Cathode Materials For Li-ion Batteries Research Articles

Stacking Faults Inducing Oxygen Anion Activities in Li2 MnO3.

Controllable anionic redox for a transformational increase in the energy density is the pursuit of next generation Li-ion battery cathode materials. Its activation mechanism is coupled with the local coordination environment around O, which posts experimental challenges for control. Here, the tuning capability of anionic redox is shown by varying O local environment via experimentally controlling the density of stacking faults in Li2 MnO3 , the parent compound of Li-rich oxides. By combining computational analysis and spectroscopic study, it is quantitatively revealed that more stacking faults can trigger smaller LiOLi bond angles and larger LiO bond distance in local Li-rich environments and subsequently activate oxygen redox reactivity, which in turn enhances the reactivity of Mn upon the following reduction process. This study highlights the critical role of local structure environment in tuning the anionic reactivity, which provides guidance in designing high-capacity layered cathodes by appropriately adjusting stacking faults.

Ultrafine FeF3·0.33H2O Nanocrystal-Doped Graphene Aerogel Cathode Materials for Advanced Lithium-Ion Batteries.

FeF3 has been extensively studied as an alternative positive material owing to its superior specific capacity and low cost, but the low conductivity, large volume variation, and slow kinetics seriously hinder its commercialization. Here, we propose the in situ growth of ultrafine FeF3·0.33H2O NPs on a three-dimensional reduced graphene oxide (3D RGO) aerogel with abundant pores by a facile freeze drying process followed by thermal annealing and fluorination. Within the FeF3·0.33H2O/RGO composites, the three-dimensional (3D) RGO aerogel and hierarchical porous structure ensure rapid diffusion of electrons/ions within the cathode, enabling good reversibility of FeF3. Benefiting from these advantages, a superior cycle behavior of 232 mAh g-1 under 0.1C over 100 cycles as well as outstanding rate performance is achieved. These results provide a promising approach for advanced cathode materials for Li-ion batteries.

Architecting “Li-rich Ni-rich” core-shell layered cathodes for high-energy Li-ion batteries

Li-rich or Ni-rich layered oxides are considered ideal cathode materials for high-energy Li-ion batteries (LIBs) owing to their high capacity (> 200 mAh g–1) and low cost. However, both are suffering from severe structural instability upon high-voltage cycling (> 4.5 V). Here, “Li-rich Ni-rich” Li1.08Ni0.9Mn0.1O2 oxides with core-shell architecture are designed and synthesized to improve their high-voltage cyclability. These oxides are determined to be composed of a less reactive “Li-rich Mn-rich” shell and a high-capacity “Li-rich Ni-rich” core. As Li-ions gradually enter into the core-shell precursor during high-temperature lithiation reaction, the interdiffusion of elements across the interphase between the Mn-rich shell and the Ni-rich core successively occurs. Such thermally-driven atomic interdiffusion could lead to a thickness-controllable “Li-rich Mn-rich” shell, which can guarantee an exceptional structural reversibility for the layered “Li-rich Ni-rich” core upon long-term cycling. As a consequence, the optimized core-shell Li1.08Ni0.9Mn0.1O2 achieves a capacity retention of 96% at 0.1 C after 100 cycles in the voltage range of 2.7–4.6 V. These findings might open up a new avenue for rational design of advanced cathode materials for LIBs and beyond.

Direct spectroscopic observation of the reversible redox mechanism in A3V2(PO4)3(A=Li,Na) cathode materials for Li-ion batteries

Alkali Vanadium (III) phosphates are a promising class of positive electrode materials for Li-, Na- and K-ion battery applications. Herein, the reversible redox mechanism of Li3V2(PO4)3 and Na3V2(PO4)3 cathodes during charge/discharge vs. Li+/Li0 is directly observed by Soft X-ray Absorption Spectroscopy. For both Li3V2(PO4)3 and Na3V2(PO4)3 spontaneous surface Li + insertion is observed after exposure to Li + electrolyte. Furthermore, for Li3V2(PO4)3 a reversible charge-discharge process is observed from 3.0 V–4.8 V with only slight increase in O contributions to O 2p - V 3d unoccupied hybridised states after charge/discharge vs. Li+/Li0. For Na3V2(PO4)3, persistent VO6 tetrahedral distortion and an accompanying V5+ state is observed, particularly at the surface, after discharge vs. Li+/Li. These observations further elucidate the particular atomic and electronic structure changes and charge-discharge mechanisms of high voltage NASICON and anti-NASICON cathode materials for Li-ion battery applications.

Unraveling the Mechanism and Practical Implications of the Sol-Gel Synthesis of Spinel LiMn2O4 as a Cathode Material for Li-Ion Batteries: Critical Effects of Cation Distribution at the Matrix Level.

Spinel LiMn2O4 (LMO) is a state-of-the-art cathode material for Li-ion batteries. However, the operating voltage and battery life of spinel LMO needs to be improved for application in various modern technologies. Modifying the composition of the spinel LMO material alters its electronic structure, thereby increasing its operating voltage. Additionally, modifying the microstructure of the spinel LMO by controlling the size and distribution of the particles can improve its electrochemical properties. In this study, we elucidate the sol-gel synthesis mechanisms of two common types of sol-gels (modified and unmodified metal complexes)-chelate gel and organic polymeric gel-and investigate their structural and morphological properties and electrochemical performances. This study highlights that uniform distribution of cations during sol-gel formation is important for the growth of LMO crystals. Furthermore, a homogeneous multicomponent sol-gel, necessary to ensure that no conflicting morphologies and structures would degrade the electrochemical performances, can be obtained when the sol-gel has a polymer-like structure and uniformly bound ions; this can be achieved by using additional multifunctional reagents, namely cross-linkers.

Optimized Morphology and Tuning the Mn3+ Content of LiNi0.5Mn1.5O4 Cathode Material for Li-Ion Batteries.

The advantages of cobalt-free, high specific capacity, high operating voltage, low cost, and environmental friendliness of spinel LiNi0.5Mn1.5O4 (LNMO) material make it one of the most promising cathode materials for next-generation lithium-ion batteries. The disproportionation reaction of Mn3+ leads to Jahn-Teller distortion, which is the key issue in reducing the crystal structure stability and limiting the electrochemical stability of the material. In this work, single-crystal LNMO was synthesized successfully by the sol-gel method. The morphology and the Mn3+ content of the as-prepared LNMO were tuned by altering the synthesis temperature. The results demonstrated that the LNMO_110 material exhibited the most uniform particle distribution as well as the presence of the lowest concentration of Mn3+, which was beneficial to ion diffusion and electronic conductivity. As a result, this LNMO cathode material had an optimized electrochemical rate performance of 105.6 mAh g-1 at 1 C and cycling stability of 116.8 mAh g-1 at 0.1 C after 100 cycles.

Accumulated Lattice Strain as an Intrinsic Trigger for the First-Cycle Voltage Decay in Li-Rich 3d Layered Oxides

Li- and Mn-rich layered oxides (LMLOs) are promising cathode materials for Li-ion batteries (LIBs) owing to their high discharge capacity of above 250 mA h g-1. A high voltage plateau related to the oxidation of lattice oxygen appears upon the first charge, but it cannot be recovered during discharge, resulting in the so-called voltage decay. Disappearance of the honeycomb superstructure of the layered structure at a slow C-rate (e.g., 0.1 C) has been proposed to cause the first-cycle voltage decay. By comparing the structural evolution of Li[Li0.2Ni0.2Mn0.6]O2 (LLNMO) at various current densities, the operando synchrotron-based X-ray diffraction results show that the lattice strain in bulk LLNMO is continuously increased over cycling, resulting in the first-cycle voltage loss upon Li-ion insertion. Unlike the LLNMO, the accumulated average lattice strain of LiNi0.8Co0.1Mn0.1O2 (NCM811) and LiNi0.6Co0.2Mn0.2O2 (NCM622) from the open-circuit voltage to 4.8 V could be released on discharge. These findings help to gain a deep understanding of the voltage decay in LMLOs.

Effects of Al content on the electrochemical performance and thermal stability of Li(Ni0.9Co0.06Mn0.04)1−xAlxO2 cathode materials for Li-ion batteries

Effects of Al content on the electrochemical performance and thermal stability of Li(Ni0.9Co0.06Mn0.04)1−xAlxO2 cathode materials for Li-ion batteries

Tuning Bulk Redox and Altering Interfacial Reactivity in Highly Fluorinated Cation-Disordered Rocksalt Cathodes

Lithium-excess, cation-disordered rocksalt (DRX) materials have been subject to intense scrutiny and development in recent years as potential cathode materials for Li-ion batteries. Despite their compositional flexibility and high initial capacity, they suffer from poorly understood parasitic degradation reactions at the cathode-electrolyte interface. These interfacial degradation reactions deteriorate both the DRX material and electrolyte, ultimately leading to capacity fade and voltage hysteresis during cycling. In this work, differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry are combined to quantify the extent of bulk redox and surface degradation reactions for a set of Mn2+/4+-based DRX oxyfluorides during initial cycling with a high-voltage charging cutoff (4.8 V vs Li/Li+). Increasing the fluorine content from 7.5 to 33.75% is shown to diminish oxygen redox and suppresses high-voltage O2 evolution from the DRX surface. Additionally, electrolyte degradation processes resulting in the formation of both gaseous species and electrolyte-soluble protic species are observed. Subsequently, DEMS is paired with a fluoride-scavenging additive to demonstrate that increasing fluorine content leads to increased dissolution of fluorine from the DRX material into the electrolyte. Finally, a suite of ex situ spectroscopy techniques (X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, and solid-state nuclear magnetic resonance spectroscopy) are employed to study the change in DRX composition during charging, revealing the dissolution of manganese and fluorine from the DRX material at high voltages. This work provides insight into the degradation processes occurring at the DRX-electrolyte interface and points toward potential routes of interfacial stabilization.

Elucidating degradation mechanisms of Co-free high-Ni layered oxide cathodes for Li-ion batteries via advanced X-ray-based characterization methods

High-Ni layered oxide cathodes without Co are being investigated as potential cathode materials for Li-ion batteries with high energy density. By decreasing the Co content, these cathodes not only boost energy density but also alleviate concerns about the supply instability and fluctuating cost of Co raw materials. However, the elevated Ni content in the layered oxides causes distinct chemo-mechanical degradation mechanisms that inhibit their commercial application. In order to gain insight into the degradation process at various scales, from the atomic to the particle and the electrode levels, and to devise ways to prevent degradation, multi-scale characterization methods are essential. In this review, we critically evaluate the role of Co substitution in high-Ni layered oxides and the impact of Co content on the chemo-mechanical degradation process. Furthermore, the use of advanced X-ray-based characterization methods, which have helped shed light on the degradation mechanisms of high-Ni cathodes, is also discussed.

One-step hydrothermal synthesis of VO2(B) as cathode materials for high-capacity and high-rate Li-ion batteries

One-step hydrothermal synthesis of VO2(B) as cathode materials for high-capacity and high-rate Li-ion batteries

Ultrathin V6O13 nanosheets assembled into 3D micro/nano structured flower-like microspheres for high-performance cathode materials of Li-ion batteries

Benefiting from its unique high theoretical capacity and energy density, V6O13 is considered an outstanding cathode candidate. Nevertheless, the lithium ions will form LixV6O13 when embedded in V6O13, resulting in volume expansion and crystal structure instability. For that reason, the construction of three-dimensional nanostructures is an awfully serviceable method to resolve the above problems. Herein, we adopt a green and convenient hydrothermal method to synthesize three-dimensional microsphere structure composed of nanoflakes, and flower-like V6O13 microspheres are synthesized by adjusting the concentration of nitric acid (HNO3). Meanwhile, the formation mechanism of flower-like V6O13 microspheres is investigated by controlling the hydrothermal reaction time and the concentration of HNO3. As a lithium-ion cathode material, flower-like V6O13 microspheres show an initial discharge specific capacity of up to 368.1 mAh/g at a current density of 0.1 A/g. There was still a discharge specific capacity of up to 313.1 mAh/g after 50 charge/discharge cycles, with a capacity retention rate of 85.1%. The flower-like V6O13 microsphere electrode also combines an excellent rate performance with a satisfactory cycling stability, which achieves a cycle retention rate of 80.2% even after 200 charge/discharge cycles, and an initial discharge specific capacity of 216.9 mA/g even at a high current density of 1 A/g. The results show that, benefitting from its large specific surface area and robust three-dimensional structure, the flower-like V6O13 microsphere electrode material exhibits excellent cycling performance, and the lithium-ion batteries which use it as the cathode material perform equally well in terms of high capacity and high rate.

Leaching kinetics of fluorine during the aluminum removal from spent Li-ion battery cathode materials

The high content of aluminum (Al) impurity in the recycled cathode powder seriously affects the extraction efficiency of Nickel, Cobalt, Manganese, and Lithium resources and the actual commercial value of recycled materials, so Al removal is crucially important to conform to the industrial standard of spent Li-ion battery cathode materials. In this work, we systematically investigated the leaching process and optimum conditions associated with Al removal from the cathode powder materials collected in a wet cathode-powder peeling and recycling production line of spent Li-ion batteries (LIBs). Moreover, we specifically studied the leaching of fluorine (F) synergistically happened along with the removal process of Al, which was not concerned about in other studies, but one of the key factors affecting pollution prevention in the recovery process. The mechanism of the whole process including the leaching of Al and F from the cathode powder was indicated by using NMR, FTIR, and XPS, and a defluoridation process was preliminarily investigated in this study. The leaching kinetics of Al could be successfully described by the shrinking core model, controlled by the diffusion process and the activation energy was 11.14 kJ/mol. While, the leaching of F was attributed to the dissolution of LiPF6 and decomposition of PVDF, and the kinetics associated was described by Avrami model. The interaction of Al and F is advantageous to realize the defluoridation to some degree. It is expected that our investigation will provide theoretical support for the large-scale recycling of spent LIBs.

Air- and Moisture Robust Surface Modification for Ni-Rich Layered Cathode Materials for Li-Ion Batteries.

The mainstream of high-energy cathode development is focused on increasing the Ni-ratio in layered structured cathode materials. The increment of the Ni portion in the layered cathode material escalates not only the deliverable capacity but also the structural degradation. High-Ni layered cathodes are highly vulnerable to exposure to air that contains CO2 and H2 O, forming problematic residual lithium compounds at the surface. In this work, a novel air- and moisture robust surface modification is reported for LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) via the sol-gel coating method that selectively coats the internal surface area of the polycrystalline morphology secondary particles. Bare-, Li2 SnO3 -coated and LiCoO2 -coated NCM811 are exposed to different ambient environments (air, hot-air, and moisture-air) to systematically investigate the correlation between the internal/external coating morphology and performance degradations. The LiCoO2 -coated NCM811s exhibit high-capacity retention after exposure to all environments, due to the internal surface coating that prevents the penetration of harmful compounds into the polycrystalline NCM811. On the other hand, the Li2 SnO3 -coated NCM811s exposed to the ambient environments show gradual capacity fading, implying the occurrence of internal degradation. This paper highlights the impact of the internal degradation of polycrystalline NCM811 after environmental exposure and the correct coating mechanisms required to successfully prevent it.

One-Dimensional Covalent Organic Framework as High-Performance Cathode Materials for Lithium-Ion Batteries.

Covalent organic frameworks (COFs) have emerged as a new class of cathode materials for energy storage in recent years. However, they are limited to two-dimensional (2D) or three-dimensional (3D) framework structures. Herein, this work reports designed synthesis of a redox-active one-dimensional (1D) COF and its composites with 1D carbon nanotubes (CNTs) via in situ growth. Used as cathode materials for Li-ion batteries, the 1D COF@CNT composites with unique dendritic core-shell structure can provide abundant and easily accessible redox-active sites, which contribute to improve diffusion rate of lithium ions and the corresponding specific capacity. This synergistic structural design enables excellent electrochemical performance of the cathodes, giving rise to 95% utilization of redox-active sites, high rate capability (81% capacity retention at 10 C), and long cycling stability (86% retention after 600 cycles at 5 C). As the first example to explore the application of 1D COFs in the field of energy storage, this study demonstrates the great potential of this novel type of linear crystalline porous polymers in battery technologies.

Evaluation of Dissolution Conditions of Li-Ion Battery Cathode Material in Nitric Acid

Bu çalışmada atık lityum-iyon pil katot malzemesinin nitrik asit çözeltisinde çözülerek metalik malzemeler ile grafitin geri kazanım koşulları belirlenmiştir. Yapılan çalışmada atık Li-iyon katot malzemesi farklı molaritelere sahip nitrik asit çözeltisinde liç edilmiş ve metallerin çözünme verimi araştırılmıştır. Çözünme verimini etkileyen katı-sıvı oranı, çözünme süresi, H2O2 katkısı parametrelerinin çözünme verimi üzerindeki etkisi incelenmiştir. Yapılan incelemeler sonucunda en uygun çözme koşullarının 2 saat liç süresi, 100 g/L katı-sıvı oranı ve 3M nitrik asit çözeltisi olduğu tespit edilmiştir. H2O2 katkısının incelendiği 2M nitrik asit çözeltisinde H2O2 katkısının olumlu etkisinin olmasına karşılık yeterli çözünme verimine ulaşılamadığı görülmüştür.

Magnetic Properties of Multifunctional 7LiFePO4 under Hydrostatic Pressure

LiFePO4 (LFPO) is an archetypical and well-known cathode material for rechargeable Li-ion batteries. However, its quasi-one-dimensional (Q1D) structure along with the Fe ions, LFPO also displays interesting low-temperature magnetic properties. Our team has previously utilized the muon spin rotation (µ +SR) technique to investigate both magnetic spin order as well as Li-ion diffusion in LFPO. In this initial study we extend our investigation and make use of high-pressure µ +SR to investigate effects on the low-T magnetic order. Contrary to theoretical predictions we find that the magnetic ordering temperature as well as the ordered magnetic moment increase at high pressure (compressive strain).

Surface modification with Li3PO4 enhances the electrochemical performance of LiNi0.9Co0.05Mn0.05O2 cathode materials for Li-Ion batteries

Although high-nickel cathodes (Ni ≥ 90%) have immense potential for use in lithium-ion batteries (LIBs) because of their high energy densities and low material costs. However, structural instability and poor cycling performance have hampered their applications. In this study, we synthesized LiNi0.9Co0.05Mn0.05O2 (denoted “NCM9055″) cathode materials and coated them with Li3PO4 by using a wet-chemical method. We employed X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to investigate the effects of Li3PO4 surface modification. The (NH4)2HPO4 precursors reacted with the surface residual lithium compounds of NCM9055 to form amorphous Li3PO4 and this active coating layer improved the chemical stability at the electrode-electrolyte interface by suppressing deleterious surface side reactions. Accordingly, the Li+ ion conductivity, rate capability, and long-term cycling performance of the material improved significantly. Measurements of the electrochemical performance revealed that after 200 cycles at a rate of 1 C and a cut-off voltage of 2.7–4.3 V, the 1 mol% Li3PO4–coated NCM9055 (denoted “1P@NCM9055”) cathode retained 90.2% of its initial discharge capacity (ca. 192.9 mA h g–1), whereas the pristine (NCM9055) retained 74.2% of its initial discharge capacity (ca. 196.8 mA h g–1) at room temperature. Our findings should encourage the development and applications of our as-prepared Ni-rich cathode materials in commercial LIBs.

Facile Deposition of the LiFePO4 Cathode by the Electrophoresis Method.

Lithium iron phosphate (LiFePO4, LFP) is one of the most advanced commercial cathode materials for Li-ion batteries and is widely applied as battery cells for electric vehicles. In this work, a thin and uniform LFP cathode film on a conductive carbon-coated aluminum foil was besieged by the electrophoretic deposition (EPD) technique. Along with the LFP deposition conditions, the impact of two types of binders, poly(vinylidene fluoride) (PVdF) and poly(vinylpyrrolidone) (PVP), on the film quality and electrochemical results has been studied. The results revealed that the LFP_PVP composite cathode had a highly stable electrochemical performance compared with the LFP_PVdF counterpart due to the negligible influence of the PVP on the pore volume and size and retaining high surface area of LFP. The LFP_PVP composite cathode film unveiled a high discharge capacity of 145 mAh g-1 at 0.1C and performed over 100 cycles with capacity retention and Coulombic efficiency of 95 and 99%, respectively. The C-rate capability test also revealed a more stable performance of LFP_PVP compared to LFP_PVdF.

Annealing effect on structural and electrochemical performance of Ti-doped LiNi1/3Mn1/3Co1/3O2 cathode materials

NMC 111 cathode materials exhibit engaging properties in high energy density and low cost, making it great potential for the next generation of high-energy lithium-ion batteries. However, it still faces challenges such as fast capacity fade, especially at high C rates. Herein, we implement the novel Ti-doped cathode material, LiNi0.3Mn0.3Co0.3Ti0.1O2 (NMCT) synthesized via the combustion method. It was discovered that NMCT can effectively improve capacity delivery at high C rates. The T80 material demonstrated superior electrochemical annealed at 800 ˚C for 72 h, with an exceptional specific discharge capacity of 148.6 mAh g-1 and excellent cycle stability (capacity retention 96.8 %) after 30th cycles at 3 C. The results demonstrated that Ti-doped NMC had superior advantages for LiNi1/3Mn1/3Co1/3O2 (NMC 111) material at the optimum temperature of 800 °C for 72 h. It is one of the potential cathode materials for Li-ion batteries.