JPH06275273A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To suppress the decomposition of an electrolyte at the final stage of a discharge and provide an excellent cycle characteristic by adding an auxiliary agent capable of discharging in the low-potential region into a positive electrode active material. CONSTITUTION:An auxiliary agent having the discharge potential of 1.4-3.5V against lithium is added to a principal agent expressed by the composition formula LixMOy for the active material of a positive electrode 1 in a nonaqueous secondary battery having a negative electrode 2 made of a prescribed carbon material, where M is a transition metal mainly made of Co or Ni, 0<=x<=1.3, 1.8<=y<=2.2. The mixing ratio is set to the principal agent of 50-99mol% and the auxiliary agent of 50-1mol%. The positive electrode 1 and the negative electrode 2 are arranged face to face via a separator 3 impregnated with a nonaqueous electrolyte, and they are stored in a case to manufacture a battery BA1. When the auxiliary agent capable of discharging in the low-potential region at the final stage of a discharge against lithium is added to the positive electrode 1, the abrupt drop of the potential of the positive electrode 1 is prevented, the decomposition of the electrolyte is suppressed, and an excellent cycle characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly to improvement of a positive electrode active material for the purpose of improving cycle characteristics.

[0002]

2. Description of the Related Art In recent years,
Because non-aqueous secondary batteries such as lithium secondary batteries do not need to consider the decomposition voltage of water unlike aqueous secondary batteries such as nickel-cadmium secondary batteries, high voltage design is possible. It is in the spotlight.

Although various materials have been proposed as materials for the positive and negative electrodes of this type of battery, it is known by the present inventors that the non-aqueous secondary battery has a high energy density and a large discharge capacity. In order to obtain the above, as a negative electrode material, a carbon material capable of inserting and extracting lithium ions, particularly a lattice plane (0
A carbon material having a high graphitization degree of which the d value (d ₀₀₂ ) of the (02) plane is 3.35 to 3.37 and the crystallite size (Lc) in the c-axis direction is 200 Å or more, and the positive electrode material Is a composition formula Li _x MO _y (where M is Co and / or Ni) showing a high discharge potential of 3.5 to 4.0 V with respect to lithium.
Alternatively, a transition metal containing these as main components, 0 ≦ x ≦ 1.
3, 1.8 ≦ y ≦ 2.2. An oxide represented by the formula (1) is preferable.

However, in a non-aqueous secondary battery in which a carbon material having a high degree of graphitization is used as the negative electrode and the above Li _x MO _y is used as the positive electrode, the charge and discharge efficiencies of the positive and negative electrodes are approximately the same, and at the end of discharge, The electric potential changes rapidly at the same time.

FIG. 4 shows the time-dependent change in the potential of each of the positive and negative electrodes during discharge (discharge characteristics), with the positive electrode potential or the negative electrode potential (V
vs. Li ^/ Li ⁺ ) is a graph showing time (capacity) on the horizontal axis. As shown in the figure, at the end of discharge, the potential of the negative electrode (natural graphite) rises sharply and the positive electrode (L
The potential of iCoO ₂ or LiNiO ₂ ) drops sharply. Then, when the discharge potential of the positive electrode with respect to lithium becomes about 1 V, decomposition of the electrolytic solution starts, although the reason is not clear.

By the way, in a normal device, two batteries are used in series, and the operation of the device is stopped when the voltage becomes 5.5 V or less (that is, the cell voltage is 2.75 V or less).
Theoretically, the discharge potential of the positive electrode with respect to lithium does not drop below 1 V, which is the decomposition voltage of the electrolytic solution.

However, in reality, since the electrode reaction in the positive electrode is non-uniform, the potential is 1 at the end of discharge.
There is a portion of V or less, and the electrolytic solution is decomposed at that portion. Therefore, it has been found that the above non-aqueous secondary battery has a problem that the cycle characteristics are not good due to the decomposition of the electrolytic solution at the end of discharge.

The present invention has been made to solve this problem, and its purpose is to prevent non-aqueous secondary electrolyte having excellent cycle characteristics, in which decomposition of the electrolytic solution does not occur on the positive electrode side at the end of discharge. To provide batteries.

[0009]

A non-aqueous secondary battery according to the present invention (hereinafter, referred to as "the battery of the present invention") for achieving the above object.
Called. ) Is the d value (d) of the lattice plane (002) plane on the negative electrode.
₀₀₂ ) is 3.35 to 3.37Å, and the size of the crystallite in the c-axis direction (Lc) is 200Å or more and is a non-aqueous secondary battery made of a carbon material capable of inserting and extracting lithium ions. In the above, as the positive electrode active material, the composition formula Li _x M
O _y (where M is Co and / or Ni or a transition metal containing these as main components, 0 ≦ x ≦ 1.3, 1.8 ≦ y
≦ 2.2. ) And a main ingredient consisting of an active material,
A mixture with an auxiliary agent composed of an active material having a discharge potential of 1.4 to 3.5 V with respect to lithium is used.

In the battery of the present invention, the electrolytic solution is decomposed at the end of discharge, which is possessed by the non-aqueous secondary battery in which the carbon material having a high degree of graphitization, which tends to make the reaction in the positive electrode uneven, is used in the negative electrode. The deterioration of cycle characteristics is solved by using a mixture of the above-mentioned main agent and auxiliary agent as a positive electrode active material.

That is, in the battery of the present invention, the main agent loses its capacity by adding an auxiliary agent which can be discharged at the end of discharge (that is, a low potential region) at a discharge potential of 1.4 to 3.5 V to lithium, to the main agent. It is designed so that the positive electrode potential does not drop sharply at the end of discharge.

The main components are LiCoO ₂ and LiNiO
₂ , LiCo _1-a Ni _a O ₂ (0 <a <1) and those obtained by substituting a part of Co and / or Ni of these composite oxides with another transition metal are exemplified.

As an auxiliary agent, it is 1.4 to 1.4 with respect to lithium.
The active material is not particularly limited as long as it has a discharge potential of 3.5 V and can discharge at the end of discharge when the positive electrode has a low potential. Preferable specific examples of such an active material include lithium-containing manganese oxide, V ₂ O ₅ , and Ti.
S _2, MoS _2, MoO ₃ and the like. These active materials may be used alone or in combination of two or more.

A suitable mixing ratio of the main agent and the auxiliary agent is as follows.
0 to 99 mol%, the auxiliary agent 50 to 1 mol%, and a more preferable compounding ratio of both agents is 70 to 95 mol% of the main agent and 30 to 5 mol% of the auxiliary agent. If the amount of the auxiliary agent added is excessive, the discharge capacity decreases, which is not preferable.

In the battery of the present invention, as described above, a mixture obtained by adding a specific auxiliary agent to the main agent is used as the positive electrode active material of a non-aqueous secondary battery in which a carbon material having a high degree of graphitization is used for the negative electrode. The greatest feature is the point. Therefore, other members such as the electrolytic solution constituting the battery of the present invention are not particularly limited, and various materials conventionally used for non-aqueous secondary batteries or proposed various materials can be used without limitation. Is.

For example, the electrolytic solution may be an organic solvent such as propylene carbonate, ethylene carbonate or vinylene carbonate, or dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane or ethoxymethoxyethane. In a mixed solvent with a low boiling point solvent such as LiPF ₆ , Li
Electrolyte solutes such as ClO ₄ and LiCF ₃ SO ₃ are added to 0.7
An example is a solution dissolved at a ratio of up to 1.5 M (mol / liter), especially 1 M.

[0017]

In the battery of the present invention, since the auxiliary agent that can be discharged in the low potential region at the end of discharge is added to the positive electrode active material, decomposition of the electrolytic solution at the end of discharge, which has been a problem in the past, does not occur.

[0018]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples, and various modifications can be made without departing from the scope of the invention. Is possible.

Example 1 A flat type non-aqueous secondary battery (the battery of the present invention) was produced.

[Preparation of Positive Electrode] LiCoO ₂ as a main component
And 80 parts by weight of a mixture of lithium-containing manganese oxide as a side agent in a molar ratio of 9: 1, 10 parts by weight of carbon powder as a conductive agent, and 10 parts by weight of polyvinylidene fluoride (PVdF) as a binder. And were kneaded to prepare a positive electrode mixture. The above LiCoO ₂ is Li ₂ CO ₃ and Co ₃ O ₄
Is obtained by calcining a mixture having a molar ratio of 3: 2 with 850 ° C. for 20 hours, and the lithium-containing manganese oxide is a mixture of LiOH and MnO ₂ having a molar ratio of 3: 7 at 375 °. It was obtained by firing at C for 20 hours. Next, the positive electrode mixture was pressure-molded at a molding pressure of 2 ton / cm ² and then heat-treated at 250 ° C. to prepare a disk-shaped positive electrode. As the positive electrode current collector, a stainless steel plate (SU
S304) was used.

[Preparation of Negative Electrode] Natural graphite (d ₀₀₂ = 3.3)
54 Å; Lc = 1000 Å) A kneaded product of 95 parts by weight of PVdF and 5 parts by weight of PVdF was pressure-molded at a molding pressure of 2 ton / cm ² and then heat-treated at 250 ° C. to prepare a disk-shaped negative electrode. . As the negative electrode current collector, a stainless steel plate (SU
S304) was used.

[Preparation of Electrolyte Solution] LiPF ₆ was dissolved in ethylene carbonate (EC) at a ratio of 1 M to prepare a non-aqueous electrolyte solution.

[Production of Battery] A flat type battery BA1 of the present invention (battery size: diameter 2
0 mm, thickness: 1.6 mm) was produced. As the separator, a polypropylene microporous film (manufactured by Polyplastics Co., trade name “Celguard”) was used and impregnated with the electrolytic solution described above.

FIG. 1 is a cross-sectional view schematically showing the produced battery BA1 of the present invention. The battery BA1 of the present invention shown in FIG.
It comprises a positive electrode 1, a negative electrode 2, a separator 3 separating these electrodes 1 and 2 from each other, a positive electrode can 4, a negative electrode can 5, a positive electrode current collector 6, a negative electrode current collector 7 and an insulating packing 8 made of polypropylene.

The positive electrode 1 and the negative electrode 2 are housed in a battery case formed by positive and negative bipolar cans 4 and 5 facing each other with a separator 3 impregnated with a non-aqueous electrolytic solution interposed therebetween. The positive electrode 1 is a positive electrode current collector. 6, and the negative electrode 2 is connected to the negative electrode can 5 via the negative electrode current collector 7 and the chemical energy generated inside the battery is converted into electrical energy from both terminals of the positive electrode can 4 and the negative electrode can 5. It can be taken out.

(Example 2) 80 parts by weight of a mixture of LiCoO ₂ and the same lithium-containing manganese oxide as that used in Example 1 in a molar ratio of 79.2: 0.8 was mixed with carbon powder 10 as a conductive agent. Parts by weight and PVdF1 as a binder
0 parts by weight was kneaded to prepare a positive electrode mixture. Then
A battery BA2 of the present invention was produced in the same manner as in Example 1 except that this positive electrode mixture was used.

(Example 3) 80 parts by weight of a mixture of LiCoO ₂ and the same lithium-containing manganese oxide as that used in Example 1 in a molar ratio of 1: 1, 10 parts by weight of carbon powder as a conductive agent, 10 parts by weight of PVdF as a binder was kneaded to prepare a positive electrode mixture. Then, a battery BA3 of the invention was produced in the same manner as in Example 1 except that this positive electrode mixture was used.

(Comparative Example) 80 parts by weight of LiCoO _2, 10 parts by weight of carbon powder as a conductive agent, and P as a binder.
10 parts by weight of VdF was kneaded to prepare a positive electrode mixture.
Next, a comparative battery BC1 was produced in the same manner as in Example 1 except that this positive electrode mixture was used.

[Change in Electrode Potential] With respect to the battery BA1 of the present invention, at the room temperature (25 ° C.) and 3 mA, the final charging voltage was 4.
After charging to 1V, discharge end voltage 2.75V at 3mA
The change with time of the potentials of the positive and negative electrodes when discharged up to. The results are shown in Figure 2.

FIG. 2 shows the time-dependent changes in the potentials of the positive and negative poles during discharge (discharge characteristics), and the vertical axis represents the potential of each pole (V vs. Li /
Is a graph showing Li ⁺ ) and time (capacity) on the horizontal axis. As shown in FIG.
It can be seen that the positive electrode potential does not drop sharply even at the end of discharge.

[Cycling Characteristics] For each battery, at room temperature (25 ° C.), the process of charging at 3 mA to the end-of-charge voltage of 4.1 V and then discharging at 3 mA to the end-of-discharge voltage of 2.75 V is one cycle. A test was conducted to evaluate the cycle characteristics of each battery. The results are shown in Fig. 3.

FIG. 3 is a graph showing the cycle characteristics of each battery, in which the vertical axis represents the discharge capacity (mAh) and the horizontal axis represents the number of cycles (times). As shown in FIG. It can be seen that the batteries BA1 to BA3 are superior to the comparative battery BC1 in cycle characteristics because decomposition of the electrolytic solution at the end of discharge does not occur.

In the above embodiments, the case where the present invention is applied to the flat type non-aqueous secondary battery has been described as an example, but the shape of the battery is not particularly limited, and various types such as a cylindrical type and a square type are used. It can be applied to a non-aqueous secondary battery having the above shape.

In the examples, a battery using a lithium-containing manganese oxide as an auxiliary agent has been described as an example, but V ₂ O ₅ , TiS having a discharge potential of 1.4 to 3.5 V with respect to lithium is used. Similar results are obtained when ₂ , ₂ , MoS ₂ , MoO ₃ or the like is used.

[0035]

INDUSTRIAL APPLICABILITY The battery of the present invention has excellent cycle characteristics because the electrolyte does not decompose at the end of discharge and thus has excellent cycle characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a flat type battery of the present invention.

FIG. 2 is a graph showing changes over time in the potentials of the positive and negative electrodes during discharge of the battery BA1 of the present invention manufactured in Example 1.

FIG. 3 is a graph showing cycle characteristics of each battery manufactured in Examples 1 to 3 and Comparative Example.

FIG. 4 is a graph showing changes over time in the potentials of the positive and negative electrodes during discharge of a conventional battery.

[Explanation of symbols]

 BA1 Inventive battery 1 Positive electrode 2 Negative electrode 3 Separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nishio 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Within the corporation

Claims (3)

[Claims] 1. Lithium having a lattice plane (002) plane d value (d ₀₀₂ ) of 3.35-3.37 Å and a crystallite size (Lc) in the c-axis direction of 200 Å or more in the negative electrode. In a non-aqueous secondary battery using a carbon material capable of occluding and releasing ions, the composition formula Li is used as the positive electrode active material.
_x MO _y (where M is Co and / or Ni or a transition metal containing these as main components, 0 ≦ x ≦ 1.3, 1.8
≦ y ≦ 2.2. ) A non-aqueous secondary battery characterized in that a mixture of a main agent composed of an active material represented by (4) and an auxiliary material composed of an active material having a discharge potential of 1.4 to 3.5 V with respect to lithium is used. . 2. The mixture contains 50 to 99 mol% of the main agent.
The non-aqueous secondary battery according to claim 1, which comprises 50 to 1 mol% of the auxiliary agent. 3. The auxiliary agent according to claim 1, which is at least one active material selected from the group consisting of lithium-containing manganese oxide, V ₂ O ₅ , TiS ₂ , MoS ₂ and MoO ₃ . Non-aqueous secondary battery.