Lithium intercalation and deintercalation processes in Li4Ti5O12 and LiFePO4

We have studied the kinetics of electrochemical lithium intercalation and deintercalation processes at different currents in lithium iron phosphate and lithium titanate based composite materials containing fine carbon particles. The results demonstrate that lithium intercalation and deintercalation processes in the electrode materials are characterized by an overvoltage: 4 and 2 mV, respectively, for a cell with a lithium titanate based electrode and 4 and 24 mV for a lithium iron phosphate based cell. Li₄Ti₅O₁₂ solubility in Li₇Ti₅O₁₂ is 1.1% (the limit of the solid solution at Li_4.03Ti₅O₁₂), and Li₇Ti₅O₁₂ solubility in Li₄Ti₅O₁₂ is 2.5% (the limit of the solid solution at Li_6.93Ti₅O₁₂). The conductivity of the phosphate and titanate solid solutions involved in the lithium intercalation and deintercalation processes has been determined.     

Novel Li4Ti5O12/Sn nano-composites as anode material for lithium ion batteries

Li₄Ti₅O₁₂/Sn nano-composites have been prepared as anode material for lithium ion batteries by high-energy mechanical milling method. Structure of the samples has been characterized by X-ray diffraction (XRD), which reveals the formation of phase-pure materials. Scanning electron microscope (SEM) and transmission electron microscope (TEM) suggests that the primary particles are around 100 nm size. The local environment of the metal cations is confirmed by Fourier transform infrared (FT-IR) and the X-ray photoelectron spectroscopy (XPS) confirms that titanium is present in Ti⁴⁺ state. The electrochemical properties have been evaluated by galvanostatic charge/discharge studies. Li₄Ti₅O₁₂/Sn-10% composite delivers stable and enhanced discharge capacity of 200 mAh g⁻¹ indicates that the electrochemical performance of Li₄Ti₅O₁₂/Sn nano-composites is associated with the size and distribution of the Sn particles in the Li₄Ti₅O₁₂ matrix. The smaller the size and more homogeneous dispersion of Sn particles in the Li₄Ti₅O₁₂ matrix exhibits better cycling performance of Li₄Ti₅O₁₂/Sn composites as compared to bare Li₄Ti₅O₁₂ and Sn particles. Further, Li₄Ti₅O₁₂ provides a facile microstructure to fairly accommodate the volume expansion during the alloying and dealloying of Sn with lithium.     

Dispersed materials for rechargeable lithium batteries: Reactive and non-reactive grinding

Reactive and non-reactive grinding has been used to prepare high dispersed lithium-transition metal cathode materials (LiMn₂O₄, LiCoO₂, LiV₃O₈, Li₃Fe₂(PO₄)₃, LiTi₂(PO₄)₃) and inorganic solid state Li-ion electrolytes (Li_1.3Al_0.3Ti_1.7(PO₄)₃) for rechargeable lithium batteries. Submicron particle size and the presence of cationic vacancies and cationic disordering positively influence electrochemical properties of as prepared cathodes, leading to larger practical capacity and stability upon intercalation-deintercalation of lithium ions. However, the advantages are observed only when the first electrochemical step is an insertion of Li⁺ ions (Li battery discharge). The conductivity of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ lithium ion electrolyte prepared by using MA was of 2-3 order of magnitude higher than that for nonactivated sample owing to the absence of non-conductive impurities and lower grain boundary resistance.     

Lithium-Battery Anode Gains Additional Functionality for Neuromorphic Computing through Metal–Insulator Phase Separation

Specialized hardware for neural networks requires materials with tunable symmetry, retention, and speed at low power consumption. The study proposes lithium titanates, originally developed as Li-ion battery anode materials, as promising candidates for memristive-based neuromorphic computing hardware. By using ex- and in operando spectroscopy to monitor the lithium filling and emptying of structural positions during electrochemical measurements, the study also investigates the controlled formation of a metallic phase (Li₇Ti₅O₁₂) percolating through an insulating medium (Li₄Ti₅O₁₂) with no volume changes under voltage bias, thereby controlling the spatially averaged conductivity of the film device. A theoretical model to explain the observed hysteretic switching behavior based on electrochemical nonequilibrium thermodynamics is presented, in which the metal-insulator transition results from electrically driven phase separation of Li₄Ti₅O₁₂ and Li₇Ti₅O₁₂. Ability of highly lithiated phase of Li₇Ti₅O₁₂ for Deep Neural Network applications is reported, given the large retentions and symmetry, and opportunity for the low lithiated phase of Li₄Ti₅O₁₂ toward Spiking Neural Network applications, due to the shorter retention and large resistance changes. The findings pave the way for lithium oxides to enable thin-film memristive devices with adjustable symmetry and retention.     

Enhanced cycling stability of microsized LiCoO2 cathode by Li4Ti5O12 coating for lithium ion battery

The effect of Li₄Ti₅O₁₂ (LTO) coating amount on the electrochemical cycling behavior of the LiCoO₂ cathode was investigated at the high upper voltage limit of 4.5 V. Li₄Ti₅O₁₂ (≤5 wt.%) is not incorporated into the host structure and leads to formation of uniform coating. The cycling performance of LiCoO₂ cathode is related with the amount of Li₄Ti₅O₁₂ coating. The initial capacity of the LTO-coated LiCoO₂ decreased with increasing Li₄Ti₅O₁₂ coating amount but showed enhanced cycling properties, compared to those of pristine material. The 3 wt.% LTO-coated LiCoO₂ has the best electrochemical performance, showing capacity retention of 97.3% between 2.5 V and 4.3 V and 85.1% between 2.5 V and 4.5 V after 40 cycles. The coulomb efficiency shows that the surface coating of Li₄Ti₅O₁₂ is beneficial to the reversible intercalation/de-intercalation of Li⁺. LTO-coated LiCoO₂ provides good prospects for practical application of lithium secondary batteries free from safety issues.     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

Lithium insertion into Li2Ti3O7

Li₂Ti₃O₇ with the ramsdellite-type structure undergoes lithium insertion reactions with n-BuLi. Li_2+xTi₃O₇ phases form with x = 0.5 and 1.0 at room temperature and at 50°C, respectively. The ESR spectrum of Li₃Ti₃O₇ confirms the partial reduction of Ti⁴⁺ ions to Ti³⁺. The electrical conductivity of the fully lithiated phase is several orders of magnitude higher than that of the host compound, suggesting charge hopping in the mixed valent lithiated compound.     

Intercalating Ti2Nb14O39 Anode Materials for Fast‐Charging,High‐Capacity and Safe Lithium–Ion Batteries

Ti–Nb–O binary oxide materials represent a family of promising intercalating anode materials for lithium‐ion batteries. In additional to their excellent capacities (388–402 mAh g^–1), these materials show excellent safety characteristics, such as an operating potential above the lithium plating voltage and minimal volume change. Herein, this study reports a new member in the Ti–Nb–O family, Ti₂Nb₁₄O₃₉, as an advanced anode material. Ti₂Nb₁₄O₃₉ porous spheres (Ti₂Nb₁₄O₃₉‐S) exhibit a defective shear ReO₃ crystal structure with a large unit cell volume and a large amount of cation vacancies (0.85% vs all cation sites). These morphological and structural characteristics allow for short electron/Li⁺‐ion transport length and fast Li⁺‐ion diffusivity. Consequently, the Ti₂Nb₁₄O₃₉‐S material delivers significant pseudocapacitive behavior and excellent electrochemical performances, including high reversible capacity (326 mAh g^?1 at 0.1 C), high first‐cycle Coulombic efficiency (87.5%), safe working potential (1.67 V vs Li/Li⁺), outstanding rate capability (223 mAh g^–1 at 40 C) and durable cycling stability (only 0.032% capacity loss per cycle over 200 cycles at 10 C). These impressive results clearly demonstrate that Ti₂Nb₁₄O₃₉‐S can be a promising anode material for fast‐charging, high capacity, safe and stable lithium‐ion batteries.     

Li-substituted P2-Na0.66LixMn0.5Ti0.5O2 as an advanced cathode material and new “bi-functional” electrode for symmetric sodium-ion batteries

In this study, we have introduced the layered materials P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ as cathode materials for sodium ion batteries (SIBs), and then P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ was employed as bi-functional electrode in SIBs. The structural stability and electrochemical properties of P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ were promoted by inserting lithium. The Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ as a cathode material can exhibit a reversible discharge capacity of 128?mA?h?g^?1 at 0.1C after 100 cycles, and even deliver 72?mA?h?g^?1 at 5C. Interestingly, the P2-Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ is studied as a “bi-functional” active material for symmetric sodium-ion batteries. This novel symmetric full cell exhibits 65?mA?h?g^?1 at a current density of 20?mA?g^?1.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

Synthesis and electrochemical characterisation of electrospun lithium titanate ultrafine fibres

The phase pure spinel lithium titanate (Li₄Ti₅O₁₂) in the form of ultrafine fibre was synthesised by the combination of sol–gel and electrospinning techniques. The electrospinning process for the preparation of Li₄Ti₅O₁₂ precursor was optimised to get bead-free fibrous mat with uniform thickness. Crystalline Li₄Ti₅O₁₂ in the form of ultrafine fibre was synthesised by the calcination of the precursor at 800 °C in air for 4 h. The material was characterised by X-ray diffraction, Raman spectroscopy and scanning electron microscopy and subsequently evaluated as an electrode active material using Li metal as a counter electrode. The material exhibited a first cycle specific capacity of 154 mAh g^?1 with good rate capability and cyclability.     

Controlled Ag-driven superior rate-capability of Li4Ti5O12 anodes for lithium rechargeable batteries

The morphology and electronic structure of a Li₄Ti₅O₁₂ anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li₄Ti₅O₁₂ nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional (1D) morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li₄Ti₅O₁₂ nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li₄Ti₅O₁₂ nanofibers, due to the Ag nanoparticles (<5 nm), which are mainly distributed at interfaces between Li₄Ti₅O₁₂ primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li₄Ti₅O₁₂ nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.      

Lithium Titanate Cuboid Arrays Grown on Carbon Fiber Cloth for High‐Rate Flexible Lithium‐Ion Batteries

High‐rate performance flexible lithium‐ion batteries are desirable for the realization of wearable electronics. The flexibility of the electrode in the battery is a key requirement for this technology. In the present work, spinel lithium titanate (Li₄Ti₅O₁₂, LTO) cuboid arrays are grown on flexible carbon fiber cloth (CFC) to fabricate a binder‐free composite electrode (LTO@CFC) for flexible lithium‐ion batteries. Experimental results show that the LTO@CFC electrode exhibits a remarkably high‐rate performance with a capacity of 105.8 mAh g^?1 at 50C and an excellent electrochemical stability against cycling (only 2.2% capacity loss after 1000 cycles at 10C). A flexible full cell fabricated with the LTO@CFC as the anode and LiNi_0.5Mn_1.5O₄ coated on Al foil as the cathode displays a reversible capacity of 109.1 mAh g^?1 at 10C, an excellent stability against cycling and a great mechanical stability against bending. The observed high‐rate performance of the LTO@CFC electrode is due to its unique corn‐like architecture with LTO cuboid arrays (corn kernels) grown on CFC (corn cob). This work presents a new approach to preparing LTO‐based composite electrodes with an architecture favorable for ion and electron transport for flexible energy storage devices.     

Effect of particle size on the conductive and electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>

We have studied the effect of final annealing temperature on the formation of lithium zinc titanate, its electrical conductivity, and its electrochemical performance. Li₂ZnTi₃O₈ has been shown to form in a wide range of annealing temperatures, from 673 to 1073 K. Its particle size increases systematically with increasing annealing temperature, whereas its conductivity decreases. The highest electrochemical capacity at low currents is offered by the materials annealed at 773 and 873 K, and the highest cycling stability is offered by the material prepared at 873 K.     

尖晶石型 Li4Ti5O12电极材料的合成与电化学性能研究

分别采用三种方法合成了尖晶石型Li4Ti5O12电极材料.考察了不同的工艺条件对目标材料性能的影响.应用XRD、SEM、LSD、CV、AC impedance以及恒流充放电测试等手段对目标材料进行了结构表征和性能测试.结果表明,利用溶剂分散湿磨可以在较短的时间内得到纯相的Li4Ti5O12.葡萄糖的加入能够提高Li4Ti5O12导电性,使材料具有良好的嵌锂性能.在0.2C倍率下进行充放电测试,其可逆比容量超过160mAh·g-1,44次循环后,容量没有明显衰减.Li4Ti5O12/LiFePO4实验电池测试表明Li4Ti5O12是可选的锂离子负极材料.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Enhanced electrochemical properties of nano-Li3PO4 coated on the LiMn2O4 cathode material for lithium ion battery at 55 °C

The electrochemical performance of LiMn₂O₄ is improved by the surface coating of nano-Li₃PO₄ via ball milling and high-temperature heating. The Li₃PO₄-coated LiMn₂O₄ powders are characterized by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). At 55 °C, capacity retention of 85% after 100 cycles was obtained for Li/Li₃PO₄-coated LiMn₂O₄ electrode at 1C rate, while that of pristine sample was only 65.6%. The Li/Li₃PO₄-coated LiMn₂O₄ electrode also showed improved rate capability especially at high C rates. At 5C-rates, the delivered capacities of pristine and Li₃PO₄-coated LiMn₂O₄ electrodes were 80.7 mAh/g and 112.4 mAh/g, respectively. The electrochemical impedance spectroscopy (EIS) indicates that the charge transfer resistance for Li/Li₃PO₄-coated LiMn₂O₄ cell was reduced compared to Li/LiMn₂O₄ cell.     

Sol-gel titania modified with Ba and Li atoms for catalytic combustion

Samples of compounds in the ternary system BaO-Li₂O-TiO₂ were synthesized by using the sol-gel method at pH 3 and pH 9, and the calcination temperatures of 600 and 800°C in the region of solid solutions which can form the ideal composition Ba₃Li₂Ti₈O₂₀. The X-ray diffraction patterns of the samples showed a mixture of three crystalline phases, the main one was isostructural with the ternary phase Ba₃Li₂Ti₈O₂₀; the other two were BaTiO₃ and Li₂TiO₃. By refining the structures with the Rietveld technique, a good fit to the experimental diffraction pattern was found, showing the partial substitution of Ti by Li in the Ba₂Ti₆O₁₃ structure. The catalytic activity in methane combustion under the stoichiometric mixture of dilute CH₄/O₂ was higher for the samples calcined at 600°C, where the Ba₃Li₂Ti₈O₂₀ ternary compound was formed. This high activity can be related with the large specific surface area, presence of anatase and low crystallite size.     

Effect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12

Crystalline Li₄Ti₅O₁₂ is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li₄Ti₅O₁₂ particles after calcination at 800 °C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li⁺ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.