A
nano silicon metal composite used for a negative
electrode of a
lithium ion battery comprises the following parts: (a) the first component part is simple substance
silicon with the content accounting for 5-75mol% of the
nano silicon metal composite; (b) the second component part contains a
metal element, a compound formed and a
silicon oxygen compound formed by the metal element and
silicon, the second component part content accounts for 25 to 95mol% of the
nano silicon metal composite; and (c) the third component part is simple substance carbon with the content accounting for 0-70mol% of the nano silicon metal composite. The preparation method is as follows: a porous block, comprising silica and metal or metal
oxide and the like, and a conductive negative
electrode current collector are compounded as a negative
electrode,
graphite or an
inert positive electrode is used as a positive electrode, the negative electrode and the positive electrode are placed in a mixed salt melt
electrolyte using CaCl2 or CaCl2 as the main components,
voltage is applied between the negative electrode and the positive electrode,
current density and electrolytic quantity are controlled, silica in the porous block is electrolyzed and reduced into nano silicon, and a nano silicon metal
composite material is prepared on the negative electrode.