Anode active material, manufacturing method thereof, and non-aqueous electrolyte secondary battery
View Patent ↗In order to provide a 3V level non-aqueous electrolyte secondary battery with a flat voltage and excellent cycle life at a high rate with low cost, the present invention provides a positive electrode represented by the formula: Li 2±α [Me] 4 O 8−x , wherein 0≦α<0.4, 0≦x<2, and Me is a transition metal containing Mn and at least one selected from the group consisting of Ni, Cr, Fe, Co and Cu, said active material exhibiting topotactic two-phase reactions during charge and discharge.
1. A positive electrode active material represented by the composition formula: Li 2±α [Me] 4 O 8−x , wherein 0≦α<0.4, 0≦x<2, and Me is a transition metal containing Mn and at least one selected from the group consisting of Ni, Cr, Fe, Co and Cu, said active material exhibiting first and second topotactic two-phase reactions respectively during first and second stages of charge and discharge, and characterized in that the phase of the transition metal has a 2×2 superlattice.
2. The positive electrode active material in accordance with claim 1 , characterized in that the ratio between Mn and other transition metal is substantially 3:1.
3. The positive electrode active material in accordance with claim 1 , characterized in that said positive electrode active material has a spinel-framework-structure and the Li and/or Me exist in the 16(c) site in the space group Fd3m.
4. The positive electrode active material in accordance with claim 1 , characterized in that said positive electrode active material has charge/discharge curves with a potential difference of 0.2 to 0.8 V.
5. The positive electrode active material in accordance with claim 1 , characterized in that said positive electrode active material has a lattice constant attributed to a cubic crystal of not greater than 8.3 Å.
6. The positive electrode active material in accordance with claim 1 , comprising a mixture of crystal particles with a particle size of 0.1 to 8 μm and secondary particles of said crystal particles with a particle size of 2 to 30 μm.
7. A non-aqueous electrolyte secondary battery comprising; a positive electrode containing the positive electrode active material in accordance with claim 1 ; a negative electrode containing a titanium oxide; and a non-aqueous electrolyte and a separator,
characterized in that said battery has a usable charging/discharging region of 2.5 to 3.5 V and a practical average voltage of 3V level.
8. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said titanium oxide has a spinel structure.
9. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said titanium oxide is Li 4 Ti 5 O 12 .
10. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said battery has an operating discharge curve with a potential difference of 0.2 to 0.8 V.
11. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said positive and negative electrodes have a current collector made of aluminum or an aluminum alloy.
12. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said non-aqueous electrolyte comprises at least one selected from the group consisting of propylene carbonate, γ-butyrolactone, γ-valerolactone, methyl diglyme, sulfolane, trimethyl phosphate triethyl phosphate and methoxymethylethyl carbonate.
13. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that said separator is made of non-woven fabric.
14. The non-aqueous electrolyte secondary battery in accordance with claim 13 , characterized in that said non-woven fabric comprises at least one selected from the group consisting of polyethylene, polypropylene and polybutylene terephthalate.
15. The non-aqueous electrolyte secondary battery in accordance with claim 7 , characterized in that the weight ratio of said negative electrode active material to said positive electrode active material is not less than 0.5 and not greater than 1.2.
16. A method for producing a positive electrode active material comprising:
(1) a step of synthesizing a eutectic compound containing a Mn compound and at least one selected from the group consisting of Ni, Cr, Fe, Co and Cu;
(2) a step of mixing said eutectic compound with a lithium compound; and
(3) a step of subjecting the mixed compounds obtained by said step (2) to a first baking at a temperature of not less than 600° C.,
whereby a positive electrode active material represented by the formula: Li 2±α [Me] 4 O 8−x , where 0≦α<0.4, 0≦x<2, and Me is a transition metal containing Mn and at least one selected from the group consisting of Ni, Cr, Fe, Co and Cu, said active material exhibiting first and second topotactic two-phase reactions respectively during first and second stages of charge and discharge is obtained.
17. The method for producing a positive electrode active material in accordance with claim 16 , characterized in that said first baking is performed at a temperature of not less than 900° C.
18. The method for producing a positive electrode active material in accordance with claim 16 , characterized in that said method further comprises a step of performing a second baking at a temperature lower than that of said first baking after said first baking.
19. The method for producing a positive electrode active material in accordance with claim 18 , characterized in that said second baking is performed at a temperature of 350 to 950° C.
20. The method for producing a positive electrode active material in accordance with claim 18 , characterized in that said second baking is performed at a temperature of 650 to 850° C.
21. The method for producing a positive electrode active material in accordance with claim 16 , characterized in that said method further comprises a step of rapidly cooling said positive electrode active material after said first baking and/or said second baking.
22. The method for producing a positive electrode active material in accordance with claim 21 , characterized in that said rapid cooling is performed at a temperature decrease rate of not less than 4.5° C./min.
23. The method for producing a positive electrode active material in accordance with claim 22 , characterized in that said rapid cooling is performed until the temperature reaches room temperature.
24. The method for producing a positive electrode active material in accordance with claim 21 , characterized in that said rapid cooling is performed at a temperature decrease rate of not less than 10° C./min.