The present invention relates to the field of solid materials for adsorbing lithium. In particular, the present invention relates to a novel method for preparing a solid, shaped crystallised material, preferably in the form of extruded products, of formula LiXx.2Al(OH)3,n H2O in which n is between 0.01 and 10, x being equal to 1 when X is an anion chosen from the chloride, hydroxide and nitrate anions, and x being equal to 0.5 when X is an anion chosen from the sulfate and carbonate anions, comprising a step a) of precipitating boehmite under specific temperature and pH conditions; and at least one step of shaping by basic mixing, said method also comprising a final hydrothermal treatment step, the method as a whole making it possible to increase the lithium adsorption capacity and the adsorption kinetics of the obtained materials relative to the materials from the prior art when used in a method for extracting lithium from saline solutions.