Irreversible Additive Comprised in Cathode Material for Secondary Battery, Cathode Material Comprising the Same, and Secondary Battery Comprising Cathode Material

Abstract

The present disclosure provides an irreversible additive contained in a cathode material for a secondary battery, wherein the irreversible additive is an oxide represented by the following chemical Formula 1, and wherein the oxide has a trigonal structure, a cathode material including the irreversible additive, and a secondary battery including the cathode material:

Li.sub.2+aNi.sub.1-bMo.sub.bO.sub.2+c  (1) in Formula 1, −0.2≤a≤0.2, 0<b≤0.2, 0≤c≤0.2.

Claims

1. An irreversible additive contained in a cathode material for a secondary battery, the irreversible additive comprising an oxide having a trigonal crystal structure and represented by the following chemical Formula 1:
Li.sub.2+aNi.sub.1-bMo.sub.bO.sub.2+c  (1) in Formula 1, −0.2≤a≤0.2, 0<b≤0.2, 0≤c≤0.2.

2. The irreversible additive according to claim 1, wherein the oxide belongs to a space group of P3-m1.

3. The irreversible additive according to claim 1, wherein the oxide has a crystal lattice of a=3.0954 Å, c=5.0700 Å and γ=120.00°.

4. The irreversible additive according to claim 1, wherein the oxide is Li.sub.2Ni.sub.0.9Mo.sub.0.1O.sub.2.

5. A cathode material comprising the irreversible additive of claim 1 and a cathode active material.

6. The cathode material according to claim 5, wherein a content of the irreversible additive is 0.1% by weight to 10% by weight based on the total weight of the cathode material.

7. A secondary battery comprising a cathode in which a cathode material is coated onto a cathode current collector, the cathode material including the irreversible additive of claim 1, wherein the irreversible additive has a trigonal system capable of converting into a monoclinic system within a secondary battery operating range of 4.0V or more.

8. The secondary battery according to claim 7, wherein the irreversible additive belongs to a space group of C2/m when the crystal structure is a monoclinic crystal system.

9. The secondary battery according to claim 7, wherein the cathode material comprises a cathode active material including an oxide represented by the following Chemical Formula 2.
Li(Ni.sub.aCo.sub.bMn.sub.c)O.sub.2  (2) in the above formula, 0<a<1, 0<b<1, 0<c<1, a+b+c=1.

10. The secondary battery according to claim 7, wherein the secondary battery has a structure in which an electrode assembly is built in a battery case together with an electrolyte, wherein the electrode assembly comprising: the cathode; an anode in which an anode material including an anode active material is coated onto an anode current collector; and a separator that is interposed between the cathode and the anode.

11. The secondary battery according to claim 7, wherein the secondary battery is a lithium secondary battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 is a graph showing the XRD measurement results of Comparative Example 1 according to Experimental Example 1;

[0080] FIG. 2 is a graph showing the XRD measurement results of Comparative Example 2 according to Experimental Example 1; and

[0081] FIG. 3 is a graph showing the XRD measurement results of Example 1 according to Experimental Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0082] Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying figures so that those skilled in the art can easily implement them. The present disclosure may be modified in various different ways, and is not limited to the embodiments set forth herein.

Comparative Example 1

[0083] 22.9 g of Li.sub.2O and 30 g of NiO (molar ratio 1:1) were mixed, and then heat-treated at 685 degrees Celsius for 18 hours under an N.sub.2 atmosphere, and then the resulting reaction product was cooled to obtain irreversible additive particles Li.sub.2NiO.sub.2.

Comparative Example 2

[0084] LiNiO.sub.2 and more than 1.5M Li.sup.+benzophenone.sup.− were reacted in the presence of THF (tetrahydrofuran) under an inert atmosphere.

[0085] Specifically, the mixture of the above materials was stirred for one day, and the mixed powders were filtered. The obtained mixed powder was washed with dry THF and dried under vacuum to obtain a pre-powder in which a small amount of trigonal Li.sub.2NiO.sub.2 and LiNiO.sub.2 were mixed.

[0086] Subsequently, the pre-powder was heat-treated at 225° C. for 14 hours under dry helium flow to obtain a Li.sub.2NiO.sub.2 powder having a trigonal crystal structure with improved crystallinity.

Example 1

[0087] 14.04 g of Li.sub.2O, 67.22 g of NiO and 14.39 g of MoO.sub.3 were mixed, and then heat-treated at 685 degrees Celsius for 18 hours under an N.sub.2 atmosphere, and then the resulting reaction product was cooled to obtain irreversible additive particles LiNi.sub.0.9Mo.sub.0.1O.sub.2.

[0088] LiNi.sub.0.9Mo.sub.0.1O.sub.2 and more than 1.5M Li.sup.+benzophenone.sup.− were reacted in the presence of THF (tetrahydrofuran) under an inert atmosphere.

[0089] Specifically, the mixture of the above materials was stirred for one day, and the mixed powders were filtered. The obtained mixed powder was washed with dry THF and dried under vacuum to obtain a pre-powder in which a small amount of trigonal Li.sub.2Ni.sub.0.9Mo.sub.0.1O.sub.2 and, Li Ni.sub.0.9Mo.sub.0.1O.sub.2 were mixed.

[0090] Subsequently, the pre-powder was heat-treated at 225° C. for 14 hours under dry helium flow to obtain a Li.sub.2Ni.sub.0.9Mo.sub.0.1O.sub.2 powder having a trigonal crystal structure with improved crystallinity.

Experimental Example 1

[0091] 2 g of the irreversible additive particles prepared in Comparative Examples 1 and 2 and Example 1 were each collected as samples, and subjected to XRD analysis. The results are shown in FIGS. 1 to 3.

[0092] XRD analysis was measured with a Bruker XRD D4 instrument, and experiment was performed from 10 degrees to 80 degrees in 0.02 steps using a Cu source target.

[0093] Referring to FIGS. 1 to 3, it can be seen that the irreversible additives having a different structure according to Comparative Examples 1 and 2 and Example 1 were formed.

[0094] Specifically, it can be seen that Comparative Example 1 is formed with an orthorhombic type crystal structure, and Example 1 is formed with a trigonal crystal structure.

Comparative Example 3 and Example 2

[0095] Using the irreversible additives prepared in Comparative Example 2 and Example 1, a cathode and a lithium secondary battery were manufactured by the following method.

[0096] Specifically, the irreversible additive prepared in Comparative Example 2 and Example 1, LiNi.sub.0.4Mn.sub.0.3Co.sub.0.3O.sub.2 as a cathode active material, a carbon black conductive material and a PVdF binder were mixed in a weight ratio of 4.6:87.9:3.5:4 in an N-methylpyrrolidone solvent to prepare a cathode slurry. The slurry was coated onto an aluminum current collector, and dried and rolled to prepare a cathode.

[0097] In addition, MCMB (mesocarbon microbead), which is an artificial graphite mixed with 10 wt. % of SiO as an anode active material, a carbon black conductive material and PVdF binder were mixed in a weight ratio of 90:5:5 in an N-methylpyrrolidone solvent to prepare a composition for forming an anode, which was coated onto a copper current collector to prepare an anode.

[0098] A porous polyethylene separator was interposed between the cathode and the anode prepared as described above to manufacture an electrode assembly. The electrode assembly was placed inside the case, and then an electrolyte was injected into a case to manufacture a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.15M lithium hexafluorophosphate (LiPF.sub.6) in an organic solvent consisting of ethylene carbonate/dimethyl carbonate/ethylmethyl carbonate (EC/DMC/EMC mixing volume ratio=3/4/3).

Experimental Example 2

[0099] 2 g of the irreversible additive particles prepared in Comparative Example 2 and Example 1 were each collected as samples, and their oxygen formation energies were measured. The results are shown in Table 1 below.

[0100] Specifically, the calculation of oxygen formation energy was performed based on the calculated value for DFT (density functional theory), PBE functional PAW_PBE pseudopotential, cut-off energy=520 eV, calculation model: supercell with Li.sub.48Ni.sub.24O.sub.48 atoms-doping/substituting one Ni with Mo (ratio-4.17 at %), oxygen vacancy (VO) production concentration=1/48 (˜2.1 at. %) O.sub.2 gas (O-rich environment).

TABLE-US-00001 TABLE 1 Oxygen (V.sub.0) formation energy (eV) Comparative Example 2 4.21 Example 1 4.54

[0101] Referring to Table 1, considering that the energy of the trigonal type irreversible additive of Example 1 is higher than that of the trigonal system of Comparative Example 2, it is presumed that the structure change in the intercalation of Li ions during charging and discharging is more robust than the trigonal system without doping or substitution. Therefore, it is expected that no side reactions will occur compared to the trigonal irreversible additives without doping and substitution.

Experimental Example 3

[0102] 2 g of the irreversible additive particles prepared in Comparative Example 2 and Example 1 were each collected as samples, and the average lithium de-intercalation voltage from P-3m1 to R-3m was measured, and the results are shown in Table 1 below.

[0103] Specifically, in the calculation of the average lithium de-intercalation voltage, the calculation model was prepared using DFT (density functional theory) calculation, PBE functional PAW_PBE pseudopotential, Hubbard U terms: Ni(6.20 eV)/Mo(4.38 ev), cut-off energy=520 eV, calculation model: 4×4×1 hexagonal supercell with Li.sub.96(Ni).sub.48O.sub.96 atoms—doping/substituting one Ni with Mo (ratio˜2.08 at %), and the lithium electrode as the counter electrode. While charging them, the average voltage when Li was de-intercalated from P-3m1 to R-3m in the irreversible additive was calculated.

TABLE-US-00002 TABLE 2 Average voltage (V vs. Li) Comparative Example 2 2.67 Example 1 2.54

[0104] Referring to Table 2, it can be seen that in the case of the trigonal irreversible additive of Example 1, lithium de-intercalation can be easily made at a lower voltage, as compared with the trigonal system of Comparative Example 2. From this, it can be seen that the irreversible additive according to the present disclosure is more useful for Li ion compensation.

INDUSTRIAL APPLICABILITY

[0105] As the irreversible additive according to the present disclosure has a trigonal crystal structure as the oxide represented by the chemical formula 1, impurities and gas generation problems associated with the de-intercalation of excess Li ions can be significantly reduced, and the structural stability can be further improved due to the doping of Mo. Therefore, a lithium secondary battery manufactured using a cathode material including the same can effectively compensate for irreversibility and exhibit more excellent electrochemical properties and lifespan characteristics.