JPH0487268A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase the operating voltage of the discharging time to improve the charging-discharging characteristics with a large current flow by using a specific spinel structure or a spinel analogous structure manganese-iron-lithium composite oxide as a positive electrode active material. CONSTITUTION:The battery is constituted of a negative electrode can 1, a negative electrode current collector 2, a negative electrode 3, a separator 4, a positive electrode 5, a positive current collector 6, a positive electrode can 7 and a gasket 8. The negative electrode 3 uses lithium or a material which can occlude and discharge lithium as an active material, and the positive electrode 5 uses a spinel-structure or a spinel-analogous-structure manganese-iron- lithium composite oxide shown in Formula I as an active material, and nonaqueous electrolyte is lithium ion conductive. The range wherein Li ion can be reversibly doped and dedoped by thus using the spinel structure or the spinel analogous structure manganese-iron-lithium composite oxide as a positive electrode active material, that is, an effective charging-discharging capacity can be improved. It is thereby possible to prevent lowering of an operating voltage at the discharging time and improve the charging-discharging characteristic with a large current flow.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a well water electrolyte secondary battery using lithium or a substance capable of intercalating and deintercalating lithium as a negative electrode active material and a lithium ion conductive non-aqueous electrolyte. It is a thing,
In particular, it concerns the improvement of royal power.

[Conventional technology]

Nonaqueous electrolyte batteries that use lithium as the negative electrode active material are
Due to its advantages of high voltage, high energy density, low self-discharge, and excellent long-term reliability, secondary batteries are already widely used as power sources for memory backups, cameras, etc.

However, in recent years, with the remarkable development of portable electronic devices, communication devices, etc.62, a wide variety of devices have appeared that require large current output from batteries as power sources. There is a strong need for rechargeable, high energy density secondary batteries. For this reason, research and development is actively being carried out to develop the non-aqueous electrolyte battery with high energy density into a secondary battery, and some of it has been put into practical use, but there are still issues with energy density, charge/discharge cycle life, reliability, etc. Not enough.

Conventionally, TiS2 has been used as a positive electrode active material for this type of secondary battery.
．． Metal chalcogenides such as Mo5z, NbSe, etc., Mn0z, MoO3, V20SL i CaO2,
A wide variety of metal oxides such as L ix Mnz 04 have been proposed.

Generally, in batteries that use metallic lithium as the negative electrode active material, those that use metal chalcogenide as the positive electrode active material have an operating voltage of 3 V or less, and most of them
V or less. On the other hand, many of the cathode active materials that use metal oxides have high voltages of 3V or more and high energy densities. This is particularly advantageous for reducing the size and weight of equipment because it requires fewer units to be connected in series.

Among these positive electrode active materials, LiMn2004, which has a spinel-type structure or a spinel-like structure, has the following properties for lithium negative electrodes: (2) Lix Mnz Oa -z L +' -
ze=L! X-2~jnz O4 (2)
(However, the battery reacts as shown in O<X≦2.-X<2≦2-x), and its operating voltage is about 4V when 0<x-i-z<1 and about 3V when 1≦X+2<2. It has the advantage that it exhibits a similar high voltage, has relatively little deterioration due to charge/discharge cycles, and is an inexpensive material.

L I Mn20h with spinel structure! For example, as described in JP-A-55-100224, JP-A-58-220362 and JP-A-63-274059, manganese oxide (M n z O 3 , Mn 30
．． 2Mn0. etc.) and lithium salts (L12CO3, LiN
(O3, LiOH, etc.) in a molar ratio of Mn:Li=2:1, and is synthesized by baking at a temperature of 800 to 900°C.

Also, L +x Mnz Oa (0< x < 1)
is the above LiMn20. is obtained by immersing it in an acid such as hydrochloric acid or sulfuric acid to dissolve and remove Li;
The second compound can be obtained by reacting the above L IM n z Os with an n-butyl-lithium solution. The crystal structure of these Lj The structure is maintained and has a spinel-like structure.

Conventionally, when metallic lithium was used as the negative electrode active material in this type of battery, there was a problem that dendrites and passive compounds were formed on the negative electrode during charging and discharging, resulting in large deterioration due to charging and discharging and short cycle life. Ta. To solve this problem, it has been proposed to use an alloy of lithium and other metals, an intercalation compound or insertion compound containing Li ions in the crystal, a conductive polymer doped with Li ions, etc. as a negative electrode. However, in general, when a material other than metallic lithium that can intercalate and release L] ions is used as a negative electrode active material, the potential of one electrode of these materials is higher than the electrode potential of metallic lithium. However, there is a drawback that the operating voltage of the battery is considerably lower than when metallic lithium is used as the negative electrode active material and L. For example, Li and A1
．． When using alloys such as ZnPb and Sn, Q is 2 to 0.
8v, average about IV for carbon-lithium intercalation compounds, Mo
0.5 to 1 for Li ion insertion compounds such as O2 and WO2
, 5■ Operating voltage decreases.

Therefore, in order to obtain a secondary battery with excellent cycle characteristics, high voltage, and high energy density by using a material that can absorb and release Li ions as a negative electrode active material, Li
A positive electrode active material is required because the electrode potential is higher than that of the active material.

In this regard, LX Mn20a is a promising material as it has a high voltage of about 4 V at the head of O<X+2<1.

[Problems to be Solved by the Invention] The charging and discharging reaction of the positive electrode of a battery in which the conventional Li x Mnz CL as described above is used as a positive electrode active material and lithium or a substance capable of intercalating and releasing lithium is used as a negative electrode active material is as follows. (2) As shown in Figure 2, during discharge, Li ions generated from the negative electrode pass through the electrolyte and absorb the positive electrode active material 1-ixMl.
-1x crystal structure, and conversely, during charging, Li ions are removed from the crystal structure of the positive electrode active material 5 LiX, Z M n 20 m.

Ideally, the range in which Li ions can reversibly tope and detope during charging and discharging, that is, the charging and discharging capacity, is preferably as large as possible, and 0≦X-2≦2. In a battery using LixMnz ○, produced by the method described above, reversible S and Li
The range in which ions can be toped and detaped is approximately O55<x+z<1.7 at a practical current density, which poses the problem that the effective charge/discharge capacity is small and becomes smaller as the current increases. Especially in the high voltage region of X+2<1 (Li
There was a problem in that the effective charge/discharge capacity at an operating voltage of about 4 cm (with respect to the negative electrode) was extremely small, only about 35% of the theoretical capacity.

In addition, because the diffusion rate of Li ions in the Li x Mn204 crystal structure is slow, the internal resistance of batteries using this as a positive electrode active material increases, the operating voltage decreases greatly during discharging, and the charging current cannot be increased. There was a problem.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention uses a spinel-type structure or a manganese-iron-lithium composite with a spinel-type structure as a positive electrode active material for this type of battery. This proposal proposes the use of oxides.

The manganese iron lithium composite oxide used as the positive electrode active material of the battery of the present invention is produced as follows. That is,
Mn, Fe, and Li metals or their respective oxides, hydroxides, carbonates, nitrates, and other salts are mixed in a predetermined ratio and heated in air or in an oxygen-containing atmosphere at a temperature of 450°C or higher, preferably 600°C or higher. It is obtained by heating and firing at a temperature of 1000°C. The atmosphere for heating and firing depends on the Mn, Fe, and Li materials used and the firing temperature: it is possible to use an inert gas or a vacuum.

Karoha time is sufficient for 4 to 50 special hours per ffl,
At temperatures above 800° C., 12 hours or less is sufficient. In addition, as for the iron content, it is possible that O<y<2, but the effect is remarkable when o, l<y-=1, which is particularly preferable. When using a manganese iron lithium composite oxide with the structure, compared to using the conventional L j X M n z 04,
The range in which Li ions can be reversibly toped and detopped, that is, the effective charge and discharge capacity is significantly improved. In particular, x+
``The charge/discharge capacity in the high potential SJi region of z<l is significantly improved, and 60% or more of the theoretical capacity (0≦X+2≦1.0) becomes possible.

Furthermore, since the internal resistance of a battery using this is reduced, the drop in operating voltage during discharging is significantly improved, and charging with a larger current becomes possible.

The reason why the charge-discharge characteristics are improved in this way is not necessarily clear, but the M
When a part of n is replaced with Fe or when Fe is contained in the gaps in the crystal structure, Fe ions are present in the crystal structure, and this Fe ion causes a change in the internal state and a change in the surface area of the crystal grain. It is presumed that this is due to the diffusion of Li ions into the container.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

FIG. 1 is a sectional view of a coin-type battery showing an example of the present invention. In the figure, 1 is a negative electrode can that also serves as a negative electrode terminal, and is made by drawing a stainless steel plate with Ni plating on one outer side. A negative electrode current collector 2 is made of a stainless steel net and is spot welded to the negative electrode can 1. The negative electrode 3 is made of an aluminum plate with a predetermined thickness and a diameter of 15 m.
A lithium foil having a predetermined thickness was punched out to a diameter of 14 mm and then crimped onto the negative electrode current collector 2. 7 is a stainless steel positive electrode can with Ni plating on one outer side, which also serves as a positive electrode terminal. Reference numeral 5 denotes a positive electrode according to the present invention, which will be described later, and is integrally press-molded with a positive electrode current collector 6 made of a stainless steel net. 4 is a sebaleta made of a porous film of polypropylene, and is impregnated with an electrolytic solution. 8 is a gasket mainly made of polypropylene, which is interposed between the negative electrode can 1 and the positive electrode can 7, and maintains electrical insulation between the positive electrode and the negative electrode, and at the same time, the opening edge of the positive electrode can is bent inward and caulked. The contents of the battery are sealed and sealed by being sealed. The electrolyte is a mixed solvent of propylene carbonate, ethylene carbonate, and tetrahydrofuran in a volume ratio of 1:1:2 and 1 mole of lithium hexafluorophosphate LiPFa/
A dissolved solution was used. The size of the battery is 20m in outer diameter.
m, thickness l, and 6 mm.

The positive electrode 5 was produced as follows. Lithium hydroxide L10
H and electrolytic manganese dioxide MnOx and iron sesquioxide FeZ
O3 and Li:Mn:Fe=1:1゜6:0.4
The mixtures were thoroughly mixed in a mortar at a molar ratio of 1,000 to 1,000 ml, and then heated and calcined in the air at a temperature of 375 to 850° C. for 24 hours. After cooling, the mixtures were pulverized and sized to a particle size of 53 μm or less. Due to the difference in calcination temperature, the obtained product is
(375°C firing), K2 (480°C), K3
(600°C) and 4 (850°C).

For comparison, LiMntO4 having a spinel structure not containing Fe was fabricated in the following manner using a conventional method. That is, lithium hydroxide [, ioH and electrolytic manganese dioxide Mn
○2 was mixed at a molar ratio of Li:Mn=1:2, this mixture was calcined in the air at a temperature of 850°C for 24 hours, and after cooling, it was pulverized and sized to a particle size of 53 μm or less. This product is
Hereinafter, it will be abbreviated as K5.

These products were used as the positive electrode active material, graphite was added as the conductive material, and fluororesin was added as the binder at a weight ratio of 60.
:35:5 to form a positive electrode mixture, and then this positive electrode mixture was passed through a positive electrode current collector pair 6 made of a stainless steel net.
2ton/cm2, diameter 15mm, thickness 0.5mm
The positive electrode was formed by pressure molding into pellets and then drying under reduced pressure at 100''C for 10 hours.

The battery thus produced was left to age for one week at room temperature, and then subjected to a charge/discharge test as described below. Through this aging, the negative electrode lithium-aluminum laminated electrode is sufficiently alloyed by contact with the non-aqueous electrolyte in the battery, and the lithium foil is substantially entirely made of Li-A.
1 alloy, the battery voltage was stabilized at a value that was about 0.4 V lower than when metallic lithium was used alone as the negative electrode.

The batteries produced in this way are hereinafter abbreviated as batteries B1 to B5, with numbers 1 to 5 corresponding to the respective positive electrode active materials used.

Figure 2 shows that the positive electrode active material prepared as described above has 1 to
shows the X-ray diffraction diagram of 5 using FeKα rays. As is clear from the figure, the diffraction patterns of Ni 4 and Ni 5 at a firing temperature of 850°C almost match the data of the spinel structure LiM n204 of ASTM Cad No. 18-736, indicating that the spinel structure is It can be seen that it has. That is, K4 is Li Mn+, a F eo, a Oa ,
K5 has a spinel structure of L r M n z Oa. On the other hand, when the firing temperature is 375-600℃,
In 3, along with the peak from the spibble crystal, FezO,
peak estimated from (e.g. 2θ#42.45,2
．． 69°7″) and other substances also appeared, and LiXM with spinel type or spinel R4Q structure
It is considered that nty Fe y Os, FezO, and other Li, Mn, Fe oxides, etc. coexist. Furthermore, as the firing temperature increases, the diffraction peaks from other coexisting substances become smaller relative to the diffraction peaks from the spinel structure, and as the crystallization of the spinel structure progresses, L ig Mnz-y Fe,0 ．． middle F
It is considered that the amount y of e is increasing.

These batteries B1 to B5 are operated with a constant current of 1 mA, with a charging end voltage of 4.0 V and a discharging end voltage of 2.0 V. FIG. 3 shows the discharge characteristics of the second cycle when charging and discharging cycles were performed under OV conditions, and FIG. 4 shows the charging characteristics. Note that the charge/discharge cycle started from charging. As is clear from FIG. 3, the battery 82B3.84 of the present invention has a larger discharge capacity than the conventional battery B5. In particular, it can be seen that the discharge capacity is large in the high voltage region of the operating voltage of 3 V or more, and the reversible head loading of charging and discharging is significantly improved. Furthermore, the operating voltage for discharging is significantly higher over the entire twi range, indicating that the internal resistance of the battery is significantly improved and large current discharge is facilitated. Further, it can be seen that this effect is greater as the firing temperature is higher and more Fe is included in the spinel structure, and the effect is particularly remarkable at firing temperatures of 600° C. or higher.

On the other hand, battery B1 using an active material fired at 375°C is
This is presumed to be because the transition to the spinel structure is insufficient and the amount of solid solution y of Fe is small, but the discharge capacity in the high voltage region of the operating voltage of 3 V or more is conversely small.

Furthermore, from FIG. 4, it can be seen that the batteries 82 to B4 of the present invention are the conventional battery B5.
It can be seen that the overvoltage during charging and therefore the internal resistance are small and the charging capacity is significantly large compared to the above.

In this example, only the case where a lithium aluminum alloy is used as the negative electrode is shown, but the present invention is not limited to the example, and metallic lithium, lithium and Zn, Sn, Pb,
Alloys with other metals such as Bi, carbon, M 001, W
It goes without saying that the present invention can be similarly applied to substances capable of intercalating and deintercalating lithium, such as lithium insertion compounds such as O.

Further, the electrolyte is not limited to the examples, and a supporting electrolyte may be a Chinese or mixed solvent such as T-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane, dimethylformamide, etc. as Li Cl 04LiPFi , LiBFa , Li
An organic electrolyte in which a Li ion dissociable salt such as CF35O* is dissolved, a polymer solid electrolyte in which the Li salt is dissolved in a polymer such as polyethylene oxide or cross-linked polyphosphazene, or an inorganic solid electrolyte such as LizN or Li+. Any non-aqueous electrolyte having Li ion conductivity such as the like may be used.

〔Effect of the invention〕

As described in detail above, the present invention uses Li as a positive electrode active material.
By using a manganese iron lithium composite oxide with a spinel type or spinel-like structure represented by It significantly increases the chargeable and dischargeable capacity in the potential region, and significantly reduces the internal resistance (inside the battery) caused by the rate of doping and dedoping of Li ions into the positive electrode active material, thereby increasing the operating voltage during discharging. It has excellent effects such as significantly improving charge/discharge characteristics at large currents.

5...Positive electrode 6... Positive electrode current collector 7...Positive electrode can 8・・・ gasket 2. Applicant: Seiko Electronic Components Co., Ltd. Agent: Patent Attorney Takayoshi Hayashi

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing an example of a battery implemented in the present invention, Figure 2 is an X-ray diffraction diagram of various positive electrode active materials, and Figures 3 and 4 are discharge diagrams of a battery of the present invention and a conventional battery, respectively. They are a comparison diagram of characteristics and a comparison diagram of charging characteristics. 1... Negative electrode can 2... Negative electrode current collector 3...
Negative electrode 4. Sebalator figure 5゜Toto head 2゜Kato master

Claims (2)

[Claims] (1) A negative electrode whose active material is lithium or a substance capable of intercalating and deintercalating lithium, and a spinel structure represented by the formula (1) Li_xMn_2_−_yFe_yO_4 (1) (where 0<x, 0<y<2) or A non-aqueous electrolyte secondary battery comprising at least a positive electrode using a manganese-iron-lithium composite oxide having a spinel-like structure as an active material, and a lithium ion conductive non-aqueous electrolyte. (2) Manganese dioxide, iron oxide or salt, and lithium salt are mixed and heat-treated at a temperature of 450°C or higher in an oxygen-containing atmosphere to form a spinel-type or spinel-like structure represented by formula (1). A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, characterized by obtaining a manganese iron lithium composite oxide.