How to iterate through various layers and export each with an additional word to its file name

I’m batch dissolving some layers in QGIS and want to save each dissolved shapefile as <layername>_dissolved.shp. I’m using a for-loop but it just shows raise QgsProcessingException(msg) _core.QgsProcessingException: There were errors executing the algorithm. error.

Here’s my code:

import processing
layers = QgsProject.instance().mapLayers().values()
for i in layers:
    processing.run("native:dissolve", 
                   {'INPUT': i,
                    'OUTPUT': r'C:UsersimperDesktop' + str(i) + '_dissolved' + '.shp'})
    iface.addVectorLayer(str(i+_dissolved), '', 'ogr')

How should I revise my 'OUTPUT' file path?

for layer in QgsProject.instance().mapLayers().values():
    layer_path = layer.dataProvider().dataSourceUri().split('|')[0]
    output_path = 'C:UsersimperDesktop' + layer.name() + '_dissolved' + '.shp'
    processing.run("native:dissolve", 
                   {'FIELD': [], 'INPUT': layer_path, 'OUTPUT': output_path})
    iface.addVectorLayer(output_path, layer.name() + '_dissolved', 'ogr')