Highly Crystalline Lithium Titanium Oxide Sheets Coated with Nitrogen‐Doped Carbon enable High‐Rate Lithium‐Ion Batteries

Abstract

Sheets of Li4Ti5O12 with high crystallinity are coated with nitrogen-doped carbon (NC-LTO) using a controlled process, comprising hydrothermal reaction followed by chemical vapor deposition (CVD). Acetonitrile (CH3 CN) vapor is used as carbon and nitrogen source to obtain a thin coating layer of nitrogen-doped carbon. The layer enables the NC-LTO material to maintain its sheet structure during the high-temperature CVD process and to achieve high crystallinity. Doping with nitrogen introduces defects into the carbon coating layer, and this increased degree of disorder allows fast transportation of lithium ions in the layer. An electrode of NC-LTO synthesized at 700 °C exhibits greatly improved rate and cycling performance due to a markedly decreased total cell resistance and enhanced Li-ion diffusion coefficient (D(Li)). Specific capacities of 159.2 and 145.8 mA h g(-1) are obtained using the NC-LTO sheets, at charge/discharge rates of 1 and 10 C, respectively. These values are much higher than values for LTO particles did not undergo the acetonitrile CVD treatment. A capacity retention value as high as 94.7% is achieved for the NC-LTO sheets after 400 cycles in a half-cell at 5 C discharge rate.

Highly-crystalline ultrathin gadolinium doped and carbon-coated Li4Ti5O12 nanosheets for enhanced lithium storage

“…Raman scattering is employed to examine the microstructure of the carbon layer on the LTO-Gd-C (5%) sample and as shown in Fig. 4a, the two small bands at 1178 and 1493 cm À1 are short-range vibration of sp 3 carbon atoms commonly observed from amorphous carbonaceous materials [50]. The two main bands at around 1330 and 1592 cm À1 can be designated as the D and G bands of sp 2 carbon, respectively.…”

“…Ultrathin LTO nanosheets are also believed to exhibit a pseudocapacitive effect as the interaction takes place on the surface thus leading to the improved rate capability [48,51]. On the other hand, the construction of a stable separating thin carbon coating around LTO has been reported to be another effective strategy to improve the electrochemical performance of LTO electrodes due to enhancement in the charge transfer kinetics in the LTO electrodes and interfacial stability between the LTO and electrolyte [27,29,50]. Moreover, according to literature, doping lanthanide (Ln 3þ ) ions (such as La 3þ , Y 3þ and Gd 3þ ) with lower valence state yields oxygen ion vacancies in LTO, which could behave as ionic charge carriers to enhance intrinsic conductivity, thereby improving long-term cyclability and rate capabilities [15].…”

Advanced composites of complex Ti-based oxides as anode materials for lithium-ion batteries

“…However, controlling the formation of nitrogen-doped carbon layers using these common methods is still difficult. To tackle this issue, Han et al [119] developed a facile CVD method for preparing uniform nitrogen-doped carbon layers on thick Li 4 Ti 5 O 12 sheets (Fig. 5a).…”

“…Organic carbon from various sources subjected to different pyrolysis shows variable degrees of graphitization. Common organic carbon sources used for Li 4 Ti 5 O 12 include glucose [99][100][101][102][103], sucrose [104][105][106][107], sugar [108,109], starch [110], melamine [111,112], malic acid [113], toluene [114], citric acid [115,116], pitch [117,118], acetonitrile [119], and polymers [120][121][122][123][124][125][126]. The differences, advantages and advanced modification approaches of inorganic and organic carbon are summarized below.…”

Polyhedral MnO nanocrystals anchored on reduced graphene oxide as an anode material with superior lithium storage capability

“…6a show that the diameter of the semicircle for the p-MnO/RGO electrode in the high-medium frequency region is much smaller than that of pure MnO powders, suggesting the lower contact and charge-transfer resistance of the p-MnO/RGO nanocomposite, which is consistent with the simulation result of shown in Table 1. The lithium ions diffusion coefficient (D Li ) can also be evaluated from EIS according to the following equations [44]:…”