Positive active material for nonaqueous electrolyte secondary battery, method of manufacturing the positive active material, electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery and method of manufacturing the secondary battery
An object of the present invention is to provide a positive active material for a nonaqueous electrolyte secondary battery which has a large discharge capacity and is superior in charge-discharge cycle performance, initial efficiency and high rate discharge performance, and a nonaqueous electrolyte secondary battery using the positive active material. The present invention pertains to a positive active material for a nonaqueous electrolyte secondary battery containing a lithium transition metal composite oxide which has a crystal structure of an α-NaFeO 2 type, is represented by a compositional formula Li 1+α Me 1−α O 2 (Me is a transition metal element including Co, Ni and Mn, α>0), and has a molar ratio Li/Me of Li to the transition metal element Me of 1.2 to 1.6, wherein a molar ratio Co/Me of Co in the transition metal element Me is 0.02 to 0.23, a molar ratio Mn/Me of Mn in the transition metal element Me is 0.62 to 0.72, and the lithium transition metal composite oxide is observed as a single phase attributed to a space group R3-m on an X-ray diffraction chart when it is electrochemically oxidized up to a potential of 5.0 V (vs. Li/Li + ).
1. A positive active material for a nonaqueous electrolyte secondary battery containing a lithium transition metal composite oxide which has a crystal structure of an α-NaFeO 2 type, is represented by a compositional formula Li 1+α Me 1−α O 2 ,
wherein Me is a transition metal element including Co, Ni and Mn, and α>0,
a molar ratio Li/Me of Li to the transition metal element Me is 1.2 to 1.6,
a molar ratio Co/Me of Co in the transition metal element Me is 0.02 to 0.23,
a molar ratio Mn/Me of Mn in the transition metal element Me is 0.625 to 0.707,
the lithium transition metal composite oxide is a single phase attributed to a space group R3-m on an X-ray diffraction chart under a condition in which the lithium transition metal composite oxide is electrochemically oxidized up to a potential of 5.0 V (vs. Li/Li + ), and
an oxygen position parameter of the lithium transition metal composite oxide is 0.260 or less, the oxygen position parameter being determined in a state of a discharge end, by crystal structure analysis by a Rietveld method, using a space group R3-m as a crystal structure model based on an X-ray diffraction pattern.
2. The positive active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein a BET specific surface area is 1.24 to 5.87 m 2 /g.
3. The positive active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein a tapped density is 1.25 g/cm 3 or more.
4. The positive active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein a ratio between the diffraction peak intensity I (003) of (003) line and the diffraction peak intensity I (114) of (114) line based on X-ray diffraction measurement before charge-discharge satisfies I (003) /I (114) ≥1.20.
5. The positive active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein the lithium transition metal composite oxide is obtained by mixing/sintering a coprecipitated precursor of compounds of the transition metal elements including Co, Ni and Mn, and a lithium compound.
6. A method of manufacturing the positive active material for a nonaqueous electrolyte secondary battery according to claim 1 , comprising the steps of coprecipitating compounds of transition metal elements including Co, Ni and Mn in a solution to produce a coprecipitated precursor; and mixing/sintering the coprecipitated precursor and a lithium compound.
7. The method of manufacturing a positive active material for a nonaqueous electrolyte secondary battery according to claim 6 , wherein a pH in the step of coprecipitating compounds of transition metal elements including Co, Ni and Mn in a solution to produce a coprecipitated precursor is 8.5 to 11.0.
8. The method of manufacturing a positive active material for a nonaqueous electrolyte secondary battery according to claim 6 , wherein a sintering temperature in the step of mixing/sintering the coprecipitated precursor and a lithium compound is 800 to 940° C.
9. An electrode for a nonaqueous electrolyte secondary battery containing the positive active material for a nonaqueous electrolyte secondary battery according to claim 1 .
10. A nonaqueous electrolyte secondary battery including the electrode for a nonaqueous electrolyte secondary battery according to claim 9 .
11. A nonaqueous electrolyte secondary battery comprising the positive active material of claim 1 ,
wherein a volume ratio of oxygen to a total of nitrogen and oxygen contained in a gas in the battery is 0.2 to 0.25 under a condition in which the battery is charged so that a maximum potential of a positive electrode of the battery is 4.5 to 4.6 V (vs. Li/Li + ).
12. A positive active material for a nonaqueous electrolyte secondary battery containing a lithium transition metal composite oxide which has a crystal structure of an α-NaFeO 2 type, is represented by a compositional formula Li 1+α Me 1−α O 2 ,
wherein Me is a transition metal element including Co, Ni and Mn, and α>0,
a molar ratio Li/Me of Li to the transition metal element Me is of 1.2 to 1.6,
a molar ratio Co/Me of Co in the transition metal element Me is 0.02 to 0.23,
a molar ratio Mn/Me of Mn in the transition metal element Me is 0.625 to 0.707,
the lithium transition metal composite oxide is a single phase attributed to a space group R3-m on an X-ray diffraction chart under a condition in which the lithium transition metal composite oxide is electrochemically oxidized up to a potential of 5.0 V (vs. Li/Li + ), and
a tapped density is 1.25 g/cm 3 or more.
13. A nonaqueous electrolyte secondary battery comprising the positive active material of claim 12 ,
wherein a volume ratio of oxygen to a total of nitrogen and oxygen contained in a gas in the battery is 0.2 to 0.25 under a condition in which the battery is charged so that a maximum potential of a positive electrode of the battery is 4.5 to 4.6 V (vs. Li/Li + ).
14. A positive active material for a nonaqueous electrolyte secondary battery containing a lithium transition metal composite oxide which has a crystal structure of an α-NaFeO 2 type, is represented by a compositional formula Li 1+α Me 1−α O 2 ,
wherein Me is a transition metal element including Co, Ni and Mn, and α>0,
a molar ratio Li/Me of Li to the transition metal element Me is of 1.2 to 1.6,
a molar ratio Co/Me of Co in the transition metal element Me is 0.02 to 0.23,
a molar ratio Mn/Me of Mn in the transition metal element Me is 0.625 to 0.707, and
the lithium transition metal composite oxide is a single phase attributed to a space group R3-m on an X-ray diffraction chart under a condition in which the lithium transition metal composite oxide is electrochemically oxidized up to a potential of 5.0 V (vs. Li/Li + ).
15. The positive active material for a nonaqueous electrolyte secondary battery according to claim 14 , wherein a BET specific surface area is 1.24 to 5.87 m 2 /g.
16. A nonaqueous electrolyte secondary battery comprising the positive active material of claim 14 ,
wherein a volume ratio of oxygen to a total of nitrogen and oxygen contained in a gas in the battery is 0.2 to 0.25 under a condition in which the battery is charged so that a maximum potential of a positive electrode of the battery is 4.5 to 4.6 V (vs. Li/Li + ).