Li-ion Diffusion Research Articles

Microwave-Assisted Sol-Gel Synthesis of High-Voltage Ruthenium-Doped LiFePO4 Cathodes for Solid-State Lithium-Ion Batteries

The demand for high voltage and high-capacity energy systems has grown due to increased use of portable electronics, electric vehicles, and grid energy storage systems. LiFePO4 (LFP) shows great promise as a cathode material due to its low cost, structural stability, safety characteristics, and low environmental impact. However, LFP cathodes possess a low Li-ion diffusion coefficient and poor electrical conductivity compared to oxide-based cathodes that are used currently. To make LFP competitive with oxide-based cathodes, LFP was modified to improve its characteristics. Doping of materials is a highly effective method for improving electrochemical characteristics in LFP cathodes. Ruthenium-doping of iron sites within LFP has shown positive effects in the promotion of Li-ion diffusion, reduction in band gap energies, and improved electrical conductivity. Previous studies have shown that ruthenium-doping at 0.01 moles has an increased specific capacity of 162 mAh g-1, better cycling characteristics, and reduced resistance compared to pristine LFP.1 Ruthenium doping levels above 0.02 moles have shown a decrease in specific capacity, cycling characteristics, and an increased resistance due to the formation of ruthenium oxide that disrupts the crystal lattice of LFP. In this study, LiFe1-xRuxPO4 (x= 0.01, 0.0075, and 0.005) and pristine LFP were prepared via microwave-assisted sol-gel synthesis to explore the effects of lower levels of ruthenium-doping on LFP electrochemical characteristics. Microwave synthesis was employed for reduced sintering time, beneficial effects on microstructure, and decreased cost. Samples were characterized via scanning electron microscopy, in-situ/ex-situ X-ray diffraction, energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry.The authors acknowledge financial support from the NSF IUCRC program for the “Center for solid-state electric power storage” (#2052631) and support from the South Dakota Board of Regents for the “Governor’s Research Center (GRC) for electrochemical energy storage”.1.) Gao, Y.; Xiong, K.; Zhang, H.; Zhu, B. Effect of RU Doping on the Properties of Lifepo4/c Cathode Materials for Lithium-Ion Batteries. ACS Omega 2021, 6 (22), 14122–14129.

Study of Li-Si Alloy Composition for Anode Materials in Sulfide-Based All-Solid-State-Batteries

Lithium alloys are promising anode materials with high specific capacity for all-solid-state-batteries (ASSBs). In this study, ASSBs were fabricated by consisting of Li-Si alloy anode, sulfide electrolytes and sulfur composite cathode. During discharge-charge cycles, changes in polarization resistance in the anode and cathode were separately traced using three-electrode system of an embedded Indium reference electrode in ASSBs. As de-alloying and alloying in Li-Si anode, Li distribution and phase changes were investigated using x-ray diffraction, optical microscopy and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMs). A half-cell was fabricated by using Indium foil as a counter electrode to study the Li ion diffusion coefficient in Galvanostatic Intermittent Titration Technique(GITT). It is observed that Li composition (22:5 ~ 1:1) in Li-Si alloy anode affected the chemo-mechanical stability and volume expansion behavior in ASSBs, which were associated with the redox behavior of sulfide solid electrolyte.

Low Temperature Niobium Tungsten Oxides as Anodes for Fast Charging Li-Ion Batteries

The development of fast-charging Li-ion batteries is one of the important steps in building electric vehicles that need high power and fast charging. The reduction in the particle size to the nanometre length scale drastically improves the charging rate by increasing the surface area but lowers the volumetric energy density and can potentially result in more rapid degradation of the electrolyte via electrode-catalysed reactions. Recent reports show that niobium tungsten oxides (NbWOs) with µm sized particles serve as good anode materials for Li-ion batteries having high volumetric capacity with good cyclability at high rates while avoiding solid electrolyte interphase formation (SEI). The high rate performance of NbWOs is attributed to the topochemical charge storage mechanism that exhibits (i) minimal, highly reversible structural changes during the charge-discharge cycles, (ii) high Li-ion diffusion coefficients due to the presence of fast conducting tunnels, and (iii) high electronic conductivity upon lithiation.1,2 The NbWOs are known to crystallize into two families of different crystal structures depending on the composition and synthesis conditions. The NbWOs phases can either have tungsten bronze-type structures or block-type structures (commonly referred to as Wadsley-Roth phases). Different NbWO phases are reported in the literature3 which could serve as potential anode materials with better performance.In this work, a series of new NbWO phases have been synthesized at reduced annealing temperatures and the structure of these phases has been established using X-ray and neutron diffraction data. The electrochemical properties of NbWO/Li half cells were examined through a series of galvanostatic (dis)charge tests at varying current rates ranging from 0.2 C to 20 C. The NbWO phases delivers a high reversible capacity of 200 and 130 mAh/g at 0.2C and 10 C respectively vs. Li metal. Here we use operando powder X-ray diffraction to investigate the structural changes occurring at the anode during the charge-discharge process in the newly synthesised NbWO phases. Reference s : 1 K. J. Griffith, K. M. Wiaderek, G. Cibin, L. E. Marbella and C. P. Grey, Nature, 2018, 559, 556–563.2 C. P. Koçer, K. J. Griffith, C. P. Grey and A. J. Morris, Chem. Mater., 2020, 32, 3980–3989.3 N. C. Stephenson, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem., 1968, 24, 637–653. Figure 1

Unlocking Li Superionic Conductivity in Fcc-Type Oxides via Face-Sharing Configurations

Li metal oxides with a face-centered cubic (fcc) anion sublattice have been generally excluded from the search for solid-state Li superionic conductors, as the structural framework is thought to be unfavorable for Li superionic conduction. Herein, we demonstrate a face-sharing design strategy that turns fcc-type oxides into superionic conductors, with a Li ionic conductivity of 3.38×10−4 S cm−1 at room temperature and a low migration barrier of 255 meV. The combination of experimental and theoretical investigations reveals that the high Li-ion conductivity is attributed to the facile Li-ion diffusion pathways comprising the face-sharing polyhedra. Our work unlocks the great potential of designing Li superionic conductors in a prototypical structural framework with vast chemical flexibility, providing a fertile ground for discovering new solid-state electrolytes for all-solid-state batteries.

Superior Rate Capability of Small Regenerated Graphite Particles Induced by Homogeneously Distributed Current Density Derived from Cracks and Intrinsic Defects.

As spent batteries can be considered as alternative raw sources of electrode materials; the development of regeneration techniques for spent graphite becomes key to realizing economic and environmental sustainability. Herein, the reutilization of small spent graphite particles is domonstrateddue to their special structural characteristics, which may directly contribute to the improvement of lithiation kinetics and high-rate charging during long-term cycling. Such intrinsic defects and external cracked channels may be introduced by the aging of intrinsic bulk structure and exfoliation of surface structure. On account of these potential advantages, a carbonized polypyrrole layer on sieved small graphite particles is developed to obtain superior rate performance. The coated amorphous/graphitic layer could repair the exposed edge and basal plane, and significantly facilitate Li ion diffusion during fast charging. Moreover, the enhanced performance may favor the improved homogeneity of current density distribution during fast charging, which is confirmed by a porous electrode model. The regenerated graphite with a disorder/order coating layer could effectively regulate the Li+ transport channel, exhibiting a high specific capacity at high-rate charging (102.7 mAh g-1 at 4 C after 500 cycles) without severe Li plating. This work provides an opportunity to utilize spent graphite in fast-charging batteries.

Isotropic Microstrain Relaxation in Ni-Rich Cathodes for Long Cycling Lithium Ion Batteries.

Developing isotropic-dominated microstrain relaxation is a vital step toward the enhancement of cyclic performance and thermal stability for high-energy-density Ni-rich cathodes. Here, a microstructure engineering strategy is employed for synthesizing the elongated primary particles radially aligned Ni-rich cathodes only by regulating the precipitation rates of cations and the distributions of flow field. The as-obtained cathode also exhibits an enlarged lattice distance and highly exposed (003) plane. The high aspect ratio and favorable atomic arrangement of primary particles not only enable isotropic strain relaxation for effectively suppressing microcrack formation and propagation, but also facilitate Li-ion diffusion with greatly reduced Li/Ni mixing. Consequently, it shows obvious superiority in the high-rate, long-cycle life, and thermal stability compared with the conventional counterparts. After modification, an exceptionally long life is achieved with a capacity retention of 90.1% at 1C and 84.3% at 5C after 1500 cycles within 3.0-4.3 V in a 1.5-Ah pouch cell. This work offers a universal strategy to achieve isotropic strain distribution for conveniently enhancing the durability of Ni-rich cathodes.

Correlation among crystal and local structure, phase transition, and Li–ion conduction of solid electrolyte Li7La3Zr2O12

The correlation among the crystal and local structure, phase transition, and Li–ion conduction of the solid electrolyte Li7La3Zr2O12 (LLZ) was investigated by quantum beam technique. According to the results of Rietveld refinement using Neutron diffraction data, the Li (8a) and Li (16f) sites have the deficiency of approximately 3∼5% in LLZ. These results of Li site occupancies were adopted to the Rietveld refinements with in situ Synchrotron X–ray Diffraction's (SR–XRD) from 300 K to 1000 K. The phase transition from the tetragonal to cubic phase was observed in in situ SR–XRD. The results of Rietveld refinements with in situ SR–XRD showed the coexistence of the tetragonal and cubic phase from 860 K to 880 K. The Li–ion conduction was discussed with respect to the atomic displacement parameters, electric density estimated by Rietveld refinements and Maximum Entropy Method (MEM) analysis, and local structure estimated by X–ray Absorption Spectra (XAS) and Pair Distribution Function (PDF) analysis. The Li–ion diffusion mechanism was discussed with crystal and local structures at high temperatures of LLZ. In particular, the coexistence of tetragonal phase at the phase transition, the bond of the Li and oxide at tetragonal phase, and the low symmetry of ZrO6 up to about 930 K are thought to inhibit Li diffusion.

Manipulating Sulfur Conversion Kinetics through Interfacial Built-In Electric Field Enhanced Bidirectional Mott-Schottky Electrocatalysts in Lithium-Sulfur Batteries.

Efficient electrocatalysts and catalytic mechanisms remain a pressing need in Li-S electrochemistry to address lithium polysulfide (LiPS) shuttling and enhance conversion kinetics. This study presents the development of multifunctional VO2@rGO heterostructures, incorporating interfacial built-in electric field (BIEF) enhancement, as a Mott-Schottky electrocatalyst for Li-S batteries. Electrochemical experiments and theoretical analysis demonstrate that the interfacial BIEF between VO2 and rGO induces self-driven charge redistribution, resulting in accelerated charge transport rates, enhanced LiPS chemisorption, reduced energy barriers for Li2S nucleation/decomposition, and improved Li-ion diffusion behavior. The Mott-Schottky electrocatalyst, combining the strengths of VO2's anchoring ability, rGO's metallic conductivity, and BIEF's optimized charge transport, exhibits an outstanding "trapping-conversion" effect. The modified Li-S battery with a VO2@rGO-modified separator achieves a highly reversible capacity of 558.0 mAh g-1 at 2 C over 600 cycles, with an average decay rate of 0.048% per cycle. This research offers valuable insights into the design of Mott-Schottky electrocatalysts and their catalytic mechanisms, advancing high-efficiency Li-S batteries and other multielectron energy storage and conversion devices.

Improving electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode via polyanionic TiP2O7 coating

Safety issues of common rechargeable Li-ion batteries (LIB) necessitate urgent development of alternative high-performance electrode materials. Lithiated nickel-rich oxides (LiNi1-x-yMnxCoyO2) are promising LIB cathode materials, but they suffer from structural instabilities causing major capacity loss. To address this issue, here we use a robust ethanol-based wet coating process to coat a LiNi0.8Co0.1Mn0.1O2 LIB cathode material with polyanionic compound TiP2O7. The coating layer does not affect the phase structure of LiNi0.8Co0.1Mn0.1O2 and ensures a remarkable electrochemical performance, evidenced by the high initial Coulombic efficiency, durable cyclic stability, and excellent rate performance. The mechanisms leading to the achieved improvements are related to the effects of the coating layer which improved the Li+ diffusion capability and the electrochemical polarization. The TiP2O7 layer protects the electrode from the electrolyte by suppressing side reactions such as HF acidic attack and the associated dissolution of transition metal ion. Moreover, the unique three-dimensional (XOn)m- framework of the TiP2O7 polyanion provides plentiful accommodation sites and channels for the Li-ions diffusion. The demonstrated approach opens new avenues for practical applications of electrochemically active coatings in diverse energy storage devices and systems.

Impact of lithium diffusion paths on electrochemical behavior of LiNi0.6Co0.2Mn0.2O2 cathode for lithium-ion batteries

Severe microcracks of polycrystal LiNixCoyMnzO2 cathodes during cycling have led to increasing attention to the development of single-crystal cathodes. The single-crystal cathode particle is considered to induce a straight Li-ion diffusion through two-dimensional pathways in bulk compared with the pathways of grain boundary and cracks inside polycrystal particles. However, the effect of different paths on diffusion kinetics and the resulting electrochemical properties still needs to be better understood. In this work, the electrochemical performance of polycrystal and single-crystal cathodes caused by different diffusion paths was compared in detail. The results showed that grain boundaries and cracks of polycrystalline cathodes facilitate Li-ion diffusion. In contrast, relatively slow Li-ion diffusion occurs in the single-crystal cathode particles due to long diffusion paths. Moreover, the single-crystal cathode particles experience severe structural inhomogeneity due to the slow diffusion kinetics and inhomogeneous Li concentrations, resulting in structural distortion and localized strain increasing during cycling.

One-step MXene selenization-conversion into carbon-scaffold-anchored TiSe2 nanosheets enabling interlayer- and vacancy-mediated ion transport mechanisms for fast lithium-ion storage

Lithium-ion capacitors (LICs) have attracted growing attention in energy storage applications. However, the sluggish Li kinetics in battery-type anodes has significantly restricted the rate capability. Herein we propose a novel one-step MXene selenization-conversion into carbon-scaffold-anchored TiSe2 nanosheets (TiSe2@CSA), which enables interlayer- and vacancy-mediated ion transport mechanisms for fast lithium-ion storage. The approach endows the TiSe2@CSA with a non-stacked structure, sufficient interlayer space and abundant Se vacancies for rapid ion transport. Through the theoretical analysis of density functional theory (DFT), this work confirms the significant role of Se vacancies in facilitating fast Li-ion storage. This is achieved by the enhancement of electron transfer and the reduction of the energy barrier for Li-ion diffusion. Moreover, the Li-ion storage mechanism and crystal phase evolution of TiSe2@CSA are investigated by the ex-situ XRD and HRTEM. The as-prepared TiSe2@CSA nanohybrid demonstrates a high capacity of 498 mAh g−1 at 0.05 A g−1 and an improved rate capability of 331 mAh g−1 at 5 A g−1, as well as long-term cyclability (80.5% capacity retention after 2000 cycles). When assembling TiSe2@CSA with activated carbon (YP-50) into a TiSe2@CSA//YP-50 LIC, a superior energy density of 96.7 Wh kg−1 is achieved at 410 W kg−1, and still retains 31.0 Wh kg−1 even at a high power density of 15700 W kg−1. The proposed MXene-derived selenization-conversion strategy can also be extended for other transition metal compounds to promote fast lithium-ion storage.

Synthesis of ternary GNP-CNT-ZrO2 nanocomposite as a high-performance anode for lithium-ion batteries

The modulation of electrical charge transport in electrodes through mesoscale structural design is crucial in developing high-performance lithium-ion batteries (LIBs). In this study, three nanocomposites were fabricated by incorporating ZrO2 nanoparticles into carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and GNP-CNT structures. The synthesizing was a simple hydrothermal method followed by annealing to prepare CNT-ZrO2 (C-Z), GNP-ZrO2 (G-Z), and GNP-CNT-ZrO2 (G-C-Z) materials for a three-dimensional highly efficient anode for LIBs. The electrochemical performance was evaluated using cyclic voltammetry (CV), which demonstrated excellent reversibility for the G-C-Z material. A study on the rate performance confirmed reversible discharge capacity of 512, 274, 248, 206, and 175 mAh/g at 0.2, 1, 5, 15, and 20 A/g, respectively, for the G-C-Z anode, which demonstrated the highest reversibility among the synthesized anodes. Even after 500 cycles at a current density of 5 A/g, this electrode maintained its specific capacity and electrochemical cycling reversibility at almost 98.5%. The lower capacity of C-Z and G-Z structures was attributed to the aggregation of constituents. The Nyquist plots after 500 cycles demonstrated the lowest charge transfer resistance (Rct) of 52.19 Ω and the highest value of Li-ion diffusion coefficient (DLi+) for the G-C-Z anode, ensuring excellent long-life electron conductivity.

Li-intercalation chemistry of few-layer borophene with ultrahigh capacity and fast kinetics

Two-dimensional borophene nanosheets (2D BNSs) have been theoretically predicted to be an ideal lithium-storage material owing to their high theoretical capacity and low Li-ion diffusion energy barrier. However, the lithium-storage capability and mechanism of 2D BNSs have not yet been reported until now. Herein, ultrathin 2D BNSs (<2 nm) were successfully fabricated by sonication-assisted liquid exfoliation, and further explored as a Li-storage host. The ultrathin BNSs delivered an ultrahigh capacity of 782.9 mAh/g over 500 cycles at 167 mA/g. The Li-storage mechanism of BNSs was revealed by in-situ X-ray diffraction and the results showed that the Li+ ions intercalate/deintercalate along (205) plane with the formation of interstitial compound of Li0.48B. The charge storage behavior of 2D BNSs was also proved to be dominated by a pseudocapacitance-control process, which contributes to the high-rate capability. This work would accelerate the exploration of emerging 2D materials for high-energy–density lithium-ion batteries.

Influence of pressure on elasticity, mechanical properties, and Li diffusion in battery electrode material LiCoO2: First-principles calculations

This study used first-principles calculations based on density functional theory with generalized gradient approximation (GGA) of the Perdew Burke and Ernzerhof (PBE) parameterized form to investigate the influence of pressure on the structural, elastic, and mechanical properties of rhombohedral LiCoO2. The results indicate that rhombohedral LiCoO2 remains stable up to 10 GPa. The calculated ground state properties agree well with experimental and other calculation data, validating the approach. Additionally, the calculated elastic constants, bulk modulus, Young's modulus, shear modulus, and Poisson's ratio at 0 GPa agree with previous results. The study found that all elastic constants continuously increase with increasing pressure. The deformation resistances along the axial direction are stronger than those in shape. The relationship between elasticity and length is such that C11 > C33, indicating that the incompressibility along the a axis is stronger than that along the c axis. The analysis of Poisson's ratio (ν) and Pugh's criterion B/G strongly suggests that rhombohedral LiCoO2 exhibits ductile behavior under pressure up to 10 GPa. The material is clearly anisotropic behavior, but the material exhibits improved isotropic behavior as pressure increases. Regarding Li ion diffusion in rhombohedral LiCoO2, the study found that the migration pathway for Li ions in rhombohedral LiCoO2 is a direct route that extends from the VLi site to the closest Li site. The diffusion process is hindered by a diffusion energy barrier of 0.87 eV, which is in good agreement with available theoretical data. Furthermore, the Li ion diffusion energy barrier increases with pressure because the decrease in dmean and polyhedral volume, along with changes in angle and torsional distortion factors of CoO6 octahedra, which can reduce the charging and discharging speeds of Li-ion batteries that use rhombohedral LiCoO2 as the cathode material.

First-principles investigation of the electronic and Li-ion diffusion properties of LiFePO4 by graphene surface modification

The structural, electronic and Li-ion diffusion properties of LiFePO4 (010) surface modified by graphene have been investigated by first-principles calculation under the DFT + U framework. The calculated formation energy indicates that the LiFePO4 (010) surface modified with graphene is energetically favourable. It is found that strong C–Fe and C–O covalent bonds are formed at the modified interface, and the band gap of LiFePO4 modified with graphene is narrowed, indicating better electronic conductive properties. The energy barrier for the diffusion of Li-ion along the b-channel perpendicular to the (010) surface is calculated using the method of finding the transition state. The results show that the energy barrier of the modified system is reduced, indicating that the surface modification of LiFePO4 by graphene can improve the surface diffusion rate of Li-ions.

Single-ion conductors functionalized graphene oxide enabling solid polymer electrolytes with uniform Li-ion transport toward stable and dendrite-free lithium metal batteries

The utilization of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) has long been deemed promising for the application of state-of-the-art lithium metal metals (LMBs), but still severely impeded by the insufficient Li-ion transporting channels and inhomogeneous Li deposition. Herein, the design of single-ion conductors (PSLi) modified graphene oxide nanosheets (GO-PSLi)-reinforced PEO-based SPEs to address these long-standing issues is proposed. The electronegative sulfonate-rich groups with lithiophilic features on GO-PSLi surface not only effectively enhance the dispersion of nanoparticles within the PEO matrix, but also provide fast Li-ion diffusion pathways. Meanwhile, introducing PSLi chains is also favorable to highly reducing the crystallization of composite SPEs through hydrogen interactions derived from the desired amide functional groups. This, in turn, facilitates segmental relaxation of the PEO backbone, leading to accelerates the Li-ion migration. As a proof of concept, the as-prepared composite SPEs demonstrate a good ionic conductivity of 2.2 × 10−4 S cm−1 and a high lithium transference number of 0.53, significantly outperforming the pure PEO SPEs (1.0 × 10−4 S cm−1 and 0.28, respectively) at 60 °C. In addition, the symmetrical Li||Li cells based on the composite SPEs show excellent reversible lithium plating/stripping performances with dendrite-free uniform lithium deposition over 1100 h under a current of 0.1 mA cm−2 at 60 °C. The Li||LiFePO4 batteries also achieve an impressive capacity of 120.2 mAh g−1 at a high current density of 4C and deliver remarkable cycling abilities with 84.6% retention after 250 cycles under 1C at 60 °C. This study offers a facile and practical strategy to develop advanced composite PEO-based SPEs for safe and dendrite-free solid-state LMBs.

Effective upcycling of waste separator and boosting the electrochemical performance of recycled graphite anode for lithium-ion batteries

The forefront of current lithium-ion battery technology in various electronic applications concerns the enormous e-waste that gives rise to end-of-life batteries. Resource sustainability of battery-grade graphite, non-biodegradable polymeric separator, and ever-growing lithium-ion battery manufacturing cost extend a strong impetus for lithium-ion battery recycling. Herein, we report an effective strategy to upcycle the waste separator to valuable carbon. The recycle separator derive carbon is turbostratic with the simultaneous presence of an order-disorder phase. The carbon anode electrochemically delivers 695 mAh g−1 capacity at 100 mA g−1, which is double the capacity of the recover graphite anode (300 mAh g−1). Despite the significant electrochemistry, the poor conversion efficiency and low product yield after carbonization may impede large-scale implementations. However, the Li-ion storage capability of recycle separator derive carbon, in minimal quantity, enhances the capacity of the recycled graphite. The composite of recycle graphite and recycle separator derive carbon outperforms the capacity of recycled graphite with higher Li-ion diffusivity. It delivers a stable discharge capacity of 380 mAh g−1 at a 0.5C rate over 1200 cycles (285 mAh g−1 for recycled graphite). This study entails sustainable recycling of spent separators and boosts the efficiency of recycled graphite for high-performance lithium-ion batteries.

Defect controlled diffusion of lithium ions in Mn doped V2O5 for potential applications as cathode material

With a motivation to unravel the effect of cation (Mn) doping-induced modifications in structure, charge transfer resistance, and Li-ion diffusion in V2O5 a systematic study using X-ray diffraction (XRD), Raman Spectroscopy and electrochemical impedance spectroscopy (EIS) has been employed using three electrodes configuration. Structural investigations using XRD suggest the selective diffusion of Mn ion towards the c-axis at a low doping percentage. Raman spectroscopy suggests the shift in 994 cm-1 modes which substantiates the uniaxial diffusion of Mn ions. Nyquist plots show that interfacial charge transfer resistance is highest for the lowest doping i.e., 1% Mn-doped V2O5 and exhibits the lowest diffusion coefficient as compared to other doped V2O5 samples. Specific capacitance calculated from cyclic voltammetry is found to be highest for the 4% Mn-doped V2O5 sample. Moreover, diffusion of Lithium ions improves with an increase in doping concentration due to higher concentration of defects as evident from Δd/d and Nelson–Riley factor (NRF) for pure V2O5 and Mn-doped V2O5.

First-principles investigation of the electronic and Li-ion diffusion properties of C and B doped LiFePO4 (0 1 0) surface

The electronic structure and Li-ion diffusion properties of the surface of LiFePO4 (010) doped with C and B elements were investigated using a first-principles approach based on density universal function theory. Calculations of the formation energy show that the surface defect energy decreases after the dopant replaces the oxygen, which is in accordance with the thermodynamic stability criteria. The difference in charge density indicates that the doped atoms on the modified surface form stronger covalent bonds with adjacent Fe atoms, while the density of states study shows that the introduction of C and B elements narrows the forbidden band of LiFePO4 and exhibits better electronic conductivity. In addition, we calculate the energy barrier for the diffusion of Li-ions along the b-channel of the (010) surface using a transition state search method. The results show that the doped system possesses a lower energy barrier, which suggests that the doping of C and B elements reduces the limitation of Li-ion migration to the surface and increases the Surface diffusion rate. At the same time, we find that element B performs better than element C in improving surface conductivity and Li-ion surface diffusion .

Molecular dynamics simulation unveiling anion charge and lattice volume dependent Li ion diffusion in lithium compounds

To fill knowledge gaps between anion sublattice models and real lithium compounds in terms of the influence of Li-anion interaction on Li ion diffusion, herein, molecular dynamics calculations were applied to systematically study impacts of anion charge and lattice volume on Li ion diffusion in lithium battery materials. Regardless of different Li occupation patterns, Li sublattice type, anion sublattice types and Li ion diffusion channels, there is a universal physical picture of anion charge dependent activation energy (Ea) for Li ion diffusion in lithium compounds, and that is the more negative anion charges increase Ea for Li ion diffusion and then decrease them. While large lattice volumes not always reduce Ea for Li ion migration, and even increase Ea, distinguished from the traditional understandings. These physical pictures of anion charge and lattice volume dependent Ea guide us to apply strains and choose appropriate elements for doping or substituting lithium compounds to reduce Ea for fast Li ion diffusion.