Fluorine gradient-doped LiNi0.5Mn1.5O4 spinel with improved high voltage stability for Li-ion batteries

Reconsideration of simultaneous bulk doping and interface structures modification of high-voltage spinel LiNi0.5Mn1.5O4 cathode materials using elemental iodine

The insufficient structural stability of high-voltage spinel cobalt-free LiNi0.5Mn1.5O4 (LNMO) throughout the cycling process hinders its widespread application. To address these issues, we incorporate elemental iodine into LNMO during the precursor preparation process using an ethanol-assisted hydrothermal method and successfully modify the bulk and interface coating structure of LNMO-3% I2. The incorporation of iodine not only induces the formation of a cavity and fast lithium-ion transfer pathway within the particles but also facilitates the development of a thin LiI coating layer on the surface of cathode materials. Compared with bared LNMO, LNMO-3% I2 exhibits a capacity retention of 90.31% following 500 cycles at 1C and a capacity retention of 88.74% even following 450cycles at a high-rate of 50C. Furthermore, the cells with LNMO-3% I2 demonstrate an excellent electrochemical performance under both high temperatures of 40 ℃ and low temperatures of -15 ℃. This study offers valuable insights into the simultaneous optimization of internal and external structures in cathode materials, thereby enhancing the long-term cycling performance of high-voltage lithium-ion batteries.

Mitigating Diffusion-Induced Intragranular Cracking in Single-Crystal LiNi0.5Mn1.5O4 via Extended Solid-Solution Behavior

Single-crystal cathodes have been investigated for their inherent resistance to intergranular cracking due to the absence of grain boundaries. However, these materials exhibit significant intragranular cracking, and the underlying mechanisms remain unclear. In this study, we examined the impact of extended solid-solution reactions on mitigating crack formation in magnesium-doped single-crystal LiNi0.5Mn1.5O4 (Mg-SC-LNMO) cathodes. With Mg acting as a structural pillar, the overall volume change was reduced by nearly 50 %, the two-phase reaction was effectively suppressed, and the Li-ion diffusion coefficient was doubled. Continuum modeling based on experimental observations demonstrates that Mg doping significantly reduces the internal stress induced by lithium diffusion, thereby preserving the mechanical integrity of single-crystal LNMO. This improvement leads to enhanced electrochemical performance and durability. Our study provides new insights into mechanically robust single-crystal cathodes and proposes a design strategy to improve the durability of next-generation Li-ion batteries.

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.

Li-Site Defects Induce Formation of Li-Rich Impurity Phases: Implications for Charge Distribution and Performance of LiNi0.5- xMxMn1.5O4 Cathodes (M = Fe and Mg; x = 0.05-0.2)

An understanding of the structural properties that allow for optimal cathode performance, and their origin, is necessary for devising advanced cathode design strategies and accelerating the commercialization of next-generation cathodes. High-voltage, Fe- and Mg-substituted LiNi0.5Mn1.5O4 cathodes offer a low-cost, cobalt-free, yet energy-dense alternative to commercial cathodes. In this work, the effect of substitution on several important structure properties is explored, including Ni/Mn ordering, charge distribution, and extrinsic defects. In the cation-disordered samples studied, a correlation is observed between increased Fe/Mg substitution, Li-site defects, and Li-rich impurity phase formation-the concentrations of which are greater for Mg-substituted samples. This is attributed to the lower formation energy of MgLi defects when compared to FeLi defects. Li-site defect-induced impurity phases consequently alter the charge distribution of the system, resulting in increased [Mn3+] with Fe/Mg substitution. In addition to impurity phases, other charge compensators are also investigated to explain the origin of Mn3+ (extrinsic defects, [Ni3+], oxygen vacancies and intrinsic off-stoichiometry), although their effects are found to be negligible.

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.

Recent Progress of High Voltage Spinel LiMn1.5Ni0.5O4 Cathode Material for Lithium-Ion Battery: Surface Modification, Doping, Electrolyte, and Oxygen Deficiency

High voltage spinel LiMn1.5Ni0.5O4 (LMNO) is a promising energy storage material for the next generation lithium batteries with high energy densities. However, due to the major controversies in synthesis, structure, and interfacial properties of LMNO, its unsatisfactory performance is still a challenge hindering the technology's practical applications. Herein, this paper provides general characteristics of LiMn1.5Ni0.5O4 such as spinel structure, electrochemical properties, and phase transition. In addition, factors such as electrolyte decomposition and morphology of LMNO that influence the electrochemical performances of LMNO are introduced. The strategies that enhance the electrochemical performances including coating, doping, electrolytes, and oxygen deficiency are comprehensively discussed. Through the discussion of the present research status and presentation of our perspectives on future development, we provide the rational design of LMNO in realizing lithium-ion batteries with improved electrochemical performances.

Identifying Element-Modulated Reactivity and Stability of the High-Voltage Spinel Cathode Materials via In Situ Time-Resolved X-Ray Diffraction

Designing and identifying a dopant-involved material is quite significant, especially for battery science. LiNi_0.5Mn_1.5O₄, being one of the most appealing candidates for high-potential lithium-ion batteries, has attracted immense attention and been investigated with Al or F dopants for its undesirable inherent structural challenges. Although the excellent performance of Al- or F-doped LiNi_0.5Mn_1.5O₄ has been reported previously, the relationship between dopants, structural variation, and electrochemistry has not been fully identified. Hence, synchronous time-resolved XRD techniques are applied for identifying a guideline of the phase variations in cathodic (Al³⁺)- and anodic (F^-)-substituted LiNi_0.5Mn_1.5O₄, which revealed a three-phase evolution as a function of structural stability. Also, the Al-substituted materials exhibit excellent reactivity and stability, which can be clearly identified via the stable buffer phase existing in high power density or after long cycling due to the improvement in reaction kinetics of phase transition and the lithium-ion diffusion coefficient, just opposite to F doping. This provides a good guideline for identifying an element-modulated mechanism of reactivity or stability of materials science.

Enhanced Electrochemical Performance of LiNi0.5Mn1.5O4 Composite Cathodes for Lithium-Ion Batteries by Selective Doping of K+/Cl- and K+/F. NANOMATERIALS 2021;11:nano11092323. [PMID: 34578639 PMCID: PMC8466396 DOI: 10.3390/nano11092323]

K⁺/Cl^- and K⁺/F^- co-doped LiNi_0.5Mn_1.5O₄ (LNMO) materials were successfully synthesized via a solid-state method. Structural characterization revealed that both K⁺/Cl^- and K⁺/F^- co-doping reduced the Li_xNi_1-xO impurities and enlarged the lattice parameters compared to those of pure LNMO. Besides this, the K⁺/F^- co-doping decreased the Mn³⁺ ion content, which could inhibit the Jahn-Teller distortion and was beneficial to the cycling performance. Furthermore, both the K⁺/Cl^- and the K⁺/F^- co-doping reduced the particle size and made the particles more uniform. The K⁺/Cl^- co-doped particles possessed a similar octahedral structure to that of pure LNMO. In contrast, as the K⁺/F^- co-doping amount increased, the crystal structure became a truncated octahedral shape. The Li⁺ diffusion coefficient calculated from the CV tests showed that both K⁺/Cl^- and K⁺/F^- co-doping facilitated Li⁺ diffusion in the LNMO. The impedance tests showed that the charge transfer resistances were reduced by the co-doping. These results indicated that both the K⁺/Cl^- and the K⁺/F^- co-doping stabilized the crystal structures, facilitated Li⁺ diffusion, modified the particle morphologies, and increased the electrochemical kinetics. Benefiting from the unique advantages of the co-doping, the K⁺/Cl^- and K⁺/F^- co-doped samples exhibited improved rate and cycling performances. The K⁺/Cl^- co-doped Li_0.97K_0.03Ni_0.5Mn_1.5O_3.97Cl_0.03 (LNMO-KCl0.03) exhibited the best rate capability with discharge capacities of 116.1, 109.3, and 93.9 mAh g^-1 at high C-rates of 5C, 7C, and 10C, respectively. Moreover, the K⁺/F^- co-doped Li_0.98K_0.02Ni_0.5Mn_1.5O_3.98F_0.02 (LNMO-KF0.02) delivered excellent cycling stability, maintaining 85.8% of its initial discharge capacity after circulation for 500 cycles at 5C. Therefore, the K⁺/Cl^- or K⁺/F^- co-doping strategy proposed herein will play a significant role in the further construction of other high-voltage cathodes for high-energy LIBs.

Advances and Prospects of High-Voltage Spinel Cathodes for Lithium-Based Batteries

Insertion compounds have been dominating the cathodes in commercial lithium-ion batteries. In contrast to layered oxides and polyanion compounds, the development of spinel-structured cathodes is a little behind. Owing to a series of advantageous properties, such as high operating voltage (≈4.7 V), high capacity (≈135 mAh g^-1 ), low environmental impact, and low fabrication cost, the high-voltage spinel LiNi_0.5 Mn_1.5 O₄ represents a high-power cathode for advancing high-energy-density Li⁺ -ion batteries. However, the wide application and commercialization of this cathode are hampered by its poor cycling performance. Recent progress in both the fundamental understanding of the degradation mechanism and the exploration of strategies to enhance the cycling stability of high-voltage spinel cathodes have drawn continuous attention toward this promising insertion cathode. In this review article, the structure-property correlations and the failure mode of high-voltage spinel cathodes are first discussed. Then, the recent advances in mitigating the cycling stability issue of high-voltage spinel cathodes are summarized, including the various approaches of structural design, doping, surface coating, and electrolyte modification. Finally, future perspectives and research directions are put forward, aiming at providing insightful information for the development of practical high-voltage spinel cathodes.

A hydrothermal synthesis of Ru-doped LiMn1.5Ni0.5O4 cathode materials for enhanced electrochemical performance

An Ru-doped spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) cathode has been prepared via a simple hydrothermal synthesis method. The as-prepared cathode is characterized via Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size distribution analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry performance tests. The FTIR spectroscopy and XRD analyses show that the Ru-doped LNMO has a good crystallinity with a disordered Fd3̄m space group structure. The disordered structure in the cathode increased and the Li_xNi_1−xO impurity phase decreased when Ru addition increased. SEM shows that all samples are octahedral particles with homogeneous sizes distribution, and the particle size analysis shows that the Ru-doped samples have smaller particle size. XPS confirms the existence of Ru ions in the sample, and reveals that the Ru induce to part of Mn⁴⁺ transfers to Mn³⁺ in the LNMO. The electrochemical property indicated that the Ru-doped cathode exhibits better electrochemical properties in terms of discharge capacity, cycle stability and rate performance. At a current density of 50 mA g⁻¹, the discharge specific capacity of the Ru-4 sample is 140 mA h g⁻¹, which is much higher than that of the other samples. It can be seen from the rate capacity curves that the Ru-doped samples exhibit high discharge specific capacity, particularly at high current density.

An Ru-doped spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) cathode has been prepared via a simple hydrothermal synthesis method.

Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the Role of Morphology on Phase Transition Behavior and Electrode/Electrolyte Interfacial Properties

LiNi_0.5Mn_1.5O₄ compound as positive electrode of the lithium ion battery with high specific energy or high specific power, has a good application prospect in the field of electric vehicles such as PHEV/EVs. The influence of the morphology of ordered LiNi_0.5Mn_1.5O₄ on phase transition behavior and electrode/electrolyte interfacial properties is investigated, including octahedral and porous spherical morphologies. Three phases named LiNi_0.5Mn_1.5O₄ (Li1), Li_0.5Ni_0.5Mn_1.5O₄ (Li0.5) and Ni_0.5Mn_1.5O₄ (Li0) are detected by in situ X-ray diffraction (XRD) measurement with high time resolution in the octahedral and porous spherical ordered LiNi_0.5Mn_1.5O₄ materials during charge and discharge, and the phase transition kinetics of the two samples at high discharge rate and after charge-discharge cycles are elucidated. It is a clear demonstration that the high-rate capability and cycle life of LiNi_0.5Mn_1.5O₄ material are influenced by crystal morphology. The porous spherical LiNi_0.5Mn_1.5O₄ material exhibits better rate performance, associated with the fast reaction kinetic of Li0.5 phase formation. It is noticed that the coexistence of three cubic phases in the initial discharge stage is observed in the cycled octahedral sample, resulting in a higher capacity fading after 200 cycles at room temperature and 1 C. However, the porous spherical sample exhibits a poor cyclic performance at 55 °C and 1 C. This may be attributed to the fact that the porous spherical sample with high specific surface area leads to an accelerated decomposition of the electrolyte at 55 °C, and the thick interfacial film and high content of LiF on the electrode surface are formed.

A porous hierarchical micro/nano LiNi0.5Mn1.5O4 cathode material for Li-ion batteries synthesized by a urea-assisted hydrothermal method

The U/TM ratio has a significant influence on the phase composition, particle morphology and size of the carbonate precursor, thus leading to different electrochemical properties of the LiNi_0.5Mn_1.5O₄ material.