Fe doping effect of vanadium oxide films for enhanced switching electrochromic performances

In the present study, Fe-doped V₂O₅ films showing impressive electrochromic (EC) performance were developed using the sol-gel spin-coating method. To confirm the optimized Fe-doping effect on the V₂O₅ films for the EC performance, we adjusted the Fe atomic percentages to 0.0, 0.5, 1.0, and 1.5?at%, respectively. With the effect of Fe doping on the V₂O₅ films, the obtained films resulted in the formation of the oxygen vacancies. As the result, when the optimum Fe atomic percentage was 1.0?at%, the enhanced switching speeds (3.7?s for the bleaching speed and 2.0?s for the coloration speed) and enhanced coloration efficiency value (47.3?cm²/C) compared to the other films were implemented. This can be attributed to the improved electrical conductivity and Li⁺ diffusion coefficient that led to efficient generation of the EC reaction activity and narrowing the optical bandgap at the coloration state to increase transmittance modulation. Therefore, this unique film can be a promising EC material to improve the performance for the EC devices.     

Improving electrochromic behavior of spray pyrolised WO3 thin solid films by Mo doping

The effects of molybdenum [Mo] doping on the electrochromic behavior of spray pyrolised tungsten trioxide [WO₃] thin films have been studied. It has been observed that the color-bleaching kinetics, coloration efficiency, and stability of electrochromic WO₃ films are closely related to molybdenum doping concentration, apart from their microstructure and crystallinity. While a nominal 6.0 at.% molybdenum doping produces best electrochromic response in WO₃ films, the electrochemical stability is highest when the nominal concentration of molybdenum is about 2.0 at.%. The improved electrochromic behavior of the Mo doped WO₃ films has been explained from the improved H⁺ ion diffusion coefficient in the films during coloration and decoloration process.     

XPS study of Li ion intercalation in V2O5 thin films prepared by thermal oxidation of vanadium metal

The intercalation and deintercalation mechanisms of lithium into V₂O₅ thin films prepared by thermal oxidation of vanadium metal have been studied by X-ray photoelectron spectroscopy (XPS) using a direct anaerobic and anhydrous transfer from the glove box (O₂ and H₂O < 1ppm), where the samples were electrochemically treated, to the XPS analysis chamber. Vanadium in the as-prepared oxide films is mostly (from 93 to 96% depending on samples) in a pentavalent state (V⁵⁺) with a stoichiometric O/V concentration ratio fitting that of V₂O₅. Four to seven percent of VO₂ is also observed. After the 1st and the 2nd intercalation steps at E = 3.3 and 2.8 V versus Li/Li⁺, respectively, the V2p core level spectra evidence a partial reduction to V⁴⁺ states with a remaining concentration of 73 and 56% of V⁵⁺, in agreement with the intercalation of about 1/2 mol of Li per V₂O₅ mol at each intercalation step. Intercalated lithium was observed at a binding energy of 56.1 eV for Li1s. Changes of the electronic structure of the V₂O₅ thin film after intercalation are evidenced by the observation, at a binding energy of 1.3 eV, of occupied V3d states (V⁴⁺) originally empty in the pristine film (V⁵⁺). The V2p and Li1s core level spectra show that the process of Li intercalation is partially irreversible. In the first cycle, 34 and 14% of the vanadium ions remain in the V⁴⁺ state after deintercalation at E = 3.4 and 3.8 V versus Li/Li⁺, respectively, indicating a partially irreversible process already after the 1st deintercalation. The analyses of C1s and O1s XP spectra show the formation of a solid-electrolyte interface (SEI). The analyzed surface layer includes lithium carbonate and Li-alkoxides.     

Synthesis of high-performance electrochromic thin films by a low-cost method

Metal-doping is an effective method to adjust the physical and chemical properties of semiconductor metal oxides. This work adopts a simple solvothermal method to synthesize Mo-doped tungsten oxide nanoparticles. The high-performance electrochromic films can be homogenously formed on ITO glass without post-annealing. Compared with pure WO₃ films, the optimized Mo-doped WO₃ films show improved electrochromic properties with significant optical contrast (68.3% at 633 nm), the short response time (6.3 s and 3.9 s for coloring and bleaching, respectively), and excellent coloration efficiency (107.2 cm² C^?1). The improved electrochromic behavior is mainly due to the increasing diffusion rate of Li⁺ in Mo-doped WO₃ films (increased 20% than that of pure WO₃ films). The porous surface of Mo-doped WO₃ film shortens the diffusion path of Li⁺. Besides, Mo doping reduces the resistance and improves conductivity. Furthermore, 2at% Mo-doped WO₃ films indicate satisfactory energy-storage properties (the specific capacitance is 73.8 F g^?1), resulting from the enhanced electrochemical activity and fast electrical conductivity. This work presents a practical and economical way of developing high-performance active materials for bifunctional electrochromic devices.     

Vacancy-engineered V2O5-x films for ultrastable electrochromic applications

In the present study, we prepared vacancy-engineered V₂O_5-x films for electrochromic (EC) applications. To investigate the vacancy effect of V₂O_5-x films with high EC performance capabilities, precursor concentrations of V-based sol solutions were varied at 1 wt%, 5 wt%, and 10 wt%. Among them, V₂O_5-x films with a precursor concentration of 5 wt% (V₂O₅-5wt%) showed superior EC performance outcomes due to the (001)-plane-oriented crystal structure, which provides high electrical conductivity with the oxygen vacancy (V_o). In addition, the gravel-like uniform surface morphology with the optimized film thickness provides a stable electrochemical reaction during the EC measurement. As a result, V₂O₅-5wt% exhibited fast switching speeds (2.1 s for coloration and 3.6 s for bleaching), high transmittance modulation (ΔT) (51.32%), high coloration efficiency (CE) (52.3 cm²/C), and excellent cycle stability (85.85% ΔT retention after 500 cycles). In addition, V₂O₅-5wt% showed energy storage capability of 443.7 F/g at a current density of 2 A/g, thus proving its potential for use in multi-functional applications. Therefore, these results provide valuable insight related to the engineering of vacancies in EC films to achieve high-performance EC devices and additional multi-functional applications.     

Synthesis and characterization of highly stable optically passive CeO2-ZrO2 counter electrode

Transparent and adherent CeO₂-ZrO₂ thin films having film thicknesses ∼543-598 nm were spray deposited onto the conducting (fluorine doped tin oxide coated glass) substrates from a blend of equimolar concentrations of cerium nitrate hexahydrate and zirconium nitrate having different volumetric proportions (0-6 vol.% of Zr) in methanol. CeO₂-ZrO₂ films were polycrystalline with cubic fluorite crystal structure and the crystallinity was improved with increasing ZrO₂ content. Films were highly transparent (T ∼ 92%), showing decrease in band gap energy from 3.45 eV for pristine CeO₂ to 3.08-3.14 eV for CeO₂-ZrO₂ films. The different morphological features of the film obtained at various CeO₂-ZrO₂ compositions had pronounced effect on the ion storage capacity and electrochemical stability. CeO₂-ZrO₂ film prepared at 5 vol.% Zr concentration exhibited higher ion storage capacity of 24 mC cm⁻² and electrochemical stability of 10,000 cycles in 0.5 M LiClO₄ + PC electrolyte due to its film thickness (584 nm) coupled with relatively larger porosity (8%). The optically passive behavior of such CeO₂-ZrO₂ film (with 5 vol.% Zr) is affirmed by its negligible transmission modulation irrespective of repeated Li⁺ and electron insertion/extraction. The coloration efficiency of spray deposited WO₃ thin film is found to enhance from 47 to 107 cm² C⁻¹ when CeO₂-ZrO₂ is coupled as a counter electrode with WO₃ in an electrochromic device (ECD). These films can be used as stable ‘passive’ counter electrodes in electrochromic smart windows as they retain full transparency in both the oxidized and reduced states and ever-reported longevity.     

New effective process to fabricate fast switching and high contrast electrochromic device based on viologen and Prussian blue/antimony tin oxide nano-composites with dark colored state

We developed a new electrochromic device by using compact Prussian blue (PB)/antimony tin oxide (ATO) nano-composites as anodic electrode and viologen anchoring on titanium dioxide (TiO₂) nano-particles as cathodic electrode. The anodic electrode was based on a transparent nanostructured ATO nano-particle film and was electro-deposited by Prussian blue to form compact Prussian blue/ATO nano-composites by means of galvanostatic electrodeposition process. Nanocrystalline TiO₂ thin films on conducting glass were modified with a mono-layer of viologen with two anchoring groups, which were much strongly adsorbed onto the surface of TiO₂ nano-particles. A polymer gel electrolyte sandwiched between the anodic and cathodic layers is used as the ionic transport layer. The 2.5 cm × 2.5 cm electrochromic device shows high contrast (64.8%, at 600 nm) very low transmittance at colored stage (0.1%, at 600 nm), fast switching time (600 and 720 ms for coloration and bleaching, respectively), high coloration efficiency of 912 cm² C⁻¹ at 600 nm and good stability. The enhanced performance of the electrochromic device can be attributed to the ATO nano-particles as inter-conductive materials.     

Oxygen vacancy enhanced room temperature ferromagnetism in Ar+ ion irradiated WO3 films

Room-temperature ferromagnetism in WO₃ films was enhanced by 130 keV Ar⁺ ion irradiation. The X-ray diffraction (XRD) and Raman measurements not only confirmed the monoclinic phase of the irradiated WO₃ films, but also showed that oxygen vacancy (V_O) defects were formed. The analysis of photoluminescence spectra strongly reconfirmed the presence of oxygen vacancy. X-ray photoelectron spectroscopy (XPS) measurements revealed that the contents of V_O and induced W⁵⁺ ions increase with increasing irradiation fluence and rich W⁵⁺-V_O defect complexes in the irradiated WO₃ films were formed. Further, the magnetic measurements exhibited a 2-fold enhancement in the saturation magnetization at the largest fluence of 3 × 10¹⁶ ions/cm². At lower irradiation fluence, a bound magnetic polaron model was proposed to reveal the ferromagnetic exchange coupling resulting from overlapping of V_O⁺ and V_O⁺⁺ defect states, and 5d¹ states of W⁵⁺. At high irradiation fluence, the carrier concentration reaches 1.02 × 10²⁰/cm³ and carrier-mediated exchange interactions result in the film's ferromagnetism.     

Effect of Ar/O2 ratio on double-sided electrochromic glass performance

This paper reports the qualities of WO₃ film and NiO film added to a counter electrode and their use in a double-sided electrochromic glass device. A mixture of argon and oxygen gasses with ratios of Ar/O₂ of 1.5, 2, 3, and 5 were used for the deposition of the working electrode of WO₃ film for EC glass. The structure of double-side EC glass consists of glass/ITO/NiO/electrolyte/WO₃/ITO/glass/ITO/WO₃/electrolyte/NiO/ITO/glass layers. The working electrode of WO₃ film controls the color presented, the applied voltage controls the color depth, and the counter electrode controls the transparency in the bleached state. The double-sided EC glass with double WO₃ films and double NiO films have faster coloration/bleaching rates than do single-sided EC glass. A mixture of Ar/O₂ ratio of 3.0 has the best coloration/bleaching property of the ratios tested. Compared to the single-sided EC glass, the double-sided EC glass has lower transmittance of about 72% and 6% than the 78% and 12% during coloration and bleaching states in the visible light region with +1.5 V and ?3.5 V applied.     

A tungsten-trioxide/prussian blue complementary electrochromic cell with a polymer electrolyte

Optically variable windows (smart windows), which control the transmission of light into buildings and vehicles, are of interest both for the control of solar heat load and for privacy applications. Such windows are likely to utilize electrochromic technology to achieve optical control. An electrochromic device consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a polymer electrolyte was made. The polymer electrolyte was prepared from polyvinyl alcohol doped with H₃PO₄ and KH₂PO₄ to accommodate the conduction of both H⁺ and K⁺ ions. The electrochromic WO₃ and PB films functioned in a complementary way such that the device was coloured or bleached by the application of –0.5 V or +0.5 V (WO₃ films vs PB film), respectively. The spectral characteristics of the coloured device confirmed the complementary colouration of WO₃ and PB in the device.     

Fast electrochromic response and high coloration efficiency of Al-doped WO3 thin films for smart window applications

Herein, vertically aligned Al:WO₃ nanoplate arrays were directly grown on ITO glass by a facile electrodeposition method and annealed in an argon atmosphere at 450 °C for 2h. Besides, this study reports the influence of Al doping on the electrochromic properties of WO₃ film in detail. Electrochromic properties such as cyclic voltammetry, chronoamperometry and optical transmittance were analyzed by protonic insertion/extraction in the 1 M LiClO₄/propylene carbonate as an electrolyte. The noticeable reversible color changing from transparent to the blue can be realized under the potential bias of ±1.0 V. XRD studies show that the produces films have highly crystalline structure. The EDS results clearly confirm the incorporation of Al element into the WO₃ network. From the optical absorption measurement, direct band gap energies are calculated as 3.62 and 3.34 eV for the WO₃ and the Al:WO₃, respectively. Compared to the as-prepared WO₃, the Al:WO₃ film exhibits outstanding electrochromic performance, including wide optical modulation (55.9%), high coloration efficiency (148.1 cm²C^-1), quick reaction kinetics (1.23 s and 1.01 s for colored and bleaching times, respectively), good rate capability and cycle durability at a wavelength of 632.8 nm. EIS measurements based on a charge-transfer resistance reveal that the dramatic improvement in the electrochemically active surface is achieved in the Al:WO₃ film. The increase of active surface facilitates transport kinetics for electron and ion intercalation/deintercalation within the porous metal oxide to enhance coloration efficiency. Comparatively energy levels of the WO₃ and the Al:WO₃ electrochromic films are also represented. From the Mott-Schottky studies, it is estimated that the donor concentration of the films is of the order of 10²⁰ cm⁻³. Taken together, these results not only provide important insight into a promising electrode for electrochromic displays applications, but also offer an economic and effective strategy for manufacturing of other doped metal oxide films.     

Characterization of luminescent SrAl2O4 films doped with terbium and europium ions deposited by ultrasonic spray pyrolysis technique

SrAl₂O₄, SrAl₂O₄:Tb³⁺ and SrAl₂O₄:Eu³⁺:Eu²⁺ films were synthesized by means of the ultrasonic spray pyrolysis technique. These samples, characterized by X-Ray Diffraction, showed the monoclinic phase of the strontium aluminate. Images of the surface morphology of these films were obtained by SEM and the chemical composition was measured by EDS and XPS. The photoluminescence and cathodoluminescence characteristics of the films were studied as a function of the terbium and europium concentrations. The optimal PL emission intensities were reached at 8?at% for terbium doped films and 6?at% for europium doped samples. The CL emission spectra for europium doped films showed the typical bands of Eu³⁺ ions and also a broadband centered at 525?nm which is attributed to Eu²⁺ ions. XPS measurements confirm the presence of Eu³⁺ and Eu²⁺ in europium doped SrAl₂O₄ films, without having been subjected to a reducing atmosphere. Chromatic diagrams exhibited green color for SrAl₂O₄:Tb³⁺ films, red and yellow colors for SrAl₂O₄:Eu³⁺:Eu²⁺ films. The PL decay curves were also obtained: the averaged decay time was 2.7?ms for SrAl₂O₄:Tb³⁺ films and 1.9?ms for SrAl₂O₄:Eu³⁺ films. Similar results were obtained by the stretched exponential model.     

In situ Raman microspectrometry investigation of electrochemical lithium intercalation into sputtered crystalline V2O5 thin films

We report here the first in situ Raman microspectrometry study of the electrochemical lithium insertion and de-insertion reaction into crystalline sputtered Li_xV₂O₅ thin films (0 ≤ x ≤ 0.94) in liquid electrolyte. We show that the orthorhombic Pmmn symmetry of the pristine material is kept upon lithium intercalation in the Li_xV₂O₅ film (0 ≤ x ≤  0.94). In fact, a subsequent and unexpected solid solution behaviour is evidenced, leading to the typical Raman fingerprint of the -LiV₂O₅ phase for the Li₀.₉₄V₂O₅ composition. After the charge, a complete recovery of the local structure is found, in good accord with the excellent electrochemical reversibility exhibited by these thin films. Such limited structural changes differ from that usually observed for the bulk material, which emphasizes the key role of the microstructure and morphology on the nature and magnitude of the structural rearrangements induced by the lithium insertion process.     

High rate capability and long-term cyclability of Li4Ti4.9V0.1O12 as anode material in lithium ion battery

Li₄Ti_4.9V_0.1O₁₂ nanometric powders were synthesized via a facile solid-state reaction method under inert atmosphere. XRD analyses demonstrated that the V-ions successfully entered the structure of cubic spinel-type Li₄Ti₅O₁₂ (LTO), reduced the lattice parameter and no impurities appeared. Compared with the pristine LTO, the electronic conductivity of Li₄Ti_4.9V_0.1O₁₂ powders is as high as 2.9 × 10⁻¹ S cm⁻¹, which should be attributed to the transformation of some Ti³⁺ from Ti⁴⁺ induced by the efficient V-ions doping and the deficient oxygen condition. Meanwhile, the results of XPS and EDS further proved the coexistence of V⁵⁺ and Ti³⁺ ions. This mixed Ti⁴⁺/Ti³⁺ ions can remarkably improve its cycle stability at high discharge–charge rates because of the enhancement of the electronic conductivity. The images of SEM showed that Li₄Ti_4.9V_0.1O₁₂ powders have smaller particles and narrower particle size distribution under 330 nm. And EIS indicates that Li₄Ti_4.9V_0.1O₁₂ has a faster lithium-ion diffusivity than LTO. Between 1.0 and 2.5 V, the electrochemical performance, especially at high rates, is excellent. The discharge capacities are as high as 166 mAh g⁻¹ at 0.5C and 117.3 mAh g⁻¹ at 5C. At the rate of 2C, it exhibits a long-term cyclability, retaining over 97.9% of its initial discharge capacity beyond 1713 cycles. These outstanding electrochemical performances should be ascribed to its nanometric particle size and high conductivity (both electron and lithium ion). Therefore, the as-prepared material is promising for such extensive applications as plug-in hybrid electric vehicles and electric vehicles.     

The distribution of lithium intercalated in V2O5 thin films studied by XPS and ToF-SIMS

The distribution of lithium in V₂O₅/V lower oxide duplex thin films prepared by thermal oxidation of V metal was analysed by XPS and ToF-SIMS after intercalation at 2.8 V versus Li/Li⁺ and de-intercalation at 3.8 V following cycling between 3.8 and 2.8 V in 1 M LiClO₄-PC. XPS analysis of the intercalated thin film evidenced a partial reduction (43 at.% V⁴⁺) of the V₂O₅ surface, the modification of its electronic structure and the presence of Li, consistent with the formation of the δ-Li_xV₂O₅ (0.9 ≤ x ≤ 1) phase. The Li in-depth distribution measured by ToF-SIMS shows a maximum in the outer layer of V₂O₅, but Li is also found at the oxide film/metal substrate interface indicating its diffusion across the inner layer of V lower oxides. The analyses performed after de-intercalation on the samples cycled 12, 120 and 300 times reveal the effect of aging on the trapping of lithium. A significant reduction (17-22 at.% V⁴⁺) of the V₂O₅ surface was measured after 300 cycles. The Li in-depth distribution shows a maximum at the interface between the outer layer of V₂O₅ and the inner layer of lower oxides. Aging favours the accumulation of lithium at this interface with a resulting enlarged distribution enriching the sub-surface of the outer layer of V₂O₅ and the inner layer of lower oxides after 300 cycles. Lithium is also found, but in smaller quantities, at the oxide film/metal substrate interface. Measurements performed in the non-electrochemically treated surface areas of the de-intercalated samples revealed the same type of modifications, evidencing the diffusion of lithium along the interfaces where it is trapped.     

The role of co-dopants on the luminescent properties of α-Al2O3:Mn4+ and BaMgAl10O17:Mn4+

Mn⁴⁺ doped aluminate materials with efficient red emission are promising components for warmer white light-emitting diodes. However, it still remains as a challenge on increasing its luminous efficiency. For Mn⁴⁺ doped aluminate phosphors, co-dopants such as Li⁺, Mg²⁺, Na⁺, Si⁴⁺, or Ge⁴⁺ ions are often added to tailor the photoluminescence properties of phosphors during preparing process. However, the role of the ions is still in debate. In this work we took BaMgAl₁₀O₁₇:Mn (BMA:Mn) and α-Al₂O₃:Mn as examples to study the effects of Li⁺, Mg²⁺, Na⁺, and Si⁴⁺ on their luminescent properties. The energy levels induced by the co-dopants and some possible intrinsic defects of hosts (Al₂O₃) were calculated using the first-principles method. It is found that the Mg²⁺ and Na⁺ ions, compared with Li⁺ and Si⁴⁺, can prefer to form hole-type defects which enhance the valence stability of Mn⁴⁺ and thus enhance the emission intensity of the as-prepared phosphors.     

The effect of Li+ incorporation in Yb3+-Nd3+ co-doped CaF2 phosphors over the NIR photoluminescence emission excited under visible light

The structural and optical characteristics of Nd³⁺-Yb³⁺ doped CaF₂ phosphors with and without the addition of Li⁺ ions are described in this work. The phosphors synthetized by hydrothermal and co-precipitation methods showed near-infrared (NIR) luminescence emission associated with inter-electronic transition of the Yb³⁺ ion in the range of 900–1050 nm via energy transfer process from Nd³⁺ ions under visible light excitation. The addition of Li⁺ to these phosphors resulted in an improvement of the NIR luminescence intensity by a factor up to 5. The effect of the incorporation of Li⁺ ions into the CaF₂ crystallite structure, the reduction of luminescence quenching states, as well as the energy transfer mechanism involved are discussed.     

Flexible electrochromic device based on poly (3,4-(2,2-dimethylpropylenedioxy)thiophene)

In this study, the design, fabrication and characterization of a flexible electrochromic device based on indium tin oxide (ITO) coated polyethylene terephthalate (PET) plastic is discussed. The working electrochromic material film was poly (3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProDOT-Me₂), while the counter layer of the device was vanadium oxide titanium oxide (V₂O₅/TiO₂) composite film, which serves as an ion storage layer. A solution type electrolyte was used as the ionic transport layer and was sandwiched between the working and counter layers. The device exhibited tuneable light transmittance between transparent and deep blue color, with a maximum contrast ratio at 580 nm wavelength. Other important properties, such as switching speed, life time, and coloration efficiency have been improved.     

Dual regulation of Li+ migration of Li6.4La3Zr1.4M0.6O12 (M = Sb,Ta, Nb) by bottleneck size and bond length of M−O

Bottleneck size is the minimum Li⁺ migration channel of Li₇La₃Zr₂O₁₂ (LLZO) and it greatly influences the Li⁺ conductivity. Doping different elements on the Zr site of LLZO can adjust the bottleneck size and improve the Li⁺ conductivity. However, the regulation mechanism is not clear. In this work, Li_6.4La₃Zr_1.4M_0.6O₁₂ (M = Sb, Ta, Nb) has been prepared and the bottleneck size has been adjusted by doping different pentavalent ions. The results manifest that the cell parameter and bottleneck size decrease with the rise of the radius of doped pentavalent ions. This is because larger pentavalent ion leads to larger bond length of M–O, and weaker covalent component between M⁵⁺ and O^2-, corresponding, the formal charge on the M⁵⁺ become larger, and the bond length of La–O slightly decreases due to the coulomb repulsion between La³⁺ and M⁵⁺ increase. While, the activation energy drop firstly and then rise with the rise of bottleneck size because of the migration of Li⁺ not only relate to the size of the migration channel but also to the strength of M–O covalent bonding. The bottleneck size and bond length of M–O synergistically affect the migration of Li⁺.     

High-performance Li4Ti5−xVxO12 (0 ≤ x ≤ 0.3) as an anode material for secondary lithium-ion battery

Powders of spinel Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were successfully synthesized by solid-state method. The structure and properties of Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were examined by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electronic microscope (SEM), galvanostatic charge–discharge test and cyclic voltammetry (CV). XRD shows that the V⁵⁺ can partially replace Ti⁴⁺ and Li⁺ in the spinel and the doping V⁵⁺ ion does almost not affect the lattice parameter of Li₄Ti₅O₁₂. Raman spectra indicate that the Raman bands corresponding to the Li–O and Ti–O vibrations have a blue shift due to the doping vanadium ions, respectively. SEM exhibits that Li₄Ti_5−xV_xO₁₂ (0.05 ≤ x ≤ 0.25) samples have a relative uniform morphology with narrow size distribution. Charge–discharge test reveals that Li₄Ti_4.95V_0.05O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 1.0 and 2.0 V; Li₄Ti_4.9V_0.1O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 0.0 and 2.0 V or between 0.5 and 2.0 V. This excellent cycling capability is mainly due to the doping vanadium. CV reveals that electrolyte starts to decompose irreversibly below 1.0 V, and SEI film of Li₄Ti₅O₁₂ was formed at 0.7 V in the first discharge process; the Li₄Ti_4.9V_0.1O₁₂ sample has a good reversibility and its structure is very advantageous for the transportation of lithium-ions.