New Material for High-Voltage Anodes in Lithium-Ion Batteries
The Goodenough Lab has synthesized a new anode material that can operate at voltages between 1.0 and 1.6 V vs. Li+/Li0. This TiNb2O7 (TNO) anode joins the ranks of the spinel lithium titanate (Li4Ti5O12) in being an anode material that operates within the window of thermodynamic stability for an organic-liquid carbonate electrolyte. Existing lithium-ion batteries have carbon anodes that operate at voltages below this window of stability, thereby resulting in decomposition of the electrolyte and formation of a thin passivating film on the anode surface. This solid electrolyte interphase (SEI) layer traps Li+ ions, causing the battery to irreversibly lose capacity on the first charge; it also limits the charge/discharge rate. Since the TNO anode does not form an SEI layer, it does not rob capacity from the cathode and is capable of a fast battery charge.
The TNO anode particles are synthesized via a traditional sol-gel route, and the resultant structure possesses 2D ionic tunnels in which Li+ ions can move easily (Fig. 1). Its theoretical specific capacity can reach 387.6 mAh/g by reducing Ti4+ to Ti3+ and Nb5+ to Nb4+. The observed capacity of 280 mAh/g at a rate of 0.1 C corresponds to 2.6 Li per formula unit and is larger than that of its competitor, lithium titanate (~170 mAh/g). The capacity and rate capability of these TNO anodes can be improved further if the size and morphology of the particles are optimized with a surface coating of 1-2% carbon.
The high capacity, fast charging capability, and better stability (and thus better safety) of TNO make Li+-ion batteries with these anodes a viable technology for hybrid electric vehicles.