Cathode active material for secondary battery and secondary battery comprising same

Patent metadata

Field	Value
Publication number	US-2020044246-A1
Application number	US-201716339638-A
Country	US
Kind code	A1
Filing date	Sep 29, 2017
Priority date	Oct 5, 2016
Publication date	Feb 6, 2020
Grant date	—

Abstract

A film-shaped coating layer including at least one lithium ion conductive compound having a band gap of 5.5 eV to 10 eV formed on the surface of a core including a lithium composite metal oxide to a thickness at which dielectric breakdown does not occur according to types of the lithium ion conductive compound and the lithium composite metal oxide under charge and discharge conditions. Thereby, an oxidation/reduction reaction is suppressed by blocking the movement of electrons at an interface between an active material and an electrolyte solution by the coating layer which surrounds the surface of particles and has lithium ion conductivity, and, as a result, a positive electrode active material for a secondary battery, which may improve energy density of an electrode and life characteristics of a battery, and a secondary battery including the same are provided.

First claim

1 . A positive electrode active material for a secondary battery, comprising:
a core including a lithium composite metal oxide; and a film-shaped coating layer disposed to surround the core, wherein the coating layer comprises at least one lithium ion conductive compound having a band gap of 5.5 eV to 10 eV, a thickness (d) of the coating layer satisfies X<d≤100X, where X is a maximum distance at which electrons are capable of passing through the coating layer by a dielectric breakdown electric field when charging to an open circuit voltage of the lithium composite metal oxide versus lithium, wherein X is determined by Equation 1, wherein d is less than 500 nm, and the lithium ion conductive compound comprises at least one selected from the group consisting of lithium sulfide, lithium nitride, and lithium hydride:
X=V/F b   [Equation 1]

wherein, in Equation 1, V is the open circuit voltage of the lithium composite metal oxide versus lithium, and F b is a dielectric breakdown electric field value calculated by Equation 2, and

F
b

=

24.442




exp


(

0.315




E

g
ω


max

)

[

Equation



2

]

wherein, in Equation 2, E g is a band gap, and ω max is a maximum phonon frequency.

2 . The positive electrode active material for a secondary battery of claim 1 , wherein the thickness (d) of the coating layer satisfies X<d<X b , where X b is the thickness of the coating layer when bulk resistance of the coating layer is calculated by Equation 3 is 10Ω:
Bulk resistance of the coating layer=lithium ion conductivity of the lithium ion conductive compound×the thickness of the coating layer.  [Equation 3]

3 . The positive electrode active material for a secondary battery of claim 1 , wherein the lithium ion conductive compound has a band gap of 5.8 eV to 10 eV.

4 . The positive electrode active material for a secondary battery of claim 1 , wherein the lithium ion conductive compound has a lithium ion conductivity at 25° C. of 1×10 −8 S/cm to 1×10 −2 S/cm and a density of 0.5 g/cm 3 or more.

5 . The positive electrode active material for a secondary battery of claim 1 , wherein the lithium ion conductive compound is selected from the group consisting of Li 2 PO 2 N, LiBH 4 , LiBH 4 —LiI, and Li 2 NH.

6 . The positive electrode active material for a secondary battery of claim 1 , wherein the lithium composite metal oxide is an oxide including lithium; and at least one metal selected from the group consisting of nickel, manganese, cobalt, and aluminum.

7 . The positive electrode active material for a secondary battery of claim 1 , wherein the lithium composite metal oxide is doped with at least one element selected from the group consisting of tungsten (W), molybdenum (Mo), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), barium (Ba), calcium (Ca), and niobium (Nb).

8 . A method of preparing a positive electrode active material for a secondary battery, comprising:
forming a film-shaped coating layer on a core including a lithium composite metal oxide to a thickness (d) satisfying X<d≤100X, where X is a maximum distance at which electrons are capable of passing through the coating layer by a dielectric breakdown electric field when charging to an open circuit voltage of the lithium composite metal oxide versus lithium, wherein X is determined by Equation 1 using at least one lithium ion conductive compound having a band gap of 5.5 eV to 10 eV, wherein the thickness (d) of the coating layer is less than 500 nm, and the lithium ion conductive compound is selected from the group consisting of lithium sulfide, lithium nitride, and lithium hydride:
X=V/F b   [Equation 1]

wherein, in Equation 1, V is the open circuit voltage of the lithium composite metal oxide versus lithium, and F b is a dielectric breakdown electric field value calculated by Equation 2, and

F
b

=

24.442




exp


(

0.315




E

g
ω


max

)

[

Equation



2

]

wherein, in Equation 2, E g is a band gap, and ω max is a maximum phonon frequency.

9 . A positive electrode for a secondary battery, comprising the positive electrode active material of claim 1 .

10 . A lithium secondary battery comprising the positive electrode of claim 9 , a negative electrode, a separator

Assignees

• Lg Chemical Ltd

Inventors

• Park Eun Kyung
• Jang Min Chul
• Chung Chan Yeup
• Sung Da Young
• Park Chang Hun

Classifications

• H01M4/366 Primary

  as layered products · CPC title

• H01M4/1391

  of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx · CPC title

• H01M4/131 Primary

  Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx · CPC title

• H01M2004/028

  Positive electrodes · CPC title

• H01M10/052

  Li-accumulators · CPC title