First, for tracking changes of ngModel you need to use (ngModelChange) instead of (onChange).
Second, you shouldn't use params.value for ngModel binding, params - is a part of grid, so just avoid mixing things and keep it separately.
Third, in refresh function inside cellRenderer you shouldn't update params, refresh function used internally for grid.
// Mandatory - Get the cell to refresh. Return true if the refresh succeeded, otherwise return false.
// If you return false, the grid will remove the component from the DOM and create
// a new component in its place with the new values.
refresh(params: any): boolean;
Fourth, if you want to update value inside cellRenderer you should use ICellEditorComp interface instead of ICellRendererComp(ICellRendererAngularComp and ICellEditorAngularComp on Angular case)
Fifth, you forgot to setup checkbox field editable: true in columnDefs
And the last one - you've just created checkbox (out of grid scope) which is looked like a working sample, but it's not.
You need to understand the full edit process if ag-grid, so just check here details about cell rendering, cell editing and much more.
And here you can see how exactly custom checkbox renderer will work :
function booleanCellRenderer(params) {
var valueCleaned = booleanCleaner(params.value);
if (valueCleaned === true) {
return "<span title='true' class='ag-icon ag-icon-tick content-icon'></span>";
} else if (valueCleaned === false) {
return "<span title='false' class='ag-icon ag-icon-cross content-icon'></span>";
} else if (params.value !== null && params.value !== undefined) {
return params.value.toString();
} else {
return null;
}
}