text: def graphite_volume_change_Ai2020(sto):
      """
      Graphite particle volume change as a function of stochiometry [1, 2].
  
      References
      ----------
       .. [1] > Ai, W., Kraft, L., Sturm, J., Jossen, A., & Wu, B. (2020).
       Electrochemical Thermal-Mechanical Modelling of Stress Inhomogeneity in
       Lithium-Ion Pouch Cells. Journal of The Electrochemical Society, 167(1), 013512
        DOI: 10.1149/2.0122001JES.
       .. [2] > Rieger, B., Erhard, S. V., Rumpf, K., & Jossen, A. (2016).
       A new method to model the thickness change of a commercial pouch cell
       during discharge. Journal of The Electrochemical Society, 163(8), A1566-A1575.
  
      Parameters
      ----------
      sto: :class:`pybamm.Symbol`
          Electrode stochiometry, dimensionless
          should be R-averaged particle concentration
      Returns
      -------
      t_change:class:`pybamm.Symbol`
          volume change, dimensionless, normalised by particle volume
      """
      p1 = 145.907
      p2 = -681.229
      p3 = 1334.442
      p4 = -1415.710
      p5 = 873.906
      p6 = -312.528
      p7 = 60.641
      p8 = -5.706
      p9 = 0.386
      p10 = -4.966e-05
      t_change = (
          p1 * sto ** 9
          + p2 * sto ** 8
          + p3 * sto ** 7
          + p4 * sto ** 6
          + p5 * sto ** 5
          + p6 * sto ** 4
          + p7 * sto ** 3
          + p8 * sto ** 2
          + p9 * sto
          + p10
      )
      return t_change
  