Cathode Materials For Li-ion Batteries Research Articles

Research progress in solid-state synthesized LiMnPO4 cathode material for Li-ion battery applications

LiMnPO4 cathode material and its derivatives are promising for energy-storage devices owing to its environmental friendliness, high energy density, and structural stability. Olivine LiMnPO4 is attractive due to its high operating voltage (4 to 5 V vs. Li+/Li), and strong P-O covalent bond, which offers many safety advantages. Despite these advantages, the commercialization of LiMnPO4-based lithium-ion batteries (LIB) has been plagued by other factors such as poor electronic and ionic conductivity, a high surface energy barrier for Li-ion diffusion, and structural degradation induced by the Jahn-Teller effect. Various strategies, including transition metal doping at the A-site and the fabrication of heterostructures with high electron mobility, have been employed to address these challenges. Notably, the exceptional electrode performance of microrods may be ascribed to their distinct three-dimensional porous hierarchical structure, which promotes rapid Li+ transport kinetics and improves structural stability in reversible electrochemical reactions. While these enhancement techniques are centered on processing, solid-state chemistry is more effective, offering convenience in overcoming obstacles related to physiochemical and electrochemical performance. The solid-state synthesis approach, typically known for its capability to tailor the size and morphology of materials, has demonstrated a significant impact on enhancing the electrochemical activity of LiMnPO4. This review critically discusses the structure dependence of LiMnPO4 cathode material on electrochemical reactions. It gives a broad overview of the research approaches being employed to enhance the structure and electrochemical performance of LiMnPO4 through the solid-state technique. It also provides a comprehensive overview of the challenges and the need for further research to fully realize the potential of LiMnPO4 cathodes as a promising cathode material for Li-Ion batteries.

A Promising Solid-State Synthesis of LiMn1- yFeyPO4 Cathode for Lithium-ion Batteries.

LiMn1-yFeyPO4 (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO4 (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn0.7Fe0.3PO4 (MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.

Feeling the strain: Enhancing the electrochemical performance of olivine LiMnPO[formula omitted] as cathode materials for Li-ion batteries through strain effects

Currently, the improvement of Li-ion batteries (LIBs) is more important than ever, especially due to the increasing spread and rapid progress of electric vehicles and high-tech applications. Materials used for positive electrodes are one of the main constituents of batteries, which typically determine their electrochemical efficiency. Phospho-olivine LiMnPO4 (LMP) material has been regarded as a potential positive electrode material for LIBs due to its outstanding properties. However, it suffers from low electronic and ionic conductivity. Therefore, this work aims to overcome these drawbacks by applying a biaxial strain to LMP. In this regard, we used density functional theory calculations to investigate the effect of biaxial strain on the dynamic and thermal stabilities, structural, electronic, ionic diffusion, electrochemical potential, and defect properties of LiMnPO4 (LMP) structure, as well as on the Average (Mn–O, Li–O and P–O) bond lengths, electrical conductivity, and charge transfer. Moreover, the influence of anti-site defects on the ionic conductivity of LMP compound was evaluated. Our findings suggest that the biaxial tensile strain has a remarkable effect on the rate performance of LMP cathode material. A biaxial tensile strain of +2% reduces the band gap of LMP from 3.51 to 3.41 eV, and ameliorates the diffusion coefficient by 100 times. Furthermore, the migration barrier was calculated to be 0.37 eV for strained (+2%) defective MP, lower than 1.12 eV for unstrained defective MP, indicating that biaxial tensile strain can mitigate the negative effect of anti-site defects on Li-ion migration. These results can prompt us to suggest biaxial tensile strain as a good strategy for improving the electrochemical performance of LMP as cathode material for LIBs. Furthermore, this study may supply insights to cathode material designers and engineers on the importance of an appropriate biaxial strain value to improve the rate performance of LiMnPO4 as cathode materials for LIB batteries.

Novel Low-Strain Layered/Rocksalt Intergrown Cathode for High-Energy Li-Ion Batteries.

Both layered- and rocksalt-type Li-rich cathode materials are drawing great attention due to their enormous capacity, while the individual phases have their own drawbacks, such as great volume change for the layered phase and low electronic and ionic conductivities for the rocksalt phase. Previously, we have reported the layered/rocksalt intergrown cathodes with nearly zero-strain operation, while the use of precious elements hinders their industrial applications. Herein, low-cost 3d Mn4+ ions are utilized to partially replace the expensive Ru5+ ions, to develop novel ternary Li-rich cathode material Li1+x[RuMnNi]1-xO2. The as-designed Li1.15Ru0.25Mn0.2Ni0.4O2 is revealed to have a layered/rock salt intergrown structure by neutron diffraction and transmission electron microscopy. The as-designed cathode exhibits ultrahigh lithium-ion reversibility, with 0.86 (231.1 mAh g-1) out of a total Li+ inventory of 1.15 (309.1 mAh g-1). The X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectra further demonstrate that the high Li+ storage of the intergrown cathode is enabled by leveraging cationic and anionic redox activities in charge compensation. Surprisingly, in situ X-ray diffraction shows that the intergrown cathode undergoes extremely low-strain structural evolution during the charge-discharge process. Finally, the Mn content in the intergrown cathodes is found to be tunable, providing new insights into the design of advanced cathode materials for high-energy Li-ion batteries.

Limiting cobalt fraction in lithium rich cathode materials for stable and fast activation

Li-rich layered oxides (LRLOs) have been considered as promising cathode materials for high-energy Li-ion batteries. However, considerable fractionsof costly Co and Ni are normally needed in LRLOs to access the high capacity. In this work, a series of Ni/Co-poor LRLOs is designed to study the effect of Ni:Co ratio on their electrochemical behavior. Due to the lowest-lying Co t2g band, the introduction of minor Co significantly promotes the activation of Li-rich phase. While high Co content exacerbates the interfacial reactions to form a thick and unstable cathode-electrolyte film. Consequently, the low-Co LRLO (ca. 4 % of transition metal) attains stable and fast activation, maintaining 233.3 mA h g−1 after 300 cycles at 1C. Moreover, the low-Co LRLO//graphite full cell retains 86.4 % of its capacity after 200 cycles. This work will shed light on the compositional design of LRLOs towards higher electrochemical performance and lower materials cost.

Effects of strontium oxide on synthesis and performance of monocrystalline ultrahigh-Ni layered cathode materials for Li-ion batteries

Monocrystalline layered cathode is of particular interest owing to the satisfactory mechanical integrity against long-term cycling. However, the high-temperature calcination, which is perceived as the indispensable reaction condition, favors the formation of Ni2+ that triggers the Li+/Ni2+ disorder and the formation of electrochemically inactive NiO. Herein, we develop a SrO-assistant method to synthesize a monocrystalline ultrahigh-Ni LiNi0.95Co0.04Mn0.01O2 under a moderate calcination temperature. The addition of an appropriate amount of SrO (0.3 wt%, SCN95–Sr-3) facilitates the formation of monocrystalline LiNi0.95Co0.04Mn0.01O2 (grain size: 2–4 μm) under 790 °C. The obtained LiNi0.95Co0.04Mn0.01O2 represents excellent electrochemical properties with an initial discharge capacity of 240.5 mAh g−1 and a Coulombic efficiency of 90.1 % at 0.1C (1C = 220 mA g−1) in a Li-metal half cell. Upon long-term cycling, the monocrystalline feature with less crystallographic defect effectively enhances the structural stability and inhibits the formation of intergranular cracks, resulting in an enhanced cyclic stability (discharge capacity of 151.0 mAh g−1 maintained after 300 cycles at 1C in a Li-metal half cell). Coupled with a graphite anode, the LiNi0.95Co0.04Mn0.01O2|| graphite full cell represents a stable cycling at 1C, with a capacity retention of 99.0 % after 100 cycles.

Performance and modification of novel nanomaterials for the anode of lithium-ion batteries

Due to the burning of fossil energy which is a non-renewable nature resource, it has caused many environmental problems, then the world began to face energy shortage and environmental problems. In order to solve these two problems, people have started to develop new energy sources and vigorously research new methods for energys efficient storage and utilization. The Li-ion battery is a research priority because it has great properties such as high specific energy and environmental friendliness, but they still need further performance improvement before it can be put into use. In this paper, the lithium-ion batterys anode is selected as the research object to investigate the performance of carbon-based nanomaterials, silicon-based nanomaterials, and metal-based nanomaterials, and to study the actual performance and modification methods to analyze the application prospects of the materials. Improving the Li-ion battery cathode material performance can significantly improve the batterys capacity and performance stability, speed up the process of putting lithium-ion batteries into use, and improve people's ability to store and use energy to cope with the energy crisis.

Recovering the Cathode Material Adhered to the Collector and Separator of Spent Lithium-Ion Batteries for Recycling Purposes

Depleted Li-ion batteries (LIBs) must be recycled for environmental and sustainability reasons. Most recycling processes are dedicated to the recovery of Li, Co, Mn, and Ni present in the cathode material of LIBs. However, separating the cathode material strongly adhered to the aluminum collector and those mechanically trapped into the polymeric separator is still challenging. Processes to separate the cathode material by dissolving its aluminum collector in NaOH solution and to extract part of this material encrusted in the separator by ultrasonic cavitation and mechanical friction are presented in tests with NMC batteries on a laboratory scale. Tests of LIB discharges were also carried out in different MnO4 solution concentrations, and the related electrochemical reactions were discussed.

Surface Modification Driven Initial Coulombic Efficiency and Rate Performance Enhancement of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 Cathode.

Due to its high energy density and low cost, Li-rich Mn-based layered oxides are considered potential cathode materials for next generation Li-ion batteries. However, they still suffer from the serious obstacle of low initial Coulombic efficiency, which is detrimental to their practical application. Here, an efficient surface modification method via NH4 H2 PO4 assisted pyrolysis is performed to improve the Coulombic efficiency of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 , where appropriate oxygen vacancies, Li3 PO4 and spinel phase are synchronously generated in the surface layer of LMR microspheres. Under the synergistic effect of the oxygen vacancies and spinel phase, the unavoidable oxygen release in the cycling process was effectively suppressed. Moreover, the induced Li3 PO4 nanolayer could boost the lithium-ion diffusion and mitigate the dissolution of transition metal ions, especially manganese ions, in the material. The optimally modified sample yielded an impressive initial Coulombic efficiency and outstanding rate performance.

Ti- and F- co-doped Li1.2Mn0.75Ni0.25O2 as efficient cathode materials for Li-ion batteries

Ti- and F- co-doped Li1.2Mn0.75Ni0.25O2 as efficient cathode materials for Li-ion batteries

Voltage hysteresis hidden in an asymmetric reaction pathway

Li-rich layered oxides are promising as next-generation cathode materials for Li-ion batteries because of their potential to provide high voltage and large capacities. However, these materials suffer from significant voltage hysteresis between charge and discharge, and the causes are not yet well understood. In this work, a comprehensive in-situ X-ray diffraction analysis, conducted in Li2RuO3 as a model of Li-rich cathode materials, reveals that a discrepancy in the intermediate crystal phases formed during Li extraction and re-insertion gives rise to different electrochemical potentials between charge and discharge, which causes the undesired voltage hysteresis. These findings enrich the understanding of voltage hysteresis in Li-rich materials.

Fundamental understanding on cyclability behaviors of ammonium vanadate nanoarchitectures as cathode materials for Li-ion batteries: A comparative insight of dual modification of precursor and morphology

Development of high-performance Li-ion battery electrodes has emerged as an important issue for satisfying good rate capability and long cycle life during electrochemical lithium (de) intercalation. As cathode materials, vanadium-based compounds are very appealing for energy-storage applications owing to their multiple valence states and coordination geometries. However, they still face bottlenecks such as less stable layered structure and intrinsically low ionic/electronic conductivity. This investigation records on two main parts of new strategic design and electrochemical lithium storage for NH4V4O10 (NHV) cathode nanostructures. NHV structures with diverse motifs (i.e. mat-like sheet, square-sheet microflowers, belt-based microflowers, and nano-belt) were systematically fabricated by tailoring the combined reducing agents (H2C2O4 + KSCN and K2C2O4 + HCl), and its concentrations under controlled hydrothermal protocol. Benefiting from H2C2O4 + KSCN as a mixed precursor in different molar ratios (2,1, 1,1, and 1:2), the electrode materials with various shapes such as mat-like sheet, square-sheet microflowers, belt-based microflowers achieved high specific capacities of 132.02, 162.54 and 172.02 mAh g−1, respectively. From results, the nanobelt-like NHV synthesized by the reducing environment of K2C2O4 + HCl with molar ratio of 1:2 at 180 °C for 24 h delivered an extraordinary discharge capacity of 196.76 mAh g−1 at a current density of 30 mA g−1 in a potential region of 1.8–4.0 V, which reach 87.28 % capacity retention over 50 cycles. However, in the process of using K2C2O4 + HCl, the change in hydrothermal conditions led to a decrease in the storage capacity and cyclability behavior. Such results will potentially help in engineering a novel strategy toward developing electrochemically appropriate constructions, which offer efficient vanadate-based nanostructures via modifying the structure and morphology with improved pathway for rapid electron transfer.

The Effect of Different Amounts of Conductive Carbon Material on the Electrochemical Performance of the LiFePO4 Cathode in Li-Ion Batteries

LiFePO4 (LFP) has undergone extensive research and is a promising cathode material for Li-ion batteries. The high interest is due to its low raw material cost, good electrochemical stability, and high-capacity retention. However, poor electronic conductivity and a low Li+ diffusion rate decrease its electrochemical reactivity, especially at fast charge/discharge rates. In this work, the volumetric energy density of lithium-ion batteries is successfully increased by using different amounts of conductive carbon (Super P) in the active material content. The particle size and morphology of the electrode material samples are studied using field emission scanning electron microscopy and dynamic light scattering. Two-point-probe DC measurements and adhesive force tests are used to determine the conductivity and evaluate adhesion for the positive electrode. Cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and charge/discharge tests are used to analyze the electrochemical properties of the battery. The samples containing 88% LFP, 5.5% Super P, and 6.5% PVDF perform best, with discharge capacities reaching 169.8 mAh g−1 at 0.1 C, and they can also manage charging/discharging of 5 C. EIS indicates that this combination produces the lowest charge-transfer impedance (67 Ω) and the highest Li+ ion diffusion coefficient (5.76 × 10−14 cm2 s−1).

Synthesis of 1D/2D VO2 (B) nanowire/g-C3N4 hybrid architectures as cathode materials for high-performance Li-ion batteries

Owing to energy density, powder density, and eco-friendliness, Li-ion batteries (LIBs) are increasingly used in transportable electronic devices and electric vehicles. Monoclinic VO2 (B) has been broadly used as a cathode owing to its abundance, affordability, high capacity, and multiple oxidation states, but it's low repeatability and slow kinetics have restricted its practical applications. To mitigate these shortcomings, novel 1D/2D VO2 (B) nanowire/g-C3N4 hybrid architecture cathode materials were synthesized via hydrothermal method, and its electrochemical activity (i.e., repeatability constancy and rate capability) for LIBs was investigated. X-ray diffraction experiments confirmed that VO2 (B) exhibited a monoclinic crystal phase. SEM images revealed that the g-C3N4 and VO2 (B) presented sheet-like morphologies and comprised nanowires of uniform thickness, respectively. Electrochemical experiments revealed that the hybrid architectures showed a capacity of 779 mAh/g, and VO2 (601.4 mAh/g) and g-C3N4 (340.6 mAh/g) at 0.1 C current density. The remarkable electrochemical activity of the materials was attributed to their distinctive structures, excellent electronic conductivity associated with g-C3N4 sheets, small transport distances for Li+ ions, and fast charge transmission owing to the presence of VO2 (B) nanowires attached to g-C3N4 sheets. Consequently, distinct VO2 (B) nanowire/g-C3N4 hybrid architectures delivered suitable electrode performance to facilitate the design of high-power LIBs and these hybrid composites can serve as suitable cathode materials for rechargeable LIBs.

Effect of crystal morphology of ultrahigh-nickel cathode materials on high temperature electrochemical stability of lithium ion batteries

Higher nickel content endows Ni-rich cathode materials LiNixCoyMn1−x−yO2 (x > 0.6) with higher specific capacity and high energy density, which is regarded as the most promising cathode materials for Li-ion batteries. However, the deterioration of structural stability hinders its practical application, especially under harsh working conditions such as high-temperature cycling. Given these circumstances, it becomes particularly critical to clarify the impact of the crystal morphology on the structure and high-temperature performance as for the ultrahigh-nickel cathodes. Herein, we conducted a comprehensive comparison in terms of microstructure, high-temperature long-cycle phase evolution, and high-temperature electrochemical stability, revealing the differences and the working mechanisms among polycrystalline (PC), single-crystalline (SC) and Al doped SC ultrahigh-nickel materials. The results show that the PC sample suffers a severe irreversible phase transition along with the appearance of microcracks, resulting a serious decay of both average voltage and the energy density. While the Al doped SC sample exhibits superior cycling stability with intact layered structure. In-situ XRD and intraparticle structural evolution characterization reveal that Al doping can significantly alleviate the irreversible phase transition, thus inhibiting microcracks generation and enabling enhanced structure. Specifically, it exhibits excellent cycling performance in pouch-type full-cell with a high capacity retention of 91.8% after 500 cycles at 55 °C. This work promotes the fundamental understanding on the correlation between the crystalline morphology and high-temperature electrochemical stability and provides a guide for optimization the Ni-rich cathode materials.

Theoretical insight into oxygen vacancy formation in Li1.25Ni0.5Mn0.25O2 cathode material

Here, we have studied the thermodynamic stability of lattice oxygen in Li-rich Co-free cathode material Li1.25Ni0.5Mn0.25O2 using first-principles calculations. It is found that the oxygen at O2 coordination is more likely to be released in Li-rich cathode Li1.25Ni0.5Mn0.25O2, and the stability of oxygen is closely related to temperature and oxygen partial pressure. The Li1.25Ni0.5Mn0.25O2 cathode will spontaneously form O-vacancies above 842 K. When the oxygen partial pressure increases to 22 atm, the lattice oxygen is stable even at 1000 K. The presence of O-vacancy will cause more localized charges, and Ni-ions will also undergo a reduction reaction in the electrode. This theoretical study gives new insight about the thermodynamic stability of lattice oxygen and will help to suppress the formation of O-vacancy in Li-rich cathode materials, paving the way for developing Li-rich cathode materials for next-generation Li-ion batteries.

The study of structural, electrochemical and optical properties of Li2ZrN2 cathode material for Li-ion battery: an Ab-initio calculations

The study of structural, electrochemical and optical properties of Li2ZrN2 cathode material for Li-ion battery: an Ab-initio calculations

Enhanced Li+ Diffusion and Lattice oxygen Stability by the High Entropy Effect in Disordered-Rocksalt Cathodes.

Cation-disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li-ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn-based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+ -Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling.

Atomic pins bridging integrated surface to assist high-rate stability for Co-free Li-rich cathode

Li- and Mn-rich oxides (LMR) have emerged as promising cathode materials for next-generation Li-ion batteries due to their cost effectiveness, impressive capacity, and high energy density. However, the poor electrochemical kinetics and structural instability in hostile interface environments have result in continuous voltage/capacity decay and undesirable rate performance, impeding the large-scale commercial application of LMR materials. In this study, we introduce an atomic pins-assisted integrated surface reconstruction (AISR) strategy to address the interfacial degradation and instability issues. Utilizing the bidirectional diffusion effect of the aluminum-containing intermediate layer during the heat treatment process, we employ aluminum atoms as bridging centers to in situ construct a composite interface structure. This approach capitalizes on the element diffusion reaction and anchoring effect to achieve multifunctional modification through the Al-based ionic conductor network constructing and near-surface Al doping for LMR material. Intriguingly multiple kinetic investigations and calculations reveal that the epitaxial ionic conductor layer suppresses interfacial side reactions, enhances ionic conductivity, and improves electronic conductivity by regulating cationic/anionic redox activity through Al surface doping.Impressively, the modified electrodes exhibited an increased reversible capacity at both 0.1C/5C rates (0.1C, 2 ∼ 4.8 V, from 264.2 mAh∙g−1 to 274 mAh∙g−1; 5C, 2 ∼ 4.6 V, from 145.5 mAh∙g−1 to 197.9 mAh∙g−1) and improved capacity retention after 250 cycles at 1C/5C rates (2 ∼ 4.6 V: 1C, from 69.46% to 81.92%; 5C from 57.73% to 81.35%). We systematically summarized the rate-dependent failure mechanism and the corresponding integrated interface reconstruction principle. These key findings offer valuable insights for the development of high-energy–density and long-life lithium-ion batteries in commercial applications.

Nanocomposite Engineering of High-Capacity Partially Ordered Cathode Materials for Li-Ion Batteries

Understanding the local cation order in the crystal structure and its correlation with cycling performances has promoted the development of high-energy Mn-rich cathode materials for Li-ion batteries, such as Li- and Mn-rich layered cathodes (LMR, e.g., Li1.2Ni0.2Mn0.6O2) that are considered as nanocomposite layered materials with C2/m Li2MnO3-type medium-range order (MRO). Also, Li diffusivity in high-capacity Mn-based disordered rock-salt (DRX) cathodes (e.g., Li1.2Mn0.6Nb0.2O2) was found to be influenced by the short-range order (SRO) of cations, highlighting the criticality of engineering the local cation order in designing high-energy materials. In this presentation, we will discuss the nanocomposite, heterogeneous nature (like MRO found in LMR) of ultrahigh-capacity partially ordered cathodes (e.g., Li1.68Mn1.6O3.7F0.3) made of distinct domains of spinel-, DRX- and layered-like phases, which is different from conventional single-phase DRX cathodes. This multi-scale understanding of ordering informs engineering the nanocomposite material via Ti doping, altering the intra-particle characteristics to increase the content of the rock-salt phase and heterogeneity within a particle. This strategy greatly improves the reversibility of Mn- and O-redox processes to enhance the cycling stability of the partially ordered DRX cathodes (nearly ~30 % improvement of capacity retention). Overall, our work sheds light on the importance of nanocomposite engineering to develop ultrahigh-performance, low-cost Li-ion cathode materials.