You can't "charge" the solution so that it contains "more negative ions". If you dissolve any salt you will get plenty of negative ions, together with positive ones, total charge will be zero. You may charge the solution like any other object - say a ball - but it doesn't mean there will be more negative ions in it, charge will be concentrated on the surface (unless you will use ultra pure water). But then you have high potential of the surface and you will face electrical discharges in form of sparks. Note that charge required for such sparks is several orders of magnitude smaller than the charge of negative ions present in the solution when you add a pinch of salt to 1L of water.