Hierarchically structured lithium titanate for ultrafast charging in long-life high capacity batteries

Structural Engineering of Anode Materials for Low-Temperature Lithium-Ion Batteries: Mechanisms, Strategies, and Prospects

The severe degradation of electrochemical performance for lithium-ion batteries (LIBs) at low temperatures poses a significant challenge to their practical applications. Consequently, extensive efforts have been contributed to explore novel anode materials with high electronic conductivity and rapid Li+ diffusion kinetics for achieving favorable low-temperature performance of LIBs. Herein, we try to review the recent reports on the synthesis and characterizations of low-temperature anode materials. First, we summarize the underlying mechanisms responsible for the performance degradation of anode materials at subzero temperatures. Second, detailed discussions concerning the key pathways (boosting electronic conductivity, enhancing Li+ diffusion kinetics, and inhibiting lithium dendrite) for improving the low-temperature performance of anode materials are presented. Third, several commonly used low-temperature anode materials are briefly introduced. Fourth, recent progress in the engineering of these low-temperature anode materials is summarized in terms of structural design, morphology control, surface & interface modifications, and multiphase materials. Finally, the challenges that remain to be solved in the field of low-temperature anode materials are discussed. This review was organized to offer valuable insights and guidance for next-generation LIBs with excellent low-temperature electrochemical performance.

Emerging Multiscale Porous Anodes toward Fast Charging Lithium-Ion Batteries

With the accelerated penetration of the global electric vehicle market, the demand for fast charging lithium-ion batteries (LIBs) that enable improvement of user driving efficiency and user experience is becoming increasingly significant. Robust ion/electron transport paths throughout the electrode have played a pivotal role in the progress of fast charging LIBs. Yet traditional graphite anodes lack fast ion transport channels, which suffer extremely elevated overpotential at ultrafast power outputs, resulting in lithium dendrite growth, capacity decay, and safety issues. In recent years, emergent multiscale porous anodes dedicated to building efficient ion transport channels on multiple scales offer opportunities for fast charging anodes. This review survey covers the recent advances of the emerging multiscale porous anodes for fast charging LIBs. It starts by clarifying how pore parameters such as porosity, tortuosity, and gradient affect the fast charging ability from an electrochemical kinetic perspective. We then present an overview of efforts to implement multiscale porous anodes at both material and electrode levels in diverse types of anode materials. Moreover, we critically evaluate the essential merits and limitations of several quintessential fast charging porous anodes from a practical viewpoint. Finally, we highlight the challenges and future prospects of multiscale porous fast charging anode design associated with materials and electrodes as well as crucial issues faced by the battery and management level.

Quenching-Induced Defects Liberate the Latent Reversible Capacity of Lithium Titanate Anode

Interest in defect engineering for lithium-ion battery (LIB) materials is sparked by its ability to tailor electrical conductivity and introduce extra active sites for electrochemical reactions. However, harvesting excessive intrinsic defects in the bulk of the electrodes rather than near their surface remains a long-standing challenge. Here, a versatile strategy of quenching is demonstrated, which is exercised in lithium titanate (Li₄ Ti₅ O₁₂ , LTO), a renowned anode for LIBs, to achieve off-stoichiometry in the interior region. In situ synchrotron analysis and atomic-resolution microscopy reveal the enriched oxygen vacancies and cation redistribution after ice-water quenching, which can facilitate the native unextractable Li ions to participate in reversible cycling. The fabricated LTO anode delivers a sustained capacity of 202 mAh g^-1 in the 1.0-2.5 V range with excellent rate capability and overcomes the poor cycling stability seen in conventional defective electrodes. The feasibility of tuning the degree of structural defectiveness via quenching agents is also proven, which can open up an intriguing avenue of research to harness the intrinsic defects for improving the energy density of rechargeable batteries.

A non-academic perspective on the future of lithium-based batteries

In the field of lithium-based batteries, there is often a substantial divide between academic research and industrial market needs. This is in part driven by a lack of peer-reviewed publications from industry. Here we present a non-academic view on applied research in lithium-based batteries to sharpen the focus and help bridge the gap between academic and industrial research. We focus our discussion on key metrics and challenges to be considered when developing new technologies in this industry. We also explore the need to consider various performance aspects in unison when developing a new material/technology. Moreover, we also investigate the suitability of supply chains, sustainability of materials and the impact on system-level cost as factors that need to be accounted for when working on new technologies. With these considerations in mind, we then assess the latest developments in the lithium-based battery industry, providing our views on the challenges and prospects of various technologies.

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.

Atomic Short-Range Order in a Cation-Deficient Perovskite Anode for Fast-Charging and Long-Life Lithium-Ion Batteries

Perovskite-type oxides are widely used for energy conversion and storage, but their rate-inhibiting phase transition and large volume change hinder the applications of most perovskite-type oxides for high-rate electrochemical energy storage. Here, it is shown that a cation-deficient perovskite CeNb₃ O₉ (CNO) can store a sufficient amount of lithium at a high charge/discharge rate, even when the sizes of the synthesized particles are on the order of micrometers. At 60 C (15 A g^-1 ), corresponding to a 1 min charge, the CNO anode delivers over 52.8% of its capacity. In addition, the CNO anode material exhibits 96.6% capacity retention after 2000 charge-discharge cycles at 50 C (12.5 A g^-1 ), indicating exceptional long-term cycling stability at high rates. The excellent cycling performance is attributed to the formation of atomic short-range order, which significantly prevents local and long-range structural rearrangements, stabilizing the host structure and being responsible for the small volume evolution. Moreover, the extremely high rate capacity can be explained by the intrinsically large interstitial sites in multiple directions, intercalation pseudocapacitance, atomic short-range order, and cation-vacancy-enhanced 3D-conduction networks for lithium ions. These structural characteristics and mechanisms can be used to design advanced perovskite electrode materials for fast-charging and long-life lithium-ion batteries.

Metal-Metal Bonding as an Electrode Design Principle in the Low-Strain Cluster Compound LiScMo3O8

Electrode materials for Li⁺-ion batteries require optimization along several disparate axes related to cost, performance, and sustainability. One of the important performance axes is the ability to retain structural integrity though cycles of charge/discharge. Metal-metal bonding is a distinct feature of some refractory metal oxides that has been largely underutilized in electrochemical energy storage, but that could potentially impact structural integrity. Here LiScMo₃O₈, a compound containing triangular clusters of metal-metal bonded Mo atoms, is studied as a potential anode material in Li⁺-ion batteries. Electrons inserted though lithiation are localized across rigid Mo₃ triangles (rather than on individual metal ions), resulting in minimal structural change as suggested by operando diffraction. The unusual chemical bonding allows this compound to be cycled with Mo atoms below a formally +4 valence state, resulting in an acceptable voltage regime that is appropriate for an anode material. Several characterization methods including potentiometric entropy measurements indicate two-phase regions, which are attributed through extensive first-principles modeling to Li⁺ ordering. This study of LiScMo₃O₈ provides valuable insights for design principles for structural motifs that stably and reversibly permit Li⁺ (de)insertion.

Developing Atomically Thin Li1.81H0.19Ti2O5·2H2O Nanosheets for Selective Photocatalytic CO2 Reduction to CO

Solar-driven CO₂ conversion to carbon-based fuels is an attractive approach to alleviate the worsening global climate change and increasing energy issues. However, exploring and designing efficient photocatalysts with excellent activity and stability still remain challenging. Herein, layered Li_1.81H_0.19Ti₂O₅·2H₂O (LHTO) nanosheets were explored as the photocatalyst for photocatalytic CO₂ reduction, and atomically thin LHTO nanosheets with one-unit-cell thickness were successfully constructed for photocatalytic CO₂ reduction. The atomically thin LHTO nanosheets exhibited excellent performance for CO₂ photoreduction to CO, with a yield rate of 4.0 μmol g^-1 h^-1, a selectivity of 93%, and over 25 h photostability, dramatically outperforming the bulk LHTO. The better performance of the atomically thin LHTO nanosheets was experimentally verified to benefit from more sites for CO₂ adsorption, faster electron transfer rate, and a more negative conduction band edge compared with bulk LHTO. This work provided a methodological basis for designing more efficient photocatalytic CO₂ reduction catalysts.

Lithium Storage Mechanism and Application of Micron-Sized Lattice-Reversible Binary Intermetallic Compounds as High-Performance Flexible Lithium-Ion Battery Anodes

A strategy of lattice-reversible binary intermetallic compounds of metallic elements is proposed for applications in flexible lithium-ion battery (LIB) anode with high capacity and cycling stability. First, the use of metallic elements can ensure excellent electronic conductivity and high capacity of the active anode substance. Second, binary intermetallic compounds possess a larger initial lattice volume than metallic monomers, so that the problem of volume expansion can be alleviated. Finally, the design of binary intermetallic compounds with lattice reversibility further improves the cycle stability. In this work, the feasibility of this strategy is verified using an indium antimonide (InSb) system. The volumetric expansion and lithium storage mechanism of InSb are investigated by in situ Raman characterization and theoretical calculations. The active material utilization is significantly improved and the growth of In whiskers is inhibited in the micron-sized ball-milled and carbon coated InSb (bInSb@C) anode, which exhibits a reversible capacity of 733.8 mAh g^-1 at 0.2 C, and provides a capacity of 411.5 mAh g^-1 after 200 cycles at 3 C with an average Coulombic efficiency of 99.95%. This strategy is validated in pouch cells, illustrating the great potential of lattice-reversible binary intermetallic compounds for use as commercial flexible LIB anodes.

Electrochemical Performance of Orthorhombic CsPbI3 Perovskite in Li-Ion Batteries

A facile solution process was employed to prepare CsPbI₃ as an anode material for Li-ion batteries. Rietveld refinement of the X-ray data confirms the orthorhombic phase of CsPbI₃ at room temperature. As obtained from bond valence calculations, strained bonds between Pb and I are identified within PbI₆ octahedral units. Morphological study shows that the as-prepared δ-CsPbI₃ forms a nanorod-like structure. The XPS analysis confirm the presence of Cs (3d, 4d), Pb (4d, 4f, 5d) and I (3p, 3d, 4d). The lithiation process involves both intercalation and conversion reactions, as confirmed by cyclic voltammetry (CV) and first-principles calculations. Impedance spectroscopy coupled with the distribution function of relaxation times identifies charge transfer processes due to Li metal foil and anode/electrolyte interfaces. An initial discharge capacity of 151 mAhg⁻¹ is found to continuously increase to reach a maximum of ~275 mAhg⁻¹ at 65 cycles, while it drops to ~240 mAhg⁻¹ at 75 cycles and then slowly decreases to 235 mAhg⁻¹ at 100 cycles. Considering the performance and structural integrity during electrochemical performance, δ-CsPbI₃ is a promising material for future Li-ion battery (LIB) application.

Inorganic-organic competitive coating strategy derived uniform hollow gradient-structured ferroferric oxide-carbon nanospheres for ultra-fast and long-term lithium-ion battery

The gradient-structure is ideal nanostructure for conversion-type anodes with drastic volume change. Here, we demonstrate an inorganic-organic competitive coating strategy for constructing gradient-structured ferroferric oxide-carbon nanospheres, in which the deposition of ferroferric oxide nanoparticles and polymerization of carbonaceous species are competitive and well controlled by the reaction thermodynamics. The synthesized gradient-structure with a uniform size of ~420 nm consists of the ferroferric oxide nanoparticles (4-8 nm) in carbon matrix, which are aggregated into the inner layer (~15 nm) with high-to-low component distribution from inside to out, and an amorphous carbon layer (~20 nm). As an anode material, the volume change of the gradient-structured ferroferric oxide-carbon nanospheres can be limited to ~22% with ~7% radial expansion, thus resulting in stable reversible specific capacities of ~750 mAh g^-1 after ultra-long cycling of 10,000 cycles under ultra-fast rate of 10 A g^-1. This unique inorganic-organic competitive coating strategy bring inspiration for nanostructure design of functional materials in energy storage.

Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles

Nanocrystalline anatase TiO₂ is a robust model anode for Li insertion in batteries. The influence of nanocrystal size on the equilibrium potential and kinetics of Li insertion is investigated with in operando spectroelectrochemistry of thin film electrodes. Distinct visible and infrared responses correlate with Li insertion and electron accumulation, respectively, and these optical signals are used to deconvolute bulk Li insertion from other electrochemical responses, such as double-layer capacitance, pseudocapacitance, and electrolyte leakage. Electrochemical titration and phase-field simulations reveal that a difference in surface energies between anatase and lithiated phases of TiO₂ systematically tunes the Li-insertion potentials with the particle size. However, the particle size does not affect the kinetics of Li insertion in ensemble electrodes. Rather, the Li-insertion rates depend on the applied overpotential, electrolyte concentration, and initial state of charge. We conclude that Li diffusivity and phase propagation are not rate limiting during Li insertion in TiO₂ nanocrystals. Both of these processes occur rapidly once the transformation between the low-Li anatase and high-Li orthorhombic phases begins in a particle. Instead, discontinuous kinetics of Li accumulation in TiO₂ particles prior to the phase transformations limits (dis)charging rates. We demonstrate a practical means to deconvolute the nonequilibrium charging behavior in nanocrystalline electrodes through a combination of colloidal synthesis, phase field simulations, and spectroelectrochemistry.

Facile assembly of layer-interlocked graphene heterostructures as flexible electrodes for Li-ion batteries

Flexible electrodes with robust mechanical properties and high electrochemical performance are of significance for the practical implementation of flexible batteries. Here we demonstrate a general and straightforward co-assembly approach to prepare flexible electrodes, where electrochemically exfoliated graphene (EG) is exploited as the film former/conducting matrix and different binary metal oxides (Li₄Ti₅O₁₂, LiCoO₂, Li₂MnO₄, LiFePO₄) are incorporated. The resultant EG-metal oxide hybrids exhibit a unique layer-interlocked structure, where the metal oxide is conformably wrapped by the highly flexible graphene. Due to numerous contact interphases generated between EG and the intercalated material, the hybrid films show high flexibility and can endure rolling, bending, folding and even twisting. When serving as the anode for Li-ion batteries, the freestanding EG-Li₄Ti₅O₁₂ hybrid presents a characteristic flat discharge plateau at 1.55 V (vs. Li/Li⁺), indicating transformation of Li₄Ti₅O₁₂ to Li₇Ti₅O₁₂. Small polarization, high rate capability and excellent cycling stability against mechanical bending are also demonstrated for the prepared EG-Li₄Ti₅O₁₂ hybrid. Finally, full cells composed of EG-Li₄Ti₅O₁₂ and EG-LiFePO₄ hybrids show impressive cycling (98% capacity retention after 100 cycles at 1C) and rate performance (84% capacity retained at 2.5C). The straightforward co-assembly approach based on EG can be extended to other two-dimensional layered materials for constructing highly efficient flexible energy storage devices.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.

High Performance of Salt-Modified–LTO Anode in LiFePO4 Battery

Highly crystalline “zero-strain” Li4Ti5O12 (LTO) has great potential as an alternative material for the anodes in a lithium ion battery. In this research, highly crystalline LTO with impressive electrochemical characteristics was synthesized via a salt-assisted solid-state reaction using TiO2, LiOH, and various amounts of NaCl as a salt additive. The LTO particles exhibited a cubic spinel structure with homogenous micron-sized particles. The highest initial specific discharge capacity of LTO was 141.04 mAh/g with 4 wt % NaCl addition, which was tested in a full-cell (LTO/LiFePO4) battery. The battery cell showed self-recovery ability during the cycling test at 10 C-rate, which can extend the cycle life of the cell. The salt-assisted process affected the crystallinity of the LTO particles, which has a favorable effect on its electrochemical performance as anodes.

Ultrafast and Stable Lithium Storage Enabled by the Electric Field Effect in Layer-Structured Tablet-Like NH4TiOF3 Mesocrystals

Design and synthesis of advanced electrode materials with fast and stable ion storage are of importance for energy storage applications. Herein, we propose that introducing the heterogeneous interface in layer-structured mesocrystals is an efficient way to greatly improve the rate capability and cycle stability of lithium-ion battery (LIB) devices. NH₄TiOF₃ mesocrystals were employed as a typical model system to demonstrate the idea. The NH₄TiOF₃ mesocrystals were obtained via the hydrothermal reaction, and the NH₄TiOF₃/TiO₂ interfaces were generated through calcining at different temperatures under an argon atmosphere. Phase composition, microstructure, and chemical analyses show that the as-prepared NH₄TiOF₃ mesocrystals possess "tablet-like" morphology, and the formation of the NH₄TiOF₃/TiO₂ interface can be controlled by the calcination temperature. When evaluated as the anode for LIBs, the optimized sample (NH₄TiOF₃ calcined at 250 °C, NTF-250) shows excellent, fast, and stable lithium storage properties. Specifically, the NTF-250 electrode holds a reversible capacity of 159.5 mA h g^-1 after 200 cycles at 0.2 A g^-1. At a high current density of 20 A g^-1, the electrode still maintains a reversible capacity of 89.6 mA h g^-1 and reaches a reversible capacity of 128.6 mA h g^-1 at a current density of 1 A g^-1 after 2000 cycles. Theoretical and experimental studies show that the synergistic effects of the heterogeneous NH₄TiOF₃/anatase TiO₂ interface in the layer-structured NH₄TiOF₃ mesocrystals lead to the upgraded electrochemical properties. Especially, the local build-in electric field induced by the nonuniform distribution of charge across the NH₄TiOF₃/anatase TiO₂ interface facilitates the charge transport during the charging and discharging cycling. The current electrode design strategy paves a new way in boosting stable ion storage and thus is of great interest in energy storage and conversion.

Localized Electrons Enhanced Ion Transport for Ultrafast Electrochemical Energy Storage

The rate-determining process for electrochemical energy storage is largely determined by ion transport occurring in the electrode materials. Apart from decreasing the distance of ion diffusion, the enhancement of ionic mobility is crucial for ion transport. Here, a localized electron enhanced ion transport mechanism to promote ion mobility for ultrafast energy storage is proposed. Theoretical calculations and analysis reveal that highly localized electrons can be induced by intrinsic defects, and the migration barrier of ions can be obviously reduced. Consistently, experiment results reveal that this mechanism leads to an enhancement of Li/Na ion diffusivity by two orders of magnitude. At high mass loading of 10 mg cm^-2 and high rate of 10C, a reversible energy storage capacity up to 190 mAh g^-1 is achieved, which is ten times greater than achievable by commercial crystals with comparable dimensions.

Surface-Engineered Li4Ti5O12 Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge-discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries. In this study, a unique solvothermal synthesis of Li₄Ti₅O₁₂ nanoparticles is proposed by using an off-stoichiometric precursor ratio. A Li-deficient off-stoichiometry leads to the coexistence of phase-separated crystalline nanoparticles of Li₄Ti₅O₁₂ and TiO₂ exhibiting reasonable high-rate performances. However, after the solvothermal process, an extended aging of the hydrolyzed solution leads to the formation of a Li₄Ti₅O₁₂ nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO₂. The Li₄Ti₅O₁₂ nanoplates with the disordered surface layer deliver ultrahigh-rate performances for both charging and discharging in the range of 50-300C and reversible capacities of 156 and 113 mAh g^-1 at these two rates, respectively. Furthermore, the electrode exhibits an ultrahigh-charging-rate capability up to 1200C (60 mAh g^-1; discharge limited to 100C). Unlike previously reported high-rate half cells, we demonstrate a high-power Li-ion battery by coupling Li₄Ti₅O₁₂ with a high-rate LiMn₂O₄ cathode. The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity, respectively. Room- (25 °C), low- (- 10 °C), and high- (55 °C) temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.

Interfacial Lattice-Strain-Driven Generation of Oxygen Vacancies in an Aerobic-Annealed TiO2 (B) Electrode

Oxygen vacancies play crucial roles in defining physical and chemical properties of materials to enhance the performances in electronics, solar cells, catalysis, sensors, and energy conversion and storage. Conventional approaches to incorporate oxygen defects mainly rely on reducing the oxygen partial pressure for the removal of product to change the equilibrium position. However, directly affecting reactants to shift the reaction toward generating oxygen vacancies is lacking and to fill this blank in synthetic methodology is very challenging. Here, a strategy is demonstrated to create oxygen vacancies through making the reaction energetically more favorable via applying interfacial strain on reactants by coating, using TiO₂ (B) as a model system. Geometrical phase analysis and density functional theory simulations verify that the formation energy of oxygen vacancies is largely decreased under external strain. Benefiting from these, the obtained oxygen-deficient TiO₂ (B) exhibits impressively high level of capacitive charge storage, e.g., ≈53% at 0.5 mV s^-1 , far surpassing the ≈31% of the unmodified counterpart. Meanwhile, the modified electrode shows significantly enhanced rate capability delivering a capacity of 112 mAh g^-1 at 20 C (≈6.7 A g^-1 ), ≈30% higher than air-annealed TiO₂ and comparable to vacuum-calcined TiO₂ . This work heralds a new paradigm of mechanical manipulation of materials through interfacial control for rational defect engineering.

Carbon-Free, High-Capacity and Long Cycle Life 1D-2D NiMoO4 Nanowires/Metallic 1T MoS2 Composite Lithium-Ion Battery Anodes

Both metallic 1T MoS₂ and conductive molybdate compounds exhibit interesting electrochemical properties, however, the properties of composite electrodes based on these materials have not been investigated. Here, 1T MoS₂ single crystal nanosheets and NiMoO₄ single crystal nanowires are synthesized and formed into a carbon-free composite lithium-ion anode using blade- and spray-coating. The composite anodes deliver charge mass specific capacity of 940.1 mAh g^-1, while the discharge mass specific capacity is up to 941.6 mAh g^-1, with a capacity retention ratio of 84.2% after 750 cycles. The charge and discharge volumetric capacity (porosity of 15.6%, full electrode basis, excluding the current collector) are 1238.7 mAh cm^-3 and 1240 mAh cm^-3, respectively, and the active materials volume fraction is 82.5%. These capacities significantly exceed that of single 1T MoS₂ or single NiMoO₄ anodes we reported. We calculate if matched vs a cathode with an average discharge voltage of 4.0 V the gravimetric energy density of the composite electrodes would be 3389.8 Wh kg^-1. Electrochemical measurements indicate that the composite electrode has excellent electrochemical reversibility, suggesting that the structure has played a crucial role in the cycling process.

Capacity Loss Mechanism of the Li4Ti5O12 Microsphere Anode of Lithium-Ion Batteries at High Temperature and Rate Cycling Conditions

Li₄Ti₅O₁₂ (LTO) as the anode of lithium (Li) ion batteries has high interfacial side reactivity with the electrolyte, which leads to severe gassing behavior and poor cycling stability. Herein, the capacity loss mechanism of the high-tap density LTO microsphere anode under different temperatures (25, 45, and 60 °C) and charge/discharge rates (1 and 5 C) is systematically investigated. The capacity retentions of the LTO/Li cell after 500 cycles at 1 C are 95.6, 90.0, and 87.1% under three temperatures, which drop to 91.9, 58.3, and 20.9% when cycling at 5 C, respectively. Results show that the high temperature and rate almost do not damage the structure of LTO, but greatly affect the thickness and components of the solid electrolyte interface (SEI), and consequently reduce the performance of the LTO/Li cells. An SEI mainly consisting of inorganic species forms on LTO after 500 cycles at 1 C, while organic compounds are observed after 500 cycles at 5 C. The capacity of cycled LTO cannot recover again because of the thick SEI although using new Li metal anodes, separators, and electrolytes. This work demonstrates that it is of great significance for LTO to construct a stable SEI for achieving excellent cycling performance at a high rate and temperature.

Highly Reversible Conversion Anodes Composed of Ultralarge Monolithic Grains with Seamless Intragranular Binder and Wiring Network

Conversion anodes enable a high capacity for lithium-ion batteries due to more than one electron transfer. However, the collapse of the host structure during cycling would cause huge volume expansion and phase separation, leading to the degradation and disconnection of the mixed conductive network of the electrode. The initial nanostructuring and loose spatial distribution of active species are often resorted to in order to alleviate the evolution of the electrode morphology, but at the cost of the decrease of grain packing density. The utilization of ultralarge microsized grains of high density as the conversion anode is still highly challenging. Here, a proof-of-concept grain architecture characterized by endogenetic binder matrix and wiring network is proposed to guarantee the structural integrity of monolithic grains as large as 50-100 μm during deep conversion reaction. Such big grains were fabricated by self-assembly and pyrolysis of a Keggin-type polyoxometalate-based complex with protonated tris[2-(2-methoxyethoxy)-ethyl]amine (TDA-1-H⁺). The metal-organic precursor can guarantee the firm adherence of numerous Mo-O clusters and nuclei into a highly elastic monolithic structure without evident grain boundaries and intergranular voids. The pyrolyzed TDA-1-H⁺ not only serves as in situ binder and conductive wire to glue adjacent Mo-O moieties but also acts as a Li-ion pathway to promote sufficient lithiation on surrounding Mo-O. Such a monolithic electrode design leads to an unusual high-conversion-capacity performance (1000 mAh/g) with satisfactory reversibility (reaching at least 750 cycles at 1 A/g). These cycled grains are not disassembled even after undergoing long-term cycling. The conception of the intragranular binder is further confirmed by consolidating the MoO₂ porous network after in situ stuffing of MoS₂ nanobinders.

Plasma-Introduced Oxygen Defects Confined in Li4Ti5O12 Nanosheets for Boosting Lithium-Ion Diffusion

Although Li₄Ti₅O₁₂ (LTO) is considered as a promising anode material for high-power Li-ion batteries with high safety, the sluggish Li-ion diffusion coefficient restricts its widespread application. In this work, oxygen vacancy was successfully incorporated into LTO by an eco-friendly and cost-effective plasma process. The deficient LTO delivers much higher capacities of 173.4 mAh g^-1 at 1C rate after 100 cycles and 140.5 mAh g^-1 at 5C after 1000 cycles than those of pristine LTO. Meanwhile, even at a high rate of 20C, it displays an ultrahigh capacity of 133.1 mAh g^-1 after 500 cycles with a Coulombic efficiency of 100%. Detailed analysis reveals that the lithium storage mechanisms in the oxygen-deficient LTO, especially at high rate, were dominated by the insertion behavior and dual-phase conversion due to the fast ion-diffusion ability, rather than the widely reported surface capacitance by other approaches. This work highlights that defect generation by plasma in nanomaterials is an effective way to promote ion mobility, especially at high rates, and thus can be extended to other electrode materials for advanced energy-storage applications.

High-quality mesoporous graphene particles as high-energy and fast-charging anodes for lithium-ion batteries

The application of graphene for electrochemical energy storage has received tremendous attention; however, challenges remain in synthesis and other aspects. Here we report the synthesis of high-quality, nitrogen-doped, mesoporous graphene particles through chemical vapor deposition with magnesium-oxide particles as the catalyst and template. Such particles possess excellent structural and electrochemical stability, electronic and ionic conductivity, enabling their use as high-performance anodes with high reversible capacity, outstanding rate performance (e.g., 1,138 mA h g-1 at 0.2 C or 440 mA h g-1 at 60 C with a mass loading of 1 mg cm-2), and excellent cycling stability (e.g., >99% capacity retention for 500 cycles at 2 C with a mass loading of 1 mg cm-2). Interestingly, thick electrodes could be fabricated with high areal capacity and current density (e.g., 6.1 mA h cm-2 at 0.9 mA cm-2), providing an intriguing class of materials for lithium-ion batteries with high energy and power performance.

Fast charging of lithium-ion batteries at all temperatures

Fast charging is a key enabler of mainstream adoption of electric vehicles (EVs). None of today's EVs can withstand fast charging in cold or even cool temperatures due to the risk of lithium plating. Efforts to enable fast charging are hampered by the trade-off nature of a lithium-ion battery: Improving low-temperature fast charging capability usually comes with sacrificing cell durability. Here, we present a controllable cell structure to break this trade-off and enable lithium plating-free (LPF) fast charging. Further, the LPF cell gives rise to a unified charging practice independent of ambient temperature, offering a platform for the development of battery materials without temperature restrictions. We demonstrate a 9.5 Ah 170 Wh/kg LPF cell that can be charged to 80% state of charge in 15 min even at -50 °C (beyond cell operation limit). Further, the LPF cell sustains 4,500 cycles of 3.5-C charging in 0 °C with <20% capacity loss, which is a 90× boost of life compared with a baseline conventional cell, and equivalent to >12 y and >280,000 miles of EV lifetime under this extreme usage condition, i.e., 3.5-C or 15-min fast charging at freezing temperatures.

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.

A study on LiFePO4/graphite cells with built-in Li4Ti5O12 reference electrodes

In this work, based on the superior electrochemical stability of Li₄Ti₅O₁₂ (LTO) electrodes, LiFePO₄ (LFP)/graphite cells with built-in LTO electrodes as reference electrodes were designed and fabricated. The characteristics of the LTO reference electrodes in the fabricated lithium-ion cells were measured and discussed. The experimental data demonstrated that the LTO built-in reference electrodes were simple to prepare and were feasible options for long-term in situ monitoring of the development of potentials and other electrochemical parameters, such as the Li⁺ diffusion coefficient (D_Li) and electrochemical impedance spectroscopy (EIS) information, for both anodes and cathodes. Moreover, it is believed that the adoption of LTO as a reference electrode could be of great significance for long-term monitoring of the charge and discharge behavior of individual electrodes in other kinds of lithium-ion cells.

The characteristics of Li₄Ti₅O₁₂ reference electrodes in fabricated LiFePO₄/graphite lithium-ion cells were measured and discussed.

Ultrathin Manganese-Based Metal-Organic Framework Nanosheets: Low-Cost and Energy-Dense Lithium Storage Anodes with the Coexistence of Metal and Ligand Redox Activities

We herein demonstrate the fabrication of Mn- and Ni-based ultrathin metal-organic framework nanosheets with the same coordination mode (termed "Mn-UMOFNs" and "Ni-UMOFNs", respectively) through an expedient and versatile ultrasonic approach and scrutinize their electrochemical properties as anode materials for rechargeable lithium batteries for the first time. The obtained Mn-UMOFNs with structure advantages over Ni-UMOFNs (thinner nanosheets, smaller metal-ion radius, higher specific surface area) exhibit high reversible capacity (1187 mAh g^-1 at 100 mA g^-1 for 100 cycles), excellent rate capability (701 mAh g^-1 even at 2 A g^-1), rapid Li⁺ diffusion coefficient (2.48 × 10^-9 cm² s^-1), and a reasonable charge-discharge profile with low average operating potential at 0.4 V. On the grounds of the low-cost and environmental benignity of Mn metals and terephthalic acid linkers, our Mn-UMOFNs show alluring promise as a low-cost high-energy anode material for future LIBs. Furthermore, the lithiation-delithiation chemistry of Mn-UMOFNs was unequivocally studied by a combination of magnetic measurements, electron paramagnetic resonance, and synchrotron-based soft X-ray spectroscopy (O K-edge and Mn L-edge) experiments, the results of which substantiate that both the aromatic chelating ligands and the Mn²⁺ centers participate in lithium storage.