Abstract: The present invention belongs to the field of materials, and relates to an environment-friendly precursor, a cathode material for a lithium-ion battery, and preparation methods thereof. The method for preparing an environment-friendly precursor provided in the present invention includes: subjecting a metal and/or a metal oxide, an oxidant, water, and a complexing agent to a chemical corrosion crystallization reaction at an electrical conductivity equal to or greater than 200 uS/cm, a redox potential ORP value equal to or less than 100 my, and a complexing agent concentration of 3-50 g/L. The precursor prepared by using the method provided in the present invention has advantages that no waste water is produced during dissolution and crystallization, and that water is constantly consumed, so that the purpose of environmental friendliness can be achieved. Moreover, the first charge and discharge efficiency of a lithium-ion battery can be effectively improved by means of the precursor.