Cathode For Sodium-ion Batteries Research Articles

In Situ Construction of Inorganics-Rich Cathode-Electrolyte Interface toward Long-Life Prussian White Cathode.

Prussian white (PW) is one of the most promising candidates as a cathode for sodium-ion batteries (SIBs) because of its high theoretical capacity, excellent rate performance, and low production cost. However, PW materials suffer severe capacity decay during long-term cycling. In this work, a robust cathode electrolyte interface (CEI) is designed on the PW cathode by employing cresyl diphenyl phosphate (CDP) and adiponitrile (ADN) as electrolyte additives. CDP and ADN possess higher highest occupied molecular orbital energy levels (HOMO) than other solvents, leading to the preferential decomposition of CDP and ADN to construct an inorganics-rich CEI layer in situ on the PW cathode. Benefiting from this CEI layer, the degradation of PW is effectively inhibited during the long cycling. The Na||PW cell achieves an excellent cycling performance with a capacity retention of 85.62% after 1400 cycles. This work presented here provides a feasible strategy for improving the cycling performance of PW by electrolyte modification.

Bismuth-doping boosting Na+ diffusion kinetics of layered oxide cathode with radially oriented {010} active lattice facet for sodium-ion batteries.

O3-type layered oxide cathodes (NaxTMO2) for sodium-ion batteries (SIBs) have attracted significant attention as one of the most promising potential candidates for practical energy storage applications. The poor Na+ diffusion kinetics is, however, one of the major obstacles to advancing large-scale practical application. Herein, we report bismuth-doped O3-NaNi0.5Mn0.5O2 (NMB) microspheres consisting of unique primary nanoplatelets with the radially oriented {010} active lattice facets. The NMB combines the advantages of the oriented and exposed electrochemical active planes for direct paths of Na+ diffusion, and the thick primary nanoplatelets for less surface parasitic reactions with the electrolyte. Consequently, the NMB cathode exhibits a long-term stability with an excellent capacity retention of 72.5% at 1C after 300 cycles and an enhanced rate capability at a 0.1C to 10C rate (1C = 240 mA g-1). Furthermore, the enhancement is elucidated by the small volume change, thin cathode-electrolyte-interphase (CEI) layer, and rapid Na+ diffusion kinetics. In particular, the radial orientation-based Bi-doping strategy is demonstrated to be effective at boosting electrochemical performance in other layered oxides (such as Bi-doped NaNi0.45Mn0.45Ti0.1O2 and NaNi1/3Fe1/3Mn1/3O2). The results provide a promising strategy of utilizing the advantages of the oriented active facets of primary platelets and secondary particles to develop high-rate layered oxide cathodes for SIBs.

Air-Stable Prussian White Cathode Materials for Sodium-Ion Batteries Enabled by ZnO Surface Modification.

Iron-based Prussian white (PW) is one of the promising cathodes for sodium-ion batteries, owing to its high capacity and low cost. However, the practical application of PW is hindered by its poor air stability. The metal-oxide coating has been proven to be an effective way to improve the air stability of electrode materials. Whereas, the target electrode materials conventionally need to be dissolved in the aqueous solution to obtain precursor composites and subsequently calcined at a high temperature during the metal-oxide coating process, which could destroy the phase structure of PW as a result of the sodium leaching into the water and thermal decomposition at the high temperature. In this work, we propose a facile method to construct a ZnO surface layer on PW by utilizing ethanol as a solvent and a mild post-treatment temperature. The ZnO coating layer effectively enhances the air stability of PW and induces the formation of the stable interface on PW. The PW-5 wt % ZnO-E (exposed in 60% humidity air after 30 days) cathode demonstrates a much higher capacity retention (94.1%) at 1 C after 200 cycles than that of PW-E (54%). This work lays a solid foundation for further application of PW.

Dual-anion ether electrolyte enables stable high-voltage Na3V2(PO4)2F3 cathode under wide temperatures

Na3V2(PO4)2F3 (denoted as NVPF) is an attractive cathode for sodium ion batteries (NIB) owning to its high theoretical capacity (128 mAh g−1) and high working potential (3.9 V vs Na/Na+). However, NVPF often suffers from low electronic conductivity and unstable cathode electrolyte interphase (CEI), seriously hindering its practical application. Here, a uniform NVPF microsphere assembled by carbon-coated NVPF nanosheets (HM-NVPF@CN) is prepared and subsequently an inorganic-rich B, F species CEI layer on its surface in dual-anion ether electrolyte is constructed to address above drawbacks. The carbon-coated NVPF nanosheets can shorten the diffusion pathway for both Na+ and e−, and provide large electrochemical reaction area. In addition, the robust CEI layer can enhance the Na+ transport and suppress the parasitic reactions. The optimized electrode exhibits a good cycling stability (70 mAh g−1 after 2000 cycles) and outstanding low temperature performance (99 mAh g−1 at −25 °C). The full cell fabricated with a hard carbon (HC) anode achieves a high capacity retention (88% after 930 cycles) and superior high temperature performance (60 °C, 72 mAh g−1 at 5C). This work provides a novel idea to regulate interfacial chemistry of cathodes for the high-voltage NIB.

Boosting Multielectron Reaction Stability of Sodium Vanadium Phosphate by High-Entropy Substitution.

Na3V2(PO4)3 (NVP) based on the multielectron reactions between V2+ and V5+ has been considered a promising cathode for sodium-ion batteries (SIBs). However, it still suffers from unsatisfactory stability, caused by the poor reversibility of the V5+/V4+ redox couple and structure evolution. Herein, we propos a strategy that combines high-entropy substitution and electrolyte optimization to boost the reversible multielectron reactions of NVP. The high reversibility of the V5+/V4+ redox couple and crystalline structure evolution are disclosed by in situ X-ray absorption near-edge structure spectra and in situ X-ray diffraction. Meanwhile, the electrochemical reaction kinetics of high-entropy substitution NVP (HE-NVP) can be further improved in the diglyme-based electrolyte. These enable HE-NVP to deliver a superior electrochemical performance (capacity retention of 93.1% after 2000 cycles; a large reversible capacity of 120 mAh g-1 even at 5.0 A g-1). Besides, the long cycle life and high power density of the HE-NVP∥natural graphite full-cell configuration demonstrated the superiority of HE-NVP cathode in SIBs. This work highlights that the synergism of high-entropy substitution and electrolyte optimization is a powerful strategy to enhance the sodium-storage performance of polyanionic cathodes for SIBs.

Designing a 3D framework NaVOPO4 as a high-power, low-strain and long-life positive electrode material for Na-ion batteries

Advances in sodium-ion batteries hugely rely on perfecting the performance of active electrode materials. In this paper, we offer a new NaVOPO4 polymorph adopting a KTiOPO4-type framework as a promising high-rate, low-strain and long-life positive electrode material for sodium-ion batteries. NaVOPO4 is prepared via a facile hydrothermally-assisted solid-state ion exchange. The crystal structure is refined based on synchrotron X-ray powder diffraction (XRD) and validated by X-ray absorption spectroscopy (XAS), transmission electron microscopy analysis and density functional theory (DFT) calculations. The electrochemical performance of NaVOPO4 is evaluated through galvanostatic charge/discharge tests, cyclic voltammetry, potentiostatic intermittent titration and electrochemical impedance spectroscopy. A carbon-coated NaVOPO4 demonstrates a specific capacity of ∼110 mAh g–1 at a C/10 rate at an average potential of ∼3.93 V vs. Na+/Na. The material exhibits decent capacity retention and rate capability, maintaining over 74 % of the initial capacity after 1000 cycles at a C/2 rate and around 87% at a 2C charge/discharge rate. Diffusion coefficients of 10–11 cm2 s–1 and DFT-calculated energy barriers of ∼0.15–0.35 eV indicate fast Na+ ion diffusion within the NaVOPO4 framework. The vanadium oxidation state and charge compensation mechanism in NaVOPO4 are studied by XAS and DFT. Moreover, the operando XRD analysis coupled with DFT elucidates several phase transitions occurring in NaVOPO4 with an exceptionally low volume variation of 2.4% in total, highlighting the reversibility and structural stability during Na+ de/insertion. Overall, NaVOPO4 exhibits attractive electrochemical performance and stability, making it a potential candidate for sodium-ion battery cathode materials.

Solid-state synthesis of low-cost and high-energy-density sodium layered-tunnel oxide cathodes: Dynamic structural evolution, Na+/vacancy disordering, and prominent moisture stability

Manganese-based layered oxides show promise as cathode materials for sodium-ion batteries (SIBs). However, several challenges including sluggish Na+ kinetics, complex phase transitions, and poor air stability hinder their practical application. Herein, we proposed a dual-function strategy that not only precisely manipulates dynamic structural evolution from layered to tunnel structure, but also effectively suppresses Na+/vacancy and charge ordering by inhibiting electron delocalization. A series of Ti-substituted Na2/3Mn1-xTixO2 (x=0, 1/9, 2/9, 1/3) as proof of concept materials were designed to demonstrate the dual-function strategy. As a result, the optimized Na2/3Mn8/9Ti1/9O2 cathode material delivers a high specific capacity of 202.9 mAh g−1 at 0.1 C within 1.5−4.3 V, equivalent to 536.6 Wh kg−1 of energy density, and exhibits 71.0% of capacity retention after 300 cycles at 1 C. Meanwhile, a highly reversible P2/Tunnel-OP4/Tunnel phase transition process and interlocking effect between the layered and tunnel structure as well as prominent moisture stability even after soak water treatment are further confirmed by in-situ charge and discharge XRD and other advanced characterization techniques. Noting that the electrode assembled with water-solution binder still displays a high capacity retention of 85.4% after 400 cycles at 1 C. Our dual-function strategy provides valuable guidance for developing high energy density and water stable practical SIB cathode materials.

O3‐Type Cathodes for Sodium‐Ion Batteries: Recent Advancements and Future Perspectives

AbstractOver recent decades, rapid advancements in energy technology have transformed human life. Lithium‐ion batteries (LIBs) have played a pivotal role nevertheless concerns about limited lithium resources and price fluctuations underscore the need for sustainability. Sodium‐ion batteries (SIBs), operating on principles akin to LIBs, have emerged as promising candidates for rechargeable batteries in the next generation of energy storage systems, primarily due to their cost‐effectiveness and sustainable attributes. Analogous to LIBs, the cathode in SIBs assumes a critical role in dictating the electrochemical performance of the battery. Therefore, the research and development of cathode materials for SIBs take on paramount significance. O3‐type SIB cathodes, inspired by the successful O3‐type LIB cathodes (e. g., LiCoO2 and NMC variants), hold promise for commercial applications. This comprehensive overview offers an in‐depth exploration of various unary‐metal oxide cathode materials characterized by an O3‐layered structure. Subsequently, nickel (Ni), manganese (Mn), and Ni/Mn‐based O3 cathode materials are conducted a comprehensive study, assessing the effects of element substitution and doping on capacity, phase transitions, and cycle life. In light of the current challenges, advancing SIB cathode materials of future directions will propose, addressing key considerations in the pursuit of enhanced performance and sustainable energy storage solutions.

Electrospun Na3MnTi(PO4)3/C film: A multielectron-reaction and free-standing cathode for sodium-ion batteries

With the continuous advancement of renewable energy sources, sodium-ion batteries are currently regarded as highly promising technologies for large-scale electric energy storage. The compound Na3MnTi(PO4)3 has garnered significant attention owing to its exceptional theoretical capacity, robust structural stability, and abundant availability of resources. Herein, hierarchical carbon-decorated Na3MnTi(PO4)3 nanofibers are synthesized via a feasible electrospinning technique followed by pyrolysis, effectively addressing the issue of poor electronic conductivity in phosphate cathodes. The free-standing Na3MnTi(PO4)3/C electrode serves as a cathode for sodium-ion batteries, exhibiting exceptional electronic conductivity and superior Na+ transport capability. Moreover, it demonstrates an impressive reversible capacity of 171.4 mA h g−1 at 0.2C and exhibits outstanding cyclic stability with a capacity retention of 63.7 % after 6300 cycles at 1C. The full cell, assembled with independent Na3MnTi(PO4)3/C cathode and hard carbon anode, exhibits a reversible capacity of 153.7 mA h g−1 at a current density of 10 mA g−1. The in-situ synthesis of nanomaterial particles within interconnected porous nanocarbon fibers can effectively enhance the materials' poor electronic conductivity, thereby further improving their cyclic stability and Na+ transport kinetics.

Solid-phase construction of high-performance sodium-ion battery cathode materials with three-dimensional porous structure: Na4MnCr(PO4)3/C

Na4MnCr(PO4)3 is a promising cathode material with high redox potential and high energy density, but the intrinsic poor electronic conductivity and substandard structural stability restrict its practical application. Herein, porous Na4MnCr(PO4)3/C with conductive networks and improved electrochemical properties is synthesized by a facile modified solid-state process using citric acid as a multifunctional additive. The results reveal that citric acid can be used as a grinding aid to make the raw materials mix more evenly and speed up the efficiency of ball milling. Besides, 3D conductive network and porous structure originated from polycondensation and carbonization of citric acid can promote the electrochemical properties of Na4MnCr(PO4)3/C by enhancing the electronic/ionic conductivity and (de)intercalation reaction kinetics. As expected, the optimal Na4MnCr(PO4)3/C delivers a high reversible capacity of 130.5 mAh g−1 at 0.1C rate, and exhibits a capacity retention of 82.62% at 10C rate after 500 cycles. In addition, the reversible biphasic reaction of the cathode is confirmed by the constant galvanostatic intermittent titration technique and ex-situ XRD, which shows great potential of the synthesized Na4MnCr(PO4)3/C for practical applications.

P/s-orbital hybridization induced by Mg-doping to active Na sites in Na2FePO4F cathode for long-life and high-rate sodium-ion batteries

The iron-based fluorophosphate Na2FePO4F (NFPF) is considered as a potential cathode for sodium-ion batteries due to the low-cost, non-toxicity and appropriate working voltage. However, the inferior intrinsic electronic conductivity and the restrained active Na sites bring the limits for full realization of electrochemical properties. Herein, Mg2+ with d0 orbital was introduced in FeO4F2 structure, aimed at activating the Na+ at Na1 site and enhancing the electronic conductivity. Different from the 3d transition metal (TM) elements that form 3d-O2p orbital interactions in the FeO4F2 structure, the Mg with d° contributes p and s orbitals mainly in Mg-O bonds, which corresponds to more stable orbital interaction and lattice structure. The electron distribution of bridge O due to the Mg-doping leads to the wooden barrel effect near the Mg site, thus activating Na+ at Na1 site by lowering the energy barrier of Na+ migration from Na1 to Na2 site. Hence, the obtained NFMPF electrode delivers high specific capacity (121.4 vs. 108.7 mAh g−1 at 0.1 C) and better cycling stability (73.8% vs. 54.2 % after 1000 cycles at 20 C). Overall, regulating the electronic structure and activating Na+ at inactive site is the key to break the bottleneck of low activity, which can be an effective strategy to design cathode materials with excellent electrochemical performance.

Advances in layered transition metal oxide cathodes for sodium-ion batteries

The rapid rise of renewable energy technology has greatly promoted the development of energy storage systems. Breaking decades of stagnation, sodium-ion batteries (SIBs) have now regained momentum in the field of energy storage and they are considered as a low-cost alternative to lithium-ion batteries. The search for suitable materials to reversibly host sodium ions has become a focal point in SIB field. Layered transition metal oxide (NaxTMO2) as the cathode material has attracted increasing attention due to its simple structure, facile synthesis, and high operating potential. Nevertheless, NaxTMO2 still faces severe challenges, including irreversible phase transitions, storage instability, insufficient performance, etc. This work provides a comprehensive review of NaxTMO2 as the cathode material for SIBs, analyzes the challenges encountered by NaxTMO2, and summarizes effective improvement strategies. Strategies including doping, composite cathode materials, high-entropy materials and microstructural modulation can effectively guide the design of NaxTMO2 with excellent performance. SIBs are bound to play a positive role in the new round of energy revolution.

Dual-complexing agent dominated synthesis of carbon coated Na3V2(PO4)3 cathodes for high-performance sodium ion batteries

The currently prevailing single complexing agent-dominated sol-gel technologies for Na3V2(PO4)3 (NVP) cathodes in sodium-ion batteries (SIBs) always result in limited modification effects, especially in regards to the particle size of NVP and the quality of carbon coatings. Herein, we report a citric acid and glycine co-complexed strategy for fabricating carbon-coated NVP. It creates a favorable synergy for optimizing the microstructure and electrochemical performance of the NVP cathode. The introduction of glycine in citric acid not only decreases the solution viscosity for facilitated metal-ion diffusion, but also induces the self-construction of a 3D network through heteromolecular hydrogen bonds. The optimized carbon-coated NVP by co-complexing of citric acid and glycine (named as NVP/CG-5.0) presents distinctly decreased particle size, improved dispersity and moderate carbon coating thickness of ∼2 nm. It also features a large specific surface area of 44.4 m2 g−1 with rich mesopores. Impressively, the NVP/CG-5.0 electrode exhibits substantially improved electrochemical performance, such as the elevated specific capacity of 108.3 mAh g−1 with high initial Coulombic efficiency (95.2%), high capacity retention of 81.3% after 2000 cycles at 2 C and excellent rate performance (88.2 mAh g−1 at 20.0 C). Furthermore, the assembled NVP/CG-5.0║hard carbon full battery also exhibits superior electrochemical performance, suggesting the great potential of the co-complexed strategy for developing high-performance NVP cathodes in SIBs.

Na4Fe1.5Mn1.5(PO4)2(P2O7): A low-cost and earth-abundant cathode for robust sodium storage

The mixed compounds of phosphates and pyrophosphates are attractive cathodes for sodium-ion batteries (SIBs) owing to their robust open framework structure and superior diffusion dynamics. However, most reported mixed phosphate cathodes generally suffer from low operating potential. Herein, we develop a bimetallic Na4Fe1.5Mn1.5(PO4)2(P2O7)/C-rGO (NFMPP/C-rGO) cathode, which possesses two working plateaus at 2.92 and 3.95 V. The obtained NFMPP/C-rGO demonstrates a stable high capacity of over 120 mAh g−1 at 0.1 C. In-situ XRD characterization discloses a solid solution reaction for the Fe2+/3+ redox couple and a two-phase reaction for the Mn2+/3+ redox couple. First-principles calculations reveal the migration of Na+ in NFMPP has low barriers. This work provides a new, low-cost, earth-abundant, and stable cathode choice for practical SIBs.

Cation/Anion-Dual regulation in Na3MnTi(PO4)3 cathode achieves the enhanced electrochemical properties of Sodium-Ion batteries

Na3MnTi(PO4)3 (NMTP) emerges as a promising cathode material with high-performance for sodium-ion batteries (SIBs). Nevertheless, its development has been limited by several challenges, including poor electronic conductivity, the Mn3+ Jahn-Teller effect, and the presence of a Na+/Mn2+ cation mixture. To address these issues, we have developed a cation/anion-dual regulation strategy to activate the redox reactions involving manganese, thereby significantly enhancing the performance of NMTP. This strategy simultaneously enhances the structural dynamics and facilitates rapid ion transport at high rates by inducing the formation of sodium vacancy. The combined effects of these modifications lead to a substantial improvement in specific capacity (79.1 mAh/g), outstanding high-rate capabilities (35.9 mAh/g at 10C), and an ultralong cycle life (only 0.040 % capacity attenuation per cycle over 250 cycles at 1C for Na3.34Mn1.2Ti0.8(PO3.98F0.02)3) when used as a cathode material in SIBs. Furthermore, its performance in full cell demonstrates impressive rate capability (44.4 mAh/g at 5C) and exceptional cycling stability (with only 0.116 % capacity decay per cycle after 150 cycles at 1C), suggesting its potential for practical applications. This work presents a dual regulation strategy targeting different sites, offering a significant advancement in the development of NASICON phosphate cathodes for SIBs.

Accelerating the Phase Formation Kinetics of Alluaudite Sodium Iron Sulfate Cathodes via Ultrafast Thermal Shock.

Alluaudite sodium iron sulfate (NFS) exhibits great potential for use in sodium-ion battery cathodes due to its elevated operating potential and abundant element reserves. However, conventional solid-state methods demonstrate a low heating/cooling rate and sluggish reaction kinetics, requiring a long thermal treatment to effectively fabricate NFS cathodes. Herein, we propose a thermal shock (TS) strategy to synthesize alluaudite sodium iron sulfate cathodes using either hydrous or anhydrous raw materials. The analysis of the phase formation process reveals that TS treatment can significantly facilitate the removal of crystal water and decomposition of the intermediate phase Na2Fe(SO4)2 in the hydrous precursor. In the case of the anhydrous precursor, the kinetics of the combination reaction between Na2SO4 and FeSO4 can be also accelerated by TS treatment. Consequently, pure NFS phase formation can be completed after a substantially shorter time of post-sintering, thereby saving significant time and energy. The TS-treated NFS cathode derived from hydrous precursor exhibits higher retention after 200 cycles at 1C and better rate capability than the counterpart prepared by conventional long-term tube furnace sintering, demonstrating the great potential of this novel strategy.

Probing the account of phase transition upon electrochemical cycling of the P2-Na0.67Ni0.15Fe0.2Mn0.65O2 layered oxide cathodes for sodium-ion batteries

Layered P2-Na0.67Ni0.15Fe0.2Mn0.65O2 (P2-NFM) cathode material has attracted great attention in sodium-ion batteries due to its high theoretical capacity, low cost, and environmental friendliness. However, P2-NFM exhibits irreversible phase transition and slip of transition metal layers in the high voltage range during charging process, leading to a gradually declined performance of the cathode material. It is therefore necessary to investigate the mechanism of phase transition of P2-NFM as well as the effect of phase transition on its performance. Herein, utilizing ex situ x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, the crystal structure and TM (transition-metal) bonding changes caused by phase transition are elucidated. It is found that P2-NFM is prone to undergo an irreversible P2-O2 phase transition at high voltage, causing changes in lattice parameters and rapid capacity decay. The irreversible phase transition is mainly due to he dynamic transformation of valence states of Fe and Ni in P2-NFM materials at high voltage. It is this process that results in irreversible fluctuations in the bond lengths between these elements and oxygen, consequently instigating interlayer slip within the material. Besides, the charge compensation mechanism of P2-NFM has been elucidated based on the study of its initial charging process. Results show that the charge compensation is mainly contributed by Ni and Fe in the high voltage range, while by a small amount of Mn in the low voltage range. It reveals the essential cause of the adverse phase transition of P2-NFM materials and points out the direction for improving the cycling stability of these layered oxide materials.

Rational design of cationic ratio tuned high-performance P2/O3 bi-phase layered oxide materials for sodium-ion batteries

Layered oxides are the widely investigated cathodes for sodium-ion batteries (SIBs), especially their pure phases (e.g., P2, O3). In this work, we report a series of Mn-Ni-Fe based cathode materials with P2/O3 bi-phase, which possesses advantages of both P2 and O3 structures. At first, the manuscript shows a synthesis phase diagram of Na0.83MnxNiyFe1-x-yO2 to pre-screen and select the P2/O3 bi-phase material Na0.83Mn1/2Ni1/3Fe1/6O2. Then, it is found that the cationic ratio has a significant impact on the phase formation. The structure of the materials gradually changes with the various of the Mn/Ni ratio. When the Mn/Ni ratio reaches 3/2, P2/O3 bi-phase is formed. Moreover, Fe content will influence the P2/O3 ratio in the bi-phase material. In particular, the synthesized bi-phase Na0.83Mn3/6Ni2/6Fe1/6O2 has a P2/O3 ratio of 71/29 wt%. It delivers a high specific capacity of 136.6 mA h g−1 (at current density 20 mA g−1) between 2.0 and 4.0 V and 94.8% retention (at current density 100 mA g−1) after 100 cycles. In addition, an 85.6 mA h g−1 discharge capacity can be maintained at a superior high current density of 2000 mA g−1. The work offers critical guidance to the rational design of the bi-phase layered cathode materials.

Homeostatic Solid Solution Reaction in Phosphate Cathode: Breaking High-Voltage Barrier to Achieve High Energy Density and Long Life of Sodium-Ion Batteries.

The stable phase transformation during electrochemical progress drives extensive research on vanadium-based polyanions in sodium-ion batteries (SIBs), especially Na3 V2 (PO4 )3 (NVP). And the electron transfer between V3+/4+ redox couple in NVP could be generally achieved, owing to the confined crystal variation during battery service. However, the more favorable V4+/5+ redox couple is still in hard-to-access situation due to the high barrier and further brings about the corresponding inefficiency in energy densities. In this work, the multilevel redox in NVP frame (MLNP) alters reaction pathway to undergo homeostatic solid solution process and breaks the high barrier of V4+/5+ at high voltage, taking by progressive transition metal (V, Fe, Ti, and Cr) redox couple. The diversified reaction paths across diffusion barriers could be realized by distinctive release/uptake of inactive Na1 site, confirmed by the calculations of density functional theory. Thereby its volume change is merely 1.73% during the multielectron-transfer process (≈2.77 electrons). MLNP cathode could achieve an impressive energy density of 440Wh kg-1 , driving the leading development of MLNP among other NASICON structure SIBs. The integration of multiple redox couples with low strain modulates the reaction pathway effectively and will open a new avenue for fabricating high-performance cathodes in SIBs.

Synergetic enhancement of structural stability and kinetics of P’2-type layered cathode for sodium-ion batteries via cation–anion co-doping

The P’2-type layered oxides attract much attention as viable cathode materials for sodium-ion batteries (SIBs), due to their high specific capacity and environmental friendliness. Nevertheless, the sluggish Na+ diffusion kinetics and drastic capacity decay triggered by irreversible phase transition limit their large-scale application. In this study, we employ a synergistic optimization strategy involving cation and anion dopants to successfully restrain intergranular strain and tune local electronic structure, strengthening structural stability and electrochemical performance of the cathode material. Specifically, the Mg2+ dopant suppresses Na+/vacancy rearrangement and Mn-O anisotropic changes, while the F− dopant facilitates Na+ transport and alleviates phase evolution in high-voltage regions. Through this co-doping design, the modified electrodes display more alleviated voltage decay and exceptional capacity retention enhancements ranging from 6.57 % to 81.23 % after 750 cycles at 1000 mA g–1. This work provides novel perspectives on precise design of cathode materials, making layered oxides promising contenders for the next generation energy storage systems.