KR101345232B1 - 5v spinel type lithium composite oxide, manufacturing method thereof, and lithium rechargeable battery including the same - Google Patents

Abstract

The present invention relates to a lithium composite oxide having a 5V class spinel structure having improved high temperature storage characteristics and lifespan characteristics, a method of manufacturing the same, and a lithium secondary battery including the same.
Lithium composite oxide of 5V class spinel structure according to the present invention is doped metal to prevent the elution of manganese has excellent structural stability and improved high temperature storage characteristics and life characteristics, the lithium secondary battery comprising the electrochemical characteristics at high temperature And life characteristics are excellent.

Description

Lithium composite oxide of 5V class spinel structure with improved high temperature storage characteristics and lifespan, manufacturing method thereof, and lithium secondary battery comprising the same

The present invention relates to a lithium composite oxide having a 5V class spinel structure having improved high temperature storage characteristics and lifespan characteristics, a method of manufacturing the same, and a lithium secondary battery including the same.

Recently, as interest in environmental problems grows, researches on electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted.

Research using lithium secondary batteries as a power source for electric vehicles and hybrid electric vehicles has been actively conducted, and some of them have been commercialized and used. Among the cathode active materials of a lithium secondary battery used as a power source for such an electric vehicle, manganese-based materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize, have a relatively low manufacturing cost, and have low environmental pollution. . Among them, LiMn ₂ O ₄ has emerged as the cathode active material having the highest applicability to electric vehicles due to the stability of a battery system.

In the structure of LiMn ₂ O ₄ , Li ions are located in tetrahedral (8a), Mn ions (Mn ^{3 +} / Mn ^{4 +} ) are octahedral (16d), and O ^{2 -} ions are octahedral (16c) Located. These ions form a cubic closed-packing array. The tetrahedral site of 8a shares a face with the octahedral site of 16c, which has a vacancy around it, forming a three-dimensional channel, providing a passage for Li ⁺ ions to move easily.

Spinel LiMn ₂ O ₄ electrochemically intercalation / deintercalation of lithium occurs at 4V when the amount of Li is 0 ≦ x ≦ 1 and 3V when 1 ≦ x ≦ 2. Intercalation / de-intercalation of lithium occurs at Looking at the structural change according to the amount of lithium, the composition of x≤1 shows a cubic spinel structure of the space group Fd3m, and in the composition of 1≤x≤2, the cubic symmetry changes to tetragonal (tetragonal). Evidence of this structural change can be seen through voltage plateaus in the charge and discharge curves of LiMn ₂ O ₄ .

However, LiMn ₂ O ₄ Compared to other active materials such as LiCoO ₂ and LiNiO ₂ , the discharge capacity is small, the discharge capacity decreases rapidly during high-rate charging and discharging, and battery life rapidly deteriorates due to elution of manganese during continuous charging and discharging at high temperatures. . In addition, LiMn ₂ O ₄ causes Jahn-Teller distortion when the average oxidation number of Mn falls below 3.5. As a result, phase shift is induced, which is considered to be a factor that degrades the electrode performance.

Therefore, there is a high need for a technology capable of solving high temperature characteristics of a cathode active material, particularly a lithium manganese oxide, in a lithium secondary battery.

An object of the present invention is to provide a lithium manganese oxide having excellent electrochemical and lifespan characteristics by improving the high temperature storage characteristics and lifespan characteristics to solve the problems of the prior art as described above.

The present invention is to solve the above problems Li _{1 + x} Ni _y Mn _{2- y- z} M _z O ₄ (0≤x≤0.1, 0≤y≤1.0, 0.001≤z≤0.1, M is V, Provided is a lithium composite oxide having a 5V spinel structure with improved high temperature storage characteristics and lifespan characteristics, which are represented by one or more of the group consisting of Ti, Cr, Co, Zr, V, Ni, Ga, and Gd).

In the lithium composite oxide of 5V class spinel structure according to the present invention, the oxidation number of Mn is +4.

In the lithium composite oxide of 5V class spinel structure according to the present invention, M is characterized in that V (vanadium).

The present invention also comprises the steps of preparing a mixture by uniformly mixing the lithium-containing compound, nickel-containing compound, manganese-containing compound and M-containing compound by the sol-gel method; Heat treating the mixture; It provides a method for producing a lithium composite oxide of 5V class spinel structure comprising a.

In the production method of a lithium complex oxide of 5V class spinel structure according to the present invention, the lithium compound is the group consisting of LiOH, LiOH and H ₂ O, LiCH ₃ COO, LiCHO _2, LiCHO ₂ and H ₂ O, and LiNO ₃ At least one selected from the group consisting of carbonates, nitrates, oxalates, sulfates, acetates, citrates, chlorides, and oxides of manganese, and the metal compound comprising metal M is selected from the group consisting of It is characterized in that at least one selected from the group consisting of carbonate, nitrate, oxalate, sulfate, acetate, citrate, chloride, oxide.

In the method for producing a lithium composite oxide of 5V class spinel structure according to the present invention, the heat treatment is characterized in that the heat treatment for 12 hours at 600 to 800 ℃.

The present invention also provides a lithium secondary battery comprising a lithium composite oxide having a 5V spinel structure with improved high temperature storage characteristics and lifespan characteristics according to the present invention.

The lithium secondary battery including the lithium composite oxide of the 5V class spinel structure according to the present invention is characterized in that the capacity change after 20 cycles at 50 ° C is within 20%.

The lithium composite oxide of 5V class spinel structure having improved high temperature storage characteristics and lifespan characteristics according to the present invention has excellent structural stability by preventing the doped metal from eluting manganese, and the lithium secondary battery including the same has high temperature storage characteristics at high temperatures. And the life characteristics are improved, and thus the electrochemical and life characteristics are excellent.

1 shows XRD patterns of positive electrode active materials of Examples and Comparative Examples.
2 and 3 show the results of evaluating the initial charge and discharge characteristics at room temperature and high temperature of the cell containing the positive electrode active material of Examples and Comparative Examples.
4 and 5 show the results of evaluating the life characteristics at room temperature and high temperature of the cell containing the positive electrode active material of Examples and Comparative Examples.
Figure 6 shows the results of measuring the impedance of the cell containing the positive electrode active material of Examples and Comparative Examples.

Hereinafter, the content of the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

< Example  1>

Lithium compounds Li (CH ₃ COO) · 2H ₂ O, nickel compounds Ni (CH ₃ COO) ₂ · 4H ₂ O, manganese compounds Mn (CH ₃ COO) ₂ · 4H ₂ O and adipic acid and dissimilar metals M as starting materials As a V (vanadium) -containing compound, vanadium pentoxide (V ₂ O ₅ ) powder having a purity of 99.6% or more was used, dissolved in distilled water, mixed, evaporated and dried at 80 ° C. for 10 hours at 450 ° C. in an air atmosphere box-type sintering furnace. After sintering, the material was resintered at 700 ° C. for 12 hours to synthesize an active material.

< Comparative Example >

Except that a different metal V (vanadium) containing compound was not added to thereby prepare a lithium composite oxide of 5V spinel structure represented by the same manner as in the above Example as _{LiMn 1 .5 Ni 0 .5 O 4} .

< Experimental Example > XRD  Characterization

XRD patterns of the Example and Comparative Example positive electrode active material prepared through the above process is shown in FIG.

As shown in FIG. 1, X-ray diffraction analysis showed no peaks related to any impurities, and it was found that they formed a well-developed spinel cubic structure of the Fd3m structure in which no impurities existed. It can be seen that the structural change of the positive electrode active material of the spinel structure did not occur by V (vanadium) doping.

<Fabrication of Test Cell>

Thus prepared positive electrode active material of Example 1 and Comparative Example, polyvinylidene fluoride (PVDF) as a binder, Super P (Super P) as a conductive material, the solvent (N-methylpyrroli in a weight ratio of 80: 10: 10 And the positive electrode active material composition slurry, and the slurry was cast in the form of a tape to prepare a plate.

A coin cell type half cell was produced using Li-foil as a counter electrode for this electrode plate and using a mixture of ethylene carbonate and dimethyl carbonate in a 1: 1 volume ratio and an electrolyte solution containing LiPF ₆ .

< Experimental Example > Initial Charging and discharging  Characterization

Initial charge and discharge characteristics of the prepared cells were evaluated. Charge and discharge experiments using electrochemical analyzer (Toscat 3000U, Japan, Toyo Co., Ltd.) in charge and discharge experiments at 3.0 ~ 5.0 V potential range and various current density conditions at room temperature (25 ℃) and high temperature (50 ℃) The changes are shown in FIGS. 2 and 3, respectively.

2 and 3, the lithium composite oxide of 5V class spinel structure according to the present invention are all 135 mAh / g or more compared to the spinel lithium composite oxide of the comparative example which is not doped with vanadium at room temperature (25 ℃) and high temperature (50 ℃) High discharge capacity.

2 and spinel lithium complex oxide according to the present invention, as shown in Figure 3 Mn ^{3 +} was an ion one additional flatness did not appear region due to, lithium composite oxide of 5V class spinel structure according to the invention therefrom is Ni ^You can see that it contains only ^{2 +} and Mn ^{4 +} .

< Experimental Example > Life Characterization

Evaluation of the life characteristics of the battery including the active material prepared in Examples and Comparative Examples was measured by changing the irreversible capacity of the normal temperature (25 ℃) and high temperature (50 ℃) cycle in the range of 3.5 to 5.0 V 5 shows the result.

As shown in Figures 4 and 5, the change in irreversible capacity at room temperature in the comparative example is 84.7%, compared to 90.0% in the case of the embodiment according to the present invention, and at high temperature from 3.5% of the comparative example to 83.1% It can be seen that the high temperature cycle life characteristics are excellent as there is almost no capacity decrease as the cycle increases overall. This result is because doped V (vanadium) prevents elution of manganese in the active material.

< Experimental Example > Impedance Measurement

In order to measure the polarization resistance of a battery including the active materials prepared in Examples and Comparative Examples, an impedance was measured by applying an AC signal having a different frequency at a high temperature of 50 ° C., and the results are shown in FIG. 6.

In FIG. 6, the resistance to the end of the semi-circle means the resistance at the interface between the surface of the active material and the electrolyte, and the slope of the line after the semi-circle is over means the conductivity in the solid state in the active material. As shown in FIG. 6, it can be seen that the resistance at the interface is somewhat increased in the embodiment doped with V (vanadium).

However, when the polarization resistance was measured again after 100 cycles, the resistance was significantly increased in the comparative example, but it was confirmed that the increase in the resistance was significantly reduced in the example.

Claims (8)

LiOH, LiOH and H ₂ O, LiCH ₃ COO, LiCHO _2, LiCHO ₂ and H ₂ O, and LiNO least one member from the group consisting of ₃ These lithium-containing compounds, nickel-containing compounds, manganese carbonate, nitrate, oxalate, sulfate Vanadium (V) carbonate, nitrate, oxalate, sulfate, acetate, citrate, chloride, vanadium selected from the group consisting of at least one manganese-containing compound selected from the group consisting of acetate, citrate, chloride, and oxide (V) uniformly mixing the containing compound by a sol-gel method to prepare a mixture; And
Heat treating the mixture at 600 to 800 ° C. for 12 hours; Prepared by the manufacturing method comprising a,
Li _{1 + x} Ni _y Mn _2-yz V _z O ₄ (0 ≦ _x ≦ 0.1, 0 ≦ _y ≦ 1.0, 0.001 ≦ _z ≦ 0.1),
The oxidation number of the Mn is +4 lithium composite oxide of 5V spinel structure with improved high temperature storage characteristics and life characteristics
delete delete delete delete delete A lithium secondary battery comprising the lithium composite oxide of claim 5V spinel structure.
8. The method of claim 7,
The lithium secondary battery comprising the lithium composite oxide of the 5V class spinel structure is a lithium secondary battery that the capacity change after 20 cycles at 50 ℃ within 20%.

Images