JPH11176444A - Manufacture of lithium-chrome-manganese oxide, and lithium secondary battery utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having superior capacity and performance in high voltage area by subjecting the lithium oxide to heat treatment, the chrome oxide and the manganese oxide for a specified time in a specified temperature area, and thereafter, gradually cooling them so as to form a specified compound. SOLUTION: Heat treatment is conducted in a temperature area at 730-760 deg.C for 40-50 hours, and thereafter gradual cooling is performed to form a compound having a formula LiCrx Mn2-x O4 (0<x<=9) used for a positive electrode of a lithium secondary battery. As a lithium oxide, at least any one of LiOH, Li2 CO3 and LiNO3 is used, and as chrome oxide, Cr2 O3 is used, and as manganese oxide, MnO2 is preferably used. A lithium secondary battery is preferably formed by containing a positive electrode of LiCrx Mn2-x O4 (0<x<=0.5), a negative electrode formed of at least one from among lithium metal, a compound containing lithium and a carbon compound, and one of the liquid electrolyte and high molecular electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lithium-chromium-manganese oxide material for an anode and a 5V-class lithium secondary battery using the same, and more particularly to a conventional lithium secondary battery anode material, lithium. A method for producing a material for an anode which is structurally stable, has a small capacity reduction and is useful as a high voltage electrode material by replacing chromium with a manganese oxide, and a 5V class lithium secondary battery using the same. is there.

[0002]

2. Description of the Related Art In general, a lithium secondary battery includes an anode, an electrolyte, and a cathode. A lithium-manganese oxide used as an anode of a conventional lithium secondary battery has a spinel structure. That is, half of the octahedral locus and the tetrahedron (tetra
aedral) is a cubic close
The vacancies in the (se-packed) oxygen array allow other ions to occupy vacant octahedral or tetrahedral vacancies.

[0003] Such an octahedral vacant locus serves as a three-dimensional vacant tunnel in the spinel structure, and this structure is called a three-dimensional "1x1" tunnel structure. LiM
n ₂ O ₄ electron charge that the anode and will by the Li ions away from the LiMn ₂ 0 ₄ active material, extremely to change the lambda-MnO ₂ and structure becomes overcharged, which when the discharged again LiMn ₂ 0 ₄ return to the structure is made.

[0004] The theoretical capacity of theoretically LiMn ₂ 0 ₄ 14
8 mAh / g, which is lower than LiCoO ₂ or LiNiO ₂ , but lithium 2
Expectations as anode active materials for secondary batteries are high. Under Li / LiMn ₂ 0 ₄ batteries equilibrium conditions Li at about 4V during discharge is inserted into the spinel framework of _Mn 2 _{0 4} forms an isotropic structure of LiMn ₂ 0 _4.

[0005] appear smooth curve near 4V when viewed in the charge-discharge curve, on the surface of the case _Li x _Mn 2 _{0 4} electrodes L
i _{1 +} δ Mn ₂ 0 ₄ is formed, the oxidation number of the time average oxidation number of manganese average molecular formula of the internal although electrodes smaller than 3.5 becomes Li _1-δ Mn ₂ 0 ₄ Manganese Greater than 3.5. This results in a difference in Jahn-Taller effect between the surface and the interior of the electrode, which results in a fast discharge capacity decrease as the cycle is repeated.

[0006]

SUMMARY OF THE INVENTION The present invention uses lithium-chromium-manganese oxide as the anode to produce lithium 2
By configuring the secondary battery, 5V-class lithium 2 whose capacity and performance are improved in a high region unlike a conventional dry battery
The purpose is to provide a secondary battery.

[0007]

According to the present invention, there is provided a method for producing a lithium-chromium-manganese oxide for an anode, which utilizes the lithium-chromium-manganese oxide. after heat treatment during the 730 ° C. to 40 hours to 50 hours in a temperature range of _{760 ℃, LiCr x Mn 2-} x 0 4 which is used as an anode material for a rechargeable lithium battery and gradually cooled (0 <x ≦ 0. 9)
Is formed.

Further, a 5V class lithium secondary battery is LiCr.
an anode consisting of _{x Mn 2-x 0 4 (} 0 <x ≦ 0.5),
The present invention is characterized in that it is configured to include any one of lithium metal, a compound containing lithium and a carbon compound.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the attached drawings. FIG. 1 is a process diagram illustrating a process of manufacturing a lithium-chromium-manganese oxide according to the present invention.

Lithium-chromium-manganese oxide (Li)
_{Cr x Mn 2-x 0 4} , x = 0,1 / 8,2 / 8,3 /
The 8,4 / 8,5 / 8,6 / 8) spinel compound is a lithium oxide of any one of LiOH, Li ₂ CO ₃ and LiNO ₃ as starting materials, a chromium oxide of Cr ₂ O ₃ , a MnO ₃ It was prepared using _2-manganese oxide.

Stoichiometric compounds (stoichiome)
tric compound) to produce Cr _20
3 and MnO ₂ are weighed (1) at an exact mole ratio.
1) In the case of Li ₂ CO ₃ , since the atomic weight of Li was very small and the vapor pressure was high, they were mixed in excess of about 5%.

The above powder was mixed and pulverized in a solid state, and then pressure was applied to produce a test piece. The above specimen was calcined at 600 ° C. for about 5 hours.
On), this was finely pulverized at room temperature to produce a test piece (12). 700 ° C to 800
Sintering (sinter) in the temperature range of 20 to 60 hours.
ing) to form a lithium-chromium-manganese oxide (Li
CrxMn _{2-x 0 4)} were prepared (13, 14, 15).

The sintering temperature of 75 was determined by examining the physical properties of each specimen.
It was found that the optimum conditions were 0 ° C. and 48 hours, and that the best cooling rate after sintering to room temperature was 1 ° C./min.

FIG. 2 is an X-ray diffraction diagram of the lithium-chromium-manganese oxide according to the present invention, and it was confirmed that the manufactured sample was in a spinel shape having a space group Fd3m. Furthermore, as the amount of substituted chromium increases, the lattice constant (cell par) increases.
a), which means that the higher the amount of substituted chromium, the better the crystallinity. Table 1 below shows lattice constants depending on the amount of substituted chromium.

[0015]

[Table 1]

[0016] Lithium - Chromium - to constitute a half of a battery of _Li / LiCr order to examine the electrode characteristics of the manganese oxide _{x Mn 2-x 0 4.} The anode is Li / LiCr _x Mn
_{2-x 0 4 (wt.89%} ) acetylene black as a conductor (acetyleneblack; wt.10
%) And PTFE (poly-tetrar) as a binder.
afluoro-ethylene; wt. 1%), lithium metal as a cathode, and ethylene carbonate (ethylene carbonate) as an electrolyte.
e) and dimethyl carbonate (dimethyl c)
1M LiPF ₆ dissolved in a solvent obtained by mixing a mixture of arbonate at a volume ratio of 2: 1 was used.

In general, in Li _x Mn ₂ O ₄ (0 ≦ x ≦ 1), all of the Li in the structure comes out in the range of 3.5 V to 5 V, and about 70% or more of Li in 3.5 V to 4.3 V. Comes out.

The charge test of the produced battery is performed in order to more specifically examine the relationship between voltage and charge / discharge characteristics.
V-4.3 V) and low voltage (4.3 V-3.5 V) regions, each of which was measured and the relationship between the change in discharge capacity and voltage at the time of the first discharge of each sample in the high voltage and low voltage regions. And the amount of Li ⁺ ions inserted / extracted during charge / discharge. The measurement was carried out by repeatedly charging and discharging a half of the battery constituted by using a constant current method in which a constant current of C / 15 (〜265 μA) was applied.

FIG. 3 is a graph showing the charging / discharging characteristics of the lithium-chromium-manganese oxide according to the present invention in the high voltage region depending on the chromium substitution amount.
LiCr _x Mn _{2-x 0 4} of the 3V～5.2V)
As a result of measuring the charge / discharge characteristics with respect to (0 ≦ x ≦ 0.7), it is found that as the amount of chromium increases, the discharge capacity increases and the discharge voltage increases. Further, it is also found that the discharge capacity is saturated when the amount of chromium is 0.5 or more.

FIG. 4 is a graph showing the charging / discharging characteristics of the lithium-chromium-manganese oxide according to the present invention in the low voltage region due to the chromium substitution, in the low voltage region (3.5 V to 4.5 V). The above LiCr _x Mn
It can be seen that the charge-discharge characteristics for _{2-xO 4} (0 ≦ x ≦ 0.7) are different from the high voltage region, and the discharge capacity decreases as the amount of chromium increases.

However, when the amount of chromium is less than 0.25, reversibility of charging and discharging has been improved. An increase in the initial discharge capacity was observed for the sample in which chromium was replaced by about 0.12.

In the case of spinel manganese oxide, 3.5V-
Insertion in 4.3V region (intercalation)
The result of measuring the amount of Li
Are involved in the reaction. The reaction of Li ions is the same number of Mn ³⁺
With an oxidation / reduction reaction.

Therefore, if the amount of chromium is replaced by less than 0.2, this corresponds to the amount of manganese which does not directly participate in the reaction, and it is assumed that no reduction in the discharge capacity appears. However, when chromium of 0.2 or more is substituted, manganese directly involved in the reaction decreases, so that the discharge capacity decreases.

That is, as a result of observing the cycle characteristics of the lithium-chromium-manganese oxide in the high voltage region and the low voltage region, the initial discharge capacity increases but increases as the amount of chromium increases in the high voltage region. A decrease in the discharge capacity appeared, and in a low voltage region, the decrease in the discharge capacity generally became smaller as the amount of chromium increased. In particular, when the chromium content was 0.12, good cycle characteristics were observed in both the high voltage and low voltage regions.

[0025]

As described above, according to the present invention, unlike the conventional lithium secondary battery, when lithium-chromium-manganese oxide is used at the anode, the capacity decrease due to cycle repetition is small, and the capacity in the high voltage region is reduced. 5V because it is large
There is a remarkable effect that can be applied to class batteries.

[Brief description of the drawings]

FIG. 1 is a process diagram of a manufacturing process of a lithium-chromium-manganese oxide according to the present invention.

FIG. 2 is an X-ray diffraction diagram of a lithium-chromium-manganese oxide according to the present invention.

FIG. 3 is a graph illustrating charge / discharge characteristics of a lithium-chromium-manganese oxide according to the present invention in a high voltage region depending on the chromium substitution amount.

FIG. 4 is a graph illustrating charge / discharge characteristics of a lithium-chromium-manganese oxide according to the present invention measured in a low voltage region depending on the amount of chromium substitution.

Claims (3)

[Claims] 1. An anode for a rechargeable lithium battery using a lithium oxide, a chromium oxide, and a manganese oxide in a temperature range of 730 ° C. to 760 ° C. for 40 hours to 50 hours, and then gradually cooling. Li used as a substance
Cr _x Mn _{2 -x} O ₄ lithium, characterized in that to form a (0 <x ≦ 0.9) - chromium - method for producing manganese oxide. 2. The lithium oxide is LiOH, Li _2
2. The lithium according to claim 1, wherein at least one of CO ₃ and LiNO ₃ is used, the chromium oxide uses Cr ₂ O ₃ , and the manganese oxide uses MnO _2. -A method for producing chromium-manganese oxide. 3. LiCr _x Mn _2-x O ₄ (0 <x ≦
0.5), a lithium metal, a cathode comprising any one of a lithium-containing compound and a carbon compound, and a liquid electrolyte and a polymer electrolyte. Characteristic 5V class lithium secondary battery.