JPH10116628A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a lithium secondary battery having high energy density. SOLUTION: Positive electrode 10 active material contains compounds whose chemical formulas are shown as follows. Li1+x Mn2 O4 , Li4+x Mn5 O12 , Li2+x Mn4 O9 , Lix V2 O5 , Lix V6 O13 , Li1+x V3 O8 , Lix Fe2 (SO4 )3 (where (x) is in a rage of 0<=x<=12). Negative electrode 12 active material contains a compound whose chemical formula is shown by Li3-y-z My2 N (where M is any of Cu, Co, Ni, (y) is in a range of 0<y<=1.5, and (z) is in a range of 0<=y<=1.5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium secondary battery.

[0002]

2. Description of the Related Art A lithium secondary battery capable of realizing a high energy density has been actively researched and developed recently as an alternative battery to a conventional lead storage battery or nickel cadmium battery. Lithium metal is considered to have the highest energy density as the negative electrode material for lithium secondary batteries. However, when charge and discharge are repeated, dendrites are formed on the negative electrode.
Of lithium, and this dendrite-like lithium extends to the positive electrode, causing an internal short circuit, which is a serious problem in terms of safety.

On the other hand, in recent years, it has been studied to use a carbon material capable of inserting and extracting lithium ions as a negative electrode active material. Since the negative electrode reaction at the time of charge and discharge is an occlusion and release reaction of lithium ions between carbon layers, metallic precipitation of lithium ions on the negative electrode is unlikely to occur, and the above problem is being essentially avoided. A lithium secondary battery using LiCoO _{2 as a} positive electrode material and combining with a carbon negative electrode has been developed.

[0004]

The lithium occlusion / release capacity of a positive electrode prepared by using LiCoO ₂ as a positive electrode active material and adding a binder and a conductive auxiliary agent, that is, the charge / discharge capacity, is 270 to 270 per volume. It is about 330 Ah / l.
On the other hand, the charge / discharge capacity of a negative electrode produced by using a carbon material as a negative electrode active material and adding a binder thereto is about 300 to 400 Ah / l per volume. In a battery constituted by these positive and negative electrodes, 240 to 280
Energy densities in the range of Wh / l have been achieved.

However, since portable devices have been remarkably reduced in size and weight in recent years, development of secondary batteries having a higher energy density than lithium secondary batteries is expected.

An object of the present invention is to provide a high-energy lithium secondary battery suitable for use in portable equipment such as a mobile phone or a notebook personal computer, or a drive power supply or an electric power storage power supply for an electric vehicle. .

[0007]

A lithium secondary battery which achieves the object of the present invention is a lithium secondary battery comprising a positive electrode and a negative electrode for reversibly inserting and extracting lithium ions, and an electrolytic solution containing the lithium ions. At least, as a positive electrode active material, the chemical formula is Li _{1 + x} Mn ₂ O ₄ , Li _{4 + x} M
_{n 5 O 12, Li 2 +} x Mn 4 O 9, Li x V 2 O 5, Li x V
₆ O ₁₃ , Li _{1 + x} V ₃ O ₈ , Li _x Fe ₂ (SO ₄ ) ₃ (where x is 0
≦ x comprise a compound represented by ≦ 12 range), and the chemical formula Li _3-yz M _y N (where M as the negative electrode active material C
u, Co, or Ni, and y is 0 <y ≦ 1.5.
And z is in the range of 0 ≦ y ≦ 1.5).

Here, the electrolytic solution of the battery according to the present invention comprises prolene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, methyl propionate,
At least one of ethyl propionate and dimethoxyethane
The type is solvent, LiPF ₆ , LiBF ₄ , LiClO ₄ , L
It is desirable to use iCF ₃ SO ₃ as an electrolyte because of its excellent charge-discharge cycle characteristics.

As described above, the volume energy density of a lithium secondary battery using LiCoO ₂ as a positive electrode active material and a carbon material as a negative electrode active material is as small as about 240 to 280 Wh / l. This is because the charge reaction of LiCoO ₂ occurs at a high potential of 3.9 V or higher with respect to the lithium reference electrode. Therefore, when charging and discharging are performed within a range where the electrolytic solution is not electrolyzed, the amount of LiCoO ₂ absorbed and released by lithium ions is considered. In other words, this is because the utilization rate of the positive electrode active material decreases. Specifically, when the charging and discharging are performed with a charging end voltage of 4.2 V at which the electrolytic solution is not electrolyzed, the utilization rate of the LiCoO ₂ active material is about 50%.

In addition, since the carbon material has a low specific gravity, the negative electrode mixture becomes bulky, and the amount of the negative electrode that can be filled in a predetermined volume is limited, which is one reason that a high energy density lithium battery cannot be formed. .

On the other hand, in the present invention, Li _{1 + x} Mn ₂ O ₄ , Li _{4 + x} Mn ₅ O ₁₂ , Li which can be used for a lithium secondary battery.
_{2 + x Mn 4 O 9,} Li x V 2 O 5, Li x V 6 O 13, Li 1 + x V 3
Positive electrode active materials such as O ₈ and Li _x Fe ₂ (SO ₄ ) ₃ are LiCo
Since the occlusion and release reaction of lithium occurs in a voltage range lower than that of O ₂ , the positive electrode can be charged and discharged at a high utilization rate within a range in which the electrolyte does not decompose.

Also, Li _3-yz Cu used as a negative electrode
_y N, Li _3-yz Co _y N, Li _3-yz Ni _y N, etc. can reversibly store and release lithium ions, and have a higher specific gravity than carbon materials, so that high density filling of electrode mixture is possible. Is possible. Therefore, in the lithium secondary battery of the present invention using the above-described battery material for the positive electrode and the negative electrode, a lithium secondary battery having a higher energy density is realized as compared with a battery using LiCoO ₂ and a carbon material for the positive and negative electrode active materials. it can.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a coin-type lithium secondary battery according to one embodiment of the present invention. The positive electrode 10, the separator 11, and the negative electrode 12 are stacked in this order, and are caulked with a battery lid 14 and a battery can 15 via a gasket 13 to hermetically seal and seal.

Hereinafter, examples of the lithium secondary battery specifically manufactured according to the present invention will be described.

Example 1 A lithium secondary battery of the example shown in FIG. 1 was manufactured as follows. LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₄ O ₉ , V
7 types of ₂ O ₅ , LiV ₆ O ₁₃ , LiV ₃ O ₈ , and Fe ₂ (SO ₄ ) ₃ , graphite powder as a conductive aid, polyvinylidene fluoride (PVDF) as a binder, and a weight ratio of 88 each
%, 7% and 5%, and N-methyl-2-pyrrolidone (NMP) was added as a solvent and mixed well to prepare a positive electrode mixture. This positive electrode mixture was applied to one side of an Al foil having a thickness of 20 μm, and NMP was dried and then formed by a roll press to prepare a positive electrode sheet. This positive electrode sheet was punched out to a size of 15 mm in diameter to produce a positive electrode. As in the preparation of the positive electrode, Li ₂ CuN, Li ₂ Co is used as the negative electrode active material.
N, Li ₂ NiN 5 types, graphite powder as conductive aid,
Using polyvinylidene fluoride (PVDF) as a binder, blended at a weight ratio of 80%, 15%, and 5%, respectively.
N-methyl-2-pyrrolidone (NMP) was added as a solvent and mixed well to prepare a negative electrode mixture. This negative electrode mixture was applied to one surface of a Cu foil having a thickness of 20 μm, NMP was dried, and then formed by a roll press to prepare a negative electrode sheet. This negative electrode sheet was punched out to a size of 16 mm in diameter to produce a negative electrode.

The separator has a thickness of 25 μm and a diameter of 18
A microporous membrane made of mm mm polyethylene was used.

The electrolyte is a mixed solvent of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 and LiP
A solution having a concentration of 1 mol / l prepared with an electrolyte of F ₆ was used.

A positive electrode, a separator, and a negative electrode were laminated in this order and impregnated with an electrolytic solution, and then caulked with a battery lid and a battery can to produce a lithium battery shown in FIG.

Using this lithium secondary battery, the charge / discharge current is 3 mA, the charge end voltage is 4.0 V, and the discharge end voltage is 1.0.
Charge and discharge were performed at 5 V.

Example 2 Li _2.5 Co _0.5 was used as the positive and negative electrode active materials prepared in Example 1 using LiMn ₂ O _4.
N, to produce a lithium battery shown in FIG. 1 using Li _{1. 8} Co _1.2 N, the negative electrode produced in the same manner as in Example 1 using the Li _1.5 Co _1.5 N.

Using this lithium secondary battery, the charge / discharge current is 3 mA, the charge end voltage is 4.0 V, and the discharge end voltage is 1.0.
The charge and discharge were performed at 5 V.

Comparative Example 1 LiCoO as a positive electrode active material
Using Example ₂ , a positive electrode was produced in the same manner as in Example 1. On the other hand, graphite powder was used as the negative electrode active material, and polyvinylidene fluoride (PVDF) was used as the binder.
%, 10%, and N-methyl-
2-Pyrrolidone (NMP) was added and mixed well to prepare a negative electrode mixture. Thereafter, a negative electrode was produced in the same manner as in Example 1, and a lithium secondary battery shown in FIG. 1 was produced.

Using this lithium secondary battery, the charge / discharge current is 3 mA, the charge end voltage is 4.2 V, and the discharge end voltage is 2.
The battery was charged and discharged at 8 V.

Table 1 shows the results of comparison between an example in which the lithium secondary battery produced according to the present invention was specifically charged and discharged and a conventional example. The discharge power was determined by multiplying the average voltage during discharge by the discharge capacity. It has been found that the lithium secondary battery of the present invention has higher discharge power than conventional lithium secondary batteries, and can achieve high energy density.

[0026]

[Table 1]

[0027]

As described above, the utilization rate of the positive electrode active material during charging and discharging is high, and the negative electrode can be filled at a high density, so that a lithium secondary battery having a high energy density can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a lithium secondary battery according to one embodiment of the present invention.

[Explanation of symbols]

10: positive electrode, 11: separator, 12: negative electrode, 13: gasket, 14: battery cover, 15: battery can.

Claims (2)

[Claims] 1. A lithium secondary battery comprising a positive electrode for reversibly inserting and extracting lithium ions, a negative electrode, and an electrolyte containing the lithium ions, wherein the positive electrode active material has a chemical formula of Li _{1 + x} Mn ₂ O ₄ , Li _{4 + x} Mn ₅ O ₁₂ , Li _{2 + x} Mn
₄ O ₉ , Li _x V ₂ O ₅ , Li _x V ₆ O ₁₃ , Li _{1 + x} V ₃ O ₈ , L
_{i x Fe 2 (SO 4)} 3 ( where x is in the range of 0 ≦ x ≦ 12) include compounds represented by the chemical formula Li as an anode active material
_3-yz M _y N (where M is Cu, Co, is either Ni, y is the range of 0 <y ≦ 1.5 and z is 0 ≦ y ≦ 1,.
5) A lithium secondary battery comprising a compound represented by the following formula: 2. The method according to claim 1, wherein the electrolyte comprises prolene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethoxyethane. A solvent, LiPF ₆ ,
LiBF _4, LiClO _4, LiCF ₃ lithium secondary battery according to claim 1 each comprising at least one as an electrolyte SO _3.