Negative-electrode active material for non-aqueous-system secondary battery and production process for the same
Providing a noble negative-electrode active material including silicon, and a production process for the same. A negative-electrode active material for non-aqueous-system secondary battery including a silicon phase and a composite oxide phase (a CaSiO 3 phase, for instance) is obtained by mixing a silicon oxide (SiO, for instance) with a silicon compound (CaSi 2 , for instance), which includes silicon and at least one member of elements being selected from the group consisting of Group 2 (or Group 2A) elements in the Periodic Table, to prepare a mixed raw material, and then reacting the mixed raw material. The composite oxide phase demonstrates the advantage of inhibiting electrolytic solutions from decomposing in a smaller amount than does the conventional SiO 2 phase.
1. A production process for negative-electrode active material for non-aqueous-system secondary battery being characterized in that:
it is a production process for the negative-electrode active material for non-aqueous-system secondary battery comprising a silicon phase as well as a metal silicate phase that includes at least one member of elements being selected from the group consisting of Group 2 (or Group 2A) elements in the Periodic Table; and
it includes:
a raw-material preparation step of preparing a mixed raw material at least including a silicon oxide, and a silicon compound; and
a reaction step of reacting said mixed raw material,
wherein said silicon oxide is SiO n , where 0.1≦“n”≦2, and
said silicon compound is a metal silicide that includes at least one member of elements being selected from the group consisting of Group 2 (or Group 2A) elements in the Periodic Table.
2. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein:
said raw-material preparation step, and said reaction step include a milling step in which milling is performed in an inert atmosphere, thereby mixing a silicon-oxide-system powder, which contains said silicon oxide, with a silicon-compound-system powder, which includes said silicon compound, and at the same time compositing the silicon-oxide-system powder and the silicon-compound-system powder.
3. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 2 , wherein said reaction step includes a heat treatment step being carried out after said milling step.
4. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 2 further including a disproportionation step of disproportionating silicon monoxide (SiO n , where 0.5≦“n”≦1.5) of a raw-material silicon oxide powder, which includes a silicon monoxide powder, into a silicon dioxide phase and a silicon phase, thereby obtaining said silicon-oxide-system powder.
5. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein said mixed raw material includes said silicon oxide more than said silicon compound by molar ratio.
6. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein said silicon oxide and said silicon compound possess compositions whose formation energy (or ΔH) being found by means of first principle calculation becomes a negative value; and are mixed in a molar ratio by which the resulting AH becomes a negative value.
7. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein said silicon compound includes at least one member of elements that is selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba).
8. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein:
said silicon compound comprises Ca, and Si; and
a molar ratio between said silicon oxide and said silicon compound is from 1.5:1 to 8:1.
9. The production process for negative-electrode active material for non-aqueous-system secondary battery as set forth in claim 1 , wherein said reaction step is a step of milling and/or heating said mixed raw material in order to react the mixed raw material.