Impact of Transition Metal Layer Vacancy on the Structure and Performance of P2 Type Layered Sodium Cathode Material.

This study explores the impact of introducing vacancy in the transition metal layer of rationally designed Na0.6[Ni0.3Ru0.3Mn0.4]O2 (NRM) cathode material. The incorporation of Ru, Ni, and vacancy enhances the structural stability during extensive cycling, increases the operation voltage, and induces a capacity increase while also activating oxygen redox, respectively, in Na0.7[Ni0.2VNi0.1Ru0.3Mn0.4]O2 (V-NRM) compound. Various analytical techniques including transmission electron microscopy, X-ray absorption near edge spectroscopy, operando X-ray diffraction, and operando differential electrochemical mass spectrometry are employed to assess changes in the average oxidation states and structural distortions. The results demonstrate that V-NRM exhibits higher capacity than NRM and maintains a moderate capacity retention of 81% after 100 cycles. Furthermore, the formation of additional lone-pair electrons in the O 2p orbital enables V-NRM to utilize more capacity from the oxygen redox validated by density functional calculation, leading to a widened dominance of the OP4 phase without releasing O2 gas. These findings offer valuable insights for the design of advanced high-capacity cathode materials with improved performance and sustainability in sodium-ion batteries.

Two birds with one stone: One-pot concurrent Ta-doping and -coating on Ni-rich LiNi0.92Co0.04Mn0.04O2 cathode materials with fiber-type microstructure and Li+-conducting layer formation.

A novel scalable Taylor-Couette reactor (TCR) synthesis method was employed to prepare Ta-modified LiNi0.92Co0.04Mn0.04O2 (T-NCM92) with different Ta contents. Through experiments and density functional theory (DFT) calculations, the phase and microstructure of Ta-modified NCM92 were analyzed, showing that Ta provides a bifunctional (doping and coating at one time) effect on LiNi0.92Co0.04Mn0.04O2 cathode material through a one-step synthesis process via a controlling suitable amount of Ta and Li-salt. Ta doping allows the tailoring of the microstructure, orientation, and morphology of the primary NCM92 particles, resulting in a needle-like shape with fine structures that considerably enhance Li+ ion diffusion and electrochemical charge/discharge stability. The Ta-based surface-coating layer effectively prevented microcrack formation and inhibited electrolyte decomposition and surface-side reactions during cycling, thereby significantly improving the electrochemical performance and long-term cycling stability of NCM92 cathodes. Our as-prepared NCM92 modified with 0.2 mol% Ta (i.e., T2-NCM92) exhibits outstanding cyclability, retaining 84.5 % capacity at 4.3 V, 78.3 % at 4.5 V, and 67.6 % at 45 â„ƒ after 200 cycles at 1C. Even under high-rate conditions (10C), T2-NCM92 demonstrated a remarkable capacity retention of 66.9 % after 100 cycles, with an initial discharge capacity of 157.6 mAh g-1. Thus, the Ta modification of Ni-rich NCM92 materials is a promising option for optimizing NCM cathode materials and enabling their use in real-world electric vehicle (EV) applications.

Simultaneous Enhancement of Lithium Transfer Kinetics and Structural Stability in Dual-Phase TiO2 Electrodes by Ruthenium Doping.

Dual-phase TiO2 consisting of bronze and anatase phases is an attractive electrode material for fast-charging lithium-ion batteries due to the unique phase boundaries present. However, further enhancement of its lithium storage performance has been hindered by limited knowledge on the impact of cation doping as an efficient modification strategy. Here, the effects of Ru4+ doping on the dual-phase structure and the related lithium storage performance are demonstrated for the first time. Structural analysis reveals that an optimized doping ratio of Ru:Ti = 0.01:0.99 (1-RTO) is vital to maintain the dual-phase configuration because the further increment of Ru4+ fraction would compromise the crystallinity of the bronze phase. Various electrochemical tests and density functional theory calculations indicate that Ru4+ doping in 1-RTO enables more favorable lithium diffusion in the bulk for the bronze phase as compared to the undoped TiO2 (TO) counterpart, while lithium kinetics in the anatase phase are found to remain similar. Furthermore, Ru4+ doping leads to a better cycling stability for 1-RTO-based electrodes with a capacity retention of 82.1% after 1200 cycles at 8 C as compared to only 56.1% for TO-based electrodes. In situ X-ray diffraction reveals a reduced phase separation in the lithiated anatase phase, which is thought to stabilize the dual-phase architecture during extended cycling. The simultaneous enhancement of rate ability and cycling stability of dual-phase TiO2 enabled by Ru4+ doping provides a new strategy toward fast-charging lithium-ion batteries.

Competing Mechanisms Determine Oxygen Redox in Doped Ni-Mn Based Layered Oxides for Na-Ion Batteries.

Cation doping is an effective strategy for improving the cyclability of layered oxide cathode materials through suppression of phase transitions in the high voltage region. In this study, Mg and Sc are chosen as dopants in P2-Na0.67Ni0.33Mn0.67O2, and both have found to positively impact the cycling stability, but influence the high voltage regime in different ways. Through a combination of synchrotron-based methods and theoretical calculations it is shown that it is more than just suppression of the P2 to O2 phase transition that is critical for promoting the favorable properties, and that the interplay between Ni and O activity is also a critical aspect that dictates the performance. With Mg doping, the Ni activity can be enhanced while simultaneously suppressing the O activity. This is surprising because it is in contrast to what has been reported in other Mn-based layered oxides where Mg is known to trigger oxygen redox. This contradiction is addressed by proposing a competing mechanism between Ni and Mg that impacts differences in O activity in Na0.67MgxNi0.33- xMn0.67O2 (x < 0 < 0.33). These findings provide a new direction in understanding the effects of cation doping on the electrochemical behavior of layered oxides.

Doping-Induced Surface and Grain Boundary Effects in Ni-Rich Layered Cathode Materials.

In this work, the effects of dopant size and oxidation state on the structure and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (NCM811) are investigated. It is shown that doping with boron (B) which has a small ionic radius and an oxidation state of 3+, leads to the formation of a boron oxide-containing surface coating (probably Li3BO3), mainly on the outer surface of the secondary particles. Due to this effect, boron only slightly affects the size of the primary particle and the initial capacity, but significantly improves the capacity retention. On the other hand, the dopant ruthenium (Ru) with a larger ionic radius and a higher oxidation state of 5+ can be stabilized within the secondary particles and does not experience a segregation to the outer agglomerate surface. However, the Ru dopant preferentially occupies incoherent grain boundary sites, resulting in smaller primary particle size and initial capacity than for the B-doped and pristine NCM811. This work demonstrates that a small percentage of dopant (2 mol%) cannot significantly affect bulk properties, but it can strongly influence the surface and/or grain boundary properties of microstructure and thus the overall performance of cathode materials.

Stabilizing Crystal Framework of an Overlithiated Li1+xMn2O4 Cathode by Heterointerfacial Epitaxial Strain for High-Performance Microbatteries.

To meet the increasing demands of high-energy and high-power-density lithium-ion microbatteries, overlithiated Li1+xMn2O4 (0 ≤ x ≤ 1) is an attractive cathode candidate due to the high theoretical capacity of 296 mAh g-1 and the interconnected lithium-ion diffusion pathways. However, overlithiation triggers the irreversible cubic-tetragonal phase transition due to Jahn-Teller distortion, causing rapid capacity degradation. In contrast to conventional lithium-ion batteries, microbatteries offer the opportunity to develop specific thin-film-based modification strategies. Here, heterointerfacial lattice strain is proposed to stabilize the spinel crystal framework of an overlithiated Li1+xMn2O4 (LMO) cathode by epitaxial thin film growth on an underlying SrRuO3 (SRO) electronic conductor layer. It is demonstrated that the lattice misfit at the LMO/SRO heterointerface results in an in-plane epitaxial constraint in the full LMO film. This suppresses the lattice expansion during overlithiation that typically occurs in the in-plane direction. It is proposed by density functional theory modeling that the epitaxial constraint can accommodate the internal lattice stress originating from the cubic-tetragonal transition during overlithiation. As a result, a doubling of the capacity is achieved by reversibly intercalating a second lithium ion in a LiMn2O4 epitaxial cathode with a complete reversible phase transition. An impressive cycling stability can be obtained with reversible capacity retentions of above 90.3 and 77.4% for the 4 and 3 V range, respectively. This provides an effective strategy toward a stable overlithiated Li1+xMn2O4 epitaxial cathode for high-performance microbatteries.

Exploiting High-Voltage Stability of Dual-Ion Aqueous Electrolyte Reinforced by Incorporation of Fiberglass into Zwitterionic Hydrogel Electrolyte.

Rechargeable zinc aqueous batteries are key alternatives for replacing toxic, flammable, and expensive lithium-ion batteries in grid energy storage systems. However, these systems possess critical weaknesses, including the short electrochemical stability window of water and intrinsic fast zinc dendrite growth. Hydrogel electrolytes provide a possible solution, especially cross-linked zwitterionic polymers that possess strong water retention ability and high ionic conductivity. Herein, an in situ prepared fiberglass-incorporated dual-ion zwitterionic hydrogel electrolyte with an ionic conductivity of 24.32 mS cm-1 , electrochemical stability window up to 2.56 V, and high thermal stability is presented. By incorporating this hydrogel electrolyte of zinc and lithium triflate salts, a zinc//LiMn0.6 Fe0.4 PO4 pouch cell delivers a reversible capacity of 130 mAh g-1 in the range of 1.0-2.2 V at 0.1C, and the test at 2C provides an initial capacity of 82.4 mAh g-1 with 71.8% capacity retention after 1000 cycles with a coulombic efficiency of 97%. Additionally, the pouch cell is fire resistant and remains safe after cutting and piercing.

Fast and Durable Lithium Storage Enabled by Tuning Entropy in Wadsley-Roth Phase Titanium Niobium Oxides.

Wadsley-Roth phase titanium niobium oxides have received considerable interest as anodes for lithium ion batteries. However, the volume expansion and sluggish ion/electron transport kinetics retard its application in grid scale. Here, fast and durable lithium storage in entropy-stabilized Fe0.4 Ti1.6 Nb10 O28.8 (FTNO) is enabled by tuning entropy via Fe substitution. By increasing the entropy, a reduction of the calcination temperature to form a phase pure material is achieved, leading to a reduced grain size and, therefore, a shortening of Li+ pathway along the diffusion channels. Furthermore, in situ X-ray diffraction reveals that the increased entropy leads to the decreased expansion along a-axis, which stabilizes the lithium intercalation channel. Density functional theory modeling indicates the origin to be the more stable FeO bond as compared to TiO bond. As a result, the rate performance is significantly enhanced exhibiting a reversible capacity of 73.7 mAh g-1 at 50 C for FTNO as compared to 37.9 mAh g-1 for its TNO counterpart. Besides, durable cycling is achieved by FTNO, which delivers a discharge capacity of 130.0 mAh g-1 after 6000 cycles at 10 C. Finally, the potential impact for practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4 ‖FTNO full cells.

Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12:Al,Ta Interface in an All-Solid-State Lithium Battery.

All-solid-state lithium batteries are promising candidates for next-generation energy storage systems. Their performance critically depends on the capacity and cycling stability of the cathodic layer. Cells with a garnet Li7La3Zr2O12 (LLZO) electrolyte can show high areal storage capacity. However, they commonly suffer from performance degradation during cycling. For fully inorganic cells based on LiCoO2 (LCO) as cathode active material and LLZO, the electrochemically induced interface amorphization has been identified as an origin of the performance degradation. This study shows that the amorphized interface can be recrystallized by thermal recovery (annealing) with nearly full restoration of the cell performance. The structural and chemical changes at the LCO/LLZO heterointerface associated with degradation and recovery were analyzed in detail and justified by thermodynamic modeling. Based on this comprehensive understanding, this work demonstrates a facile way to recover more than 80% of the initial storage capacity through a thermal recovery (annealing) step. The thermal recovery can be potentially used for cost-efficient recycling of ceramic all-solid-state batteries.

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN part II: frequency dependence and slow jump relaxation.

Specific aspects of the Li+ cation conductivity of anhydrous Li(SCN) are investigated, in particular the high migration enthalpy of lithium vacancies. Close inspection of impedance spectra and conductivity data reveals two bulk relaxation processes, with comparatively fast ion transport at high frequencies and slow ion migration at low frequencies. The impedance results are supported by solid state nuclear magnetic resonance (ssNMR), and pair distribution function (PDF) analysis. This behavior reflects a frequency dependent conductivity, which is related to the extremely slow thiocyanate (SCN)- anion lattice relaxation that occurs when a Li+ cation jumps to the next available site. Two possible migration models are proposed: the first model considers an asymmetric energy landscape for Li+ cation hopping, while the second model is connected to the jump relaxation model and allows for 180° rotational disorder of the (SCN)- anion. A complete kinetic analysis for the hopping of Li+ cations is presented, which reveals new fundamental insights into the ion transport mechanism of materials with complex anions.

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN Part I: ionic conductivity and defect chemistry.

This work reports on the ion transport properties and defect chemistry in anhydrous lithium thiocyanate Li(SCN), which is a pseudo-halide Li+ cation conductor. An extensive doping study was conducted, employing magnesium, zinc and cobalt thiocyanate as donor dopants to systematically vary the conductivity and derive a defect model. The investigations are based on impedance measurements and supported by other analytical techniques such as X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, and density functional theory (DFT) calculations. The material was identified as Schottky disordered with lithium vacancies being the majority mobile charge carriers. In the case of Mg2+ as dopant, defect association with lithium vacancies was observed at low temperatures. Despite a comparably low Schottky defect formation enthalpy of (0.6 ± 0.3) eV, the unexpectedly high lithium vacancy migration enthalpy of (0.89 ± 0.08) eV distinguishes Li(SCN) from the chemically related lithium halides. A detailed defect model of Li(SCN) is presented and respective thermodynamic and kinetic data are given. The thiocyanate anion (SCN)- has a significant impact on ion mobility due to its anisotropic structure and bifunctionality in forming both Li-N and Li-S bonds. More details about the impact on ion dynamics at local and global scale, and on the defect chemical analysis of the premelting regime at high temperatures are given in separate publications (Part II and Part III).

Study of LiCoO2/Li7La3Zr2O12:Ta Interface Degradation in All-Solid-State Lithium Batteries.

The garnet-type Li7La3Zr2O12 (LLZO) ceramic solid electrolyte combines high Li-ion conductivity at room temperature with high chemical stability. Several all-solid-state Li batteries featuring the LLZO electrolyte and the LiCoO2 (LCO) or LiCoO2-LLZO composite cathode were demonstrated. However, all batteries exhibit rapid capacity fading during cycling, which is often attributed to the formation of cracks due to volume expansion and the contraction of LCO. Excluding the possibility of mechanical failure due to crack formation between the LiCoO2/LLZO interface, a detailed investigation of the LiCoO2/LLZO interface before and after cycling clearly demonstrated cation diffusion between LiCoO2 and the LLZO. This electrochemically driven cation diffusion during cycling causes the formation of an amorphous secondary phase interlayer with high impedance, leading to the observed capacity fading. Furthermore, thermodynamic analysis using density functional theory confirms the possibility of low- or non-conducting secondary phases forming during cycling and offers an additional explanation for the observed capacity fading. Understanding the presented degradation paves the way to increase the cycling stability of garnet-based all-solid-state Li batteries.

Bio-Derived Surface Layer Suitable for Long Term Cycling Ni-Rich Cathode for Lithium-Ion Batteries.

Since Ni-rich cathode material is very sensitive to moisture and easily forms residual lithium compounds that degrade cell performance, it is very important to pay attention to the selection of the surface modifying media. Accordingly, hydroxyapatite (Ca5 (PO4 )3 (OH)), a tooth-derived material showing excellent mechanical and thermodynamic stabilities, is selected. To verify the availability of hydroxyapatite as a surface protection material, lithium-doped hydroxyapatite, Ca4.67 Li0.33 (PO4 )3 (OH), is formed with ≈10-nm layer after reacting with residual lithium compounds on Li[Ni0.8 Co0.15 Al0.05 ]O2 , which spontaneously results in dramatic reduction of surface lithium residues to 2879 ppm from 22364 ppm. The Ca4.67 Li0.33 (PO4 )3 (OH)-modified Li[Ni0.8 Co0.15 Al0.05 ]O2 electrode provides ultra-long term cycling stability, enabling 1000 cycles retaining 66.3% of its initial capacity. Also, morphological degradations such as micro-cracking or amorphization of surface are significantly suppressed by the presence of Ca4.67 Li0.33 (PO4 )3 (OH) layer on the Li[Ni0.8 Co0.15 Al0.05 ]O2 , of which the Ca4.67 Li0.33 (PO4 )3 (OH) is transformed to CaF2 via Ca4.67 Li0.33 (PO4 )3 F during the long term cycles reacting with HF in electrolyte. In addition, the authors' density function theory (DFT) results explain the reason of instability of NCA and why CaF2 layers can delay the micro-cracking during electrochemical reaction. Therefore, the stable Ca4.67 Li0.33 (PO4 )3 F and CaF2 layers play a pivotal role to protect the Li[Ni0.8 Co0.15 Al0.05 ]O2 with ultra-long cycling stability.

Molecular engineering towards efficientwhite-light-emitting perovskite.

Low-dimensional hybrid perovskites have demonstrated excellent performance as white-light emitters. The broadband white emission originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparing new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. Halogen-substituted phenyl molecules are applied to synthesize perovskite crystals. The halogen-substituents will withdraw electrons from the branched chain (-R-NH3+) of the phenyl molecule. This will result in positive charge accumulation on -R-NH3+, and thus stronger Coulomb force of bond (-R-NH3+)-(PbBr42-), which facilitates excitons self-trapping. Our designed white perovskites exhibit photoluminescence quantum yield of 32%, color-rendering index of near 90 and chromaticity coordinates close to standard white-light. Our joint experiment-theory study provides insights into the STEs formation in perovskites and will benefit tailoring white perovskites with boosting performance.

Tuning Surface Energy of Zn Anodes via Sn Heteroatom Doping Enabled by a Codeposition for Ultralong Life Span Dendrite-Free Aqueous Zn-Ion Batteries.

Aqueous Zn-ion batteries (AZBs) have been considered as one of the most promising large-scale energy storage systems, owing to the advantages of raw material abundance, low cost, and eco-friendliness. However, the severe growth of Zn dendrites leads to poor stability and low Coulombic efficiency of AZBs. Herein, to effectively inhibit the growth of Zn dendrites, a new strategy has been proposed, i.e., tuning the surface energy of the Zn anode. This strategy can be achieved by in situ doping of Sn heteroatoms in the lattice of metallic Zn via codeposition of Sn and Zn with a small amount of the SnCl2 electrolyte additive. Density functional theory calculations have suggested that Sn heteroatom doping can sharply decrease the surface free energy of the Zn anode. As a consequence, driven by the locally strong electric field, metallic Sn tends to deposit at the tips of the Zn anode, thus decreases the surface energy and growth of Zn at the tips, resulting in a dendrite-free Zn anode. The positive effect of the SnCl2 additive has been demonstrated in both the Zn∥Zn symmetric battery and the Zn/LFP and Zn/HATN full cell. This novel strategy can light a new way to suppress Zn dendrites for long life span Zn-ion batteries.

Size induced structural changes in maricite-NaFePO4: an in-depth study by experiment and simulations.

Rechargeable batteries based on the most abundant elements, such as sodium and iron, have a great potential in the development of cost effective sodium ion batteries for large scale energy storage devices. We report, for the first time, crystallite size dependent structural investigations on maricite-NaFePO4 through X-ray diffraction, X-ray absorption spectroscopy and theoretical simulations. Rietveld refinement analysis on the X-ray diffraction data reveals that a decrease in the unit cell parameters leads to volume contraction upon reduction in the crystallite size. Further, the atomic multiplet simulations on X-ray absorption spectra provide unequivocally a change in the site symmetry of transition metal ions. The high resolution oxygen K-edge spectra reveal a substantial change in the bonding character with the reduction of crystallite size, which is the fundamental cause for the change in the unit cell parameters of maricite-NaFePO4. In parallel, we performed first-principles density functional theory (DFT) calculations on maricite-NaFePO4 with different sodium ion vacancy concentrations. The obtained structural parameters are in excellent agreement with the experimental observations on the mesostructured maricite-NaFePO4. The volumetric changes with respect to crystallite size are related to the compressive strain, resulting in the improvement in the electronic diffusivity. The nano-crystalline maricite-NaFePO4 with improved kinetics will open a new avenue for its usage as a cathode material in sodium ion batteries.

Promoting the Transformation of Li2 S2 to Li2 S: Significantly Increasing Utilization of Active Materials for High-Sulfur-Loading Li-S Batteries.

Lithium-sulfur (Li-S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether-based Li-S batteries involve sophisticated multistep solid-liquid-solid-solid electrochemical reaction mechanisms. Recently, studies on Li-S batteries have widely focused on the initial solid (sulfur)-liquid (soluble polysulfide)-solid (Li2 S2 ) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li-S batteries. Nonetheless, the sluggish kinetics of the solid-solid conversion from solid-state intermediate product Li2 S2 to the final discharge product Li2 S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS3 ) is proposed to decrease the dissociation energy of Li2 S2 and propel the electrochemical transformation of Li2 S2 to Li2 S. The CoS3 catalyst plays a critical role in improving the sulfur utilization, especially in high-loading sulfur cathodes (3-10 mg cm-2 ). Accordingly, the Li2 S/Li2 S2 ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS3 catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g-1 ) compared to the counterpart sulfur electrode without CoS3 .

Rechargeable aluminum batteries: effects of cations in ionic liquid electrolytes.

Room temperature ionic liquids (RTILs) are solvent-free liquids comprised of densely packed cations and anions. The low vapor pressure and low flammability make ILs interesting for electrolytes in batteries. In this work, a new class of ionic liquids were formed for rechargeable aluminum/graphite battery electrolytes by mixing 1-methyl-1-propylpyrrolidinium chloride (Py13Cl) with various ratios of aluminum chloride (AlCl3) (AlCl3/Py13Cl molar ratio = 1.4 to 1.7). Fundamental properties of the ionic liquids, including density, viscosity, conductivity, anion concentrations and electrolyte ion percent were investigated and compared with the previously investigated 1-ethyl-3-methylimidazolium chloride (EMIC-AlCl3) ionic liquids. The results showed that the Py13Cl-AlCl3 ionic liquid exhibited lower density, higher viscosity and lower conductivity than its EMIC-AlCl3 counterpart. We devised a Raman scattering spectroscopy method probing ILs over a Si substrate, and by using the Si Raman scattering peak for normalization, we quantified speciation including AlCl4 -, Al2Cl7 -, and larger AlCl3 related species with the general formula (AlCl3) n in different IL electrolytes. We found that larger (AlCl3) n species existed only in the Py13Cl-AlCl3 system. We propose that the larger cationic size of Py13+ (142 Å3) versus EMI+ (118 Å3) dictated the differences in the chemical and physical properties of the two ionic liquids. Both ionic liquids were used as electrolytes for aluminum-graphite batteries, with the performances of batteries compared. The chloroaluminate anion-graphite charging capacity and cycling stability of the two batteries were similar. The Py13Cl-AlCl3 based battery showed a slightly larger overpotential than EMIC-AlCl3, leading to lower energy efficiency resulting from higher viscosity and lower conductivity. The results here provide fundamental insights into ionic liquid electrolyte design for optimal battery performance.

Unraveling the Role of Earth-Abundant Fe in the Suppression of Jahn-Teller Distortion of P'2-Type Na2/3MnO2: Experimental and Theoretical Studies.

Layered Na2/3MnO2 suffers from capacity loss due to Jahn-Teller (J-T) distortion by Mn3+ ions. Herein, density functional theory calculations suggest Na2/3[Fe xMn1- x]O2 suppresses the J-T effect. The Fe substitution results in a decreased oxygen-metal-oxygen length, leading to decreases in the b and c lattice parameters but an increase in the a lattice constant. As a result, the capacity retention and rate capability are enhanced with an additional redox pair associated with Fe4+/3+. Finally, the thermal properties are improved, with the Fe substitution delaying the exothermic reaction and reducing exothermic heat.