The present invention relates to an energy storage device comprising a silicate comprises a formula:
M.sub.vM1.sub.wM2.sub.xSi.sub.yO.sub.z
where M is selected from the group consisting of Li, Na, K, Al, and Mg M1 is selected from the group consisting of alkaline metals, alkaline earth metals, Ti, Mn, Fe, La, Zr, Ce, Ta, Nb, V and combinations thereof; M2 is selected from the group consisting of B, Al, Ga, Ge or combinations thereof; v, y and z are greater than 0; w and/or x is greater than 0; y≥x; and wherein M.sub.vM1.sub.wM2.sub.xSi.sub.yO.sub.z accounts for at least 90 wt % of the composition.

A negative electrode active material comprising: particles of negative electrode active material, wherein the particles of negative electrode active material contain particles of silicon compound containing a silicon compound (SiO.sub.x:0.5≤x≤1.6), and wherein the particles of silicon compound have, as chemical shift values obtained from a .sup.29Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in −40 to −60 ppm, an intensity B of a peak derived from silicon dioxide obtained in the vicinity of −110 ppm, and an intensity C of a peak derived from Si obtained in the vicinity of −83 ppm, which satisfy the following formula 1 and formula 2.

B≤1.5×A  (1)

B<C  (2)

A negative electrode active material comprising: particles of negative electrode active material, wherein the particles of negative electrode active material contain particles of silicon compound containing a silicon compound (SiO.sub.x:0.5≤x≤1.6), and wherein the particles of silicon compound have, as chemical shift values obtained from a .sup.29Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in −40 to −60 ppm, an intensity B of a peak derived from silicon dioxide obtained in the vicinity of −110 ppm, and an intensity C of a peak derived from Si obtained in the vicinity of −83 ppm, which satisfy the following formula 1 and formula 2.

B≤1.5×A  (1)

B<C  (2)

To produce a silicon oxide-based negative electrode material containing Li and having uniform distribution of a Li concentration both inside particles and between particles although a C-coating film is formed on a surface, and yet in which generation of SiC is suppressed. A SiO gas and a Li gas are simultaneously generated by heating a Si-lithium silicate-containing raw material under reduced pressure. The Si-lithium silicate-containing raw material includes Si, Li, and O, in which a part of the Si is present as a Si simple substance and the Li is present as lithium silicate. By cooling the generated gases, Li-containing silicon oxide having an average composition of SiLi.sub.xO.sub.y (0.05<x<y and 0.5<y<1.5 are satisfied) is prepared. After adjusting the particle size, a C-coating film having an average film thickness of 0.5 to 10 nm is formed on a surface of particles at a treatment temperature of 900° C. or less.

To produce a silicon oxide-based negative electrode material containing Li and having uniform distribution of a Li concentration both inside particles and between particles although a C-coating film is formed on a surface, and yet in which generation of SiC is suppressed. A SiO gas and a Li gas are simultaneously generated by heating a Si-lithium silicate-containing raw material under reduced pressure. The Si-lithium silicate-containing raw material includes Si, Li, and O, in which a part of the Si is present as a Si simple substance and the Li is present as lithium silicate. By cooling the generated gases, Li-containing silicon oxide having an average composition of SiLi.sub.xO.sub.y (0.05<x<y and 0.5<y<1.5 are satisfied) is prepared. After adjusting the particle size, a C-coating film having an average film thickness of 0.5 to 10 nm is formed on a surface of particles at a treatment temperature of 900° C. or less.

A non-aqueous electrolyte secondary battery that contains a silicon material as a negative-electrode active material has improved cycle life. A negative-electrode active material particle (10) according to an embodiment includes a lithium silicate phase (11) represented by Li.sub.2zSiO.sub.(2+z) (0<z<2), silicon particles (12) dispersed in the lithium silicate phase (11), and a metallic compound (15) (other than lithium compounds and silicon oxides) dispersed in the lithium silicate phase (11). The metallic compound (15) is preferably selected from zirconium oxide, aluminum oxide, zirconium carbide, tungsten carbide, and silicon carbide.

The present invention provides a positive-electrode active material for a lithium-ion secondary cell or a sodium-ion secondary cell, which can effectively exhibit more excellent charge/discharge characteristics; and a method for manufacturing the positive-electrode active material. Namely, the present invention relates to a positive-electrode active material for a secondary cell comprising an oxide represented by formula (A): LiFe.sub.aMn.sub.bM.sub.cPO.sub.4, formula (B): LiFe.sub.aMn.sub.bM.sub.cSiO.sub.4, or formula (C): NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4; and carbon derived from a cellulose nanofiber supported thereon.

The present invention provides a positive-electrode active material for a lithium-ion secondary cell or a sodium-ion secondary cell, which can effectively exhibit more excellent charge/discharge characteristics; and a method for manufacturing the positive-electrode active material. Namely, the present invention relates to a positive-electrode active material for a secondary cell comprising an oxide represented by formula (A): LiFe.sub.aMn.sub.bM.sub.cPO.sub.4, formula (B): LiFe.sub.aMn.sub.bM.sub.cSiO.sub.4, or formula (C): NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4; and carbon derived from a cellulose nanofiber supported thereon.

A nonlinear optical crystal has a chemical formula Li.sub.2X.sub.4TiOSi.sub.4O.sub.12, wherein X=K or Rb. The nonlinear optical crystal belongs to tetragonal system with space group P4nc and Z=2. The unit cell parameters of Li.sub.2K.sub.4TiOSi.sub.4O.sub.12 are a=b=11.3336(5) Å, c=5.0017(2) Å; and the unit cell parameters of Li.sub.2Rb.sub.4TiOSi.sub.4O.sub.12 are a=b=11.5038(6) Å, c=5.1435(3) Å. The two crystals are thermally stable and show strong second harmonic generation with high laser damage threshold.

A nonlinear optical crystal has a chemical formula Li.sub.2X.sub.4TiOSi.sub.4O.sub.12, wherein X=K or Rb. The nonlinear optical crystal belongs to tetragonal system with space group P4nc and Z=2. The unit cell parameters of Li.sub.2K.sub.4TiOSi.sub.4O.sub.12 are a=b=11.3336(5) Å, c=5.0017(2) Å; and the unit cell parameters of Li.sub.2Rb.sub.4TiOSi.sub.4O.sub.12 are a=b=11.5038(6) Å, c=5.1435(3) Å. The two crystals are thermally stable and show strong second harmonic generation with high laser damage threshold.