Highly Reversible Anion Redox of Manganese-Based Cathode Material Realized by Electrochemical Ion Exchange for Lithium-Ion Batteries

Anion energy storage provides the possibility to achieve higher specific capacity in lithium-ion battery cathode materials, but the problems of capacity attenuation, voltage degradation, and inconsistent redox behavior are still inevitable. In this paper, a novel O2-type manganese-based layered cathode material Li_x[Li_0.2Mn_0.8]O₂ with a ribbon superlattice structure is prepared by electrochemical ion exchange, which realizes the highly reversible redox of anions and excellent cycle performance. Through low-voltage pre-cycling treatment, the specific capacity of the material can reach 230 mAh g⁻¹ without obvious voltage attenuation. During the electrochemical ion exchange, the precursor with P2 structure transforms into Li_x[Li_0.2Mn_0.8]O₂ with O2 structure through the slippage and shrink of adjacent slabs, and the special superlattice structure in Mn slab is still retained. Simultaneously, a certain degree of lattice mismatch and reversible distortion of the MnO₆ octahedron occur. In addition, the anion redox catalyzes the formation of the solid electrolyte interface, stabilizing the electrode/electrolyte interface and inhibiting the dissolution of Mn. The mechanism of electrochemical ion exchange is systematically studied by comprehensive structural and electrochemical characterization, opening an attractive path for the realization of highly reversible anion redox.     

Quasi-Zero Volume Strain Cathode Materials for Sodium Ion Battery through Synergetic Substitution Effect of Li and Mg

P2-type layered oxide material Na_2/3Ni_1/3Mn_2/3O₂ is a competitive candidate for sodium-ion batteries (SIBs). Nevertheless, it suffers from the strong P2–O2 phase transition during charging to the high voltage regime, rendering drastic volume variations and poor cycling performance. Here, a Quasi-zero strain P2-Na_0.75Li_0.15Mg_0.05Ni_0.1Mn_0.7O₂ cathode is synthesized, which reflects the vanishing P2–O2 transition with a volume change as low as 0.49%, thus resulting in the material an excellent cycling performance (83.9% capacity retention after 500 cycles at 5 C). The low-volume strain can be attributed to two aspects: (1) the Mg²⁺ riveted in the Na layer can act as a “pillar” to stabilize the crystal structure under the condition of sodium removal, thus restricting the structural changes under high voltage. (2) The entry of Li⁺ into the transition metal (TM) layer can mitigate the electron localization in the highly desodiation state and can effectively immobilize the coordination oxygen atoms, thus suppressing the slip of P2–O2 transition. This study not only provides a new insight of Li and Mg synergetic substitution effect on the structural stability of P2-type cathode, but also an efficient avenue for developing cathode materials of SIBs with ultralow bulk strain.     

Lithium-Substituted Tunnel/Spinel Heterostructured Cathode Material for High-Performance Sodium-Ion Batteries

Sodium manganese oxides as promising cathode materials for sodium-ion batteries (SIBs) have attracted interest owing to their abundant resources and potential low cost. However, their practical application is hindered due to the manganese disproportionation associated with Mn³⁺, resulting in rapid capacity decline and poor rate capability. Herein, a Li-substituted, tunnel/spinel heterostructured cathode is successfully synthesized for addressing these limitations. The Li dopant acts as a pillar inhibiting unfavorable multiphase transformation, improving the structural reversibility, and sodium storage performance of the cathode. Meanwhile, the tunnel/spinel heterostructure provides 3D Na⁺ diffusion channels to effectively enhance the redox reaction kinetics. The optimized [Na_0.396Li_0.044][Mn_0.97Li_0.03]O₂ composite delivers an excellent rate performance with a reversible capacity of 97.0 mA h g^–1 at 15 C, corresponding to 82.5% of the capacity at 0.1 C, and a promising cycling stability over 1200 cycles with remarkable capacity retention of 81.0% at 10 C. Moreover, by combining with hard carbon anodes, the full cell demonstrates a high specific capacity and favorable cyclability. After 200 cycles, the cell provides 105.0 mA h g^–1 at 1 C, demonstrating the potential of the cathode for practical applications. This strategy might apply to other sodium-deficient cathode materials and inform their strategic design.     

Decoding Li+/Na+ Exchange Route Toward High-Performance Mn-Based Layered Cathodes for Li-Ion Batteries

Li⁺/Na⁺ exchange has been extensively explored as an effective method to prepare high-performance Mn-based layered cathodes for Li-ion batteries, since the first report in 1996 by P. G. Bruce (Nature, 1996. 381, 499–500). Understanding the detailed structural changes during the ion-exchange process is crucial to implement the synthetic control of high-performance layered Mn-based cathodes, but less studied. Herein, in situ synchrotron X-ray diffraction, density functional theory calculations, and electrochemical tests are combined to conduct the systemic studies into the structural changes during the ion-exchange process of an Mn-only layered cathode O3-type Li_0.67[Li_0.22Mn_0.78]O₂ (LLMO) from the corresponding counterpart P3-type Na_0.67[Li_0.22Mn_0.78]O₂ (NLMO). The temperature-resolved observations combined with theoretical calculations reveal that the Li⁺/Na⁺ exchange is favorable thermodynamically and composited with two tandem topotactic phase transitions: 1) from NLMO to a layered intermediate through ≈60% of Li⁺/Na⁺ exchange. 2) then to the final layered product LLMO through further Li insertion. Moreover, the intermediate-dominate composite is obtained by slowing down the exchange kinetics below room temperature, showing better electrochemical performance than LLMO obtained by the traditional molten-salt method. The findings provide guides for the synthetic control of high-performance Mn-based cathodes under mild conditions.     

A Novel Cathode Material with a Concentration‐Gradient for High‐Energy and Safe Lithium‐Ion Batteries

A high‐energy functional cathode material with an average composition of Li[Ni_0.72Co_0.18Mn_0.10]O₂, mainly comprising a core material Li[Ni_0.8Co_0.2]O₂ encapsulated completely within a stable manganese‐rich concentration‐gradient shell is successfully synthesized by a co‐precipitation process. The Li[Ni_0.72Co_0.18Mn_0.10]O₂ with a concentration‐gradient shell has a shell thickness of about 1 µm and an outer shell composition rich in manganese, Li[Ni_0.55Co_0.15Mn_0.30]O₂. The core material can deliver a very high capacity of over 200 mA h g^?1, while the manganese‐rich concentration‐gradient shell improves the cycling and thermal stability of the material. These improvements are caused by a gradual and continuous increase of the stable tetravalent Mn in the concentration‐gradient shell layer. The electrochemical and thermal properties of this cathode material are found to be far superior to those of the core Li[Ni_0.8Co_0.2]O₂ material alone. Electron microscopy also reveals that the original crystal structure of this material remains intact after cycling.     

Manipulating the Electronic Structure of Li‐Rich Manganese‐Based Oxide Using Polyanions: Towards Better Electrochemical Performance

Lithium‐rich manganese‐based layered oxides show great potential as high‐capacity cathode materials for lithium ion batteries, but usually exhibit a poor cycle life, gradual voltage drop during cycling, and low thermal stability in the highly delithiated state. Herein, a strategy to promote the electrochemical performance of this material by manipulating the electronic structure through incorporation of boracic polyanions is developed. As‐prepared Li[Li_0.2Ni_0.13Co_0.13Mn_0.54](BO₄)_0.015(BO₃)_0.005O_1.925 shows a decreased M‐O covalency and a lowered O 2p band top compared with pristine Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂. As a result, the modified cathode exhibits a superior reversible capacity of 300 mA h g^?1 after 80 cycles, excellent cycling stability with a capacity retention of 89% within 300 cycles, higher thermal stability, and enhanced redox couple potentials. The improvements are correlated to the enhanced oxygen stability that originates from the tuned electronic structure. This facile strategy may further be extended to other high capacity electrode systems.     

Adiponitrile (C6H8N2): A New Bi‐Functional Additive for High‐Performance Li‐Metal Batteries

Rechargeable batteries with a Li metal anode and Ni‐rich Li[Ni_xCo_yMn_1?x?y]O₂ cathode (Li/Ni‐rich NCM battery) have been emerging as promising energy storage devices because of their high‐energy density. However, Li/Ni‐rich NCM batteries have been plagued by the issue of the thermodynamic instability of the Li metal anode and aggressive surface chemistry of the Ni‐rich cathode against electrolyte solution. In this study, a bi‐functional additive, adiponitrile (C₆H₈N₂), is proposed which can effectively stabilize both the Li metal anode and Ni‐rich NCM cathode interfaces. In the Li/Ni‐rich NCM battery, the addition of 1 wt% adiponitrile in 0.8 m LiTFSI + 0.2 M LiDFOB + 0.05 M LiPF₆ dissolved in EMC/FEC = 3:1 electrolyte helps to produce a conductive and robust Li anode/electrolyte interface, while strong coordination between Ni⁴⁺ on the delithiated Ni‐rich cathode and nitrile group in adiponitrile reduces parasitic reactions between the electrolyte and Ni‐rich cathode surface. Therefore, upon using 1 wt% adiponitrile, the Li/full concentration gradient Li[Ni_0.73Co_0.10Mn_0.15Al_0.02]O₂ battery achieves an unprecedented cycle retention of 75% over 830 cycles under high‐capacity loading of 1.8 mAh cm^?2 and fast charge–discharge time of 2 h. This work marks an important step in the development of high‐performance Li/Ni‐rich NCM batteries with efficient electrolyte additives.     

Hierarchical Engineering of Porous P2‐Na2/3Ni1/3Mn2/3O2 Nanofibers Assembled by Nanoparticles Enables Superior Sodium‐Ion Storage Cathodes

Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium‐ion batteries (SIBs) by virtue of their facile 2D Na⁺ diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2‐type Na_2/3Ni_1/3Mn_2/3O₂ as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2‐Na_2/3Ni_1/3Mn_2/3O₂ nanofibers exhibit exceptional rate capability (166.7 mA h g^?1 at 0.1 C with 73.4 mA h g^?1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/extraction are verified by in operando X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na‐ion full battery built with a Na_2/3Ni_1/3Mn_2/3O₂ nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg^?1. The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na‐storage performance of layered TMO cathode materials.     

Understanding the Role of Alumina (Al2O3), Pentalithium Aluminate (Li5AlO4), and Pentasodium Aluminate (Na5AlO4) Coatings on the Li and Mn-Rich NCM Cathode Material 0.33Li2MnO3·0.67Li(Ni0.4Co0.2Mn0.4)O2 for Enhanced Electrochemical Performance

The active role of alumina, pentalithium aluminate (Li₅AlO₄, Li-aluminate), and pentasodium aluminate (Na₅AlO₄, Na-aluminate) as the surface protection coatings produced via atomic layer deposition on Li and Mn-rich NCM cathode materials 0.33Li₂MnO₃·0.67LiNi_0.4Co_0.2Mn_0.4O₂ is discussed. A notable improvement in the electrochemical behavior of the coated cathodes has been found while tested in Li-coin cells at 30 °C. Though all the coated cathodes demonstrate enhanced electrochemical cycling and rate performances, Na-aluminate coated cathodes exhibit exemplary behavior. Prolonged cycling and rate capability testing demonstrate that after more than 400 cycles at 1 C rate, the uncoated cathode delivers only 63 mAh g⁻¹, while those with alumina, Li-aluminate, and Na-aluminate coatings exhibit approximately two times higher specific capacities. The coated cathodes display steady average discharge potential and lower evolution of the voltage hysteresis during prolonged cycling compared to the uncoated cathode. Importantly, Na-aluminate coated cathode shows a lowering in gases (O₂, CO₂, H₂, etc.) evolution. Post-cycling analysis of the electrodes demonstrates higher morphological integrity of the coated cathode materials and lower transition metals dissolution from them. The coatings mitigate undesirable side reactions between the electrodes and the electrolyte solution in the cells.     

Perfluoro Macrocyclic Ether as an Ambifunctional Additive for High-Performance SiO and Nickel 88%-Based High-Energy Li-ion Battery

State-of-the-art lithium (Li)-ion batteries employ silicon anode active material at a limited fraction while strongly relying on fluoroethylene carbonate (FEC) electrolyte additive exceeding 10 wt.% to enable stable cycling. The swelling issue of silicon in the aspect of solid electrolyte interphase (SEI) instability and a risk of safety hazards and high manufacturing cost due to FEC has motivated the authors to design a well-working fluorinated additive substitute. High-capacity cells employing nickel-rich oxide cathode are pursued by operating at > 4.2 V versus Li/Li⁺, for which anodic stability of electrolyte is required. Herein, a highly effective new ambifunctional additive of icosafluoro-15-crown 5-ether is proposed at a little fraction of 0.4 wt.% for the stabilized interfaces and reduced swelling of high capacity (3.5 mAh cm⁻²) 5 wt.% SiO-graphite anode and LiNi_0.88Co_0.08Mn_0.04O₂ cathode. Utilizing together with a lowered fraction of FEC, reversible long 300 cycles at 4.35 V and 1 C (225 mA g⁻¹) are achieved. Material characterization results reveal that such stabilization is derived from the surface passivation of both anode and cathode with perfluoro ether, LiF, and Li_xPF_y species. The present study gives insight into electrolyte formulation design with lower cost and both-side stabilization strategies for silicon and nickel-rich active materials and their interfaces.     

Combined First‐Principle Calculations and Experimental Study on Multi‐Component Olivine Cathode for Lithium Rechargeable Batteries

The electrochemical properties and phase stability of the multi‐component olivine compound LiMn_1/3Fe_1/3Co_1/3PO₄ are studied experimentally and with first‐principles calculation. The formation of a solid solution between LiMnPO₄, LiFePO₄, and LiCoPO₄ at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first‐principle results indicate that there are three distinct regions in the electrochemical profile at quasi‐open‐circuit potentials of ～3.5 V, ～4.1 V, and ～4.7 V, which are attributed to Fe³⁺/Fe²⁺, Mn³⁺/Mn²⁺, and Co³⁺/Co²⁺ redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1 V of Mn³⁺/Mn²⁺ redox couples, implying an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one‐phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of Li_xMn_1/3Fe_1/3Co_1/3PO₄ (0 ≤ x ≤ 1) at room temperature. This is the first demonstration that the well‐ordered, non‐nanocrystalline (less than 1% Li–M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one‐phase mode.     

A High‐Energy Li‐Ion Battery Using a Silicon‐Based Anode and a Nano‐Structured Layered Composite Cathode

High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni‐rich Li[Ni_0.75Co_0.1Mn_0.15]O₂, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C‐IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C‐IWGS anode delivers a high capacity of >800 mAh g^?1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (～6 wt%). The cathode (Li[Ni_0.75Co_0.1Mn_0.15]O₂) is structurally optimized (Ni‐rich core and a Ni‐depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g^?1) with excellent stability at high voltage (～4.3 V). A novel lithium ion battery system based on the Si/C‐IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg^?1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.     

Advanced Concentration Gradient Cathode Material with Two‐Slope for High‐Energy and Safe Lithium Batteries

Li[Ni_0.65Co_0.13Mn_0.22]O₂ cathode with two‐sloped full concentration gradient (TSFCG), maximizing the Ni content in the inner part of the particle and the Mn content near the particle surface, is synthesized via a specially designed batch‐type reactor. The cathode delivers a discharge capacity of 200 mAh g^?1 (4.3 V cutoff) with excellent capacity retention of 88% after 1500 cycles in a full‐cell configuration. Overall electrochemical performance of the TSFCG cathode is benchmarked against conventional cathode (CC) with same composition and commercially available Li[Ni_0.8Co_0.15Al_0.05]O₂ (NCA). The TSFCG cathode exhibits the best cycling stability, rate capability, and thermal stability of the three electrodes. Transmission electron microscopy analysis of the cycled TSFCG, CC, and NCA cathodes shows that the TSFCG electrode maintains both its mechanical and structural integrity whereas the NCA electrode nearly pulverizes due to the strain during cycling.     

Tuning Anionic Redox Activity and Reversibility for a High‐Capacity Li‐Rich Mn‐Based Oxide Cathode via an Integrated Strategy

When fabricating Li‐rich layered oxide cathode materials, anionic redox chemistry plays a critical role in achieving a large specific capacity. Unfortunately, the release of lattice oxygen at the surface impedes the reversibility of the anionic redox reaction, which induces a large irreversible capacity loss, inferior thermal stability, and voltage decay. Therefore, methods for improving the anionic redox constitute a major challenge for the application of high‐energy‐density Li‐rich Mn‐based cathode materials. Herein, to enhance the oxygen redox activity and reversibility in Co‐free Li‐rich Mn‐based Li_1.2Mn_0.6Ni_0.2O₂ cathode materials by using an integrated strategy of Li₂SnO₃ coating‐induced Sn doping and spinel phase formation during synchronous lithiation is proposed. As an Li⁺ conductor, a Li₂SnO₃ nanocoating layer protects the lattice oxygen from exposure at the surface, thereby avoiding irreversible oxidation. The synergy of the formed spinel phase and Sn dopant not only improves the anionic redox activity, reversibility, and Li⁺ migration rate but also decreases Li/Ni mixing. The 1% Li₂SnO₃‐coated Li_1.2Mn_0.6Ni_0.2O₂ delivers a capacity of more than 300 mAh g^?1 with 92% Coulombic efficiency. Moreover, improved thermal stability and voltage retention are also observed. This synergic strategy may provide insights for understanding and designing new high‐performance materials with enhanced reversible anionic redox and stabilized surface lattice oxygen.     

The Role of Ni and Co in Suppressing O-Loss in Li-Rich Layered Cathodes

Lithium-rich transition metal cathodes can deliver higher capacities than stoichiometric materials by exploiting redox reactions on oxygen. However, oxidation of O²⁻ on charging often results in loss of oxygen from the lattice. In the case of Li₂MnO₃ all the capacity arises from oxygen loss, whereas doping with Ni and/or Co leads to the archetypal O-redox cathodes Li[Li_0.2Ni_0.2Mn_0.6]O₂ and Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂, which exhibit much reduced oxygen loss. Understanding the factors that determine the degree of reversible O-redox versus irreversible O-loss is important if Li-rich cathodes are to be exploited in next generation lithium-ion batteries. Here it is shown that the almost complete eradication of O-loss with Ni substitution is due to the presence of a less Li-rich, more Ni-rich (nearer stoichiometric) rocksalt shell at the surface of the particles compared with the bulk, which acts as a self-protecting layer against O-loss. In the case of Ni and Co co-substitution, a thinner rocksalt shell forms, and the O-loss is more abundant. In contrast, Co doping does not result in a surface shell yet it still suppresses O-loss, although less so than Ni and Ni/Co doping, indicating that doping without shell formation is effective and that two mechanisms exist for O-loss suppression.     

A Water Stable,Near‐Zero‐Strain O3‐Layered Titanium‐Based Anode for Long Cycle Sodium‐Ion Battery

Layered transition metal (TM) oxides of the stoichiometry Na_xMO₂ (M = TM) have shown great promise in sodium‐ion batteries (SIBs); however, they are extremely sensitive to moisture. To date, most reported titanium‐based layered anodes exhibit a P2‐type structure. In contrast, O3‐type compounds are rarely investigated and their synthesis is challenging due to their higher percentage of unstable Ti³⁺ than the P2 type. Here, a pure phase and highly crystalline O3‐type Na_0.73Li_0.36Ti_0.73O₂ with high performance is successfully proposed in SIBs. This material delivers a reversible capacity of 108 mAh g^?1 with a stable and safe potential of 0.75 V versus Na/Na⁺. In situ X‐ray diffraction reveals that this material does not undergo any phase transitions and exhibits a near‐zero volume change upon Na⁺ insertion/de‐insertion, which ensures exceptional long cycle life over 6000 cycles. Importantly, it is found that this O3‐Na_0.73Li_0.36Ti_0.73O₂ shows superior moisture stability, even when immersed into water, which are both elusive for conventional layered TM oxides in SIBs. It is believed that the small interlayer distance and high occupation of interlayer vacancy promise such unprecedented water stability.     

Kinetic Control of Long-Range Cationic Ordering in the Synthesis of Layered Ni-Rich Oxides

Deciphering the sophisticated interplay between thermodynamics and kinetics of high-temperature lithiation reaction is fundamentally significant for designing and preparing cathode materials. Here, the formation pathway of Ni-rich layered ordered LiNi_0.6Co_0.2Mn_0.2O₂ (O-LNCM622O) is carefully characterized using in situ synchrotron radiation diffraction. A fast nonequilibrium phase transition from the reactants to a metastable disordered Li_1−x(Ni_0.6Co_0.2Mn_0.2)_1+xO₂ (D-LNCM622O, 0 < x < 0.95) takes place while lithium/oxygen is incorporated during heating before the generation of the equilibrium phase (O-LNCM622O). The time evolution of the lattice parameters for layered nonstoichiometric D-LNCM622O is well-fitted to a model of first-order disorder-to-order transition. The long-range cation disordering parameter, Li/TM (TM = Ni, Co, Mn) ion exchange, decreases exponentially and finally reaches a steady-state as a function of heating time at selected temperatures. The dominant kinetic pathways revealed here will be instrumental in achieving high-performance cathode materials. Importantly, the O-LNCM622O tends to form the D-LNCM622O with Li/O loss above 850 °C. In situ XRD results exhibit that the long-range cationic (dis)ordering in the Ni-rich cathodes could affect the structural evolution during cycling and thus their electrochemical properties. These insights may open a new avenue for the kinetic control of the synthesis of advanced electrode materials.     

A Simple Electrode‐Level Chemical Presodiation Route by Solution Spraying to Improve the Energy Density of Sodium‐Ion Batteries

The formation of a solid electrolyte interface (SEI) on the surface of a carbon anode consumes the active sodium ions from the cathode and reduces the energy density of sodium‐ion batteries (SIBs). Herein, a simple electrode‐level presodiation strategy by spraying a sodium naphthaline (Naph‐Na) solution onto a carbon electrode is reported, which compensates the initial sodium loss and improves the energy density of SIBs. After presodiation, an SEI layer is preformed on the surface of carbon anode before battery cycling. It is shown that a large irreversible capacity of 60 mAh g^?1 is replenished and 20% increase of the first‐cycle Coulombic efficiency is achieved for a hard carbon anode using this presodiation strategy, and the energy density of a Na_0.9[Cu_0.22Fe_0.30Mn_0.48]O₂||carbon full cell is increased from 141 to 240 Wh kg^?1 by using the presodiated carbon anode. This simple and scalable electrode‐level chemical presodiation route also shows generality and value for the presodiation of other anodes in SIBs.     

Interconnected Metallic Membrane Enabled by MXene Inks Toward High-Rate Anode and High-Voltage Cathode for Li-Ion Batteries

The ever-increasing popularity of smart electronics demands advanced Li-ion batteries capable of charging faster and storing more energy, which in turn stimulates the innovation of electrode additives. Developing single-phase conductive networks featuring excellent mechanical strength/integrity coupled with efficient electron transport and durability at high-voltage operation should maximize the rate capability and energy density, however, this has proven to be quite challenging. Herein, it is shown that a 2D titanium carbide (known as MXene) metallic membrane can be used as single-phase interconnected conductive binder for commercial Li-ion battery anode (i.e., Li₄Ti₅O₁₂) and high-voltage cathodes (i.e., Ni_0.8Mn_0.1Co_0.1O₂). Electrodes are fabricated directly by slurry-casting of MXene aqueous inks composited with active materials without any other additives or solvents. The interconnected metallic MXene membrane ensures fast charge transport and provides good durability, demonstrating excellent rate performance in the Li//Li₄Ti₅O₁₂ cell (90 mAh g⁻¹ at 45 C) and high reversible capacity (154 mAh g⁻¹ at 0.2 C/0.5 C) in Li//Ni_0.8Mn_0.1Co_0.1O₂ cell coupled with high-voltage operation (4.3 V vs Li/Li⁺). The LTO//NMC full cell demonstrates promising cycling stability, maintaining capacity retention of 101.4% after 200 cycles at 4.25 V (vs Li/Li⁺) operation. This work provides insights into the rational design of binder-free electrodes toward acceptable cyclability and high-power density Li-ion batteries.     

Tungsten Boride Stabilized Single-Crystal LiNi0.83Co0.07Mn0.1O2 Cathode for High Energy Density Lithium-Ion Batteries: Performance and Mechanisms

Transition metal doped LiNiO₂ layered compounds have attracted significant interest as cathode materials for lithium-ion batteries (LIBs) in recent years due to their high energy density. However, a critical issue of LiNiO₂-based cathodes is caused particularly at highly delithiated state by irreversible phase transition, initiation/propagation of cracks, and extensive reactions with electrolyte. Herein, a tungsten boride (WB)-doped single-crystalline LiNi_0.83Co_0.07Mn_0.1O₂ (SNCM) cathode is reported that affectively addresses these drawbacks. In situ/ex situ microscopic and spectroscopic evidence that B³⁺ enters the bulk of the SNCM, enlarging the interlayer spacing, thus facilitating Li⁺ diffusion, while W³⁺ forms an amorphous surface layer consisting of Li_xW_yO_z (LWO) and Li_xB_yO_z (LBO), which aids the construction of a robust cathode-electrolyte interphase (CEI) film, are shown. It is also shown that WB doping is effective in controlling the degree of the c-axis contraction and release of oxygen-containing gases at high voltages. The best doping concentration of WB is 0.6 wt.%, at which the capacity retention rate of the SNCM reaches 93.2% after 200 cycles at 2.7–4.3 V, while the morphology and structure of the material remain largely unchanged. The presented modification strategy offers a new way for the design of new stable SNCM cathodes for high-energy-density LIBs.