Both Sony WX220 and Sony WX500 have 18.0 MP resolution sensors but Sony WX220's sensor is 1/2.3' (6.17 x 4.55 mm ) and Sony WX500's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Sony WX500's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Sony WX220.
Below you can see the WX220 and WX500 sensor size comparison.
Sony WX220 and Sony WX500 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.