JP2003142077A - Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode having high energy density, an excellent heavy load characteristic and an excellent low-temperature characteristic and to provide a nonaqueous electrolyte secondary battery using it. SOLUTION: This negative electrode 4 is composed by disposing band-like negative electrode active material layers 19 and 20 containing a carbon material capable of storing and releasing lithium ions on both sides of a band-like negative electrode collector 17. This negative electrode is characterized in that the thickness T1 of the collector 17 and the total thickness (T2 +T3 ) of the material layers 19 and 20 satisfied relational expressions of 8.0<=(T2 +T3 )/T1 and (T2 +T3 )<=200 μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art Lithium metal has the lowest base potential among metals and has a small specific gravity of 0.534. Therefore, a non-aqueous electrolyte secondary battery using this as a negative electrode is compared with a conventional secondary battery. And large energy density can be expected.

However, with lithium metal, dendrites are easily generated when the charge / discharge cycle is repeated, and the safety is low.

Therefore, a non-aqueous electrolyte secondary battery using a carbon material capable of inserting and extracting lithium ions as a negative electrode active material has been developed.

However, in this non-aqueous electrolyte secondary battery, the heavy load characteristics and the low temperature characteristics are not always sufficient, and improvement of the heavy load characteristics and the low temperature characteristics has been earnestly desired. Further, improvement of energy density is also desired.

[0006]

The present invention has been completed based on the above-mentioned circumstances, and in the case of containing a carbon material in the negative electrode active material, high energy density, excellent heavy load characteristics, The present invention also relates to a negative electrode having excellent low temperature characteristics, and a non-aqueous electrolyte secondary battery using the same.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to develop a negative electrode that can solve the above problems and a non-aqueous electrolyte secondary battery using the negative electrode. As a result, in a negative electrode in which a strip-shaped negative electrode active material layer containing a carbon material capable of absorbing and releasing lithium ions is arranged on both sides of the strip-shaped negative electrode collector, the thickness T1 of the negative electrode collector and the negative electrode active material are The total thickness of the material layers (T2 + T3) is 8.0 ≦ (T2 + T
3) / T1, and (T2 + T3) ≦ 200 μm, the non-aqueous electrolyte secondary battery negative electrode is characterized by having a high energy density, excellent heavy load characteristics, and excellent low temperature characteristics. The inventors have found that a non-aqueous electrolyte secondary battery can be obtained, and completed the present invention.

That is, the invention of claim 1 is a negative electrode in which a strip-shaped negative electrode active material layer containing a carbon material capable of absorbing and releasing lithium ions is arranged on both sides of the strip-shaped negative electrode current collector. The thickness T1 of the electric body and the total thickness (T2 + T3) of the negative electrode active material layer are 8.0 ≦ (T2 + T
3) / T1, and (T2 + T3) ≦ 200 μm was satisfied, and a negative electrode for a non-aqueous electrolyte secondary battery was obtained. According to a second aspect of the present invention, a strip-shaped negative electrode current collector is provided on both sides with a strip-shaped negative electrode active material layer containing a carbon material capable of absorbing and releasing lithium ions, and a strip-shaped positive electrode current collector is provided with a positive electrode. In a non-aqueous electrolyte secondary battery including a positive electrode having an active material layer and a non-aqueous electrolyte, a thickness T1 of the negative electrode current collector.
And the total thickness of the negative electrode active material layer (T2 + T3) is 8.0 ≦ (T2 + T3) / T1, and (T2 + T)
3) A non-aqueous electrolyte secondary battery characterized by satisfying the relation of ≦ 200 μm.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a prismatic non-aqueous electrolyte secondary battery 1 according to an embodiment of the present invention. The prismatic non-aqueous electrolyte secondary battery 1 includes a positive electrode 3 and
A flat wound electrode group 2 in which a negative electrode 4 is wound via a separator 5 and a non-aqueous electrolytic solution (not shown) containing an electrolyte salt are housed in a battery case 6.

A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, the positive electrode terminal 10 is connected to the positive electrode 3 via a positive electrode lead 11, and the negative electrode 4 is an inner wall of the battery case 6. Is electrically connected by contact with.

As shown in FIG. 2, the positive electrode 3 is made of, for example, a positive electrode current collector 13 made of, for example, aluminum, nickel, or stainless steel. Positive electrode active material layer 15,
16 is provided. This positive electrode active material layer 1
5, 16 contain a positive electrode active material. The positive electrode active material is not particularly limited, and known lithium-containing composite metal oxides, that is, lithium-containing cobalt oxide, lithium-containing manganese oxide, lithium-containing nickel oxide or a composite oxide thereof, or a mixture thereof. There is no particular limitation as long as it is a compound mainly composed of a lithium-transition metal composite oxide having a basic structure represented by LiMO ₂ (where M is one or more transition metals).
₂ , LiNiO ₂ , and also LiMnO ₄ , L
_{iMn 2 O 4, LiM y Mn} 2-y O 4 (M = Cr, C
It is also possible to use o, Ni) or the like, or a complex oxide or mixture thereof. When a compound mainly composed of a lithium-transition metal composite oxide having a basic structure represented by LiMO ₂ (where M is one or more transition metals) is used, the transition metal M is particularly preferable because of its high discharge voltage. Co,
It is desirable to select and use from Ni and Mn.

The positive electrode 3 is manufactured as follows, for example. A positive electrode active material is mixed with a conductive agent such as graphite or carbon black and a binder such as polyvinylidene fluoride to prepare a positive electrode mixture. Then, this positive electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to obtain a slurry. This is applied to both surfaces of the positive electrode current collector 13, dried, and then compressed and smoothed by a roll press or the like to manufacture the positive electrode 3. The positive electrode active material layer 1 is formed not only on both sides but also on one side.
It does not matter even if it has a structure in which 5, 16 are provided.

As shown in FIG. 3, the negative electrode 4 is composed of a negative electrode current collector 17 made of, for example, copper, nickel, or stainless steel. The structure has material layers 19 and 20.

The negative electrode 4 is manufactured, for example, as follows. The negative electrode active material is mixed with a binder such as polyvinylidene fluoride to prepare a negative electrode mixture. Then, this negative electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to form a slurry. This is applied on both sides of the negative electrode current collector 17, dried, and then compressed and smoothed by a roll press or the like to manufacture the negative electrode 4.

The negative electrode active material is not particularly limited as long as it is a carbon material capable of inserting and extracting lithium ions, and examples thereof include known cokes, glassy carbons, graphites, non-graphitizable carbons, and thermal decomposition. Carbons, carbon fibers, etc. can be used alone or in admixture of two or more.

Here, the thickness of the negative electrode current collector 17 of the negative electrode 4 is set to T1, and the thicknesses of the negative electrode active material layers 19 and 20 are respectively set.
Let T2 and T3. In this embodiment, the total thickness T1 of the negative electrode current collector 17 and the thickness of the negative electrode active material layer (T2 + T3).
And 8.0 ≦ (T2 + T3) / T1 and (T2 + T
3) The relationship of ≦ 200 μm is satisfied.

The value of (T2 + T3) / T1 is 8.0 ≦
(T2 + T3) / T1 is required, and preferably
10.0 ≦ (T2 + T3) / T1, especially 12.0 ≦ (T
2 + T3) / T1 is preferable. (T2 + T
This is because when the value of 3) / T1 is less than 8.0, the proportion of the negative electrode current collector 17 in the negative electrode 4 increases and the energy density decreases.

Further, it is necessary that (T2 + T3) ≦ 200 μm, preferably (T2 + T3) ≦ 180 μm,
It is particularly preferable that (T2 + T3) ≦ 160 μm. As described above, when the thickness is 200 μm or less, it is considered that the discharge capacity under heavy load can be improved for the following reason.

In the non-aqueous electrolyte secondary battery, during discharge, the lithium ions occluded in the negative electrode 4 are stored in the negative electrode active material layer 19,
It moves to the surface of the negative electrode 4 while diffusing in 20. Then, it is released from the surface of the negative electrode 4, moves in the electrolyte, and reaches the positive electrode 3.

In this discharge, the diffusion speed of lithium ions in the negative electrode active material layers 19 and 20 is slow. Therefore, when the total thickness of the negative electrode active material layers 19 and 20 is thicker than 200 μm, the lithium ions stored in the negative electrode active material layers 19 and 20 near the negative electrode current collector 17 move to the surface of the negative electrode 4. It is considered that it takes a long time to move and it takes a very long time to move.

As a result, at the time of heavy load, only the lithium ions occluded near the surface of the negative electrode 4 are utilized, the lithium ions occluded near the negative electrode current collector 17 cannot be effectively utilized, and the discharge capacity is increased. It is thought that it will decrease.

Therefore, in this embodiment, (T2 + T3)
≦ 200 μm, the negative electrode current collector 17 of the negative electrode 4
The lithium ions occluded in the vicinity are quickly moved to the surface of the negative electrode 4. As a result, the negative electrode active material layers 19 and 20 near the negative electrode current collector 17 are effectively used,
It is possible to improve the discharge capacity under heavy load.

If (T2 + T3) ≦ 200 μm, the discharge capacity can be ensured even at a low temperature where the diffusion rate of lithium ions in the negative electrode active material layers 19 and 20 is slower.

Thus, the thickness T1 of the negative electrode current collector 17
Total thickness of positive electrode active material layers 19 and 20 (T2 + T3)
Is 8.0 ≦ (T2 + T3) / T1, and (T2 + T
3) It is necessary to satisfy the relationship of ≦ 200 μm.

The separator 5 is not particularly limited,
For example, a known woven fabric, non-woven fabric, synthetic resin microporous film, or the like can be used, and a synthetic resin microporous film can be preferably used. Among them, a polyolefin-based microporous film such as a polyethylene and polypropylene microporous film or a composite microporous film thereof is preferably used in terms of thickness, film strength, film resistance and the like.

Further, by using a solid electrolyte such as a polymer solid electrolyte, it can also serve as a separator.
In this case, the solid polymer electrolyte may further contain an electrolytic solution, for example, by using a porous solid polymer electrolyte membrane as the solid polymer electrolyte.

As the non-aqueous electrolyte of the present invention, either a non-aqueous electrolytic solution or a solid electrolyte can be used. When the non-aqueous electrolytic solution is used, it is not particularly limited, and for example, a mixed solvent of ethylene carbonate and methyl ethyl carbonate or a mixed solvent of ethylene carbonate and dimethyl carbonate is used. In the mixed solvent, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyl lactone, acetyl-γ-butyrolactone, γ-valerolactone, sulfolane, 1,2-dimethoxy. Ethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate , Dipropyl carbonate, methyl propyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate, etc. may be used alone or in admixture of two or more.

The electrolyte salt as a solute of the non-aqueous electrolyte is not particularly limited, and may be, for example, LiClO ₄ , LiAsF ₆ , Li.
PF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ C
F ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN
_{(CF 3 SO 2) 2,} LiN (C 2 F 5 SO 2) 2 and the like may be used alone or as a mixture of two or more. Among them, LiPF ₆ is preferably used as the electrolyte salt.

As the solid electrolyte, known solid electrolytes can be used, for example, inorganic solid electrolytes and polymer solid electrolytes can be used.

[0030]

EXAMPLES Examples of the present invention will be shown below.
It is not limited to this. Examples 1 to 12 and comparative example
1 to 6, the prismatic non-aqueous electrolyte secondary battery 1 shown in FIG.
Made First, as a positive electrode active material, lithium carbonate 1.0
Moles and 2.0 moles of manganese dioxide are mixed to form a mixture
Was baked in air at a temperature of 800 ° C. for 15 hours. Product
X-ray diffraction measurement was performed on the JCPDS
LiMn registered in the file₂O_FourMatches well with the peak of
Was there. Therefore, the product is LiMn₂O _FourConfirmed
It was This LiMn₂O_FourCrushed and obtained by laser diffraction method
With a cumulative 50% particle size of 15 μm₂O_FourPowder
And And LiM_TwoO_Four90 parts by weight of conductive material
5 parts by weight of acetylene black and polyvinyl fluoride as a binder
Mix with 5 parts by weight of Nylidene to give N-methyl-2-pyrrolid
Don was appropriately added and dispersed to prepare a slurry. this
Aluminum slurry positive electrode current collector with a thickness of 15 μm
After uniformly coating and drying on both sides of 13, roll press
The positive electrode 3 was produced by compression molding with.

The negative electrode mixture was prepared by mixing 90 parts by weight of scaly graphite and 10 parts by weight of polyvinylidene fluoride and adding N-methyl-2-pyrrolidone as appropriate to disperse the slurry. The slurry is uniformly applied to a copper negative electrode current collector 17 having a predetermined thickness (T1) as shown in Table 1, dried, and then compression-molded by a roll press to form the negative electrode 4.
Was produced. When the negative electrode 4 was produced, the thickness of the negative electrode active material layers 19 and 20 (T2 +) shown in Table 1 was adjusted by adjusting the coating amount of the slurry and the compression pressure of the roll press.
Negative electrodes 4 having different values of (T3) and (T2 + T3) / T1 were prepared. In addition, in Examples 1 to 12 and Comparative Examples 1 to 6, only the negative electrode 4 is different and the other constituent elements are the same.

For the separator 5, a microporous polyethylene film having a thickness of 25 μm was used.

Using the above components, a rated capacity of 550
A square nonaqueous electrolyte secondary battery 1 having a width of 22 mm, a height of 47 mm, and a thickness of 7.8 mm in mAh was produced.

As the non-aqueous electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and LiPF ₆ was added to this solution in an amount of 1.2.
Mol / liter dissolved therein was used.

[0035]

[Table 1]

(Normal temperature low load battery capacity test) The prismatic nonaqueous electrolyte secondary batteries 1 of Examples 1 to 12 and Comparative Examples 1 to 6 described above were charged at a constant current and constant voltage of 4.2 V at 25 ° C. and 1 C current ( After performing initial charge) for 3 hours, a room temperature low load battery capacity test was performed in which constant current discharge was performed at a current density of 0.2 C in a 25 ° C. environment to a final voltage of 2.5 V. The capacity of this room temperature low load battery capacity test is represented by C1.

(Normal temperature heavy load battery capacity test) The rectangular non-aqueous electrolyte secondary batteries 1 of Examples 1 to 12 and Comparative Examples 1 to 6 described above were charged at a constant current and a constant voltage of 4.2 V at 25 ° C. and 1 C current ( After performing initial charge) for 3 hours, a room temperature heavy load battery capacity test was performed in which constant current discharge was performed at a current density of 2 C in a 25 ° C. environment to a final voltage of 2.5 V. Here, when the discharge capacity in the room temperature heavy load battery capacity test is C2 and the capacity in the room temperature low load battery capacity test is C1, the heavy load characteristic is C2 /
It is represented by C1.

(Low-temperature low-load battery capacity test) The prismatic nonaqueous electrolyte secondary batteries 1 of Examples 1 to 12 and Comparative Examples 1 to 6 described above were charged at a constant current and a constant voltage of 4.2 V at 25 ° C. and 1 C current ( After performing the initial charging) for 3 hours, the battery was left in an environment of 0 ° C. for 5 hours, and then a low temperature low load battery capacity test was performed in which constant current discharge was performed at a current density of 0.2 C to a final voltage of 2.5 V. here,
When the discharge capacity of the low temperature low load battery capacity test is C3 and the capacity of the room temperature low load battery capacity test is C1, the low temperature load characteristic is represented by C3 / C1.

(Test Results) Table 2 shows the test results of the room temperature low load battery capacity test, the room temperature heavy load battery capacity test, and the low temperature low load battery capacity test.

[0040]

[Table 2]

First, the influence of the value of (T2 + T3) / T1 on the capacity C1 in the room temperature low load battery capacity test will be examined. Here, in Examples 1 to 7 in which 8.0 ≦ (T2 + T3) / T1, the energy density increased and the discharge capacity C1 was larger than in Comparative Examples 1 to 2 in which 8.0> (T2 + T3) / T1. I found out. In addition, C of Example 3
Since 1 is larger than C1 of Examples 1 and 2, 1
It has been found that 0.0 ≦ (T2 + T3) / T1 is preferable. Furthermore, since C1 of Examples 5 to 7 is larger than C1 of Examples 1 to 4, in particular, 12.0 ≦
It has been found that (T2 + T3) / T1 is preferable.

Next, the influence of the value of (T2 + T3) on the heavy load characteristic C2 / C1 and the low temperature load characteristic C3 / C1 will be examined. Here, C2 / C1 of Examples 8 to 12 in which (T2 + T3) ≦ 200 μm is (T2 + T3)>
It was found to be larger than C2 / C1 of Comparative Examples 3 to 6 having a size of 200 μm. In addition, C2 / C1 of Example 11
Is larger than C2 / C1 of Example 12,
It has been found that it is preferable that (T2 + T3) ≦ 180 μm. Furthermore, C2 / C1 of Examples 8 to 10
Since it was larger than C2 / C1 of Example 11, it was found that (T2 + T3) ≦ 160 μm is particularly preferable.

Regarding the low temperature load characteristic C3 / C1, (T
2 + T3) ≦ 200 μm C3 / of Examples 8-12
C1 is (T2 + T3)> 200 μm Comparative Example 3 to
6 was found to be larger than C3 / C1.

Such a result is obtained by (T2 +
T3) ≦ 200 μm, the negative electrode current collector 17 of the negative electrode 4
Lithium ions occluded in the vicinity quickly move to the surface of the negative electrode 4, and as a result, the negative electrode active material layers 19 and 20 in the vicinity of the negative electrode current collector 17 are effectively used, and the discharge capacity under heavy load is improved. It is thought that it was done. In addition, (T2 +
By setting T3) ≦ 200 μm, it is considered that the discharge capacity was secured even at a low temperature where the diffusion rate of lithium ions in the negative electrode active material layers 19 and 20 was even slower.

From the above results, the thickness T1 of the negative electrode current collector is
And the total thickness (T2 + T3) of the negative electrode active material layer,
8.0 ≦ (T2 + T3) / T1, and (T2 + T3) ≦
By satisfying the relationship of 200 μm, it can be seen that a non-aqueous electrolyte secondary battery having high energy density, excellent heavy load characteristics, and excellent low temperature characteristics can be obtained.

In this example, LiMn ₂ O ₄ was used as the positive electrode active material, but as the positive electrode active material, a known lithium-containing composite metal oxide, that is, cobalt oxide containing lithium or lithium was contained. It is clear that the same effect can be obtained by using a manganese oxide, a nickel oxide containing lithium, a composite oxide thereof, or a mixture thereof.

<Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition to the above, various modifications can be made without departing from the scope of the invention.

In the above embodiment, the prismatic non-aqueous electrolyte secondary battery 1 has been described, but the battery structure is not particularly limited, and it is needless to say that it may be a cylindrical battery, a lithium polymer battery or the like.

[0049]

According to the negative electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery using the same according to the present invention, it is possible to obtain a high energy density, an excellent heavy load characteristic, and an excellent low temperature characteristic. it can.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a positive electrode according to an embodiment of the present invention.

FIG. 3 is a vertical sectional view of a negative electrode according to an embodiment of the present invention.

[Explanation of symbols]

4 ... Negative electrode 17 ... Negative electrode current collector 19 ... Negative electrode active material layer 20 ... Negative electrode active material layer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5H029 AJ02 AJ03 AK03 AL06 AL07                       AL08 AL18 AM02 AM03 AM04                       AM05 AM07 AM16 BJ02 BJ14                       DJ07 EJ04 EJ12 HJ04                 5H050 AA02 AA06 AA08 BA17 CA08                       CA09 CB07 CB08 CB09 CB29                       DA03 DA04 EA10 EA24 FA05                       HA04

Claims (2)

[Claims] 1. A negative electrode comprising a strip-shaped negative electrode current collector and a strip-shaped negative electrode active material layer containing a carbon material capable of absorbing and desorbing lithium ions, disposed on both sides of the strip negative electrode current collector. And the total thickness (T2 + T3) of the negative electrode active material layer is 8.0 ≦ (T2 + T3) /
A negative electrode for a non-aqueous electrolyte secondary battery, which satisfies T1 and (T2 + T3) ≦ 200 μm. 2. A negative electrode in which a negative electrode active material layer containing a carbon material capable of absorbing and desorbing lithium ions is arranged on both sides of a negative electrode current collector, and a positive electrode active material on the positive electrode current collector. In a non-aqueous electrolyte secondary battery including a positive electrode including a layer and a non-aqueous electrolyte, the thickness T1 of the negative electrode current collector and the total thickness (T2 + T3) of the negative electrode active material layer are 8. 0 ≦ (T2 + T3) /
A non-aqueous electrolyte secondary battery characterized by satisfying a relationship of T1 and (T2 + T3) ≦ 200 μm.