SILICON NANOPARTICLES, NON-AQUEOUS SECONDARY BATTERY NEGATIVE ELECTRODE ACTIVE MATERIAL USING SAID SILICON NANOPARTICLES, AND SECONDARY BATTERY

Silicon nanoparticles are obtained which significantly contribute to enhancing the performance of negative electrode active materials. A negative electrode active material is obtained which allows a battery to attain excellent charging/discharging capacities, high initial Coulombic efficiency and good capacity retention after charging and discharging repetitions. [0002] The present invention pertains to silicon nanoparticles for negative electrode active material in lithium ion secondary batteries in which the silicon nanoparticles have a Si-NMR peak which has a half width of 20 ppm to 50 ppm centered at -80 ppm and is broad ranging from 50 ppm to -150 ppm, and the silicon nanoparticles have a length in the major axis direction of 70 to 300 nm and a thickness of 15 to 70 nm or less. The present invention also pertains to a negative electrode active material for lithium ion secondary batteries that includes the silicon nanoparticles and a silicon inorganic compound in which the silicon nanoparticles are embedded, the silicon inorganic compound having a Si-NMR peak assigned to SiC bond structural units and having an equivalent composition ratio [SiC bonds/(SiC bond structural units + D units (SiOC) + T units (SiOC) + Q units (SiO))] in the range of 0.05 to 0.55. The present invention also pertains to a negative electrode for lithium ion secondary batteries including the negative electrode active material, and to a lithium ion secondary battery including the negative electrode.