Li-ion Diffusion Coefficient Research Articles

Improving the electrochemical properties of SiO@C anode for high-energy lithium ion battery by adding graphite through fluidization thermal chemical vapor deposition method

A series SiO/graphite@C (SGC) composites electrode are successfully prepared by a fluidization thermal chemical vapor deposition (FTCVD) route in a kilogram-scale fluidized bed CVD equipment. This strategy can avoid the effect of particle agglomeration on carbon coating during heating reaction. The phase composition, element distribution, particle appearance and electrochemical properties of the as-obtained SGC composite is investigated in detail. The charge specific capacity of SGC-37 is close to 799.1 mAh g−1 after 100 cycles at 200 mA g−1. The SGC-37 shows a high capacity retention of 93.7% after 100 cycles, which much higher than that of SiO, SiO@C, SGC-73 and SGC-55 (the retention rates are 26.3%, 56.8%, 75.5% and 89.6%, respectively). The reason is mainly because improve Li ion diffusion coefficient, shorten transfer pathway of Li ion and ease to the volume change of SiO due to surface carbon coating and graphite addition. The FTCVD methods is not only an efficient method to prepared SGC anode, but also is may easy to apply to surface carbon coating of another particle material.

Electrochemical performance of heat treated SnO2–SnCu@C-Felt anode materials for lithium ion batteries

Standalone, self-supported SnO2–Cu6Sn5@C-Cloth/C-Felt anodes have been successfully synthesized through electroless metallization of the surface of C-Felt by Cu and Sn and subsequent heating at respective temperatures of 200 °C and 400 °C. X-ray diffraction (XRD), scanning electron miscroscopy (SEM), and the nitrogen (N2) adsorption/desorption isotherms were used to obtain the composition, structure and morphology of the electrode. The electrochemical characteristics were assessed using a two-electrode cell arrangement versus lithium metal. Results presented show that SnO2–Cu6Sn5 nanoparticles or thin film uniformly coated the C-Felt tubular network (matrix) establishing a binder-free anode. Galvanostatic charge/discharge cycling of the SnO2–Cu6Sn5@C-Cloth/C-Felt anode exhibited a reversible discharge capacity of 641 mAh/g and 681 mAh/g after 140 cycles at the current density of 150 mA/g, for the samples heated at the respective temperatures of 200 °C and 400 °C. We attributed the high capacity performances of the synthesized 400 °C anode to the higher content of SnO2, smaller particle sizes, higher Li ion diffusion coefficient and higher surface area. The outstanding cycle and rate capacity performances indicated that the heat-treated electrodes might be potentially applicable in lithium ion batteries.

Highly enhancement of the SiOx nanocomposite through Ti-doping and carbon-coating for high-performance Li-ion battery

Lithium-ion batteries (LIBs) with SiOx anodes possess high energy density, stemming from the Li-Si alloying reaction. However, several issues hinder the application of SiOx anodes in commercialized LIBs. In particular, the low electronic conductivity and sluggish kinetics of SiOx result in inadequate electrochemical performance. Herein, we report the use of a selective alcoholysis-based reaction to prepare a (C-TixSi1-xOy)@C composite using SiCl4, TiCl4, and ethylene glycol (EG) with benzene. The preferential reaction between EG and TiCl4 results in Ti3+ doping as well as the formation of a homogenous distribution of Ti ions. During the selective alcoholysis reaction, the Ti-Si-O-C-H sol transforms into a (C-TixSi1-xOy)@C composite and benzene decomposes into conductive carbon matrices through dispersion forces. The combination of Ti doping and carbon coating greatly enhance the conductivity of SiOx; in addition, the incorporated carbon acts as an effective oxide buffer, preventing structural degradation. Thus, the (C-TixSi1-xOy)@C composite exhibits a high Li-ion diffusion coefficient and low charge-transfer resistance, resulting in excellent capacity retention of 88.9% over 600 cycles at a high current density of 1 A g−1 with a high coulombic efficiency of ∼99%.

Improved electrochemical performance of Li2FeSiO4/CNF/rGO nanocomposites for lithium ion batteries

We have investigated electrochemical performance of Li2FeSiO4 (LFS) nanocomposites prepared with carbon nanofibers (CNF) and reduced graphene oxide (rGO) as conducting fillers. LFS/CNF(10 wt%) and LFS/CNF(5 wt%)/rGO(5 wt%) nanocomposites were synthesized using solvothermal method followed by annealing at 600 °C for 4 h under continuous flow of argon. Rietveld refinement of X-ray diffraction data confirmed the formation of monoclinic P21/n LFS without any impurity phase. Although both samples exhibit very similar electrical conductivity of 1.2 ± 0.2 S·cm−1, LFS/CNF/rGO shows a higher surface area of 88 m2/g compared to 62 m2/g for LFS/CNF. Correspondingly, the glavanostatic charge–discharge curves show an improved discharge capacity of 260 mAh·g−1 and 135 mAh·g−1 at C/20 and 8 C rates for LFS/CNF/rGO, compared to 230 mAh·g−1 and 116 mAh·g−1 at the same rates for LFS/CNF. This is further corroborated by the analysis of electrochemical impedance spectroscopy (EIS) data using a modified Randles circuit showing a factor of two increase in Li-ion diffusion coefficient (4.2 × 10−13 cm2/s) and higher exchange current density in LFS/CNF/rGO nanocomposite. Increased porosity caused by conducting fillers of CNF/rGO seems to provide a large contact area between the LFS nanoparticles and electrolyte for efficient insertion/extraction of Li-ions.

Ultrafine SnO2 nanoparticles encapsulated in ordered mesoporous carbon framework for Li-ion battery anodes

Ultrafine SnO2 particles are encapsulated in the hollow nanochannels of ordered mesoporous carbon (OMC) framework by simple infiltration of tin precursor and heat treatment. The SnO2@OMC anode delivers excellent cyclic stability with a reversible specific capacity of ∼1000 mAh g−1 after 100 cycles at 100 mA g−1 for Li-ion batteries (LIBs). It also presents an excellent rate performance with a specific capacity of 680 mA g−1 at a high current density of 500 mA g−1. Several functional features and ameliorating geometries play positive roles in Li-storage performance and stability of the electrode. They include (i) the intimate electrical contacts between the SnO2 nanoparticles and the walls of OMC channels to facilitate fast ion/electron transfer, (ii) the large surface area originating from the unique architecture of the composite, and (iii) the encapsulation of SnO2 particles within the channels to suppress their volume expansion during charge/discharge cycles. The reversibility of the conversion reaction is also supported by the high Li-ion diffusion coefficient with enhanced electrochemical reaction kinetics. Based on the above findings, this work may offer new insights into the rational nanostructural design of electrode materials for high performance rechargeable batteries.

Characterization and Electrochemical Modeling of Advanced SiO Anode Material for Li-Ion Batteries

Silicon monoxide (SiO) anodes have recently received much attention for their high energy density and improved cyclability, and this technology is being currently commercialized. Although numerous studies have focused on the electrochemical properties of SiO anodes, experimental observations of the key features such as the volume expansion upon lithiation, the open circuit potential (OCP) and its related hysteresis are still poorly understood. In this regard, we investigated the electrochemical properties of SiO anodes by combing experimental characterization and high fidelity modeling. In this study, we performed experimental studies by comparing electrochemical properties between SiO and Si anodes. The OCP of each anode was measured by using Galvanostatic Intermittent Titration Technique (GITT) in Fig. 1. The differential capacity (dQ/dV) of SiO anode, which was recorded at C/20 rate, showed similarity to the Si anode (see, Fig. 2). However, Scanning Electron Microscopy (SEM) analysis revealed that SiO particles experienced 118% volume expansion during cycling, which is much less than that of Si particles (c.a. 280% [1]). In addition, the diffusion coefficient of Li-ions in SiO particles was calculated by GITT data, which ranges from 10-8 to 10-12 cm2/s, as shown in Fig. 3. We adopted the experimental data as parameters for a high-fidelity electrochemical model, which was developed for predicting the performance of SiO anodes and gaining a deeper understanding of the physical phenomena that determine the electrochemical behavior. The model stems from the Enhanced Single Particle Model (ESPM) [2]; however it includes a prediction of the volume change effects on the solid/liquid diffusion and electrode porosity. Unlike other existing electrochemical models for silicon-based anodes where the convective flux induced by particle expansion/contraction during lithiation and delithiation is neglected in the solid diffusion [3, 4], such convective flux is considered here. The resulting solid diffusion equation with moving boundary is converted to a traditional fixed boundary problem using Landau Transformation [5]. An expression for volume change is derived based on the work by Obrovac et al. [1]. Porosity changes in the SiO electrode region due to particle volume changes are also included in the model. An extra convective term arises in the liquid diffusion equation as a consequence of porosity changes. The resulting model will be calibrated and validated with experimental data from rate capability tests. Model-based analyses will be performed to investigate the effect of cell design parameters on the cell performance.

Defect Chemistry and Lithium Transport in ANTI-Perovksite Superionic Conductors

Solid state electrolyte with fast lithium conduction is the core of the all-solid-state Li battery technology. By substituting the organic electrolyte with a piece of non-flammable ceramic material, we can achieve a better safety, a higher specific capacity and a higher energy density. To date, the major bottle neck for this technology is the slow bulk diffusion of solid state electrolyte and the interfacial incompatibility between the electrolyte and electrodes. To resolve these issues, several families of fast ionic conductors have been developed. The understanding of Li diffusion in these materials is essential to the development of novel family fast ionic conductors. In this sense, atomistic modeling provides us with a unique tool to obtain comprehensive information on the atom motion which is so far hard to access with experimental techniques. In this work, we use density functional theory (DFT) calculations as well as large scale classical molecular dynamics (MD) simulations to simulate the Li diffusion in a novel family of superionic conductor, lithium-rich anti-perovskites and provide an understanding of the Li diffusion behavior. Lithium-rich anti-perovskites (LiRAPs) are a promising family of solid electrolytes, which exhibit ionic conductivities above 10−3 S cm−1 at room temperature, among the highest reported values to date. We investigate the defect chemistry and the associated lithium transport in Li3OCl, a prototypical LiRAP, using DFT calculations and classical MD simulations. We studied three types of charge neutral defect pairs, namely the LiCl Schottky pair, the Li2O Schottky pair, and the Li interstitial with a substitutional defect of O on the Cl site. Among them the LiCl Schottky pair has the lowest binding energy and is the most energetically favorable for diffusion as computed by DFT. This is confirmed by classical MD simulations, where the computed Li ion diffusion coefficients for LiCl Schottky systems are significantly higher than those for the other two defects considered and the activation energy in LiCl deficient Li3OCl is comparable to experimental values. The high conductivities and low activation energies of LiCl Schottky systems are explained by the low energy pathways of Li between the Cl vacancies. We propose that Li vacancy hopping is the main diffusion mechanism in highly conductive Li3OCl.

Towards high-performance cathode materials for lithium-ion batteries: Al2O3-coated LiNi0.8Co0.15Zn0.05O2

Zn-doped LiNi0.8Co0.2O2 exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi0.8Co0.15Zn0.05O2 as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al2O3 layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al2O3-coated LiNi0.8Co0.15Zn0.05O2 cathode delivers a highly reversible capacity of 182 mA h g−1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi0.8Co0.15Zn0.05O2 cathode. The enhanced electrochemistry performance can be attributed to the Al2O3-coated protective layer, which prevents the direct contact between the LiNi0.8Co0.15Zn0.05O2 and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al2O3-coated LiNi0.8Co0.15Zn0.05O2, which rationally illuminates the protection mechanism of the Al2O3-coated layer.

Facile strategy to fabricate Na2Li2Ti6O14@Li0.33La0.56TiO3 composites as promising anode materials for lithium-ion battery

A robust strategy has been developed to fabricate Na2Li2Ti6O14@Li0.33La0.56TiO3 composites as promising anode materials for lithium-ion battery. Li0.33La0.56TiO3 modification does not change the basic structure of Na2Li2Ti6O14 but enhances the lattice parameter because few trivalent lanthanum ions enter the crystal lattice of Na2Li2Ti6O14. All samples show similar morphology with a narrow size distribution ranged from 100 to 500 nm. HRTEM test demonstrates that a good conductive connection between the Na2Li2Ti6O14 and Li0.33La0.56TiO3 layer is successfully formed. The electrochemical tests show that Na2Li2Ti6O14@Li0.33La0.56TiO3 (5 wt%) sample exhibits the lowest charge-transfer resistance, highest reversibility of lithium insertion/extraction, and the largest Li-ion diffusion coefficient among all samples, and then shows the best electrochemical activity. Hence, the Na2Li2Ti6O14@Li0.33La0.56TiO3 (5 wt%) electrode reveals the largest lithiation and delithiation capacities at each current density. The Na2Li2Ti6O14@Li0.33La0.56TiO3 (5 wt%) shows excellent cycling stability with a delithiation capacity of 166.8 mAh g−1 at 500 mA g−1 after 100 cycles. However, the corresponding delithiation capacity of pristine Na2Li2Ti6O14 is only 136.9 mAh g−1 after 100 cycles. Li.33La.56TiO3 modification is a direct and powerful design method to enhance the delithiation and lithiation capacities and cycling stability of Na2Li2Ti6O14.

Combined modification by LiAl11O17 and NaAl11O17 to enhance the electrochemical performance of Li4Ti5O12

The intrinsically moderate Li-ion diffusion coefficient and poor electronic conductivity of Li4Ti5O12 (LTO) restricts the practical application in Li-ion batteries. In view of the rapid two-dimensional diffusion channels in ionic conductor of LiNaAl22O34 for Li-ions, the LTO modified by combining equivalent molar ratio of LiAl11O17 with NaAl11O17 (LNAO) was fabricated by a simple reaction between LiNO3, Na2CO3, Al(NO3)3⋅9H2O and LTO at various sintering temperatures. The product with a LNAO/LTO mass ratio of 0.0106 and calcined at 600 °C achieved reversible capacities of 163.8, 160.6, 156.5, 150.9, 132.9 and 163.4 mAh g−1 at the current rates of 100, 200, 400, 800, 1600 and 100 mA g−1, respectively. Even cycled 800 times at 500 mA g−1, a capacity of 147.9 mAh g−1 was retained. The outstanding cycling and rate performance is attributable to the simultaneously formed LNAO coating on the LTO particles and superficial Al3+ doping in the LTO, achieving combined improvement in the ionic and electronic conductivities of LTO and thus boosting the comprehensive electrochemical performance of LTO.

Enabling high rate charge and discharge capability, low internal resistance, and excellent cycleability for Li-ion batteries utilizing graphene additives

A liquid-phase mixing method is adopted to uniformly disperse the graphene nanosheets onto LiNi1/3Co1/3Mn1/3O2 cathode for high-performance Li-ion batteries (LIBs). The electrochemical performance was characterized using a full pouch cells with state-of-the-art electrode areal loading (compared to half coin cells). The addition of graphene sheets (i.e., only 1 wt%) significantly improves the high rate capability for charging and discharging operation. For example, 6 times improvement in 5 C charging was achieved providing further insights in enabling extreme fast charging for LIBs. Other benefits include longer cycleability, lower internal resistance, and higher lithium ion diffusion coefficient, demonstrated by charge-discharge cycling tests and electrochemical impedance spectroscopy. Higher capacity retention of 88.2% and decreased internal resistance of ∼0.9 Ω are observed after 400 cycles. The diffusion coefficient of Li ions is 6.49 × 10−8 cm2 s−1 when charged to 4.2 V, which is approximately 1.37 times higher compared to the configuration with no graphene sheet (4.74 × 10−8 cm2 s−1). The improved performance is ascribed to a robust network among the active materials formed by graphene sheets, which serves as an extended current conductor and facilitates charge transfer, ionic reversibility, and ionic transportation.

Effect of Ti3AlC2 precursor on the electrochemical properties of the resulting MXene Ti3C2 for Li-ion batteries

The presented work compared the etching behavior between combustion synthesized Ti3AlC2 (SHS-Ti3AlC2) and pressureless synthesized Ti3AlC2 (PLS-Ti3AlC2). Because the former had a more compact structure, it was harder to be etched than PLS-Ti3AlC2 under the same conditions. When served as anode material for Li-ion batteries, SHS-Ti3C2 showed much lower capacity than PLS-Ti3C2 at 1 C (52.7 and 87.4 mAh g−1, respectively) due to the smaller d-spacing. Furthermore, Potentiostatic Intermittent Titration Technique (PITT) was used to determine the Li-ion chemical diffusion coefficient (DLi+) of Ti3C2 in the range of 10−10 − 10−9 cm2 s−1, indicating that Ti3C2 could exhibit an excellent diffusion mobility for Li-ion.

N-doped hollow urchin-like anatase TiO2@C composite as a novel anode for Li-ion batteries

N-doped hollow urchin-like anatase TiO2 spheres (HUTSs) with carbon coating (HUTS@C) are prepared through a facile and scalable hydrothermal reaction followed by coating of polypyrrole and carbonization. The HUTS is composed of radially grown anatase nanorods and possesses an enhanced percentage of exposed {001} facets compared with P25 TiO2 nanoparticles. After the carbon coating, the HUTS@C retains the hollow nanostructure although covered with an N-doped carbon layer. As an anode for Li-ion batteries, the HUTS@C delivers a higher capacity of 165.1 mAh g−1 at 1C after 200 cycles and better rate capability (111.7 mAh g−1 at 10C) than the HUTS. Further electrochemical studies reveal that the HUTS@C has a better electrochemical reversibility, lower charge-transfer resistance, and higher Li-ion diffusion coefficient due to its unique nanosctructure including the hollow core, anatase phase of TiO2 microspheres with high exposed {001} facets and the N-doped carbon layer, which facilitates mass transport and enhances electrical conductivity.

Understanding the Improved Kinetics and Cyclability of a Li2MnSiO4 Cathode with Calcium Substitution.

Limited practical capacity and poor cyclability caused by sluggish kinetics and structural instability are essential aspects that constrain the potential application of Li2MnSiO4 cathode materials. Herein, Li2Mn1- xCa xSiO4/C nanoplates are synthesized using a diethylene-glycol-assisted solvothermal method, targeting to circumvent its drawbacks. Compared with the pristine material, the Ca-substituted material exhibits enhanced electrochemical kinetics and improved cycle life performance. In combination with experimental studies and first-principles calculations, we reveal that Ca incorporation enhances electronic conductivity and the Li-ion diffusion coefficient of the Ca-substituted material, and it improves the structural stability by reducing the lattice distortion. It also shrinks the crystal size and alleviates structure collapse to enhance cycling performance. It is demonstrated that Ca can alleviate the two detrimental factors and shed lights on the further searching for suitable dopants.

Exploring pristine and Li-doped Mg2NiH4 compounds with potential lithium-storage properties: Ab initio insight

In this work, pure and Li-doped Mg2NiH4 hydrides are explored for potential Li-ion battery conversion anode materials applications from state-of-the-art Density functional theory. The most thermodynamically stable Li-doped Mg2NiH4 structure is determined, which possesses a smaller band gap than pure material and owns a theoretical specific capacity of 975.35 mA h g−1 and an average voltage of 0.437 V (vs. Li+/Li0). The Li-doping also improves the diffusion behavior of Li-ion in electrode material especially at 300 K, which implies the promising rate capability of the device at room temperature when the anode material is doped utilizing Li element. The non-empirical values of diffusion coefficients of Li-ion in both pure and Li-doped Mg2NiH4 system are also quantitatively determined from ab initio molecular dynamics. After Li-doping, the diffusion coefficient of Li-ion in the electrode is evidently increased to 1.791 × 10−9 m2 s−1 from the pristine 1.431 × 10−9 m2 s−1 at 300 K and the Li-ion conductivity is also increased. This theoretical study is proposed to encourage the design and experimental modification of better light-metal based hydrides for Li-ion battery conversion anodes applications.

Study on electrochemical performance of Mg-doped Li2FeSiO4 cathode material for Li-ion batteries

In this paper, Li2Fe1−yMgySiO4/C (y = 0, 0.01, 0.02, 0.03, 0.05), a cathode material for lithium-ion battery was synthesized by solid-state method and modified by doping Mg2+ on the iron site. The effects of Mg2+ doping on the crystal structure and electrochemical performance Li2FeSiO4 was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests. Electrochemical methods of measurement were applied including constant current charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), to determine the electrochemical performance of the material and the optimal doping ion and ratio. The results showed that Li2Fe0.98Mg0.02SiO4/C has the higher specific capacity and better cycle stability as well as lower impedance and better reversibility. The enhanced electrochemical performance can be attributed to the increased electronic conductivity, the decreased charge transfer impedance, and the improved Li-ion diffusion coefficient. Then, further study on the synthesis conditions was performed to find the optimal combustion temperature and time. According to the study, the material which has the best electrochemical performance, shows initial discharge specific capacity of 142.3 mAh g−1 at 0.1 C (1 C = 166 mA g−1) and coulomb efficiency of 95.6%, under the condition that the temperature is 700 °C and the calcining time is 10 h.

Exposing the {010} Planes by Oriented Self-Assembly with Nanosheets To Improve the Electrochemical Performances of Ni-Rich Li[Ni0.8Co0.1Mn0.1]O2 Microspheres.

A modified Ni-rich Li[Ni0.8Co0.1Mn0.1]O2 cathode material with exposed {010} planes is successfully synthesized for lithium-ion batteries. The scanning electron microscopy images have demonstrated that by tuning the ammonia concentration during the synthesis of precursors, the primary nanosheets could be successfully stacked along the [001] crystal axis predominantly, self-assembling like multilayers. According to the high-resolution transmission electron microscopy results, such a morphology benefits the growth of the {010} active planes of final layered cathodes during calcination treatment, resulting in the increased area of the exposed {010} active planes, a well-ordered layer structure, and a lower cation mixing disorder. The Li-ion diffusion coefficient has also been improved after the modification based on the results of potentiostatic intermittent titration technique. As a consequence, the modified Li[Ni0.8Co0.1Mn0.1]O2 material exhibits superior initial discharges of 201.6 mA h g-1 at 0.2 C and 185.7 mA h g-1 at 1 C within 2.8-4.3 V (vs Li+/Li), and their capacity retentions after 100 cycles reach 90 and 90.6%, respectively. The capacity at 10 C also increases from 98.3 to 146.5 mA h g-1 after the modification. Our work proposes a novel approach for exposing high-energy {010} active planes of the layered cathode material and again confirms its validity in improving electrochemical properties.

Improving electrochemical performance by Na, Mg and Al-ion doping of PbLi2Ti6O14 as anode materials for Li-ion batteries

In recent years, titanium-based oxides have attracted great attention in the research field of secondary Li-ion batteries. However, they suffer from poor electronic conductivity due to a huge band gap. In this paper, PbLi2Ti6O14 is fabricated by a simple one-step solid-state reaction method. To enhance its conductance and Li-storage capability, PbLi1.95Na0.05Ti6O14, PbLi1.95Mg0.05Ti6O14 and PbLi1.95Al0.05Ti6O14 are fabricated by Na, Mg and Al-ion doping. More impressively, PbLi1.95Al0.05Ti6O14 presents a superior reversible capability with a reversible charge capacity of 152.8mAhg−1 after 100 cycles at current density 100mAg−1. In addition, it also clearly demonstrates that PbLi1.95Al0.05Ti6O14 has good structural stability and electrochemical reversibility by in situ XRD observation. Besides, it also presents a high Li-ion diffusion coefficient of 1.978 × 10–12cm2s−1. All of these make it possible to become a superior performance anode material for Li-ion batteries.

Study on the influences of calcination temperature on structure and its electrochemical performance of Li2FeSiO4/C nano cathode for Lithium Ion Batteries

The Li2FeSiO4/C nanomaterial has been prepared by sol-gel method. Systematic studies have been carried out to examine the impact of calcination temperature on structure and its electrochemical properties of Li2FeSiO4/C. The TG/DTA analysis has been used to evaluate the influence of temperature on the pure phase Li2FeSiO4/C nanocomposites. From the Rietveld refined XRD patterns, it is confirmed that the sample calcined at 700 °C and 850 °C possess orthorhombic (Pmn21) and monoclinic (P21/n) structures without any impurity phases. The SEM micrographs indicated the increase of the grain size with increase in the calcination temperature. The results of electrochemical impedance reveal that the orthorhombic Li2FeSiO4/C exhibits higher electronic conductivity of 1.29 × 10−4 Scm−1, which is far better than other samples. The electrochemical behavior of Li2FeSiO4/C in aqueous electrolyte has been studied by cyclic voltammetry (CV). The sample prepared at 700 °C exhibited an excellent electrochemical performance in an aqueous electrolyte, in which almost symmetric CV curves are observed after 50 cycles that indicate good redox reversibility and cycling stability. The Li-ion diffusion coefficient of the sample calcined at 700 °C is 6.24 × 10−12 cm2s−1, revealing a good ionic mobility inside the orthorhombic cage.

Surface modified Li4Ti5O12 by paper templated approach for enhanced interfacial Li+ charge transfer in Li-ion batteries.

The Li4Ti5O12 (LTO) and lithium silicate (LS) surface modified LTO have been demonstrated by a unique paper templated method. Comparative study of structural characterization with electrochemical analysis was demonstrated for pristine and modified Li4Ti5O12. Structural and morphological study shows the existence of the cubic spinel structure with highly crystalline 250–300 nm size particles. The LS modified LTO shows the deposition of 10–20 nm sized LS nanoparticles on cuboidal LTO. Further, X-ray photoelectron spectroscopy (XPS) confirms the existence of Li2SiO3 (LS) in the modified LTO. The electrochemical performance was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge. The modified LTO with 2% LS (LTS2) exhibited excellent rate capability compare to pristine LTO i.e. 182 mA h g−1 specific capacity at a current rate, 50 mA g−1 with remarkable cycling stability up to 1100 cycles at a current rate of 800 mA g−1. The lithium ion full cell of modified LTO with LS as an anode and LiCoO2 as a cathode exhibited a remarkably reversible specific capacity i.e. 110 mA h g−1. Both electronic and ionic conductivities of pristine LTO are observed to be enhanced by incorporation of appropriate amount of LS in LTO due to a larger surface contact at the interface of electrode and electrolyte. More significantly, the versatile paper templated synthesis approach of modified LTO with LS provides densely packed highly crystalline particles. Additionally, it exhibits lower Warburg coefficient and higher Li ion diffusion coefficient which in turn accelerate the interfacial charge transfer process, which is responsible for enhanced stable electrochemical performance. The detailed mechanism is expressed and elaborated for better understanding of enhanced electrochemical performance due to the surface modification.