JP4365633B2 - Lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery that is mounted on an electronic device or used as a storage battery.
[0002]
[Prior art]
In recent years, lithium secondary batteries have become widespread because they have high energy density, little self-discharge, and can be lightweight. FIG. 2 shows a basic structure of a so-called coin-type lithium secondary battery. The lithium secondary battery 10 includes a negative electrode 3, a positive electrode 4, and a separator 6 disposed between the negative electrode 3 and the positive electrode 4, and these are non-aqueous materials in which a lithium salt is dissolved. It is schematically configured in contact with the electrolyte solvent.
In this lithium secondary battery 10, a negative electrode 3, a separator 6, and a positive electrode 4 are sequentially laminated on a substantially flat cylindrical battery case 1 made of stainless steel or the like, and a sealing plate 2 made of stainless steel or the like is formed thereon. Further, an annular gasket 7 made of polypropylene is disposed between the battery case 1 and the sealing plate 2. The gasket 7 and the sealing plate 2 are fixed by crimping the upper end portion of the battery case 1 inside.
Glass wool filter papers 5 and 5 are inserted between the separator 6 and the positive electrode 4 and the negative electrode 3.
The nonaqueous electrolyte solvent is impregnated in the positive electrode 4, the negative electrode 3, the separator 6, and the glass wool filter papers 5 and 5.
[0003]
In FIG. 3, the principal part enlarged view of this lithium secondary battery 10 is shown. In the lithium secondary battery 10, the positive electrode 4 contains at least one positive electrode active material 11, 11... Such as a lithium-containing transition metal oxide and is opposite to the surface on the separator 6 side. A positive electrode current collector 12 such as an aluminum foil is laminated on the surface. Further, the negative electrode 3 contains a carbon material as a main component as a negative electrode active material, and a negative electrode current collector 13 such as a copper foil is laminated on the surface opposite to the surface on the separator 6 side. Here, for example, a graphite material can be used as the negative electrode 3 (see, for example, Patent Document 1).
[0004]
By the way, the lithium secondary battery is required to have higher performance as the equipment to be mounted has higher performance. For example, the capacity of the lithium secondary battery is required to be increased. Therefore, it has been studied to use metallic lithium or an alloy thereof for the negative electrode for the purpose of increasing the capacity of the lithium secondary battery.
[0005]
[Patent Document 1]
JP 2002-050403 A (Claims, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, a negative electrode made of metallic lithium or an alloy thereof has a large thickness change during expansion / contraction due to charge / discharge, and thus the battery may be deformed. In addition, while charging / discharging was repeated, there was a problem that lithium dendrite, which was a needle-like crystal, was generated and further grown to cause an internal short circuit in the electrode.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium secondary battery that can prevent deformation of the battery and can increase the capacity without causing an internal short circuit.
[0007]
[Means for Solving the Problems]
The lithium secondary battery of the present invention includes a negative electrode containing an inorganic compound powder. Since the negative electrode provided in the lithium secondary battery contains the inorganic compound powder, the change in thickness at the time of expansion / contraction associated with charge / discharge can be reduced, so that deformation of the battery can be prevented. In addition, on the inorganic compound powder, the surface diffusion of lithium ions is fast and also sterically hindered, so that lithium dendrite is not easily generated even when charging and discharging are repeated, and internal short circuit is prevented. Furthermore, since lithium ions move into the inorganic compound powder, the capacity is increased.
[0008]
In the lithium secondary battery of the present invention, the inorganic compound powder, lithium directly chemically react with no metal oxide powder Der Ru gamma - alumina is α- alumina or silica. Since these materials can accelerate the surface diffusion of lithium ions, the generation of lithium dendrite can be further suppressed.
[0009]
The negative electrode preferably contains a conductive material such as carbon black or silver particles. Since the inorganic compound powder has low conductivity, it is possible to reduce the internal resistance of the lithium secondary battery by mixing a conductive material such as carbon black or silver particles.
[0010]
Negative electrode of the above you containing metallic lithium. If the negative electrode contains metallic lithium , the capacity of the lithium secondary battery can be increased .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a lithium secondary battery of the present invention will be described with reference to the drawings. The lithium secondary battery of the present embodiment is a coin-type lithium secondary battery, and has the same basic structure as that shown in FIG. That is, it has the negative electrode 3, the positive electrode 4, and the separator 6 arrange | positioned between the negative electrode 3 and the positive electrode 4, and these are in contact with the non-aqueous electrolyte solvent in which lithium salt was dissolved. It is roughly structured.
In FIG. 1, the principal part enlarged view of the lithium secondary battery of the example of this embodiment is shown. In this lithium secondary battery, the negative electrode 3 is obtained by dispersing inorganic compound powders 15, 15... In a lithium-containing metal 14, and copper is formed on the surface opposite to the surface on the separator 6 side. A negative electrode current collector 13 such as a foil is laminated. The positive electrode 4 contains at least one kind of positive electrode active material 11, 11... Such as a lithium-containing transition metal oxide, and an aluminum foil is provided on the surface opposite to the surface on the separator 6 side. A positive electrode current collector 12 such as is laminated.
[0012]
The inorganic compound powder 15 in the negative electrode 3 is preferably a metal oxide such as γ-alumina, α-alumina, and silica because it is easily available and the surface diffusion of lithium ions is faster.
The inorganic compound powder 15 preferably has a particle size of 0.01 to 10 μm, more preferably 0.05 to 0.5 μm, and particularly preferably around 0.1 μm. If the particle diameter of the inorganic compound powder 15 is in the above range, it is easy to obtain and inexpensive, and therefore, deformation can be prevented and production of lithium dendrite can be suppressed without increasing costs.
[0013]
When the lithium-containing metal 14 is included in the negative electrode 3 and the inorganic compound powders 15, 15... Are dispersed in the lithium-containing metal 14 as in the present embodiment, the lithium-containing metal 14 Inorganic compound powders 15, 15... Can be bound.
As a method for dispersing the inorganic compound powder 15 in the lithium-containing metal 14, for example, the lithium-containing metal 14 and the inorganic compound powders 15, 15... Are mixed and then forcibly mixed with a kneader or the like. Examples include a method of dispersing. By forcibly mixing in this way, the clay-like lithium-containing metal and the inorganic compound powder 15 can be uniformly mixed.
[0014]
As the lithium-containing metal 14 in the negative electrode 3, it becomes possible to increase the capacity. Therefore, the lithium is simple, lithium includes a group 3B element (that is, B, Al, Ga, In, Tl) or a group 4B element (that is, , C, Si, Ge, Sn, Pb) or a group 1A element (ie, Na, K, Rb, Cs, Fr) or a group 2A element (ie, Be, Mg, Ca, An alloy to which Sr, Ba, Ra) is added is preferable.
[0015]
The negative electrode 3 contains the inorganic compound powder 15 in an amount of preferably 20 to 80% by volume, more preferably 30 to 60% by volume, and particularly preferably 40 to 50% by volume. If the negative electrode electrode 3 contains the inorganic compound powder 15 in the above range, the surface diffusion of lithium ions can be accelerated and the negative electrode 3 can be easily molded.
[0016]
As the positive electrode active material 11 in the positive electrode 4, for example, lithium-containing transition metal oxides such as lithium manganate, lithium cobaltate, lithium nickelate, lithium ironate, and lithium vanadate, vanadium oxide, and the like are preferably used. it can.
These positive electrode active materials 11 are bound by a binder 16. Here, as the binder 16, for example, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, an imide resin, an amide resin, or the like can be used.
Moreover, as the separator 6, since it is excellent in a physical property and it is cheap, a porous polypropylene film is used suitably.
[0017]
The lithium secondary battery according to the embodiment described above includes the negative electrode 3 in which the inorganic compound powder 15, 15... Is dispersed in the lithium-containing metal 14, and is expanded and contracted due to charge / discharge. Since the change in thickness of the battery is small, deformation of the battery is prevented. Further, the surface diffusion of lithium ions on the inorganic compound powder 15 is fast and also causes steric hindrance, so that the generation of lithium dendrite is suppressed and internal short circuit is prevented. Furthermore, since the negative electrode 3 contains the lithium-containing metal 14, the capacity is further increased.
[0018]
Note that the present invention is not limited to the above-described embodiments. For example, in the embodiment described above, the negative electrode includes a lithium-containing metal, but the lithium-containing metal may not be included. However, when the lithium-containing metal is not included in the negative electrode, that is, when the inorganic compound powder is simple, it is difficult to bind the inorganic compound powder to each other. . Here, as the binder, for example, a fluorine resin such as polyvinylidene fluoride and polytetrafluoroethylene, an imide resin, an amide resin, or the like can be used.
[0019]
【Example】
( Reference Example 1)
Γ-alumina powder (inorganic compound powder) having an average particle size of 0.1 μm is added to NMP (N-methylpyrrolidone) in which PVdF (polyvinylidene fluoride) is dissolved, and mixed for 1 hour with a mixer. A slurry of alumina: PVdF: NMP = 50: 5: 45 was prepared. And this was formed into a film on a copper foil and dried to form a negative electrode film having a thickness of 50 μm. On the other hand, lithium manganate and carbon black are added to NMP (N-methylpyrrolidone) in which PVdF (polyvinylidene fluoride) is dissolved, mixed with a mixer for 1 hour, and this is formed on an aluminum foil and dried. A positive electrode film having a thickness of 100 μm was prepared.
Next, a separator made of a porous polypropylene film is sandwiched between the negative electrode and the positive electrode, and this is accommodated in an aluminum laminate foil, and then an electrolytic solution 1.0M-LiPF ₆ is contained in the aluminum laminate foil. / Ethylene carbonate + dimethyl carbonate (weight ratio: 1/2) was injected. Next, the liquid inlet was heat sealed to obtain a sheet type lithium secondary battery.
[0020]
( Reference Example 2)
Silicon dioxide (silica) powder having an average particle size of 0.1 μm is added to NMP (N-methylpyrrolidone) in which PVdF (polyvinylidene fluoride) is dissolved, and mixed with a mixer for 1 hour, and SiO ₂ : PVdF: NMP = 50: A 5:45 slurry was prepared. This slurry was formed on a copper foil and dried to form a negative electrode. A separator and a positive electrode were stacked on the negative electrode in the same manner as in Reference Example 1, and a battery was manufactured by pouring an electrolyte solution.
[0021]
( Reference Example 3)
Carbon black (C) with an average particle size of 40 nm is mixed with γ-alumina powder with an average particle size of 0.1 μm, and NMP (N-methylpyrrolidone) in which PVdF (polyvinylidene fluoride) is dissolved is added and mixed with a mixer for 1 hour. Then, a slurry of γ-alumina: C: PVdF: NMP = 45: 5: 5: 45 by weight composition was prepared. This slurry was formed on a copper foil to form a negative electrode. A separator and a positive electrode were stacked on the negative electrode in the same manner as in Reference Example 1, and a battery was manufactured by injecting an electrolyte solution.
[0022]
(Example 1 )
Metal lithium was dissolved, and γ-alumina powder having an average particle size of 0.1 μm was added thereto so that the volume concentration thereof was 50% by volume, and forcedly mixed by a kneader. This mixture was then give foil extrusion with a thickness of 100μm, and a separator of this foil, a negative electrode by causing crimped onto a copper foil as a current collector, in the same manner as in Reference Example 1 in the negative electrode, positive electrode A battery was manufactured by injecting an electrolyte solution.
[0023]
(Comparative example)
A sheet-type lithium secondary battery was obtained in the same manner as in Reference Example 1 except that a commercially available metal lithium foil (thickness: 100 μm) was used as the negative electrode, and this was crimped onto the copper foil.
[0024]
In the sheet-type lithium secondary batteries of Examples , Reference Examples and Comparative Examples, a charge / discharge cycle in which the battery was charged to the upper limit of 4.2 V and discharged to 3.0 V was repeated.
As a result, in the lithium secondary battery of Reference Example 1, a capacity of about 100 Ah / kg was obtained with respect to the weight of γ-alumina, and the expansion and contraction of the negative electrode due to charging / discharging was suppressed, so the battery was not deformed. It was prevented. Further, no significant capacity drop or internal short circuit occurred before 100 cycles.
In Reference Example 2, a capacity of about 120 Ah / kg relative to the weight of silica was obtained, and the battery was not deformed. Further, there was no significant capacity drop or internal short circuit before 100 cycles.
In Reference Example 3, a capacity of about 200 Ah / kg with respect to the weight of γ-alumina was obtained, and further, there was no battery deformation, significant capacity drop before 100 cycles, and no internal short circuit.
In Example 1 , a capacity of about 400 Ah / kg with respect to the weight of γ-alumina was obtained, and further, there was no battery deformation, significant capacity reduction before 100 cycles, and no internal short circuit.
On the other hand, in the lithium secondary battery of the comparative example, although the capacity was high, the negative electrode did not contain inorganic compound powder. Therefore, the lithium secondary battery was deformed by about 10% from before the start of the charge / discharge cycle, and the capacity was about 50 cycles. Decreased and an internal short circuit occurred.
[0025]
【The invention's effect】
According to the lithium secondary battery of the present invention, the thickness change during expansion / contraction associated with charging / discharging can be reduced, so that deformation of the battery can be prevented, lithium dendrite is not easily generated even after repeated charging / discharging, and internal short circuit is prevented. Has been. Furthermore, since lithium ions move into the inorganic compound powder, the capacity is increased.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a main part of an embodiment of a lithium secondary battery according to the present invention.
FIG. 2 is a cross-sectional view of a coin-type lithium secondary battery.
FIG. 3 is an enlarged cross-sectional view showing a main part of a conventional lithium secondary battery.
[Explanation of symbols]
3 Negative electrode 14 Lithium-containing metal 15 Inorganic compound powder

Claims (3)

  It comprises a negative electrode in which an inorganic compound powder composed of any one of γ-alumina, α-alumina, and silica is contained in metallic lithium, and the negative electrode has an inorganic compound powder in a range of 20 to 80% by volume. A lithium secondary battery characterized by being contained. The lithium secondary battery according to claim 1, wherein the negative electrode contains a conductive material. The lithium secondary battery according to claim 1 or 2 the particle size of the inorganic compound powder is characterized in that it is a 0.01 to 10 [mu] m.

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