Positive electrode, method for preparing the same and electrochemical device

1. A positive electrode comprising

a current collector;

a positive electrode active material layer arranged on at least one surface of the current collector, wherein the positive electrode active material layer contains positive electrode active material particles, and

an inorganic layer having a thickness of 250 nm to 1650 nm arranged on a surface of at least one positive electrode active material layer containing positive electrode active material particles away from the current collector, wherein the inorganic layer is a porous dielectric layer containing no binder, and the inorganic layer has a porosity of 30%˜40%,

wherein the inorganic layer has a porous structure formed by stacked nanoclusters, and pores for ion transmission formed between the nanoclusters have an average pore diameter in a range from 0.1 nm to 100 nm; and

wherein the inorganic layer further contains a material selected from a group consisting of aluminum oxide, AlO (OH), aluminum nitride, aluminum fluoride, silicon oxide, silicon nitride, silicon fluoride, titanium oxide, titanium nitride, titanium fluoride, zinc oxide, zinc nitride, zinc fluoride, magnesium oxide, magnesium nitride, magnesium fluoride, zirconium oxide, zirconium nitride, zirconium fluoride, calcium oxide, calcium nitride, calcium fluoride, barium oxide, barium nitride, barium fluoride, or combinations thereof, and

wherein the inorganic layer has a mass per unit area in a range from 0.88 g/m 2 to 4.16 g/m 2 .

2. The positive electrode according to claim 1 , wherein the thickness of the inorganic layer is in a range of 250 nm to 1500 nm.

3. The positive electrode according to claim 1 , wherein the inorganic layer is prepared by vapor deposition method, the vapor deposition method comprising at least one of atomic layer deposition, chemical vapor deposition, physical vapor deposition or thermal evaporation deposition.

4. The positive electrode according to claim 1 , wherein the nanoclusters have an average particle size in a range from 2 nm to 500 nm.

5. The positive electrode according to claim 1 , wherein the porosity of the inorganic layer is higher than a porosity of the positive electrode active material layer.

6. The positive electrode according to claim 1 , wherein the positive electrode active material is selected from a group consisting of Li z Co 1−(x+y) Ni x Mn y O 2 , LiCoO 2 , LiNiO 2 , LiCo a Ni 1−a O 2 , LiVPO 4 , Li 2 MnO 3 , LiMn 2−b M b O 4 , LiFe c Mn 1−c PO 4 , or combinations thereof, wherein 0<x<1, 0<y<1,0.9<z<1.2,0<a<1,0 b<2,0<c 1, and M is selected from a group consisting of Li, Al, Mg, Zn, Cr, La, Nd, Ti, Sn, V, or combinations thereof.

7. The positive electrode according to claim 1 , wherein particles of the positive electrode active material are provided with a coating layer, and the coating layer contains at least one of A 1 2 O 3 , CaO, SiO 2 , TiO 2 , B 2 O 3 , MgO, ZrO 2 or lithium transition metal phosphates.

8. The positive electrode according to claim 1 , wherein the thickness of the inorganic layer is in a range of 250 nm to 1000 nm.

9. The positive electrode according to claim 1 , wherein the thickness of the inorganic layer is in a range of 250 nm to 500 nm.

10. The positive electrode according to claim 1 , wherein particles of the positive electrode active material are provided with a coating layer, and the coating layer contains at least one of A 1 2 O 3 , CaO, SiO 2 , TiO 2 , B 2 O 3 , MgO, ZrO 2 or lithium transition metal phosphates, and

the coating layer has a thickness in a range from 5 nm to 500 nm.

11. The positive electrode according to claim 1 , wherein the inorganic layer is disposed on the surface of the positive electrode active material layer and inner walls of pores on the surface of the positive electrode active material layer, and

a ratio of a depth of the inorganic layer in the pores of the positive electrode active material layer to a thickness of the positive electrode active material layer is in a range from 1/1000 to 1/10.

12. A method for preparing a positive electrode, comprising at least following steps:

preparing a slurry by mixing a positive electrode active material, a binder and a conductive agent;

coating on at least one surface of a current collector with the slurry and drying the slurry to form a positive electrode active material layer; and

preparing an inorganic layer having a thickness of 250 nm to 1650 nm on a surface of the at least one positive electrode active material layer away from the current collector by vapor deposition method, wherein the inorganic layer is a porous dielectric layer containing no binder, and the inorganic layer has a porosity of 30%˜40%.

wherein the inorganic layer has a porous structure formed by stacked nanoclusters, and pores for ion transmission formed between the nanoclusters have an average pore diameter in a range from 0.1 nm to 100 nm; and

wherein the inorganic layer further contains a material selected from a group consisting of aluminum oxide, AlO (OH), aluminum nitride, aluminum fluoride, silicon oxide, silicon nitride, silicon fluoride, titanium oxide, titanium nitride, titanium fluoride, zinc oxide, zinc nitride, zinc fluoride, magnesium oxide, magnesium nitride, magnesium fluoride, zirconium oxide, zirconium nitride, zirconium fluoride, calcium oxide, calcium nitride, calcium fluoride, barium oxide, barium nitride, barium fluoride, or combinations thereof, and

wherein the inorganic layer has a mass per unit area in a range from 0.88 g/m 2 to 4.16 g/m 2 .

13. The method for preparing a positive electrode according to claim 12 , wherein the vapor deposition method comprises at least one of atomic layer deposition, chemical vapor deposition, physical vapor deposition, or thermal evaporation deposition.

14. An electrochemical device, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode is the positive electrode according to claim 1 .

15. The electrochemical device according to claim 14 , wherein the electrochemical device is a lithium-ion secondary battery, and the thickness of the inorganic layer has no change when the lithium-ion secondary battery reaches a voltage of at least 5 V.