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.

References

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[2] C.-P. Yang, Y.-X. Yin, H. Ye, K.-C. Jiang, J. Zhang, Y.-G. Guo, ACS Appl. Mater. Interfaces, 6 (2014) 8789−8795.

[3] Z. Liang, P. Hui-Lin, H. Yong-Sheng, L. Hong, C. Li-Quan, Chin. Phys. B 21 (2012) 028201.

[4] D. H. Long, M.-G. Jeong, Y.-S. Lee, W.C Choi, J. K. Lee, I.-H. Oh, H.-G. Jung, ACS Appl. Mater. Interfaces, 7 (2015), 10250−10257.

[5] N. Donald A., Semiconductor Physics and Devices: Basic Principles, Third ed., Mc Graw-Hill, New York, 2003.

[6] Y. A. Kim, K. Fujisawa, H. Muramatsu, T Hayashi, M. Endo, T. Fujimori, K. Kaneko, M. Terrones,  J. Behrends,, A. Eckmann, C. Casiraghi, K. S. Novoselov, R. Saito, M. S. Dresselhaus, ACS Nano, 6 (2012) 6293-6300.

[7] W. Shen, H. Li, C. Wang, Z. Li, Q. Xu, H. Liu, Y, Wang, J. Mater. Chem. A, 3 (2015) 15190-15201.

[8] D. Das, S.C. Kim, K.-R. Lee, A. K. Singh, Phys.Chem. Chem. Phys., 15 (2013) 15128-15134.