We report an amorphous boron nanorod anode material for lithium ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mAh g^-1 by alloying with Li to form B₄Li₅.¹ However, experimental studies of boron anode were rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of bulk crystalline boron anode material are poor at room temperature. In this work, we developed amorphous nanostructured one-dimensional (1D) boron material aiming at improving lithium ion diffusion in boron at room temperature. The amorphous boron nanorod anode exhibited, at room temperature, a reversible capacity of 170 mAh g^-1 at a current rate of 10 mA g^-1 between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. Lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration technique (GITT). The sweep voltammetric analysis suggested that the contributions from lithium ions diffusion into boron as well as the capacitive process are 57% and 43%, respectively. Results from GITT indicated that the discharge capacity at higher potentials (> ~ 0.2 V vs, Li/Li⁺) could be ascribed to a capacitive process and at lower potentials (< ~0.2 V vs, Li/Li⁺) to diffusion control. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod.

References:

1. M. Worle and R. Nesper, Angew Chem Int Edit, 2000, 39, 2349-2353.