Evaluation of Cathode Electrodes in Lithium-Ion Battery: Pitfalls and the Befitting Counter Electrode

Boosting energy density and reducing the cost of lithium-ion batteries are critical to accelerating their applications in transportation and grid energy storage. Battery design with increasing electrode thickness is an effective way to combine higher energy density and lower cost. However, the evaluation of electrodes with increased thickness is challenging and requires more attention. Here, some pitfalls are to be avoided and a reasonable evaluation strategy is provided for cathode electrodes regarding the choice of counter electrode. Though as the most common counter electrode, lithium metal anode is actually not suitable for evaluating cycling performance, which exhibits fast cell capacity decline, especially, in the case of areal capacity higher than 2 mAh cm^-2 . Two commercial anode materials, graphite and Li₄ Ti₅ O₁₂ (LTO) as the potential alternatives, are systematically evaluated and compared, demonstrating LTO as the more suitable choice. The thick cathode electrode coupled with LTO exhibits excellent rate capability, stable cycling performance, and easy interpretation of charge/discharge profile. The relationship between cell balance and battery performance is further analyzed in detail. This strategy enables a reasonable evaluation of the cathode electrodes and advances the designing of thick electrode.

Dual-Band Electrochromic Optical Modulation Improved by a Precise Control of Lithium Content in Li4+xTi5O12

Dual-band electrochromic smart windows that can dynamically and independently control incident solar irradiation and visible light are envisioned as intelligent technology to reduce power consumption of buildings. However, there is still a great challenge to put the dual-band electrochromic technology into practice due to some limits in material systems and preparation techniques. Herein, a new electrochromic material of Li₄Ti₅O₁₂ is developed to implement the dual-band optical modulation behavior, which could be further improved by a precise control of the lithium content in the active material. It could separately modulate the light and heat based on regulation of the transmittance of visible and near-infrared light. This enables Li₄Ti₅O₁₂ to operate in three distinct modes of bright, cool, and dark, so as to meet various indoor needs. The optical transmittance contrast reaches over 60% at both visible- and near-infrared-light regions between different modes, and a large range of apparent temperature adjustments (7 °C) could be achieved. The prototype device based on dual-band electrochromic Li₄Ti₅O₁₂ is further developed into a smart window of a house model, which exhibits good optical and thermal modulation behaviors in response to a high-temperature environment. This work provides a new material system for achieving dual-band electrochromic optical modulation toward smart energy-saving window applications.

Investigation of Water-Soluble Binders for LiNi0.5 Mn1.5 O4 -Based Full Cells

Two water‐soluble binders of carboxymethyl cellulose (CMC) and sodium alginate (SA) have been studied in comparison with N‐methylpyrrolidone‐soluble poly(vinylidene difluoride–co‐hexafluoropropylene) (PVdF‐HFP) to understand their effect on the electrochemical performance of a high‐voltage lithium nickel manganese oxide (LNMO) cathode. The electrochemical performance has been investigated in full cells using a Li₄Ti₅O₁₂ (LTO) anode. At room temperature, LNMO cathodes prepared with aqueous binders provided a similar electrochemical performance as those prepared with PVdF‐HFP. However, at 55 °C, the full cells containing LNMO with the aqueous binders showed higher cycling stability. The results are supported by intermittent current interruption resistance measurements, wherein the electrodes with SA showed lower resistance. The surface layer formed on the electrodes after cycling has been characterized by X‐ray photoelectron spectroscopy. The amount of transition metal dissolutions was comparable for all three cells. However, the amount of hydrogen fluoride (HF) content in the electrolyte cycled at 55 °C is lower in the cell with the SA binder. These results suggest that use of water‐soluble binders could provide a practical and more sustainable alternative to PVdF‐based binders for the fabrication of LNMO electrodes.

Mesoporous Single-Crystal Lithium Titanate Enabling Fast-Charging Li-Ion Batteries

There remain significant challenges in developing fast-charging materials for lithium-ion batteries (LIBs) due to sluggish ion diffusion kinetics and unfavorable electrolyte mass transportation in battery electrodes. In this work, a mesoporous single-crystalline lithium titanate (MSC-LTO) microrod that can realize exceptional fast charge/discharge performance and excellent long-term stability in LIBs is reported. The MSC-LTO microrods are featured with a single-crystalline structure and interconnected pores inside the entire single-crystalline body. These features not only shorten the lithium-ion diffusion distance but also allow for the penetration of electrolytes into the single-crystalline interior during battery cycling. Hence, the MSC-LTO microrods exhibit unprecedentedly high rate capability, achieving a specific discharge capacity of ≈174 mAh g^-1 at 10 C, which is very close to its theoretical capacity, and ≈169 mAh g^-1 at 50 C. More importantly, the porous single-crystalline microrods greatly mitigate the structure degradation during a long-term cycling test, offering ≈92% of the initial capacity after 10 000 cycles at 20 C. This work presents a novel strategy to engineer porous single-crystalline materials and paves a new venue for developing fast-charging materials for LIBs.

Probing the Physicochemical Behavior of Variously Doped Li4Ti5O12 Nanoflowers

This study thoroughly investigated the synthesis of not only 4 triply-doped metal oxides but also 5 singly-doped analogues of Li₄Ti₅O₁₂ for electrochemical applications. In terms of synthetic novelty, the triply-doped materials were fabricated using a relatively facile hydrothermal method for the first-time, involving the simultaneous substitution of Ca for the Li site, Ln (i.e., Dy, Y, or Gd) for the Ti site, and Cl for the O site. Based on XRD, SEM, and HRTEM-EDS measurements, the resulting materials, incorporating a relatively homogeneous and uniform dispersion of both the single and triple dopants, exhibited a micron-scale flower-like morphology that remained apparently undamaged by the doping process. Crucially, the surface chemistry of all of the samples was probed using XPS in order to analyze any nuanced changes associated with either the various different lanthanide dopants or the identity of the metal precursor types involved. In the latter case, it was observed that the use of a nitrate salt precursor versus that of a chloride salt enabled not only a higher lanthanide incorporation but also the potential for favorable N-doping, all of which promoted a concomitant increase in conductivity due to a perceptible increase in Ti³⁺ content. In terms of the choice of lanthanide system, it was observed via CV analysis that dopant incorporation generally (albeit with some notable exceptions, especially with Y-based materials) led to the formation of higher amounts of Ti³⁺ species within both the singly and triply-doped materials, which consequentially led to the potential for increased diffusivity and higher mobility of Li⁺ species with the possibility for enabling greater capacity within these classes of metal oxides.

Linear and Symmetric Li-Based Composite Memristors for Efficient Supervised Learning

Emerging energy-efficient neuromorphic circuits are based on hardware implementation of artificial neural networks (ANNs) that employ the biomimetic functions of memristors. Specifically, crossbar array memristive architectures are able to perform ANN vector-matrix multiplication more efficiently than conventional CMOS hardware. Memristors with specific characteristics, such as ohmic behavior in all resistance states in addition to symmetric and linear long-term potentiation/depression (LTP/LTD), are required in order to fully realize these benefits. Here, we demonstrate a Li-based composite memristor (LCM) that achieves these objectives. The LCM consists of three phases: Li-doped TiO₂ as a Li reservoir, Li₄Ti₅O₁₂ as the insulating phase, and Li₇Ti₅O₁₂ as the metallic phase, where resistive switching correlates with the change in the relative fraction of the metallic and insulating phases. The LCM exhibits a symmetric and gradual resistive switching behavior for both set and reset operations during a full bias sweep cycle. This symmetric and linear weight update is uniquely enabled by the symmetric bidirectional migration of Li ions, which leads to gradual changes in the relative fraction of the metallic phase in the film. The optimized LCM in ANN simulation showed that exceptionally high accuracy in image classification is realized in fewer training steps compared to the nonlinear behavior of conventional memristors.

Lithium titanate nanoplates embedded with graphene quantum dots as electrode materials for high-rate lithium-ion batteries

Anode materials based on lithium titanate (LTO)/graphene composites are considered as ideal candidates for high-rate lithium-ion batteries (LIBs). Considering the blocking effects of graphene nanosheets in electrodes during ion-transfer processes, construction of LTO/graphene composite structures with enhanced electrical and ionic conductivity via facile and scalable techniques is still challenging for high-rate LIB. In this work, structures of anode materials based on LTO nanoplates embedded with graphene quantum dots (GQDs) are demonstrated for high-rate LIB. The hybrids can be facilely prepared viain situintroduction of GQDs during the process LTO preparation, which enables a uniform dispersion of GQDs within LTO. This method is convenient, rapid, and can be easily scaled-up. The introduction of 0.05 wt.% GQDs can greatly enhance the electrochemical performance of the electrodes. The electrodes with 0.05 wt.% GQDs deliver a specific discharge capacity of 185, 181 and 179 mAh g^-1at 5, 10, and 20 C, respectively. The performance enhancement is suggested to be due to the synergistic interactions between LTO and GQDs. The strategy as well as as-designed structures of LTO/GQDs show potentials for application as high-rate anode materials in LIBs application.

Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials

Nickel-rich layered oxides, such as LiNi_0.6Co_0.2Mn_0.2O₂ (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li⁺), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (<5 nm) coatings of TiO_x (TO) and Li_xTi_yO_z (LTO) were deposited over NMC622 composite electrodes using atomic layer deposition. It was found that these coatings provided a protective surface and also reinforced the electrode structure. Under high-voltage range (3.0-4.6 V) cycling, the coatings enhance the NMC electrochemical behavior, enabling longer cycle life and higher capacity. Cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray diffraction analyses of the coated NMC electrodes suggest that the enhanced electrochemical performance originates from reduced side reactions. In situ dilatometry analysis shows reversible volume change for NMC-LTO during the cycling. It revealed that the dilation behavior of the electrode, resulting in crack formation and consequent particle degradation, is significantly suppressed for the coated sample. The ability of the coatings to mitigate the electrode degradation mechanisms, illustrated in this report, provides insight into a method to enhance the performance of Ni-rich positive electrode materials under high-voltage ranges.

Electrochromic Behavior and Phase Transformation in Li4+xTi5O12 upon Lithium-Ion Deintercalation/Intercalation

The impact of phase transformation from spinel-structured Li₄Ti₅O₁₂ to rocksalt-type Li₇Ti₅O₁₂ on the electrochromic properties of the material is studied. Thin films of Li₄Ti₅O₁₂ are deposited on platinum-coated substrates using radio-frequency-ion beam sputtering. In situ and ex situ optical spectroscopy (in reflectance geometry) is performed along with electrochemical characterization. In situ measurements demonstrate the reversible electrochromic behavior of the deposited thin films and the effect of the change of lithium content on the reflectance spectrum. Ex situ measurements quantify the optical constants of thin films for different charge states by modeling the reflectance spectrum with a Clausius-Mossotti relation. The model reveals the presence of one or two dominant resonant frequencies in the case of Li₄Ti₅O₁₂ or Li₇Ti₅O₁₂, respectively, in the UV/visible/NIR region of light. The single strong resonance in the case of Li₄Ti₅O₁₂ is assigned to transition from O 2p to Ti t_2g, that is, across the band gap, whereas for the Li₇Ti₅O₁₂ phase, the two resonances correspond to the electronic transitions from O 2p to empty Ti t_2g and from filled Ti t_2g to empty Ti e_g. The concentration dependence of the derived dielectric constants points out a fast lithium ion transport through the grain boundaries, thereby segregating a conductive lithium-rich phase at the grain boundaries. This increases the electronic conductivity of the thin films in the initial stages of intercalation and explains the debated mechanism of the fast discharge/charge capability of Li₄Ti₅O₁₂ electrodes.

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 (Li₄ Ti₅ O₁₂ , 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_0.5 Mn_1.5 O₄ 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.

One-Step Synthesis of a Nanosized Cubic Li2TiO3-Coated Br, C, and N Co-Doped Li4Ti5O12 Anode Material for Stable High-Rate Lithium-Ion Batteries

Nanosized Li₄Ti₅O₁₂ with both a Li₂TiO₃ coating and C-N-Br co-doping (CLLTO) was successfully synthesized via a facile reverse microemulsion method in one step using hexadecyl trimethyl ammonium bromide as a surface control agent and as a carbon, nitrogen, and bromine source. A uniform Li₂TiO₃ layer was formed on the surface and strongly adhered to the host material Li₄Ti₅O₁₂ (LTO), which played an important role in improving the cyclic stability of CLLTO. The thin and stable Li₂TiO₃ layer has the same cubic structure as LTO, which provides many three-dimensional channels for ion transport. C, N, and Br co-doping in CLLTO promoted the transition of Ti⁴⁺ to Ti³⁺ in Li₄Ti₅O₁₂, which could improve the capacity and facilitate the Li⁺ ion and electron transfer at the interface. The conductive behavior induced by co-doping was estimated by UV-vis diffuse reflectance spectra and further supported by theoretical calculations. The electrical conductivity of both p-type and n-type LTO can be well improved by co-doping C, N, and Br. This improvement may be due to the band gap reduction and the increased n-type electronic modification of the entire LTO. Owing to the synergistic effect of coating, co-doping, and nanosizing at one time, the CLLTO exhibits a high discharge capacity of 177.3-153.9 mA h g^-1 at the working rate of 0.1C-20C, with a capacity retention of 86%. The stable cycling of CLLTO is also obtained after 500 cycles at 20C, with a capacity retention of 95.5% (approximately 8 times higher than that of pure LTO) and almost 100% Coulombic efficiency. With high capacity, excellent rate performance, and good cycling stability, CLLTO can be applied in high-power lithium-ion batteries.

Lithium Titanate Matrix-Supported Nanocrystalline Silicon Film as an Anode for Lithium-Ion Batteries

A facile preparation method of a Si-based anode with excellent cycling property is urgently required in the process of preparing lithium-ion batteries (LIBs). Here, lithium titanate (LTO) matrix-supported nanocrystalline Si film is prepared by radio frequency (RF) magnetron cosputtering utilizing LTO and silicon (Si) targets as the sputtering source. LTO-supported nanocrystalline Si film electrodes revealed a repeatable specific capacity of 1200 mA h g^-1 at 150 mA g^-1 with a maintenance of more than 75% even after 800 cycles. The remarkable electrochemical properties of the LTO-Si composite films could be attributed to the LTO matrix, preventing the electrolyte from directly making contact with the nanocrystalline Si materials, alleviating the stress of the periodic volume change and further providing efficient and rapid pathways for lithium-ion transport. The results suggest that Si-based LTO composite films are prospective anodes for LIBs, with high capacities and long cycling stabilities.

Pine-Needle-Like Cu-Co Skeleton Composited with Li4 Ti5 O12 Forming Core-Branch Arrays for High-Rate Lithium Ion Storage

High-performance of lithium-ion batteries (LIBs) rely largely on the scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. In this work, the pine-needle-like Cu-Co skeleton is reported to support highly active Li₄ Ti₅ O₁₂ (LTO) forming Cu-Co/LTO core-branch arrays via a united hydrothermal-atomic layer deposition (ALD) method. ALD-formed LTO layer is uniformly anchored on the pine-needle-like heterostructured Cu-Co backbone, which consists of branched Co nanowires (diameters in 20 nm) and Cu nanowires (250-300 nm) core. The designed Cu-Co/LTO core-branch arrays show combined advantages of large porosity, high electrical conductivity, and good adhesion. Due to the unique positive features, the Cu-Co/LTO electrodes are demonstrated with enhanced electrochemical performance including excellent high-rate capacity (155 mAh g^-1 at 20 C) and noticeable long-term cycles (144 mAh g^-1 at 20 C after 3000 cycles). Additionally, the full cell assembled with activated carbon positive electrode and Cu-Co/LTO negative electrode exhibits high power/energy densities (41.6 Wh kg^-1 at 7.5 kW kg^-1 ). The design protocol combining binder-free characteristics and array configuration opens a new door for construction of advanced electrodes for application in high-rate electrochemical energy storage.

Smart Construction of Integrated CNTs/Li4Ti5O12 Core/Shell Arrays with Superior High-Rate Performance for Application in Lithium-Ion Batteries

Exploring advanced high-rate anodes is of great importance for the development of next-generation high-power lithium-ion batteries (LIBs). Here, novel carbon nanotubes (CNTs)/Li₄Ti₅O₁₂ (LTO) core/shell arrays on carbon cloth (CC) as integrated high-quality anode are constructed via a facile combined chemical vapor deposition-atomic layer deposition (ALD) method. ALD-synthesized LTO is strongly anchored on the CNTs' skeleton forming core/shell structures with diameters of 70-80 nm the combined advantages including highly conductive network, large surface area, and strong adhesion are obtained in the CC-LTO@CNTs core/shell arrays. The electrochemical performance of the CC-CNTs/LTO electrode is completely studied as the anode of LIBs and it shows noticeable high-rate capability (a capacity of 169 mA h g^-1 at 1 C and 112 mA h g^-1 at 20 C), as well as a stable cycle life with a capacity retention of 86% after 5000 cycles at 10 C, which is much better than the CC-LTO counterpart. Meanwhile, excellent cycling stability is also demonstrated for the full cell with LiFePO₄ cathode and CC-CNTs/LTO anode (87% capacity retention after 1500 cycles at 10 C). These positive features suggest their promising application in high-power energy storage areas.

Scalable in Situ Synthesis of Li4Ti5O12/Carbon Nanohybrid with Supersmall Li4Ti5O12 Nanoparticles Homogeneously Embedded in Carbon Matrix

Li₄Ti₅O₁₂ (LTO) is regarded as a promising lithium-ion battery anode due to its stable cyclic performance and reliable operation safety. The moderate rate performance originated from the poor intrinsic electron and lithium-ion conductivities of the LTO has significantly limited its wide applications. A facile scalable synthesis of hierarchical Li₄Ti₅O₁₂/C nanohybrids with supersmall LTO nanoparticles (ca. 17 nm in diameter) homogeneously embedded in the continuous submicrometer-sized carbon matrix is developed. Difunctional methacrylate monomers are used as solvent and carbon source to generate TiO₂/C nanohybrid, which is in situ converted to LTO/C via a solid-state reaction procedure. The structure, morphology, crystallinity, composition, tap density, and electrochemical performance of the LTO/C nanohybrid are systematically investigated. Comparing to the control sample of the commercial LTO composited with carbon, the reversible specific capacity after 1000 cycles at 175 mA g^-1 and rate performance at high current densities (875, 1750, and 3500 mA g^-1) of the Li₄Ti₅O₁₂/C nanohybrid have been significantly improved. The enhanced electrochemical performance is due to the unique structure feature, where the supersmall LTO nanoparticles are homogeneously embedded in the continuous carbon matrix. Good tap density is also achieved with the LTO/C nanohybrid due to its hierarchical micro-/nanohybrid structure, which is even higher than that of the commercial LTO powder.

Preparation of Lithium Titanate/Reduced Graphene Oxide Composites with Three-Dimensional "Fishnet-Like" Conductive Structure via a Gas-Foaming Method for High-Rate Lithium-Ion Batteries

With use of ammonium chloride (NH₄Cl) as the pore-forming agent, three-dimensional (3D) "fishnet-like" lithium titanate/reduced graphene oxide (LTO/G) composites with hierarchical porous structure are prepared via a gas-foaming method. Scanning electron microscopy and transmission electron microscopy images show that, in the composite prepared with the NH₄Cl concentration of 1 mg mL^-1 (1-LTO/G), LTO particles with sizes of 50-100 nm disperse homogeneously on the 3D "fishnet-like" graphene. The nitrogen-sorption analyses reveal the existence of micro-/mesopores, which is attributed to the introduction of NH₄Cl into the gap between the graphene sheets that further decomposes into gases and produces hierarchical pores during the thermal treatment process. The loose and porous structure of 1-LTO/G composites enables the better penetration of electrolytes, providing more rapid diffusion channels for lithium ion. As a result, the 1-LTO/G electrode delivers an ultrahigh specific capacity of 176.6 mA h g^-1 at a rate of 1 C. Even at 3 and 10 C, the specific capacity can reach 167.5 and 142.9 mA h g^-1, respectively. Moreover, the 1-LTO/G electrode shows excellent cycle performance with 95.4% capacity retention at 10 C after 100 cycles. The results demonstrate that the LTO/G composite with these properties is one of the most promising anode materials for lithium-ion batteries.

High-Density Microporous Li4Ti5O12 Microbars with Superior Rate Performance for Lithium-Ion Batteries

Nanosized Li₄Ti₅O₁₂ (LTO) materials enabling high rate performance suffer from a large specific surface area and low tap density lowering the cycle life and practical energy density. Microsized LTO materials have high density which generally compromises their rate capability. Aiming at combining the favorable nano and micro size properties, a facile method to synthesize LTO microbars with micropores created by ammonium bicarbonate (NH₄HCO₃) as a template is presented. The compact LTO microbars are in situ grown by spinel LTO nanocrystals. The as-prepared LTO microbars have a very small specific surface area (6.11 m² g^-1) combined with a high ionic conductivity (5.53 × 10^-12 cm^-2 s^-1) and large tap densities (1.20 g cm^-3), responsible for their exceptionally stable long-term cyclic performance and superior rate properties. The specific capacity reaches 141.0 and 129.3 mAh g^-1 at the current rate of 10 and 30 C, respectively. The capacity retention is as high as 94.0% and 83.3% after 500 and 1000 cycles at 10 C. This work demonstrates that, in situ creating micropores in microsized LTO using NH₄HCO₃ not only facilitates a high LTO tap density, to enhance the volumetric energy density, but also provides abundant Li-ion transportation channels enabling high rate performance.

A Strategy for Synthesis of Nanosheets Consisting of Alternating Spinel Li4Ti5O12 and Rutile TiO2 Lamellas for High-Rate Anodes of Lithium-Ion Batteries

Ultrathin dual phase nanosheets consisting of alternating spinel Li₄Ti₅O₁₂ (LTO) and rutile TiO₂ (RT) lamellas are synthesized through a facile and scalable hydrothermal method, and the formation mechanism is explored. The thickness of constituent lamellas can be controlled exactly by adjusting the mole ratio of Li:Ti in the original reactants. Alternating insertion of the RT lamellas significantly improves the electrochemical performance of LTO nanosheets, especially at high charge/discharge rates. As anodes in lithium-ion batteries (LIBs), the dual phase nanosheet electrode with the optimized phase ratio can deliver stable discharge capacities of 178.5, 154.9, 148.4, 142.3, 138.2, and 131.4 mA h g^-1 at current densities of 1, 10, 20, 30, 40, and 50 C, respectively. Meanwhile, they inherit the excellent cyclic stability of pure spinel LTO and exhibit a capacity retention of 93.1% even after 500 cycles at 50 C. Our results indicate that the alternating nanoscaled lamella structure is a good alternative to facilitate the transfer of both the Li ions and electrons into the spinel LTO, giving rise to an excellent cyclability and fast rate performance. Therefore, the newly prepared carbon-free LTO-RT nanosheets with high safety provide a new opportunity to develop high-power anodes for LIBs.

Chromium-Modified Li4Ti5O12 with a Synergistic Effect of Bulk Doping, Surface Coating, and Size Reducing

Bulk doping, surface coating, and size reducing are three strategies for improving the electrochemical properties of Li4Ti5O12 (LTO). In this work, chromium (Cr)-modified LTO with a synergistic effect of bulk doping, surface coating, and size reducing is synthesized by a facile sol-gel method. X-ray diffraction (XRD) and Raman analysis prove that Cr dopes into the LTO bulk lattice, which effectively inhibits the generation of TiO2 impurities. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) verifies the surface coating of Li2CrO4 on the LTO surface, which decreases impedance of the LTO electrode. More importantly, the size of LTO particles can be significantly reduced from submicroscale to nanoscale as a result of the protection of the Li2CrO4 surface layer and the suppression from Cr atoms on the long-range order in the LTO lattice. As anode material, Li4-xCr3xTi5-2xO12 (x = 0.1) delivers a reversible capacity of 141 mAh g(-1) at 10 °C, and over 155 mAh g(-1) at 1 °C after 1000 cycles. Therefore, the Cr-modified Li4Ti5O12 prepared via a sol-gel method has potential for applications in high-power, long-life lithium-ion batteries.

Ultrathin Li4Ti5O12 Nanosheets as Anode Materials for Lithium and Sodium Storage

Ultrathin Li4Ti5O12 (LTO) nanosheets with ordered microstructures were prepared via a polyether-assisted hydrothermal process. Pluronic P123, a polyether, can impede the growth of Li2TiO3 in the precursor and also act as a structure-directing agent to facilitate the (Li1.81H0.19)Ti2O5·2H2O precursor to form the LTO nanosheets with the ordered microstructure. Moreover, the addition of P123 can suppress the stacking of LTO nanosheets during calcining of the precursor, and the thickness of the nanosheets can be controlled to be about 4 nm. The microstructure of the as-prepared ultrathin and ordered nanosheets is helpful for Li(+) or Na(+) diffusion and charge transfer through the particles. Therefore, the ultrathin P123-assisted LTO (P-LTO) nanosheets show a rate capability much higher than that of the LTO sample without P123 in a Li battery with over 130 mAh g(-1) of capacity remaining at the 64C rate. For intercalation of larger size Na(+) ions, the P-LTO still exhibits a capacity of 115 mAh g(-1) at a current rate of 10 C and a capacity retention of 96% after 400 cycles.

Quasi-Solid Electrolytes for High Temperature Lithium Ion Batteries

Rechargeable batteries capable of operating at high temperatures have significant use in various targeted applications. Expanding the thermal stability of current lithium ion batteries requires replacing the electrolyte and separators with stable alternatives. Since solid-state electrolytes do not have a good electrode interface, we report here the development of a new class of quasi-solid-state electrolytes, which have the structural stability of a solid and the wettability of a liquid. Microflakes of clay particles drenched in a solution of lithiated room temperature ionic liquid forming a quasi-solid system has been demonstrated to have structural stability until 355 °C. With an ionic conductivity of ∼3.35 mS cm(-1), the composite electrolyte has been shown to deliver stable electrochemical performance at 120 °C, and a rechargeable lithium battery with Li4Ti5O12 electrode has been tested to deliver reliable capacity for over several cycles of charge-discharge.

Coating lithium titanate with nitrogen-doped carbon by simple refluxing for high-power lithium-ion batteries

Nitrogen-doped carbon is coated on lithium titanate (Li4Ti5O12, LTO) via a simple chemical refluxing process, using ethylenediamine (EDA) as the carbon and nitrogen source. The process incorporates a carbon coating doped with a relatively high amount of nitrogen to form a conducting network on the LTO matrix. The introduction of N dopants in the carbon matrix leads to a higher density of C vacancies, resulting in improved lithium-ion diffusion. The uniform coating of nitrogen-doped carbon on Li4Ti5O12 (CN-LTO) enhances the electronic conductivity of a CN-LTO electrode and the corresponding electrochemical properties of the cell employing the electrode. The results of our study demonstrate that the CN-LTO anode exhibits higher rate capability and cycling performance over 100 cycles. From the electrochemical tests performed, the specific capacity of CN-LTO electrode at higher rates of 20 and 50 C are found to be 140.7 and 82.3 mAh g(-1), respectively. In addition, the CN-Li4Ti5O12 anode attained higher capacity retention of 100% at 1 C rate after 100 cycles and 92.9% at 10 C rate after 300 cycles.

The electrorheological behavior of suspensions based on molten-salt synthesized lithium titanate nanoparticles and their core-shell titanate/urea analogues

This paper concerns the preparation of novel electrorheological (ER) materials using microwave-assisted synthesis as well as utilizing a suitable shell-providing system with enhanced ER performance. Lithium titanate nanoparticles were successfully synthesized, and their composition was confirmed via X-ray diffraction. Rheological properties were investigated in the absence as well as in the presence of an external electric field. Dielectric properties clarified the response of the particles to the application of an electric field. The urea-coated lithium titanate nanoparticle-based suspension exhibits higher ER performance in comparison to suspensions based on bare particles.

Donut-shaped Li4Ti5O12 structures as a high performance anode material for lithium ion batteries

Lithium titanate (LTO) spinel 3D porous sub-micrometer donuts synthesized by combined sol-gel and electrospraying reveal a wall thickness of 200-250 nm with grain sizes in the range of 60-100 nm. Electrochemical testing of sub-micrometer donuts in half-cell mode exhibited a reversible specific capacity of 141 mAh/g even after 200 cycles of charging and discharging at 1C rate. The LTO structures with nanograins effectively reduce the Li ion diffusion path length, providing easy charge and discharge with good cyclability.