Surface-coated positive electrode active material, method of preparing the same, and lithium secondary battery including the same

Patent metadata

Field	Value
Publication number	US-2017040647-A1
Application number	US-201515039730-A
Country	US
Kind code	A1
Filing date	Jan 28, 2015
Priority date	Jan 28, 2014
Publication date	Feb 9, 2017
Grant date	—

Abstract

The present invention relates to a surface-coated positive electrode active material including: a positive electrode active material; and a nanofilm coated on the surface of the positive electrode active material, wherein the nanofilm includes polyimide (PI) and a fibrous carbon material, and a method of preparing the same. According to an embodiment of the present invention, when the surface of a positive electrode active material is coated with a nanofilm including polyamide and a fibrous carbon material, a direct contact between the positive electrode active material and an electrolytic solution is prevented, and thus side reactions between the positive electrode active material and the electrolytic solution may be inhibited. Therefore, cycle life characteristics of a secondary battery may be significantly improved. Particularly under a high-temperature and high-voltage condition, cycle life characteristics and conductivity may be improved.

First claim

1 . A surface-coated positive electrode active material, comprising:
a positive electrode active material; and a nanofilm coated on the surface of the positive electrode active material, wherein the nanofilm includes polyimide (PI) and a carbon nanotube.

2 . (canceled)

3 . The surface-coated positive electrode active material of claim 1 , wherein the nanofilm has a thickness in the range of 1 to 200 nm.

4 . The surface-coated positive electrode active material of claim 1 , wherein the polyimide and the carbon nanotube are included at the weight ratio of 1:1 to 1:10.

5 . The surface-coated positive electrode active material of claim 1 , wherein the content of the carbon nanotube is 0.05 to 5 wt %, based on total weight of the surface-coated positive electrode active material.

6 . The surface-coated positive electrode active material of claim 1 , wherein the carbon nanotube has an average diameter of 5 to 100 nm and an average major axis length of 0.1 to 5 μm.

7 . The surface-coated positive electrode active material of claim 1 , wherein the carbon nanotube has an aspect ratio of 1 to 1,000.

8 . The surface-coated positive electrode active material of claim 1 , wherein the positive electrode active material is any one or a mixture of two or more selected from the group consisting of oxides having Chemical Formulas 1 to 3 below, V 2 O 5 , TiS, and MoS:
Li 1+x [Ni a Co b Mn c ]O 2   <Chemical Formula 1>
(−0.5≦x≦0.6; 0≦a, b, c≦1; and x+a+b+c=1);
LiMn 2−x M x O 4   <Chemical Formula 2>

(M is at least one selected from the group consisting of Ni, Co, Fe, P, S, Zr, Ti, and Al; and 0≦x≦2);
Li 1+a Fe 1−x M x (PO 4−b )X b   <Chemical Formula 3>

(M is at least one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X is at least one selected from the group consisting of F, S, and N; −0.5≦x≦0.5; 0≦x≦0.5; and 0≦b≦0.1).

9 . The surface-coated positive electrode active material of claim 8 , wherein the positive electrode active material is any one or a mixture of two or more selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li[Ni a Co b Mn c ]O 2 (0<a, b, c≦1, and a+b+c=1), and LiFePO 4 .

10 . A method of preparing a surface-coated positive electrode active material, the method comprising:
mixing and dispersing a carbon nanotube into an organic solvent in which a polyamic acid is diluted to prepare a mixed solution; dispersing a positive electrode active material into the mixed solution to form, on the surface of the positive electrode active material, a film including the polyamic acid and the carbon nanotube; and performing imidization of the positive electrode active material including the film.

11 . The method of claim 10 , wherein the imidization includes holding for 10 to 120 minutes in the range of 300 to 400° C.

12 . The method of claim 11 , wherein the imidization further includes heating up to 300 to 400° C. at a heating rate of 3° C./min with intervals of 50 to 100° C. prior to the holding temperature.

13 - 15 . (canceled)

16 . The method of claim 10 , wherein the carbon nanotube is used in the amount of 0.05 to 5 parts by weight, based on 100 parts by weight of the positive electrode active material.

17 . The method of claim 10 , wherein the polyamic acid is diluted in the amount of 0.1 to 1 part by weight, based on 100 parts by weight of the organic solvent.

18 . The method of claim 10 , wherein the polyamic acid is prepared by making aromatic anhydride react with diamine in the same equivalent weight.

19 . The method of claim 18 , wherein the aromatic anhydride is any one or a mixture of two or more selected from the group consisting of phthalic anhydride, pyromellitic dianhydride, 3,3′4,4′-biphenyltetracarboxylic dianhydride, 4′4-oxydiphthalic anhydride, 3,3′4,4′-benzophenonetetracarboxylic dianhydride, trimellitic ethylene glycol, 4,4′-(4′4-isopropylbiphenoxy)biphthalic anhydride, and trimellitic anhydride.

20 . The method of claim 18 , wherein the diamine is any one or a mixture of two or more selected from the group consisting of 4,4′-oxydianiline, p-phenyl diamine, 2,2-bis(4-(4-aminophenoxy)-phenyl)propane, p-methylenedianiline, propyltetramethyldisiloxane, polyaromatic amine, 4,4′-diaminodiphenyl sulfone, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, and 3,5-diamino-1,2,4-triazole.

21 . The method of claim 10 , wherein the polyamic acid includes a quaternary polyamic acid.

22 . The method of claim 21 , wherein the quaternary polyamic acid includes pyromellitic dianhydride, biphenyl dianhydride, phenylenediamine, and oxydianiline.

23 . The method of claim 10 , wherein the organic solvent includes any one or a mixture of two or more selected from the group consisting of cyclohexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

24 - 26 . (canceled)

Assignees

• Lg Chemical Ltd
• Unist (Ulsan Nat Inst Of Science And Technology)

Inventors

• Jang Wook
• Lee Sang Young
• Cho Seung Beom
• Park jang hoon
• Kim Ju Myung

Classifications

• H01M4/366 Primary

  as layered products · CPC title

• H01M4/525

  of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy · CPC title

• H01M4/625

  Carbon or graphite · CPC title

• H01M2004/028

  Positive electrodes · CPC title

• H01M4/505

  of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy · CPC title