Synthesis and electrochemical performance of a nanocrystalline Li4Ti5O12/C composite for lithium-ion batteries prepared using resorcinol–formaldehyde resins

Triple Conductive Wiring by Electron Doping, Chelation Coating and Electrochemical Conversion in Fluffy Nb2 O5 Anodes for Fast-Charging Li-Ion Batteries

High-rate anode material is the kernel of developing fast-charging lithium ion batteries (LIBs). T-Nb2 O5 , well-known for its "room and pillar" structure and bulk pseudocapacitive effect, is expected to enable the fast lithium (de)intercalation. But this property is still limited by the low electronic conductivity or insufficient wiring manner. Herein, a strategy of triple conductive wiring through electron doping, chelation coating, and electrochemical conversion inside the microsized porous spheres consisting of dendrite-like T-Nb2 O5 primary particles is proposed to achieve the fast-charging and durable anodes for LIBs. The penetrative implanting of conformal carbon coating (derivative from polydopamine chelate) and NbO domains (induced by excess discharging) reinforces the global supply of electronically conductive wires, apart from those from Co/Mn heteroatom or O vacancy doping. The polydopamine etching on T-Nb2 O5 spheres promotes their evolution into fluffy morphology with better electrolyte infiltration. The synergic electron and ion wiring at different scales endow the modified T-Nb2 O5 anode with ultralong cycling life (143 mAh g-1 at 1 A g-1 after 8500 cycles) and high-rate performance (144.1 mAh g-1 at 10.0 A g-1 ). The permeation of multiple electron wires also enables a high mass loading of T-Nb2 O5 (4.5 mg cm-2 ) with a high areal capacity of 0.668 mAh cm-2 even after 150 cycles.

Surface nitridation of Li4Ti5O12 by thermal decomposition of urea to improve quick charging capability of lithium ion batteries

As the application of lithium-ion batteries in electric vehicles increases, the demand for improved charging characteristics of batteries is also increasing. Lithium titanium oxide (Li₄Ti₅O₁₂, LTO) is a negative electrode material with high rate characteristics, but further improvement in rate characteristics is needed for achieving the quick-charging performance required by electric vehicle markets. In this study, the surface of LTO was coated with a titanium nitride (TiN) layer using urea and an autogenic reactor, and electrochemical performance was improved (initial Coulombic efficiency and the rate capability were improved from 95.6 to 4.4% for pristine LTO to 98.5% and 53.3% for urea-assisted TiN-coated LTO, respectively. We developed a process for commercial production of surface coatings using eco-friendly material to further enhance the charging performance of LTO owing to high electronic conductivity of TiN.

One-Step Synthesis of a Nanosized Cubic Li2TiO3-Coated Br, C, and N Co-Doped Li4Ti5O12 Anode Material for Stable High-Rate Lithium-Ion Batteries

Nanosized Li₄Ti₅O₁₂ with both a Li₂TiO₃ coating and C-N-Br co-doping (CLLTO) was successfully synthesized via a facile reverse microemulsion method in one step using hexadecyl trimethyl ammonium bromide as a surface control agent and as a carbon, nitrogen, and bromine source. A uniform Li₂TiO₃ layer was formed on the surface and strongly adhered to the host material Li₄Ti₅O₁₂ (LTO), which played an important role in improving the cyclic stability of CLLTO. The thin and stable Li₂TiO₃ layer has the same cubic structure as LTO, which provides many three-dimensional channels for ion transport. C, N, and Br co-doping in CLLTO promoted the transition of Ti⁴⁺ to Ti³⁺ in Li₄Ti₅O₁₂, which could improve the capacity and facilitate the Li⁺ ion and electron transfer at the interface. The conductive behavior induced by co-doping was estimated by UV-vis diffuse reflectance spectra and further supported by theoretical calculations. The electrical conductivity of both p-type and n-type LTO can be well improved by co-doping C, N, and Br. This improvement may be due to the band gap reduction and the increased n-type electronic modification of the entire LTO. Owing to the synergistic effect of coating, co-doping, and nanosizing at one time, the CLLTO exhibits a high discharge capacity of 177.3-153.9 mA h g^-1 at the working rate of 0.1C-20C, with a capacity retention of 86%. The stable cycling of CLLTO is also obtained after 500 cycles at 20C, with a capacity retention of 95.5% (approximately 8 times higher than that of pure LTO) and almost 100% Coulombic efficiency. With high capacity, excellent rate performance, and good cycling stability, CLLTO can be applied in high-power lithium-ion batteries.

Low-cost and environmentally friendly synthesis of an Al3+ and Mn4+ co-doped Li4Ti5O12 composite with carbon quantum dots as an anode for lithium-ion batteries

To increase the specific capacity and conductivity of lithium titanate (LTO), low-cost and environmentally friendly carbon quantum dots (CQDs) were used to composite with Al³⁺ and Mn⁴⁺ co-doped Li₄Ti₅O₁₂ (LTO-Al/Mn) to improve its electrical properties. The Al³⁺ and Mn⁴⁺ were successfully substituted for Ti located at (16d) sites in the LTO and the CQDs formed a composite with LTO-Al/Mn. The specific capacity of the first cycle at 0.1C increased to 296.5 mA h g⁻¹, and the impedance decreased to 16.8 Ω. The specific capacity maintained 236.0 mA h g⁻¹ after 100 cycles.

To increase the specific capacity and conductivity of lithium titanate, low-cost and environmentally friendly carbon quantum dots (CQDs) were used to composite with Al³⁺ and Mn⁴⁺ co-doped Li₄Ti₅O₁₂ (LTO-Al/Mn) to improve its electrical properties.