Composite particles, manufacturing method thereof, electrode material for secondary battery, and secondary battery
Provided is positive electrode material for a highly safe lithium-ion secondary battery that can charge and discharge a large current while having long service life. Disclosed are composite particles comprising: at least one carbon material selected from the group consisting of (i) fibrous carbon material, (ii) chain-like carbon material, and (iii) carbon material produced by linking together fibrous carbon material and chain-like carbon material; and lithium-containing phosphate, wherein at least one fine pore originating from the at least one carbon material opens to outside the composite particle. Preferably, the composite particles are coated with carbon. The fibrous carbon material is preferably a carbon nanotube with an average fiber size of 5 to 200 nm. The chain-like carbon material is preferably carbon black produced by linking, like a chain, primary particles with an average particle size of 10 to 100 nm.
1. A process for producing composite particles, the process comprising:
a first step of subjecting to surface treatment at least one carbon material selected from the group consisting of (i) fibrous carbon material, (ii) chain-like carbon material, and (iii) carbon material produced by linking together fibrous carbon material and chain-like carbon material;
a second step of mixing the at least one surface-treated carbon material and source material for lithium-containing phosphate,
wherein the second step of mixing the source material for the lithium-containing phosphate and the at least one surface-treated carbon material is a step of dispersing and mixing the at least one surface-treated carbon material into a solution having dissolved into a solvent a lithium ion (Li + ), a phosphate ion (PO 4 3− ), and a metal ion other than from lithium,
a third step of heating the solution to form composite particles comprising: the at least one surface-treated carbon material; and a lithium-containing phosphate precursor and/or the lithium-containing phosphate,
wherein a method using a pressured and heated solvent is used for the steps comprising: dispersing the at least one surface-treated carbon material into the solution; mixing the solution; and then heating the solution to form composite particles comprising: the at least one surface-treated carbon material; and a lithium-containing phosphate precursor and/or the lithium-containing phosphate; and
a fourth step of heating the composite particles to create at least one fine pore opening to outside the composite particle, wherein the at least one fine pore originates from the at least one surface-treated carbon material, and
the composite particles comprise:
at least one carbon material selected from the group consisting of (i) fibrous carbon material, (ii) chain-like carbon material, and (iii) carbon material produced by linking together fibrous carbon material and chain-like carbon material; and
lithium-containing phosphate,
wherein the composite particles comprise at least one fine pore originating from the at least one carbon material and opening to outside the composite particles, thus connecting the inside of the composite particles with the outside of the composite particles,
a portion of the at least one carbon material is located inside the composite particle,
the size of the at least one fine pore is from 0.5 nm to 12 nm,
the at least one fine pore is made by subjecting to surface treatment the at least one carbon material and heating the composite particles, wherein the surface treatment of the at least one carbon material is a method using a polymer dispersant,
and
the polymer dispersant is one or more selected from the group consisting of polyvinylpyrrolidone and poly(allylamine hydrochloride).
2. The process for producing composite particles according to claim 1 , further comprising the step of adding a heat-degradable carbon source compound in one or more steps from the second to fourth steps.
3. The process for producing composite particles according to claim 2 , wherein the composite particles are coated with carbon.
4. The process for producing composite particles according to claim 1 , wherein the third and fourth steps are continuously performed.
5. The process for producing composite particles according to claim 1 , wherein the fourth step of heating the composite particles comprising the at least one surface-treated carbon material and the lithium-containing phosphate precursor and/or the lithium-containing phosphate to create the at least one fine pore is a step of heating the composite particles comprising the at least one surface-treated carbon material and the lithium-containing phosphate precursor and/or the lithium-containing phosphate under an inert atmosphere or reducing atmosphere in vacuo to volatilize an oxygen-containing functional group on a surface of the at least one surface-treated carbon material or to decompose the polymer dispersant on the surface of the at least one surface-treated carbon material.
6. The process for producing composite particles according to claim 1 , wherein the fibrous carbon material is a carbon nanotube with an average fiber size of 5 to 200 nm.
7. The process for producing composite particles according to claim 1 , wherein the chain-like carbon material is carbon black produced by linking, like a chain, primary particles with an average particle size of 10 to 100 nm.
8. The process for producing composite particles according to claim 1 , wherein the lithium-containing phosphate is LiFePO 4 , LiMnPO 4 , lithium magnesium iron phosphate, LiCoPO 4 , or Li 3 V 2 (PO 4 ) 3 .
9. The process for producing composite particles according to claim 1 , wherein the composite particles have an average primary particle size of 0.02 to 20 μm.