Update NCA_Kim2011.py

Fixing #2744. to make sure we hit the voltage cut-off, instead of the particle stoichiometry going above 1.
Using the function in Kim2011 article to take the place of pybamm\input\parameters\lithium_ion\data\nca_ocp_Kim2011_data.csv for parameter 'Positive electrode OCP[V]' in Kim2011 parameter set.
The function 'nca_ocp_Kim2011(sto)' in pybamm\input\parameters\lithium_ion\NCA_Kim2011.py is edited.

Author: 1836005678

pybamm/input/parameters/lithium_ion/NCA_Kim2011.py

@@ -260,16 +260,35 @@ def electrolyte_conductivity_Kim2011(c_e, T):
     return sigma_e
 
 
-# Load data in the appropriate format
-path, _ = os.path.split(os.path.abspath(__file__))
-nca_ocp_Kim2011_data = pybamm.parameters.process_1D_data(
-    "nca_ocp_Kim2011_data.csv", path=path
-)
-
-
 def nca_ocp_Kim2011(sto):
-    name, (x, y) = nca_ocp_Kim2011_data
-    return pybamm.Interpolant(x, y, sto, name=name, interpolator="linear")
+    
+    """
+    References
+    ----------
+    Graphite Open Circuit Potential (OCP) as a function of the stochiometry [1].
+    ----------
+    .. [1] Kim, G. H., Smith, K., Lee, K. J., Santhanagopalan, S., & Pesaran, A.
+    (2011). Multi-domain modeling of lithium-ion batteries encompassing
+    multi-physics in varied length scales. Journal of The Electrochemical
+    Society, 158(8), A955-A969.
+    """
+    
+    U_posi = (
+        1.638 * sto ** 10
+        - 2.222 * sto ** 9
+        + 15.056 * sto ** 8
+        - 23.488 * sto ** 7
+        + 81.246 * sto ** 6
+        - 344.566 * sto ** 5
+        + 621.3475 * sto ** 4
+        - 554.774 * sto ** 3
+        + 264.427 * sto ** 2
+        - 66.3691 * sto
+        + 11.8058
+        - 0.61386 * pybamm.exp(5.8201*sto**136.4)
+    )
+
+    return U_posi
 
 
 # Call dict via a function to avoid errors when editing in place