cl bonding further increases the covalency of Mn─O band to further stabilize the O2 n- species and enhance the reversible distortion of MnO6 octahedron. The strengthening electronic conductivity, together with the epitaxial structure Li2MoO4 facilitates the fast Li+ kinetics. As a result, the dual doping material exhibits enhanced anionic redox reversibility and suppressed oxygen release with increased cyclic stability and excellent rate performance. This strategy provides some guidance to design high-energy-density LLOs with desirable anionic redox reversibility and stable crystal structure via band structure engineering.

In-Situ Construction of Electronically Insulating and Air-Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High-Performance Garnet-Type Solid-State Batteries.

Lithophobic Li2CO3/LiOH contaminants and high-resistance lithium-deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short-circuiting of all-solid-state batteries (ASSBs). Herein, a stably lithiophilic Li2ZO3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO2 and Li2CO3 (Z+C) co-sintering to eliminate the detrimental contaminants and lithium-deficient phases. The Li2ZO3 formed on the modified electrolyte (LLZTO-(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li2ZO3 formed at GBs broadens the energy bandgaps of LLZTO-(Z+C) and significantly inhibits lithium dendrite generation. More Li+ transport paths found in LLZTO-Z+C by first-principles calculations increase Li+ conductivity from 1.04×10-4 to 7.45×10-4 S cm-1. Eventually, the Li|LLZTO-(Z+C)|Li symmetric cell maintains stable cycling for over 2000 h at 0.8 mA cm-2. The capacity retention of LiFePO4|LLZTO-(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4 C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.

Stabilized Anionic Redox by Rational Structural Design from Surface to Bulk for Long-Life Fast-Charging Li-Rich Oxide Cathodes.

On account of high capacity and high voltage resulting from anionic redox, Li-rich layered oxides (LLOs) have become the most promising cathode candidate for the next-generation high-energy-density lithium-ion batteries (LIBs). Unfortunately, the participation of oxygen anion in charge compensation causes lattice oxygen evolution and accompanying structural degradation, voltage decay, capacity attenuation, low initial columbic efficiency, poor kinetics, and other problems. To resolve these challenges, a rational structural design strategy from surface to bulk by a facile pretreatment method for LLOs is provided to stabilize oxygen redox. On the surface, an integrated structure is constructed to suppress oxygen release, electrolyte attack, and consequent transition metals dissolution, accelerate lithium ions transport on the cathode-electrolyte interface, and alleviate the undesired phase transformation. While in the bulk, B doping into Li and Mn layer tetrahedron is introduced to increase the formation energy of O vacancy and decrease the lithium ions immigration barrier energy, bringing about the high stability of surrounding lattice oxygen and outstanding ions transport ability. Benefiting from the specific structure, the designed material with the enhanced structural integrity and stabilized anionic redox performs an excellent electrochemical performance and fast-charging property..

High-Entropy Doping Boosts Ion/Electronic Transport of Na4 Fe3 (PO4 )2 (P2 O7 )/C Cathode for Superior Performance Sodium-Ion Batteries.

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na4 Fe2.85 (Ni,Co,Mn,Cu,Mg)0.03 (PO4 )2 P2 O7 (NFPP-HE) cathode can release 122 mAh g-1 at 0.1 C, even 85 mAh g-1 at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g-1 at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na+ migration path and energy barrier boost the Na+ kinetics and improve the interfacial electronic transfer, thus improving performance.

High-Density Cationic Defects Coupling with Local Alkaline-Enriched Environment for Efficient and Stable Water Oxidation.

The inferior activity and stability of non-noble metal-based electrocatalysts for oxygen evolution reaction (OER) seriously limit their practical applications in various electrochemical energy conversion systems. Here we report, a drastic nonequilibrium precipitation approach to construct a highly disordered crystal structure of layered double hydroxides as a model OER catalyst. The unconventional crystal structure contains high-density cationic defects coupled with a local alkaline-enriched environment, enabling ultrafast diffusion of OH- ions and thus avoiding the formation of a local acidic environment and dissolution of active sites during OER. An integrated experimental and theoretical study reveals that high-density cationic defects, especially di-cationic and multi-cationic defects, serve as highly active and durable catalytic sites. This work showcases a promising strategy of crystal structure engineering to construct robust active sites for high-performance oxygen evolution in an alkaline solution.

Ion/Electron Redistributed 3D Flexible Host for Achieving Highly Reversible Li Metal Batteries.

3D carbon frameworks are promising hosts to achieve highly reversible lithium (Li) metal anodes, whereas insufficient effects are attributed to their single electron conductivity causing local aggregating of electron/Li+ and uncontrollable Li dendrites. Herein, an ion/electron redistributed 3D flexible host is designed by lithiophilic carbon fiber cloth (CFC) modified with metal-organic framework (MOF)-derived porous carbon sheath with embedded CoP nanoparticles (CoP-C@CFC). Theory calculations demonstrate the strong binding energy and plenty of charge transfer from the reaction between CoP and Li atom are presented, which is beneficial to in situ construct a Li3 P@Co ion/electron conductive interface on every single CoP-C@CFC. Thanks to the high ionic conductive Li3 P and electron-conductive Co nanoparticles, the rapid dispersion of Li+ and obviously reduced local current density can be achieved simultaneously. Furthermore, in situ optical microscopy observations display obvious depression for volume expansion and Li dendrites. As expected, a miraculous average Coulombic efficiency (CE) of 99.96% over 1100 cycles at 3 mA cm-2 and a low overpotential of 11.5 mV with prolonged cycling of over 3200 h at 20% depth of discharge are successfully obtained. Consequently, the CoP-C@CFC-Li||LiFePO4 full cells maintain a capacity retention of 95.8% with high CE of 99.96% over 500 cycles at 2 C and excellent rate capability.

Full Activation of Mn4+ /Mn3+ Redox in Na4 MnCr(PO4 )3 as a High-Voltage and High-Rate Cathode Material for Sodium-Ion Batteries.

Developing high-voltage cathode materials is critical for sodium-ion batteries to boost energy density. NASICON (Na super-ionic conductor)-structured Nax MnM(PO4 )3 materials (M represents transition metal) have drawn increasing attention due to their features of robust crystal framework, low cost, as well as high voltage based on Mn4+ /Mn3+ and Mn3+ /Mn2+ redox couples. However, full activation of Mn4+ /Mn3+ redox couple within NASICON framework is still a great challenge. Herein, a novel NASICON-type Na4 MnCr(PO4 )3 material with highly reversible Mn4+ /Mn3+ redox reaction is discovered. It proceeds a two-step reaction with voltage platforms centered at 4.15 and 3.52 V versus Na+ /Na, delivering a capacity of 108.4 mA h g-1 . The Na4 MnCr(PO4 )3 cathode also exhibits long durability over 500 cycles and impressive rate capability up to 10 C. The galvanostatic intermittent titration technique (GITT) test shows fast Na diffusivity which is further verified by density functional theory calculations. The high electrochemical activity derives from the 3D robust framework structure, fast kinetics, and pseudocapacitive contribution. The sodium storage mechanism of the Na4 MnCr(PO4 )3 cathode is deeply studied by ex situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS), revealing that both solid-solution and two-phase reactions are involved in the Na+ ions extraction/insertion process.

Tailoring Anisotropic Li-Ion Transport Tunnels on Orthogonally Arranged Li-Rich Layered Oxide Nanoplates Toward High-Performance Li-Ion Batteries.

High-performance Li-rich layered oxide (LRLO) cathode material is appealing for next-generation Li-ion batteries owing to its high specific capacity (>300 mAh g-1). Despite intense studies in the past decade, the low initial Coulombic efficiency and unsatisfactory cycling stability of LRLO still remain as great challenges for its practical applications. Here, we report a rational design of the orthogonally arranged {010}-oriented LRLO nanoplates with built-in anisotropic Li+ ion transport tunnels. Such a novel structure enables fast Li+ ion intercalation and deintercalation kinetics and enhances structural stability of LRLO. Theoretical calculations and experimental characterizations demonstrate the successful synthesis of target cathode material that delivers an initial discharge capacity as high as 303 mAh g-1 with an initial Coulombic efficiency of 93%. After 200 cycles at 1.0 C rate, an excellent capacity retention of 92% can be attained. Our method reported here opens a door to the development of high-performance Ni-Co-Mn-based cathode materials for high-energy density Li-ion batteries.

Flower-like MoSe2 /C Composite with Expanded (0 0 2) Planes of Few-layer MoSe2 as the Anode for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have caught considerable attention in last few years owing to the abundance of sodium in comparison to lithium. The commercial graphite anode is demonstrated unsuitable as an anode material for SIBs due to the larger radius of Na+ ions, whereas the transition metal dichalcogenides (TMDs) show great potential as anodes for SIBs because of their high achievable capacity. The sluggish kinetics, large volume expansion, and aggregation of those materials however results in severe decay of the electrochemical performance. In this work, a flower-like MoSe2 /C composite is synthesized with ethylenediamine and cassava starch (denoted as MoSe2 /Ccas ) and designed based on these principles: 1) expand the d-spacing of (0 0 2) planes of MoSe2 to enhance the kinetics for the intercalation-deintercalation of Na+ ions and 2) embed MoSe2 into the carbon matrix to enhance the conductivity and restrict the volume expansion and aggregation of MoSe2 . As a result, MoSe2 /Ccas exhibits superior cycle performance and rate capability for sodium storage. It shows durable long-life cycle capability with a reversible capacity of 360 mAh g-1 after 350 cycles at 0.5 Ag-1 . At the current density of 4 Ag-1 , the reversible capacity is still maintained at 266 mAh g-1 .

N/S Co-Doped 3 D Porous Carbon Nanosheet Networks Enhancing Anode Performance of Sodium-Ion Batteries.

A facile and scalable method is realized for the in situ synthesis of N/S co-doped 3 D porous carbon nanosheet networks (NSPCNNs) as anode materials for sodium-ion batteries. During the synthesis, NaCl is used as a template to prepare porous carbon nanosheet networks. In the resultant architecture, the unique 3 D porous architecture ensures a large specific surface area and fast diffusion paths of both electrons and ions. In addition, the import of N/S produces abundant defects, increased interlayer spacings, more active sites, and high electronic conductivity. The obtained products deliver a high specific capacity and excellent long-term cycling performance, specifically, a capacity of 336.2 mA h g-1 at 0.05 A g-1 , remaining as large as 214.9 mA h g-1 after 2000 charge/discharge cycles at 0.5 A g-1 . This material has great prospects for future applications of scalable, low-cost, and environmentally friendly sodium-ion batteries.

DFT investigation of capacious, ultrafast and highly conductive hexagonal Cr2C and V2C monolayers as anode materials for high-performance lithium-ion batteries.

To assess the potential of hexagonal Cr2C and V2C monolayers as anode materials in lithium-ion batteries, first-principles calculations and AIMD simulations were carried out. AIMD simulations and phonon calculations revealed that the honeycomb structure of the hexagonal Cr2C and V2C monolayers is thermodynamically and dynamically stable. A single lithium atom is preferentially absorbed over the center of the honeycomb hollow. The full lithium storage phases of the hexagonal Cr2C and V2C monolayers correspond to Li6Cr2C and Li6V2C, with considerable theoretical specific capacities of 1386 and 1412 mA h g-1, respectively. Interestingly, lithium ion diffusion on the hexagonal Cr2C and V2C monolayers is extremely fast, with low energy barriers of 32 and 28 meV, respectively; these values are much lower than those of other widely investigated anode materials. Moreover, the lithiated hexagonal Cr2C and V2C monolayers show enhanced metallic characteristics and excellent electronic conductivity during the entire lithiation process; these values are superior to those of other anode materials with semiconducting characteristics. The findings in our study suggest that hexagonal Cr2C and V2C monolayers are promising anode materials with high capacities and high rate capabilities for next generation high-performance lithium-ion batteries.

Bismuth Nanoparticles Embedded in Carbon Spheres as Anode Materials for Sodium/Lithium-Ion Batteries.

Sodium-ion batteries (SIBs) are regarded as an attractive alternative to lithium-ion batteries (LIBs) for large-scale commercial applications, because of the abundant terrestrial reserves of sodium. Exporting suitable anode materials is the key to the development of SIBs and LIBs. In this contribution, we report on the fabrication of Bi@C microspheres using aerosol spray pyrolysis technique. When used as SIBs anode materials, the Bi@C microsphere delivered a high capacity of 123.5 mAh g(-1) after 100 cycles at 100 mA g(-1) . The rate performance is also impressive (specific capacities of 299, 252, 192, 141, and 90 mAh g(-1) are obtained under current densities of 0.1, 0.2, 0.5, 1, and 2 A g(-1) , respectively). Furthermore, the Bi@C microsphere also proved to be suitable LIB anode materials. The excellent electrochemical performance for both SIBs and LIBs can attributed to the Bi@C microsphere structure with Bi nanoparticles uniformly dispersed in carbon spheres.

Sulfur encapsulated in a TiO2-anchored hollow carbon nanofiber hybrid nanostructure for lithium-sulfur batteries.

A hollow carbon nanofiber hybrid nanostructure anchored with titanium dioxide (HCNF@TiO2) was prepared as a matrix for effective trapping of sulfur and polysulfides as a cathode material for Li-S batteries. The synthesized composites were characterized and examined by X-ray diffraction, nitrogen adsorption-desorption measurements, field-emission scanning electron microscopy, scanning transmission electron microscopy, and electrochemical methods such as galvanostatic charge/discharge, rate performance, and electrochemical impedance spectroscopy tests. The obtained HCNF@TiO2-S composite showed a clear core-shell structure with TiO2 nanoparticles coating the surface of the HCNF and sulfur homogeneously distributed in the coating layer. The HCNF@TiO2-S composite exhibited much better electrochemical performance than the HCNF-S composite, which delivered an initial discharge capacity of 1040 mA h g(-1) and maintained 650 mAh g(-1) after 200 cycles at a 0.5 C rate. The improvements of electrochemical performances might be attributed to the unique hybrid nanostructure of HCNF@TiO2 and good dispersion of sulfur in the HCNF@TiO2-S composite.

Anterior Cruciate Ligament Rupture Combined with Complete Radial Tear of the Posterior Horn of the Lateral Meniscus: Suture or Resection?

Anterior cruciate ligament (ACL) rupture often presents with a tear of the posterior horn of the lateral meniscus. There is no clear preference between ACL reconstruction with suture and resection of the meniscus. We aimed to compare the clinical efficacy of ACL reconstruction with suture versus resection in patients presenting with arthroscopic ACL rupture and radial complete tear of the posterior corner of the lateral meniscus. We retrospectively analyzed 157 patients with ACL rupture and complete radial tear of the posterior horn of the lateral meniscus. Between May 2010 and April 2015, 86 of 157 patients underwent ACL reconstruction and meniscus suture (study group, 54.78%) and 71 of 157 patients underwent ACL reconstruction and meniscus resection (control group, 45.22%) in our department. All patients were monitored over the 12 to 72-month follow-up period. The primary evaluation indices were the Lysholm scores, the International Knee Documentation Committee (IKDC) scores, pivot shift test, the Barret criteria, and magnetic resonance imaging (MRI) findings of meniscal healing. The majority of 157 patients were relatively young men (29.64 ± 7.79 years) with low body mass index (BMI) (23.79 ± 2.74). The postoperative Lysholm and IKDC scores of the two groups were significantly improved over the corresponding preoperative scores (p < 0.05). The clinical results and excellent and good rates were significantly better for the study group than for the control group (both, p < 0.05). MRI showed that the meniscal healed rate of the study group was 96.51%. There was no significant difference in BMI between subgroups for any functional outcome. For patients with ACL rupture and complete radial tear of the posterior horn of the lateral meniscus, ACL reconstruction and both simultaneous suture and resection of the posterior horn of the lateral meniscus were found to be safe and effective. There was no association between outcomes and BMI. However, the former was associated with a superior long-term clinical effect and may restore the integrity of the meniscus and is particularly recommended for young patients.

A quantitative analysis method of complex sulfide components for understanding initial capacity degradation mechanism in lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are a strong contender for the new-generation battery system to meet the growing energy demand due to their significantly high energy density (2600 Wh/kg) and cost-effectiveness. However, the practical operating conditions yield an initial capacity of less than 80 % of the theoretical capacity, resulting in a limited lifespan and hindering broader application. What's worse, current mechanism, especially the evolution process of sulfides for the initial capacity degradation is not clear due to the practical difficulties of effective separation and detection of sulfur-containing components. Herein, we have developed an instrumental analysis method enabling graded leaching and quantitative determination of sulfur-containing components. This technology achieves a detection precision surpassing 99.11 %, addressing the inherent deficiency in calculating sulfur-containing components using the decrement method. Applying this method reveals that the presence of lithium polysulfides in the electrolyte (26.34 wt%) after discharging is the primary factor causing insufficient capacity utilization in Li-S batteries. This work not only demonstrates the unique behavior of Li-S batteries at high sulfur loading but also provides a systematic evaluation method to guide further research on high-energy-density batteries, and provides theoretical and technical support to promote the development of high-energy, long-life Li-S batteries.

Anion Substitution Strategy toward an Advanced NASICON-Na4Fe3(PO4)2P2O7 Cathode for Sodium-Ion Batteries.

Superior sodium-ion batteries (SIBs) greatly need cathode materials with higher capacity and better durability. Herein, the anion group substitution strategy is proposed to design a cathode material with extraordinary Na+ storage performance, NASICON-Na4Fe3(PO4)1.9(SiO4)0.1P2O7 (NFPP-Si0.1). The experimental and theoretical research revealed that modification in the local structure by anion substitution significantly boosts the ionic/electronic transfer kinetics via optimizing the electronic conductivity and reducing the Na+ diffusion energy barrier. Furthermore, the SiO44- substitution generates a slight expansion of the crystal lattice to broaden the Na+ diffusion channel. Specifically, the custom-designed NFPP-Si0.1 could deliver a high rate capability of 77.6 mAh g-1 at constant 50 C charge-discharge and excellent recyclability of 79.4% retention rate after 7000 cycles at 10 C. Besides, it also possesses outstanding low temperature reversible capacity of 95.5 mAh g-1 at 0.1 C and long-term cyclability of 93.6% capacity retention after 1000 cycles at 5 C in -10 °C. This strategy of heterogeneous and isostructural anion group substitution provides a method for unlocking high-rate and long-life-span mixed polyanionic cathodes.

Harmless pre-lithiation via advantageous surface reconstruction in sacrificial cathode additives for lithium-ion batteries.

Sacrificial cathode additives have emerged as a tempting strategy to compensate the initial capacity loss (ICL) in Li-ion batteries (LIBs) manufacturing. However, the utilization of sacrificial cathode additives inevitably brings residuals, side reactions, and negative impacts in which relevant researches are still in the early stage. In this study, we conduct a systematic investigation on the effects of employing a nickel-based sacrificial additive, Li2Cu0.1Ni0.9O2 (LCNO), and propose a feasible strategy to achieve advantageous surface reconstruction on LCNO. Specifically, we build a Li5AlO4 (LAO) coating layer on the LCNO through dry ball milling and annealing treatment. This process not only consumes surface residual lithium compounds on LCNO but also demonstrates minimal detrimental effects on its performance. The surface reconstructed LCNO (SR-LCNO) reveals mitigated gas generation and suppressed structure degradation under high working voltage (＞4.1 V), thereby causing negligible negative effects on the cycling capability and rate performance of commercial cathode materials. The full cells containing SR-LCNO deliver significantly improved electrochemical properties, with no observed exacerbation of side reactions. This work awakes the awareness of the prudent utilization of sacrificial cathode additives and provides an effective strategy for harmless pre-lithiation via surface reconstructed sacrificial cathode additives.

Highly efficient ion-transport "polymer-in-ceramic" electrolytes boost stable all-solid-state Li metal batteries.

"Polymer-in-ceramic" (PIC) electrolytes are widely investigated for all-solid-state batteries (ASSBs) due to their good thermal stability and mechanical performance. However, achieving fast and diversified lithium-ion transport inside the PIC electrolyte and uniform Li+ deposition at the electrolyte/Li anode interface simultaneously remains a challenge. Besides, the effect of ceramic particle size on Li+ transport and Li anodic compatibility is still unclear, which is essential for revealing the enhanced mechanism of the performance for PIC electrolytes. Herein, PIC with moderate ceramic size and contents are prepared and studied to strike a balance between ionic conductivity and anodic compatibility. Through moderate filler-filler interfacial impedance and appropriate surface roughness, a particle size of 17 µm is optimized to facilitate homogeneous Li+ flux on anode and enhance Li+ conductivity of the electrolyte. The PIC electrolyte with ceramic particle size of 17 µm achieves a high lithium ion transference number (0.74) and an ionic conductivity of 4.11 × 10-4 S cm-1 at 60 °C. The Li/PIC/Li symmetric cell can stably cycle for 2800 h at 0.2 mA cm-2 with 0.2 mAh cm-2. Additionally, the Li/PIC/LiFePO4 cell also delivers a superior cycling performance at 0.5C, a high capacity retention of 93.28% after 100 cycles and 83.17% after 200 cycles, respectively.

Ferrocene-Based Artificial Interfacial Layer for High-Performance Lithium Metal Anodes: Continuous Regulation of Li+ Diffusion Behavior.

The diversified design of hybrid artificial layers is a promising method for suppressing the Li dendrite growth and maintaining high Colombic efficiency of lithium (Li) metal anode. Previously, various kinds of organic/inorganic hybrid artificial layers were constructed on the Li metal anode and possessed a positive effect on electrochemical performance. However, the tunable synthesis of artificial layers to continuously regulate the Li diffusion behavior remains a challenge. In this work, the Li diffusion behavior could be tuned by modulating the proportion of components (LiClO4, PMMA and ferrocene (Fc)) in the hybrid artificial layer (LF layer). After optimizing the proportion of each component, the resultant artificial SEI layer exhibits a high Li+ transference number (tLi+ = 0.66) and a high Young's modulus (4.8 GPa). Based on the excellent properties of the as-constructed Fc-based artificial SEI layer, a high-performance lithium anode with no volume effect and dendrite growth is achieved. The Li||Li symmetric cells with a Fc-based artificial SEI layer yielded a stable cycle performance for 1500 h with a high current density of 10 mA cm-2. The pouch cell with LF@Li anode coupled with high-loading LiFePO4 cathode (12.8 mg cm-2) exhibits excellent cyclic stability for 250 cycles with a capacity retention of 75% at 0.5C rate.

Rational design of intergrowth P2/O3 biphasic layered structure with reversible anionic redox chemistry and structural evolution for Na-ions batteries.

Layered oxides have attracted unprecedented attention for their outstanding performance in sodium-ion battery cathodes. Among them, the two typical candidates P2 and O3 type materials generally demonstrate large diversities in specific capacity and cycling endurance with their advantages. Thus, composite materials that contain both P2 and O3 have been widely designed and constructed. Nevertheless, the anionic/cationic ions' behavior and structural evolution in such complex structures remain unclear. In this study, a deep analysis of an advanced Na0.732Ni0.273Mg0.096Mn0.63O2 material that contains 78.39 wt% P2 phase and 21.61 wt% O3 phase is performed based on two typical cathodes P2 Na0.67Ni0.33Mn0.67O2 and O3 NaNi0.5Mn0.5O2 that have the same elemental constitution but different crystal structures. Structural analysis and density functional theory (DFT) calculations suggest that the composite is preferred to form a symbiotic structure at the atomic level, and the complex lattice texture of the biphase structure can block unfavorable ion and oxygen migration in the electrode process. Consequently, the biphase structure has significantly improved the electrochemical performance and kept preferable anionic oxygen redox reversibility. Furthermore, the hetero-epitaxy-like structure of the intergrowth of P2 and O3 structures share multi-phase boundaries, where the inconsistency in electrochemical behavior between P2 and O3 phases leads to an interlocking effect to prevent severe structural collapse and relieves the lattice strain from Na+ de/intercalation. Hence, the symbiotic P2/O3 composite materials exhibited a preferable capacity and cyclability (∼130 mAh g-1 at 0.1 C, 73.1% capacity retention after 200 cycles at 1 C), as well as reversible structural evolution. These findings confirmed the advantages of using the bi/multi-phase cathode for high-energy Na-ion batteries.