Cyclic Aminosilane‐Based Additive Ensuring Stable Electrode–Electrolyte Interfaces in Li‐Ion Batteries

Ni‐rich cathodes are considered feasible candidates for high‐energy‐density Li‐ion batteries (LIBs). However, the structural degradation of Ni‐rich cathodes on the micro‐ and nanoscale leads to severe capacity fading, thereby impeding their practical use in LIBs. Here, it is reported that 3‐(trimethylsilyl)‐2‐oxazolidinone (TMS‐ON) as a multifunctional additive promotes the dissociation of LiPF₆, prevents the hydrolysis of ion‐paired LiPF₆ (which produces undesired acidic compounds including HF), and scavenges HF in the electrolyte. Further, the presence of 0.5 wt% TMS‐ON helps maintain a stable solid–electrolyte interphase (SEI) at Ni‐rich LiNi_0.7Co_0.15Mn_0.15O₂ (NCM) cathodes, thus mitigating the irreversible phase transformation from layered to rock‐salt structures and enabling the long‐term stability of the SEI at the graphite anode with low interfacial resistance. Notably, NCM/graphite full cells with TMS‐ON, which exhibit an excellent discharge capacity retention of 80.4%, deliver a discharge capacity of 154.7 mAh g^?1 after 400 cycles at 45 °C.     

Advanced Electrolytes for Fast‐Charging High‐Voltage Lithium‐Ion Batteries in Wide‐Temperature Range

LiNi_xMn_yCo_1?x?yO₂ (NMC) cathode materials with Ni ≥ 0.8 have attracted great interest for high energy‐density lithium‐ion batteries (LIBs) but their practical applications under high charge voltages (e.g., 4.4 V and above) still face significant challenges due to severe capacity fading by the unstable cathode/electrolyte interface. Here, an advanced electrolyte is developed that has a high oxidation potential over 4.9 V and enables NMC811‐based LIBs to achieve excellent cycling stability in 2.5–4.4 V at room temperature and 60 °C, good rate capabilities under fast charging and discharging up to 3C rate (1C = 2.8 mA cm^?2), and superior low‐temperature discharge performance down to ?30 °C with a capacity retention of 85.6% at C/5 rate. It is also demonstrated that the electrode/electrolyte interfaces, not the electrolyte conductivity and viscosity, govern the LIB performance. This work sheds light on a very promising strategy to develop new electrolytes for fast‐charging high‐energy LIBs in a wide‐temperature range.     

High Voltage LiNi0.5Mn0.3Co0.2O2/Graphite Cell Cycled at 4.6 V with a FEC/HFDEC‐Based Electrolyte

A high voltage LiNi_0.5Mn_0.3Co_0.2O₂/graphite cell with a fluorinated electrolyte formulation 1.0 m LiPF₆ fluoroethylene carbonate/bis(2,2,2‐trifluoroethyl) carbonate is reported and its electrochemical performance is evaluated at cell voltage of 4.6 V. Comparing with its nonfluorinated electrolyte counterpart, the reported fluorinated one shows much improved Coulombic efficiency and capacity retention when a higher cut‐off voltage (4.6 V) is applied. Scanning electron microscopy/energy dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy data clearly demonstrate the superior oxidative stability of the new electrolyte. The structural stability of the bulk cathode materials cycled with different electrolytes is extensively studied by X‐ray absorption near edge structure and X‐ray diffraction.     

Membrane‐Free Zn/MnO2 Flow Battery for Large‐Scale Energy Storage

The traditional Zn/MnO₂ battery has attracted great interest due to its low cost, high safety, high output voltage, and environmental friendliness. However, it remains a big challenge to achieve long‐term stability, mainly owing to the poor reversibility of the cathode reaction. Different from previous studies where the cathode redox reaction of MnO₂/MnOOH is in solid state with limited reversibility, here a new aqueous rechargeable Zn/MnO₂ flow battery is constructed with dissolution–precipitation reactions in both cathodes (Mn²⁺/MnO₂) and anodes (Zn²⁺/Zn), which allow mixing of anolyte and catholyte into only one electrolyte and remove the requirement for an ion selective membrane for cost reduction. Impressively, this new battery exhibits a high discharge voltage of ≈1.78 V, good rate capability (10C discharge), and excellent cycling stability (1000 cycles without decay) at the areal capacity ranging from 0.5 to 2 mAh cm^‐2. More importantly, this battery can be readily enlarged to a bench scale flow cell of 1.2 Ah with good capacity retention of 89.7% at the 500th cycle, displaying great potential for large‐scale energy storage.     

Countering Voltage Decay and Capacity Fading of Lithium‐Rich Cathode Material at 60 °C by Hybrid Surface Protection Layers

Li‐rich layered metal oxides have attracted much attention for their high energy density but still endure severe capacity fading and voltage decay during cycling, especially at elevated temperature. Here, facile surface treatment of Li_1.17Ni_0.17Co_0.17Mn_0.5O₂ (0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂) spherical cathode material is designed to address these drawbacks by hybrid surface protection layers composed of Mg²⁺ pillar and Li‐Mg‐PO₄ layer. As a result, the surface coated Li‐rich cathode material exhibits much enhanced cycling stability at 60 °C, maintaining 72.6% capacity retention (180 mAh g^?1) between 3.0 and 4.7 V after 250 cycles. More importantly, 88.7% average discharge voltage retention can be obtained after the rigorous cycle test. The strategy developed here with novel hydrid surface protection effect can provide a vital approach to inhibit the undesired side reactions and structural deterioration of Li‐rich cathode materials and may also be useful for other layered oxides to increase their cycling stability at elevated temperature.     

An In Situ Interface Reinforcement Strategy Achieving Long Cycle Performance of Dual‐Ion Batteries

Dual‐ion batteries (DIBs) with high operation voltage offer promising candidates for low‐cost clean energy chemistries. However, there still exist tough issues, including structural collapse of the graphite cathode due to solvent co‐intercalation and electrolyte decomposition on the electrode/electrolyte interface, which results in unsatisfactory cyclability and fast battery failure. Herein, Li₄Ti₅O₁₂ (LTO) modified mesocarbon microbeads (MCMBs) are proposed as a cathode material. The LTO layer functions as a skeleton and offers electrocatalytic active sites for in situ generation of a favorable and compatible cathode electrolyte interface (CEI) layer. The synergetic LTO‐CEI network can change the thermodynamic behavior of the PF₆^? intercalation process and maintain the structural integrity of the graphite cathode, as a “Great Wall” to protect the cathode from structural collapse and electrolyte decomposition. Such LTO‐CEI reinforced cathode exhibits a prolonged cyclability with 85.1% capacity retention after 2000 cycles even at cut‐off potential of 5.4 V versus Li⁺/Li. Moreover, the LTO‐modified MCMB (+)//prelithiated MCMB (?) full cell exhibits a high energy density of ≈200 Wh kg^?1, remarkably enhanced cyclability with 93.5% capacity retention after 1000 cycles. Undoubtedly, this work offers in‐depth insight into interface chemistry, which can arouse new originality to boost the development of DIBs.     

Mn‐Rich P′2‐Na0.67[Ni0.1Fe0.1Mn0.8]O2 as High‐Energy‐Density and Long‐Life Cathode Material for Sodium‐Ion Batteries

Herein, P′2‐type Na_0.67[Ni_0.1Fe_0.1Mn_0.8]O₂ is introduced as a promising new cathode material for sodium‐ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na⁺ de/intercalation. The O? Ni? O? Mn? O? Fe? O bond in the octahedra of transition‐metal layers is used to suppress the elongation of the Mn? O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g^?1 (≈605 Wh kg^?1) is delivered at 0.05 C (13 mAg^?1) with a high reversible capacity of ≈140 mAh g^?1 at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P′2–OP4 phase transition and small volume change upon charge and discharge (≈3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of ≈542 Wh kg^?1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg^?1).     

A Novel Surface Treatment Method and New Insight into Discharge Voltage Deterioration for High‐Performance 0.4Li2MnO3–0.6LiNi1/3Co1/3Mn1/3O2 Cathode Materials

The Li‐rich cathode materials have been considered as one of the most promising cathodes for high energy Li‐ion batteries. However, realization of these materials for use in Li‐ion batteries is currently limited by their intrinsic problems. To overcome this barrier, a new surface treatment concept is proposed in which a hybrid surface layer composed of a reduced graphene oxide (rGO) coating and a chemically activated layer is created. A few layers of GO are first coated on the surface of the Li‐rich cathode material, followed by a hydrazine treatment to produce the reducing agent of GO and the chemical activator of the Li₂MnO₃ phase. Compared to previous studies, this surface treatment provides substantially improved electrochemical performance in terms of initial Coulombic effiency and retention of discharge voltage. As a result, the surface‐treated 0.4Li­₂MnO_3–0.6LiNi_1/3Co_1/3Mn_1/3O₂ exhibits a high capacity efficiency of 99.5% during the first cycle a the discharge capacity of 250 mAh g^?1 (2.0–4.6 V under 0.1C), 94.6% discharge voltage retention during 100 cycles (1C) and the superior capacity retention of 60% at 12C at 24 °C.     

High Voltage Operation of Ni‐Rich NMC Cathodes Enabled by Stable Electrode/Electrolyte Interphases

The lithium (Li) metal battery (LMB) is one of the most promising candidates for next‐generation energy storage systems. However, it is still a significant challenge to operate LMBs with high voltage cathodes under high rate conditions. In this work, an LMB using a nickel‐rich layered cathode of LiNi_0.76Mn_0.14Co_0.10O₂ (NMC76) and an optimized electrolyte [0.6 m lithium bis(trifluoromethanesulfonyl)imide + 0.4 m lithium bis(oxalato)borate + 0.05 m LiPF₆ dissolved in ethylene carbonate and ethyl methyl carbonate (4:6 by weight)] demonstrates excellent stability at a high charge cutoff voltage of 4.5 V. Remarkably, these Li||NMC76 cells can deliver a high discharge capacity of >220 mA h g^?1 (846 W h kg^?1) and retain more than 80% capacity after 1000 cycles at high charge/discharge current rates of 2C/2C (1C = 200 mA g^?1). This excellent electrochemical performance can be attributed to the greatly enhanced structural/interfacial stability of both the Ni‐rich NMC76 cathode material and the Li metal anode using the optimized electrolyte.     

Efficient Li‐Ion‐Conductive Layer for the Realization of Highly Stable High‐Voltage and High‐Capacity Lithium Metal Batteries

Recently, a consensus has been reached that using lithium metal as an anode in rechargeable Li‐ion batteries is the best way to obtain the high energy density necessary to power electronic devices. Challenges remain, however, with respect to controlling dendritic Li growth on these electrodes, enhancing compatibility with carbonate‐based electrolytes, and forming a stable solid–electrolyte interface layer. Herein, a groundbreaking solution to these challenges consisting in the preparation of a Li₂TiO₃ (LT) layer that can be used to cover Li electrodes via a simple and scalable fabrication method, is suggested. Not only does this LT layer impede direct contact between electrode and electrolyte, thus avoiding side reactions, but it assists and expedites Li‐ion flux in batteries, thus suppressing Li dendrite growth. Other effects of the LT layer on electrochemical performance are investigated by scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique analyses. Notably, LT layer‐incorporating Li cells comprising high‐capacity/voltage cathodes with reasonably high mass loading (LiNi_0.8Co_0.1Mn_0.1O₂, LiNi_0.5Mn_1.5O₄, and LiMn₂O₄) show highly stable cycling performance in a carbonate‐based electrolyte. Therefore, it is believed that the approach based on the LT layer can boost the realization of high energy density lithium metal batteries and next‐generation batteries.     

Polymer‐in‐“Quasi‐Ionic Liquid” Electrolytes for High‐Voltage Lithium Metal Batteries

Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.     

High‐Temperature Treatment of Li‐Rich Cathode Materials with Ammonia: Improved Capacity and Mean Voltage Stability during Cycling

Li‐rich electrode materials of the family x Li₂MnO₃·(1?x )LiNi_a Co_b Mn_c O₂ (a + b + c = 1) suffer a voltage fade upon cycling that limits their utilization in commercial batteries despite their extremely high discharge capacity, ≈250 mA h g^?1. Li‐rich, 0.35Li₂MnO₃·0.65LiNi_0.35Mn_0.45Co_0.20O₂, is exposed to NH₃ at 400 °C, producing materials with improved characteristics: enhanced electrode capacity and a limited average voltage fade during 100 cycles in half cells versus Li. Three main changes caused by NH₃ treatment are established. First, a general bulk reduction of Co and Mn is observed via X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure. Next, a structural rearrangement lowers the coordination number of Co? O and Mn? O bonds, as well as formation of a surface spinel‐like structure. Additionally, Li⁺ removal from the bulk causes the formation of surface LiOH, Li₂CO₃, and Li₂O. These structural and surface changes can enhance the voltage and capacity stability of the Li‐rich material electrodes after moderate NH₃ treatment times of 1–2 h.     

Grafting Benzenediazonium Tetrafluoroborate onto LiNixCoyMnzO2 Materials Achieves Subzero‐Temperature High‐Capacity Lithium‐Ion Storage via a Diazonium Soft‐Chemistry Method

Subzero‐temperature Li‐ion batteries (LIBs) are highly important for specific energy storage applications. Although the nickel‐rich layered lithium transition metal oxides(LiNi_xCo_yMn_zO₂) (LNCM) (x > 0.5, x + y +z = 1) are promising cathode materials for LIBs, their very slow Li‐ion diffusion is a main hurdle on the way to achieve high‐performance subzero‐temperature LIBs. Here, a class of low‐temperature organic/inorganic hybrid cathode materials for LIBs, prepared by grafting a conducting polymer coating on the surface of 3 µm sized LiNi_0.6Co_0.2Mn_0.2O₂ (LNCM‐3) material particles via a greener diazonium soft‐chemistry method is reported. Specifically, LNCM‐3 particles are uniformly coated with a thin polyphenylene film via the spontaneous reaction between LNCM‐3 and C₆H₅N₂⁺BF₄^?. Compared with the uncoated one, the polyphenylene‐coated LNCM‐3 (polyphenylene/LNCM‐3) has shown much improved low‐temperature discharge capacity (≈148 mAh g^?1 at 0.1 C, ?20 °C), outstanding rate capability (≈105 mAh g^?1 at 1 C, ?20 °C), and superior low‐temperature long‐term cycling stability (capacity retention is up to 90% at 0.5 C over 1150 cycles). The low‐temperature performance of polyphenylene/LNCM‐3 is the best among the reported state‐of‐the art cathode materials for LIBs. The present strategy opens up a new avenue to construct advanced cathode materials for wider range applications.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

In Situ Synthesis of Hierarchical Core Double‐Shell Ti‐Doped LiMnPO4@NaTi2(PO4)3@C/3D Graphene Cathode with High‐Rate Capability and Long Cycle Life for Lithium‐Ion Batteries

Olivine‐type LiMnPO₄ (LMP) cathodes have gained enormous attraction for Li‐ion batteries (LIBs), thanks to their large theoretical capacity, high discharge platform, and thermal stability. However, it is still hugely challenging to achieve encouraging Li‐storage behaviors owing to their low electronic conductivity and limited lithium diffusion. Herein, the core double‐shell Ti‐doped LMP@NaTi₂(PO₄)₃@C/3D graphene (TLMP@NTP@C/3D‐G) architecture is designed and constructed via an in situ synthetic methodology. A continuous electronic conducting network is formed with the unfolded 3D‐G and conducting carbon nanoshell. The Nasicon‐type NTP nanoshell with exceptional ionic conductivity efficiently inhibits gradual enrichment in by‐products, and renders low surfacial/interfacial electron/ion‐diffusion resistance. Besides, a rapid Li⁺ diffusion in the bulk structure is guaranteed with the reduction of Mn_Li+˙ antisite defects originating from the synchronous Ti‐doping. Benefiting from synergetic contributions from these design rationales, the integrated TLMP@NTP@C/3D‐G cathode yields high initial discharge capacity of ≈164.8 mAh g^?1 at 0.05 C, high‐rate reversible capacity of ≈116.2 mAh g^?1 at 10 C, and long‐term capacity retention of ≈93.3% after 600 cycles at 2 C. More significantly, the electrode design developed here will exert significant impact upon constructing other advanced cathodes for high‐energy/power LIBs.     

A High Energy Density Aqueous Battery Achieved by Dual Dissolution/Deposition Reactions Separated in Acid‐Alkaline Electrolyte

Aqueous batteries are facing big challenges in the context of low working voltages and energy density, which are dictated by the narrow electrochemical window of aqueous electrolytes and low specific capacities of traditional intercalation‐type electrodes, even though they usually represent high safety, low cost, and simple maintenance. For the first time, this work demonstrates a record high‐energy‐density (1503 Wh kg^?1 calculated from the cathode active material) aqueous battery system that derives from a novel electrolyte design to expand the electrochemical window of electrolyte to 3 V and two high‐specific‐capacity electrode reactions. An acid‐alkaline dual electrolyte separated by an ion‐selective membrane enables two dissolution/deposition electrode redox reactions of MnO₂/Mn²⁺ and Zn/Zn(OH)₄^2? with theoretical specific capacities of 616 and 820 mAh g^?1, respectively. The newly proposed Zn–Mn²⁺ aqueous battery shows a high Coulombic efficiency of 98.4% and cycling stability of 97.5% of discharge capacity retention for 1500 cycles. Furthermore, in the flow battery based on Zn–Mn²⁺ pairs, more excellent stability of 99.5% of discharge capacity retention for 6000 cycles is achieved due to greatly improved reversibility of the Zn anode. This work provides a new path for the development of novel aqueous batteries with high voltage and energy density.     

High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li⁺/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi_0.895Co_0.085Mn_0.02O₂ is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni²⁺O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni²⁺O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials.     

A New P2‐Type Layered Oxide Cathode with Extremely High Energy Density for Sodium‐Ion Batteries

Herein, a new P2‐type layered oxide is proposed as an outstanding intercalation cathode material for high energy density sodium‐ion batteries (SIBs). On the basis of the stoichiometry of sodium and transition metals, the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode is synthesized without impurities phase by partially substituting Ni and Fe into the Mn sites. The partial substitution results in a smoothing of the electrochemical charge/discharge profiles and thus greatly improves the battery performance. The P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode delivers an extremely high discharge capacity of 221.5 mAh g^?1 with a high average potential of ≈2.9 V (vs Na/Na⁺) for SIBs. In addition, the fast Na‐ion transport in the P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂ cathode structure enables good power capability with an extremely high current density of 2400 mA g^?1 (full charge/discharge in 12 min) and long‐term cycling stability with ≈80% capacity retention after 500 cycles at 600 mA g^?1. A combination of electrochemical profiles, in operando synchrotron X‐ray diffraction analysis, and first‐principles calculations are used to understand the overall Na storage mechanism of P2‐type Na_0.55[Ni_0.1Fe_0.1Mn_0.8]O₂.     

Mn versus Al in Layered Oxide Cathodes in Lithium‐Ion Batteries: A Comprehensive Evaluation on Long‐Term Cyclability

Nickel‐rich layered oxide cathodes with the composition LiNi_1?x?yCo_xMn_yO₂ (NCM, (1?x?y) ≥ 0.6) are under intense scrutiny recently to contend with commercial LiNi_0.8Co_0.15Al_0.05O₂ (NCA) for high‐energy‐density batteries for electric vehicles. However, a comprehensive assessment of their electrochemical durability is currently lacking. Herein, two in‐house cathodes, LiNi_0.8Co_0.15Al_0.05O₂ and LiNi_0.7Co_0.15Mn_0.15O₂, are investigated in a high‐voltage graphite full cell over 1500 charge‐discharge cycles (≈5–10 year service life in vehicles). Despite a lower nickel content, NCM shows more performance deterioration than NCA. Critical underlying degradation processes, including chemical, structural, and mechanical aspects, are analyzed via an arsenal of characterization techniques. Overall, Mn substitution appears far less effective than Al in suppressing active mass dissolution and irreversible phase transitions of the layered oxide cathodes. The active mass dissolution (and crossover) accelerates capacity decline with sustained parasitic reactions on the graphite anode, while the phase transitions are primarily responsible for cell resistance increase and voltage fade. With Al doping, on the other hand, secondary particle pulverization is the more limiting factor for long‐term cyclability compared to Mn. These results establish a fundamental guideline for designing high‐performing Ni‐rich NCM cathodes as a compelling alternative to NCA and other compositions for electric vehicle applications.     

High‐Voltage Oxygen‐Redox‐Based Cathode for Rechargeable Sodium‐Ion Batteries

Recently, anionic‐redox‐based materials have shown promising electrochemical performance as cathode materials for sodium‐ion batteries. However, one of the limiting factors in the development of oxygen‐redox‐based electrodes is their low operating voltage. In this study, the operating voltage of oxygen‐redox‐based electrodes is raised by incorporating nickel into P2‐type Na_2/3[Zn_0.3Mn_0.7]O₂ in such a way that the zinc is partially substituted by nickel. As designed, the resulting P2‐type Na_2/3[(Ni_0.5Zn_0.5)_0.3Mn_0.7]O₂ electrode exhibits an average operating voltage of 3.5 V and retains 95% of its initial capacity after 200 cycles in the voltage range of 2.3–4.6 V at 0.1C (26 mA g^?1). Operando X‐ray diffraction analysis reveals the reversible phase transition: P2 to OP4 phase on charge and recovery to the P2 phase on discharge. Moreover, ex situ X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies reveal that the capacity is generated by the combination of Ni²⁺/Ni⁴⁺ and O^2?/O^1? redox pairs, which is supported by first‐principles calculations. It is thought that this kind of high voltage redox species combined with oxygen redox could be an interesting approach to further increase energy density of cathode materials for not only sodium‐based rechargeable batteries, but other alkali‐ion battery systems.