Negative electrode active material for nonaqueous electrolyte secondary batteries
A negative electrode active material for nonaqueous secondary batteries is disclosed. The active material contains a silicon solid solution having one or more than one of a group 3 semimetal or metal element, a group 4 semimetal or metal element except silicon, and a group 5 nonmetal or semimetal element incorporated in silicon as a solute element. The solute element is present more on the crystal grain boundaries of the silicon solid solution than inside the grains.
1. A negative electrode active material for nonaqueous secondary batteries, comprising a silicon solid solution as a matrix having one or more than one element selected from the group consisting of boron, germanium, tin, arsenic, antimony and bismuth and being incorporated as a solute in silicon, the one or more than one element being present more on crystal grain boundaries of the silicon solid solution than inside crystal grains,
wherein the amount of the one or more than one element in the silicon solid solution is 1 to 6 at % relative to silicon atom, and
wherein the silicon solid solution has a particulate form in which a particle size of the silicon solid solution is 2 to 10 μm in terms of D 50 as measured by a laser diffraction scattering.
2. A process for producing the negative electrode active material for nonaqueous secondary batteries as set forth in claim 1 , comprising the steps of:
preparing a mixed melt of silicon and a semimetal element selected from the group consisting of boron, germanium, tin, arsenic, antimony and bismuth
introducing the mixed melt into a liquid coolant to form a vapor film covering the mixed melt in the coolant,
rupturing the vapor film to bring the mixed melt and the coolant into direct contact to cause boiling as a result of spontaneous nucleation,
rending and atomizing the mixed melt by making use of a pressure wave resulting from the boiling while cooling and solidifying the mixed melt to give a silicon solid solution as a matrix having said semimetal element incorporated as a solute, and
heating the silicon solid solution at 500° to 1200° C. for 0.3 to 20 hours.
3. A negative electrode for nonaqueous secondary batteries comprising the negative electrode active material set forth in claim 1 .
4. A nonaqueous secondary battery comprising the negative electrode set forth in claim 3 .
5. The negative electrode active material according to claim 1 , wherein the amount of the element in the silicon solid solution is 1 to 3 at %.