diff --git a/input/parameters/lithium-ion/parameters/LCO.csv b/input/parameters/lithium-ion/parameters/LCO.csv
index 141cb2ed..9d8b59c2 100644
--- a/input/parameters/lithium-ion/parameters/LCO.csv
+++ b/input/parameters/lithium-ion/parameters/LCO.csv
@@ -51,5 +51,5 @@ alpha,0.5,,Charge transfer coefficient,Scott Moura,
 ,,,,,
 # Initial Conditions,,,,,
 ce0,1000,mol.m-3, Initial lithium ion concentration in electrolyte,,
-cn0,1000,mol.m-3, Initial lithium concentration in positive electrode,,
-cp0,1000,mol.m-3, Initial lithium concentration in negative electrode,,
+cn0,1998.6,mol.m-3, Initial lithium concentration in positive electrode,,
+cp0,3073.1,mol.m-3, Initial lithium concentration in negative electrode,,
diff --git a/pybamm/models/li_ion/single_particle_model.py b/pybamm/models/li_ion/single_particle_model.py
index 445b2cc9..fcf2e535 100644
--- a/pybamm/models/li_ion/single_particle_model.py
+++ b/pybamm/models/li_ion/single_particle_model.py
@@ -79,7 +79,7 @@ class SPM(pybamm.BaseModel):
         Nn = - gamma_n * D_n(cn) * pybamm.grad(cn)
         dcndt = - pybamm.div(Nn)
         Np = - gamma_p * D_p(cp) * pybamm.grad(cp)
-        dcpdt = -pybamm.div(Np)
+        dcpdt = - pybamm.div(Np)
         self.rhs = {cn: dcndt, cp: dcpdt}
 
         # Boundary conditions
@@ -88,7 +88,7 @@ class SPM(pybamm.BaseModel):
             Nn: {"left": pybamm.Scalar(0),
                  "right": pybamm.Scalar(1) / ln / beta_n},
             Np: {"left": pybamm.Scalar(0),
-                 "right": pybamm.Scalar(1) / lp / beta_p / C_hat_p},
+                 "right": - pybamm.Scalar(1) / lp / beta_p / C_hat_p},
         }
 
         # Initial conditions

Test in SPM failing
One of the [tests](https://github.com/tinosulzer/PyBaMM/blob/61fa60306919edab1bcb6e7c162329217da3311b/tests/test_models/test_li_ion.py#L21) for the SPM isn't inside the testing class so isn't being called, but once put inside the class it fails (`cp_surf` not increasing with time). Both `cn_surf` and `cp_surf` quickly go negative.
My guess is this is due to parameter values being wrong, but could be something else. Could you have a look @rtimms ?
diff --git a/tests/test_models/test_li_ion.py b/tests/test_models/test_li_ion.py
index d14c23c8..e0a1e59c 100644
--- a/tests/test_models/test_li_ion.py
+++ b/tests/test_models/test_li_ion.py
@@ -17,23 +17,24 @@ class TestLiIonSPM(unittest.TestCase):
 
         modeltest.test_all()
 
+    def test_surface_concentrartion(self):
+        model = pybamm.li_ion.SPM()
+        params = model.default_parameter_values
+        params.process_model(model)
+        disc = model.default_discretisation
+        disc.process_model(model)
+        t_eval = np.linspace(0, 1, 100)
+        solver = model.default_solver
+        solver.solve(model, t_eval)
+        T, Y = solver.t, solver.y
 
-def test_surface_concentrartion(self):
-    model = pybamm.li_ion.SPM()
-    disc = model.default_discretisation
-    disc.process_model(model)
-    t_eval = np.linspace(0, 1, 100)
-    solver = model.default_solver
-    solver.solve(model, t_eval)
-    T, Y = solver.t, solver.y
-
-    # check surface concentration decreases in negative particle and
-    # increases in positive particle for discharge
-    np.testing.assert_array_less(
-        model.variables["cn_surf"].evaluate(T, Y)[:, 1:],
-        model.variables["cn_surf"].evaluate(T, Y)[:, :-1],
-    )
-    np.testing.assert_array_less(
-        model.variables["cp_surf"].evaluate(T, Y)[:, :-1],
-        model.variables["cp_surf"].evaluate(T, Y)[:, 1:],
-    )
+        # check surface concentration decreases in negative particle and
+        # increases in positive particle for discharge
+        np.testing.assert_array_less(
+            model.variables["cn_surf"].evaluate(T, Y)[:, 1:],
+            model.variables["cn_surf"].evaluate(T, Y)[:, :-1],
+        )
+        np.testing.assert_array_less(
+            model.variables["cp_surf"].evaluate(T, Y)[:, :-1],
+            model.variables["cp_surf"].evaluate(T, Y)[:, 1:],
+        )

pip install -e .[dev,docs]
parse_log_pytest
requirements.txt
pytest
apt-get update apt-get install -y python3-dev gfortran gcc libopenblas-dev liblapack-dev
3.6
requirements.txt requirements-dev.txt requirements-docs.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
anyio==3.6.2
anytree==2.8.0
argon2-cffi==21.3.0
argon2-cffi-bindings==21.2.0
async-generator==1.10
attrs==22.2.0
Babel==2.11.0
backcall==0.2.0
bleach==4.1.0
certifi==2021.5.30
cffi==1.15.1
charset-normalizer==2.0.12
comm==0.1.4
contextvars==2.4
cycler==0.11.0
dataclasses==0.8
decorator==5.1.1
defusedxml==0.7.1
docutils==0.18.1
entrypoints==0.4
flake8==3.9.2
guzzle-sphinx-theme==0.7.11
idna==3.10
imagesize==1.4.1
immutables==0.19
importlib-metadata==4.8.3
iniconfig==1.1.1
ipykernel==5.5.6
ipython==7.16.3
ipython-genutils==0.2.0
ipywidgets==7.8.5
jedi==0.17.2
Jinja2==3.0.3
json5==0.9.16
jsonschema==3.2.0
jupyter==1.1.1
jupyter-client==7.1.2
jupyter-console==6.4.3
jupyter-core==4.9.2
jupyter-server==1.13.1
jupyterlab==3.2.9
jupyterlab-pygments==0.1.2
jupyterlab-server==2.10.3
jupyterlab_widgets==1.1.11
kiwisolver==1.3.1
MarkupSafe==2.0.1
matplotlib==3.3.4
mccabe==0.6.1
mistune==0.8.4
nbclassic==0.3.5
nbclient==0.5.9
nbconvert==6.0.7
nbformat==5.1.3
nest-asyncio==1.6.0
notebook==6.4.10
numpy==1.19.5
packaging==21.3
pandas==1.1.5
pandocfilters==1.5.1
parso==0.7.1
pexpect==4.9.0
pickleshare==0.7.5
Pillow==8.4.0
pluggy==1.0.0
prometheus-client==0.17.1
prompt-toolkit==3.0.36
ptyprocess==0.7.0
py==1.11.0
-e git+https://github.com/tinosulzer/PyBaMM.git@9469e1606bb76c7e184da03884ab7abb6c78b402#egg=pybamm
pycodestyle==2.7.0
pycparser==2.21
pyflakes==2.3.1
Pygments==2.14.0
pyparsing==3.1.4
pyrsistent==0.18.0
pytest==7.0.1
python-dateutil==2.9.0.post0
pytz==2025.2
pyzmq==25.1.2
requests==2.27.1
scipy==1.5.4
Send2Trash==1.8.3
six==1.17.0
sniffio==1.2.0
snowballstemmer==2.2.0
Sphinx==5.3.0
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
terminado==0.12.1
testpath==0.6.0
tomli==1.2.3
tornado==6.1
traitlets==4.3.3
typing_extensions==4.1.1
urllib3==1.26.20
wcwidth==0.2.13
webencodings==0.5.1
websocket-client==1.3.1
widgetsnbextension==3.6.10
zipp==3.6.0

name: PyBaMM
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - anyio==3.6.2
      - anytree==2.8.0
      - argon2-cffi==21.3.0
      - argon2-cffi-bindings==21.2.0
      - async-generator==1.10
      - attrs==22.2.0
      - babel==2.11.0
      - backcall==0.2.0
      - bleach==4.1.0
      - cffi==1.15.1
      - charset-normalizer==2.0.12
      - comm==0.1.4
      - contextvars==2.4
      - cycler==0.11.0
      - dataclasses==0.8
      - decorator==5.1.1
      - defusedxml==0.7.1
      - docutils==0.18.1
      - entrypoints==0.4
      - flake8==3.9.2
      - guzzle-sphinx-theme==0.7.11
      - idna==3.10
      - imagesize==1.4.1
      - immutables==0.19
      - importlib-metadata==4.8.3
      - iniconfig==1.1.1
      - ipykernel==5.5.6
      - ipython==7.16.3
      - ipython-genutils==0.2.0
      - ipywidgets==7.8.5
      - jedi==0.17.2
      - jinja2==3.0.3
      - json5==0.9.16
      - jsonschema==3.2.0
      - jupyter==1.1.1
      - jupyter-client==7.1.2
      - jupyter-console==6.4.3
      - jupyter-core==4.9.2
      - jupyter-server==1.13.1
      - jupyterlab==3.2.9
      - jupyterlab-pygments==0.1.2
      - jupyterlab-server==2.10.3
      - jupyterlab-widgets==1.1.11
      - kiwisolver==1.3.1
      - markupsafe==2.0.1
      - matplotlib==3.3.4
      - mccabe==0.6.1
      - mistune==0.8.4
      - nbclassic==0.3.5
      - nbclient==0.5.9
      - nbconvert==6.0.7
      - nbformat==5.1.3
      - nest-asyncio==1.6.0
      - notebook==6.4.10
      - numpy==1.19.5
      - packaging==21.3
      - pandas==1.1.5
      - pandocfilters==1.5.1
      - parso==0.7.1
      - pexpect==4.9.0
      - pickleshare==0.7.5
      - pillow==8.4.0
      - pluggy==1.0.0
      - prometheus-client==0.17.1
      - prompt-toolkit==3.0.36
      - ptyprocess==0.7.0
      - py==1.11.0
      - pycodestyle==2.7.0
      - pycparser==2.21
      - pyflakes==2.3.1
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pyrsistent==0.18.0
      - pytest==7.0.1
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyzmq==25.1.2
      - requests==2.27.1
      - scipy==1.5.4
      - send2trash==1.8.3
      - six==1.17.0
      - sniffio==1.2.0
      - snowballstemmer==2.2.0
      - sphinx==5.3.0
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - terminado==0.12.1
      - testpath==0.6.0
      - tomli==1.2.3
      - tornado==6.1
      - traitlets==4.3.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - websocket-client==1.3.1
      - widgetsnbextension==3.6.10
      - zipp==3.6.0
prefix: /opt/conda/envs/PyBaMM

tests/test_models/test_li_ion.py::TestLiIonSPM::test_surface_concentrartion
tests/test_models/test_li_ion.py::TestLiIonSPM::test_basic_processing
pybamm/models/li_ion/single_particle_model.py input/parameters/lithium-ion/parameters/LCO.csv
pybamm/models/li_ion/single_particle_model.py input/parameters/lithium-ion/parameters/LCO.csv