JP3082117B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using a lithium composite oxide as a positive electrode active material and a negative electrode using a carbon material.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices such as audio / video devices and personal computers have been rapidly advanced.
There is a high demand for a secondary battery that is lightweight and has a high energy density. From such a viewpoint, non-aqueous secondary batteries, particularly lithium secondary batteries, are expected to have high voltage and high energy density.

As a layered compound capable of intercalating and deintercalating lithium as a positive electrode active material satisfying the above demand, for example, Li
_1-x NiO ₂ (where 0 ≦ x <1, US Pat. No. 4,302,518)
Specification), Li _y Ni _2-y O ₂ (JP-A-2-40861)
Publication) or Li _y Ni _x Co _1-x O ₂ (where 0 <x ≦
0.75, y ≦ 1, JP-A-63-299056)
And lithium-transition metal-based composite oxides (hereinafter referred to as lithium composite oxides) have been proposed, and a battery system using a carbon material for the negative electrode has attracted attention as a lithium secondary battery with a high energy density Are gathering. The feature of this battery system is that the battery voltage is high (for example, Li _1-x NiO ₂
i) because it has a high voltage of 4V with respect to i)
The negative electrode utilizes active material intercalation and deintercalation. In particular, since metal Li is not used for the negative electrode, dendritic Li
The safety is improved without causing a short circuit or the like due to the precipitation of, and rapid charging can be expected.

[0004]

Generally, a secondary battery of this type is basically required to have a high output, a high capacity and a long life. With the recent advancement of electronic devices,
Even when the equipment is not used, the power consumption by memory backup and control of other control circuits has increased. That is, if the battery is left attached to the device, the battery continues to be discharged, the capacity runs out, and the battery voltage finally reaches 0V. Therefore, a battery is poor in practicality unless it can be recovered by recharging even after experiencing such discharge (hereinafter, referred to as overdischarge).

However, a positive electrode made of Li _1-x NiO ₂ ,
After charging and discharging a negative electrode made of a carbon material and a Li secondary battery made of an organic electrolyte, and connecting a resistor to overdischarge, L
The unipolar potential behavior of each of the positive and negative electrodes based on the i reference electrode is as shown in FIG. When the positive and negative electrodes become equipotential (battery voltage is 0 V), both the positive and negative electrodes become 3.
It can be seen that the potential has reached near 2V. The positive electrode is usually used in this potential region, and it is considered that there is no problem. However, since the negative electrode is usually used at a potential of 1 V or less with respect to Li, the negative electrode is extremely noble due to overdischarge. When the potential is maintained, the crystal phase of the carbon material is destroyed by the oxidation reaction, and the battery capacity is reduced without being restored to the original capacity even when charged again.

The relationship between the potential of the negative electrode and the deterioration of the battery performance was examined by a constant potential step method. As a result, it was found that when the voltage exceeded 3 V with respect to Li, the capacity characteristics of the negative electrode were significantly deteriorated.

[0007] Therefore, if the potential can be maintained at a lower level (3 V or less) when the positive and negative electrodes become equipotential, it is considered that overdischarge deterioration due to the oxidation reaction of the negative electrode can be suppressed.

For this purpose, a positive electrode material which has a stable region even when the open circuit potential is 3 V or less and is rich in electrochemical reversibility corresponding to a charge / discharge reaction is desired.

Therefore, as means for suppressing the potential of the negative electrode to a lower potential level, Japanese Patent Laid-Open Publication No.
includes already Li such i _x MoO _3, and Li _1-x NiO ₂
A method is disclosed in which an oxide having a lower discharge potential is added to a positive electrode.

According to this method, an increase in the number of Li sources contained in the positive electrode provided some effect in suppressing deterioration due to overdischarge. However, this is largely due to the fact that the equilibrium potential of the positive electrode slightly decreased due to the mixed potential with the added low-potential additive, and the effect was not sufficient. It is almost the same as the added one.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery that sufficiently suppresses long-term over-discharge deterioration and has good charge recovery properties. Is what you do.

[0012]

In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention has a chemical formula of Li _y Ni _1-x M
_{n x O 2 (0.01 ≦ x} ≦ 0.4,0.4 ≦ y <1.6)
A positive electrode made of a material represented by
Carbon material that can be intercalated and deintercalated
A negative electrode comprising: a non-aqueous electrolyte;
Material expressed by the chemical formula _{Li y Ni 1-x Mn x} O 2 charging and discharging of the
Is the space group P

[0013]

[Outside 3]

Ml and space group R

[0015]

[Outside 4]

M is performed in an area having two types of m , and overdischarge is performed.
Even if the positive and negative electrodes become equipotential, the negative electrode potential is changed to lithium metal.
Is maintained at 3 V or less.

[0017]

According to this structure, when a battery in a discharged state is used as a positive electrode active material, a large amount of Li is held in advance.
The use of _{i y Ni 1-x Mn x} O 2 (1.0 <y <1.6), the positive electrode active material has the following low potential region 3V,
In the charged state (0.4 <y <1.0) in which Li is deintercalated from the positive electrode active material, by having a high potential region of 3 V or more, electrochemical reversibility is obtained even in a normal charge / discharge reaction. And the negative electrode potential can be maintained at a lower potential of 3 V or less where overdischarge deterioration due to the oxidation reaction of the negative electrode does not occur even if the positive electrode and the negative electrode become equipotential by overdischarge.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to one embodiment of the present invention will be described below with reference to the drawings.

A potential determinant was found from a positive electrode material which had a stable region even at an open circuit potential of 3 V or less and was rich in electrochemical reversibility corresponding to a charge / discharge reaction and caused by the amount of Li in the active material. formula _{Li y Ni 1-x Mn x} O 2 system the results of open-circuit potential with respect to the y value of the compounds in FIG. 2, also propylene carbonate and lithium perchlorate 1 mole equal volume mixed solvent of ethylene carbonate as an electrolyte FIG. 3 shows the charge / discharge behavior (current density: 1 mA / g, positive electrode active material) in a solution dissolved at a rate of 1 / liter.

This substance has a potential given by the y value in the formula, has electrochemical reversibility in the range of 0.4 ≦ y <1.6, and has a y value (open circuit potential of 3 V or less). y> 1). In other words, more Li
Is maintained (1.0 <y <1.6) and a low potential region of 3 V or less is provided, and Li is deintercalated by charge reaction (0.4 ≦ y ≦ 1.0) to obtain a normal voltage. Even when used in charge and discharge, electrochemical reversibility can be maintained.

In the crystal structure having two potential regions divided near 3 V, the high potential region corresponds to the space group R.

[0022]

[Outside 5]

In m, the low-potential region mainly includes the space group P

[0024]

[Outside 6]

Ml and some space groups R

[0026]

[Outside 7]

It is known from the X-ray diffraction diagram shown in FIG. 4 that it belongs to the mixed crystal of m, and it is considered that there is reversibility between these two crystal phases having a layered structure.

As a result, the negative electrode potential can be maintained at a low potential (3 V or less) even if the positive and negative electrodes become equal in potential due to overdischarge.
The problem of deterioration of the negative electrode can be solved.

[0029] _{Li y Ni 1-x Mn x} O 2 (0.01 ≦ x ≦
In the synthesis of 0.4, 0.4 ≦ y ≦ 1.0), for example, Li ₂ O, LiNO ₃ , LiOH, L
at least one lithium compound selected from the group of i ₂ CO ₃ and at least one nickel compound selected from the group of Ni (OH) ₂ , NiO, NiCO ₃ and MnO
₂ , x value is stoichiometric, and y value is 1.1 to 1.
The amount of Li added was equivalent to three times the number of moles of Li atoms, and synthesis was performed at a firing temperature of 700 to 900 ° C. in an oxidizing atmosphere such as air or oxygen.

[0030] Thus obtained positive electrode active material, the lattice constant in the crystal structure of the layered is a ₀ 2.83~2.88Å, also c ₀ is 14.15~14.31Å, and the space group R

[0031]

[Outside 8]

It can be seen that it belongs to m.

Further, as _{Li y Ni 1-x Mn x} O 2 (0.
The synthesis of 01 ≦ x ≦ 0.4, 1.0 <y <1.6) is the same as the above method, but the y value is equivalent to 1.3 times the number of moles of Li atoms indicated by y. Or an active material having a y value of 0.4 ≦ y ≦ 1.0 can be obtained by inserting Li by an electrochemical reduction treatment.

The positive electrode active material thus obtained has a layered crystal structure, mainly having a lattice constant, and a ₀ of 3.09 to 3.0.
11}, space group P in which c ₀ is 5.07 to 5.11

[0035]

[Outside 9]

Attributed to ml and partly a ₀ is 2.8
3 to 2.88 ° and the space group R whose c ₀ is 14.15 to 14.31 °

[0037]

[Outside 10]

It was found that the property belongs to m.
When x = 0.2, the lattice constants corresponding to various y values are shown in FIG.
Shown in From this figure, when y is 1.0, R

[0039]

[Outside 11]

Although the crystal structure assigned to m is maintained, the space group P

[0041]

[Outside 12]

Ml and space group R

[0043]

[Outside 13]

M has a mixed crystal form, and as y increases, the space group R

[0045]

[Outside 14]

It was found that the peak assigned to m decreased. That is, the space group R at the y value of 1.0

[0047]

[Outside 15]

From the m subject to the space group P

[0049]

[Outside 16]

It was found that the content changed to mainly ml.

In order to select the optimum composition value of the positive electrode active material,
The peak current value of the cathode response current was examined by scanning the potential of the sample electrode. The structure of the sample electrode is a positive electrode mixture in which a positive electrode active material, acetylene black and a fluororesin-based binder are mixed at a weight ratio of 7: 1.5: 1.5.
cm ² electrode, the counter electrode Li, the reference electrode is another Li,
The electrolyte was prepared by dissolving 1 mol of LiPF ₆ in 1 liter of a mixed solvent of ethylene carbonate and propylene carbonate at a ratio of 1: 1 and scanning at a scanning speed of 2 mV / s.
The test was performed in a range of 5V.

Let y be 0.2, 0.4, 1.0, 1.6,
FIG. 6 shows the peak current value of the cathode response current corresponding to each x value when 1.8 is set.

As can be seen from FIG. 6, Li _y Ni _1-x Mn
_When the x value of xO ₂ is 0.01 to 0.4, a good peak current value is obtained. Further, the y value is the best when it is 1, but the peak current value decreases when it is 0.2 and 1.8.
From these results, good characteristics can be obtained when x is in the range of 0.01 to 0.4 and y is in the range of 0.4 to 1.6.

Hereinafter, the evaluation using the battery will be described.

In FIG. 1, the positive electrode 1 was prepared by mixing a carbon powder, which is a conductive agent, as an active material with 5% by weight of the active material, and a polytetrafluoroethylene resin powder as an adhesive with 7% by weight with respect to the active material. This is press-formed on a titanium net 3 fixed to the inside of the positive electrode case 2 by spot welding. The negative electrode 4 is a mixture of a carbon material powder (here, pitch-based spheroidal graphite is used) and a polyacrylic acid-based resin powder serving as a binder mixed at 5% by weight with respect to the carbon material. It is press-formed on a stainless steel net 6 fixed inside by spot welding. Then, a polypropylene separator 7 is arranged between these positive and negative electrodes,
An appropriate amount of electrolyte 8 was injected, and the sealing plate 5 was sealed with the case 2 via a gasket 9 made of polypropylene to obtain a completed battery having a diameter of 20 mm and a height of 1.6 mm. In addition,
The electrolytic solution used was a solution in which 1 mol of lithium perchlorate was dissolved in 1 liter of an equal volume mixed solvent of propylene carbonate and ethylene carbonate.

This battery is in a discharged state immediately after trial production, and starts from charging. First, as the positive electrode active material of the battery of Comparative _{Example, Li y Ni 1-x Mn} x O 2 with 0.01 ≦ x ≦ 0.4,
A battery using 0.4 ≦ y ≦ 1.0 will be described. The curve shown by the broken line in FIG. 9 is the charge / discharge voltage characteristic at the 10th cycle when the constant current charge / discharge of 2 mA is performed with the charge end voltage set to 4.1 V and the discharge end voltage 3.0 V.

Next, the degree of deterioration of battery performance due to overdischarge of the battery of the comparative example was examined. Overdischarge is 10
After charge / discharge of a cycle is performed, the battery is taken out in a discharged state, discharged with a constant resistance load of 50Ω, and, after reaching 0 V, left for another 10 days with the resistance connected. As a result of experiencing this overdischarge at the 10th cycle and performing charge / discharge again, the charge / discharge voltage characteristic shows that the capacity is reduced by nearly 20% as shown by the solid line in FIG. Remained low. Therefore, it was found that the capacity characteristics of this battery were deteriorated by experiencing overdischarge.

Next, as the positive electrode active material of the battery of this embodiment, L
_{i y Ni 1-x Mn x} O 2 (0.01 ≦ x ≦ 0.4,1.0 <
A battery using y <1.6) will be described.

FIG. 7 shows the results of the charge / discharge voltage characteristics after overdischarge when y = 1.5. The broken line is the same as the broken line in FIG. The solid line is the space group P of this embodiment.

[0060]

[Outside 17]

6 is a charge / discharge voltage curve after overdischarge using a positive electrode active material having a ml structure. As can be seen from FIG.
The charge / discharge characteristics were improved even after experiencing overdischarge at the tenth cycle, and the capacity did not deteriorate even if the charge / discharge cycle was repeated. The cause of this result will be described with reference to FIG. As shown in FIG. 8, when observing the unipolar potential behavior of the positive and negative electrodes immediately before the battery reaches overdischarge, even when both the positive and negative electrodes reach the same potential, the potential is near 2.4 V with respect to Li. And reaches an equilibrium in a potential region of 3 V or less.

This is because a larger amount of Li
Can accumulate and have an open circuit potential of 3 V or less in potential.

[0063]

[Outside 18]

This is due to the use of the positive electrode active material having a ml structure, which prevents deterioration of the carbon material of the negative electrode due to an oxidation reaction even if the potentials of the positive and negative electrodes reach the same potential due to overdischarge. .

[0065]

As is clear from the above description, according to the nonaqueous electrolyte secondary battery of the present invention, even if the battery mounted on the device is overdischarged, the performance is improved by recharging. Since it recovers, it is possible to provide a non-aqueous electrolyte secondary battery which is extremely advantageous in practice and has a high capacity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention.

[2] the positive electrode active material _{Li y Ni 1-x Mn x} O 2 (0.0
Graph showing the open circuit potential on the basis of Li when 1 ≦ x ≦ 0.4)

[3] the positive electrode active material _{Li y Ni 1-x Mn x} O 2 (0.0
A graph showing the charge / discharge behavior on the Li basis (1 ≦ x ≦ 0.4)

[4] the positive electrode active material _{Li y Ni 1-x Mn x} O 2 (0.0
X-ray diffraction diagram of 1 ≦ x ≦ 0.4, y = 0.4, 1.6)

[5] the positive electrode active material _{Li y Ni 1-x Mn x} O 2 (x =
Graph showing lattice constant of 0.2)

[6] the positive electrode active material _{Li y Ni 1-x Mn x} O 2 (y =
Graph showing cathode peak current values of 0.2, 0.4, 1.0, 1.6, 1.8)

FIG. 7 is a graph showing the same charge / discharge voltage characteristics.

FIG. 8 is a graph showing the potential behavior of the positive and negative electrodes during overdischarge.

FIG. 9 is a graph showing charge / discharge voltage characteristics of a battery of a comparative example.

FIG. 10 is a graph showing the potential behavior of the conventional battery when the positive and negative electrodes are overdischarged.

[Explanation of symbols]

 1 positive electrode 4 negative electrode 7 separator

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuhiro Okamura 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-141954 (JP, A) (58) Survey Fields (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/36-4/62

Claims (1)

(57) [Claims] 1. A chemical formula _{Li y Ni 1-x Mn x} O 2 (0.01 ≦
x ≦ 0.4, 0.4 ≦ y <1.6)
Comprising a positive electrode, a negative electrode consisting of intercalating and de-intercalation carbon material capable of lithium, a nonaqueous electrolyte secondary battery comprising a nonaqueous electrolytic solution, the chemical formula Li a charge and discharge of the battery represented by _{y Ni 1-x Mn x O} 2
The material to be used is in a region in which two types of space group P [1] ml and space group R [2] m are taken.
The negative electrode potential is kept at 3 V with respect to lithium metal even if
A non-aqueous electrolyte secondary battery characterized in that it can be maintained as follows.