Enhancing the electrochemical performance of commercial TiO2 by eliminating sulfate radicals and coating carbon

Synergistic modification of commercial TiO2 by combined carbon sources of citric acid and sodium carboxymethyl cellulose

The performance of a commercial TiO₂ anode was optimized by adjusting the ratio of citric acid and CMC-Na to modulate the carbon and Na⁺-doping content.

A uniform few-layered carbon coating derived from self-assembled carboxylate monolayers capable of promoting the rate properties and durability of commercial TiO2

The poor cyclability and rate property of commercial TiO₂ (c-TiO₂) hinder its utilization in lithium-ion batteries (LIBs). Coating carbon is one of the ways to ameliorate the electrochemical performance. However, how to effectively form a uniform thin carbon coating is still a challenge. On the basis of the strong interaction of the TiO₂ surface with carboxyl groups, herein a new tactic to achieve uniform and thin carbon layers on the c-TiO₂ particles was proposed. When mixing c-TiO₂ with citric acid containing carboxyl groups in deionized water, the high-affinity adsorption of TiO₂ for carboxyl groups resulted in self-assembled carboxylate monolayers on the surface of TiO₂ which evolved into a uniform few-layered amorphous carbon coating during carbonizing at 750 °C. The product derived from the mixture of c-TiO₂ and citric acid with a mass ratio of 1 : 0.3 exhibits the optimal performance, revealing a high specific capacity (256.6 mA h g⁻¹ after 50 cycles at 0.1 A g⁻¹) and outstanding cycling stability (retaining a capacity of 160.0 mA h g⁻¹ after 1000 cycles at 0.5 A g⁻¹). The greatly enhanced capacity and cyclability correlate with the uniform few-layered carbon coating which not only ameliorates the electronic conductivity of c-TiO₂ but also avoids the reduction in ionic conductivity caused by thick carbon layers and redundant carbon.

The uniform and thin carbon-coating formed on c-TiO₂ particles by virtue of the high-affinity adsorption of TiO₂ for carboxyl groups results in superior rate and cycling performance.

Ethers as Oxygen Donor and Carbon Source in Non-hydrolytic Sol-Gel: One-Pot, Atom-Economic Synthesis of Mesoporous TiO2 -Carbon Nanocomposites

Mesoporous TiO₂ -carbon nanocomposites were synthesized using an original non-hydrolytic sol-gel (NHSG) route, based on the reaction of simple ethers (diisopropyl ether or tetrahydrofuran) with titanium tetrachloride. In this atom-economic, solvent-free process, the ether acts not only as an oxygen donor but also as the sole carbon source. Increasing the reaction temperature to 180 °C leads to the decomposition of the alkyl chloride by-product and to the formation of hydrocarbon polymers, which are converted to carbon by pyrolysis under argon. The carbon-TiO₂ nanocomposites and their TiO₂ counterparts (obtained by calcination) were characterized by nitrogen physisorption, XRD, solid state ¹³ C NMR and Raman spectroscopies, SEM, and TEM. The nanocomposites are mesoporous with surface areas of up to 75 m²  g^-1 and pore sizes around 10 nm. They are composed of aggregated anatase nanocrystals coated by an amorphous carbon film. Playing on the nature of the ether and on the reaction temperature allows control over the carbon content in the nanocomposites. The nature of the ether also influences the size of the TiO₂ crystallites and the morphology of the nanocomposite. To further characterize the carbon coating, the behavior of the carbon-TiO₂ nanocomposites and bare TiO₂ samples toward lithium insertion-deinsertion was investigated in half-cells. This simple NHSG approach should provide a general method for the synthesis of a wide range of carbon-metal oxide nanocomposites.