4.8 Article

Operando calorimetry informs the origin of rapid rate performance in microwave-prepared TiNb2O7 electrodes

Journal

JOURNAL OF POWER SOURCES
Volume 490, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.jpowsour.2021.229537

Keywords

Lithium ion batteries; Reversible heat generation; Entropy; Microwave synthesis; Thermal signature; Lithium diffusion

Funding

  1. U.S. Department of Energy, Office of Science, Basic Energy Sciences [DESC0019381]
  2. MRSEC Program of the NSF [DMR 1720256]

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TiNb2O7, a shear-phase compound, has emerged as a safe and high-volumetric density replacement for graphite anodes in lithium ion batteries, retaining capacity even at high cycling rates. Pure and crystalline TiNb2O7 can be rapidly prepared using a high-temperature microwave synthesis method, with operando calorimetry revealing key thermodynamic parameters and Joule heating dominating heat generation. The small enthalpy of mixing across different degrees of lithiation indicates the rapid rate performance is due to the high rate of lithium ion diffusion.
The shear-phase compound TiNb2O7 has recently emerged as a safe and high-volumetric density replacement for graphite anodes in lithium ion batteries. An appealing feature of TiNb2O7 is that it retains capacity even at high cycling rates. Here, we demonstrate that phase pure and crystalline TiNb2O7 can be rapidly prepared using a high-temperature microwave synthesis method. Studies of the charging and discharging of this material, including through operando calorimetry, permit key thermodynamic parameters to be revealed. The nature of heat generation is dominated by Joule heating, which sensitively changes as the conductivity of the electrode increases with increasing lithiation. The enthalpy of mixing, obtained from operando calorimetry, is found to be small across the different degrees of lithiation, pointing to the high rate of lithium ion diffusion at the origin of rapid rate performance.

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