Asymmetric SEI reaction

benchmarks/different_model_options.py

@@ -123,11 +123,13 @@ class TimeBuildModelSEI:
         [
             "none",
             "constant",
-            "reaction limited",
+            "reaction limited (symmetric)",
+            "reaction limited (asymmetric)",
             "solvent-diffusion limited",
             "electron-migration limited",
             "interstitial-diffusion limited",
-            "ec reaction limited",
+            "ec reaction limited (symmetric)",
+            "ec reaction limited (asymmetric)",
         ],
     )
 
@@ -142,11 +144,13 @@ class TimeSolveSEI:
         [
             "none",
             "constant",
-            "reaction limited",
+            "reaction limited (symmetric)",
+            "reaction limited (asymmetric)",
             "solvent-diffusion limited",
             "electron-migration limited",
             "interstitial-diffusion limited",
-            "ec reaction limited",
+            "ec reaction limited (symmetric)",
+            "ec reaction limited (asymmetric)",
         ],
     )
 

examples/scripts/calendar_ageing.py

@@ -4,15 +4,17 @@
 pb.set_logging_level("INFO")
 
 models = [
-    pb.lithium_ion.SPM({"SEI": "reaction limited"}),
-    pb.lithium_ion.SPMe({"SEI": "reaction limited"}),
+    pb.lithium_ion.SPM({"SEI": "reaction limited (symmetric)"}),
+    pb.lithium_ion.SPMe({"SEI": "reaction limited (symmetric)"}),
     pb.lithium_ion.SPM(
-        {"SEI": "reaction limited", "surface form": "algebraic"}, name="Algebraic SPM"
+        {"SEI": "reaction limited (symmetric)", "surface form": "algebraic"},
+        name="Algebraic SPM",
     ),
     pb.lithium_ion.SPMe(
-        {"SEI": "reaction limited", "surface form": "algebraic"}, name="Algebraic SPMe"
+        {"SEI": "reaction limited (symmetric)", "surface form": "algebraic"},
+        name="Algebraic SPMe",
     ),
-    pb.lithium_ion.DFN({"SEI": "reaction limited"}),
+    pb.lithium_ion.DFN({"SEI": "reaction limited (symmetric)"}),
 ]
 
 sims = []

examples/scripts/cycling_ageing.py

@@ -3,7 +3,7 @@
 pb.set_logging_level("NOTICE")
 model = pb.lithium_ion.DFN(
     {
-        "SEI": "ec reaction limited",
+        "SEI": "ec reaction limited (symmetric)",
         "SEI film resistance": "distributed",
         "SEI porosity change": "true",
         "lithium plating": "irreversible",

pybamm/models/full_battery_models/base_battery_model.py

@@ -121,9 +121,11 @@ class BatteryModelOptions(pybamm.FuzzyDict):
 
                 - "none": :class:`pybamm.sei.NoSEI` (no SEI growth)
                 - "constant": :class:`pybamm.sei.Constant` (constant SEI thickness)
-                - "reaction limited", "solvent-diffusion limited",\
-                    "electron-migration limited", "interstitial-diffusion limited", \
-                    or "ec reaction limited": :class:`pybamm.sei.SEIGrowth`
+                - "reaction limited (symmetric)", "reaction limited (asymmetric)", \
+                    "solvent-diffusion limited", "electron-migration limited", \
+                    "interstitial-diffusion limited", \
+                    "ec reaction limited (symmetric)" \
+                    or "ec reaction limited (asymmetric)": :class:`pybamm.sei.SEIGrowth`
             * "SEI film resistance" : str
                 Set the submodel for additional term in the overpotential due to SEI.
                 The default value is "none" if the "SEI" option is "none", and
@@ -254,11 +256,13 @@ def __init__(self, extra_options):
             "SEI": [
                 "none",
                 "constant",
-                "reaction limited",
+                "reaction limited (symmetric)",
+                "reaction limited (asymmetric)",
                 "solvent-diffusion limited",
                 "electron-migration limited",
                 "interstitial-diffusion limited",
-                "ec reaction limited",
+                "ec reaction limited (symmetric)",
+                "ec reaction limited (asymmetric)",
             ],
             "SEI film resistance": ["none", "distributed", "average"],
             "SEI on cracks": ["false", "true"],

pybamm/models/full_battery_models/lithium_ion/Yang2017.py

@@ -5,7 +5,7 @@
 class Yang2017(DFN):
     def __init__(self, options=None, name="Yang2017", build=True):
         options = {
-            "SEI": "ec reaction limited",
+            "SEI": "ec reaction limited (symmetric)",
             "SEI film resistance": "distributed",
             "SEI porosity change": "true",
             "lithium plating": "irreversible",

pybamm/models/submodels/interface/sei/base_sei.py

@@ -198,8 +198,9 @@ def _get_standard_concentration_variables(self, variables):
                 )
             v_bar = phase_param.v_bar
             z_sei = phase_param.z_sei
-            # Set scales for the "EC Reaction Limited" model
-            if self.options["SEI"] == "ec reaction limited":
+            # Set scales for the "EC Reaction Limited" models (both symmetric and
+            # asymmetric)
+            if self.options["SEI"].startswith("ec reaction limited"):
                 L_inner_0 = 0
                 L_outer_0 = 1
                 L_inner_crack_0 = 0

pybamm/models/submodels/interface/sei/sei_growth.py

@@ -56,7 +56,7 @@ def get_fundamental_variables(self):
 
         L_inner, L_outer = Ls
 
-        if self.options["SEI"] == "ec reaction limited":
+        if self.options["SEI"].startswith("ec reaction limited"):
             L_inner = 0 * L_inner  # Set L_inner to zero, copying domains
 
         variables = self._get_standard_thickness_variables(L_inner, L_outer)
@@ -100,9 +100,16 @@ def get_coupled_variables(self, variables):
         # Thermal prefactor for reaction, interstitial and EC models
         prefactor = 1 / (1 + self.param.Theta * T)
 
-        if self.options["SEI"] == "reaction limited":
+        # Define alpha_SEI depending on whether it is symmetric or asymmetric. This
+        # applies to "reaction limited" and "EC reaction limited"
+        if self.options["SEI"].endswith("(asymmetric)"):
+            alpha_SEI = phase_param.alpha_SEI
+        else:
+            alpha_SEI = 0.5
+
+        if self.options["SEI"].startswith("reaction limited"):
             C_sei = phase_param.C_sei_reaction
-            j_sei = -(1 / C_sei) * pybamm.exp(-0.5 * prefactor * eta_SEI)
+            j_sei = -(1 / C_sei) * pybamm.exp(-alpha_SEI * prefactor * eta_SEI)
 
         elif self.options["SEI"] == "electron-migration limited":
             U_inner = phase_param.U_inner_electron
@@ -117,7 +124,7 @@ def get_coupled_variables(self, variables):
             C_sei = phase_param.C_sei_solvent
             j_sei = -1 / (C_sei * L_sei_outer)
 
-        elif self.options["SEI"] == "ec reaction limited":
+        elif self.options["SEI"].startswith("ec reaction limited"):
             C_sei_ec = phase_param.C_sei_ec
             C_ec = phase_param.C_ec
 
@@ -129,7 +136,7 @@ def get_coupled_variables(self, variables):
             # so
             #  j_sei = -C_sei_ec * exp() / (1 + L_sei * C_ec * C_sei_ec * exp())
             #  c_ec = 1 / (1 + L_sei * C_ec * C_sei_ec * exp())
-            C_sei_exp = C_sei_ec * pybamm.exp(-0.5 * prefactor * eta_SEI)
+            C_sei_exp = C_sei_ec * pybamm.exp(-alpha_SEI * prefactor * eta_SEI)
             j_sei = -C_sei_exp / (1 + L_sei * C_ec * C_sei_exp)
             c_ec = 1 / (1 + L_sei * C_ec * C_sei_exp)
 
@@ -150,7 +157,7 @@ def get_coupled_variables(self, variables):
                 }
             )
 
-        if self.options["SEI"] == "ec reaction limited":
+        if self.options["SEI"].startswith("ec reaction limited"):
             inner_sei_proportion = 0
         else:
             inner_sei_proportion = phase_param.inner_sei_proportion
@@ -224,7 +231,7 @@ def set_rhs(self, variables):
 
         Gamma_SEI = self.phase_param.Gamma_SEI
 
-        if self.options["SEI"] == "ec reaction limited":
+        if self.options["SEI"].startswith("ec reaction limited"):
             self.rhs = {L_outer: -Gamma_SEI * a * j_outer + spreading_outer}
         else:
             v_bar = self.phase_param.v_bar
@@ -247,7 +254,7 @@ def set_initial_conditions(self, variables):
         else:
             L_inner_0 = self.phase_param.L_inner_0
             L_outer_0 = self.phase_param.L_outer_0
-        if self.options["SEI"] == "ec reaction limited":
+        if self.options["SEI"].startswith("ec reaction limited"):
             self.initial_conditions = {L_outer: L_inner_0 + L_outer_0}
         else:
             self.initial_conditions = {L_inner: L_inner_0, L_outer: L_outer_0}

pybamm/parameters/lithium_ion_parameters.py

@@ -704,6 +704,7 @@ def _set_dimensional_parameters(self):
             self.E_sei_dimensional = pybamm.Parameter(
                 f"{pref}SEI growth activation energy [J.mol-1]"
             )
+            self.alpha_SEI = pybamm.Parameter(f"{pref}SEI growth transfer coefficient")
 
             # EC reaction
             self.c_ec_0_dim = pybamm.Parameter(

tests/integration/test_models/test_full_battery_models/test_lithium_ion/base_lithium_ion_half_cell_tests.py

@@ -50,7 +50,11 @@ def test_sei_constant(self):
         self.run_basic_processing_test(options)
 
     def test_sei_reaction_limited(self):
-        options = {"SEI": "reaction limited"}
+        options = {"SEI": "reaction limited (symmetric)"}
+        self.run_basic_processing_test(options)
+
+    def test_sei_asymmetric_reaction_limited(self):
+        options = {"SEI": "reaction limited (asymmetric)"}
         self.run_basic_processing_test(options)
 
     def test_sei_solvent_diffusion_limited(self):
@@ -66,7 +70,11 @@ def test_sei_interstitial_diffusion_limited(self):
         self.run_basic_processing_test(options)
 
     def test_sei_ec_reaction_limited(self):
-        options = {"SEI": "ec reaction limited"}
+        options = {"SEI": "ec reaction limited (symmetric)"}
+        self.run_basic_processing_test(options)
+
+    def test_sei_asymmetric_ec_reaction_limited(self):
+        options = {"SEI": "ec reaction limited (asymmetric)"}
         self.run_basic_processing_test(options)
 
     def test_constant_utilisation(self):

tests/integration/test_models/test_full_battery_models/test_lithium_ion/base_lithium_ion_tests.py

@@ -166,7 +166,11 @@ def test_irreversible_plating_with_porosity(self):
         self.run_basic_processing_test(options, parameter_values=param)
 
     def test_sei_reaction_limited(self):
-        options = {"SEI": "reaction limited"}
+        options = {"SEI": "reaction limited (symmetric)"}
+        self.run_basic_processing_test(options)
+
+    def test_sei_asymmetric_reaction_limited(self):
+        options = {"SEI": "reaction limited (asymmetric)"}
         self.run_basic_processing_test(options)
 
     def test_sei_solvent_diffusion_limited(self):
@@ -182,7 +186,17 @@ def test_sei_interstitial_diffusion_limited(self):
         self.run_basic_processing_test(options)
 
     def test_sei_ec_reaction_limited(self):
-        options = {"SEI": "ec reaction limited", "SEI porosity change": "true"}
+        options = {
+            "SEI": "ec reaction limited (symmetric)",
+            "SEI porosity change": "true",
+        }
+        self.run_basic_processing_test(options)
+
+    def test_sei_asymmetric_ec_reaction_limited(self):
+        options = {
+            "SEI": "ec reaction limited (asymmetric)",
+            "SEI porosity change": "true",
+        }
         self.run_basic_processing_test(options)
 
     def test_loss_active_material_stress_negative(self):
@@ -246,7 +260,7 @@ def test_composite_graphite_silicon_sei(self):
         options = {
             "particle phases": ("2", "1"),
             "open circuit potential": (("single", "current sigmoid"), "single"),
-            "SEI": "ec reaction limited",
+            "SEI": "ec reaction limited (symmetric)",
         }
         parameter_values = pybamm.ParameterValues("Chen2020_composite")
         name = "Negative electrode active material volume fraction"

tests/unit/test_citations.py

@@ -222,11 +222,15 @@ def test_brosaplanella_2022(self):
         pybamm.lithium_ion.SPMe(build=False, options={"SEI": "constant"})
         self.assertNotIn("BrosaPlanella2022", citations._papers_to_cite)
 
-        pybamm.lithium_ion.SPM(build=False, options={"SEI": "ec reaction limited"})
+        pybamm.lithium_ion.SPM(
+            build=False, options={"SEI": "ec reaction limited (symmetric)"}
+        )
         self.assertIn("BrosaPlanella2022", citations._papers_to_cite)
         citations._reset()
 
-        pybamm.lithium_ion.SPMe(build=False, options={"SEI": "ec reaction limited"})
+        pybamm.lithium_ion.SPMe(
+            build=False, options={"SEI": "ec reaction limited (symmetric)"}
+        )
         self.assertIn("BrosaPlanella2022", citations._papers_to_cite)
         citations._reset()
 

tests/unit/test_experiments/test_simulation_with_experiment.py

@@ -259,7 +259,7 @@ def test_run_experiment_termination_capacity(self):
             * 10,
             termination="99% capacity",
         )
-        model = pybamm.lithium_ion.SPM({"SEI": "ec reaction limited"})
+        model = pybamm.lithium_ion.SPM({"SEI": "ec reaction limited (symmetric)"})
         param = pybamm.ParameterValues("Chen2020")
         param["SEI kinetic rate constant [m.s-1]"] = 1e-14
         sim = pybamm.Simulation(model, experiment=experiment, parameter_values=param)
@@ -281,7 +281,7 @@ def test_run_experiment_termination_capacity(self):
             * 10,
             termination="5.04Ah capacity",
         )
-        model = pybamm.lithium_ion.SPM({"SEI": "ec reaction limited"})
+        model = pybamm.lithium_ion.SPM({"SEI": "ec reaction limited (symmetric)"})
         param = pybamm.ParameterValues("Chen2020")
         param["SEI kinetic rate constant [m.s-1]"] = 1e-14
         sim = pybamm.Simulation(model, experiment=experiment, parameter_values=param)

tests/unit/test_models/test_full_battery_models/test_base_battery_model.py

@@ -34,7 +34,7 @@
 'particle phases': '1' (possible: ['1', '2'])
 'particle shape': 'spherical' (possible: ['spherical', 'no particles'])
 'particle size': 'single' (possible: ['single', 'distribution'])
-'SEI': 'none' (possible: ['none', 'constant', 'reaction limited', 'solvent-diffusion limited', 'electron-migration limited', 'interstitial-diffusion limited', 'ec reaction limited'])
+'SEI': 'none' (possible: ['none', 'constant', 'reaction limited (symmetric)', 'reaction limited (asymmetric)', 'solvent-diffusion limited', 'electron-migration limited', 'interstitial-diffusion limited', 'ec reaction limited (symmetric)', 'ec reaction limited (asymmetric)'])
 'SEI film resistance': 'none' (possible: ['none', 'distributed', 'average'])
 'SEI on cracks': 'false' (possible: ['false', 'true'])
 'SEI porosity change': 'false' (possible: ['false', 'true'])

tests/unit/test_models/test_full_battery_models/test_lithium_ion/base_lithium_ion_half_cell_tests.py

@@ -52,7 +52,11 @@ def test_well_posed_constant_sei(self):
         self.check_well_posedness(options)
 
     def test_well_posed_reaction_limited_sei(self):
-        options = {"SEI": "reaction limited"}
+        options = {"SEI": "reaction limited (symmetric)"}
+        self.check_well_posedness(options)
+
+    def test_well_posed_asymmetric_reaction_limited_sei(self):
+        options = {"SEI": "reaction limited (asymmetric)"}
         self.check_well_posedness(options)
 
     def test_well_posed_solvent_diffusion_limited_sei(self):
@@ -68,7 +72,11 @@ def test_well_posed_interstitial_diffusion_limited_sei(self):
         self.check_well_posedness(options)
 
     def test_well_posed_ec_reaction_limited_sei(self):
-        options = {"SEI": "ec reaction limited"}
+        options = {"SEI": "ec reaction limited (symmetric)"}
+        self.check_well_posedness(options)
+
+    def test_well_posed_asymmetric_ec_reaction_limited_sei(self):
+        options = {"SEI": "ec reaction limited (asymmetric)"}
         self.check_well_posedness(options)
 
     def test_well_posed_lumped_thermal(self):