JPH09293536A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance charging/discharging cycle performance by regulating the balance of the reversible capacities of a positive electrode and a negative electrode in the specified range. SOLUTION: A positive electrode and a negative electrode of a battery use a material capable of absorbing/releasing lithium as an active material. The balance of reversible capacities of the positive electrode and the negative electrode is specified to 1.05 < negative electrode/positive electrode <=1.30 so that the reversible capacity of the negative electrode is larger than that of the positive electrode. Therefore, lithium ions are sufficiently absorbed in the negative electrode in overcharge, and lithium is hardly deposited. Heat generation and rupture are reduced and safety is enhanced. Deterioration attendant on repeated charge/discharge cycles is reduced and good cycle characteristics are obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode using a substance capable of occluding and releasing lithium as an active material, a negative electrode using a substance capable of occluding and releasing lithium as an active material, and a lithium ion conductive non-aqueous electrolyte. The present invention relates to a non-aqueous electrolyte secondary battery comprising at least, and particularly to a highly reliable positive and negative electrode configuration having excellent charge and discharge cycle performance.

[0002]

Non-aqueous electrolyte batteries using lithium as a negative electrode active material have advantages of high voltage, high energy density, small self-discharge and excellent long-term reliability. It has already been widely used as a power source for such devices. However, in recent years, with the remarkable development of portable electronic devices and communication devices, a wide variety of devices that require a large current output for a battery as a power source have emerged, and from the viewpoint of economy and reduction in size and weight of the device, high cost is achieved. There is a strong demand for secondary batteries with energy density. Therefore, non-aqueous electrolyte secondary batteries having high voltage and high energy density have been actively researched and developed, and have been partially put into practical use.

Conventionally, the following three types of positive electrode active materials constituting the positive electrode of this type of secondary battery have been found depending on the form of charge / discharge reaction. The first type is Ti
Metal chalcogenides such as S ₂ , MoS ₂ and NbSe ₃ ,
MnO ₂ , MoO ₃ , V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO
₂ , such as Li _x MnO _{4 and} other metal oxides, a type in which only lithium ions (cations) enter and leave by intercalation, deintercalation reactions, etc. between crystal layers or between lattice positions or gaps. The second type is a type such as a conductive polymer such as polyaniline, polypyrrole, polyparaphenylene, etc., in which mainly anions are stably doped and desorbed by the reaction. The third type is a type (intercalation, deintercalation or dope, dedope reaction, etc.) in which both lithium cations and anions can enter and exit, such as graphite intercalation compounds and conductive polymers such as polyacene. is there.

On the other hand, as the negative electrode active material constituting the negative electrode of this type of secondary battery, the electrode potential is the most base when metal lithium is used alone, so the above positive electrode active material was used. It has the highest output voltage and high energy density as a battery combined with the positive electrode, but it is preferable because lithium-like acicular deposits and passivation compounds are formed on the negative electrode during charging and discharging, resulting in significant deterioration due to charging and discharging and cycle life. There was a short problem. Further, lithium acicular deposits grow by repeated charging and discharging, and eventually break through the separator,
There is also a safety issue in that a short circuit occurs inside the battery, causing rupture in the worst case such as heat generation. In order to solve this problem, as a negative electrode active material, (1) lithium and A
l, Zn, Sn, Pb, Bi, Pb, and other alloys, (2) WO ₂ , MnO ₂ , Fe ₂ O ₃ , TiS _{2 and} other inorganic compounds, graphite, and carbon obtained by firing an organic substance Use intercalation compounds or intercalation compounds in which lithium ions are occluded in the crystal structure of organic materials, (3) Conductive polymers such as polyacene and polyacetylene doped with lithium ions, and the like that can occlude and release lithium ions Is proposed.

It has been reported that in the storage and release of lithium ions in the positive electrode and the negative electrode of this type of battery, there is an irreversible component in which some of the stored lithium ions are not released in both the positive electrode and the negative electrode. This is one of the causes of poor performance. By setting the ratio of the reversible capacity on the positive electrode side and the reversible capacity on the negative electrode side capable of occluding / releasing lithium, that is, the ratio of the active material amounts of both electrodes so that the reversible capacity balance is almost equal, the volumetric energy density and the weight energy density Has been proposed (see, for example, JP-A-6-36798).

[0006]

Charge / discharge cycle performance has been conventionally emphasized in this type of secondary battery. The required charge / discharge cycle performance value differs depending on the equipment used, but one guideline is that the initial capacity is 70 at 70 cycles.
% Can be maintained. However, in the method of setting the ratio of the active material amounts of both electrodes so that the reversible capacities on the positive electrode side and the negative electrode side are substantially equal to each other, deterioration due to charging / discharging is large and the charge / discharge cycle performance is insufficient. Further, when the reversible capacity balances of the positive electrode and the negative electrode are substantially equal, lithium is deposited on the negative electrode during overcharge. As a result, the amount of passive lithium increases, leading to a decrease in battery capacity and deterioration of cycle characteristics. The present inventors have found that the reversible capacity balance between the negative electrode and the positive electrode has a great influence on such problems.

[0007]

In order to solve the above problems, the present invention sets the balance of the reversible capacities of the positive electrode and the negative electrode to 1.05 <negative electrode / positive electrode ≦ 1.30, and Also increased the reversible capacity of the negative electrode. For this reason, lithium ions can be sufficiently occluded in the negative electrode during charging or overcharging, so that lithium deposition is less likely to occur. As a result, it is possible to achieve a high-performance battery with little deterioration even after repeated charging and discharging and improved safety.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the reversible capacity balance of negative electrode / positive electrode is increased to 1.05 <negative electrode / positive electrode ≦ 1.30. When the reversible capacity balance is 1.05 or less, the reversible capacity balance may locally become 1 or less due to variations in electrode manufacturing. Also, 1.30
If it is larger than that, the mixture that does not participate in charge and discharge is excessively present, and considering that the mixture is inserted into a battery of a constant volume, the amount of the mixture that can be charged and discharged must be substantially reduced. Further, when the negative electrode active material changes in potential depending on the amount of stored lithium, if the negative electrode mixture is present in excess, the negative electrode potential does not drop during charging, and substantially overdischarge of the positive electrode active material occurs. As mentioned above, the reversible capacity balance is 1.05 <
The optimal range is negative electrode / positive electrode ≦ 1.30. It is preferably 1.10 or more and 1.20 or less. By setting the reversible capacity balance between the negative electrode and the positive electrode of the present invention, lithium is not deposited even when overcharged, so there is little risk of heat generation and bursting, and the cycle characteristics due to repeated charging and discharging are good. A secondary battery can be provided.

As the positive electrode active material used in the present invention,
TiS_Two, MoS_Two, NbSe_ThreeMetal chalcogenides such as
Or MnO_Two, MoO_Three, V_TwoO_Five, Li_xCoO_Two, Li_xNiO
_Two, Li _xMn_TwoO_FourMetal oxides such as polyaniline, polypo
High conductivity of rolls, polyparaphenylene, polyacene, etc.
Molecule, and lithium ion such as graphite intercalation compound
Various substances that can occlude and / or release anions and / or anions
Can be used.

In particular, metal chalcogenides, metal oxides, etc.
The electrode potential for metallic lithium is 2 V or higher, and
Preferably V_TwoO_Five, MnO_Two, Li_xCoO_Two, Li_xNiO_Two,
Li _xMn_TwoO_FourIt has a high potential of 3V to 4V or higher such as
(Active) active material and metallic lithium described later
Electrode material having a low electric potential of 1 V or less (base) active material
High energy by combining with the negative electrode using
It is more preferable because a secondary battery having a high density can be obtained.

As the negative electrode active material, metallic lithium, carbonaceous material, Li _x Si, metal oxide, nitride, silicide, carbide, Li _x Si _1-y M _y O _z (0 ≦ x, 0 ≦ y <1,0 <z ≦
3, and M can be various substances capable of occluding and releasing anion and / or lithium ion such as silicon oxide represented by a metal excluding alkali metal or a similar metal excluding silicon).

In particular, Li _x Si _{1- y My} O _z (0 ≦ x, 0 ≦ y <
1,0 <z ≦ 3, and M is a metal oxide other than alkali metal or a similar metal other than silicon), such as a silicon oxide, which has a large charge / discharge capacity in a region where the electrode potential with respect to metallic lithium is 1 V or less. Therefore, by combining with the positive electrode using the positive electrode active material, a secondary battery with high voltage and high energy density can be obtained, which is more preferable. When an oxide such as silicon oxide is used as the negative electrode, generally, the reversible capacity balance is 1.05 <negative electrode / positive electrode because the irreversible component of lithium ions stored by the first charge that is not discharged is relatively large. Setting within the range of ≤1.30 is particularly effective in improving cycle characteristics. Furthermore, a negative electrode using the above silicon oxide or carbonaceous material as a negative electrode active material,
Li _x CoO ₂ , Li _x NiO ₂ , Li _x M as the positive electrode active material
n ₂ O ₄ or Li _a M _b L _c O _d (0 <a ≦ 1.15, 0.8 ≦
b + c ≦ 1.3, 0 ≦ c, 1.5 ≦ d ≦ 2.5, M is C
one or more transition metals such as o, Ni, Mn, Fe and Ti,
L is B, Al, In, Si, Ge, Sn, Pb, Mg,
When combined with a positive electrode using a transition metal oxide containing lithium (one or more selected from Zn, Cu and P), lithium that is repeatedly occluded and released by the negative electrode and the positive electrode during a charge / discharge cycle is substantially Lithium, which is included in the positive electrode active material during battery manufacture, is balanced by reversible capacity of 1.05 <negative electrode / positive electrode ≦ 1.30 as described above, so that not only overcharge but also overdischarge can be achieved. It is particularly preferable since a battery having no lithium deposition on the positive electrode and having particularly small cycle deterioration can be obtained.

As the electrolyte, γ-butyrolactone, pr
Ropylene carbonate, ethylene carbonate (E
C), butylene carbonate, dimethyl carbonate,
Diethyl carbonate, methyl formate, 1,2-
Dimethoxyethane, tetrahydrofuran, dioxola
And non-aqueous organic solvents such as dimethylformamide and dimethylformamide.
LiClO alone or in a mixed solvent as a supporting electrolyte_Four, L
iPF₆, LiBF_Four, LiCF _ThreeSO_Three, LiC (SO_TwoCF_Three)
_Three, LiN (SO_TwoCF_Three)_TwoLithium ion dissociable salts such as
Dissolved organic non-aqueous electrolytes, polyethylene oxide and poly
The lithium salt is fixed to a polymer such as crosslinked phosphazene.
Molten polymer solid electrolyte or Li3N, LiN, etc.
Non-aqueous electrolysis of lithium ion conductive materials such as inorganic solid electrolytes
Quality can be used.

In particular, the above-mentioned Li _x Si is used as the negative electrode active material.
_1-y M _y O _z (0 ≦ x, 0 ≦ y <1, 0 <z ≦ 3, M is a metal except alkali metal or a metal except silicon)
In the case of using the silicon oxide represented by, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate
It is preferred to use a mixed solvent of R ₁ R ₂ type alkyl carbonate such as carbonate and EC. Further, the volume mixing ratio of EC and R ₁ R ₂ type alkyl carbonate is about 3: 1 to about 1:
The range of 3 is more preferable.

[0015]

Embodiments Hereinafter, embodiments will be described in detail. Lithium-cobalt composite oxide represented by LiCoO ₂ as a positive electrode active material and graphite as a conductive agent crushed and mixed in a mortar are mixed and dispersed in a solution in which a binder is dissolved to prepare a positive electrode mixture slurry. did. This positive electrode mixture slurry was applied onto both surfaces of an aluminum foil current collector, dried, and rolled using a roll press to produce a positive electrode plate. A negative electrode was produced in the same manner. Commercially available silicon monoxide (SiO) as a negative electrode active material and graphite, which was a conductive agent, were crushed and mixed in a mortar, and mixed and dispersed in a binder solution to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied onto both surfaces of a copper foil current collector, dried, and rolled using a roll press to produce a negative electrode plate. Using the positive electrode plate / negative electrode plate thus manufactured, the positive electrode capacity is 751.2 mAh and the negative electrode capacity is 8
Reversible capacity balance at 21.6 mAh (negative / positive) =
A 1.09 prismatic battery C was produced. Hereinafter, in the same manner, Battery A with reversible capacity balance of 0.94, Battery B with reversible capacity balance of 1.01, and Reversible capacity balance of 1.18.
Batteries D, B of reversible capacity balance 1.30, B of reversible capacity balance 1.41 and B of reversible capacity balance 1.50 were prepared in the same manner.

The battery thus produced was charged at an upper limit voltage of 4.2 V and a charging time of 2.5 at a constant current and constant voltage of 400 mA.
A charging / discharging cycle was performed under the conditions of a constant current of 400 mA and an end-of-discharge voltage of 2.7 V for an hour. Reversible capacity balance 0.9
FIG. 1 shows the cycle characteristics of Battery A of No. 4 and Battery D of reversible capacity of 1.18 up to 300 cycles. As is clear from FIG. 1, the capacity retention rate was different depending on the reversible capacity balance between the negative electrode and the positive electrode, and the value of Battery A having a reversible capacity balance of 0.94 was lower than 70% after 300 cycles. The battery D having a reversible capacity balance of 1.18 has achieved 70% or more. In the battery B having a reversible capacity balance of 1.01, the cycle deterioration was large as in the battery A. Batteries F and G having a reversible capacity balance larger than 1.3 had little cycle deterioration, but had a small capacity from the initial cycle. After 300 cycles, when disassembling each battery in the charged state, reversible capacity balances of 0.94 and 1.01 of batteries A and B were confirmed to deposit a small amount of lithium between the separator and the negative electrode plate. , Batteries with capacity balance greater than 1.05 C, D, E, F, G
In, lithium deposition was not confirmed. In the examples, the negative electrode / positive electrode combination is described as a composite oxide / silicon oxide of lithium and cobalt, but any of the above-mentioned substances capable of inserting and extracting lithium can be used for the negative electrode and the positive electrode.

[0017]

The present invention is embodied in the form described above and has the following effects. I. Excellent cycle performance. B. Strong against overcharge. C. Highly safe because there is no lithium deposition.

[Brief description of drawings]

FIG. 1 is a diagram showing cycle characteristics of a battery according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumiharu Iwasaki 1-8 Nakase, Mihama-ku, Chiba, Chiba Seiko Electronics Co., Ltd. (72) Shinichi Takasugi 1-chome, Nakase, Mihama-ku, Chiba 8 Seiko Electronics Co., Ltd. (72) Inventor Tsuneaki Tamachi 1-8 Nakase, Nakase Mihama-ku, Chiba Chiba Electronics Co., Ltd.

Claims (2)

[Claims] 1. A non-aqueous electrolyte comprising at least a positive electrode having a substance capable of occluding and releasing lithium as an active material, a negative electrode having a substance capable of occluding and releasing lithium as an active material, and a non-aqueous electrolyte having a lithium ion conductivity. In the secondary battery, the capacity balance of the reversible capacities of the positive electrode and the negative electrode is 1.05 <negative electrode / positive electrode ≦
A non-aqueous electrolyte secondary battery characterized by being regulated within the range of 1.30. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is a carbonaceous material and / or a silicon oxide.