JPH1125983A - Active materials for lithium batteries - Google Patents

Abstract

(57) [Problem] To provide a positive electrode active material that enables a high-voltage lithium battery with a high energy density. Kind Code: A1 LiM _1-X Me _X PO having an olivine structure which can be used as a positive electrode active material in a lithium ion battery system.
₄ (M: Co, Ni, Mn, Me: Mg, Fe, Ni, Co, Mn, Zn, Ge,
An active material represented by Cu, Cr) (0 ≦ x ≦ 0.5).

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a lithium battery.

2. Description of the Related Art With the rapid progress and miniaturization of electronics, there is a need for batteries that are reliable, lightweight and have a high energy density. In this regard, lithium batteries are promising. Because lithium batteries are
It has a high voltage and energy density, and has a long service life. However, the chemical reactivity of most metallic lithium anodes with non-aqueous electrolytes, as well as the safety issues associated with metallic Li, have hindered the development of rechargeable lithium batteries for several years. Recently, there has been renewed interest in secondary lithium batteries. this is,
Related to making "lithium-ion" batteries by utilizing a Li insertion compound as the anode instead of metallic Li. However, in this system, attention must be paid to the choice of cathode and anode hosts. Layered LiMO ₂ (M: Co, Ni) [Mat. Res.
Bull. 15 (1980) 783, J. Appl. Phys. 19 (1980) 30
5] and three-dimensional spinel oxide LiMn ₂ O ₄ [Mat. Res. Bu
ll. 18 (1983) 461, Mat. Res. Bull. 19 (1984) 179]
Has a discharge intermediate voltage of about 4V with respect to lithium,
It has become an attractive cathode for lithium-ion batteries. More recently, studies have been conducted to determine whether other types of cathode materials can be used in lithium ion systems. These compounds include Li _X M ₂ (PO ₄ ) ₃ (M: Ti, V, Fe) and M ₂ (SO ₄ ) ₃
(M: Ti, Fe) [Solid State Ionic 92 (1996) 1].

SUMMARY OF THE INVENTION An object of the present invention is to provide an active material for a lithium battery, which has not been achieved by the conventional positive electrode active material and which can obtain a high voltage with a high energy density.

SUMMARY OF THE INVENTION The gist of the present invention is to provide a LiM _1-X M which can be used as a positive electrode active material for a lithium secondary battery.
e _X PO ₄ (M: Co, Ni, Mn), (Me: Mg, Fe, Ni, Co, Mn, Z
n, Ge, Cu, Cr) (0 ≦ x ≦ 0.5), which are characterized by exhibiting an olivine structure having orthorhombic symmetry and a space group Pmnb.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described by way of examples with reference to experiments performed by the present inventors and with reference to the accompanying drawings, but is not limited thereto. Example 1 LiMnPO ₄ of the present invention was prepared by a one-step reaction using a stoichiometric mixture of Li ₂ CO ₃ , MnCO ₃ , and (NH ₄ ) ₂ HPO ₄ . The mixture is first ground in an agate mortar, pressed at 400 kgf / cm ² into pellets, and then calcined at 450 ° C. in air for 4 hours, then 800 ° C.
For 24 hours. Example 2 Li ₂ CO ₃ , MnCO ₃ , (NH ₄ ) ₂ HPO ₄ , and one of the following: FeC ₂ O ₄ , 2H ₂ as an iron source
O, MgO, by one step reaction using a mixture of Co ₃ O _4, or nickel source consisting NiO as the stoichiometric ratio as cobalt source as the magnesium source, LiMn of the present invention
_1-X Me _X PO ₄ (Me: Mg, Ni, Co, Fe) was prepared. The mixture was first ground in an agate mortar and pressed at 400 kgf / cm ² into pellets, then calcined at 450 ° C. in air for 4 hours and then heated at 800 ° C. for 24 hours. When doping with iron, calcination was performed under a nitrogen flow. Example 3 The present invention was prepared by a one-step reaction using a stoichiometric mixture of Li ₂ CO ₃ , NiO, and (NH ₄ ) ₂ HPO ₄ .
LiNiPO ₄ was prepared. First ground in an agate mortar and the mixture pressurized and pelleted at 400 kgf / cm ^2, then
Calcination at 350 ° C under nitrogen flow for 8 hours, then 750
Heated at ° C. for 15 hours. Example 4 Li ₂ CO ₃ , MnCO ₃ , (NH ₄ ) ₂ HPO ₄ , and one of the following: FeC ₂ O ₄ , 2H ₂ as an iron source
O, MgO as a source of magnesium, Co ₃ O ₄ as a source of cobalt, or a stoichiometric mixture of MnCO ₃ as a source of manganese, a single-step reaction using
Ni _1-X Me _X PO ₄ (0 ≦ x ≦ 0.5) (Me: Mg, Mn, Co, Fe) was prepared. This mixture is first ground in an agate mortar,
Pressed at 400 kgf / cm ² into pellets, then calcined at 350 ° C. in air for 8 hours, then heated at 750 ° C. for 24 hours. When doping with iron, calcination was performed under a nitrogen flow. Example 5 LiCoPO ₄ of the present invention was prepared by a two-step reaction using a stoichiometric mixture of Li ₂ CO ₃ , Co ₃ O ₄ , and (NH ₄ ) ₂ HPO ₄ . This mixture was first ground in an agate mortar, pressed at 400 kgf / cm ² into pellets, and then calcined at 350 ° C. in air for 9 hours. The material was cooled, ground and pressed again at 400 kgf / cm ² into pellets, then heated at 750 ° C. for 30 hours. Example 6 Li ₂ CO ₃ , Co ₃ O ₄ , (NH ₄ ) ₂ HPO ₄ , and one of the following, ie, FeC ₂ O ₄ , 2H ₂ as an iron source
O, MgO as a magnesium source, NiO as a nickel source, or a stoichiometric mixture consisting of MnCO ₃ as a manganese source to provide the LiCo of the present invention.
_1-X Me _X PO ₄ (0 ≦ x ≦ 0.5) (Me: Mg, Mn, Ni, Fe) was prepared. This mixture is first ground in an agate mortar, 40
Pressed at 0 kgf / cm ² into pellets, then calcined in air at 350 ° C. for 8 hours, then heated at 750 ° C. for 24 hours. When doping with iron, calcination was performed under a nitrogen flow. 1A, 1B and 1C show the X-ray diffraction patterns of pure LiMnPO ₄ , LiNiPO ₄ and LiCoPO ₄ respectively obtained according to the present invention. All three X-ray diffraction patterns can be assigned to orthorhombic symmetry and space group Pmnb. LiMnPO ₄ X
The unit cell parameters of LiMnPO ₄ derived after the assignment of the line diffraction pattern are: a = 6.11 ± 0.5 °, b = 10.46 ± 0.5 °, c
= 4.73 ± 0.5 °; unit cell parameters for LiNiPO ₄ are a = 5.86 ± 0.5 °, b = 10.07 ± 0.2 °, c = 4.68 ± 0.5
Å; the unit cell parameter for LiCoPO ₄ is a = 5.92 ±
0.5 °, b = 10.21 ± 0.5 °, c = 4.70 ± 0.5 °. Figure 2
Represents an example of the cyclic voltammetry of LiCoPO _4. This material has one oxidation peak at 5.1V and one reduction peak at 4.7V. Further, another strong reduction peak was observed around 0.7 V, but no corresponding oxidation peak was observed. In this case, LiPF ₆ dissolved in sulfolane, which is known to withstand up to 6 V, was used as the electrolyte. FIG. 3 shows the charge and discharge of the substance LiCoPO ₄ of the present invention in the first cycle. The test was performed at a current density of 0.1 mA / cm ² in a Teflon container using LiPF ₆ + sulfolane as an electrolyte. The battery includes a negative electrode (87% active material of the present invention, 5% carbon black, 8% PVDF composition), a lithium counter electrode, and a lithium reference electrode. First, the battery is charged to extract lithium from the material of the present invention, and then discharged back to the point where lithium ions are inserted. During discharge, the battery exhibited a flat portion at 4.7 V and a capacity of 80 mAh /
g. However, the charging capacity is slightly higher, about 1
It is 05 mAh / g. This value is still lower than the theoretical capacity of 167 mAh / g when one lithium is inserted and inserted, but shows that it can be improved by optimizing the preparation conditions. FIG. 4 shows the charge and discharge in the first cycle of the substance LiCoPO ₄ of the present invention. The test was conducted in a Teflon battery case using LiPF ₆ + sulfolane as the electrolyte.
The test was performed at a current density of 0.1 mA / cm ² . The charge / discharge potential range of this battery was 1 ≦ V ≦ 5.3. 4.7 V during discharging
In addition to the flat portion observed at the position, another flat portion was observed near 1V. The overall capacity is very high,
It is about 350 mAh / g.

According to the present invention, a formula having an olivine structure is provided.
LiM _1-X Me _X PO ₄ (M: Co, Ni, Mn, Me: Mg, Fe, Ni, Co,
The active material represented by Mn, Zn, Ge, Cu, Cr (0 ≦ x ≦ 0.5) can be used as a positive electrode active material in a lithium ion battery system, has a large capacity of 170 mAh / g, and has a potential of 5 V And high,
It has an excellent effect.

[Brief description of the drawings]

FIG. 1A shows the X-ray diffraction pattern of the substance LiMnPO _{4 according to} the invention.

FIG. 1B is a diagram showing an X-ray diffraction pattern of a substance LiNiPO ₄ of the present invention.

FIG. 1C shows the X-ray diffraction pattern of the substance LiCoPO _{4 according to} the invention.

FIG. 2 shows a cyclic voltammogram of the substance LiCoPO _{4 according to} the invention. (Scanning speed was 2mV / min)

FIG. 3 shows a first cycle charge / discharge curve of a battery including a lithium counter electrode, a lithium reference electrode, and an electrode made of the active material LiCoPO _{4 of the} present invention. In this case, the battery was charged to 5.3V and discharged to 1.5V.

FIG. 4 shows a first cycle charge / discharge curve of a battery comprising a lithium counter electrode, a lithium reference electrode, and an electrode made from the active material LiCoPO _{4 of the} present invention. In this case, the battery was charged to 5.3V and discharged to 1V.

Claims (6)

[Claims] 1. The method of claim 1, wherein the olivine structure is LiM _1-X Me _X PO
₄ (M: Co, Ni, Mn), (Me: Mg, Fe, Ni, Co, Mn, Zn, G
e, Cu, Cr) (0 ≦ x ≦ 0.5). An active material for a lithium battery. 2. The active material for a lithium battery according to claim 1, wherein the olivine structure has an orthorhombic symmetry. 3. The unit cell parameter of the orthorhombic phase is:
LiMnPO the case of ₄ a = 6.11 ± 0.50Å, b = 10.46 ± 0.50
Å, c = 4.73 ± 0.50Å, a = 5.86 ± 0.5 for LiNiPO ₄
0Å, b = 10.07 ± 0.20Å, c = 4.68 ± 0.50Å, in the case of LiCoPO ₄ a = 5.92 ± 0.50Å, b = 10.21 ± 0.50Å, c = 4.70
3. The active material for a lithium battery according to claim 2, wherein the angle is ± 0.50 °. 4. The active material for a lithium battery according to claim 2, wherein the orthorhombic symmetry has a space group Pmnb. 5. An electrode comprising the active material for a lithium battery according to claim 1 as a positive electrode active material for a lithium battery. 6. An electrode according to claim 5, wherein the electrode comprises an electrolyte, Li, Li-
A battery including an alloy, Li _X SnO ₂ , and a negative electrode active material that is a carbon material.