Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

In-situ imaging of Li-ion migration at interfaces in an all solid Li-ion battery

We investigated the migration of Li ions at an interface between a Li_xTi₅O₁₂ (LTO) and a solid electrolyte in an all-solid Li-ion battery. The optical reflection of LTO changes with variations in the Li content because the band structures of LTO vary with the changes in the Li content. This enables us to observe Li-ion migration in the interface between the LTO and the solid electrolyte using an optical microscope. To observe the LTO particles optically, they were coated on an indium tin oxide on a glass substrate. Variations in Li migration caused by charging/discharging were clearly observed through the changes in the reflection of the LTO. LTO changed between an insulator Li₄Ti₅O₁₂ of the spinel structure and a conductor Li₇Ti₅O₁₂ of the rock-salt structure according to the changes in the Li content. The spinel LTO has a bandgap energy of approximately 2 eV. When electron–hole pairs were generated, electric strains were produced. Surface force microscopy detected the strains and imaged the distribution of lithiation/delithiation of LTO. Interfacial conduction between a sputtered LTO and Li₃PO₄ particles was imaged with high spatial resolution.     

Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion Batteries

Li₄Ti₅O₁₂ (LTO) nanoparticles were prepared by gel‐hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid‐state reaction or by sol‐gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X‐ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge‐discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li₄Ti₅O₁₂ anode material prepared through gel‐hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g^?1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g^?1. The gel‐hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells.     

A Porous Mooncake-Shaped Li4Ti5O12 Anode Material Modified by SmF3 and Its Electrochemical Performance in Lithium Ion Batteries

Reasonably designing and synthesizing advanced electrode materials is significant to enhance the electrochemical performance of lithium ion batteries (LIBs). Herein, a metal–organic framework (MOF, Mil-125) was used as a precursor and template to successfully synthesize the porous mooncake-shaped Li₄Ti₅O₁₂ (LTO) anode material assembled from nanoparticles. Even more critical, SmF₃ was used to modify the prepared porous mooncake-shaped LTO material. The SmF₃-modified LTO maintained a porous mooncake-shaped structure with a large specific surface area, and the SmF₃ nanoparticles were observed to be attach on the surface of the LTO material. It has been proven that the SmF₃ modification can further facilitate the transition from Ti⁴⁺ to Ti³⁺, reduce the polarization of electrode, decrease charge transfer impedance (R_ct) and solid electrolyte interface impedance (R_sei), and increase the lithium ion diffusion coefficient (D_Li), thereby enhancing the electrochemical performance of LTO. Therefore, the porous mooncake-shaped LTO modified using 2 wt % SmF₃ displays a large specific discharge capacity of 143.8 mAh g⁻¹ with an increment of 79.16 % compared to pure LTO at a high rate of 10 C (1 C=170 mAh g⁻¹), and shows a high retention rate of 96.4 % after 500 cycles at 5 C-rate.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

High‐Throughput Production of Zr‐Doped Li4Ti5O12 Modified by Mesoporous Libaf3 Nanoparticles for Superior Lithium and Potassium Storage

Li₄Ti₅O₁₂ is a promising anode for lithium‐ion batteries due to its zero‐strain properties. However, its low conductivity has greatly affected its rate performance. At the same time, the electrolyte decomposition during cycling also needs to be solved, especially at low cut‐off voltage. Herein, using a high‐throughput two‐step method, we synthesized Zr‐doped LTO modified by mesoporous LiBaF₃ nanoparticles for alkali‐ion storage. The doping of Zr can enhance the electronic conductivity and facilitate the rate performance. Meanwhile, the coating of mesoporous LiBaF₃ nanoparticles can form a mesoporous surface with large pore size (ca. 3–10 nm), which can benefit the alkali ion diffusion and simultaneously restrain the formation of an excess solid electrolyte interface to a reasonable range. The optimized material is used as an advanced anode for both lithium‐ion and potassium‐ion batteries, and good battery behavior including high‐rate performance and high stability is achieved.     

The synergic effects of Ca and Sm co-doping on the crystal structure and electrochemical performances of Li4-xCaxTi5-xSmxO12 anode material

Li₄Ti₅O₁₂ as the well-known “zero strain” anode material for lithium ion batteries (LIBs) suffers from low intrinsic ionic and electronic conductivity. The strategy of lattice doping has been widely taken to relieve the intrinsic issues. But the roles of the dopants are poorly understood. Herein, we propose to modulate the crystal structure and improve the electrochemical performance of Li₄Ti₅O₁₂ by substituting Li and Ti with Ca and Sm, respectively. The roles of Ca and Sm on the crystal structure and electrochemical performances have been comprehensively investigated by means of X-ray diffraction (XRD), neutron diffraction (ND) and electrochemical analysis. The Rietveld refinement of ND data indicate that Ca and Sm prefer to take 8a site (tetrahedral site) and 16d site (octahedral site), respectively. Li_3.98Ca_0.02Ti_4.98Sm_0.02O₁₂ has the longer Li1-O bond and shorter Ti-O bond length which reduces Li⁺ migration barrier as well as enhances the structure stability. Ca-Sm co-doping also alleviates the electrode polarization and enhances the reversibility of oxidation and reduction. In compared to bare Li₄Ti₅O₁₂ and Li_3.95Ca_0.05Ti_4.95Sm_0.05O₁₂, Li_3.98Ca_0.02Ti_4.98Sm_0.02O₁₂ electrode shows the lower charge transfer resistance, higher Li⁺ diffusion coefficient, better rate capability and cycling performance. The proposed insights on the roles of dopants are also instructive to design high performance electrode materials by lattice doping.     

Electrochemical properties of spinel Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles prepared via a low-temperature solid route

Spinel phase Li₄Ti₅O₁₂ (s-LTO) with an average primary particle size of 150 nm was synthesised via a solid state route by calcining a precursor mixture at 600 °C. The precursor was prepared from a stoichiometric mixture of TiO₂ nanoparticles and an ethanolic solution of Li acetate and activated by ball-milling. Effects of the calcination temperature and atmosphere are examined in relation to the coexistence of impurity phases by X-ray diffraction and ⁶Li MAS NMR. The charge capacity of s-LTO, determined from cyclic voltammogram at a scan rate of 0.1 mV/s, was 142 mAh/g. The capacity of our optimised material is superior to that of commercially available spinel (a-LTO), despite the considerably smaller BET-specific surface area of the former. The superior properties of our material were also demonstrated by galvanostatic charging/discharging. From these observations, we conclude that the presented low-temperature solid state synthesis route provides LTO with improved electrochemical performance.     

Li4Ti5O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices

Spinel Li₄Ti₅O₁₂, known as a zero‐strain material, is capable to be a competent anode material for promising applications in state‐of‐art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li₄Ti₅O₁₂ offers a high operating potential of ∼1.55 V vs Li/Li⁺, negligible volume expansion during Li⁺ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li₄Ti₅O₁₂ been presented, there still remains the issue of Li₄Ti₅O₁₂ suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li₄Ti₅O₁₂ will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self‐supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li₄Ti₅O₁₂‐based energy storage device and deliver a deep inspiration.     

Synthesis and electrochemical performances of Li4Ti4.95Zr0.05O12/C as anode material for lithium-ion batteries

Spinel Li₄Ti_5 − x Zr _x O₁₂/C (x = 0, 0.05) were prepared by a solution method. The structure and morphology of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances including charge–discharge (0–2.5 V and 1–2.5 V), cyclic voltammetry, and ac impedance were also investigated. The results revealed that the Li₄Ti_4.95Zr_0.05O₁₂/C had a relatively smaller particle size and more regular morphology than that of Li₄Ti₅O₁₂/C. Zr⁴⁺ doping enhanced the ability of lithium-ion diffusion in the electrode. It delivered a discharge capacity 289.03 mAh g⁻¹ after 50 cycles for the Zr⁴⁺-doped Li₄Ti₅O₁₂/C while it decreased to 264.03 mAh g⁻¹ for the Li₄Ti₅O₁₂/C at the 0.2C discharge to 0 V. Zr⁴⁺ doping did not change the electrochemical process, instead enhanced the electronic conductivity and ionic conductivity. The reversible capacity and cycling performance were effectively improved especially when it was discharged to 0 V.     

Steady-state polarization measurements of lithium insertion electrodes for high-power lithium-ion batteries

Steady-state polarization measurements of lithium titanium oxide (LTO; Li[Li_1/3Ti_5/3]O₄) were carried out using the 0-V lithium-ion cells consisting of two identical LTO-electrodes with a parallel-plate symmetrical electrode configuration. The sinusoidal voltage with the peak amplitude of 1.0 V was imposed at 0.1 Hz upon the 0-V cells and the current response was measured as a function of time. The steady-state polarization, obtained by plotting the current versus applied voltage, was linear in current up to approximately 60 mA cm^?2 or 4 A g^?1 based on the LTO weight and suggested the resistance polarization only for the lithium insertion electrode of the LTO. The method was also applied to lithium aluminum manganese oxide (LAMO; Li[Li_0.1Al_0.1Mn_1.8]O₄) and the resistance polarization of the LAMO-electrode was determined for currents up to approximately 25 mA cm^?2 or 2 A g^?1 based on the LAMO weight. The validity of the results was examined for the polarization measurements of the 2.5-V lithium-ion battery consisting of LTO and LAMO, and the significance of the polarization measurements of lithium insertion electrodes for high-power applications was discussed.     

Phase transition in ceria alumina

Al-doped CeO₂ samples were prepared by conventional solid state reaction. The electrical conductivity of CeO₂ doped with Al₂O₃ has been studied at different temperatures for various molar ratios. The isothermal conductivity increases with dopant concentration due to the vacancy migration phenomenon induced by doping. It has been found that the conductivity increases and shows a jump from 450 to 520°C due to the phase transition of ceria from cubic to orthorhombic type. A slight deflection is seen for 0.5 and 0.6 moles of alumina at about 250°C due to its phase transition from γ to α type. AC impedance measurements proved that the oxide ion conductivity predominantly arises from the grain and grain boundary contribution as two well defined semi-circles are clearly seen. The sample characterization and the study of phase transition changes were done by using X-ray diffraction analysis, Fourier transform infrared spectral and differential scanning calorimetry (DSC) measurements. On increasing the concentration of dopant, the transition temperature shifts towards lower side which is confirmed by DSC as well as conductivity measurements.     

First-principles calculations of the Ti-doping effects on layered NaNiO2 cathode materials for advanced Na-ion batteries

The NaNiO₂ structure is a promising cathode material for sodium ion batteries due to its reasonably high capacity (～120 mAh/g), environmental friendliness and the low cost of required raw materials. First-principles calculations have been carried out to study the Ti ions doped NaNi_1-xTi_xO₂ (x = 0, 0.037, 0.056, 0.083 and 0.167) phases. Results show that Ti doping can lead to a higher average intercalation voltage and improved electronic conductivity. The optimized NaNi_0.917Ti_0.083O₂ sample can effectively suppress the volume change of the unit cell by 4% upon full desodiation and an increased ion mobility was found in this sample by nudged elastic band calculation. We suggest that the NaNi_0.917Ti_0.083O₂ cathode could be a promising candidate for Na-ion batteries.     

Electrophysical properties of layered perovskites LnBaCo<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5 + δ</Subscript> (Ln = Sm,Nd) for solid oxide fuel cells

The influence of doping with copper oxide on the phase composition, electric conductivity, and linear thermal expansion coefficient (LTEC) of SmBaCo₂O_{5 + δ} and NdBaCo₂O_{5 + δ} was studied. The sample homogeneity region has been determined with using XRD. The samples conductivity decreased as the dopant concentration increased. The character of the temperature dependence of conductivity changed at high copper contents. In a reductive atmosphere, the conductivity of the samples at first decreased and then remained constant. The linear thermal expansion coefficient decreased as the amount of the incorporated dopant increased.     

钛掺杂钙钛矿制备高效率钙钛矿太阳能电池

采用钛离子掺杂钙钛矿薄膜的方法修饰钙钛矿晶界缺陷。研究表明钛离子富集在晶界处,有效地钝化了晶界缺陷,同时有助于连续、平整、高质量薄膜的形成。经过钛离子掺杂后的钙钛矿太阳能电池电流(JSC)达到22.3 mA·cm~(-2),开路电压(VOC)达1.1 V,填充因子(FF)高达72.4%,光电转换效率(PCE)优化至17.4%,远高于未掺杂钙钛矿太阳能电池。     

Phosphorus-Doping-Induced Surface Vacancies of 3D Na2Ti3O7 Nanowire Arrays Enabling High-Rate and Long-Life Sodium Storage

Sodium-ion batteries have attracted interest as an alternative to lithium-ion batteries because of the abundance and cost effectiveness of sodium. However, suitable anode materials with high-rate and stable cycling performance are still needed to promote their practical application. Herein, three-dimensional Na₂Ti₃O₇ nanowire arrays with enriched surface vacancies endowed by phosphorus doping are reported. As anodes for sodium-ion batteries, they deliver a high specific capacity of 290 mA h g⁻¹at 0.2 C, good rate capability (50 mA h g⁻¹at 20 C), and stable cycling capability (98 % capacity retention over 3100 cycles at 20 C). The superior electrochemical performance is attributed to the synergistic effects of the nanowire arrays and phosphorus doping. The rational structure can provide convenient channels to facilitate ion/electron transport and improve the capacitive contributions. Moreover, the phosphorus-doping-induced surface vacancies not only provide more active sites but also improve the intrinsic electrical conductivity of Na₂Ti₃O₇, which will enable electrode materials with excellent sodium storage performance. This work may provide an effective strategy for the synthesis of other anode materials with fast electrochemical reaction kinetics and good sodium storage performance.     

Synthesis of W‐doped TiO2 by low‐temperature hydrolysis: Effects of annealing temperature and doping content on the surface microstructure and photocatalytic activity

A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase W_yTi_1‐yO₂ appeared for 5.00 wt% W‐TiO₂ annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti³⁺, Ti⁴⁺, O^2?, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO₂ annealed at 700 °C.     

A Shuttle-Free Solid-State Cu−Li Battery Based on a Sandwich-Structured Electrolyte

Cu−Li batteries leveraging the two-electron redox property of Cu can offer high energy density and low cost. However, Cu−Li batteries are plagued by limited solubility and a shuttle effect of Cu ions in traditional electrolytes, which leads to low energy density and poor cycling stability. In this work, we rationally design a solid-state sandwich electrolyte for solid-state Cu−Li batteries, in which a deep-eutectic-solvent gel with high Cu-ion solubility is devised as a Cu-ion reservoir while a ceramic Li_1.4Al_0.4Ti_1.6(PO₄)₃ interlayer is used to block Cu-ion crossover. Because of the high ionic conductivity (0.55 mS cm⁻¹ at 25 °C), wide electrochemical window (>4.5 V vs. Li⁺/Li), and high Cu ion solubility of solid-state sandwich electrolyte, a solid-state Cu−Li battery demonstrates a high energy density of 1 485 Wh kg_Cu⁻¹and long-term cyclability with 97 % capacity retention over 120 cycles. The present study lays the groundwork for future research into low-cost solid-state Cu−Li batteries.