Cathode active material and lithium secondary battery comprising same
View Patent ↗Provided is a positive active material for a lithium secondary battery, the positive active material including: a secondary particle comprising a group of a plurality of primary particles, in which the primary particles comprise first primary particles provided on a surface portion of the secondary particle and each having a spinel structure at an end thereof, and the primary particle is made of lithium (Li), nickel (Ni), manganese (Mn), and tungsten (W) which is a doping element.
1 . A positive active material for a lithium secondary battery, the positive active material comprising:
a secondary particle comprising a group of a plurality of primary particles,
wherein the primary particles comprise a first primary particles provided on a surface portion of the secondary particle, and the primary particle is made of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and tungsten (W), which is a doping element, and
wherein the secondary particle has a chemical formula Li x (Ni y M 1−y−z W z )O 2 , wherein Mis Co and Mn, x is 0.9 to 1.2, y is 0.85 to 0.95, and z is 0.005 to 0.02,
a concentration of W varies within the secondary particle,
wherein the primary particle has a layered structure and comprises a spinel structure in a first region which is the end of the first primary particle, and
wherein the first primary particle has a transverse section having a flake shape having a major axis and a minor axis, and the first region accounts for 0.5% to 4% of an average length of the major axis of the first primary particle.
2 . The positive active material of claim 1 , wherein the first region is formed at a depth of 5 nm to 50 nm inward from an outermost surface of the first primary particle.
3 . The positive active material of claim 1 , wherein the secondary particle is formed in a spherical shape, and the first region accounts for 0.2% to 1.3% of an average radius of the secondary particle in a direction from the outermost surface to a center of the secondary particle.
4 . The positive active material of claim 1 , wherein the positive active material has a concentration gradient of W,
as a tungsten content in the positive active material increases, an area of the first region of the first primary particle increases, a length of a lattice parameter a increases, and a length of a lattice parameter c decreases.
5 . The positive active material of claim 1 , wherein a BET specific surface area of the secondary particle is 0.15 m 2 /g to 0.6 m 2 /g, and the BET specific surface area increases as a tungsten content increases.
6 . The positive active material of claim 1 , wherein in an X-ray diffraction pattern measured by a powder X-ray diffraction device (XRD) using a CuKα1 ray, a peak intensity ratio (003)/(104) of intensity of peak ascribed to (003) plane to intensity of peak ascribed to (104) plane is 1.05 to 1.75, and the peak intensity ratio (003)/(104) decreases as the amount of addition of the doping element increases.
7 . The positive active material of claim 1 , wherein an exothermal peak of 190° C. to 220° C. is obtained during a differential scanning calorimetry (DSC) analysis after charging is performed with a constant current at 4.4V cut-off.
8 . The positive active material of claim 1 , wherein the spinel structure provided in the first region is formed before initial charging is performed.
9 . The positive active material of claim 1 , wherein based on a total amount of nickel (Ni), cobalt (Co), manganese (Mn), and tungsten (W) which is the doping element, nickel (Ni) accounts for 85 mol % or more, and tungsten (W), which is the doping element, accounts for 0.1 mol % to 2 mol %.
10 . The positive active material of claim 8 , wherein nickel (Ni) accounts for 90 mol % or more.
11 . A positive electrode for a secondary battery, comprising the positive active material for a lithium secondary battery according to claim 1 .
12 . A lithium secondary battery comprising:
the positive electrode according to claim 11 ;
a negative electrode made of graphite or lithium metal; and
an electrolyte.
13 . The lithium secondary battery of claim 12 , wherein when the negative electrode is made of graphite, a capacity retention rate with respect to an initial capacity is 80% or more after 500 cycles charging and discharging is performed at 3.0 V to 4.3 V at room temperature.
14 . A battery module comprising the lithium secondary battery according to claim 12 as a unit cell.
15 . A battery pack comprising the battery module according to claim 14 , wherein the battery pack is used as a power source for medium and large devices, and the medium and large devices are selected from a group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and an electric power storage system.