Ultrathin Anatase TiO2 Nanosheets Embedded with TiO2‐B Nanodomains for Lithium‐Ion Storage: Capacity Enhancement by Phase Boundaries

A new form of TiO₂ microspheres comprised of anatase/TiO₂‐B ultrathin composite nanosheets has been synthesized successfully and used as Li‐ion storage electrode material. By comparison between samples obtained with different annealing temperatures, it is demonstrated that the anatase/TiO₂‐B coherent interfaces may contribute additional lithium storage venues due to a favorable charge separation at the boundary between the two phases. The as‐prepared hierarchical nanostructures show capacities of 180 and 110 mAh g^?1 after 1000 cycles at current densities of 3400 and 8500 mA g^?1. The ultrathin nanosheet structure which provides short lithium diffusion length and high electrode/electrolyte contact area also accounts for the high capacity and long‐cycle stability.     

Redox Shuttles with Axisymmetric Scaffold for Overcharge Protection of Lithium‐Ion Batteries

The derivatives of 1,4‐dimethoxybenzene are thus far the best performing redox shuttle additives for overcharge protection of Li‐ion batteries. The most durable molecules of this kind typically possess two in‐plane methoxy groups that are equivalent by inversion symmetry. However, such geometry leads to a vanishing average dipole moment that causes poor solubility of these molecules in carbonate‐based electrolytes. In this study, a novel redox shuttle additive, 1,2,3,4‐tetrahydro‐6,7‐dimethoxy‐1,1,4,4‐tetramethyl‐naphthalene (TDTN), is introduced. It has been demonstrated that reversible oxidation at 4.05 V versus Li⁺/Li, high polarity, high solubility (around 0.4 m ), and excellent electrochemical stability (150 overcharge cycles at C/2 rate with 100% overcharge) can all be achieved simultaneously by the imposition of axial symmetry in the corresponding radical cation that is generated by electrochemical oxidation of TDTN in the battery. The intricate interplay between the symmetry and the chemical stability of the radical cation is scrutinized using magnetic resonance spectroscopy and electron structure modeling.     

An All‐Organic Non‐aqueous Lithium‐Ion Redox Flow Battery

A non‐aqueous lithium‐ion redox flow battery employing organic molecules is proposed and investigated. 2,5‐Di‐tert‐butyl‐1,4‐bis(2‐methoxyethoxy)benzene and a variety of molecules derived from quinoxaline are employed as initial high‐potential and low‐potential active materials, respectively. Electrochemical measurements highlight that the choice of electrolyte and of substituent groups can have a significant impact on redox species performance. The charge‐discharge characteristics are investigated in a modified coin‐cell configuration. After an initial break‐in period, coulombic and energy efficiencies for this unoptimized system are ～70% and ～37%, respectively, with major charge and discharge plateaus between 1.8‐2.4 V and 1.7‐1.3 V, respectively, for 30 cycles. Performance enhancements are expected with improvements in cell design and materials processing.     

Extraordinary Performance of Carbon‐Coated Anatase TiO2 as Sodium‐Ion Anode

The synthesis of in situ polymer‐functionalized anatase TiO₂ particles using an anchoring block copolymer with hydroxamate as coordinating species is reported, which yields nanoparticles (≈11 nm) in multigram scale. Thermal annealing converts the polymer brushes into a uniform and homogeneous carbon coating as proven by high resolution transmission electron microscopy and Raman spectroscopy. The strong impact of particle size as well as carbon coating on the electrochemical performance of anatase TiO₂ is demonstrated. Downsizing the particles leads to higher reversible uptake/release of sodium cations per formula unit TiO₂ (e.g., 0.72 eq. Na⁺ (11 nm) vs only 0.56 eq. Na⁺ (40 nm)) while the carbon coating improves rate performance. The combination of small particle size and homogeneous carbon coating allows for the excellent electrochemical performance of anatase TiO₂ at high (134 mAh g^?1 at 10 C (3.35 A g^?1)) and low (≈227 mAh g^?1 at 0.1 C) current rates, high cycling stability (full capacity retention between 2nd and 300th cycle at 1 C) and improved coulombic efficiency (≈99.8%).     

Silicon‐Microtube Scaffold Decorated with Anatase TiO2 as a Negative Electrode for a 3D Litium‐Ion Microbattery

An optimized scaffold based on silicon microtubes is designed to increase the surface capacity of 3D lithium‐ion microbatteries. High‐depth, mechanically robust microstructures are fabricated using microelectronic facilities. Conformal deposition of anatase TiO₂ is achieved using atomic layer deposition, realizing the targeted improvement for microbatteries; a surface capacity of 0.2 mA h cm^–2 at a charge rate of C/10 is obtained in standard liquid electrolyte. This work paves the way for the fabrication of solid‐state 3D Li‐ion microbatteries with an efficient 3D scaffold.     

Graphene‐Containing Nanomaterials for Lithium‐Ion Batteries

Graphene‐containing nanomaterials have emerged as important candidates for electrode materials in lithium‐ion batteries (LIBs) due to their unique physical properties. In this review, a brief introduction to recent developments in graphene‐containing nanocomposite electrodes and their derivatives is provided. Subsequently, synthetic routes to nanoparticle/graphene composites and their electrochemical performance in LIBs are highlighted, and the current state‐of‐the‐art and most recent advances in the area of graphene‐containing nanocomposite electrode materials are summarized. The limitations of graphene‐containing materials for energy storage applications are also discussed, with an emphasis on anode and cathode materials. Potential research directions for the future development of graphene‐containing nanocomposites are also presented, with an emphasis placed on practicality and scale‐up considerations for taking such materials from benchtop curiosities to commercial products.     

Nanoarchitectured Array Electrodes for Rechargeable Lithium‐ and Sodium‐Ion Batteries

Rechargeable ion batteries have contributed immensely to shaping the modern world and been seriously considered for the efficient storage and utilization of intermittent renewable energies. To fulfill their potential in the future market, superior battery performance of high capacity, great rate capability, and long lifespan is undoubtedly required. In the past decade, along with discovering new electrode materials, the focus has been shifting more and more toward rational electrode designs because the performance is intimately connected to the electrode architectures, particularly their designs at the nanoscale that can alleviate the reliance on the materials' intrinsic nature. The utilization of nanoarchitectured arrays in the design of electrodes has been proven to significantly improve the battery performance. A comprehensive summary of the structural features and fabrications of the nanoarchitectured array electrodes is provided, and some of the latest achievements in the area of both lithium‐ and sodium‐ion batteries are highlighted. Finally, future challenges and opportunities that would allow further development of such advanced electrode configuration are discussed.     

Introducing Highly Redox‐Active Atomic Centers into Insertion‐Type Electrodes for Lithium‐Ion Batteries

The development of alternative anode materials with higher volumetric and gravimetric capacity allowing for fast delithiation and, even more important, lithiation is crucial for next‐generation lithium‐ion batteries. Herein, the development of a completely new active material is reported, which follows an insertion‐type lithiation mechanism, metal‐doped CeO₂. Remarkably, the introduction of carefully selected dopants, herein exemplified for iron, results in an increase of the achievable capacity by more than 200%, originating from the reduction of the dopant to the metallic state and additional space for the lithium ion insertion due to a significant off‐centering of the dopant atoms in the crystal structure, away from the original Ce site. In addition to the outstanding performance of such materials in high‐power lithium‐ion full‐cells, the selective reduction of the iron dopant under preservation of the crystal structure of the host material is expected to open up a new field of research.     

Thermodynamic Aspects of Cathode Coatings for Lithium‐Ion Batteries

Metal oxide cathode coatings are capable of scavenging the hydrofluoric acid (HF) (present in LiPF₆‐based electrolytes) and improving the electrochemical performance of Li‐ion batteries. Here, a first‐principles thermodynamic framework is introduced for designing cathode coatings that consists of four elements: i) HF‐scavenging enthalpies, ii) volumetric and iii) gravimetric HF‐scavenging capacities of the oxides, and iv) cyclable Li loss into coating components. 81 HF‐scavenging reactions involving binary s‐, p‐ and d‐block metal oxides and fluorides are enumerated and these materials are screened to find promising coatings based on attributes (i‐iv). The screen successfully produces known effective coating materials (e.g., Al₂O₃ and MgO), providing a validation of our framework. Using this design strategy, promising coating materials, such as trivalent oxides of d‐block transition metals Sc, Ti, V, Cr, Mn and Y, are predicted. Finally, a new protection mechanism that successful coating materials could provide by scavenging the wide bandgap and low Li ion conductivity LiF precipitates from the cathode surfaces is suggested.     

Side by Side Battery Technologies with Lithium‐Ion Based Batteries

In recent years, the electrochemical power sources community has launched massive research programs, conferences, and workshops on the “post Li battery era.” However, in this report it is shown that the quest for post Li‐ion and Li battery technologies is incorrect in its essence. This is the outcome of a three day discussion on the future technologies that could provide an answer to a question that many ask these days: Which are the technologies that can be regarded as alternative to Li‐ion batteries? The answer to this question is a rather surprising one: Li‐ion battery technology will be here for many years to come, and therefore the use of “post Li‐ion” battery technologies would be misleading. However, there are applications with needs for which Li‐ion batteries will not be able to provide complete technological solutions, as well as lower cost and sustainability. In these specific cases, other battery technologies will play a key role. Here, the term “side‐by‐side technologies” is coined alongside a discussion of its meaning. The progress report does not cover the topic of Li‐metal battery technologies, but covers the technologies of sodium‐ion, multivalent, metal–air, and flow batteries.     

Transition Metal Oxide Anodes for Electrochemical Energy Storage in Lithium‐ and Sodium‐Ion Batteries

Lithium‐ion batteries (LIBs) with outstanding energy and power density have been extensively investigated in recent years, rendering them the most suitable energy storage technology for application in emerging markets such as electric vehicles and stationary storage. More recently, sodium, one of the most abundant elements on earth, exhibiting similar physicochemical properties as lithium, has been gaining increasing attention for the development of sodium‐ion batteries (SIBs) in order to address the concern about Li availability and cost—especially with regard to stationary applications for which size and volume of the battery are of less importance. Compared with traditional intercalation reactions, conversion reaction‐based transition metal oxides (TMOs) are prospective anode materials for rechargeable batteries thanks to their low cost and high gravimetric specific capacities. In this review, the recent progress and remaining challenges of conversion reactions for LIBs and SIBs are discussed, covering an overview about the different synthesis methods, morphological characteristics, as well as their electrochemical performance. Potential future research directions and a perspective toward the practical application of TMOs for electrochemical energy storage are also provided.     

Silicon‐Based Nanomaterials for Lithium‐Ion Batteries: A Review

There are growing concerns over the environmental, climate, and health impacts caused by using non‐renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium‐ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid‐electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.     

Exploiting Lithium–Ether Co‐Intercalation in Graphite for High‐Power Lithium‐Ion Batteries

The intercalation of lithium ions into graphite electrode is the key underlying mechanism of modern lithium‐ion batteries. However, co‐intercalation of lithium‐ions and solvent into graphite is considered undesirable because it can trigger the exfoliation of graphene layers and destroy the graphite crystal, resulting in poor cycle life. Here, it is demonstrated that the [lithium–solvent]⁺ intercalation does not necessarily cause exfoliation of the graphite electrode and can be remarkably reversible with appropriate solvent selection. First‐principles calculations suggest that the chemical compatibility of the graphite host and [lithium–solvent]⁺ complex ion strongly affects the reversibility of the co‐intercalation, and comparative experiments confirm this phenomenon. Moreover, it is revealed that [lithium–ether]⁺ co‐intercalation of natural graphite electrode enables much higher power capability than normal lithium intercalation, without the risk of lithium metal plating, with retention of ≈87% of the theoretical capacity at current density of 1 A g^?1. This unusual high rate capability of the co‐intercalation is attributed to the (i) absence of the desolvation step, (ii) negligible formation of the solid–electrolyte interphase on graphite surface, and (iii) fast charge‐transfer kinetics. This work constitutes the first step toward the utilization of fast and reversible [lithium–solvent]⁺ complex ion intercalation chemistry in graphite for rechargeable battery technology.