Li4Ti5O12 Nanoparticles Embedded in a Mesoporous Carbon Matrix as a Superior Anode Material for High Rate Lithium Ion Batteries

A mesoporous Li₄Ti₅O₁₂/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK‐3 as a hard template. Modified CMK‐3 template is impregnated with Li₄Ti₅O₁₂ precursor, followed by heat treatment at 750 °C for 6 h under N₂. Li₄Ti₅O₁₂ nanocrystals of up to several tens of nanometers are successfully synthesized in micrometer‐sized porous carbon foam to form a highly conductive network, as confirmed by field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, and nitrogen sorption isotherms. The composite is then evaluated as an anode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li₄Ti₅O₁₂, and shows an excellent rate capability (73.4 mA h g^?1 at 80 C) with significantly enhanced cycling performance (only 5.6% capacity loss after 1000 cycles at a high rate of 20 C). The greatly enhanced lithium storage properties of the mesoporous Li₄Ti₅O₁₂/C nanocomposite may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and the small Li₄Ti₅O₁₂ nanocrystallites that increase the ionic and electronic conduction throughout the electrode.     

Challenges of Spinel Li4Ti5O12 for Lithium‐Ion Battery Industrial Applications

Rechargeable lithium‐ion batteries (LIBs) offer the advantages of having great electrical energy storage and increased continuous and pulsed power output capabilities, which enable their applications in grid energy storage and electric vehicles (EVs). For safety, high power and durability considerations, spinel Li₄Ti₅O₁₂ is one of the most appealing potential candidate as an anode material for power LIBs due to its excellent cycling stability and thermal stability. However, there are still a number of challenges remaining for Li₄Ti₅O₁₂ battery applications. Herein, an updated overview of the latest advances in Li₄Ti₅O₁₂ research is provided and key challenges for its future development (i.e., fast‐charging, specific capacity, swelling, interface chemistry, matching cathode and electrolyte as well as batteries design and manufacturing) are highlighted.     

Amorphous Carbon Coated High Grain Boundary Density Dual Phase Li4Ti5O12‐TiO2: A Nanocomposite Anode Material for Li‐Ion Batteries

This work introduces an effective, inexpensive, and large‐scale production approach to the synthesis of a carbon coated, high grain boundary density, dual phase Li₄Ti₅O₁₂‐TiO₂ nanocomposite anode material for use in rechargeable lithium‐ion batteries. The microstructure and morphology of the Li₄Ti₅O₁₂‐TiO₂‐C product were characterized systematically. The Li₄Ti₅O₁₂‐TiO₂‐C nanocomposite electrode yielded good electrochemical performance in terms of high capacity (166 mAh g^?1 at a current density of 0.5 C), good cycling stability, and excellent rate capability (110 mAh g^?1 at a current density of 10 C up to 100 cycles). The likely contributing factors to the excellent electrochemical performance of the Li₄Ti₅O₁₂‐TiO₂‐C nanocomposite could be related to the improved morphology, including the presence of high grain boundary density among the nanoparticles, carbon layering on each nanocrystal, and grain boundary interface areas embedded in a carbon matrix, where electronic transport properties were tuned by interfacial design and by varying the spacing of interfaces down to the nanoscale regime, in which the grain boundary interface embedded carbon matrix can store electrolyte and allows more channels for the Li+ ion insertion/extraction reaction. This research suggests that carbon‐coated dual phase Li₄Ti₅O₁₂‐TiO₂ nanocomposites could be suitable for use as a high rate performance anode material for lithium‐ion batteries.     

Hierarchically Porous Li4Ti5O12 Anode Materials for Li‐ and Na‐Ion Batteries: Effects of Nanoarchitectural Design and Temperature Dependence of the Rate Capability

Integrated design of both porous structure and crystalline morphology is expected to open up the way to a new class of materials. This report demonstrates new nanostructured Li₄Ti₅O₁₂ materials with hierarchically porous structures and flower‐like morphologies. Electrochemical studies of the electrodes of Li‐ion and Na‐ion batteries clearly reveal the advantage of nanoarchitectural design of active materials. In addition, the temperature dependence of Na⁺‐insertion/extraction capacity in relation to Li₄Ti₅O₁₂ electrodes is for the first time evaluated and it is found that elevation of the cell operating temperature effectively improves the rate capability of the Na‐ion batteries. Based on the new findings, it is suggested that specially designed Li₄Ti₅O₁₂ materials allow for high‐performance Na‐ion batteries that are available as large‐scale storage devices for applications such as automotive and stationary energy storage.     

Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li+ Conductors

All‐solid‐state Li‐ion batteries based on Li₇La₃Zr₂O₁₂ (LLZO) garnet structures require novel electrode assembly strategies to guarantee a proper Li⁺ transfer at the electrode–electrolyte interfaces. Here, first stable cell performances are reported for Li‐garnet, c‐Li_6.25Al_0.25La₃Zr₂O₁₂, all‐solid‐state batteries running safely with a full ceramics setup, exemplified with the anode material Li₄Ti₅O₁₂. Novel strategies to design an enhanced Li⁺ transfer at the electrode–electrolyte interface using an interface‐engineered all‐solid‐state battery cell based on a porous garnet electrolyte interface structure, in which the electrode material is intimately embedded, are presented. The results presented here show for the first time that all‐solid‐state Li‐ion batteries with LLZO electrolytes can be reversibly charge–discharge cycled also in the low potential ranges (≈1.5 V) for combinations with a ceramic anode material. Through a model experiment, the interface between the electrode and electrolyte constituents is systematically modified revealing that the interface engineering helps to improve delivered capacities and cycling properties of the all‐solid‐state Li‐ion batteries based on garnet‐type cubic LLZO structures.     

Integrated Intercalation‐Based and Interfacial Sodium Storage in Graphene‐Wrapped Porous Li4Ti5O12 Nanofibers Composite Aerogel

Sodium storage in both solid–liquid and solid–solid interfaces is expected to extend the horizon of sodium‐ion batteries, leading to a new strategy for developing high‐performance energy‐storage materials. Here, a novel composite aerogel with porous Li₄Ti₅O₁₂ (PLTO) nanofibers confined in a highly conductive 3D‐interconnected graphene framework (G‐PLTO) is designed and fabricated for Na storage. A high capacity of 195 mA h g^?1 at 0.2 C and super‐long cycle life up to 12 000 cycles are attained. Electrochemical analysis shows that the intercalation‐based and interfacial Na storage behaviors take effect simultaneously in the G‐PLTO composite aerogel. An integrated Na storage mechanism is proposed. This study ascribes the excellent performance to the unique structure, which not only offers short pathways for Na⁺ diffusion and conductive networks for electron transport, but also guarantees plenty of PLTO–electrolyte and PLTO–graphene interfacial sites for Na⁺ adsorption.     

Li2O:Li–Mn–O Disordered Rock‐Salt Nanocomposites as Cathode Prelithiation Additives for High‐Energy Density Li‐Ion Batteries

The irreversible loss of lithium from the cathode material during the first cycles of rechargeable Li‐ion batteries notably reduces the overall cell capacity. Here, a new family of sacrificial cathode additives based on Li₂O:Li_2/3Mn_1/3O_5/6 composites synthesized by mechanochemical alloying is reported. These nanocomposites display record (but irreversible) capacities within the Li–Mn–O systems studied, of up to 1157 mAh g^?1, which represents an increase of over 300% of the originally reported capacity in Li_2/3Mn_1/3O_5/6 disordered rock salts. Such a high irreversible capacity is achieved by the reaction between Li₂O and Li_2/3Mn_1/3O_5/6 during the first charge, where electrochemically active Li₂O acts as a Li⁺ donor. A 13% increase of the LiFePO₄ and LiCoO₂ first charge gravimetric capacities is demonstrated by the addition of only 2 wt% of the nanosized composite in the cathode mixture. This result shows the great potential of these newly discovered sacrificial additives to counteract initial losses of Li⁺ ions and improve battery performance.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

Biomimetic Spider‐Web‐Like Composites for Enhanced Rate Capability and Cycle Life of Lithium Ion Battery Anodes

It is crucial to control the structure and composition of composite anode materials to enhance the cell performance of such anode materials for lithium ion batteries. Herein, a biomimetic strategy is demonstrated for the design of high performance anode materials, inspired by the structural characteristics and working principles of sticky spider‐webs. Hierarchically porous, sticky, spider‐web‐like multiwall carbon nanotube (MWCNT) networks are prepared through a process involving ozonation, ice‐templating assembly, and thermal treatment, thereby integrating the networks with γ‐Fe₂O₃ particles. The spider‐web‐like MWCNT/γ‐Fe₂O₃ composite network not only traps the active γ‐Fe₂O₃ materials tightly but also provides fast charge transport through the 3D internetworked pathways and the mechanical integrity. Consequently, the composite web shows a high capacity of ≈822 mA h g^?1 at 0.05 A g^?1, fast rate capability with ≈72.3% retention at rates from 0.05 to 1 A g^?1, and excellent cycling stability of >88% capacity retention after 310 cycles with a Coulombic efficiency >99%. These remarkable electrochemical performances are attributed to the complementarity of the 3D spider‐web‐like structure with the strong attachment of γ‐Fe₂O₃ particles on the sticky surface. This synthetic strategy offers an environmentally safe, simple, and cost‐effective avenue for the biomimetic design of high performance energy storage materials.     

The Fine Line between a Two‐Phase and Solid‐Solution Phase Transformation and Highly Mobile Phase Interfaces in Spinel Li4+xTi5O12

Phase transitions play a crucial role in Li‐ion battery electrodes being decisive for both the power density and cycle life. The kinetic properties of phase transitions are relatively unexplored and the nature of the phase transition in defective spinel Li_4+xTi₅O₁₂ introduces a controversy as the very constant (dis)charge potential, associated with a first‐order phase transition, appears to contradict the exceptionally high rate performance associated with a solid–solution reaction. With the present density functional theory study, a microscopic mechanism is put forward that provides deeper insight in this intriguing and technologically relevant material. The local substitution of Ti with Li in the spinel Li_4+xTi₅O₁₂ lattice stabilizes the phase boundaries that are introduced upon Li‐ion insertion. This facilitates a subnanometer phase coexistence in equilibrium, which although very similar to a solid solution should be considered a true first‐order phase transition. The resulting interfaces are predicted to be very mobile due to the high mobility of the Li ions located at the interfaces. This highly mobile, almost liquid‐like, subnanometer phase morphology is able to respond very fast to nonequilibrium conditions during battery operation, explaining the excellent rate performance in combination with a first‐order phase transition.     

A New Spinel‐Layered Li‐Rich Microsphere as a High‐Rate Cathode Material for Li‐Ion Batteries

Li‐rich layered materials are considered to be the promising low‐cost cathodes for lithium‐ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres are reported as a new high‐rate cathode material for Li‐ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel‐like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li‐Mn‐Co‐O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium‐ion batteries, the spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g^?1 at a very high current density of 1200 mA g^?1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge‐discharge rates. Therefore, the present spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres represent an attractive alternative to high‐rate electrode materials for lithium‐ion batteries.     

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

Silicon is attracting enormous attention due to its theoretical capacity of 4200 mAh g^?1 as an anode for Li‐ion batteries (LIBs). It is of fundamental importance and challenge to develop low‐temperature reaction route to controllably synthesize Si/Ti₃C₂ MXene LIBs anodes. Herein, a novel and efficient strategy integrating in situ orthosilicate hydrolysis and a low‐temperature reduction process to synthesize Si/Ti₃C₂ MXene composites is reported. The hydrolysis of tetraethyl orthosilicate leads to homogenous nucleation and growth of SiO₂ nanoparticles on the surface of Ti₃C₂ MXene. Subsequently, SiO₂ nanoparticles are reduced to Si via a low‐temperature (200 °C) reduction route. Importantly, Ti₃C₂ MXene not only provides fast transfer channels for Li⁺ and electrons, but also relieves volume expansion of Si during cycling. Moreover, the characteristics of excellent pseudocapacitive performance and high conductivity of Ti₃C₂ MXene can synergistically contribute to the enhancement of energy storage performance. As expected, Ti₃C₂/Si anode exhibits an outstanding specific capacity of 1849 mAh g^?1 at 100 mA g^?1, even retaining 956 mAh g^?1 at 1 A g^?1. The low‐temperature synthetic route to Si/Ti₃C₂ MXene electrodes and involved battery‐capacitive dual‐model energy storage mechanism has potential in the design of novel high‐performance electrodes for energy storage devices.     

Wet‐Chemical Processing of Phosphorus Composite Nanosheets for High‐Rate and High‐Capacity Lithium‐Ion Batteries

Phosphorus‐based materials are promising for high‐performance lithium‐ion battery (LIB) applications due to their high theoretical specific capacity. Currently, the existing physical methods render great difficulty toward rational engineering on the nanostructural phosphorus or its composites, thus limiting its high‐rate LIB applications. For the first time, a sublimation‐induced synthesis of phosphorus‐based composite nanosheets by a chemistry‐based solvothermal reaction is reported. Its formation mechanism involves solid–vapor–solid transformation driven by continuous vaporization–condensation process, as well as subsequent bottom‐up assembly growth. The proof‐of‐concept LIBs composed of the phosphorus‐based nanosheets achieve a high capacity of 630 mAh g^?1 at an ultrahigh current density of 20 A g^?1, which is attributed to efficient lithium‐ion diffusion and electron transfer. Such simple sublimation‐induced transformation opens up new prospects for rational engineering of phosphorus‐based materials for enhancing electrochemical performance.     

Hierarchical NiCo2S4@NiO Core–Shell Heterostructures as Catalytic Cathode for Long‐Life Li‐O2 Batteries

The critical challenges of Li‐O₂ batteries lie in sluggish oxygen redox kinetics and undesirable parasitic reactions during the oxygen reduction reaction and oxygen evolution reaction processes, inducing large overpotential and inferior cycle stability. Herein, an elaborately designed 3D hierarchical heterostructure comprising NiCo₂S₄@NiO core–shell arrays on conductive carbon paper is first reported as a freestanding cathode for Li‐O₂ batteries. The unique hierarchical array structures can build up multidimensional channels for oxygen diffusion and electrolyte impregnation. A built‐in interfacial potential between NiCo₂S₄ and NiO can drastically enhance interfacial charge transfer kinetics. According to density functional theory calculations, intrinsic LiO₂‐affinity characteristics of NiCo₂S₄ and NiO play an importantly synergistic role in promoting the formation of large peasecod‐like Li₂O₂, conducive to construct a low‐impedance Li₂O₂/cathode contact interface. As expected, Li‐O₂ cells based on NiCo₂S₄@NiO electrode exhibit an improved overpotential of 0.88 V, a high discharge capacity of 10 050 mAh g^?1 at 200 mA g^?1, an excellent rate capability of 6150 mAh g^?1 at 1.0 A g^?1, and a long‐term cycle stability under a restricted capacity of 1000 mAh g^?1 at 200 mA g^?1. Notably, the reported strategy about heterostructure accouplement may pave a new avenue for the effective electrocatalyst design for Li‐O₂ batteries.