High-performance LiNi0.5Mn1.5O4 spinel controlled by Mn3+ concentration and site disorder

From Mining to Manufacturing: Scientific Challenges and Opportunities behind Battery Production

This Review explores the status and progress made over the past decade in the areas of raw material mining, battery materials and components scale-up, processing, and manufacturing. While substantial advancements have been achieved in understanding battery materials, the transition to large-scale manufacturing introduces scientific challenges that must be addressed from multiple perspectives. Rather than focusing on new material discoveries or incremental performance improvements, this Review focuses on the critical issues that arise in battery manufacturing and highlights the importance of cost-oriented fundamental research to bridge the knowledge gap between fundamental research and industrial production. Challenges and opportunities in integrating machine learning (ML) and artificial intelligence (AI) to digitalize the manufacturing process and eventually realize fully autonomous production are discussed. The review also emphasizes the pressing need for workforce development to meet the growing demands of the battery industry. Potential strategies are suggested for accelerating the manufacturing of current and future battery technologies, ensuring that the workforce is equipped with the necessary skills to support research, development, and large-scale production.

Mg2+ and Cr3+ Co-Doped LiNi0.5Mn1.5O4 Derived from Ni/Mn Bimetal Oxide as High-Performance Cathode for Lithium-Ion Batteries

In this study, pure and Mg2+/Cr3+ co-doped Ni/Mn bimetallic oxides were used as precursors to synthesize pristine and doped LNMO samples. The LNMO samples exhibited the same crystal structure as the precursors. XRD analysis confirmed the successful synthesis of LNMO cathode materials using Ni/Mn bimetallic oxides as precursors. FTIR and Raman spectroscopy reveal that Mg2+/Cr3+ co-doping promotes the formation of the Fd3m disordered phase, effectively reducing electrochemical polarization and charge transfer resistance. Furthermore, co-doping significantly lowers the Mn3+ content on the LNMO surface, thereby mitigating Mn3+ dissolution. Significantly, Mg2+/Cr3+ co-doping induces the emergence of high-surface-energy {100} crystal facets in LNMO grains, which promote lithium-ion transport and, finally, enhance rate capability and cycling performance. Electrochemical analysis indicates that the initial discharge capacities of LNMO-0, LNMO-0.005, LNMO-0.010, and LNMO-0.015 were 126.4, 125.3, 145.3, and 138.2 mAh·g-1, respectively, with capacity retention rates of 82.45%, 82.93%, 83.32%, and 82.08% after 100 cycles. Furthermore, the impedance of LNMO-0.010 prior to cycling was 97.38 Ω, representing a 14.35% reduction compared to the pristine sample. After 100 cycles, its impedance was only 58.61% of that of the pristine sample, highlighting its superior rate capability and cycling stability. As far as we know, studies on the synthesis of LNMO cathode materials via the design of Ni/Mn bimetallic oxides remain limited. Accordingly, this work provides an innovative approach for the preparation and modification of LNMO cathode materials. The investigation of Ni/Mn bimetallic oxides as precursors, combined with co-doping by Mg2+ and Cr3+, for the synthesis of high-performance LiNi0.5Mn1.5O4 (LNMO) aims to provide insights into improving rate capability, cycling stability, reducing impedance, and enhancing capacity retention.

Operando Synchrotron X-Ray Absorption Spectroscopy: A Key Tool for Cathode Material Studies in Next-Generation Batteries

Rechargeable batteries are central to modern energy storage systems, from portable electronics to electric vehicles. The cathode material, a critical component, largely dictates a battery's energy density, capacity, and overall performance. This review focuses on the application of operando X-ray absorption spectroscopy (XAS) to study cathode materials in Li-ion, Na-ion, Li-S, and Na-S batteries. Operando XAS provides real-time insights into the local electronic structure, oxidation states, and coordination environments, which are crucial for understanding complex electrochemical processes, such as redox reactions, phase transitions, and structural degradation. The review highlights the strengths of hard and soft XAS techniques in probing transition metal (TM) and anionic redox processes, particularly in layered oxide cathodes, where reversible oxygen redox and TM behavior are pivotal. The role of operando XAS is also explored in analyzing conversion-type S-based cathodes, where it helps unravel the intricate reaction mechanisms. Furthermore, the review addresses the challenges of in situ cell design for operando XAS, especially under ultrahigh vacuum conditions for soft XAS. By discussing recent advancements and future directions, this review underscores the critical role of operando XAS in driving innovation and improving the design and performance of next-generation battery technologies.

Understanding and Controlling Structural Defects and Disordering in LiNi0.5Mn1.5O4 Cathodes for Direct Recycling

Despite significant progress in recycling spent lithium-ion batteries (LIBs), nondestructive, direct recycling methods still face untenable discrepancies in multiple cathode chemistries, which primarily originate from a variety of structure stabilities during the recycling process. Through systematic investigation of the microstructure evolution during the relithiation treatment, we observed the inevitably induced defects and Li/Mn disordering in the LiNi0.5Mn1.5O4 cathode, contributing to the sluggish Li+ transport and irreversible capacity loss. Employing a defect engineering approach to achieve twin boundaries and preferred grain orientation, we show the regenerated cathodes demonstrate a substantial enhancement of Li+ diffusion and cycling stability, retaining 97.4% capacity after 100 cycles and 87.96% after 200 cycles at C/3. This work not only elaborates on a systematic investigation of defect inducement and structural restoration mechanism but also provides an effective approach to directly recycle high-voltage spinel-type cathodes, contributing to the sustainability of next-generation LIBs.

Zr-Doped High-Voltage Spinel LiNi0.5Mn1.5O4 Manufactured via the Coprecipitation Method

Lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO) provides an elevated operating potential of 4.7 V and a theoretical capacity of 147 mAh g-1, without the need for expensive cobalt. Zr-doped LNMO was synthesized using the coprecipitation technique with Couette-Taylor flow. FE-SEM images and TEM SAED patterns revealed that Zr-doped LNMO formed truncated octahedral structures with exposed (100) crystal facets. When compared to undoped LNMO, Zr-doped LNMO exhibited superior electrochemical performance. Electrochemical evaluations showed that Zr0.1-LNMO achieved 85.9% rate capability at 10 C, significantly outperforming the 69.1% of bare LNMO. In addition, Zr0.1-LNMO exhibited high stability, maintaining 76.8% of the discharge capacity even after 100 cycles.

Improving Fast-Charging Capability of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode under Long-Term Cyclability through Co-Doping Strategy

Co-free spinel LiNi0.5Mn1.5O4 (LNMO) is emerging as a promising contender for designing next generation high-energy-density and fast-charging Li-ion batteries, due to its high operating voltage and good Li+ diffusion rate. However, further improvement of the Li+ diffusion ability and simultaneous resolution of Mn dissolution still pose significant challenges for their practical application. To tackle these challenges, a simple co-doping strategy is proposed. Compared to Pure-LNMO, the extended lattice in resulting LNMO-SbF sample provides wider Li+ migration channels, ensuring both enhanced Li+ transport kinetics, and lower energy barrier. Moreover, Sb creating structural pillar and stronger TM─F bond together provides a stabilized spinel structure, which stems from the suppression of detrimental irreversible phase transformation during cycling related to Mn dissolution. Benefiting from the synergistic effect, the LNMO-SbF material exhibits a superior reversible capacity (111.4 mAh g-1 at 5C, and 70.2 mAh g-1 after 450 cycles at 10C) and excellent long-term cycling stability at high current density (69.4% capacity retention at 5C after 1000 cycles). Furthermore, the LNMO-SbF//graphite full cell delivers an exceptional retention rate of 96.9% after 300 cycles, and provides a high energy density at 3C even with a high loading. This work provides valuable insight into the design of fast-charging cathode materials for future high energy density lithium-ion batteries.

Magnetic Field-induced Disordered Phase of Spinel Oxides for High Battery Performance

The disordered phase of spinel LiMn1.5Ni0.5O4 (LNMO) is more appealing as high-voltage cathode due to its superior electrochemical performance compared to its ordered counterpart. Various methods are developed to induce a phase transition. However, the resulting materials often suffer from capacity degradation due to the adverse influence of accompanying Mn3+ ions. This study presents the utilization of local magnetic fields generated by a magnetic Fe3O4 shell to induce a disordered phase transition in LNMO at lower temperature, transitioning it from an order state without significantly increasing the Mn3+ content. The pivotal role played by the local magnetic fields is evidenced through comparisons with samples with nonmagnetic Al2O3 shell, samples subjected to sole heat treatment, and samples heat-treated within magnetic fields. The key finding is that magnetic fields can initiate a radical pair mechanism, enabling the induction of order-disorder phase transition even at lower temperatures. The disordered spinal LNMO with a magnetic Fe3O4 shell exhibits excellent cycling stability and kinetic properties in electrochemical characterization as a result. This innovation not only unravels the intricate interplay between the disordered phase and Mn3+ content in the cathode spinel but also pioneers the use of magnetic field effects for manipulating material phases.

Modulating the Coordination Chemistry of Cobalt Catalytic Sites by Ruthenium Species to Accelerate the Polysulfide Conversion Kinetics in Lithium-Sulfur Batteries

The performance of lithium-sulfur batteries is compromised by the loss of sulfur as dissolved polysulfides in the electrolyte and consequently the polysulfide redox shutting effect. Accelerating the conversion kinetics of polysulfide intermediates into sulfur or lithium sulfide through electrocatalysis has emerged as a root-cause solution. Co-N-C composite electrocatalyst is commonly used for this purpose. It is illustrated here that how the effectiveness can be improved by modulating the coordination chemistry of Co-N-C catalytic sites through introducing Ru species (RuCo-NC). The well-dispersed Ru in the Co-NC carbon matrix altered the total charge distribution over the Co-N-C catalytic sites and led to the formation of electron-rich Co-N, which is highly active for the polysulfide conversion reactions. Using Ru to modulate the electronic structure in the Co-N-C configuration and the additional catalytic sites over the Ru-Nx species can manifest optimal adsorption behavior of polysulfides. Consequently, the sulfur cathode with RuCo-NC can reduce the capacity fade rate from 0.11 % per cycle without catalyst (initial capacity of 701 mAh g-1) to 0.054 % per cycle (initial capacity of 1074 mAh g-1) over 400 cycles at 0.2 C rate. The results of this study provide the evidence for a feasible catalyst modification strategy for the polysulfide electrocatalysis.

High-Voltage Spinel Cathode Materials: Navigating the Structural Evolution for Lithium-Ion Batteries

High-voltage LiNi0.5Mn1.5O4 (LNMO) spinel oxides are highly promising cobalt-free cathode materials to cater to the surging demand for lithium-ion batteries (LIBs). However, commercial application of LNMOs is still challenging despite decades of research. To address the challenge, the understanding of their crystallography and structural evolutions during synthesis and electrochemical operation is critical. This review aims to illustrate and to update the fundamentals of crystallography, phase transition mechanisms, and electrochemical behaviors of LNMOs. First, the research history of LNMO and its development into a LIB cathode material is outlined. Then the structural basics of LNMOs including the classic and updated views of the crystal polymorphism, interconversion between the polymorphs, and structure-composition relationship is reviewed. Afterward, the phase transition mechanisms of LNMOs that connect structural and electrochemical properties are comprehensively discussed from fundamental thermodynamics to operando dynamics at intra- and inter-particle levels. In addition, phase evolutions during overlithiation as well as thermal-/electrochemical-driven phase transformations of LNMOs are also discussed. Finally, recommendations are offered for the further development of LNMOs as well as other complex materials to unlock their full potential for future sustainable and powerful batteries.

Chemical capacitance measurements reveal the impact of oxygen vacancies on the charge curve of LiNi0.5Mn1.5O4-δ thin films

The level of oxygen deficiency δ in high-voltage spinels of the composition LiNi0.5Mn1.5O4-δ (LNMO) significantly influences the thermodynamic and kinetic properties of the material, ultimately affecting the cell performance of the corresponding lithium-ion batteries. This study presents a comprehensive defect chemical analysis of LNMO thin films with oxygen vacancy concentrations of 2.4% and 0.53%, focusing particularly on the oxygen vacancy regime around 4 V versus Li+/Li. A set of electrochemical properties is extracted from impedance measurements as a function of state-of-charge for the full tetrahedral-site regime (3.8 to 4.9 V versus Li+/Li). A defect chemical model (Brouwer diagram) is derived from the data, providing a coherent explanation for all important trends of the electrochemical properties and charge curve. Highly resolved chemical capacitance measurements allow a refining of the defect model for the oxygen vacancy regime, showing that a high level of oxygen deficiency not only impacts the amount of redox active Mn3+/4+, but also promotes the trapping of electrons in proximity to an oxygen vacancy. The resulting stabilisation of Mn3+ thereby mitigates the voltage reduction in the oxygen vacancy regime. These findings offer valuable insights into the complex influence of oxygen deficiency on the performance of lithium-ion batteries based on LNMO.

Application of 5V spinel material LiNi0.5Mn1.5O4 in Li-ion batteries: single crystalline or polycrystalline?

The 5V spinel LiNi_0.5Mn_1.5O₄ cathode materials with different morphology were prepared by a solid state calcination method and characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), field emission scanning electron microscope (FE-SEM). Electrochemical properties of cathode material were investigated by electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT) and electrochemical performance tests. Compared with polycrystalline morphology (PLNMO), LiNi_0.5Mn_1.5O₄ material with single crystalline morphology (SLNMO) proved smaller electrochemical polarization or voltage difference, lower internal resistance, faster lithium-ion diffusivity, arising from higher Mn³⁺ content. Differential scanning calorimetry (DSC) showed that SLNMO was more stable than PLNMO at full charged state with organic electrolyte, which exhibited initial discharge capacity of 140.2 mA h g^-1 at 0.1C, coulombic efficiency of 96.1%, and specific capacity retention of 89.2% after 200 cycles at 2.5C, a little inferior to that of 91.7% for PLNMO.

Controlling Cell Components to Design High-Voltage All-Solid-State Lithium-Ion Batteries

All-solid-state batteries with solid ionic conductors packed between solid electrode films can release the dead space between them, enabling a greater number of cells to stack, generating higher voltage to the pack. This Review is focused on using high-voltage cathode materials, in which the redox peak of the components is extended beyond 4.7 V. Li-Ni-Mn-O systems are currently under investigation for use as the cathode in high-voltage cells. Solid electrolytes compatible with the cathode, including halide- and sulfide-based electrolytes, are also reviewed. Discussion extends to the compatibility between electrodes and electrolytes at such extended potentials. Moreover, control over the thickness of the anode is essential to reduce solid-electrolyte interphase formation and growth of dendrites. The Review discusses routes toward optimization of the cell components to minimize electrode-electrolyte impedance and facilitate ion transportation during the battery cycle.

Transition Metal Dissolution Mechanisms and Impacts on Electronic Conductivity in Composite LiNi0.5Mn1.5O4 Cathode Films

The high-voltage LiNi0.5Mn1.5O4 (LNMO) spinel cathode material offers high energy density storage capabilities without the use of costly Co that is prevalent in other Li-ion battery chemistries (e.g., LiNixMnyCozO2 (NMC)). Unfortunately, LNMO-containing batteries suffer from poor cycling performance because of the intrinsically coupled processes of electrolyte oxidation and transition metal dissolution that occurs at high voltage. In this work, we use operando electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopies to demonstrate that transition metal dissolution in LNMO is tightly coupled to HF formation (and thus, electrolyte oxidation reactions as detected with operando and in situ solution NMR), indicative of an acid-driven disproportionation reaction that occurs during delithiation (i.e., battery charging). Leveraging the temporal resolution (s-min) of magnetic resonance, we find that the LNMO particles accelerate the rate of LiPF6 decomposition and subsequent Mn2+ dissolution, possibly due to the acidic nature of terminal Mn-OH groups. X-ray photoemission electron microscopy (XPEEM) provides surface-sensitive and localized X-ray absorption spectroscopy (XAS) measurements, in addition to X-ray photoelectron spectroscopy (XPS), that indicate disproportionation is enabled by surface reconstruction upon charging, which leads to surface Mn3+ sites on the LNMO particle surface that can disproportionate into Mn2+(dissolved) and Mn4+(s). During discharge of the battery, we observe high quantities of metal fluorides (in particular, MnF2) in the cathode electrolyte interphase (CEI) on LNMO as well as the conductive carbon additives in the composite. Electronic conductivity measurements indicate that the MnF2 decreases film conductivity by threefold compared to LiF, suggesting that this CEI component may impede both the ionic and electronic properties of the cathode. Ultimately, to prevent transition metal dissolution and the associated side reactions in spinel-type cathodes (particularly those that operate at high voltages like LNMO), the use of electrolytes that offer improved anodic stability and prevent acid byproducts will likely be necessary.

The Effects of Ru4+ Doping on LiNi0.5Mn1.5O4 with Two Crystal Structures

Doping of Ru has been used to enhance the performance of LiNi_0.5Mn_1.5O₄ cathode materials. However, the effects of Ru doping on the two types of LiNi_0.5Mn_1.5O₄ are rarely studied. In this study, Ru⁴⁺ with a stoichiometric ratio of 0.05 is introduced into LiNi_0.5Mn_1.5O₄ with different space groups (Fd3¯m, P4₃32). The influence of Ru doping on the properties of LiNi_0.5Mn_1.5O₄ (Fd3¯m, P4₃32) is comprehensively studied using multiple techniques such as XRD, Raman, and SEM methods. Electrochemical tests show that Ru⁴⁺-doped LiNi_0.5Mn_1.5O₄ (P4₃32) delivers the optimal electrochemical performance. Its initial specific capacity reaches 132.8 mAh g^-1, and 97.7% of this is retained after 300 cycles at a 1 C rate at room temperature. Even at a rate of 10 C, the capacity of Ru⁴⁺-LiNi_0.5Mn_1.5O₄ (P4₃32) is still 100.7 mAh g^-1. Raman spectroscopy shows that the Ni/Mn arrangement of Ru⁴⁺-LiNi_0.5Mn_1.5O₄ (Fd3¯m) is not significantly affected by Ru⁴⁺ doping. However, LiNi_0.5Mn_1.5O₄ (P4₃32) is transformed to semi-ordered LiNi_0.5Mn_1.5O₄ after the incorporation of Ru⁴⁺. Ru⁴⁺ doping hinders the ordering process of Ni/Mn during the heat treatment process, to an extent.

Investigation of Ordering on Oxygen-Deficient LiNi0.5 Mn1.5 O4-δ Thin Films for Boosting Electrochemical Performance in All-Solid-State Thin-Film Batteries

All-solid-state thin-film batteries (ASSTFBs) are promising next-generation battery systems, but critical challenges such as low-energy-density remain. The low-energy-density might persist with low-voltage cathode material; hence, high-voltage cathode material development is required. While LiNi_0.5 Mn_1.5 O₄ (LNM) has been considered a promising high-voltage cathode material. This study investigates the electrochemical properties of LNM thin films based on the correlation between the ordering of cations (Ni and Mn) and oxygen vacancies (V_O ). The authors find that the cations' order changes from a disordered structure to an ordered structure with an increased oxygen flow rate during deposition. The optimized LNM fabricated using a 60:40 ratio of Ar to O₂ exhibits the highest rate capability (321.4 mAh cm^-3 @ 20 C) and most prolonged cycle performance for 500 cycles. The role of V_O within the LNM structure and the lower activation energy of ordered LNM compared to disordered LNM through first-principles density functional theory calculations is elucidated. The superior electrochemical performance (276.9 mAh cm^-3 @ 0.5 C) and high cyclic performance (at 93.9%, 500 cycles) are corroborated by demonstrating flexible ASSTFB cells using LiPON solid-state electrolyte and thin-film Li anode. This work paves the way for future research on the fabrication of high-performance flexible ASSTFBs.

Lithium-Rich Rock Salt Type Sulfides-Selenides (Li2TiSexS3-x): High Energy Cathode Materials for Lithium-Ion Batteries

Lithium-rich disordered rocksalt Li2TiS3 offers large discharge capacities (>350 mAh·g−1) and can be considered a promising cathode material for high-energy lithium-ion battery applications. However, the quick fading of the specific capacity results in a poor cycle life of the system, especially when liquid electrolyte-based batteries are used. Our efforts to solve the cycling stability problem resulted in the discovery of new high-energy selenium-substituted materials (Li2TiSexS3−x), which were prepared using a wet mechanochemistry process. X-ray diffraction analysis confirmed that all compositions were obtained in cation-disordered rocksalt phase and that the lattice parameters were expanded by selenium substitution. Substituted materials delivered large reversible capacities, with smaller average potentials, and their cycling stability was superior compared to Li2TiS3 upon cycling at a rate of C/10 between 3.0−1.6 V vs. Li+/Li.

MoO3 Nanoparticle Coatings on High-Voltage 5 V LiNi0.5Mn1.5O4 Cathode Materials for Improving Lithium-Ion Battery Performance

To reduce surface contamination and increase battery life, MoO₃ nanoparticles were coated with a high-voltage (5 V) LiNi_0.5Mn_1.5O₄ cathode material by in-situ method during the high-temperature annealing process. To avoid charging by more than 5 V, we also developed a system based on anode-limited full-cell with a negative/positive electrode (N/P) ratio of 0.9. The pristine LiNi_0.5Mn_1.5O₄ was initially prepared by high-energy ball-mill with a solid-state reaction, followed by a precipitation reaction with a molybdenum precursor for the MoO₃ coating. The typical structural and electrochemical behaviors of the materials were clearly investigated and reported. The results revealed that a sample of 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode exhibited an optimal electrochemical activity, indicating that the MoO₃ nanoparticle coating layers considerably enhanced the high-rate charge-discharge profiles and cycle life performance of LiNi_0.5Mn_1.5O₄ with a negligible capacity decay. The 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode could achieve high specific discharge capacities of 131 and 124 mAh g^-1 at the rates of 1 and 10 C, respectively. In particular, the 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode retained its specific capacity (87 mAh g^-1) of 80.1% after 500 cycles at a rate of 10 C. The Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ full cell based on the electrochemical-cell (EL-cell) configuration was successfully assembled and tested, exhibiting excellent cycling retention of 93.4% at a 1 C rate for 100 cycles. The results suggest that the MoO₃ nano-coating layer could effectively reduce side reactions at the interface of the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte, thus improving the electrochemical performance of the battery system.

Defect-Engineered β-MnO2-δ Precursors Control the Structure-Property Relationships in High-Voltage Spinel LiMn1.5Ni0.5O4-δ

This study examines the role of defects in structure-property relationships in spinel LiMn_1.5Ni_0.5O₄ (LMNO) cathode materials, especially in terms of Mn³⁺ content, degree of disorder, and impurity phase, without the use of the traditional high-temperature annealing (≥700 °C used for making disordered LMNO). Two different phases of LMNO (i.e., highly P4₃32-ordered and highly Fd3̅m-disordered) have been prepared from two different β-MnO_2-δ precursors obtained from an argon-rich atmosphere (β-MnO_2-δ (Ar)) and a hydrogen-rich atmosphere [β-MnO_2-δ (H₂)]. The LMNO samples and their corresponding β-MnO_2-δ precursors are thoroughly characterized using different techniques including high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman spectroscopy, powder neutron diffraction, X-ray photoelectron spectroscopy, synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy, and electrochemistry. LMNO from β-MnO_2-δ (H₂) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO_2-δ (Ar). For the first time, defective β-MnO_2-δ has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn³⁺ content, and impurity contents without the need for conventional methods of doping with metal ions, high synthetic temperature, use of organic compounds, postannealing, microwave, or modification of the temperature-cooling profiles. The results show that the oxygen vacancy changes concurrently with the degree of disorder and Mn³⁺ content, and the best electrochemical performance is only obtained at 850 °C for LMNO-(Ar). The findings in this work present unique opportunities that allow the use of β-MnO_2-δ as viable precursors for manipulating the structure-property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.

High Voltage-Stabilized Graphdiyne Cathode Interface

Suppressing the irreversible interfacial reactions is an important scientific bottleneck in the development of stable high-energy-density lithium-ion battery. The interfacial chemistry of graphdiyne (GDY) on the high-voltage cathode of LiNi_0.5 Mn_1.5 O₄ (LNMO) shows a very interesting process, in which the sp-hybridization carbon atoms chemically scavenge the hydrofluoric acid (HF) and in situ form the fluorinated GDY interface. It first turns the harmful HF into profit, and greatly enhances the interfacial stability and restrains the side reaction on the cathode under high working voltage. The GDY-coated LNMO cathode obviously alleviates the electrolyte degradation, achieves high Coulombic efficiency and reliability. Due to atomic-level selectivity and chemical trapping of HF by GDY, it effectively suppresses the dissolution of Mn, Ni elements. These results highlight the unparalleled advantages of GDY in the formation of high stable interfaces and protection of high-energy-density electrodes.

Visualization of Structural Heterogeneities in Particles of Lithium Nickel Manganese Oxide Cathode Materials by Ptychographic X-ray Absorption Fine Structure

A heterogeneous phase/structure distribution in the bulk of spinel lithium nickel manganese oxides (LNMOs) is the key to maximizing the performance and stability of the cathode materials of lithium-ion batteries. Herein, we report the use of two-dimensional ptychographic X-ray absorption fine structure (XAFS) to visualize the density and valence maps of manganese and nickel in as-prepared LNMO particles and unsupervised learning to classify the three-phase group in terms of different elemental compositions and chemical states. The described approach may increase the supply of information for nanoscale characterization and promote the design of suitable structural domains to maximize the performance and stability of batteries.

Structural and Electrochemical Properties of the High Ni Content Spinel LiNiMnO4

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4, for Li-ion batteries operating in the 5-V region. The LiNiMnO4 compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite (LNM@NMO), including non-stoichiometric LiNiMnO4-δ spinel and a secondary Ni6MnO8 cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi0.5Mn1.5O4 bare. A comparison of the electrochemical performances of 4-V spinel LiMn2O4 and 5-V spinel LiNi0.5Mn1.5O4 with those of LNM@NMO composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the LNM@NMO electrode exhibits an initial specific capacity as low as 57 mAh g−1 but shows an excellent electrochemical stability at 1C rate for 1000 cycles with a capacity decay of 2.7 × 10−3 mAh g−1 per cycle.

Ultra-Microtome for the Preparation of TEM Specimens from Battery Cathodes

With the wide application of ultra-microtome sectioning in the preparation of transmission electron microscopy (TEM) specimens with bio- and organic materials, here, we report an ultra-microtome-based method for the preparation of TEM specimens from cathodes of Li-ion batteries. The ultra-microtome sectioning reduces the sample thickness to tens of nanometers and yields atomic resolution from the core region of particles of hundreds of nanometers. Analysis indicates that the mechanical cross-sectioning introduces no observable microstructural artifacts or structural damage, such as microcracking and nanoporosity. These results demonstrate the high efficiency of the ultra-microtome approach in preparing well-thinned specimens of particulate materials that allow for atomic-scale TEM imaging of a large number of sectioned particles in one single TEM specimen, thereby providing statistically significant results of the TEM analysis.

Tuning the Morphology and Electronic Properties of Single-Crystal LiNi0.5Mn1.5O4-δ: Exploring the Influence of LiCl-KCl Molten Salt Flux Composition and Synthesis Temperature

Single-crystal materials have played a unique role in the development of high-performance cathode materials for Li batteries due to their favorable chemomechanical stability. The molten salt synthesis method has become one of the most prominent techniques used to synthesize single-crystal layered and spinel materials. In this work, the molten salt synthesis method is used as a technique to tune both the morphology and Mn³⁺ content of high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathodes. The resulting materials are thoroughly characterized by a suite of analytical techniques, including synchrotron X-ray core-level spectroscopy, which are sensitive to the material properties on multiple length scales. The multidimensional characterization allows us to build a materials library according to the molten salt phase diagram as well as to establish the relationship among synthesis, material properties, and battery performance. The results of this work show that the Mn³⁺ content is primarily dependent on the synthesis temperature and increases as the temperature is increased. The particle morphology is mostly dependent on the composition of the molten salt flux, which can be tailored to obtain well-defined octahedrons enclosed by (111) facets, plates with predominant (112̅) facets, irregularly shaped particles, or mixtures of these. The electrochemical measurements indicate that the Mn³⁺ content has a larger contribution to the battery performance of LNMO than do morphological characteristics and that a significant amount of Mn³⁺ could become detrimental to the battery performance. However, with similar Mn³⁺ contents, morphology still plays a role in influencing the battery cycle life and rate performance. The insights of molten salt synthesis parameters on the formation of LNMO, with deconvolution of the roles of Mn³⁺ and morphology, are crucial to continuing studies in the rational design of LNMO cathode materials for high-energy Li batteries.

Low-Bandgap Se-Deficient Antimony Selenide as a Multifunctional Polysulfide Barrier toward High-Performance Lithium-Sulfur Batteries

The shuttling behavior and sluggish conversion kinetics of the intermediate lithium polysulfides (LiPSs) represent the main obstructions to the practical application of lithium-sulfur (Li-S) batteries. Herein, an anion-deficient design of antimony selenide (Sb₂ Se_{3- x} ) is developed to establish a multifunctional LiPS barrier toward the inhibition of polysulfide shuttling and enhancement of battery performance. The defect chemistry in the as-developed Sb₂ Se_{3- x} promotes the intrinsic conductivity, strengthens the chemical affinity to LiPSs, and catalyzes the sulfur electrochemical conversion, which are verified by a series of computational and experimental results. Attributed to these unique superiorities, the obtained LiPS barrier efficiently promotes and stabilizes the sulfur electrochemistry, thus enabling excellent Li-S battery performance, e.g., outstanding cyclability over 500 cycles at 1.0 C with a minimum capacity fading rate of 0.027% per cycle, a superb rate capability up to 8.0 C, and a high areal capacity of 7.46 mAh cm^-2 under raised sulfur loading. This work offers a defect engineering strategy toward fast and durable sulfur electrochemistry, holding great promise in developing practically viable Li-S batteries as well as enlightening the material design of related energy storage and conversion systems.

Exploring the origin of electrochemical performance of Cr-doped LiNi0.5Mn1.5O4

Discorded LiNi0.5Mn1.5O4 has become a promising candidate for Li ion batteries due to its high specific energy. However, its poor structural stability restricts its practical application. After extensive exploration, Cr-doped disordered LiNi0.5Mn1.5O4 demonstrates enhanced structural stability and electrochemical performance. Thus far, its origin at the electronic structural level remains elusive, which is important to further performance improvement. First-principles calculations disclose that a Cr atom prefers to substitute Ni rather than a Mn atom. The transferred charge from Cr to Mn induces the reduction of Mn ions and lengthens the Li-O bond distance, which are mainly responsible for the lower Li ion diffusion energy barrier and Li vacancy formation energy. The heavy oxidation of O ions is a main factor to induce the structural degeneration. In this case, the reduced Mn ion delays the oxidation of the O ion, enhancing the structural stability. In addition, Cr doping increases the thermodynamic stability of intermediate phases during delithiation, decreasing the structural strain in the delithiation process. Ordered and disordered LiNi0.5Mn1.5O4 are also included for comparison. Our work provides an opportunity to fully understand Cr-doped LiNi0.5Mn1.5O4 at the atomic scale.

Propelling Polysulfide Conversion by Defect-Rich MoS2 Nanosheets for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have tremendous energy density and are cost effective and environmentally compatible, thereby deemed one of the most promising secondary energy storage systems. However, Li-S batteries present sluggish polysulfide intermediate redox kinetics due to the unavoidable "shuttle effect", thus hindering their industrialization and resulting in low sulfur utilization, rapid capacity fading, poor Coulombic efficiency, and anode corrosion. Herein, the present study updates a one-step hydrothermal method to synthesize a highly efficient sulfur host integrating three-dimensional porous graphene aerogel (GA) with uniformly dispersed defect-rich MoS₂ nanosheets (200-300 nm) (GA-DR-MoS₂). The electrochemical studies reveal that these MoS₂ nanosheets with abundant defects could provide strong chemical adsorption for polysulfides, as well as act as an electrocatalyst to markedly accelerate polysulfide redox reactions during the charge/discharge process. The resultant GA-DR-MoS₂ composites (70 wt % of sulfur loading) present a high initial discharge capacity of 1429 mAh g^-1 at 0.2C, an outstanding cycling stability with a low capacity decay rate of 0.085% per cycle over 500 cycles at 0.2C, and a superior rate performance with an improved capacity from 290 to 581 mAh g^-1 at 5C. The presented strategy is effective in achieving high-energy-density Li-S batteries from the point of electrocatalysis and facilitating their practical applications.

Stabilizing a high-voltage LiNi0.5Mn1.5O4 cathode towards all solid state batteries: a Li-Al-Ti-P-O solid electrolyte nano-shell with a host material

LiNi0.5Mn1.5O4 (LNMO) spinel has drawn increasing attention due to its high voltage, stabilized electrochemical performance and safety features as a cathode for lithium-ion batteries. However, the main challenge lies in its unstable surface structure, especially at elevated temperatures. In this paper, we decorate the LNMO precursor with a solid electrolyte of Li1.4Al0.4Ti1.6(PO4)3 (LATP) via a facile sol-gel method, followed by a co-crystallization process at 820 °C, to successfully generate a LATP modification shell at the surface of LNMO. The LATP modification shell could not only optimize the morphology of LNMO including the limitation of particle growth and control of crystalline orientation, but also realize ion doping during the co-crystallization process. By tuning the LATP contents, the 2 wt% LATP modification is found to be the most effective at balancing the interfacial stability and Li+ diffusion kinetics of LNMO, as well as enhancing its rate capability and capacity retention at high temperatures. As a result, the 2 wt% LATP-modified LNMO cathode exhibits a high reversible capacity of 84.8 mA h g-1 after 500 cycles with a capacity retention of 68.9%, and a superior rate capability (102.0 mA h g-1 at 20 C) at room temperature. Moreover, this electrode also delivers a good capacity retention of 85.7% after 100 cycles at 55 °C, which is ascribed to the stabilized interface with a LATP protective layer.

One-Step Integrated Surface Modification To Build a Stable Interface on High-Voltage Cathode for Lithium-Ion Batteries

As one of the most promising cathode materials for next-generation energy storage applications, spinel LiNi_0.5Mn_1.5O₄ (LNMO) has been highlighted due to many advantages. However, it is still hindered by poor electrochemical stability derived from the bulk/interface structure degradation and side reactions under high working voltage. In this work, fast ion conductor Li₃V₂(PO₄)₃ (LVPO) is adopted to modify the surface of spinel LNMO by a one-step facile method to harvest the maximum benefit of interface properties. It is found that 1 wt % LVPO-LNMO exhibits the most excellent cycling performances, retaining great capacity retention of 87.8% after 500 cycles at room temperature and 82.4% for 150 cycles at 55 °C. Moreover, the rate performance is also significantly improved (90.4 mAh g^-1 under 20C). It is revealed that the LVPO-involved layer could effectively suppress the surface side reactions under high working voltage, which mainly contributes to an improved interface with desirable structural stability and excellent kinetics behavior without sacrificing the surface electrochemical activity in an electrochemical environment. Thus, the dissolution of transition-metal ions is effectively mitigated, avoiding further structure degradation of the bulk material. Especially, it is also established that the vanadium (V) ions in LVPO could be to a certain extent migrated into the surface lattice of LNMO to generate a V-involved transition layer (Li-Ni-Mn-V-O surface solid solution), which greatly co-contributes to the enhanced electrochemical performances owing to the prominently depressed charge-transfer resistance.

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries

While Li2MnO3 as an over-lithiated layered oxide (OLO) shows a significantly high reversible capacity of 250 mA h g-1 in lithium-ion batteries (LIBs), it has critical issues of poor cycling performance and deteriorated high rate performance. In this study, modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO at different temperatures (400, 500, and 600 °C) in the presence of polyvinylpyrrolidone (PVP) under an N2 atmosphere. Compared to the as-prepared OLO, the OLO sample heated at 500 °C with PVP exhibited a high initial discharge capacity of 206 mA h g-1 and high rate capability of 111 mA h g-1 at 100 mA g-1. The superior performance of the OLO sample heated at 500 °C with PVP is attributed to an improved electronic conductivity and Li+ ionic motion, resulting from the formation of the graphitic carbon structure and increased Mn3+ ratio during the decomposition of PVP.