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

Sn0.1-Li4Ti5O12/C as a promising cathode material with a large capacity and high rate performance for Mg-Li hybrid batteries

The development prospects of conventional Li-ion batteries are limited by the paucity of Li resources. Mg-Li hybrid batteries (MLIBs) combine the advantages of Li-ion batteries and magnesium batteries. Li+ can migrate rapidly in the cathode materials, and the Mg anode has the advantage of being dendrite-free. In this study, a type of Li4Ti5O12 composite material doped with Sn4+ and a conductive carbon skeleton (Li4Ti4.9Sn0.1O12/C, Sn0.1-LTO/C) was prepared by a simple one-pot sol-gel method. The doped Sn4+ replaces part of Ti4+ in the crystal lattice, which makes Ti3+ require charge compensation, thus improving the ionic conductivity. The intervention of the conductive carbon skeleton further improves the conductivity of the Sn0.1-LTO/C composite material. The performance of Sn0.1-LTO/C as the cathode of MLIBs is explored. The initial discharge capacity was 159.1 mA h g-1 at 0.5 C, and it was maintained at 105 mA h g-1 even after 500 cycles. The excellent electrochemical performance is attributed to a small amount of Sn doping and the involvement of the conductive carbon skeleton, which indicated that the Sn0.1-LTO/C composite material provides great potential application in MLIBs.

Defensive and Ion Conductive Surface Layer Enables High Rate and Durable O3-type NaNi1/3 Fe1/3 Mn1/3 O2 Sodium-Ion Battery Cathode

Na-based layered transition metal oxides with an O3-type structure are considered promising cathodes for sodium-ion batteries. However, rapid capacity fading, and poor rate performance caused by serious structural changes and interfacial degradation hamper their use. In this study, a NaPO3 surface modified O3-type layered NaNi1/3 Fe1/3 Mn1/3 O2 cathode is synthesized, with improved high-voltage stability through protecting layer against acid attack, which is achieved by a solid-gas reaction between the cathode particles and gaseous P2 O5 . The NaPO3 nanolayer on the surface effectively stabilizes the crystal structure by inhibiting surface parasitic reactions and increasing the observed average voltage. Superior cyclic stability is exhibited by the surface-modified cathode (80.1% vs 63.6%) after 150 cycles at 1 C in the wide voltage range of 2.0 V-4.2 V (vs Na+ /Na). Moreover, benefiting from the inherent ionic conduction of NaPO3 , the surface-modified cathode presents excellent rate capability (103 mAh g-1  vs 60 mAh g-1 ) at 10 C. The outcome of this study demonstrates a practically relevant approach to develop high rate and durable sodium-ion battery technology.

Synchronous Manipulation of Ion and Electron Transfer in Wadsley-Roth Phase Ti-Nb Oxides for Fast-Charging Lithium-Ion Batteries

Implementing fast-charging lithium-ion batteries (LIBs) is severely hindered by the issues of Li plating and poor rate capability for conventional graphite anode. Wadsley-Roth phase TiNb₂ O₇ is regarded as a promising anode candidate to satisfy the requirements of fast-charging LIBs. However, the unsatisfactory electrochemical kinetics resulting from sluggish ion and electron transfer still limit its wide applications. Herein, an effective strategy is proposed to synchronously improve the ion and electron transfer of TiNb₂ O₇ by incorporation of oxygen vacancy and N-doped graphene matrix (TNO_{- x} @N-G), which is designed by combination of solution-combustion and electrostatic self-assembly approach. Theoretical calculations demonstrate that Li⁺ intercalation gives rise to the semi-metallic characteristics of lithiated phases (Li_y TNO_{- x} ), leading to the self-accelerated electron transport. Moreover, in situ X-ray diffraction and Raman measurements reveal the highly reversible structural evolution of the TNO_{- x} @N-G during cycling. Consequently, the TNO_{- x} @N-G delivers a higher reversible capacity of 199.0 mAh g^-1 and a higher capacity retention of 86.5% than those of pristine TNO (155.8 mAh g^-1 , 59.4%) at 10 C after 2000 cycles. Importantly, various electrochemical devices including lithium-ion full battery and hybrid lithium-ion capacitor by using the TNO_{- x} @N-G anode exhibit excellent rate capability and cycling stability, verifying its potential in practical applications.

N/S Co-doped microporous carbon derived from PSSH-Melamine salt solution as cathode host for Lithium-Selenium batteries

Selenium cathode attracts great attention due to its high theoretical volumetric capacity and better electrical conductivity than sulfur cathode. Herein, N/S co-doped microporous carbon (NS-K-PC) is designed and prepared as Se host by a spray drying process of the poly(styrenesulfonic acid)-melamine salt solution followed by carbonization and activation process. The as-prepared NS-K-PC shows a very high micropore contribution of 94.8% in the total surface area, and a total N/S heteroatom doping level of 2.5 wt% in the carbon matrix. The NS-K-PC/Se cathode delivers a high reversible capacity of 499.2 mA h g^-1 at 0.1C, superior rate capacity of 324 mA h g^-1 at 8C, and great cycling stability with a capacity decay of 0.081% per cycle over 500 cycles at 1C. Additionally, a comparative study demonstrates that NS-K-PC/Se cathode with the carbonate-based electrolytes exhibit better cycling stability than those with ether-based electrolytes primarily resulted from a direct solid-solid conversion of Se to Li₂Se bypassing the formation of soluble polyselenides.

Wadsley-Roth Crystallographic Shear Structure Niobium-Based Oxides: Promising Anode Materials for High-Safety Lithium-Ion Batteries

Wadsley-Roth crystallographic shear structure niobium-based oxides are of great interest in fast Li+ storage due to their unique 3D open tunnel structures that offer facile Li+ diffusion paths. Their moderate lithiation potential and reversible redox couples hold the great promise in the development of next-generation lithium-ion batteries (LIBs) that are characterized by high power density, long lifespan, and high safety. Despite these outstanding merits, there is still extensive advancement space for further enhancing their electrochemical kinetics. And the industrial feasibility of Wadsley-Roth crystallographic shear structure niobium-based oxides as anode materials for LIBs requires more systematic research. In this review, recent progress in this field is summarized with the aim of realizing the practical applications of Wadsley-Roth phase anode materials in commercial LIBs. The review focuses on research toward the crystalline structure analyses, electrochemical reaction mechanisms, modification strategies, and full cell performance. In addition to highlighting the current research advances, the outlook and perspective on Wadsley-Roth anode materials is also concisely provided.

Engineering Hierarchical Co@N-Doped Carbon Nanotubes/α-Ni(OH)2 Heterostructures on Carbon Cloth Enabling High-Performance Aqueous Nickel-Zinc Batteries

Searching for high-performance Ni-based cathodes plays an important role in developing better aqueous nickel-zinc (Ni-Zn) batteries. For this purpose, herein, we demonstrate the design and synthesis of ultrathin α-Ni(OH)₂ nanosheets branched onto metal-organic frameworks (MOFs)-derived 3D cross-linked N-doped carbon nanotubes encapsulated with tiny Co nanoparticles (denoted as Co@NCNTs/α-Ni(OH)₂), which are directly supported on a flexible carbon cloth (CC). An aqueous Ni-Zn battery employing the hierarchical CC/Co@NCNTs/α-Ni(OH)₂ as the binder-free cathode and a commercial Zn plate as the anode is fabricated, which displays an ultrahigh capacity (316 mAh g^-1) and energy density (540.4 Wh kg^-1) at 1 A g^-1 as well as excellent rate capability (238 mAh g^-1 at 10 A g^-1) and superior cycling performance (about 84% capacity retention after 2000 cycles at 10 A g^-1). The impressive electrochemical performance might benefit from the rich active sites, rapid electron transfer, cushy electrolyte access, rapid ion transport, and robust structural stability. In addition, the quasi-solid-state CC/Co@NCNTs/α-Ni(OH)₂//Zn batteries are also successfully assembled with polymer electrolyte, indicating the great potential for portable and wearable electronics. This work might provide important guidance for constructing carbon-based hybrid materials directly supported on conductive substrates as high-performance electrodes for energy-related devices.

Highly Efficient Multicomponent Gel Biopolymer Binder Enables Ultrafast Cycling and Applicability in Diverse Battery Formats

Electrode materials with a high performance and stable cycling have been commercialized, but the utilization of state-of-the-art Li-ion batteries in high-current rate applications is restricted because of limitations in other battery components, in particular, the lack of an efficient binder. Herein, a novel multicomponent polymer gel binder (PGB) is presented, comprising the biopolymer chitosan as the host, embedded with the 1-butyl-1-methylpyrrolidinium dicyanamide (PYR₁₄DCA) ionic liquid and the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. The multicomponent approach leads to carbon black arrangement along well-distributed chitosan chains in the electrodes, forming a highly electronic conductive network. Furthermore, the plasticizing effect of the ionic liquid leads to an enhanced ionic conductivity. As a result, shorter charge-transfer paths are enabled, leading to an exceptionally high rate capability in LiFePO₄ and Li₄Ti₅O₁₂ half cells, up to 50C. LiFePO₄||Li₄Ti₅O₁₂ full cells using the PGB for both electrodes also demonstrated stable cycling at 10C, with an impressively high discharge capacity of 173 mA h·g^-1 after 1000 cycles. In addition, freestanding electrodes could also be realized and functioning flexible Li-ion cells were successfully demonstrated. Thus, the novel water-processable binder offers multifaceted advantages, making the approach highly promising for industrial implementation.

The α-Fe2O3/graphite anode composites with enhanced electrochemical performance for lithium-ion batteries

The α-Fe₂O₃/graphite composites were prepared by a thermal decomposition method using the expanded graphite as the matrix. The α-Fe₂O₃ nanoparticles with the size of 15-30 nm were embedded into interlayers of graphite, forming a laminated porous nanostructure with a main pore distribution from 2 to 20 nm and the Brunauer-Emmett-Teller surface area of 33.54 m² g^-1. The porous structure constructed by the graphite sheets can alleviate the adverse effects caused by the huge volume change of the α-Fe₂O₃ grains during the charge/discharge process. The composite electrode exhibits a high reversible capacity of 1588 mAh g^-1 after 100 cycles at 100 mA g^-1, 702 mAh g^-1 at 5 A g^-1, 460 mAh g^-1 at 10 A g^-1 after 160 cycles, respectively, showing good cycle stability and outstanding rate capability at high current densities.

Stabilizing Liquid Electrolytes in a Porous PVDF Matrix Incorporated with Star Polymers with Linear PEG Arms and CycloPEG Cores

Porous membranes fabricated from poly(vinylidene fluoride) (PVDF) and a star polymer with linear poly(ethylene glycol) (PEG) arms and cycloPEG cores were fabricated via the phase-separation method. The porous gel polymer electrolytes (PGPEs) were obtained by immersing the porous membranes in the electrolyte solution. When the additive amount of star polymer was up to 20 wt %, the prepared membrane had the largest porosity and the pores were uniformly distributed in the membrane. The star polymer can not only decrease the crystallization of PVDF and enhance the absorption of liquid electrolyte but also offer ion conduction channels (cycloPEG cores). Therefore, the PGPE with 20 wt % star polymers exhibited competitive ionic conductivities of 1.27 mS cm^-1 at 30 °C and 2.89 mS cm^-1 at 80 °C. To stabilize the liquid electrolyte in the holes of porous membranes, a gelator was introduced in the liquid electrolyte to form gelled porous gel polymer electrolytes (GPGPEs), and the leakage of liquid electrolytes was thus remarkably reduced. The ionic conductivity of GPGPEs with 20 wt % star polymer and 1.5 wt % gelator was importantly improved at high temperatures (6.02 mS cm^-1 at 80 °C). We systematically investigated the electrochemical performances of PGPEs without star polymer, PGPEs with star polymer, and GPGPEs with star polymer. The incorporation of star polymers with linear PEG arms and cycloPEG cores into the PGPEs and GPGPEs significantly improved the electrochemical performances of the lithium metal/LiFePO₄ cell assembled with the PGPEs or GPGPEs.

Hierarchical Ti3C2Tx MXene/Ni Chain/ZnO Array Hybrid Nanostructures on Cotton Fabric for Durable Self-Cleaning and Enhanced Microwave Absorption

The increasing demand for wearable electronics and the intensification of electromagnetic pollution have boosted the exploration of high-performance flexible microwave absorption (MA) materials. Herein, the hierarchical Ti₃C₂T_x MXene/Ni chain/ZnO array hybrid nanostructures are rationally constructed on cotton fabric for acquiring enhanced MA performance and durable self-cleaning ability. Based on the high dielectric loss capacity of MXenes and ZnO arrays, by controlling dip-coating numbers of Ni chains, the magnetic loss can be manipulated to modulate the impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < -10 dB). The minimum RL value of the designed fabric can reach -35.1 dB at 8.3 GHz with a thickness of 2.8 mm, and its EAB can cover the whole X-band with only a 2.2 mm thickness. In addition, the designed fabric also exhibits superior liquid repellency and durable self-cleaning ability due to the combination of the hybrid nanostructures and a superhydrophobic coating. This work provides an insight for rational design of textile-based MA materials, showing potential applications in flexible and wearable functional electronics.

Ultrafast and Stable Li-(De)intercalation in a Large Single Crystal H-Nb2 O5 Anode via Optimizing the Homogeneity of Electron and Ion Transport

Exploring anode materials with fast, safe, and stable Li-(de)intercalation is of great significance for developing next-generation lithium-ion batteries. Monoclinic H-type niobium pentoxide possesses outstanding intrinsic fast Li-(de)intercalation kinetics, high specific capacity, and safety; however, its practical rate capability and cycling stability are still limited, ascribed to the asynchronism of phase change throughout the crystals. Herein this problem is addressed by homogenizing the electron and Li-ion conductivity surrounding the crystals. An amorphous N-doped carbon layer is introduced on the micrometer single-crystal H-Nb₂ O₅ particle to optimize the homogeneity of electron and Li-ion transport. As a result, the as-prepared H-Nb₂ O₅ exhibits high reversible capacity (>250 mAh g^-1 at 50 mA g^-1 ), unprecedented high-rate performance (≈120 mAh g^-1 at 16.0 A g^-1 ) and excellent cycling stability (≈170 mAh g^-1 at 2.0 A g^-1 after 1000 cycles), which is by far the highest performance among the H-Nb₂ O₅ materials. The inherent principle is further confirmed via operando transmission electron microscopy and X-ray diffraction. A novel insight into the further development of electrode materials forlithium-ion batteries is thus provided.

The rational design of carbon coated Fe2(MoO4)3 nanosheets for lithium-ion storage with high initial coulombic efficiency and long cycle life

Binary metal oxides are potential anode materials for lithium-ion storage due to their high theoretical specific capacities. However, the practical applications of metal oxides are limited due to their large volume changes and sluggish reaction kinetics. Herein, carbon coated Fe₂(MoO₄)₃ nanosheets are prepared via a simple method, adopting urea as the template and carbon source. The carbon coating on the surface helps to elevate the conductivity of the active material and maintain structural integrity during the lithium storage process. Combining this with a catalytic effect from the generated Fe, leading to the reversible formation of a solid electrolyte interface layer, a high initial coulombic efficiency (>87%) can be obtained. Based on this, the carbon coated Fe₂(MoO₄)₃ nanosheets show excellent rate capability (a reversible discharge capacity of 983 mA h g^-1 at 5 A g^-1) and stable cycling performance (1376 mA h g^-1 after 250 cycles at 0.5 A g^-1 and 864 mA h g^-1 after 500 cycles at 2 A g^-1). This simple in situ carbonization and template method using urea provides a facile way to optimize electrode materials for next-generation energy storage devices.

Achieving Ultrahigh-Rate and High-Safety Li+ Storage Based on Interconnected Tunnel Structure in Micro-Size Niobium Tungsten Oxides

Developing advanced high-rate electrode materials has been a crucial aspect for next-generation lithium ion batteries (LIBs). A conventional nanoarchitecturing strategy is suggested to improve the rate performance of materials but inevitably brings about compromise in volumetric energy density, cost, safety, and so on. Here, micro-size Nb₁₄ W₃ O₄₄ is synthesized as a durable high-rate anode material based on a facile and scalable solution combustion method. Aberration-corrected scanning transmission electron microscopy reveals the existence of open and interconnected tunnels in the highly crystalline Nb₁₄ W₃ O₄₄ , which ensures facile Li⁺ diffusion even within micro-size particles. In situ high-energy synchrotron XRD and XANES combined with Raman spectroscopy and computational simulations clearly reveal a single-phase solid-solution reaction with reversible cationic redox process occurring in the NWO framework due to the low-barrier Li⁺ intercalation. Therefore, the micro-size Nb₁₄ W₃ O₄₄ exhibits durable and ultrahigh rate capability, i.e., ≈130 mAh g^-1 at 10 C, after 4000 cycles. Most importantly, the micro-size Nb₁₄ W₃ O₄₄ anode proves its highest practical applicability by the fabrication of a full cell incorporating with a high-safety LiFePO₄ cathode. Such a battery shows a long calendar life of over 1000 cycles and an enhanced thermal stability, which is superior than the current commercial anodes such as Li₄ Ti₅ O₁₂ .

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.

Li(Na)2FeSiO4/C hybrid nanotubes: promising anode materials for lithium/sodium ion batteries

Porous Li(Na)₂FeSiO₄/C hybrid nanotubes were successfully synthesized by a modified sol–gel strategy and a subsequent calcination process. These nanohybrids exhibited excellent electrochemical performances as anodes for lithium/sodium ion batteries.

Core-shell (nano-SnX/nano-Li4Ti5O12)@C spheres (X = Se,Te) with high volumetric capacity and excellent cycle stability for lithium-ion batteries

Among binary tin chalcogenides as anode materials for lithium-ion batteries, SnSe and SnTe have attracted attention due to their high theoretical volumetric capacity. However, they suffer from sluggish dynamics and serious agglomeration during lithiation/delithiation processes, which leads to inferior cycling performance. This study reports core-shell structure (nano-SnSe/nano-Li₄Ti₅O₁₂)@C and (nano-SnTe/nano-Li₄Ti₅O₁₂)@C [denoted as (n-SnX/n-LTO)@C] with extraordinary lithium storage stability. Benefiting from the well-designed structural merits, the core-shell structure of (n-SnX/n-LTO)@C is well preserved over 500 cycles, suggesting its high structural integrity. The (n-SnSe/n-LTO)@C and (n-SnTe/n-LTO)@C anodes deliver high initial volumetric capacities of 3470.1 and 3885.4 mA h cm^-3 at 0.2 A g^-1 and maintain capacities of 2066.0 and 1975.3 mA h cm^-3 even after 500 cycles, respectively. This work provides a new avenue for designing novel binary tin chalcogenide lithium-ion battery anodes with high volumetric capacity and superior long-term cycling performance.

Designs of Experiments for Beginners—A Quick Start Guide for Application to Electrode Formulation

In this paper, we will describe in detail the setting up of a Design of Experiments (DoE) applied to the formulation of electrodes for Li-ion batteries. We will show that, with software guidance, Designs of Experiments are simple yet extremely useful statistical tools to set up and embrace. An Optimal Combined Design was used to identify influential factors and pinpoint the optimal formulation, according to the projected use. Our methodology follows an eight-step workflow adapted from the literature. Once the study objectives are clearly identified, it is necessary to consider the time, cost, and complexity of an experiment before choosing the responses that best describe the system, as well as the factors to vary. By strategically selecting the mixtures to be characterized, it is possible to minimize the number of experiments, and obtain a statistically relevant empirical equation which links responses and design factors.

Ti3+ Self-Doped Li4 Ti5 O12 Anchored on N-Doped Carbon Nanofiber Arrays for Ultrafast Lithium-Ion Storage

Omnibearing acceleration of charge/ion transfer in Li₄ Ti₅ O₁₂ (LTO) electrodes is of great significance to achieve advanced high-rate anodes in lithium-ion batteries. Here, a synergistic combination of hydrogenated LTO nanoparticles (H-LTO) and N-doped carbon fibers (NCFs) prepared by an electrodeposition-atomic layer deposition method is reported. Binder-free conductive NCFs skeletons are used as strong support for H-LTO, in which Ti³⁺ is self-doped along with oxygen vacancies in LTO lattice to realize enhanced intrinsic conductivity. Positive advantages including large surface area, boosted conductivity, and structural stability are obtained in the designed H-LTO@NCF electrode, which is demonstrated with preeminent high-rate capability (128 mAh g^-1 at 50 C) and long cycling life up to 10 000 cycles. The full battery assembled by H-LTO@NCFs anode and LiFePO₄ cathode also exhibits outstanding electrochemical performance revealing an encouraging application prospect. This work further demonstrates the effectiveness of self-doping of metal ions on reinforcing the high-rate charge/discharge capability of batteries.

Coupling Niobia Nanorods with a Multicomponent Carbon Network for High Power Lithium-Ion Batteries

High power lithium-ion batteries require highly conductive electrodes. For an active electrode material that has limited electron conductivity, it is critical to build a carbon network that is not only highly conductive itself but also highly compatible with the electroactive material for efficient interfacial charge transfer. Herein, we design a multicomponent carbon network that is optimized for electrical coupling with the electroactive Nb₂O₅ nanorods for efficient electron injection. The self-support electrode is constructed by using 0D polypyrrole-derived (Ppy) carbon nanoparticles as glue to bind the Nb₂O₅ nanorods with 1D carbon nanotubes (CNTs) and 2D graphene nanosheets (GNSs). The 0D carbon nanoparticles also cross-link 1D CNTs with 2D GNSs, which can effectively prevent the GNSs from aggregation and form the 3D CNT/GNS network that provides continuous electronic and ionic pathways. This 3D Nb₂O₅@C self-support electrode exhibits a high discharge capacity of 246.3 mA h g^-1 at 0.5 C and 100 mA h g^-1 at 20 C and excellent Coulombic efficiency of 99.98% at 20 C. Even increasing the mass loading to 7.1 mg cm^-2, the Nb₂O₅@C electrode can still reach a discharge capacity of 172.4 mA h g^-1 at 0.5 C after 100 cycles. A high power density of 1043 W kg^-1 can be achieved at an energy density of 104.3 W h kg^-1 based on the electrode weight, which is among the highest values demonstrated so far for Nb₂O₅ electrodes. The results pave the way toward practical applications of Nb₂O₅ anodes in high-power lithium-ion batteries.

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.

Boosting High-Rate Sodium Storage Performance of N-Doped Carbon-Encapsulated Na3 V2 (PO4 )3 Nanoparticles Anchoring on Carbon Cloth

The further development of high-power sodium-ion batteries faces the severe challenge of achieving high-rate cathode materials. Here, an integrated flexible electrode is constructed by smart combination of a conductive carbon cloth fiber skeleton and N-doped carbon (NC) shell on Na₃ V₂ (PO₄ )₃ (NVP) nanoparticles via a simple impregnation method. In addition to the great electronic conductivity and high flexibility of carbon cloth, the NC shell also promotes ion/electron transport in the electrode. The flexible NVP@NC electrode renders preeminent rate capacities (80.7 mAh g^-1 at 50 C for cathode; 48 mAh g^-1 at 30 C for anode) and superior cycle performance. A flexible symmetric NVP@NC//NVP@NC full cell is endowed with fairly excellent rate performance as well as good cycle stability. The results demonstrate a powerful polybasic strategy design for fabricating electrodes with optimal performance.

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.

Dendrite-Free Zinc Deposition Induced by Multifunctional CNT Frameworks for Stable Flexible Zn-Ion Batteries

The current boom of safe and renewable energy storage systems is driving the recent renaissance of Zn-ion batteries. However, the notorious tip-induced dendrite growth on the Zn anode restricts their further application. Herein, the first demonstration of constructing a flexible 3D carbon nanotube (CNT) framework as a Zn plating/stripping scaffold is constituted to achieve a dendrite-free robust Zn anode. Compared with the pristine deposited Zn electrode, the as-fabricated Zn/CNT anode affords lower Zn nucleation overpotential and more homogeneously distributed electric field, thus being more favorable for highly reversible Zn plating/stripping with satisfactory Coulombic efficiency rather than the formation of Zn dendrites or other byproducts. As a consequence, a highly flexible symmetric cell based on the Zn/CNT anode presents appreciably low voltage hysteresis (27 mV) and superior cycling stability (200 h) with dendrite-free morphology at 2 mA cm^-2 , accompanied by a high depth of discharge (DOD) of 28%. Such distinct performance overmatches most of recently reported Zn-based anodes. Additionally, this efficient rechargeability of the Zn/CNT anode also enables a substantially stable Zn//MnO₂ battery with 88.7% capacity retention after 1000 cycles and remarkable mechanical flexibility.

Niobium-Based Oxides Toward Advanced Electrochemical Energy Storage: Recent Advances and Challenges

Niobium-based oxides including Nb₂ O₅ , TiNb_x O_2+2.5x compounds, M-Nb-O (M = Cr, Ga, Fe, Zr, Mg, etc.) family, etc., as the unique structural merit (e.g., quasi-2D network for Li-ion incorporation, open and stable Wadsley- Roth shear crystal structure), are of great interest for applications in energy storage systems such as Li/Na-ion batteries and hybrid supercapacitors. Most of these Nb-based oxides show high operating voltage (>1.0 V vs Li⁺ /Li) that can suppress the formation of solid electrolyte interface film and lithium dendrites, ensuring the safety of working batteries. Outstanding rate capability is impressive, which can be derived from their fast intercalation pseudocapacitive kinetics. However, the intrinsic poor electrical conductivity hinders their energy storage applications. Various strategies including structure optimization, surface engineering, and carbon modification are effectively used to overcome the issues. This review provides a comprehensive summary on the latest progress of Nb-based oxides for advanced electrochemical energy storage applications. Major impactful work is outlined, promising research directions, and various performance-optimizing strategies, as well as the energy storage mechanisms investigated by combining theoretical calculations and various electrochemical characterization techniques. In addition, challenges and perspectives for future research and commercial applications are also presented.

SnO2 Nanoflake Arrays Coated with Polypyrrole on a Carbon Cloth as Flexible Anodes for Sodium-Ion Batteries

SnO₂ has been extensively studied as an anode material for sodium-ion batteries, which, however, has long been subjected to poor conductivity and large volume expansion accompanied with an unsatisfactory electrochemical performance. Here, novel interlaced SnO₂ nanoflakes are synthesized directly on a carbon cloth collector via hydrothermal and annealing treatment and then coated with polypyrrole (PPy) via electrodeposition. The as-prepared flexible SnO₂@PPy on the carbon cloth exhibits a high initial capacity of 1172.1 mAh g^-1 and an outstanding cycling stability with 85% capacity retention after 300 cycles at 0.1 A g^-1, which can be contributed to the interlaced SnO₂ nanoflakes as well as the coating of PPy. This result shows promising potential for construction of an electrode in high-performance energy storage fields.

Functionalized N-Doped Carbon Nanotube Arrays: Novel Binder-Free Anodes for Sodium-Ion Batteries

Boosting electrochemical sodium storage properties is achieved by utilizing functionalized N-doped carbon nanotube arrays (NCNAs) as anode materials. The NCNA anodes are first fabricated by self-polymerization of dopamine on cobalt hydroxide nanorod arrays as the template. The NCNAs with diameters of 100-120 nm are grown vertically to Ni foam, forming self-supported nanotube arrays. Such a structure has attractive advantages including large porosity and surface area, good electrical conductivity and mechanical strength. Consequently, the NCNAs are demonstrated to achieve excellent sodium storage performances with high capacity (335 mA h g^-1 at 100 mA g^-1), good rate capability (140 mA h g^-1 at 2 A g^-1), and superior capacity retention of 90.9% after 500 cycles. Especially, high performance is verified in the assembled full cells by using an NCNA anode and Na₃V₂(PO₄)₃/C cathode. The developed synthetic strategy provides an effective approach for the fabrication of advanced heteroatom-doped carbon-based electrodes for electrochemical energy storage.

Regulating Lithium Nucleation via CNTs Modifying Carbon Cloth Film for Stable Li Metal Anode

Li metal is demonstrated as one of the most promising anode materials for high energy density batteries. However, uncontrollable Li dendrite growth and repeated growth of solid electrolyte interface during the charge/discharge process lead to safety issues and capacity decay, preventing its practical application. To address these issues, an effective strategy is to realize uniform Li nucleation. Here, a stable lithium-scaffold composite electrode (CC/CNT@Li) is designed by melting of lithium metal into 3D interconnected lithiophilic carbon nanotube (CNT) on a porous carbon cloth (CC). The 3D interconnected CNTs successfully change the lithiophobic CC into lithiophilic nature, reducing the polarization of the electrode, ensuring homogenous Li nucleation and continuous smooth Li plating. The CNTs on the surface of CC provide adequate Li nucleation sites and reduce the areal current density to avoid Li dendrite growth. The 3D porous structure of CC/CNT offers enough free room for buffering the huge volume change during Li plating/stripping. The CC/CNT@Li composite anode exhibits dendrite-free morphology and superior cycling performances over 500 h with low voltage hysteresis of 18, 23, and 71 mV at the current density of 1, 2, and 5 mA cm^-2 , respectively.

Construction of Sb2Se3 nanocrystals on Cu2−xSe@C nanosheets for high performance lithium storage

Cu_2−xSe@C@Sb₂Se₃ with enhanced electrochemical performance was designed and fabricated, where Sb₂Se₃ nanoparticles were anchored on Cu_2−xSe@C nanosheets.