Organic tailored batteries materials using stable open-shell molecules with degenerate frontier orbitals

Journal name:
Nature Materials
Volume:
10,
Pages:
947–951
Year published:
DOI:
doi:10.1038/nmat3142
Received
Accepted
Published online

Secondary batteries using organic electrode-active materials promise to surpass present Li-ion batteries in terms of safety and resource price1, 2. The use of organic polymers for cathode-active materials has already achieved a high voltage and cycle performance comparable to those of Li-ion batteries3, 4, 5, 6. It is therefore timely to develop approaches for high-capacity organic materials-based battery applications. Here we demonstrate organic tailored batteries with high capacity by using organic molecules with degenerate molecular orbitals (MOs) as electrode-active materials. Trioxotriangulene (TOT), an organic open-shell molecule, with a singly occupied MO (SOMO) and two degenerate lowest-unoccupied MOs (LUMOs) was investigated. A tri-tert-butylated derivative ((t-Bu)3TOT)exhibited a high discharge capacity of more than 300 A h kg−1, exceeding those delivered by Li-ion batteries. A tribrominated derivative (Br3TOT) was also shown to increase the output voltage and cycle performance up to 85% after 100 cycles of the charge–discharge processes.

At a glance

Figures

  1. Chemical structures and energy diagrams for only the SOMO and LUMO(s) of 6-oxophenalenoxyl (6OPO) (left), tri-tert-butylated trioxotriangulene ((t-Bu)3TOT) (centre) and tribrominated trioxotriangulene (Br3TOT) (right).
    Figure 1: Chemical structures and energy diagrams for only the SOMO and LUMO(s) of 6-oxophenalenoxyl (6OPO) (left), tri-tert-butylated trioxotriangulene ((t-Bu)3TOT) (centre) and tribrominated trioxotriangulene (Br3TOT) (right).

    The radical 6OPO possesses a SOMO and a LUMO with an energy gap of 0.94 eV. The radicals (t-Bu)3TOT and Br3TOT show a SOMO and two degenerate LUMOs with energy gaps of 0.82 and 0.56 eV, respectively. The frontier-MOs of Br3TOT have lower-lying energy level than those of 6OPO and (t-Bu)3TOT. The quantum chemical calculations were carried out using GAUSSIAN 03 with the ROB3LYP/6-31G(d,p) based on the molecular geometries optimized at the UB3LYP/6-31G(d,p). The crosses denote the bulky tert-butyl functional groups.

  2. Redox behaviours of (t-Bu)3TOT and Br3TOT in solution.
    Figure 2: Redox behaviours of (t-Bu)3TOT and Br3TOT in solution.

    a, Cyclic voltammograms (CV) measured using Bu4N+ salts of anions of (t-Bu)3TOT(1×10−3 M) (upper) and Br3TOT (3×10−3 M) (lower) in THF solutions containing 0.1 M Bu4NClO4 as a supporting electrolyte at 290 K. In CV of Br3TOT anion, the potentials of three redox waves between −2 and −3.05 V are peak potentials of the cathodic waves. b, The four-stage one-electron redox ability of TOT derivatives is schematically shown.

  3. Charge–discharge curves and cycle performances for 100 cycles of discharge processes on the coin-type cells.
    Figure 3: Charge–discharge curves and cycle performances for 100 cycles of discharge processes on the coin-type cells.

    a, Measurements of 6OPO cell at 1 C between 2.0 and 4.0 V versus Li/Li+. Average voltages of the charge and discharge processes: 3.5 and 2.9 V (the first cycle), 3.1 and 2.9 V (after the second cycle), respectively. b, Measurements of (t-Bu)3TOT cell (Cell-1) at 0.3 C between 1.4 and 3.8 V. Average voltage: 2.3 V (the first discharge process), 2.6 and 2.4 V (charge and discharge processes after the second cycle, respectively). c, Four-cycle measurement of K+ salt of (t-Bu)3TOT anion cells at 0.3 C between 1.2 and 4.0 V. Average voltage: 2.3 V (the first discharge process), 2.7 and 2.4 V (charge and discharge processes after the second cycle, respectively). The cycle performance measured at 2 C between 1.5 and 4.0 V. d, Four-cycle measurement of Li+ salt of (t-Bu)3TOT anion cells (Cell-Li1) at 0.1 C between 1.4 and 4.0 V. Average voltage: 2.5 V (the first discharge process), 2.7 and 2.6 V (charge and discharge processes after the second cycle, respectively). The cycle performance measured at 0.7 C between 1.5 and 4.0 V. In ad, the first and second charge–discharge curves are shown as red and blue lines, respectively. The others are denoted in black.

  4. Charge–discharge properties of the coin-type cells of Br3TOT.
    Figure 4: Charge–discharge properties of the coin-type cells of Br3TOT.

    a, The four-cycle measurement of Br3TOT cell at 1 C between 1.4 and 4.0 V versus Li/Li+. Average voltage: 2.6 V (the discharge processes) and 2.8 (the charge processes after the second cycle). The first and second charge–discharge curves are shown as red and blue lines, respectively. The others are denoted in black. b, The cycle performance of the discharge processes of Br3TOT cells measured at 1 C (red dots) and 2 C (blue dots) for 100 cycles between 1.4 and 4.0 V.

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Affiliations

  1. Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

    • Yasushi Morita,
    • Shinsuke Nishida,
    • Tsuyoshi Murata,
    • Miki Moriguchi &
    • Akira Ueda
  2. Department of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan

    • Shinsuke Nishida,
    • Kazunobu Sato &
    • Takeji Takui
  3. Murata Manufacturing Co., Ltd., Yasu, Shiga 520-2393, Japan

    • Masaharu Satoh
  4. JEOL Ltd., Akishima, Tokyo 196-0022, Japan

    • Kazunori Arifuku

Contributions

Y.M., S.N. and T.T. planned this project and carried out the experimental and theoretical work. M.S. and K.A. fabricated the coin-type cells and performed the charge–discharge experiments. T.M., M.M. and A.U. took part in the synthesis work for the molecules. K.S. carried out theoretical calculations.

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The authors declare no competing financial interests.

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