JP2001023614A - Positive electrode and secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode and a secondary battery using it capable of having a high energy density and providing an excellent heavy loading characteristic and a low temperature characteristic. SOLUTION: Since a lithium manganese combined oxide has a spinel structure, a diffusion coefficient of lithium is small. Therefore, in a positive electrode containing the lithium manganese combined oxide as a positive electrode current- collecting body 210 and a total thickness (T2+T3) of the positive electrode active substance layer 211A, 211B are set so as to satisfy formulae: 2.0<=(T2+T3)/T1 and (T2+T3)<=200 μm. Thereby, a secondary battery indicating an excellent heavy loading characteristic and a low temperature characteristic while a high energy density is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode containing a lithium manganese composite oxide and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has enabled electronic devices to become smaller and lighter one after another. Along with this, there is an increasing demand for a battery as a portable power supply to be smaller and lighter and have a higher energy density.

[0003] Conventionally, aqueous batteries such as lead batteries and nickel-cadmium batteries have been the mainstream as secondary batteries for general use. These batteries can satisfy the cycle characteristics to some extent, but have a low battery weight and energy. The properties were not satisfactory in terms of density.

Therefore, recently, research and development of a nonaqueous electrolyte secondary battery using a material such as lithium, a lithium alloy, a metal alloying with lithium, and a carbon material capable of occluding and releasing lithium ions for a negative electrode have been actively conducted. It has been done. This secondary battery has a high energy density by using a lithium-containing composite oxide represented by a lithium-cobalt composite oxide having a high discharge voltage as a positive electrode material, and has a low self-discharge.
It has excellent properties of light weight, and is currently in practical use as a lithium ion secondary battery. In this lithium ion secondary battery, lithium ions are doped into the carbon material of the negative electrode during charging, and the lithium ions diffuse into the lithium-containing composite oxide during discharging.

However, in this lithium ion secondary battery, there is a problem that Co (cobalt), which is a raw material of the positive electrode material (lithium-cobalt composite oxide), is small in amount and expensive.

In order to solve such a problem, research and development of a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide having a spinel structure as a cathode material have been actively conducted recently. Department has been put to practical use. Mn (manganese), which is a raw material of the lithium manganese composite oxide, is an inexpensive material with a large output.

[0007]

The electrolytic solution of the above-mentioned non-aqueous electrolyte secondary battery is used by dissolving a lithium salt in an organic solvent. Small. Therefore, non-aqueous electrolyte secondary batteries
Basically, it is inferior to an aqueous secondary battery in terms of heavy load characteristics and low temperature characteristics.

Therefore, the same applicant as the present applicant firstly
The thickness T1 of the positive electrode current collector is taken into consideration in consideration of safety and reliability in the event of an external short circuit, while compensating for the disadvantages of the nonaqueous electrolyte secondary battery.
A technique has been proposed in which the ratio of the total thickness (T2 + T3) of the positive electrode active material layer to the following is set in a relationship of 2.0 ≦ (T2 + T3) /T1≦7.0 (JP-A-8-64253). No.). As a result, it is possible to obtain a secondary battery having a high energy density, excellent heavy load characteristics and low temperature characteristics, and excellent safety and reliability at the time of external short circuit.

However, Japanese Patent Application Laid-Open No. 8-64253 discloses
As disclosed in the examples, the technology disclosed in the publication is limited to a secondary battery using a layered structure active material typified by a lithium cobalt composite oxide and a lithium nickel composite oxide as a positive electrode active material. Things. This is because lithium manganese composite oxide is an active material having a spinel structure, and in that case, the lithium ion diffusion coefficient is as small as about 1/10 to 1/100 of that of a layered active material (PG Bruce, A. Lisowski- Oleksiak, MYSaidi and C.
A. Vincent: Solid State Ionics, 57, 353 (1992); MGS
R. Thomas, PG Bruceand, JB Goodenough: Solid State I
onics, 18/19, 794 (1986); JBBates, FX, Hart, D Lub
ben, BSKwak and A. van Zomeren: Proc. of the Sympo
sium on Rechargeable Lithium and Lithium-ion Batte
ries, 94-28, 342 (1995)). Therefore, in the lithium manganese composite oxide having a special structure of spinel structure, conventionally, there was a problem that it was difficult to obtain a battery excellent in heavy load characteristics and low temperature characteristics while maintaining high energy density. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cathode active material containing a lithium manganese composite oxide, which has a high energy density,
An object of the present invention is to provide a positive electrode excellent in heavy load characteristics and low-temperature characteristics, and a secondary battery using the positive electrode.

[0011]

The positive electrode according to the present invention the means for solving problem], the positive electrode active material _{layer, Li X Mn 2-Y M} Y O 4 (0.95
≦ x ≦ 1.25, 0.01 ≦ y ≦ 0.20, M is T
i, Cr, Fe, Co, Ni, Zn, and at least one metal selected from the group consisting of Al) and the sum of the thickness T1 of the positive electrode current collector and the thickness of the positive electrode active material layer (T2 + T3).
Is 2.0 ≦ (T2 + T3) / T1, and (T2 + T3)
≦ 200 μm.

A secondary battery according to the present invention comprises a positive electrode including a band-shaped positive electrode current collector and a band-shaped positive electrode active material layer disposed on both sides of the positive electrode current collector, lithium, a lithium alloy,
A strip-shaped negative electrode including a negative electrode active material layer made of a material that can be alloyed with lithium or a material that can occlude and release lithium ions, wherein the positive electrode active material layer is Li _X Mn _2-Y M _Y O ₄
(0.95 ≦ x ≦ 1.25, 0.01 ≦ y ≦ 0.2
0 and M are Ti, Cr, Fe, Co, Ni, Zn, Al
At least one metal selected from the group consisting of
The sum of the thickness T1 of the positive electrode current collector and the thickness of the positive electrode active material layer (T
2 + T3) is 2.0 ≦ (T2 + T3) / T1, and (T2 + T3)
≦ 200 μm.

The positive electrode according to the present invention uses Li _X as an active material.
Mn _2-Y M _Y O ₄ (0.95 ≦ x ≦ 1.25, 0.01
≦ y ≦ 0.20, M is Ti, Cr, Fe, Co, N
i, Zn and at least one metal selected from Al), and the thickness (T2 + T3) of the active material layer and the thickness T1 of the current collector are 2.0 ≦ (T2 + T3) / T1,
In addition, since the configuration is such that the relationship of (T2 + T3) ≦ 200 μm is satisfied, the density of the active material that contributes to the battery capacity is kept high, and at the same time, the discharge capacity does not decrease at a heavy load and at a low temperature. Therefore, the secondary battery of the present invention using this positive electrode has a high energy density and excellent heavy load characteristics and low temperature characteristics.

[0014]

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

FIG. 2 is a sectional view of a non-aqueous electrolyte secondary battery including a positive electrode containing a lithium manganese composite oxide according to an embodiment of the present invention. FIG. 1 is a positive electrode portion of the non-aqueous electrolyte secondary battery. Respectively represent the cross-sectional structures. First, the structure of the positive electrode 21 will be described with reference to FIG.

The positive electrode 21 has a structure in which strip-like positive electrode active material layers 211A and 211B are provided on both sides of a strip-like positive electrode current collector 210. Here, the thickness of the positive electrode current collector 210 is T1, and the thicknesses of the positive electrode active material layers 211A and 211B are T2 and T3, respectively. Therefore, the positive electrode active material layer 2
The total thickness of 11A and 211B is represented by (T2 + T3).

The positive electrode active material layers 211A and 211B are made of Li
_X Mn _2-Y M _Y O ₄ (0.95 ≦ x ≦ 1.25, 0.
01 ≦ y ≦ 0.20, M is Ti, Cr, Fe, Co,
At least one metal selected from Ni, Zn, and Al). That is, the positive electrode active material layers 211A and 211B are made of a lithium manganese composite oxide having a spinel structure.

The positive electrode current collector 210 is made of, for example, a metal foil such as an aluminum (Al) foil, a nickel (Ni) foil or a stainless steel foil, and is preferably porous. This is because the porous layer can increase the adhesive strength between the positive electrode active material layers 211A and 211B. Note that a positive electrode lead 25 is attached to the positive electrode current collector 210 as described later (see FIG. 2).

In the present embodiment, in such a positive electrode 21, the sum (T2 + T3) of the thickness T1 of the positive electrode current collector 210 and the thickness of the positive electrode active material layers 211A and 211B is 2.0 ≦ (T2 + T3 ) / T1 and (T2 + T3)
≦ 200 μm.

The ratio (T2) between the thickness T1 of the positive electrode current collector 210 and the thickness (T2 + T3) of the positive electrode active material layers 211A and 211B.
When the value of (+ T3) / T1 is 2.0 or more, preferably 3.0 or more, more preferably 4.0 or more, a high energy density can be obtained. On the other hand, (T2 + T3) / T
If the value of 1 is less than 2.0, the desired high energy density cannot be obtained. Although the detailed reason is unknown, it is considered as follows. That is,
When (T2 + T3) / T1 is less than 2.0, the ratio of the active material to the battery volume decreases, and the ratio of the current collector and the separator that do not contribute to the battery capacity increases. Therefore, the energy density of the battery is reduced.

Incidentally, in the secondary battery disclosed in the above-mentioned JP-A-8-64253, (T2 + T3) /
When T1 is equal to or greater than 7.0, the rise in the battery surface temperature during an external short circuit is considered to be large.
In the secondary battery using, even when the value of (T2 + T3) / T1 is 7.0 or more, the rise in the battery surface temperature during an external short circuit is small. The reason is considered as follows. The rise in the battery surface temperature during an external short circuit occurs due to the difference between heat generated by Joule heat generated during an external short circuit and heat dissipation by the battery constituent materials. However, the lithium manganese composite oxide used in the positive electrode active material layer of the present embodiment is used. Has a spinel structure as described above, and the diffusion coefficient of lithium ions is 1/10 to 1/10 of that of a material having a layered structure represented by a lithium-cobalt composite oxide.
0. Therefore, when the lithium manganese composite oxide is used for the positive electrode active material, the short-circuit current flowing during external short-circuiting is lower than when a layered material represented by the lithium cobalt composite oxide is used for the positive electrode active material. Become smaller. When the short-circuit current becomes smaller, the generated Joule heat also becomes smaller, and even if the ratio of the thickness of the current collector to the thickness of the positive electrode active material layer becomes smaller, the heat dissipation effect of the battery constituent materials except the positive electrode current collector causes It is considered that since the heat is sufficiently dissipated, the rise in the battery surface temperature during an external short circuit can be suppressed to a low level. That is, when a material having a spinel structure represented by a lithium manganese composite oxide is used for the positive electrode active material,
It is not necessary to limit the value of (T2 + T3) / T1 to 7.0 or less.

From the above results, it can be said that when a lithium manganese composite oxide having a spinel structure is used as a positive electrode active material, a battery must be manufactured in consideration of the small diffusion coefficient of lithium ions.

In order to obtain a battery having excellent low-temperature characteristics and heavy load characteristics, (T2 + T3) must be 200 μm or less, preferably 180 μm or less, and more preferably 160 μm or less.

In the region of (T2 + T3) ≦ 200 μm, good low-temperature characteristics and heavy load characteristics are exhibited, but (T2 + T3)>
At 200 μm, the low temperature characteristics and heavy load characteristics deteriorate. Although the detailed reason is unclear, it is considered that the lithium ion diffusion coefficient of the lithium manganese composite oxide having a spinel structure is small, in other words, it is caused by the slow diffusion of lithium ions. At the time of battery discharge, lithium ions move from the negative electrode to the positive electrode in the electrolyte. The lithium ions that have migrated to the positive electrode first diffuse into the lithium manganese composite oxide on the surface of the positive electrode, and gradually move through the electrolyte existing in the active material layer, while gradually moving through the lithium manganese composite oxide on the current collector side. It also spreads in objects.

However, since the diffusion of lithium ions into the active material layer is slow as in the case of the lithium manganese composite oxide, lithium ions stay near the surface of the active material layer,
Hinders the movement of lithium ions in the electrolyte. for that reason,
In the active material located near the positive electrode current collector, diffusion of lithium ions does not proceed smoothly. That is, the active material located near the positive electrode current collector is less likely to be used during discharge. At the time of low load discharge, (T2 + T3)> 200
Even at μm, the movement of lithium ions in the electrolyte is slow,
Active material located near the current collector can also be used for discharging,
Although sufficient discharge capacity can be obtained, during heavy load discharge, more lithium ions stay on the surface of the active material layer, so that the active material located near the positive electrode current collector is not used during discharge, and The capacity decreases.

On the other hand, when (T2 + T3) ≦ 200 μm, since the thickness of the active material layer is small, the moving distance of lithium ions in the electrolyte is short. The diffusion of lithium ions in the active material located near the electric body proceeds. That is, a lithium ion reaction occurs with the active material, and a sufficient discharge capacity can be obtained even during heavy load discharge.

Next, the low-temperature characteristics are considered as follows. At low temperatures, the movement speed of lithium ions in the electrolytic solution is slowed down, but the diffusion of lithium ions in the lithium manganese composite oxide is further slowed down. Therefore, unless the active material layer is (T2 + T3) ≦ 200 μm, diffusion of lithium ions in the active material located near the current collector does not proceed, and it is considered that a sufficient discharge capacity cannot be obtained at low temperatures. .

Therefore, in the positive electrode 21 of the present embodiment in which the positive electrode active material contains the lithium manganese composite oxide, the thickness of the positive electrode current collector 210 and the positive electrode active material layer 211A,
By regulating the ratio of the thickness of 211B to be equal to or less than a certain value and making the thickness of the positive electrode active material layers 211A and 211B equal to or less than a certain value, a secondary battery having high energy density, excellent heavy load characteristics and low temperature characteristics is provided. Can be obtained.

Such a positive electrode 21 can be manufactured, for example, by the following method.

First, a lithium manganese composite oxide as a positive electrode active material includes, for example, lithium carbonate, nitrate, oxide or hydroxide, and manganese carbonate, nitrate,
Oxide or hydroxide is pulverized and mixed to have a desired composition, and 600 to 1000 in an oxygen-containing atmosphere.
It is obtained by firing at a temperature in the range of ° C.

The cathode active material of the present embodiment is mixed with a conductive agent such as graphite or carbon black and a binder such as polyvinylidene fluoride to form a cathode mixture, and this cathode mixture is mixed with N-methylpyrrolidone or the like. In the positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry is applied to both surfaces of a positive electrode current collector such as a belt-like aluminum foil, dried, and then compressed and smoothed by a roll press or the like to obtain a belt-like positive electrode 21.

The positive electrode 21 manufactured in this manner is specifically used for, for example, a cylindrical nonaqueous electrolyte secondary battery shown in FIG.

FIG. 2 shows a sectional structure of a secondary battery using the electrolytic solution according to the present embodiment. This secondary battery is a so-called cylindrical type. A band-shaped positive electrode 21 and a negative electrode 22 are provided inside a substantially hollow cylindrical battery can 11.
Electrode body 20 is wound with a separator 23 interposed therebetween.
have. The battery can 11 is made of, for example, nickel-plated iron, and has one end closed and the other end open. The size of the battery can 11 and the size of the spirally wound electrode body 20 are respectively adjusted such that the spirally wound electrode body 20 is properly fitted inside the battery can 11. Inside the battery can 11, a pair of insulating plates 12 and 13 are respectively arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

At the open end of the battery can 11, a battery cover 14 is provided.
And a safety valve mechanism 15 provided inside the battery lid 14.
The PTC (Positive Temperature Coefficient) element 16 is attached by caulking via a gasket 17, and the inside of the battery can 11 is sealed. The battery cover 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is a PTC
The disk plate 15a is electrically connected to the battery cover 14 through the element 16, and when the internal pressure of the battery becomes higher than a predetermined value due to an internal short circuit or external heating, the disk plate 15a is inverted and wound around the battery cover 14. This disconnects the electrical connection with the electrode body 20 to prevent the battery from bursting. PTC element 16
When the temperature rises, the current is limited by an increase in the resistance value, and a large current flows due to an external short circuit or the like to prevent the battery from abnormally generating heat.For example, barium titanate-based semiconductor ceramics It is configured. The gasket 17 is made of, for example, an insulating material, and its surface is coated with asphalt.

For example, the wound electrode body 20 is wound around the center pin 24 with the negative electrode 22 inside the positive electrode 21 here. Further, for example, the length of the negative electrode 22 is slightly longer than that of the positive electrode 21, and the outermost peripheral portion of the wound electrode body 20 is also the negative electrode 22. Separators 23 are provided between the innermost peripheral portion of the negative electrode 22 and the center pin 24 and between the outermost peripheral portion of the negative electrode 22 and the battery can 11, respectively.
Is wound. A positive electrode lead 25 made of aluminum or the like is connected to the innermost peripheral side of the positive electrode 21, and the tip is pulled out from the wound electrode body 20 and welded to the safety valve mechanism 15 to connect the battery cover 14 to the electric power Connected. A negative electrode lead 26 made of nickel or the like is connected to the outermost peripheral side of the negative electrode 22, and the tip is pulled out from the wound electrode body 20 and welded to the battery can 11 to be electrically connected.

The positive electrode 21 has the above-described structure.
In some cases, the positive electrode active material layer is provided only on one side, not both sides, of the end on the innermost peripheral side. Center pin 2
This is to reduce the step at the beginning of winding when winding around the center 4.

The negative electrode 22 is, for example, similar to the positive electrode 21,
It has a structure in which negative electrode active material layers are provided on both surfaces of a negative electrode current collector, respectively. Further, as in the case of the positive electrode 21, a negative electrode active material layer may be provided only on one side of the innermost peripheral end. The negative electrode current collector is, for example, copper (Cu).
It is preferably made of a metal foil such as a foil, a nickel foil or a stainless steel foil, and is preferably porous like the positive electrode current collector 210. This is because the adhesive strength with the negative electrode active material layer can be increased. In addition, the negative electrode lead 2
Reference numeral 6 is attached to the negative electrode current collector.

The negative electrode active material layer contains, for example, one or more of a lithium metal or lithium alloy, or a carbon material, an oxide or a polymer material capable of inserting and extracting lithium ions. It is configured. Among them, a carbon material is preferable because the change in the crystal structure that occurs during charge and discharge is very small. As the carbon material, for example, pyrolytic carbons, cokes, graphites,
Examples include glassy carbons, organic polymer compound fired bodies, carbon fibers and activated carbon. Among them, cokes include pitch coke, needle coke, petroleum coke, etc. An organic polymer compound fired body is obtained by firing a polymer material such as phenol resin or furan resin at an appropriate temperature to carbonize. Means what you do.

The oxide capable of inserting and extracting lithium includes metal oxides. Among them, oxides containing a transition metal are preferable, and iron oxide, ruthenium oxide,
Crystalline compounds or amorphous compounds mainly composed of molybdenum oxide, tungsten oxide, titanium oxide, tin oxide, silicon oxide, etc. can be used as the negative electrode active material. desirable.

The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass therethrough while preventing current short circuit due to contact between the two electrodes. The separator 23 is made of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. May be laminated.

The electrolyte is a solution in which a lithium salt is dissolved in an organic solvent, and exhibits ion conductivity by ionization of the lithium salt. As the electrolyte,
For example, a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent is used. As a non-aqueous solvent for dissolving the electrolyte, it is premised that a relatively high dielectric constant such as ethylene carbonate is used as a main solvent, but in order to complete the battery of the present embodiment, a low viscosity of a plurality of components is further required. It is necessary to add a solvent.

As the high dielectric constant solvent, propylene carbonate, butylene carbonate, vinylene carbonate, sulfolane, butyrolactone, valerolactone and the like can be used. Examples of low-viscosity solvents include symmetric or asymmetric chain carbonates such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate, and carboxylate esters such as methyl propionate and ethyl propionate, and trimethyl phosphate and phosphoric acid. Phosphate esters such as triethyl can be used, and good results can be obtained even when two or more kinds are used in combination.

In particular, when a graphite material is used for the negative electrode, ethylene carbonate is preferred as a main solvent of the non-aqueous solvent, but a compound having a structure in which a hydrogen atom of ethylene carbonate is replaced by a halogen element is also preferred.

Although it is reactive with a graphite material like propylene carbonate, it is partially substituted with ethylene carbonate as a main solvent or a compound having a structure in which a hydrogen atom of ethylene carbonate is replaced with a halogen element. By substituting with a two-component solvent, good characteristics can be obtained.

The second component solvents include propylene carbonate, butylene carbonate, vinylene carbonate, 1,2-dimethoxyethane, 1,2-dimethoxymethane, γ-butyrolactone, valerolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 3
-Dioxolane, 4-methyl, 1,3-dioxolane,
Sulfolane, methylsulfolane, and the like can be used.

Of these, carbonate solvents such as propylene carbonate, butylene carbonate, and vinylene carbonate are preferred, and the amount added is 40 mol%.
Or less, more preferably 20 mol% or less.

As the electrolyte dissolved in such a non-aqueous solvent, any electrolyte used in this type of battery can be used by mixing one or more kinds. LiPF ₆ is preferable as the main component in the case of single use or mixed use, but other than LiClO ₄ , LiAsF ₆ ,
BF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, C
F ₃ SO ₃ Li, LiN (CF ₃ SO ₂ ) ₂ , LiC
(CF ₃ SO ₂ ) ₃ , LiCl, LiBr and the like can also be used.

As the positive electrode active material, a lithium composite metal oxide which is a material having a spinel structure as described above and contains a sufficient amount of lithium is preferable. The spinel structure can be easily confirmed by X-ray diffraction analysis.

Since the present invention aims at achieving a particularly high capacity, the positive electrode 21 has a charge / discharge of 250 mAh or more per gram of the negative carbonaceous material in a steady state (for example, after repeating charge / discharge about 5 times). It is necessary to contain lithium equivalent to the capacity, and more preferably to contain lithium equivalent to the charge / discharge capacity of 300 mAh or more.

It is not always necessary to supply all of the lithium from the positive electrode material. In short, it is sufficient that lithium is present in the battery system at a charge / discharge capacity of 250 mAh or more per gram of the carbonaceous material. The amount of lithium can be determined by measuring the discharge capacity of the battery.

This secondary battery can be manufactured, for example, as follows.

First, a positive electrode 21 and a negative electrode 22 are formed. The method for manufacturing the positive electrode 21 is as described above. For the negative electrode 22, for example, a carbon material and a binder such as polyvinylidene fluoride are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to form a paste. This is a negative electrode mixture slurry. The negative electrode mixture slurry is applied to both surfaces of a negative electrode current collector made of a metal foil, and the solvent is dried. Then, the slurry is compression-molded by a roller press or the like.

Subsequently, the positive electrode lead 2 is connected to the positive electrode current collector 210.
5 is attached by welding or the like, and the anode lead 26 is attached to the anode current collector by welding or the like. after that,
The positive electrode 21 and the negative electrode 22 are wound with the separator 23 interposed therebetween, and the distal end of the negative electrode lead 26 is welded to the battery can 11, and the distal end of the positive electrode lead 25 is welded to the safety valve mechanism 15. The negative electrode 22 is sandwiched between the pair of insulating plates 12 and 13 and housed inside the battery can 11. Positive electrode 2
After storing the first and negative electrodes 22 inside the battery can 11,
The electrolyte is injected into the battery can 11 and impregnated in the separator 23. After that, the battery cover 14, the safety valve mechanism 15, and the PTC element 16 are fixed to the open end of the battery can 11 by caulking through the gasket 17. Thereby, the secondary battery shown in FIG. 2 is formed.

In the secondary battery having such a configuration, when charged, lithium ions are separated from the lithium-manganese composite oxide, which is the active material of the positive electrode 21, and pass through the separator 23 via the electrolytic solution. It is occluded by the negative electrode 22.
Thereafter, when discharging is performed, lithium ions are released from the negative electrode 22, pass through the separator 23 via the electrolytic solution, return to the positive electrode 21, and are occluded by the lithium-manganese composite oxide. Here, the ratio (T2 + T3) / T1 of the thickness (T2 + T3) to the thickness T1 of the positive electrode current collector of the lithium-manganese composite oxide constituting the positive electrode 21 is 2.0 or more, and (T2 + T3) Is defined to be 200 μm or less, so that the positive electrode 21 has a high ratio of the active material to the battery capacity, and has a short moving distance of lithium ions in the electrolytic solution. The diffusion of lithium ions proceeds sufficiently, and the discharge capacity does not decrease.

As described above, in this embodiment, the ratio (T2 + T3) / T1 of the thickness (T2 + T3) of the positive electrode active material layer to the thickness T1 of the positive electrode current collector is 2.0 or more, and (T2 + T3 ) Is defined to be 200 μm or less. Therefore, by constructing a secondary battery using this positive electrode, it is possible to have a high energy density and excellent heavy load characteristics and low temperature characteristics. .

[0056]

EXAMPLES Further, specific examples of the present invention will be described in detail.

Example 1 First, a positive electrode 21 was manufactured as follows. Lithium carbonate 1.
0 mol and 2.0 mol of manganese dioxide were mixed, and this mixture was calcined in air at a temperature of 800 ° C. for 15 hours. X-ray diffraction measurement was performed on the obtained material.
It coincided well with the peak of LiMn ₂ O ₄ registered in the S file.

[0058] The LiMn ₂ O ₄ was ground and laser diffractometry cumulative 50% particle diameter obtained by the 15μm of LiMn ₂
O ₄ powder was used. A positive electrode mixture was prepared by mixing 91 parts by weight of this LiMn ₂ O ₄ powder, 5.5 parts by weight of flake graphite as a conductive agent, 0.5 parts by weight of carbon black, and 3 parts by weight of polyvinylidene fluoride as a binder. Was adjusted and dispersed in N-methylpyrrolidone to form a slurry (paste).

Using a strip-shaped aluminum foil having a thickness of 15 μm as the cathode current collector 210, the above-mentioned cathode mixture slurry is uniformly applied to both sides of the current collector, dried, and then compression-molded to form the strip-shaped cathode 21. Produced. At this time, the thickness (T2 + T3) of the active material layer was 200 μm. Therefore, (T
2 + T3) / T1 was 13.3.

The negative electrode 22 was manufactured as follows.

For 100 parts by weight of coal-based coke serving as a filler, coal-tar pitch serving as a binder is added to 3 parts.
After adding 0 parts by weight and mixing at about 100 ° C., the mixture was compression-molded with a press to obtain a precursor of a carbon molded body. This precursor is
The carbon material molded body obtained by heat treatment at 000 ° C. or less is further impregnated with a binder bitch melted at 200 ° C. or less, and heat-treated at 1000 ° C. or less.
The firing step was repeated several times. Thereafter, the carbon molded body was heat-treated at 2700 ° C. in an inert atmosphere to obtain a graphitized molded body, and then pulverized and classified to produce a graphite powder.

A mixture of 90 parts by weight of the sample powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder was prepared to prepare a negative electrode mixture, and the mixture was dispersed in N-methylpyrrolidene as a solvent to obtain a slurry ( (Paste).

Using a 10 μm-thick strip-shaped copper foil as the negative electrode current collector, a negative electrode mixture slurry was applied to both sides of the current collector, dried, and then compression-molded at a constant pressure to form a strip-shaped negative electrode 2.
2 was produced.

Next, the strip-shaped negative electrode 22 and the strip-shaped positive electrode 21 manufactured as described above were separated by a thickness of 2 as shown in FIG.
A negative electrode 22, a separator 23, a positive electrode 21, and a separator 23 were laminated in this order via a separator 23 made of a 5 μm microporous polypropylene film, and then wound many times to produce a spiral electrode body having an outer diameter of 18 mm.

The spiral electrode body thus manufactured is
It was stored in a nickel-plated iron battery can 11. The insulating plate 13 is disposed on both upper and lower surfaces of the spiral electrode, the aluminum positive electrode lead 25 is led out from the positive electrode current collector 210, and the nickel negative electrode lead 26 is led out from the negative electrode current collector to the battery cover 14. And welded to the battery can 11.

In this battery can 11, a mixed solvent of ethylene carbonate and dimethyl carbonate in an equal volume
An electrolytic solution in which PF ₆ was dissolved at a ratio of 1.5 mol / l was injected. Next, the battery can 11 is caulked via an insulating sealing gasket 17 coated with asphalt to fix the safety valve mechanism 15 having a current cut-off mechanism, the PTC element 16 and the battery lid 14, thereby improving the airtightness of the battery. The cylindrical non-aqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

Example 2 T1 = 20 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 180 μm. (T2 + T3)
/ T1 was 9.0.

[Embodiment 3] T1 = 30 μm, T2 + T3
= Cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that it was 160 µm. (T2 + T3) /
T1 was 5.3.

Embodiment 4 T1 = 20 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 150 μm. (T2 + T3) /
T1 was 7.5.

[Embodiment 5] T1 = 30 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 120 μm. (T2 + T3) /
T1 was 4.0.

Embodiment 6 T1 = 20 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 70 μm. (T2 + T3) / T
1 was 3.5.

Embodiment 7 T1 = 30 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 75 μm. (T2 + T3) / T
1 was 2.5.

Comparative Example 1 T1 = 15 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that = 18 μm. (T2 + T3) /
T1 was 1.2.

Comparative Example 2 T1 = 30 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 45 μm. (T2 + T3) /
T1 was 1.5.

Comparative Example 3 T1 = 20 μm, T2 + T3
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that = 220 μm. (T2 + T3) /
T1 was 11.0.

Comparative Example 4 T1 = 30 μm, T2 + T3
= Cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 240 μm was used. (T2 + T3) /
T1 was 8.0.

With respect to the battery manufactured as described above,
The following three types of tests were performed.

First, at a constant current of 0.5 A under an environment of 23 ° C.,
A constant-temperature low-load battery capacity test is performed in which constant-current constant-voltage charging is performed with a maximum voltage of 4.2 V and a charging time of 4.0 hours, and discharge is performed at a constant current of 0.5 A and a final voltage of 2.75 V in an environment of 23 ° C. Was. FIG. 3 shows the relationship between (T2 + T3) / T1 and the room temperature low load battery capacity C1. (T2 + T3) / T1 is
Comparative Examples 1 and 2, which are less than 2, have the disadvantage that the ratio of the thickness of the current collector to the thickness of the active material layer is large, so that the amount of the active material is small and the battery capacity at room temperature and low load is small. However, Examples 1 to 7 and (Comparative Examples 3 and 4) where (T2 + T3) / T1 was 2.0 or more did not show such a defect.

Next, a constant current of 0.5 A under an environment of 23 ° C.
A constant-temperature low-load battery capacity test is performed in which constant-current constant-voltage charging is performed with a maximum voltage of 4.2 V and a charging time of 4.0 hours, and discharge is performed at a constant current of 3.0 A and a final voltage of 2.75 V in an environment of 23 ° C. Was. The heavy load characteristic is represented by a ratio C2 / C1 of the discharge capacity C2 in the normal temperature heavy load battery capacity test and the discharge capacity C1 in the normal temperature low load battery capacity test. FIG. 4 shows (T2 + T3)
And shows the relationship between C2 / C1. (T2 + T3) is 200 μ
In Comparative Examples 3 and 4, which were larger than m, the disadvantage that the heavy load characteristics deteriorated was observed. This is because the active material layer is thick, so that the active material near the current collector can be used at low temperature and low load discharge,
Although sufficient discharge capacity was obtained, during normal temperature heavy load discharge, the lithium ion diffusion speed of the lithium manganese composite oxide could not catch up with the movement speed of lithium ions in the electrolyte, and the activity of the portion near the current collector was not sufficient. It is considered that the discharge capacity was reduced because the substance could not be used. On the other hand, 20
In Examples 1 to 7 and Comparative Examples 1 and 2 each having a size of 0 μm or less, such a defect was not found.

Next, a constant current of 0.5 A under an environment of 23 ° C.
Constant current constant voltage charging was performed with a maximum voltage of 4.2 V and a charging time of 4.0 hours.
A low-temperature low-load battery capacity test was conducted in which the battery was discharged to a constant current of 0.5 A and a final voltage of 2.75 V after being left for a while. The low-temperature characteristics are represented by a ratio C3 / C1 of the discharge capacity C3 in the low-temperature low-load battery capacity test and the discharge capacity C1 in the normal-temperature low-load battery capacity test. FIG. 5 shows the relationship between (T2 + T3) and C3 / C1. Comparative Example 3 in which (T2 + T3) is larger than 200 μm
In No. 4, a defect that the low-temperature characteristics deteriorate was observed. this is,
Since the active material layer is thick, the lithium-manganese composite oxide has a sufficient lithium ion diffusion rate during low-temperature discharge at room temperature, so the active material near the current collector can be used, and sufficient discharge capacity can be obtained. However, at the time of low-temperature low-load discharge, the lithium ion diffusion rate of the lithium-manganese composite oxide became slow, and the active material in a portion close to the current collector could not be used. On the other hand, in Examples 1 to 7 and Comparative Examples 1 and 2, which were 200 μm or less, such a defect was not found.

From the above results, the thickness T1 of the current collector of the positive electrode
And the thickness of the active material layer (T2 + T3) is set to 2.0 ≦ (T2 + T
3) By defining the relationship of / T1 and (T2 + T3) ≦ 200 μm, a battery excellent in heavy load characteristics and low-temperature characteristics can be obtained without impairing the battery capacity. Note that in this embodiment, LiMn is used as the positive electrode active material.
_{Although 2} O ₄ was used, if it has a spinel structure,
General formula Li _X Mn ₂ O ₄ (0.95 ≦ x ≦ 1.25,
0.01 ≦ y ≦ 0.20, M is Ti, Cr, Fe, C
It is apparent that the same effect can be obtained by using an active material represented by at least one metal selected from o, Ni, Zn, and Al).

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and can be variously modified. For example, in the above embodiments and examples, the configuration of a cylindrical secondary battery having a wound structure has been specifically described by way of example. However, the present invention provides a cylindrical secondary battery having another configuration. The present invention can also be applied to batteries.

[0083]

According to the positive electrode of the present invention as described above, according to the present _{invention, Li X Mn 2-Y M} Y O 4 (0 as the positive electrode active material layer.
95 ≦ y ≦ 1.25, 0.01 ≦ y ≦ 0.20, M is
A material containing at least one metal selected from Ti, Cr, Fe, Co, Ni, Zn, and Al) is used, and the thickness T1 of the positive electrode current collector and the thickness of the active material layer (T2 + T
3) is 2.0 ≦ (T2 + T3) / T1, and (T2 + T
3) Since the relationship was set so as to satisfy ≦ 200 μm,
By using this positive electrode to constitute the secondary battery of the present invention, it is possible to obtain a secondary battery in which the density of the active material contributing to the battery capacity is kept high and the discharge capacity does not decrease at heavy load and at low temperature. Can be. That is, a secondary battery having high energy density and excellent heavy load characteristics and low temperature characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a positive electrode used in a battery according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of an entire battery according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a ratio (T2 + T3) / T1 of a thickness T1 of a positive electrode current collector to a thickness (T2 + T3) of an active material layer of the present invention and a normal temperature low load discharge capacity C1.

FIG. 4 is a characteristic diagram showing a relationship between a thickness (T2 + T3) of a positive electrode active material layer of the present invention and a ratio C2 / C1 of a normal temperature low load discharge capacity C1 and a normal temperature heavy load discharge capacity C2.

FIG. 5 is a characteristic diagram showing a relationship between a thickness (T2 + T3) of a positive electrode active material layer of the present invention and a ratio C3 / C1 of a low-temperature low-load discharge capacity C1 and a low-temperature low-load discharge capacity C3.

[Explanation of symbols]

210: positive electrode current collector, 211A, 211B: positive electrode active material layer, 21: positive electrode, 22: negative electrode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yosuke Hosoya 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Masayuki Nagamine 1 Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Address 1 Sony Energy Tech Co., Ltd. F-term (reference) 5H003 AA01 AA02 BB02 BB05 BC05 BD00 BD02 5H014 AA04 CC01 EE05 EE10 HH01 HH06 5H029 AJ03 AJ06 AK03 AL02 AL06 AL07 AL08 AL12 AL16 AM02 AM03 BJ04 AM05 HJ02 HJ04

Claims (2)

[Claims] 1. A positive electrode including a strip-shaped positive electrode current collector and strip-shaped positive electrode active material layers disposed on both sides of the positive electrode current collector, wherein the positive electrode active material layer is Li _X Mn _2-Y M _Y O ₄ (0.9
5 ≦ x ≦ 1.25, 0.01 ≦ y ≦ 0.20, M is
At least one metal selected from the group consisting of Ti, Cr, Fe, Co, Ni, Zn, and Al), and the sum of the thickness T1 of the positive electrode current collector and the thickness of the positive electrode active material layer (T
2 + T3), wherein 2.0 ≦ (T2 + T3) / T1 and (T2 + T3) ≦ 200 μm. 2. A positive electrode including a belt-like positive electrode current collector, and a band-like positive electrode active material layer disposed on both sides of the positive electrode current collector, lithium, a lithium alloy, a material alloyable with lithium, or lithium. a secondary battery and a strip of negative electrode containing a negative electrode active material layer formed ions from capable of inserting and extracting material, the positive active material _{layer, Li X Mn 2-Y M} Y O 4 (0.9
5 ≦ x ≦ 1.25, 0.01 ≦ y ≦ 0.20, M is
At least one metal selected from the group consisting of Ti, Cr, Fe, Co, Ni, Zn, and Al), and the sum of the thickness T1 of the positive electrode current collector and the thickness of the positive electrode active material layer (T
2 + T3), wherein 2.0 ≦ (T2 + T3) / T1 and (T2 + T3) ≦ 200 μm.