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In this study we used a spray-drying process and in situ polymerization to construct ternary composites of Li 4 Ti 5 O 12 (LTO) embedded with multi-walled carbon nanotubes (MWCNTs) and interfacially modified with polyaniline (PANI). In these composites, the introduced MWCNTs served as conductive backbones within the spray-dried LTO microspheres, thereby lowering the internal resistance of the microcomposites. The polymerized PANI acted as a conductive adhesive to strengthen the interactions between the MWCNTs and the LTO, leading to a sturdier interface and enhanced ionic transport properties. With the combined effects of the embedded MWCNTs and the interfacially polymerized PANI, we observed significant enhancements in both the conductivity and the ionic diffusion kinetics of the LTO composites. As a result, the ternary composites displayed outstanding electrochemical performance, including enhanced rate capability and remarkable cycling stability. The ternary system delivered a discharge capacitance (134.98 mA h/g) at 20 C that was higher than those of bare LTO (38.6 mA h/g) and MWCNT/LTO (114.88 mA h/g). Furthermore, the composites also exhibited 92.7% retention of their specific capacitance after 200 repeated charge/discharge tests, indicating their excellent cycling life. [ABSTRACT FROM AUTHOR]

Li 4 Ti 5 O 12 (LTO) has attracted much attention for its use as an anode material within lithium-ion batteries (LIBs), owing to its excellent safety and outstanding cyclability. Unfortunately, the poor electronic conductivity of LTO greatly limits the rate capability of the LIBs and, therefore, its practical applications. The conductivity of LTO can be enhanced significantly through thermal treatment under hypoxic conditions to form oxygen vacancies. The defective LTO with oxygen vacancies has a much higher electric conductivity, owing to partial reduction of the Ti ions (from Ti4+ to Ti3+). Too many oxygen vacancies generated in the LTO will, however, also cause severe lattice distortion, inhibiting ionic transfer. In this study, we optimized the Ti3+/Ti4+ ratio of LTO by annealing it under various conditions. We also modified the surface of LTO with a thin layer of poly (dimethyl 3,4-propylenedioxythiophene) (PProDOT-Me 2) through in situ chemical polymerization. Studies of the surface morphology and chemical composition confirmed that PProDOT-Me 2 had been successfully capped on the LTO surface. Combining the effects of the optimal Ti3+/Ti4+ ratio and the surface modification with PProDOT-Me 2 resulted in the charge and ionic transport properties of LTO both improving significantly. Accordingly, the nanocomposites displayed greatly enhanced rate capabilities, relative to those of the unmodified material. [ABSTRACT FROM AUTHOR]

Abstract Spray-drying technique has been widely used for synthesis of energy storage materials due to its low cost and easy scale up. However, in mass production, this method usually suffers from the incomplete solid-state reaction owing to the aggregation or poor reactivity of precursors caused by their large particle size and unfavorable morphology. In this study, spinel Li 4 Ti 5 O 12 (LTO) has been synthesized by using TiO 2 nanosheets as precursor through spray-drying for large-scale production. The TiO 2 nanosheets are prepared via a facile and scalable wet grinding method. The high aspect ratio TiO 2 nanosheets can efficiently reduce the diffusion length of Li element during the solid-state reaction leading to higher reactivity. It has been found that the temperature required for the formation of LTO phase can be significantly reduced by using the two-dimensional (2D) TiO 2 nanosheets as starting materials. As a result, through a pilot-scale spray drying process, the LTO reacted from the TiO 2 nanosheets shows a pure spinel structure due to the better morphology of TiO 2 nanosheets. In contrast, using the unprocessed TiO 2 as precursor, the resulting LTO still reveals other impure phases leading to a poor electrochemical performance. The pure LTO shows a higher discharge capacity of ∼160.8 mAh/g at 0.1 C, with an excellent rate performance and superior cycling life in comparison with the LTO containing impurity phases. Highlights • TiO 2 with sheet-like structure has been prepared as the starting material. • LTO microspheres with pure phase have been prepared by spray-drying. • The reactivity of LTO precursor has been enhanced by grinding treatment. • Excellent rate performance along with superior cycling life is achieved. [ABSTRACT FROM AUTHOR]

Abstract In this study we prepared Mg2+ and Cr3+ co-doped and phosphidated Li 4 Ti 5 O 12 (LTO) microspheres using a spray-drying method. Doping with both Mg2+ and Cr3+ improved the electronic conduction of LTO, due to partial reduction of Ti4+ (from Ti4+ to Ti3+) and narrowing of the band gap, respectively. Moreover, the phosphidation process formed a uniform conductive glass layer on the LTO surface, leading to higher ionic conductivity. As a result, the modified LTO exhibited improved rate capability and cyclic stability, compared with those of the pristine LTO. In particular, the Mg2+ and Cr3+ co-doped and phosphidated LTO exhibited superior performance as a result of the combined effects of ion-doping and interfacial modification. Finally, the capacity improved significantly, especially at high C rates [e.g., 127.72 mA h g–1 at 20 C—77.6% of the value recorded at 0.1 C (164.62 mA h g–1)], due to the dual effects of the enhanced electric and ionic conductivities. [ABSTRACT FROM AUTHOR]

In this article, hierarchical porous carbon (HPC) with high surface area of 1604.9 m2/g is prepared by the pyrolysis of rubberwood sawdust using CaCO3 as a hard template. The bio-oil pyrolyzed from the rubber sawdust, followed by the polymerization reaction to form resole phenolic resin, can be used as a carbon source to prepare HPC. The biomass-derived HPC shows a three-dimensionally interconnected morphology which can offer a continuous pathway for ionic transport. The symmetrical supercapacitors based on the as-prepared HPC were tested in 1.0 M tetraethylammonium tetrafluoroborate/propylene carbonate electrolyte. The results of electrochemical analysis show that the HPC-based supercapacitor exhibits a high specific capacitance of 113.3 F/g at 0.5 A/g with superior rate capability and cycling stability up to 5000 cycles. Hybrid lithium-ion capacitors (LICs) based on the HPC and Li4Ti5O12 (LTO) were also fabricated. The LICs have a maximum energy density of 113.3 Wh/kg at a power density of 281 W/kg. Moreover, the LIC also displays a remarkable cycling performance with a retention of 92.8% after 3000 cycles at a large current density of 0.75 A/g, suggesting great potential application in the energy storage of the LIC. [ABSTRACT FROM AUTHOR]

Carbon-coated Li4Ti5O12 (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g). [ABSTRACT FROM AUTHOR]

• The biomass-derived HMMC has been synthesized through pyrolysis of rubber wood. • LIC based on a biomass-derived carbon and a high-rate LTO has been fabricated. • The as-fabricated LIC shows a high energy/power density of 142 Wh/kg at 253 W/kg. • Enhanced rate capability improved intrinsic kinetic imbalance between HMMC and LTO. In this study we prepared a biomass-derived porous carbon and a high-rate Li 4 Ti 5 O 12 (LTO) as cathode and anode materials, respectively, for Li-ion capacitors (LICs). We synthesized the bio-derived carbon through pyrolysis of rubberwood as the carbon source. The as-synthesized carbon featured a hierarchical micro/mesoporous architecture with a surface area of 1365 m2 g−1 and excellent electrochemical properties. A symmetric supercapacitor (SC) based on the bio-derived carbon material exhibited excellent capacitance characteristics and remarkable cycling stability. Furthermore, the rate performance of the spray-dried LTO modified through ionic doping and surface coating was much better than that of the unmodified LTO, due to enhanced conductivity and ionic diffusivity. Because of the outstanding rate capability of the modified LTO, the kinetic mismatch between the cathode and anode—a general problem for LICs—was overcome. After coupling the bio-derived porous carbon with the high-rate LTO, the as-fabricated LIC displayed a high energy/power density of 142 Wh kg−1/253 W kg−1, and even provided a value of 52.9 Wh kg−1 at 4556 W kg−1. In addition, this LIC retained 85.7% of its original capacity after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Dual improvement on electrochemical kinetics and lifespan of LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode material is of great significance for realizing high-power and durable lithium-ion batteries (LIBs). To achieve this goal, the Mg2+−Cr3+ co-doping LNMO microspheres were prepared via the coprecipitation route. FTIR, Raman spectra and magnetic susceptibility verify that both the Mg2+ and Cr3+ doping are beneficial for the formation of disordered Fd 3m phase leading to the improvement of electronic conductivity and decrease in electrochemical polarization and the charge transfer resistance (R ct). Meanwhile, the doping also reduces the content of Mn3+ in LNMO which can diminish the dissolution of Mn3+ resulting in the enhancement of cycling life. As a result, the Mg2+−Cr3+ co-doping sample (MC-LNMO) exhibits an improved electrochemical performance (EP). A discharge capacity (DC) of 110.7 mAh/g at 10C can be obtained for MC-LNMO which is higher than that of pure LNMO (only 53 mAh/g) and after 200 cycles the capacity fade is only 4.6% at 25 °C. To further evaluate the MC-LNMO electrode for practical application, in this study, the full cells were also fabricated using the MC-LNMO as cathode and Li 4 Ti 5 O 12 (LTO) as anode. In the combination, the full device exhibits high energy density (ED) and long cycle life due to the large difference in the working potential of LNMO (4.7 V) and LTO (1.55 V) and their excellent lifespan. These findings provide a simple and scalable method to boost the EP of LNMO, which can be used to fabricate high-quality LIBs. [Display omitted] [ABSTRACT FROM AUTHOR]