Synthesis and electrochemical properties of Li 4 Ti 5 O 12 spheres and its application for hybrid supercapacitors

Enhanced Electrochemical Performance of Rare-Earth Metal-Ion-Doped Nanocrystalline Li4Ti5O12 Electrodes in High-Power Li-Ion Batteries

A comprehensive and comparative exploration research performed, aiming to elucidate the fundamental mechanisms of rare-earth (RE) metal-ion doping into Li₄Ti₅O₁₂ (LTO), reveals the enhanced electrochemical performance of the nanocrystalline RE-LTO electrodes in high-power Li-ion batteries. Pristi ne Li₄Ti₅O₁₂ (LTO) and rare-earth metal-doped Li_4-x/3Ti_5-2x/3Ln_xO₁₂ (RE-LTO with RE = Dy, Ce, Nd, Sm, and Eu; x ≈ 0.1) nanocrystalline anode materials were synthesized using a simple mechanochemical method and subsequent calcination at 850 °C. The X-ray diffraction (XRD) patterns of pristine and RE-LTO samples exhibit predominant (111) orientation along with other characteristic peaks corresponding to cubic spinel lattice. No evidence of RE-doping-induced changes was seen in the crystal structure and phase. The average crystallite size for pristine and RE-LTO samples varies in the range of 50-40 nm, confirming the formation of nanoscale crystalline materials and revealing the good efficiency of the ball-milling-assisted process adopted to synthesize nanoscale particles. Raman spectroscopic analyses of the chemical bonding indicate and further validate the phase structural quality in addition to corroborating with XRD data for the cubic spinel structure formation. Transmission electron microscopy (TEM) reveals that both pristine and RE-LTO particles have a similar cubic shape, but RE-LTO particles are better interconnected, which provide a high specific surface area for enhanced Li⁺-ion storage. The detailed electrochemical characterization confirms that the RE-LTO electrodes constitute promising anode materials for high-power Li-ion batteries. The RE-LTO electrodes deliver better discharge capacities (in the range of 172-198 mAh g^-1 at 1C rate) than virgin LTO (168 mAh g^-1). Among them, Eu-LTO provides the best discharge capacity of 198 mAh g^-1 at a 1C rate. When cycled at a high current rate of 50C, all RE-LTO electrodes show nearly 70% of their initial discharge capacities, resulting in higher rate capability than virgin LTO (63%). The results discussed in this work unfold the fundamental mechanisms of RE doping into LTO and demonstrate the enhanced electrochemical performance derived via chemical composition tailoring in RE-LTO compounds for application in high-power Li-ion batteries.

A Safer High-Energy Lithium-Ion Capacitor Using Fast-Charging and Stable ω-Li3 V2 O5 Anode

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li₄ Ti₅ O₁₂ anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li₃ V₂ O₅ (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

Lithium-Ion Capacitors: A Review of Design and Active Materials

Lithium-ion capacitors (LICs) have gained significant attention in recent years for their increased energy density without altering their power density. LICs achieve higher capacitance than traditional supercapacitors due to their hybrid battery electrode and subsequent higher voltage. This is due to the asymmetric action of LICs, which serves as an enhancer of traditional supercapacitors. This culminates in the potential for pollution-free, long-lasting, and efficient energy-storing that is required to realise a renewable energy future. This review article offers an analysis of recent progress in the production of LIC electrode active materials, requirements and performance. In-situ hybridisation and ex-situ recombination of composite materials comprising a wide variety of active constituents is also addressed. The possible challenges and opportunities for future research based on LICs in energy applications are also discussed.

Synthesis of Li4 Ti5 O12 with Tunable Morphology Using l-Cysteine and Its Enhanced Lithium Storage Properties

Nitrogen and sulfur co-doped carbon-coated Li₄ Ti₅ O₁₂ (denoted as LTO/NSC) was developed to enhance the electrochemical performance of LTO material. l-Cysteine served as both the carbon source and the heteroatom doping source. The morphology of LTO was tuned by Ti-C bond formation during carbonation process, accompanied by a change in the original orientation growth of the LTO lattice plane. Consequently, LTO transformed from nanosheets to nanoparticles. SEM data proved that the structure of LTO/NSC nanoparticles was more stable than that of LTO nanosheets after hundreds of charge/discharge process. The N,S co-doped carbon layer can moderate particle aggregation and may help to shorten the electron transport length and enhance lithium storage capacity. The structural superiority and the N,S co-doped carbon layer endows LTO/NSC particles with high reversible specific capacity (183 mA h g^-1 at 0.1 C), significantly enhanced rate capability (122 mA h g^-1 at 10 C) and excellent cycling stability (capacity retention of 96.3 % after 200 cycles) relative to these features of LTO nanosheets. Thus, LTO/NSC is a promising anode material for high-performance lithium ion batteries.

Ti-Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium-based oxides including TiO₂ and M-Ti-O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium-ion batteries, sodium-ion batteries, and hybrid pseudocapacitors. Further, Ti-based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in-depth understanding on the morphologies control, surface engineering, bulk-phase doping of Ti-based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti-based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium-ion batteries to sodium-ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.

Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors

Nano-sized Mo-doped titania (Mo_0.1Ti_0.9O₂) and Nb-doped titania (Nb_0.25Ti_0.75O₂) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO₂ negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5-3.0 V, the Mo_0.1Ti_0.9O₂/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg^-1 at a power of 180 W kg^-1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb_0.25Ti_0.75O₂/AC hybrid supercapacitor maintained its energy density of 45 Wh kg^-1 at 180 W kg^-1 better, showing 36 Wh g^-1 at 3200 W kg^-1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0-3.0 V led to an increase in power density, with the Mo_0.1Ti_0.9O₂/AC hybrid supercapacitor giving energy densities of 12 Wh kg^-1 and 2.5 Wh kg^-1 at power densities of 6700 W kg^-1 and 14 000 W kg^-1, respectively.

Agricultural waste-derived activated carbon for high performance lithium-ion capacitors

The optimized AC//LTO LIC is worth noting that our device outperformed most of the similar constructions concerning carbonaceous materials as cathode and LTO as anode and some other constructions.

Preparation and electrochemical properties of double-shell LiNi0.5Mn1.5O4 hollow microspheres as cathode materials for Li-ion batteries

Double shell LiNi_0.5Mn_1.5O₄ have been synthesized via a molten salt and annealing method with excellent cycling stability as cathode materials.

Improvement of the Ar/N2 binary plasma-treated carbon passivation layer deposited on Li4Ti5O12 electrodes for stable high-rate lithium ion batteries

Improvement of the Ar/N₂ binary plasma-treated carbon passivation layer deposited on Li₄Ti₅O₁₂ electrodes for stable high-rate lithium ion battery.

Hydrothermal synthesis of Li4Ti5O12 nanosheets as anode materials for lithium ion batteries

Spinel Li₄Ti₅O₁₂ nanosheets prepared by hydrothermal method were used as anode materials for lithium ion batteries.