Irreversible Additive, Positive Electrode Including the Irreversible Additive, and Lithium Secondary Battery Including the Positive Electrode

Abstract

Provided is a method of preparing an irreversible positive electrode additive for a secondary battery, which includes mixing Li.sub.2O, NiO, and NH.sub.4VO.sub.3 and performing thermal treatment to prepare a lithium nickel composite oxide represented by Chemical Formula 1 below, wherein the NH.sub.4VO.sub.3 is mixed in an amount of 1.5 to 6.5 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Li.sub.2+aNi.sub.1−b−cM.sup.1.sub.bV.sub.cO.sub.2−dA.sub.d  [Chemical Formula 1]

In Chemical Formula 1,

M.sup.1 is at least one selected from the group consisting of Cu, Mg, Pt, Al, Co, P, W, Zr, Nb, and B, A is at least one selected from the group consisting of F, S, Cl, and Br, and 0≤a≤0.2, 0≤b≤0.5, 0.01≤c≤0.065, and 0≤d≤0.2 are satisfied.

Claims

1. A method of preparing an irreversible positive electrode additive for a secondary battery, the method comprising: mixing Li.sub.2O, NiO, and NH.sub.4VO.sub.3 and performing thermal treatment to prepare a lithium nickel composite oxide represented by Chemical Formula 1 below, wherein the NH.sub.4VO.sub.3 is mixed in an amount of 1.5 to 6.5 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3:
Li.sub.2+aNi.sub.1−b−cM.sup.1.sub.bV.sub.cO.sub.2−dA.sub.d  [Chemical Formula 1] in Chemical Formula 1, M.sup.1 is at least one selected from the group consisting of Cu, Mg, Pt, Al, Co, P, W, Zr, Nb, and B, A is at least one selected from the group consisting of F, S, Cl, and Br, and 0≤a≤0.2, 0≤b≤0.5, 0.01≤c≤0.065, and 0≤d≤0.2 are satisfied.

2. The method of claim 1, wherein the NH.sub.4VO.sub.3 is mixed in an amount of 2 to 5.5 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

3. The method of claim 1, wherein, in Chemical Formula 1, 0.015≤c≤0.055 is satisfied.

4. The method of claim 1, wherein the Li.sub.2O and NiO are mixed in a Li.sub.2O/NiO molar ratio of 0.9 to 1.1.

5. The method of claim 1, wherein the thermal treatment is performed at 600 to 800° C.

6. The method of claim 1, wherein the lithium nickel composite oxide is Li.sub.2Ni.sub.1−cV.sub.cO.sub.2 (c′ ranges from 0.01 to 0.065).

7. A method of manufacturing a positive electrode for a secondary battery, the method comprising: mixing an irreversible positive electrode additive for a secondary battery prepared according to claim 1, a conductive material, and a binder to prepare a positive electrode slurry; and applying the positive electrode slurry onto a positive electrode current collector to manufacture a positive electrode.

8. An irreversible positive electrode additive for a secondary battery, comprising a lithium nickel composite oxide represented by Chemical Formula 1 below, Li.sub.2O, and NiO, wherein the lithium nickel composite oxide is included in an amount of 90 to 95 wt % with respect to a total weight of the lithium nickel composite oxide, Li.sub.2O, and NiO:
Li.sub.2+aNi.sub.1−b−cM.sup.1.sub.bV.sub.cO.sub.2−dA.sub.d  [Chemical Formula 1] in Chemical Formula 1, M.sup.1 is at least one selected from the group consisting of Cu, Mg, Pt, Al, Co, P, W, Zr, Nb, and B, A is at least one selected from the group consisting of F, S, Cl, and Br, and 0≤a≤0.2, 0≤b≤0.5, 0.01≤c≤0.065, and 0≤d≤0.2 are satisfied.

9. The irreversible positive electrode additive of claim 8, wherein, in Chemical Formula 1, 0.015≤c≤0.055 is satisfied.

10. A positive electrode for a secondary battery, comprising the irreversible positive electrode additive for a secondary battery according to claim 8, a conductive material, and a binder.

11. A lithium secondary battery comprising: the positive electrode for a secondary battery according to claim 10; a negative electrode disposed to face the positive electrode; and a separator interposed between the positive electrode and the negative electrode.

Description

EXAMPLE 1

[0065] Li.sub.2O and NiO were mixed so that a Li/Ni molar ratio was 2.0, and NH.sub.4VO.sub.3 was mixed therewith in an amount of 2 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3. Afterward, thermal treatment was performed at 685° C. under a N.sub.2 atmosphere for 10 hours to prepare an irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.982V.sub.0.018O.sub.2.

Example 2

[0066] An irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.972V.sub.0.028O.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was mixed in an amount of 3 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Example 3

[0067] An irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.963V.sub.0.037O.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was mixed in an amount of 4 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Example 4

[0068] An irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.948V.sub.0.052O.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was mixed in an amount of 5.5 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Comparative Example 1

[0069] An irreversible positive electrode additive represented by Li.sub.2NiO.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was not mixed.

Comparative Example 2

[0070] An irreversible positive electrode additive was prepared in the same manner as in Example 1, except that VO was mixed in an amount of 3 parts by weight instead of NH.sub.4VO.sub.3.

Comparative Example 3

[0071] An irreversible positive electrode additive was prepared in the same manner as in Example 1, except that NH.sub.4Cl was mixed in an amount of 3 parts by weight instead of NH.sub.4VO.sub.3.

Comparative Example 4

[0072] An irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.991V.sub.0.009O.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was mixed in an amount of 1 part by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Comparative Example 5

[0073] An irreversible positive electrode additive represented by Li.sub.2Ni.sub.0.933V.sub.0.067O.sub.2 was prepared in the same manner as in Example 1, except that NH.sub.4VO.sub.3 was mixed in an amount of 7 parts by weight with respect to a total of 100 parts by weight of the Li.sub.2O, NiO, and NH.sub.4VO.sub.3.

Experimental Example 1: XRD Analysis

[0074] X-ray diffraction (XRD) data for the irreversible positive electrode additives prepared according to Examples 1 to 4 and Comparative Examples 1 to 5 was obtained and then analyzed, and results thereof are shown in Table 1 below.

[0075] An XRD measurement instrument, a sample preparation method, and measurement conditions are follows. XRD data was analyzed by a Rietveld refinement method using the complete structure model of phases present in a sample.

[0076] Instrument: XRD-12-D8 Endeavor 2 equipped with a Lynxeye XE-T detector

[0077] Sample preparation method: A sample was prepared by putting powder into the groove in the center of a general powder holder and making the surface even, that is, making the powder height equal to the height of the edge of the holder, using a slide glass.

[0078] Analysis conditions:

[0079] Measurement range (2 theta): 100 to 90°

[0080] Step size (2 theta): 0.006°

[0081] Measurement time (time/step): 38.4 s

[0082] X-ray (Cu): 40 kV and 40 mA

[0083] Divergence slit: 0.2°

[0084] Goniometer radii: 200.5 mm

TABLE-US-00001 TABLE 1 Lithium nickel composite oxide Li.sub.2O NiO (wt %) (wt %) (wt %) Example 1 91.7 2.9 5.4 Example 2 90.3 2.8 6.9 Example 3 92.4 2.4 5.2 Example 4 91.0 0.1 8.9 Comparative Example 1 88.7 4.9 6.4 Comparative Example 2 not synthesized — — Comparative Example 3 89.2 2 8.8 Comparative Example 4 89.6 3 7.4 Comparative Example 5 86.5 7 6.5

[0085] Referring to Table 1, Examples 1 to 4 exhibited increased synthesis rates of a lithium nickel composite oxide and reduced amounts of unreacted materials Li.sub.2O and NiO as compared to Comparative Examples 1 to 5. For reference, in the case of Comparative Example 5, a reduction reaction of NiO and the like became dominant over a formation reaction of a lithium nickel composite oxide due to the presence of excessive ammonium in the preparation of an irreversible positive electrode additive, and thus a synthesis rate of a lithium nickel composite oxide was degraded.

Experimental Example 2: Evaluation of Battery Performance

[0086] Each of the irreversible positive electrode additives prepared in Examples 1 to 4 and Comparative Examples 1 and 3 to 5, a Super-P conductive material, and a PVDF binder were mixed in a weight ratio of 95:2:3 in a N-methyl pyrrolidone solvent to prepare a positive electrode slurry, and the slurry was then applied onto one surface of an aluminum current collector, dried at 100° C., and then roll-pressed to manufacture a positive electrode.

[0087] As a negative electrode, lithium metal was used.

[0088] A porous polyethylene separator was interposed between the manufactured positive electrode and the negative electrode to manufacture an electrode assembly. Then, the electrode assembly was placed inside a case, and an electrolyte solution was injected into the case to manufacture a lithium secondary battery. In this case, the electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF.sub.6) in an organic solvent containing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate (EC/EMC/DEC volumetric mixing ratio=3/4/3).

[0089] Each manufactured lithium secondary battery cell was charged at 25° C. in the CC/CV mode of 0.1 C up to 4.25 V (final current: 1/20 C) and discharged at a constant current of 0.1 C up to 2.5 V, and the charge and discharge capacities thereof were measured. Then, a change in the volume of the monocell was measured using a volumometer, to which Archimedes volume measurement is applied, to measure a gas generation amount at the 50.sup.th cycle, and results thereof are shown in the following Table 2.

TABLE-US-00002 TABLE 2 Charge Discharge Gas generation capacity capacity amount (@50.sup.th (mAh/g) (mAh/g) cycle) (μl/g) Example 1 395.2 147.01 7.15 Example 2 390.6 145.7 6.90 Example 3 398.3 149.4 6.83 Example 4 397.1 149.7 4.67 Comparative Example 1 376.3 145.4 8.3 Comparative Example 3 386.9 149.4 7.85 Comparative Example 4 390.1 144.4 7.89 Comparative Example 5 400.0 135.7 5.24

[0090] Referring to Table 2, it can be seen that Examples 1 to 4 exhibited improved capacity characteristics and reduced gas generation amounts at the 50.sup.th cycle as compared to Comparative Examples 1, 3, and 4. Meanwhile, Comparative Example 5 had a high impurity content due to a low synthesis rate of a lithium nickel composite oxide, and accordingly, the severest gelation occurred in the manufacture of a positive electrode.

Experimental Example 3: Evaluation of High-Temperature Storage

[0091] A lithium secondary battery cell was manufactured using each of the irreversible positive electrode additives prepared in Examples 1 to 4 and Comparative Examples 1, 3, and 4 as in Experimental Example 2, except that a negative electrode, which was manufactured by mixing graphite as a negative electrode active material, a carbon black conductive material, and a PVDF binder in a weight ratio of 95:1:4 in a N-methyl pyrrolidone solvent to prepare a composition for forming a negative electrode and applying the composition onto one surface of a copper current collector, was used.

[0092] Each manufactured lithium secondary battery monocell was charged in the CC/CV mode of 0.1 C up to 4.2 V (final current: 1/20 C). The charged monocell was stored in a chamber set to 60° C. for 4 weeks, and then a change in the volume of the monocell was measured using a volumometer, to which Archimedes volume measurement is applied, to evaluate a gas generation amount. Results thereof are shown in the following Table 3.

TABLE-US-00003 TABLE 3 Gas generation amount (μl/g) Example 1 4.04 Example 2 3.35 Example 3 2.67 Example 4 2.02 Comparative Example 1 4.30 Comparative Example 3 5.07 Comparative Example 4 4.10

[0093] Referring to Table 3, it can be seen that Examples 1 to 4 exhibited substantially reduced gas generation amounts after 4-week storage compared to Comparative Examples 1, 3, and 4.