Cathode Active Material for Lithium-Ion Secondary Battery, Preparation Methods and Uses Thereof

Abstract

The present invention provides a spinel-structured cathode active material, comprising lithium-containing compound particles having a chemical formula of LiNi.sub.0.5xMn.sub.1.5y{A}.sub.uO.sub.z and a first metal oxide and a second metal oxide coated on the surface of the lithium-containing compound particles, wherein the first metal oxide is an oxide of a metal having a valence of four or higher than four, and partially covers on the surface of the lithium-containing compound particles as a coating material; the second metal oxide is an oxide of a metal having a valence of lower than four, and the other areas on the surface of the lithium-containing compound particles that are not covered by the first metal oxide are coated with the second metal oxide in a thickness of 1-20 nm or forms a shallow gradient solid solution with a depth of less than 200 nm. When the cathode active material is applied to a lithium ion secondary battery, it has better cycling stability than an uncoated lithium transition metal oxide.

Claims

1. A cathode active material with a spinel structure, characterized in that, the cathode active material comprises particles of a lithium-containing compound having a chemical formula of LiNi.sub.0.5xMn.sub.1.5y {A}.sub.uO.sub.z and a first metal oxide and a second metal oxide coating the surface of the particles of the lithium-containing compound, wherein the first metal oxide is an oxide of at least one metal having a valence of four or higher, and partially covers the surface of the particles of the lithium-containing compound in an island shape, the second metal oxide is an oxide of at least one metal having a valence of less than four and covers the partial surface of the particles of the lithium-containing compound that is not covered by the first metal oxide; wherein {A} is a doping composition represented by a formula of w.sub.iB.sub.i, wherein B.sub.i is a doping element for replacing Ni and/or Mn, w.sub.i is the atomic percentage of B.sub.i in the entire doping composition {A}, and w.sub.i=1; and wherein u=x+y; 0x0.2; 0y0.2; 0u0.4; and 3.8z4.2.

2. The cathode active material according to claim 1, wherein the first metal oxide is selected from one or more of TiO.sub.2, ZrO.sub.2, SnO.sub.2, SiO.sub.2, GeO.sub.2, CeO.sub.2, HfO.sub.2, and Nb.sub.2O.sub.5.

3. The cathode active material according to claim 1 or 2, wherein the second metal oxide is selected from one or more of Al.sub.2O.sub.3, MgO, ZnO, Ce.sub.2O.sub.3, and CaO.

4. The cathode active material according to any one of claims 1 to 3, wherein u>0.

5. The cathode active material according to any one of claims 1 to 4, wherein B.sub.i is selected from one or more of the group consisting of Al, Mg, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ce, W, Zr, Ca and Sr.

6. The cathode active material according to any one of claims 1 to 5, wherein the particles of the lithium-containing compound have a particle size of 1-20 m; and the first metal oxide has a particle size of 10-500 nm.

7. The cathode active material according to any one of claims 1 to 6, wherein the coverage of the first metal oxide on the surface of the particles of the lithium-containing compound is 1-75%.

8. The cathode active material according to any one of claims 1 to 7, wherein, in the other area on the surface of the particles of the lithium-containing compound than that is covered by the first metal oxide, the second metal oxide has a thickness of 1-20 nm or a shallow gradient solid solution with a depth of less than 200 nm is formed.

9. A method for preparing a cathode active material according to any one of claims 1 to 8, the method comprising the steps of: (1) mixing source compounds of Li, Ni, Mn and optionally {A} and a source compound of a first metal oxide uniformly in a stoichiometric ratio; (2) sintering the mixture obtained in step (1) sequentially at a temperature of 400-500 C. and then at a temperature of 800-1000 C. and cooling the same to prepare a lithium-containing compound with the surface covered by the first metal oxide in an island shape; (3) mixing the lithium-containing compound with the surface covered by the first metal oxide in an island shape prepared in step (2) with a source compound of a second metal oxide; (4) sintering the mixture obtained in step (3) at a temperature of 400-800 C. and cooling the same to prepare the cathode active material.

10. The preparation method according to claim 9, wherein the mixing in step (1) is dry mixing, and the mixing in step (3) is wet mixing.

11. A positive electrode for a lithium-ion battery, the positive electrode comprising a current collector, and a cathode active material, a carbon material conductive additive and a binder loaded on the current collector, characterized in that the cathode active material is a cathode active material according to any one of claims 1 to 8 or a cathode active material prepared by a method according to any one of claims 9 to 10.

12. A lithium-ion battery, the battery comprising a battery case, an electrode group and an electrolyte, the electrode group and the electrolyte being sealed in the battery case, the electrode group comprising a positive electrode, a separator, and a negative electrode, characterized in that the positive electrode is a positive electrode according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the following, the embodiments of the present invention are described in detail with reference to the accompanying drawings, in which:

[0029] FIG. 1 shows the XRD spectra of the cathode active materials A2 and A18 prepared in Example 2 and Example 18 (Comparative examples) respectively.

[0030] FIG. 2 shows the SEM image of the cathode active material A18 prepared in Example 18.

[0031] FIG. 3 shows the SEM image of the cathode active material A2 prepared in Example 2.

[0032] FIG. 4 is a trend graph of the discharge capacity changing over the number of cycles for the batteries B2 and B18 assembled from the materials A2 and A18 prepared in Example 2 and Example 18 (Comparative example) under a high-temperature test environment of 55 C.

[0033] FIG. 5 is a trend graph of the discharge capacity changing over the number of cycles for the batteries B2 and B18 assembled from the materials A2 and A18 prepared in Example 2 and Example 18 (Comparative example) under a room temperature test environment of 25 C.

[0034] FIG. 6 is a trend graph of the discharge capacity changing over the number of cycles for the full-batteries C2 and C18 respectively assembled from the positive electrode plates respectively prepared from the materials A2 and A18 paring with graphite negative electrode under a room temperature test environment of 25 C.

DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the specific embodiments, and the examples are given to illustrate the present invention, rather than to limit the scope of the present invention.

Example 1

[0036] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7795 g of TiO.sub.2 (the particles had a particle size of about 100 nm) were placed in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, pre-sintered at 500 C. for 5 hours first, then heated to 900 C. sintered for 12 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) (this material was referred to as A1).

Example 2

[0037] 183 g of the A1 material prepared in Example 1 and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.97%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A2).

Example 3

[0038] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 1.245 g of ZrO.sub.2 (purity was 99%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, pre-sintered at 500 C. for 5 hours first, then heated to 900 C. sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by ZrO.sub.2 particles (the coverage was about 20%; the particle size of ZrO.sub.2 particles was about 100 nm).

[0039] 184 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by ZrO.sub.2 particles (the coverage was about 20%; the particle size of ZrO.sub.2 particles was about 100 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by ZrO.sub.2 particles (the coverage was about 20%; the particle size of the ZrO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A3).

Example 4

[0040] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 2.66 g of Nb.sub.2O.sub.5 (purity was 99%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, pre-sintered at 500 C. for 5 hours first, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by Nb.sub.2O.sub.5 particles (the coverage was about 20%; the particle size of Nb.sub.2O.sub.5 particles was about 100 nm).

[0041] 185 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by Nb.sub.2O.sub.5 particles (the coverage was about 20%; the particle size of Nb.sub.2O.sub.5 particles was about 100 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by Nb.sub.2O.sub.5 particles (the coverage was about 20%; the particle size of the Nb.sub.2O.sub.5 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A4).

Examples 5

[0042] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 1.599 g of TiO.sub.2 (purity was 99%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, pre-sintered at 500 C. for 5 hours first, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm).

[0043] 184 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 40%; the particle size of TiO.sub.2 particles was about 100 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 40%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A5).

Example 6

[0044] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 2.4 g of TiO.sub.2 (purity was 99%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 60%; the particle size of TiO.sub.2 particles was about 100 nm).

[0045] 184 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 60%; the particle size of TiO.sub.2 particles was about 100 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 60%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A6).

Example 7

[0046] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 50 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 50 nm).

[0047] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 50 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 50 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A7).

Example 8

[0048] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 150 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 150 nm).

[0049] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 150 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 150 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A8).

Example 9

[0050] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 200 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 200 nm).

[0051] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 200 nm) and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 200 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A9).

Example 10

[0052] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm).

[0053] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) and 4.29 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 6 nm) (this material was referred to as A10).

Example 11

[0054] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm).

[0055] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) and 6.435 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 9 nm) (this material was referred to as A11).

Example 12

[0056] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm).

[0057] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) and 2.263 g of Zn(CH.sub.3COO).sub.2.2H.sub.2O (purity was 97%) were placed in a beaker containing 500 ml of deionized water, the beaker was added in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with ZnO (the thickness of the ZnO coating layer was about 3 nm) (this material was referred to as A12).

Example 13

[0058] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm).

[0059] 183 g of the above prepared LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) and 4.13 g of aluminum isopropoxide (purity was 99%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with Al.sub.2O.sub.3 (the thickness of the Al.sub.2O.sub.3 coating layer was about 3 nm) (this material was referred to as A13).

Example 14

[0060] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.2Mn.sub.0.75Mg.sub.0.05(OH).sub.2, and 0.7995 g of TiO.sub.2 (purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.4Mn.sub.1.5Mg.sub.0.1O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) (this material was referred to as A14).

Example 15

[0061] 183 g of the A14 material prepared in Example 14 and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.4Mn.sub.1.5Mg.sub.0.1O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A15).

Example 16

[0062] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%), 179.7537 g of Ni.sub.0.225Mn.sub.0.725Al.sub.0.05(OH).sub.2, and 0.7995 g of TiO.sub.2 (purchased from Alfa Aesar Corporation, purity was 99.9%, the particle size of the particles was about 100 nm) were added in a planetary ball mill and mixed evenly by dry method. The mixture was added in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.45Mn.sub.1.45Al.sub.0.1O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of TiO.sub.2 particles was about 100 nm) (this material was referred to as A16).

Example 17

[0063] 183 g of the A16 material prepared in Example 16 and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.997%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 500 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.45Mn.sub.1.45Al.sub.0.1O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%) and the remaining area completely coated with MgO (the thickness of the MgO coating layer was about 3 nm) (this material was referred to as A17).

Example 18 (Comparative Example)

[0064] 37.323 g of Li.sub.2CO.sub.3 (purity was 99%) and 179.7537 g of Ni.sub.0.25Mn.sub.0.75(OH).sub.2 were added in a planetary ball mill and mixed evenly by dry method. The mixture was placed in a crucible, placed in a muffle furnace, first pre-sintered at 500 C. for 5 hours, then heated to 900 C., sintered for 12 h, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material (this material was referred to as A18).

Example 19

[0065] 183 g of the A1 material prepared in Example 1 and 2.145 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O (purity was 99.97%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 600 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area forming a LiNi.sub.0.5xMn.sub.1.5Mg.sub.xO.sub.4 shallow solid solution with a thickness of 20 nm (this material was referred to as A19).

Example 20

[0066] 183 g of the A1 material prepared in Example 1 and 4.13 g of aluminum isopropoxide (purity was 99%) were added in a beaker containing 500 ml of deionized water, the beaker was placed in a magnetic stirrer for uniformly stirring for 12 hours (stirring speed was 500 rpm), and then the deionized water was completely evaporated. The resulting mixture was then placed in a muffle furnace (under air atmosphere), sintered at 60 C. for 5 hours, and naturally cooled to obtain the LiNi.sub.0.5Mn.sub.1.5O.sub.4 particle material with the surface partially covered by TiO.sub.2 particles (the coverage was about 20%; the particle size of the TiO.sub.2 particles was about 100 nm) and the remaining area forming a LiNi.sub.0.5xMn.sub.1.5yAl.sub.x+yO.sub.4 shallow solid solution with a thickness of 20 nm (this material was referred to as A20).

[0067] Morphology Characterization

[0068] FIG. 1 shows the XRD spectra of the materials A2 and A18 (comparative material), there being almost no difference in XRDs of the two and both being cubic spinel-structured, indicating that the LiNi.sub.0.5Mn.sub.1.5O.sub.4 material after being coated with TiO.sub.2 and MgO (A2 material) has no change in the structure.

[0069] FIG. 2 and FIG. 3 show the SEM images of A18 (comparative material) and A2 respectively, the morphology of A18 (comparative material) being a regular truncated octahedron with a smooth surface, and the surface of A2 material being partially covered by TiO.sub.2 particles and the other area being covered with MgO material. In FIG. 3, LiNi.sub.0.5Mn.sub.1.5O.sub.4 particles have a particle size of 1-20 m and TiO.sub.2 particles have a particle size of 50-200 nm.

[0070] Performance Test

[0071] The materials A1 to A20 prepared in Examples 1 to 20 were assembled into button batteries in accordance with the following steps.

[0072] (1) Preparation of Positive Plate and Negative Plate

[0073] The materials A1 to A20 prepared in Examples 1 to 20 were respectively used as a cathode active material, carbon black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder, and they were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, mixed uniformly, and prepared into a uniform cathode slurry. The uniform cathode slurry was evenly coated on an aluminum foil current collector having a thickness of 15 m, dried at 55 C. to form a electrode plate with a thickness of 100 m, the electrode plate was rolled under a roller press (pressure was about 1 MPa1.5 cm.sup.2), the electrode plate was cut into a round plate having a diameter of 14 mm, and the round plate was placed in a vacuum oven and baked at 120 C. for 6 h, naturally cooled, then taken out and placed in a glove box as a positive plate.

[0074] Graphite was used as a anode active material, carbon black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder, and they were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, mixed uniformly, and prepared into a uniform anode slurry. The uniform anode slurry was evenly coated on an aluminum foil current collector having a thickness of 8 m, dried at 55 C. to form a electrode plate having a thickness of 100 m, the electrode plate was rolled under a roller press (pressure was about 1 MPa1.5 cm.sup.2), the electrode plate was cut into a round plate having a diameter of 15 mm, and the round plate was placed in a vacuum oven and baked at 120 C. for 6 h, naturally cooled, then taken out and placed in a glove box as a negative plate.

[0075] (2) Assembling the Lithium Ion Secondary Battery

[0076] In a glove box filled with an inert atmosphere, lithium metal was used as the negative electrode of the battery, a double-aluminum oxide coated PP/PE/PP three-layer membrane as a separator was placed between the positive electrode and negative electrode, a non-aqueous electrolyte with 1M LiPF.sub.6 dissolved in EC/DMC (1:1, a volume ratio) was added dropwise, and the positive plate prepared in the step (1) was used as the positive electrode, to assemble into a button battery having a model number CR2032 (referred to as B1 to B20).

[0077] In a glove box filled with an inert atmosphere, the graphite negative plate prepared in the step (1) was used as the negative electrode of the battery, a double-aluminum oxide coated PP/PE/PP three-layer film as a separator was placed between the positive electrode and the negative electrode, a non-aqueous electrolyte with 1M LiPF.sub.6 dissolved in EC/DMC (1:1, a volume ratio) was added dropwise, and the positive plate prepared in the step (1) was used as the positive electrode, to assemble into a button battery having a model number CR2032 (referred to as C1 to C20).

Test Examples 1 to 20

[0078] The prepared button batteries B1 to B20 were allowed to stand for 10 hours at room temperature (25 C.), and then the above-prepared button batteries were subjected to a charge-discharge cycle test using a Land battery charge-discharge tester. First at room temperature (25 C.), it was cycled at a ratio of 0.1 C for 1 cycle, and then was continued to be cycled at a ratio of 0.2 C for 4 cycles, wherein the charge-discharge voltage of the battery was controlled to range from 3.5V to 4.9V. Then, the button battery was transferred to a high temperature environment of 55 C., and was continued to be cycled at a ratio of 0.2 C for 200 cycles, and at the same time, the charge-discharge voltage of the battery was still controlled to range from 3.5 V to 4.9 V. The capacity retention ratios of the button batteries B1 to B20 after they were cycled in a high-temperature environment of 55 C. for 200 cycles were referred to as D1 to D20, respectively.

[0079] The prepared button batteries B1 to B20 were allowed to stand for 10 hours at room temperature (25 C.), and then the above-prepared button batteries were subjected to a charge-discharge cycle test using a Land battery charge-discharge tester. First at room temperature (25 C.), it was cycled at a ratio of 0.1 C for 1 cycle and then was continued to be cycled at a ratio of 0.2 C for 199 cycles, wherein the charge-discharge voltage of the battery was controlled to range from 3.5V to 4.9V. The capacity retention ratios of the button batteries B1 to B20 after they were cycled in a room temperature environment of 25 C. for 200 cycles were referred to as E1 to E20, respectively.

[0080] The prepared button batteries C1 to C20 were allowed to stand for 10 hours at room temperature (25 C.), and then the above-prepared button batteries were subjected to a charge/discharge cycle test using a Land battery charge-discharge tester (purchased from Wuhan Land Electronics Co., Ltd.). First at room temperature (25 C.), it was cycled at a ratio of 0.1 C for 1 cycle, and then was continued to be cycled at a ratio of 0.2 C for 199 cycles, wherein the charge-discharge voltage of the battery was controlled to range from 3.4V to 4.8V. The capacity retention ratios of the button batteries C1 to C20 after they were cycled for 200 cycles in a room temperature environment of 25 C. were referred to as F1 to F20, respectively. Table 1 shows the test results for the Test Examples 1 to 18 (D1 to D20 and E1 to E20 and F1 to F20).

TABLE-US-00001 TABLE 1 The capacity The capacity The capacity retention ratios retention ratios retention ratios D1 to D20 of B1 to E1 to E20 of B1 to F1 to F20 of C1 to B18 after cycled B18 after cycled C18 after cycled for 200 cycles in a for 200 cycles in a for 200 cycles in a high-temperature room temperature room temperature of 55 C. of 25 C. of 25 C. D1 was 82% E1 was 91% F1 was 65% D2 was 88% E2 was 95% F2 was 68% D3 was 87% E3 was 92% F3 was 67% D4 was 86% E4 was 93% F4 was 66% D5 was 85% E5 was 92% F5 was 67% D6 was 86% E6 was 91% F6 was 63% D7 was 87% E7 was 93% F7 was 64% D8 was 86% E8 was 92% F8 was 68% D9 was 86% E9 was 95% F9 was 65% D10 was 85% E10 was 96% F10 was 66% D11 was 88% E11 was 95% F11 was 63% D12 was 86% E12 was 91% F12 was 64% D13 was 87% E13 was 94% F13 was 65% D14 was 85% E14 was 93% F14 was 65% D15 was 86% E15 was 92% F15 was 67% D16 was 87% E16 was 94% F16 was 68% D17 was 85% E17 was 93% F17 was 64% D18 was 86% E18 was 88% F18 was 62% D19 was 85% E19 was 90% F19 was 64% D20 was 87% E20 was 92% F20 was 65%

[0081] FIG. 4 is a trend graph of the discharge capacity changing over the number of cycles for batteries B2 and B18 assembled from materials A2 and A18 prepared in Example 2 and Example 18 (Comparative example) under a high-temperature test environment of 55 C. The results showed that, the battery B18 assembled from uncoated A18 (comparative material) had a capacity retention ratio of about 60% after 200 cycles under a high temperature test environment of 55 C., and the capacity fading was rapid. This is because under the high temperature test environment, the decomposition of the electrolyte and the dissolution of Mn were exacerbated, which resulted in rapid fading of the capacity of the material. Battery B2 assembled from A2 material had a capacity retention ratio of about 88% after 200 cycles under a high temperature test environment of 55 C. This is because after being coated with TiO.sub.2 and MgO, the direct contact between the LiNi.sub.0.5Mn.sub.1.5O.sub.4 material and the electrolyte was hindered, and the decomposition of the electrolyte and the dissolution of Mn were suppressed, thus the cycling stability of the battery being improved.

[0082] FIG. 5 is a trend graph of the discharge capacity changing over the number of cycles for batteries B2 and B18 assembled from materials A2 and A18 prepared in Example 2 and Example 18 (Comparative example) under a room temperature test environment of 25 C. The results showed that B2 battery assembled from A2 material had a capacity retention ratio of about 95% after 200 cycles under a room temperature test environment of 25 C., while B18 battery assembled from A18 (comparative material) material had a capacity retention ratio of about 88% after 200 cycles under a room temperature test environment of 25 C. The capacity retention ratios (88% and 95%) of both A18 material and A2 material under a room temperature test environment of 25 C. were higher than the capacity retention ratios (60% and 88%) under a high temperature test environment of 55 C., because the decomposition of the electrolyte and the dissolution of Mn were less under the room temperature than under the high temperature, thus the capacity retention ratios under the room temperature being higher.

[0083] FIG. 6 is a trend graph of the discharge capacity changing over the number of cycles for full-batteries C2 and C18 respectively assembled from the positive plates respectively prepared from materials A2 and A18 paring with graphite negative electrode under a room temperature test environment of 25 C. The results showed that full-battery C2 had a capacity retention ratio of about 68% after 200 cycles under a room temperature test environment of 25 C., while full-battery C18 had a capacity retention ratio of about 62% after 200 cycles under a room temperature test environment of 25 C. This is because an SEI film would form on the surface of the graphite negative electrode during cycling of the full-battery, the recyclable lithium ions from the cathode material were consumed, and at the same time the electrolyte decomposed and Mn dissolved, resulting in that the uncoated material A18 had poorer cycling stability under room temperature, while the full-battery assembled from TiO.sub.2 and MgO coated A2 material had its cycling stability improved, and the capacity retention ratio after 200 cycles was about 68%.

[0084] Finally, it should be explained that the foregoing examples are merely intended to illustrate the technical solutions of the present invention, but not to limit it; although the present invention is described in detail with reference to the foregoing examples, it should be understood by those skilled in the art that, the technical solutions recited in the foregoing examples may still be modified or equivalent replacements may be made to part or all of the technical features therein; and these modifications or replacements do not make the nature of the corresponding technical solution depart from the scope of the technical solutions of the examples of the present invention.