Figures 4 - uploaded by Dr Dharmendra Pal Singh
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a) and (b) show the variation of dielectric constant (ε′) versus frequency curves for manganese doped derivatives at various temperatures. The curves have the same nature for MSLT-1 and MSLT-2. The value of dielectric constant (ε′) is lower at higher frequency. Manganese doping increases the value of dielectric constant (ε′) for MSLT-1 and MSLT-2. All these curves have same nature as for polar dielectrics. It is reported (Mac Chesney et al 1963) that when the frequency of alternating voltage increases, the value of dielectric constant of polar dielectric remains invariable, but beginning with a certain frequency (f 0 ), when polarization fails to settle itself during one half period, dielectric constant (ε′) begins to drop approaching very high frequencies. Dielectric dispersion is seen for these compounds. LnσT versus frequency curves at different temperatures are shown in figures 5(a′) and (b′). From these curves, it is clear that the dependence of a.c. conductivity on frequency decreases with increase in temperature. Thus the electronic hopping conduction is dominant at lower temperature and diminishes with the rise in temperature. EPR spectra of all the manganese doped derivatives show two distinct peaks 'A' with g≈4·22 and 'B' with g≈2·04. Peak A with g≈4·22 indicates that lower percentage of Mn 3+ doping (3d 4 configuration) substitutes at Ti 4+ sites. The broad peak 'B' with g≈2·04 indicates that at higher concentration of doping manganese, ions enter as Mn 2+ at the interlayer alkali
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The manganese doped layered ceramic samples (Na1·9Li0·1)Ti3O7 : XMn(0·01 ≤ X ≤ 0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn3+ at Ti4+ sites, whereas for higher pe...
Citations
... However, electrodes made from LTO without any materials modifications usually show poor rate performance, which mainly results from the poor electronic conductivity [6]. To enhance the electronic conductivity of this material, three methods were mainly proposed, including synthesis of nanosized particles [7][8][9][10][11], deposition of metal powder or carbon on LTO particle surface [12][13][14][15][16], substituting Li or Ti by doping it with metal ions (such as AI 3+ [6], Ag + [17], Na + [18], Mg 2+ [19], V 5+ [19,20], Zr 4+ [21], Ni 2+ [22], Nb 5+ [23], La 3+ [24] and Ru 4+ [25][26][27]). Doping can have a direct impact on the structure and stability of LTO during lithium intercalation and deintercalation. ...
... As shown in Fig. 7, the charge-discharge curves of doped and undoped LTO electrodes display distinct potential plateaus around 1.5 V (vs. Li/Li + ) at 0.5 C, 1 C and 3 C, corresponding to the two-phase insertion reaction between Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 [18]. As can be seen, the voltage plateaus during lithium insertion process are nearly identical when the current rate was below 5 C. ...
... Despite the above mentioned advantages, the LTO shows poor electronic conductivity due to the empty Ti 3d state with a band energy of about 2 eV [6], which seriously hinders its high rate performance [7]. To enhance the electronic conductivity of LTO, several methods have been proposed, including: (i) coating with conductive materials, such as amorphous carbon, carbon nanotube or a metallic conducting layer [8][9][10][11][12][13][14][15]; (ii) reducing particle size [16][17][18][19][20][21]; (iii) doping with metal ions (such as Na + [22], Zn 2+ [23], Mg 2+ [24], AI 3+ [25], Co 3+ [26], Ni 2+ [27], Mn 4+ [27], La 3+ [28], Zr 4+ [29,30], Ru 4+ [31,32], V 5+ [33], Nb 5+ [34,35], Ta 5+ [36]) or non-metal ions (such as F − [37], Br − [38]) in Li, Ti or O sites. ...
Sodium trititanate doped with nickel in different amounts for the first time have been prepared through one-step hydrothermal synthesis. Both cation substitution and interstitial doping are realized with a formation of oxygen-deficient Na2+xTi3–yNix+yO7–δ solid solutions. The Ni-doping results in the sodium trititanate unit cell expansion. The morphology was found to be evolved with increasing dopant concentration from nanotubes to nanosheets. The specific surface area ranges from 121 to 78 m² g–1 depending on dopant content. With nickel-doping, the bandgap narrowed from 3.45 up to 2.43 eV. The conductivity of sodium trititanate increases in 3–6 fold after the nickel incorporation. A deviation from the Arrhenius temperature dependence of the conductivity is observed above 350 K indicating that mixed ionic-electronic conductors based on Ni-doped sodium trititanate are formed. This paper contributes to the advance understanding doping principles and effects for Na2Ti3O7-based materials, which are currently under consideration.
“Zero-strain” Li4Ti5O12 has become one of the most promising anode materials for lithium-ion battery but its low electronic and ionic conductivity lead to the poor rate capability. Herein, the high-rate performance and the cycling stability of Li4Ti5O12 have been largely enhanced by replacing Li and Ti with a little amount of Mg and La, respectively. The synergistic modulation mechanism of Mg and La co-doping on the crystal/electronic structure and electrochemical performances has been unveiled. Firstly, Mg and La co-doping enlarges the lattice parameters, unit cell volume and Li1–O bond. These facilitate the lithium-ion migration and enhance the rate capability. Secondly, Ti–O bond is shortened which enhances the structure stability and cyclic performance. Thirdly, the first-principles calculations further confirm that Mg/La co-doping modulates the electronic density of states and decreases the Li⁺ migration barrier. The polarization and charge transfer impedance are effectively alleviated. Moreover, the diffusion coefficient of lithium ions is further improved because of the reduction of much more Ti³⁺. At 10C, it delivers a discharge capacity of 107.8mAh/g after 500cyles which reserves 92.2% of the initial capacity. This study provides some insights into optimizing the electrochemical performances of Li4Ti5O12 by tuning the crystal and electronic structure with lattice doping.
Dense and stoichiometric \(\hbox {Ba}_{0.8}\hbox {Mg}_{0.2}(\hbox {Zr}_{0.1}\hbox {Ti}_{0.8}\hbox {Ce}_{0.1})\hbox {O}_{3}\) (BMZTCO) ceramics have been synthesised and their excitation was experimentally evaluated by applying an electric field. The processed sample exhibits superior frequency-independent and temperature-dependent dielectric parameters. The prepared sample has combined the tetragonal and cubic phases of \(\hbox {BaTiO}_{3}\) and \(\hbox {Ce}_{2}\hbox {O}_{3}\). The Bode plots suggest non-Debye type of relaxation mechanism and positive temperature coefficient-type behaviour. The excitation intensity reaches a peak when the driving frequency matches with the natural frequency of the prepared sample.
One-dimensional (1D) nanostructures provide shortened Li⁺ diffusion pathways, structural stability and large interfacial area between the active material and electrolyte, which enhances the reversibility and cycling performance of spinel Li4Ti5O12 (LTO). Herein, we have successfully synthesized iodine (I) doping 1D LTO nanofibers by an electrospinning technique and studied the I doping effect on the lattice parameter, morphology and electrochemical properties of 1D LTO nanofibers. The 1D Li4Ti5O12-xIx (x=0.3) nanofibers have excellent rate capability, specific capacity and cycling stability because of the shortened diffusion length for Li⁺ transport, which are mainly due to cubic lattice parameter of LTO increase with I doping. Also, Cyclic voltammetry (CV) and Electrochemical impedance spectroscopy (EIS) results confirmed that I doping can reduce the electrochemical polarization of LTO and increase the lithium ion diffusion coefficient, which can improve the electrochemical performance of LTO.
The TiN coated Li4Ti5O12 (LTO) submicrospheres with high electrochemical performance as anode materials for lithium-ion battery were synthesized successfully by solvothermal method and subsequent nitridation process in the presence of ammonia. The XRD results revealed that the crystal structure of LTO did not change after thermal nitridation process. The submicrospheres morphology of LTO and TiN film on the surface of LTO submicrospheres were characterized by FESEM and HRTEM, respectively. XPS result confirmed that a small amount of Ti changed from Ti4+ to Ti3+ after nitridation process, which will increase the electronic conductivity of LTO. Electrochemical results showed that eletrochemical performance of TiN coated LTO anode materials compared favorably with that of pure LTO. Also its rate capability and cycling performance were apparently superior to those of pure LTO. The reversible capacity of TiN-LTO is 105.2 mAh·g-1 at a current density of 10 C after 100 cycles and maintain 92.9% of its initial discharge capacity, while that of pure LTO is only 83.6 mAh·g-1 with a capacity retention of 90.3%. Even at 20 C, the discharge capacity of TiN coated LTO sample is 101.3 mAh·g-1, compared with 77.3 mAh·g-1 for pristine LTO in the potential range 1.0-2.5 V (vs. Li/Li+).
Sm-doped Li4Ti5O12 (LTO) in the form of Li4-x/3Ti5-2x/3SmxO12 (x=0, 0.01, 0.03, 0.05 and 0.10) are synthesized successfully by a simple solid-state reaction in air. XRD analysis and Rietveld refinement demonstrates that traces of the doped Sm3+ ions have successfully entered the lattice structure of bulk LTO and the Sm doping does not change the spinel structure of LTO. However, one interesting is the lattice parameter increases gradually with the increase of Sm doping amount, which is potentially beneficial for intercalation and de-intercalation of lithium-ion. XPS results further identify the existence of Ti3+ ion and the transition of a small quantity of Ti ions from Ti4+ to Ti3+, which will improve the conductivity of LTO. All materials are well crystallized with a uniform and narrow size distribution in the range of 0.5-1.2 μm. The results of electrochemical measurement reveal that the Sm-doping can improve the rate capability and cycling stability of LTO. Among all samples, the Li4-x/3Ti5-2x/3SmxO12 (x=0.03) exhibits the best electrochemical properties. The specific capacities of the Li4-x/3Ti5-2x/3SmxO12 (x=0.03) sample at charge and discharge rates of 5C and 10C are 131.1 mAh·g-1 and 119.2 mAh·g-1, respectively, compared with 64 mAh·g-1 (5C) and 47 mAh·g-1 (10C) for the pristine LTO in the potential range 1.0-2.5 V (vs. Li/Li+). This result can be attributed to the Li4-x/3Ti5-2x/3SmxO12 (x=0.03) with a diffusion coefficient of 1.3×10-12 cm2·s-1, which is higher than 7.4×10-14 cm2·s-1 for the LTO electrode without Sm-doping. In the meantime, the discharge capacity of Li4-x/3Ti5-2x/3SmxO12 (x=0.03) can still reach 125.1 mAh·g-1 even after 100 cycles and maintain 95.2% of its initial discharge capacity at 5C. Therefore, Sm doping have a great impact on discharge capacity, rate capability and cycling performance of LTO anode materials for lithium-ion batteries.
Lithium mixed Potassium tetra titanates with 0.2, 0.4, 0.6, 0.8 and 1.0 molar percentage of Li2CO3 (general formula K2−XLiXTi4O9) have prepared by a high temperature solid-state reaction route. The XRD results indicate that Lithium ions enter the unit cell maintaining the layered structure of solid solution. The crystals are monoclinic for x = 0.2, 0.4 and 0.6 while crystals are orthorhombic for x = 0.8 and 1.0 with a small
change in ratio c/a in both cases. EPR analysis, The Lithium ions are accommodated with the Potassium ions in the interlayer space. The EPR spectra of Lithium mixed Potassium tetra titanates confirm the partial reduction of Ti4+ ions to Ti3+.
