Chunfu Lin

Ru0.01Ti0.99Nb2O7 as an intercalation-type anode material with a large capacity and high rate performance for lithium-ion batteries

RuxTi1−xNb2O7 (x = 0 and 0.01) materials have been synthesized via a solid-state reaction method. X-ray diffraction combined with Rietveld refinements demonstrates that both samples have a Wadsley–Roth shear structure with a C2/m space group without any impurities, and that the unit cell volume increases after the trace Ru4+ doping. Scanning electron microscopy and specific surface area tests reveal that the Ru4+ doping decreases the average particle size. The Li+ ion diffusion coefficient and electronic conductivity of Ru0.01Ti0.99Nb2O7 are respectively 64% and at least two orders of magnitude larger than those of the pristine TiNb2O7. First-principles calculations show that the increased electronic conductivity can result from the formation of impurity bands after the Ru4+ doping. Ru0.01Ti0.99Nb2O7 exhibits a large initial discharge capacity of 351 mA h g−1 at 0.1 C between 3.0 and 0.8 V vs. Li/Li+, approaching its theoretical capacity (388 mA h g−1). At 5 C, unlike the pristine TiNb2O7 with a small charge capacity of 115 mA h g−1, Ru0.01Ti0.99Nb2O7 delivers a large value of 181 mA h g−1, even exceeding the theoretical capacity of the popular spinel Li4Ti5O12 (175 mA h g−1). After 100 cycles, Ru0.01Ti0.99Nb2O7 shows a large capacity retention of 90.1%. These outstanding electrochemical performances can be attributed to its improved Li+ ionic and electronic conductivity as well as smaller particle size.

Cr0.5Nb24.5O62 Nanowires with High Electronic Conductivity for High-Rate and Long-Life Lithium-Ion Storage

Intercalation-type TiNbxO2+2.5x (x = 2, 5, and 24) anode materials have recently become more interesting for lithium-ion batteries (LIBs) due to their large theoretical capacities of 388-402 mAh g-1. However, the Ti4+/Nb5+ ions in TiNbxO2+2.5x with empty 3d/4d orbitals usually lead to extremely low electronic conductivity of <10-9 S cm-1, greatly restricting their practical capacity and rate capability. Herein, we report a class of highly conductive Cr0.5Nb24.5O62 nanowires as an intercalation-type anode material for high-performance LIBs. The as-made Cr0.5Nb24.5O62 nanowires show an open shear ReO3 crystal structure (C2 space group) with 4% tetrahedra and a conducting characteristic with ultrahigh electronic conductivity of 3.6 × 10-2 S cm-1 and a large Li+-ion diffusion coefficient of 2.19 × 10-13 cm2 s-1. These important characteristics make them deliver outstanding electrochemical properties in term of the largest reversible capacity (344 mAh g-1 at 0.1 C) in all the known niobium- and titanium-based anode materials, safe working potential (∼1.65 V vs Li/Li+), high first-cycle Coulombic efficiency (90.8%), superior rate capability (209 mAh g-1 at 30 C), and excellent cycling stability, making them among the best for LIBs in niobium- and titanium-based anode materials.

Defective Ti2Nb10O27.1: an advanced anode material for lithium-ion batteries.

To explore anode materials with large capacities and high rate performances for the lithium-ion batteries of electric vehicles, defective Ti2Nb10O27.1 has been prepared through a facile solid-state reaction in argon. X-ray diffractions combined with Rietveld refinements indicate that Ti2Nb10O27.1 has the same crystal structure with stoichiometric Ti2Nb10O29 (Wadsley-Roth shear structure with A2/m space group) but larger lattice parameters and 6.6% O2– vacancies (vs. all O2– ions). The electronic conductivity and Li+ion diffusion coefficient of Ti2Nb10O27.1 are at least six orders of magnitude and ~2.5 times larger than those of Ti2Nb10O29, respectively. First-principles calculations reveal that the significantly enhanced electronic conductivity is attributed to the formation of impurity bands in Ti2Nb10O29–x and its conductor characteristic. As a result of the improvements in the electronic and ionic conductivities, Ti2Nb10O27.1 exhibits not only a large initial discharge capacity of 329 mAh g–1 and charge capacity of 286 mAh g–1 at 0.1 C but also an outstanding rate performance and cyclability. At 5 C, its charge capacity remains 180 mAh g–1 with large capacity retention of 91.0% after 100 cycles, whereas those of Ti2Nb10O29 are only 90 mAh g–1 and 74.7%.

Porous TiNb24O62 microspheres as high-performance anode materials for lithium-ion batteries of electric vehicles

TiNb24O62 is explored as a new anode material for lithium-ion batteries. Microsized TiNb24O62 particles (M-TiNb24O62) are fabricated through a simple solid-state reaction method and porous TiNb24O62 microspheres (P-TiNb24O62) are synthesized through a facile solvothermal method for the first time. TiNb24O62 exhibits a Wadsley-Roth shear structure with a structural unit composed of a 3 × 4 octahedron-block and a 0.5 tetrahedron at the block-corner. P-TiNb24O62 with an average sphere size of ∼2 μm is constructed by nanoparticles with an average size of ∼100 nm, forming inter-particle pores with a size of ∼8 nm and inter-sphere pores with a size of ∼55 nm. Such desirable porous microspheres are an ideal architecture for enhancing the electrochemical performances by shortening the transport distance of electrons/Li+-ions and increasing the reaction area. Consequently, P-TiNb24O62 presents outstanding electrochemical performances in terms of specific capacity, rate capability and cyclic stability. The reversible capacities of P-TiNb24O62 are, respectively, as large as 296, 277, 261, 245, 222, 202 and 181 mA h g-1 at 0.1, 0.5, 1, 2, 5, 10 and 20 C, which are obviously larger than those of M-TiNb24O62 (258, 226, 210, 191, 166, 147 and 121 mA h g-1). At 10 C, the capacity of P-TiNb24O62 still remains at 183 mA h g-1 over 500 cycles with a decay of only 0.02% per cycle, whereas the corresponding values of M-TiNb24O62 are 119 mA h g-1 and 0.04%. These impressive results indicate that P-TiNb24O62 can be a promising anode material for lithium-ion batteries of electric vehicles.

Porous ZrNb24O62 nanowires with pseudocapacitive behavior achieve high-performance lithium-ion storage

The ever-increasing power and energy demands for modern consumer electronics and electric vehicles are driving the pursuit of energy-storage technologies beyond the current horizon. Pseudocapacitive charge storage is one of the most effective and promising approaches to fill this technology gap, owing to its potential to deliver both high power and energy densities. Typically, titanium niobium oxides (TiNbxO2+2.5x (x = 2, 5 and 24)) with intrinsic pseudocapacitance, high safety and theoretical capacities of 388–402 mA h g−1 are recognized as promising anode materials for lithium-ion batteries. However, their poor conductivity and low Li+-ion diffusion coefficient are known to be the major hurdles limiting the full utilization of their pseudocapacitive effects, leading to their lackluster rate capabilities. Herein, we employ a facile electrospinning method to prepare one-dimensional hierarchically porous ZrNb24O62 nanowires (P-ZrNb24O62) with an ultra-large Li+-ion diffusion coefficient as a new intercalating pseudocapacitive material for boosting Li+-ion storage. The P-ZrNb24O62 exhibits excellent electrochemical performances, including a high reversible capacity (320 mA h g−1 at 0.1C), safe working potential (∼1.67 V vs. Li/Li+), high initial coulombic efficiency (90.1%), outstanding rate capability (182 mA h g−1 at 30C) and durable long-term cyclability (90.2% capacity retention over 1500 cycles).

Heavily Cr3+-modified Li4Ti5O12: An advanced anode material for rechargeable lithium-ion batteries

Heavily Cr3+-modified Li4Ti5O12 powders with a designed nominal composition of Li3Cr7Ti2O16 have been prepared by one-step solid-state reaction. X-ray diffraction (XRD) combined with Rietveld refinement indicates that these powders contain 96.5wt.% spinel Li0.759Cr1.724Ti0.517O4 and 3.5wt.% Cr2O3. Due to the combination of Ti3+/Ti4+ and Cr2+/Cr3+ redox couples in Li0.759Cr1.724Ti0.517O4 and the existence of Cr2O3, the composite exhibits a large first-cycle discharge capacity of 315mAh⋅g−1 at a small current density of 62.5mA⋅g−1. Li0.759Cr1.724Ti0.517O4 shows an improved Li+ ion diffusion coefficient and electronic conductivity, respectively arising from the small O2− ion fractional coefficient and unpaired 3d electrons in Cr3+ ions. The majority of Cr2O3 is reduced to Cr after the first two lithiation processes, which benefits the electrical conduction between the Li0.759Cr1.724Ti0.517O4 particles. Consequently, the composite exhibits a good rate performance and cyclability. Its capacity at 1000mA⋅g−1 is as large as 141mAh⋅g−1 with large retention of 90.1% after 100 cycles.

Metallic Graphene‐Like VSe2 Ultrathin Nanosheets: Superior Potassium‐Ion Storage and Their Working Mechanism

Potassium-ion batteries (KIBs) are receiving increasing interest in grid-scale energy storage owing to the earth abundant and low cost of potassium resources. However, their development still stays at the infancy stage due to the lack of suitable electrode materials with reversible depotassiation/potassiation behavior, resulting in poor rate performance, low capacity, and cycling stability. Herein, the first example of synthesizing single-crystalline metallic graphene-like VSe2 nanosheets for greatly boosting the performance of KIBs in term of capacity, rate capability, and cycling stability is reported. Benefiting from the unique 2D nanostructure, high electron/K+ -ion conductivity, and outstanding pseudocapacitance effects, ultrathin VSe2 nanosheets show a very high reversible capacity of 366 mAh g-1 at 100 mA g-1 , a high rate capability of 169 mAh g-1 at 2000 mA g-1 , and a very low decay of 0.025% per cycle over 500 cycles, which are the best in all the reported anode materials in KIBs. The first-principles calculations reveal that VSe2 nanosheets have large adsorption energy and low diffusion barriers for the intercalation of K+ -ion. Ex situ X-ray diffraction analysis indicates that VSe2 nanosheets undertake a reversible phase evolution by initially proceeding with the K+ -ion insertion within VSe2 layers, followed by the conversion reaction mechanism.

TiNb2O7 nanorods as a novel anode material for secondary lithium-ion batteries

TiNb2O7 nanorods have been successfully fabricated by a sol–gel method with a sodium dodecyl surfate (SDS) surfactant. X-ray diffraction indicates that the TiNb2O7 nanorods have a Ti2Nb10O29-type crystal structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the nanorods have an average diameter of ∼100nm and an average length of ∼300nm. As a result of such nanosizing effect, this new material exhibits advanced electrochemical performances in terms of specific capacity, rate capability and cyclic stability. At 0.1C, it delivers a large first-cycle discharge/charge capacity of 337/279 mAh g−1. Its capacities remain 248, 233, 214, 182, 154 and 122mAh g−1 at 0.5, 1, 2, 5, 10 and 20C, respectively. After 100 cycles, its capacity at 10C remains 140mAh g−1 with large capacity retention of 91.0%.

Hollow Si/SiOx nanosphere/nitrogen-doped carbon superstructure with a double shell and void for high-rate and long-life lithium-ion storage

Silicon (Si) is a promising anode candidate for lithium-ion batteries (LIBs) owing to its unprecedented theoretical capacity of 4200 mA h g−1 and earth-abundant supply (26.2 wt%). Nevertheless, the huge volume expansion and unstable solid-electrolyte interface (SEI) of Si in multiple cycles make it very hard to simultaneously achieve high-energy and long-term cycle life for applications in large-scale renewable energy storage. Herein, we demonstrate a new class of Si/SiOx@void@nitrogen-doped carbon double-shelled hollow superstructure (Si/SiOx-DSHS) electrodes that are capable of accommodating huge volume changes without pulverization during cycling. Benefiting from the unique double-shelled hollow superstructure, Si/SiOx-DSHSs can facilitate the formation of a highly stable SEI layer and provide superior kinetics toward Li+-ion storage. The diffusion-controlled process and the capacitance-type reaction can work together to endow Si/SiOx-DSHSs with remarkable electrochemical characteristics, especially at high current density. These important characteristics make Si/SiOx-DSHSs deliver a large reversible capacity (1290 mA h g−1 at 0.1C), high first-cycle coulombic efficiency (71.7%), superior rate capability (360 mA h g−1 at 10C), and excellent cycling behavior up to 1000 cycles with a small capacity decay of 10.2%. The Si/SiOx-DSHSs are among the best Si-based anode materials for LIBs reported to date.

Intercalating Ti2Nb14O39 Anode Materials for Fast-Charging, High-Capacity and Safe Lithium-Ion Batteries

Ti-Nb-O binary oxide materials represent a family of promising intercalating anode materials for lithium-ion batteries. In additional to their excellent capacities (388-402 mAh g-1 ), these materials show excellent safety characteristics, such as an operating potential above the lithium plating voltage and minimal volume change. Herein, this study reports a new member in the Ti-Nb-O family, Ti2 Nb14 O39 , as an advanced anode material. Ti2 Nb14 O39 porous spheres (Ti2 Nb14 O39 -S) exhibit a defective shear ReO3 crystal structure with a large unit cell volume and a large amount of cation vacancies (0.85% vs all cation sites). These morphological and structural characteristics allow for short electron/Li+ -ion transport length and fast Li+ -ion diffusivity. Consequently, the Ti2 Nb14 O39 -S material delivers significant pseudocapacitive behavior and excellent electrochemical performances, including high reversible capacity (326 mAh g-1 at 0.1 C), high first-cycle Coulombic efficiency (87.5%), safe working potential (1.67 V vs Li/Li+ ), outstanding rate capability (223 mAh g-1 at 40 C) and durable cycling stability (only 0.032% capacity loss per cycle over 200 cycles at 10 C). These impressive results clearly demonstrate that Ti2 Nb14 O39 -S can be a promising anode material for fast-charging, high capacity, safe and stable lithium-ion batteries.