Boron-Doped Carbon Coated Lithium Titanate As Anode Material for High-Rate Sodium-Ion Batteries
Authors: Yun Bin-Na , Long Du Hoang , Lee Yoon-sung , Sun Yang-Kook , Jung Hun-Gi 
Published: February 2020

Growth in interest to sodium-ion batteries (SIBs), research for the suitable anode material has been extensively progressed.1,2 Among various anode materials, lithium titanate (Li4Ti5O12, LTO) is expected to be a promising anode material in SIBs due to the outstanding performances have already been shown in lithium-ion batteries (LIBs) such as stable cycle-life, safety aspect, etc.3,4 However, LTO, as sodium anode material, is still facing with insulating properties and sluggish Na+ diffusion.1

To solve these problems, boron-doped carbon coated LTO was introduced by low-cost and facile one-pot wet-chemical method. Boron acts as a positive-type dopant (electron acceptor) because it possesses the fewer electrons than the carbon.5 Hence, boron could generate the positive charged holes to carry electrons through carbon structure, which enhances the electric conductivity.6,7 Furthermore, BC2O and BCO2 doped type formed by boron-doping in carbon matrix which were confirmed by XPS analysis remarkably create abundant extraneous defects and active sites; thereby can effectively reduce the adsorption energy as well as the energy barrier in order to contribute the rapid surface Na+ absorption along with ultrafast Na+ diffusion into carbon coated layer.7,8 For further investigation purpose, conductivity measurement and galvanostatic intermittent titration technique (GITT) were also carried out.
So as to confirm the boron-doping effects in SIBs, electrochemical evaluation was implemented with rate-capability and cycle tests at room temperature. Boron-doped carbon coated Li4Ti5O12 (CB-LTO) was compared to not only carbon coated LTO (C-LTO) but also pristine LTO sample through electrodes applied in CR2032 coin-type sodium-ion cells. Consequently, CB-LTO electrode shows higher specific capacity of 140.5 mAh g-1 at 0.5 C rate (50 mA g-1) than 120.8 mAh g-1 of C-LTO. Moreover, CB-LTO anode attained high capacity retention of about 100 % at 0.5 C rate (50 mA g-1) and 85% at 10 C rate (1000 mA g-1) after 250 cycles. With those developments of LTO material in our study, we suggest a high-capacity anode for SIBs.
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