Cathode additive, preparation method thereof, and cathode and lithium secondary battery comprising the same

Abstract

The present disclosure relates to a cathode additive, a method for preparing the same, and a cathode and a lithium secondary battery including the same. More specifically, one embodiment of the present disclosure provides a cathode additive that can offset an irreversible capacity imbalance, increase the initial charge capacity of a cathode, and simultaneously inhibit the generation of a gas in a battery.

Claims

1. A cathode additive comprising: a core, the composition of which is represented by the following Chemical Formula 1; and a coating layer positioned on a surface of the core, and comprising a phosphorus (P) compound:
{.sub.x(Li.sub.2+aNi.sub.bM.sub.1−bO.sub.2+c)}.Math.{.sub.y(NiO)}.Math.{.sub.z(Li.sub.2O)}  [Chemical Formula 1] wherein, in Chemical Formula 1, M is one or more metal atoms forming a divalent cation or a trivalent cation, −0.2≤a≤0.2, 0.5≤b≤1.0, −0.2≤c≤0.2, 0.7≤x≤1.0, 0<y≤0.15, 0<z≤0.15, and x+y+z=1.

2. The cathode additive according to claim 1, wherein the phosphorus (P) compound includes one or more selected from the group consisting of lithium phosphate (Li.sub.3PO.sub.4) and ammonium phosphate (NH.sub.4H.sub.2PO.sub.4).

3. The cathode additive according to claim 1, wherein the coating layer is included in a content of 500 to 9000 ppm, based on a total amount of the cathode additive.

4. The cathode additive according to claim 1, wherein the core includes a lithium nickel oxide represented by the following Chemical Formula 1-1, nickel oxide (NiO), and lithium oxide (Li.sub.2O), and has a whole composition represented by the above Chemical Formula 1:
Li.sub.2+aNi.sub.bM.sub.1−bO.sub.2+c  [Chemical Formula 1-1] wherein, in Chemical Formula 1-1, M, a, b, and c are as defined in Chemical Formula 1.

5. The cathode additive according to claim 1, wherein y=z.

6. The cathode additive according to claim 5, wherein for the core, a peak by lithium oxide (Li.sub.2O) is detected in at least one of a range which 2θ is 30 to 35°, a range in which 2θ is 35 to 40°, or a range in which 2θ is 55 to 60°, by XRD (X-Ray Diffraction) measurement by Fe Kα X-ray (X-rα).

7. The cathode additive according to claim 5, wherein a content of lithium oxide (Li.sub.2O) in a total amount of the core (100 wt %) is greater than 0 wt % and equal to or less than 15 wt %.

8. The cathode additive according to claim 5, wherein for the core, a peak by nickel oxide (N.sub.iO) is detected in at least one of a range in which 2θ is 35 to 40°, a range in which 2θ is 40 to 45°, or a range in which 2θ is 50 to 55°, by XRD (X-Ray Diffraction) measurement by Fe Kα X-ray (X-rα).

9. The cathode additive according to claim 5, wherein the content of nickel oxide (N.sub.iO) in the total amount of the core (100 wt %) is greater than 0 wt % and equal to or less than 15 wt %.

10. A method for preparing the cathode additive of claim 1, comprising steps of: preparing a nickel-based oxide represented by the following Chemical Formula 3; heat treating a mixture of the nickel-based oxide and lithium oxide (Li.sub.2O) to obtain a core; and heat treating a mixture of the core and ammonium phosphate (NH.sub.4H.sub.2PO.sub.4) to form a coating layer on the surface of the core:
(Ni.sub.dM.sub.1−d)O.sub.2  [Chemical Formula 3] wherein, in Chemical Formula 3, M is a metal atom forming a divalent cation or a trivalent cation, and 0.5≤d≤1.0.

11. The method for preparing a cathode additive according to claim 10, wherein the step of forming a coating layer on the surface of the core is conducted under an inert atmosphere.

12. The method for preparing a cathode additive according to claim 10, wherein the step of forming a coating layer on the surface of the core is conducted at 600 to 800° C.

13. The method for preparing a cathode additive according to claim 10, wherein the step of obtaining the core is conducted under an inert atmosphere.

14. The method for preparing a cathode additive according to claim 10, wherein the step of obtaining the core is conducted at 600 to 800° C.

15. A cathode mixture comprising: the cathode additive of claim 1; and a cathode active material.

16. The cathode mixture according to claim 15, wherein the cathode additive is included in the content of 1 to 30 wt %, based on the total weight of the mixture (100 wt %).

17. The cathode mixture according to claim 15, wherein the cathode active material includes lithium and one or more composite oxides selected from the group consisting of a metal of cobalt, manganese, nickel, and a combination thereof.

18. The cathode mixture according to claim 15, further comprising a conductive material, a binder, or a mixture thereof.

19. A lithium secondary battery comprising: a cathode comprising the cathode mixture of claim 15; an electrolyte; and an anode.

20. The lithium secondary battery according to claim 19, wherein the anode includes one or more anode active materials selected from the group consisting of a carbon-based anode active material, as lithium metal, as lithium alloy, Si, SiO.sub.x (0<x<2), a Si—C composite, a Si-Q alloy (wherein Q is an alkali metal, an alkali earth metal, an atom of Groups 13 to 16, a transition metal, a rare earth atom, or a combination thereof, provided that it is not Si), Sn, SnO.sub.2, a Sn—C composite, and a Sn—R (where R is an alkali metal, an alkali earth metal, an atom of Groups 13 to 16, a transition metal, a rare earth metal, or a combination thereof, provided that it is not Sn).

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing the initial charge/discharge property of each lithium secondary battery of Preparation Examples 1 to 3, and Comparative Example 1.

(2) FIG. 2 is a graph measuring and recording the amount of gas generation according to the charge/discharge cycle (1st˜4th cycle), for each battery of Examples 1 to 8 and each battery of Preparation Examples 1 to 3 and Comparative Example 1.

(3) FIG. 3 is a graph measuring and recording the initial (1.sup.st) charge/discharge property, for each battery of Examples 1 to 8 and each battery of Preparation Examples 1 to 3 and Comparative Example 1.

(4) FIG. 4 is a graph measuring and recording the initial (1.sup.st) charge/discharge property and long-time charge/discharge ((˜200.sup.th) property, for each battery of Comparative Examples 2 to 4, and Examples 7 and 8.

MODE FOR CERTAIN EMBODIMENTS OF THE PRESENT DISCLOSURE

(5) Hereinafter, the actions and effects of the present disclosure will be explained in more detail through specific examples herein. However, these examples are presented only as the illustrations of the present disclosure, and the scope of the right of the present disclosure is not limited thereby.

(6) I. Confirmation of Advantages of a Core Including Lithium Nickel Oxide, Nickel Oxide (NiO), and Lithium Oxide (Li.sub.2O)

Preparation Example 1: {.SUB.x.(Li.SUB.2.NiO.SUB.2.)}.Math.{.SUB.y.(NiO)}.Math.{.SUB.z.(Li.SUB.2.O)}, x=0.86, y=0.07, z=0.07, Bare

(7) (1) Preparation of a Core

(8) A nickel hydroxide precursor, Ni(OH).sub.2, was heat treated under an inert atmosphere at 600° C. for 10 hours to obtain a nickel-based oxide (NiO).

(9) The nickel-based oxide NiO was mixed with lithium oxide (Li.sub.2O) at a mole ratio (NiO:Li.sub.2O) of 1:1.1, and heat treated at 680° C. (inert atmosphere) for 18 hours. At this time, the heating and cooling rates were fixed to 5° C. per minute.

(10) After the heat treatment was finished, {.sub.x(Li.sub.2NiO.sub.2)}.Math.{.sub.y(NiO)}.Math.{.sub.z(Li.sub.2O)}, x=0.86, y=0.07, z=0.07 was finally obtained, which was designated as a core of Preparation Example 1.

(11) The above chemical formula was calculated from Experimental Example 1 described below.

(12) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(13) A cathode was prepared using the core of Preparation Example 1 as a cathode additive, and a lithium secondary battery including the prepared cathode was manufactured.

(14) Specifically, the core of Preparation Example 1 (cathode additive) {.sub.0.86(Li.sub.2NiO.sub.2)}.Math.{.sub.0.07NiO}.Math.{.sub.0.07Li.sub.2O}, conductive material (Super-P, Denka black), and a binder (PVdF) were mixed in an organic solvent (NMP) at a weight ratio of 85:10:5 (cathode additive:conductive material:binder), to prepare a cathode mixture in the form of a slurry, and then the cathode mixture was coated on an aluminum current collector, and dried in a vacuum oven at 120° C. for 30 minutes to prepare a cathode.

(15) As a counter electrode, Li-metal was used, and as an electrolyte, a solution of 2 wt % of VC dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:2 was used.

(16) A 2032 coin half-cell was manufactured using the above-described constructional elements, according to a common manufacturing method.

Preparation Example 2: {.SUB.x.(Li.SUB.2.NiO.SUB.2.)}.Math.{.SUB.y.(NiO)}.Math.{.SUB.z.(Li.SUB.2.O)}, x=0.80, y=0.10, z=0.10, Bare

(17) (1) Preparation of a Core

(18) {.sub.x(Li.sub.2NiO.sub.2)}.Math.{.sub.y(NiO)}.Math.{.sub.z(Li.sub.2O)}, x=0.80, y=0.10, z=0.10 was obtained by the same method as Preparation Example 1, except that the nickel-based oxide (NiO) was mixed with lithium oxide (Li.sub.2O) at a mole ratio of 1:1.2, and it was designated as a core (cathode additive) of Preparation Example 2.

(19) The above chemical formula was calculated from Experimental Example 1 described below.

(20) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(21) The cathode and lithium secondary battery of Preparation Example 2 were manufactured by the same method as Preparation Example 1, except that the core (cathode additive) of Preparation Example 2 was used instead of the core (cathode additive) of Preparation Example 1.

Preparation Example 3: {.SUB.x.(Li.SUB.2.NiO.SUB.2.)}.Math.{.SUB.y.(NiO)}.Math.{.SUB.z.(Li.SUB.2.O)}, x=0.76, y=0.12, z=0.12, Bare

(22) (1) Preparation of a Core

(23) {.sub.x(Li.sub.2NiO.sub.2)}.Math.{.sub.y(NiO)}.Math.{.sub.z(Li.sub.2O)}, x=0.76, y=0.12, z=0.12 was obtained by the same method as Preparation Example 1, except that the nickel-based oxide NiO was mixed with lithium oxide (Li.sub.2O) at a mole ratio of 1:1.3, and the above chemical formula was calculated from Experimental Example 1 described below.

(24) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(25) The cathode and lithium secondary battery of Preparation Example 3 were manufactured by the same method as Preparation Example 1, except that the core (cathode additive) of Preparation Example 3 was used instead of the core (cathode additive) of Preparation Example 1.

Comparative Example 1: .SUB.x.(Li.SUB.2.NiO.SUB.2.), x=0.86, Bare

(26) (1) Preparation of Cathode Additive

(27) A cathode additive was prepared by the same method as Preparation Example 1, and then a non-reacted nickel-based oxide (NiO) and lithium oxide (Li.sub.2O) were sieved through a 400 mesh sieve, to finally obtain x (Li.sub.2NiO.sub.2), x=0.86, having an orthorhombic crystal structure with a point group of Immm, which was designated as the cathode additive of Comparative Example 1.

(28) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(29) The cathode and lithium secondary battery of Comparative Example 1 were manufactured by the same method as Preparation Example 1, except that the cathode additive of Comparative Example 1 was used instead of the cathode additive of Preparation Example 1.

Experimental Example 1: XRD Analysis of the Core

(30) For each core (cathode additive) of Preparation Examples 1 to 3 and Comparative Example 1, XRD (X-Ray Diffraction) analysis by Cu Kα X ray (X-rα) was conducted, and the results are recorded in the following Table 1.

(31) Specifically, the lithium nickel oxide and the nickel oxide (NiO) can be detected as crystalloids, through XRD (X-Ray Diffraction) by Cu Kα X ray (X-rα).

(32) Particularly, quantitative analysis results were obtained through the calculation of intensity after XRD (X-Ray Diffraction) analysis.

(33) TABLE-US-00001 TABLE 1 Structural analysis Quantitative cell parameter crystallite analysis (Å) volume size NiO Li.sub.2O a axis c axis (Å.sup.3) (nm) (wt %) (wt %) Comparative 2.779 9.025 93.98 182 0 0 Example 1 Preparation 2.779 9.026 94.01 182 7 7 Example 1 Preparation 2.779 9.028 93.96 205 10 10 Example 2 Preparation 2.780 9.028 93.96 210 12 12 Example 3

(34) It is already known that Comparative Example 1 has an orthorhombic crystal structure with a point group of Immm. Further, from the results of structural analysis of Table 1, it can be seen that Comparative Example 1 and Preparation Examples 1 to 3 have identical crystal structures. Thus, it can be seen that Preparation Examples 1 to 3 also include a compound represented by Li.sub.2+aNi.sub.bM.sub.1−bO.sub.2+c.

(35) From the results of quantitative analysis of Table 1, it can be confirmed that Li.sub.2O was not detected in Comparative Example 1. However, it can be confirmed that in Preparation Examples 1 to 3, based on the total amount (100 wt %), 7 wt % (Preparation Example 1), 10 wt % (Preparation Example 2), and 12 wt % (Preparation Example 3) of Li.sub.2O were respectively detected.

Experimental Example 2: Evaluation of the Initial Charge/Discharge Property of a Battery Applying the Core as a Cathode Additive

(36) For each battery of Preparation Examples 1 to 3 and Comparative Example 1, the initial charge/discharge property was evaluated under the following conditions. The results of evaluation are recorded in FIG. 1 and the following Table 2.

(37) Charge: 0.1 C, CC/CV, 4.25 V, 0.05 C cut-off

(38) Discharge: 0.1 C, CC, 2.5 V, cut-off

(39) According to FIG. 1 and Table 2, it can be confirmed that in Preparation Examples 1 to 3, the initial irreversible capacity of an anode decreased, and the initial efficiency of a cathode increased, compared to Comparative Example 1.

(40) TABLE-US-00002 TABLE 2 Anode 0.1 C 0.1 C Cathode Charge Discharge Efficiency 1.sup.st Cycle (mAh/g) (mAh/g) (%) Capacity Comparative 329.8 95.2 28.9 (mAh/g) Example 1 Preparation 382 142.3 37.3 Example 1 Preparation 394.2 142.8 36.2 Example 2 Preparation 402.2 143.6 35.7 Example 3

(41) In Preparation Examples 1 to 3, in order to confirm the effect of improvement in the initial performance of a battery by the core in the cathode additive of one embodiment, a cathode mixture was prepared using each cathode additive in the same amount as the common cathode active material, and a cathode and a lithium secondary battery were manufactured.

(42) As explained above, the core can irreversibly discharge lithium ions and oxygen at the initial charge voltage, for example, 2.5 to 4.25 V (vs. Li/Li+), and then can be converted into a composition capable of reversible intercalation and deintercalation of lithium ions. Thus, as in Preparation Examples 1 to 3, the core may be utilized as an additive for compensating the initial irreversible capacity of an anode, and also as an active material enabling reversible intercalation and deintercalation of lithium.

(43) However, since it may have small reversible capacity compared to a common cathode active material due to the Li content and the structural limitation, in case the initial performance of a battery is to be improved while simultaneously securing the long-time cycle life characteristic, the cathode additive of one embodiment including the core may be mixed with the cathode active material at an appropriate mixing ratio according to the aimed properties of a battery.

(44) II. Confirmation of Advantages of a Cathode Additive Including a Core Including a Lithium Nickel Oxide, a Nickel Oxide (NiO), and a Lithium Oxide (Li.sub.2O); and a Phosphorus Coating Layer

Example 1 (Core: Preparation Example 1, Coating Amount: 2000 ppm)

(45) (1) Preparation of Cathode Additive

(46) {.sub.x(Li.sub.2NiO.sub.2)}.Math.{.sub.y(NiO)}.Math.{.sub.z(Li.sub.2O)}, x=0.86, y=0.07, z=0.07, was finally obtained by the same method as Preparation Example 1, and it was designated as the core of Example 1.

(47) The core of Example 1 and ammonium phosphate (NH.sub.4H.sub.2PO.sub.4) were mixed, and the mixture was heat treated under an inert atmosphere of 700° C. for 10 hours to obtain a cathode additive of Example 1.

(48) During the mixing, the amount of the ammonium phosphate was adjusted to 2000 ppm, based on the total amount of the mixture.

(49) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(50) The cathode and lithium secondary battery of Example 1 were manufactured by the same method as Preparation Example 1, except that the cathode additive of Example 1 was used instead of the core (cathode additive) of Preparation Example 1.

Example 2 (Core: Preparation Example 1, Coating Amount: 500 ppm)

(51) (1) Preparation of a Cathode Additive

(52) The cathode additive of Example 2 was obtained by the same method as Example 1, except that while mixing the core of Preparation Example 1 and ammonium phosphate, the amount of the ammonium phosphate was adjusted to 500 ppm, based on the total amount of the mixture.

(53) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(54) The cathode and lithium secondary battery of Example 2 were manufactured by the same method as Example 1, except that the cathode additive of Example 2 was used instead of the core (cathode additive) of Example 1.

Example 3 (Core: Preparation Example 1, Coating Amount: 4000 ppm)

(55) (1) Preparation of Cathode Additive

(56) The cathode additive of Example 3 was obtained by the same method as Example 1, except that while mixing the core of Preparation Example 1 and ammonium phosphate, the amount of the ammonium phosphate was adjusted to 4000 ppm, based on the total amount of the mixture.

(57) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(58) The cathode and lithium secondary battery of Example 3 were manufactured by the same method as Example 1, except that the cathode additive of Example 3 was used instead of the core (cathode additive) of Example 1.

Example 4 (Core: Preparation Example 1, Coating Amount: 8000 ppm)

(59) (1) Preparation of Cathode Additive

(60) The cathode additive of Example 4 was obtained by the same method as Example 1, except that while mixing the core of Preparation Example 1 and ammonium phosphate, the amount of the ammonium phosphate was adjusted to 8000 ppm, based on the total amount of the mixture.

(61) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(62) The cathode and lithium secondary battery of Example 4 were manufactured by the same method as Example 1, except that the cathode additive of Example 4 was used instead of the core (cathode additive) of Example 1.

Example 5 (Core: Preparation Example 2, Coating Amount: 2000 ppm)

(63) (1) Preparation of Cathode Additive

(64) The cathode additive of Example 5 was obtained by the same method as Example 1, except that the core of Preparation Example 2 was used instead of the core of Preparation Example 1.

(65) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(66) The cathode and lithium secondary battery of Example 5 were manufactured by the same method as Example 1, except that the cathode additive of Example 5 was used instead of Example 1.

Example 6 (Core: Preparation Example 3, Coating Amount: 2000 ppm)

(67) (1) Preparation of Cathode Additive

(68) The cathode additive of Example 6 was obtained by the same method as Example 1, except that the core of Preparation Example 3 was used instead of the core of Preparation Example 1.

(69) (2) Manufacture of a Cathode and a Lithium Secondary Battery (Coin Half-Cell)

(70) The cathode and lithium secondary battery of Example 6 were manufactured by the same method as Example 1, except that the cathode additive of Example 6 was used instead of the cathode additive of Example 1.

Experimental Example 3: Confirmation of the Formation of a Coating Layer and the Constituents

(71) For the cathode additive of Example 1, in order to confirm whether or not a coating layer was formed on the surface of the core of Preparation Example 1, and if formed, to confirm the components, XPS analysis was conducted.

(72) More specifically, as the result of measuring binding energy for the cathode additive of Example 1 by XPS analysis, a peak was detected at about 134 eV. This corresponds to the binding energy of Li.sub.3PO.sub.4 known in the art.

(73) Thus, it can be seen that in the cathode additive of Example 1, through the process of forming a coating layer using NH.sub.4H.sub.2PO.sub.4 as the raw material for coating, a lithium by-product LiOH existing on the surface of the core of Preparation Example 1 and NH.sub.4H.sub.2PO.sub.4 reacted to form a coating layer including Li.sub.3PO.sub.4 on the surface of the core.

(74) Although only the cathode additive of Example 1 was confirmed, it is inferred that a coating layer of the same component as Example 1 is formed on the surface of each core of Examples 2 to 6 which use the same raw materials and processes as Example 1, and only the coating amounts are different.

Experimental Example 4: Evaluation of the Properties of Li by-Product Reduction According to the Formation of a Coating Layer

(75) For each cathode additive of Examples 1 to 6 and each core of Preparation Examples 1 to 3 and Comparative Example 1, the initial pH and the content of Li by-products remaining on the surface were measured. The measurement results are shown in the following Table 3.

(76) The initial pH was measured by a pH titration method, wherein 10 g of each cathode additive was introduced into 100 ml of H.sub.2O, and the mixture was stirred for 5 minutes and then titrated with 0.1N HCl. Based on the inflection point that first appeared during the pH titration, the content of the base was measured as the content of LiOH, and the content of the total Li by-products was measured, and then the content of Li.sub.2 CO.sub.3 was calculated by subtracting the content of LiOH from the content of the total Li by-products.

(77) Here, each content of LiOH and Li.sub.2 CO.sub.3 and the total content of these lithium by-products are based on the total amount (100 wt %) of the cathode additive or core.

(78) TABLE-US-00003 TABLE 3 Composition of additives excess Li Coating Total Core amount initial LiOH Li.sub.2CO.sub.3 ex. Li ({.sub.x(Li.sub.2NiO.sub.2)}•{.sub.y(NiO)}•{.sub.z(Li.sub.2O)}) (ppm) pH (wt %) (wt %) (wt %) Comparative x = 0.86, y = 0, z = 0 — 12.13 3.650 0.432 4.082 Example 1 Preparation x = 0.86, y = 0.07, z = 0.07 — 12.45 3.808 0.451 4.259 Example 1 Preparation x = 0.80, y = 0.10, z = 0.10 — 12.47 3.987 0.456 4.443 Example 2 Preparation x = 0.76, y = 0.12, z = 0.12 — 12.49 4.013 0.459 4.472 Example 3 Example 1 Preparation Example 1; 2000 12.24 1.414 0.220 1.634 Example 2 x = 0.86, y = 0.07, z = 0.07 500 12.28 2.015 0.240 2.255 Example 3 4000 12.21 1.398 0.218 1.616 Example 4 8000 12.19 1.367 0.205 1.572 Example 5 Preparation Example 2; 2000 12.25 1.426 0.225 1.681 x = 0.80, y = 0.10, z = 0.10 Example 6 Preparation Example 3; 2000 12.24 1.429 0.229 1.658 x = 0.76, y = 0.12, z = 0.12

(79) From Table 3 it can be seen that although the content of lithium by-products increases as the content of Li.sub.2O in the core increases, by forming a phosphorus (P) compound as in each cathode additive of Example 1 to 6, lithium by-products can be reduced.

(80) Moreover, in Examples 1 to 6, it can be seen that as the coating amount of a phosphorus (P) compound increases, lithium by-products can be more effectively reduced.

Experimental Example 5: Evaluation of the Properties of Reducing Battery Gas Generation According to the Formation of a Coating Layer

(81) For each battery of Examples 1 to 6, Preparation Examples 1 to 3, and Comparative Example 1, the amount of gas generation during the 1.sup.st cycle charge and the amount of gas generation according to charge/discharge cycles (1.sup.st˜4.sup.th cycle) were measured under the following conditions. Specifically, using a differential electrochemical mass spectrometer (DEMS), gas pressure during the charging of each battery was measured in real time.

(82) Charge: 0.1 C, CC/CV, 4.25 V, 0.05 C cut-off

(83) Discharge: 0.1 C, CC, 2.5 V, cut-off

(84) The measurement results are described in the following Table 4 and shown in FIG. 2. As illustrated in Table 4, the phosphorus (P) coating limits gas generation.

(85) TABLE-US-00004 TABLE 4 Gas generation amount (uL) Charge/ Formation 2.sup.nd 3rd 4th Total Discharge cycle Accumulation cycle Accumulation Cycle accumulation cycle accumulation accumulation Comparative 341.2 341.2 8.1 349.3 5.3 354.6 0 354.6 354.6 Example 1 Preparation 395.5 395.5 9.6 405.1 6.6 411.7 0 411.1 411.1 Example 1 Preparation 401.6 401.6 9.4 411.0 5.1 416.1 0 416.1 416.1 Example 2 Preparation 407.8 407.8 10.0 417.8 5.9 423.7 0 423.7 423.7 Example 3 Example 1 265.2 265.2 10.2 275.4 6.4 281.8 1.0 282.8 282.8 Example 2 310.6 310.6 9.5 320.1 7.0 327.1 0 327.1 327.1 Example 3 258.4 258.4 8.9 267.3 5.8 273.1 0 273.1 273.1 Example 4 249.9 249.9 7.7 257.6 5.9 263.5 0 263.5 263.5 Example 5 270.3 270.3 9.8 280.1 6.5 286.6 0 286.6 286.6 Example 6 275.9 275.9 8.7 284.6 6.1 290.7 1.0 291.7 291.7

Experimental Example 6: Evaluation of the Properties of Improvement in the Initial Charge/Discharge of a Battery, According to the Formation of a Coating Layer

(86) For each battery of Examples 1 to 6, Preparation Examples 1 to 3, and Comparative Example 1, the initial charge/discharge properties were measured under the following conditions. The measurement results are recorded in FIG. 3 and the following Table 5.

(87) Charge: 0.1 C, CC/CV, 4.25 V, 0.05 C cut-off

(88) Discharge: 0.1 C, CC, 2.5 V, cut-off

(89) According to the following Table 5, it can be confirmed that in Preparation Examples 1 to 3, the initial irreversible capacity of an anode decreased, and the initial efficiency of a cathode increased, compared to Comparative Example 1. Moreover, it can be confirmed that in Examples 1 to 6, the initial efficiency of a cathode further increased, compared to Preparation Examples 1 to 3. However, if the coating amount is excessively increased, the initial charge capacity may be decreased, and thus, it may be required to control within 500 to 9000 ppm.

(90) TABLE-US-00005 TABLE 5 Anode 0.1 C 0.1 C Cathode Charge Discharge Efficiency 1.sup.st Cycle (mAh/g) (mAh/g) (%) Capacity Comparative 329.8 95.2 28.9 (mAh/g) Example 1 Preparation 382 142.3 37.3 Example 1 Preparation 394.2 142.8 36.2 Example 2 Preparation 402.2 143.6 35.7 Example 3 Example 1 385 143.6 37.3 Example 2 383 142.5 37.2 Example 3 387 141.8 36.6 Example 4 381 143.4 37.6 Example 5 396.0 144.4 36.5 Example 6 404.1 145.9 36.1

(91) Comprehensively reviewing Tables 3 and 4 and FIGS. 2 and 3 with Table 5, it can be seen that although the cores of Preparation Examples 1 to 3 irreversibly discharge lithium ions and oxygen at the initial cycle voltage, for example, 2.5 to 4.25 V (vs. Li/Li+), thereby decreasing the initial irreversible capacity of an anode and increasing the initial efficiency of a cathode compared to Comparative Example 1, there is a limit in increasing the initial efficiency of a cathode due to the presence of lithium by-products.

(92) On the other hand, it can be seen that in Examples 1 to 6, by forming a coating layer on the cores of Preparation Examples 1 to 3, the initial efficiency of a cathode can be further improved. This is considered to be because, as each cathode additive of Examples 1 to 6 has the effects of removing lithium by-products and inhibiting gas generation by the coating layer, while maintaining the effects of the core (namely, decreasing the initial irreversible capacity of an anode and increasing the initial efficiency of a cathode), the initial properties of a battery are further improved.

(93) Meanwhile, in Examples 1 to 6, in order to confirm the effect of improvement in the initial performance of a battery, a cathode mixture was prepared using each cathode additive in the same amount as a common cathode active material, and a cathode and a lithium secondary battery were manufactured. However, if the initial performance of a battery is to be improved while simultaneously securing the long-time life cycle characteristic, the cathode active material may be mixed with the cathode additive of one embodiment at an appropriate mixing ratio according to the aimed battery properties.

III. Examples of Practical Application Forms of a Cathode Additive Including a Core Including a Lithium Nickel Oxide, Nickel Oxide (NiO), and Lithium Oxide (Li.SUB.2.O) and a Phosphorus Compound Coating Layer

Examples 7 and 8: Application of the Cathode Additive of Example 1 in Combination with the Cathode Active Material

(94) For the practical application form of the cathode additive of Example 1, the cathode additive of Example 1 was used in combination with the cathode active material to prepare a cathode, and a lithium secondary battery including the prepared cathode was manufactured.

(95) Specifically, the cathode additive of Example 1 (core: Preparation Example, 1 coating amount: 2000 ppm), cathode active material of NCM (LiNi.sub.0.8 Co.sub.0.1Mn.sub.0.1O.sub.2), conductive material (Super-P, Denka Black) and a binder (PVdF) were mixed in an organic solvent (NMP) to prepare a cathode mixture in the form of a slurry, and then the cathode mixture was coated on an aluminum current collector and dried in a vacuum oven at 120° C. for 30 minutes, to manufacture each cathode of Example 7 and 8.

(96) In Examples 7 and 8, the weight ratios of the cathode additive of Example 1: cathode active material:conductive material:binder were 4.825:91.675:1.5:2 (Example 7) and 9.65:86.85:1.5: 2.0 (Example 8), respectively.

(97) Each 2032 coin half-cell was manufactured by the same method as Example 1, using each cathode of Examples 7 and 8 instead of the cathode of Example 1

Comparative Example 2: Application of Cathode Active Material Alone

(98) A cathode was prepared by the same method as Example 1, except that no cathode additive was used, and instead of the cathode additive of Example 1, the same amount of the cathode active material (LiNi.sub.0.8 Co.sub.0.1Mn.sub.0.1O.sub.2) was used, and a lithium secondary battery including the prepared cathode was manufactured.

Comparative Examples 3 and 4: Application of the Cathode Additive of Preparation Example 1 in Combination with the Cathode Active Material

(99) For the practical application of the cathode additive of Preparation Example 1, the cathode additive of Preparation Example 1 was used in combination with the cathode active material to prepare a cathode, and a lithium secondary battery including the prepared cathode was manufactured.

(100) Specifically, the cathode additive of Preparation Example 1 (core: Preparation Example 1, bare), the cathode active material of NCM (LiNi.sub.0.8 Co.sub.0.1Mn.sub.0.1O.sub.2), the conductive material (Super-P, Denka Black) and the binder (PVdF) were mixed in an organic solvent (NMP) to prepare a cathode mixture in the form of a slurry, and then the cathode mixture was coated on an aluminum current collector and dried in a vacuum oven at 120° C. for 30 minutes, to prepare each cathode of Comparative Examples 3 and 4.

(101) In Comparative Examples 3 and 4, the weight ratios of the cathode additive of Preparation Example 1: cathode active material:conductive material:binder were 4.825:91.67:1.5:2 (Preparation Example 3) and 9.65:86.85:1.5:2.0 (Preparation Example 4), respectively.

(102) Each 2032 coin half-cell was manufactured by the same method as Example 1, using each cathode of Comparative Examples 3 and 4 instead of the cathode of Example 1

Experimental Example 7: Evaluation of the Practical Application Form of the Cathode Additive (Evaluation of the Initial Capacity and Cycle Life Characteristic of A Battery)

(103) Specifically, charge/discharge of each battery of Comparative Examples 2 to 4 and Examples 7 and 8 was progressed at a room temperature of 25° C., under the following conditions. The results are shown in FIG. 4 and the following Table 6.

(104) Charge: 0.2 C, CC/CV, 4.25 V, 0.005 C cut-off

(105) Discharge: 0.2 C, CC, 2.5 V, cut-off

(106) According to FIG. 4 and Table 6, it is confirmed that compared to the case of using the cathode active material only (Comparative Example 2), in case the cathode additive of Preparation Example 1 or the cathode additive of Example 1 was used in combination with the cathode active material (Comparative Examples 3 and 4 Examples 7 and 8), both the initial charge capacity and the cycle life characteristic of a battery are improved.

(107) Further, in case the weight ratio of the additive:active material is identical, when the cathode additive of Example 1 is applied rather than the cathode additive of Preparation Example 1, the initial charge capacity and the life cycle characteristic of a battery are further improved.

(108) TABLE-US-00006 TABLE 6 Long-term operation Initial operation property of a battery Composition of additives Additive: property of a battery Capacity Capacity Coating active 0.2 C 0.2 C Retention Retention Core amount material Charge Discharge (%, @ 100.sup.th (%, @ 200.sup.th ({.sub.x(Li.sub.2NiO.sub.2)}•{.sub.y(NiO)}•{.sub.z(Li.sub.2O)}) (ppm) (weight ratio) (mAh/g) (mAh/g) cycle) cycle) Comparative — — Active 226.1 206.2 92.8 89.5 Example 2 material 100% (Ref.) Comparative x = 0.86, y = 0.07, z = 0.07 —  5:95 235.7 204.5 94.2 91.8 Example 3 Example 7 x = 0.86, y = 0.07, z = 0.07 2000  5:95 235.9 203.5 94.8 92.5 Comparative x = 0.86, y = 0.07, z = 0.07 — 10:90 243.0 199.3 95.1 92.9 Example 4 Example 8 x = 0.86, y = 0.07, z = 0.07 2000 10:90 243.1 199.1 95.4 93.6

(109) Putting the above results and Experimental Examples 1 to 6 together, it can be confirmed that the core commonly applied in Comparative Examples 3 and 4 and Examples 7 and 8 (a core including the lithium nickel oxide, nickel oxide (NiO), and lithium oxide (Li.sub.2O)) irreversibly discharges lithium ions and oxygen preferentially over the cathode active material at the initial voltage charge of a battery, thereby compensating the initial irreversible capacity of an anode and increasing the initial charge capacity of a cathode.

(110) However, in case the core is not coated, there is a limit in increasing the initial efficiency of a cathode due to the existence of lithium by-products, while in case the core is coated with a phosphorus compound, the effects of removing lithium by-products and inhibiting gas generation can be obtained by the coating layer while maintaining the effect of the core (namely, decreasing the initial irreversible capacity of an anode and increasing the initial efficiency of a cathode), and thus the initial properties of a battery are further improved.

(111) Moreover, according to FIG. 4 and Table 6, it can be confirmed that when the cycle number of batteries are identical, the capacity retention rates of Examples 7 and 8 are remarkably high, compared to the capacity retention rates of Comparative Examples 2 to 4.

(112) Such a difference in the capacity retention rates becomes severe as the cycle number of a battery increases, and particularly, it is confirmed that in Comparative Example 2, after the operation of 100 cycles, 92.8% of the initial capacity is maintained, and after the operation of 200 cycles, 89.5% is maintained. On the other hand, it is confirmed that in the case of Examples 7 and 8, after the operation of 100 cycles, 94.8% or more of the initial capacity is maintained, and even after the operation of 200 cycles, 92.5% or more of the initial capacity is maintained. This means that in case battery cycles are progressed while the initial capacity of a cathode increases by the cathode additive of one embodiment, the capacity loss decreases. It also means that after the cathode additive of one embodiment irreversibly discharges lithium ions and oxygen at the initial charge voltage of a battery, it is converted into a composition capable of reversible intercalation and deintercalation of lithium ions, thus partly contributing to the capacity even during the progression of battery cycles.

(113) Moreover, it can be confirmed that under conditions where the core composition of the additive, and the mixing ratio of the additive and the active material are identical, the initial property and the long-term operation property of a battery vary according to whether or not a surface coating exists. Specifically, it is confirmed that the initial property and the long-term operation property of the battery of Example 7 are improved compared to Comparative Example 3, and the initial property and the long-term operation property of the battery of Example 8 are improved compared to Comparative Example 4.

(114) It is considered that under conditions where the core composition of the additive, and the mixing ratio of the additive and the active material are identical, in case the surface of the additive is coated, lithium by-products (Li.sub.2 CO.sub.3, LiOH, etc.) remaining on the surface of the core are removed, thus inhibiting gas generation in a battery.

(115) Meanwhile, among Examples 7 and 8, in Example 8 wherein a cathode mixture including a higher content of the cathode additive of one embodiment is used, the initial charge capacity and the cycle life characteristic of a battery are further improved. This means that as a cathode mixture including a high content of the cathode additive of one embodiment is used, the initial charge capacity of a battery is further improved, and thus the cycle life characteristic can be more effectively improved. Thus, as explained above, in case the initial performance of a battery is to be improved while simultaneously securing the long-term cycle life characteristic, the cathode additive of one embodiment may be used in combination with the cathode active material at an appropriate mixing ratio, according to the aimed battery properties.