JP2002093463A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery having a large capacity, excellent life performance, and improved safety. SOLUTION: In this nonaqueous electrolyte battery provided with a positive electrode containing a material storing or releasing lithium ions and a negative electrode having metal lithium, a current collector made of copper is used for the negative electrode, a porous polymer solid electrolyte is provided in the battery, and the capacity density of the positive electrode is set to 400 mAh/cm2 or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a non-aqueous electrolyte battery.

[0002]

2. Description of the Related Art With the spread of various small portable electronic devices such as cellular phones and portable electronic terminals in recent years, secondary batteries as power sources for these devices play an important role. In particular, lithium secondary batteries and lithium ion batteries using a non-aqueous electrolyte have been spotlighted because they have higher energy densities than aqueous solution batteries such as nickel-cadmium storage batteries or nickel-hydrogen storage batteries.

[0003] Currently available lithium ion batteries include a positive electrode plate containing a positive electrode active material composed of a composite oxide of a transition metal such as lithium cobalt oxide and a negative electrode active material composed of a carbon-based material such as graphite. The battery comprises a negative electrode plate, a separator such as polyethylene or polypropylene, and an electrolytic solution in which a lithium salt such as LiPF ₆ is dissolved in various carbonates such as ethylene carbonate.

[0004] On the other hand, lithium secondary batteries using metallic lithium for the negative electrode can have higher energy density than the above-mentioned lithium ion batteries. Low capacity due to low charge / discharge efficiency, and short circuit is likely to occur due to dendritic deposition of metallic lithium during charge / discharge,
There is a disadvantage that the life is short, and because of the high reactivity of metallic lithium, it is difficult to ensure safety, and it has not been put to practical use.

[0005] In a non-aqueous electrolyte battery, a flammable organic solvent is generally used as an electrolyte, and therefore, there is a possibility that heat and smoke are generated due to misuse of the battery.
For this reason, it is necessary to use various safety elements, and there has been a problem that the energy density in consideration of the weight and volume of these elements is low and the cost is high.

To overcome this problem, many attempts have been made to use polymer electrolytes having lower reactivity with the electrodes than the electrolyte. However, since the diffusion coefficient of lithium ions in the polymer electrolyte is small, there is a problem that the charge / discharge characteristics at a high rate are poor. To solve this problem,
It has been proposed that a polymer electrolyte be made porous and an electrolyte be contained in the pores, and some reports have been made (Summary of the 39th Battery Symposium, 1998, p.3).
37).

[0007]

SUMMARY OF THE INVENTION A lithium secondary battery using lithium metal is subject to repeated charge / discharge cycles.
There is a problem that the capacity is reduced due to low charge / discharge efficiency of the metal lithium, and a dendrite of the metal lithium is generated at the time of charging to cause a short circuit and shorten the life. Further, there is a problem that it is difficult to ensure safety because of high reactivity of metallic lithium. In addition, there is a problem that fine lithium metal particles that are difficult to discharge accumulate in the vicinity of the negative electrode, and the current collecting performance of the negative electrode plate is reduced. When the temperature rises due to the heat generated by the short circuit, the lithium metal particles that are difficult to discharge and accumulate may melt or react with oxygen generated by decomposing from the positive electrode active material, generating a large amount of heat. May be impaired. In addition, these phenomena appear remarkably in charge / discharge at a high rate, that is, when the current density is large.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a nonaqueous electrolyte battery having a large capacity, excellent life performance, and improved safety.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a nonaqueous electrolyte battery comprising a positive electrode plate containing a substance capable of inserting and extracting lithium ions and a negative electrode plate provided with metallic lithium, wherein the negative electrode plate comprises copper. A current collector, a porous polymer solid electrolyte in the battery, and a positive electrode having a capacity density of 40
0 mAh / cm ² or more. Also,
A solid polymer film containing carbon particles is provided between the positive electrode and the negative electrode, and the solid polymer film has an ion conduction path.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A battery according to the present invention is a non-aqueous electrolyte battery comprising a positive electrode plate containing a substance capable of inserting and extracting lithium ions, and a negative electrode plate comprising metallic lithium.
A current collector made of copper is used for the negative electrode plate, a porous polymer solid electrolyte is provided in the battery, and the capacity density of the positive electrode plate is 400 m
Ah / cm ² or more.

Here, the "capacity density of the positive electrode plate" means the capacitance density of the entire positive electrode plate including the positive electrode mixture including the positive electrode active material, the conductive auxiliary agent, the binder, and the like, and the positive electrode current collector. .

Metal lithium as a negative electrode active material has an extremely large capacity density as compared with carbonaceous materials and the like. To take advantage of this advantage, it is necessary to increase the capacity density of the positive electrode. As the means, it is conceivable to use a positive electrode active material having a large capacity density or to reduce the content of a conductive auxiliary agent or a binder in the positive electrode mixture. When the porous polymer solid electrolyte is present in the positive electrode mixture, in addition to the improvement in safety described later, the porous polymer solid electrolyte also functions as a binder, and the binding in the positive electrode mixture is performed. There is also an advantage that the content of the agent can be reduced.

In the structure of the battery of the present invention, copper is used for the current collector of the negative electrode plate. Since copper has low reactivity with lithium and does not form an alloy, copper functions stably as a current collector of the negative electrode plate for a long time. In addition, copper has a higher electrical conductivity than other stainless steels and the like, so that the polarization in the electrode is small and the current distribution becomes uniform, so that there is an effect that the electrode reaction occurs uniformly. Therefore, it is possible to suppress a reduction in capacity caused by repetition of charge / discharge cycles, generation of dendrites of metal lithium during charging, and generation / accumulation of fine metal lithium particles that are difficult to discharge.

Further, the non-aqueous electrolyte battery according to the present invention comprises:
The porous polymer electrolyte is provided in the battery, preferably at any one or more locations in the positive electrode, the positive electrode surface, the positive electrode hole, the negative electrode, the negative electrode surface, the negative electrode hole, and between the positive electrode and the negative electrode. .

The porous polymer electrolyte used here is preferably swelled or wetted with an electrolytic solution. In the porous polymer electrolyte, ions move in the electrolyte held in the pores, and at the same time, the polymer swelled or wetted with the electrolyte is also ion conductive.

The porous polymer electrolyte which swells or wets with such an electrolytic solution can spread the electrolytic solution uniformly over the entire electrode. Therefore, when a small amount of electrolyte is held in the battery than the amount of electrolyte sufficient to occupy all of the pores such as the pores of the porous polymer electrolyte and the electrodes, that is, the porous polymer electrolyte, Even in the case where a gas portion is left in the hole of the electrolyte or in the hole of the electrode, sufficient battery performance can be obtained by spreading the electrolyte over the entire electrode. In addition, when the amount of the electrolytic solution, which is a flammable organic solvent, can be reduced, there is an effect that the safety can be improved.

Further, the nonaqueous electrolyte battery according to the present invention is more effective when the capacity density of the positive electrode plate is 400 mAh / cm ² or more. Here, the fact that the capacity density of the positive electrode plate is 400 mAh / cm ² or more means, for example, that
In an electrolyte solution in which ethylene carbonate (EC) containing 1 mol / l of LiPF ₆ and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 in a positive electrode single plate test using metallic lithium as a counter electrode and a reference electrode, 80mA
/ Cm ² refers to an electrode capable of discharging for 5 hours or more when discharging to 1.5 V after charging to 4.2 V with a current value corresponding to / cm ² .

In general, when a battery having the same capacity is formed using electrodes having different capacity densities, the use of an electrode having a lower capacity density increases the volume occupied by the positive electrode plate in the battery as compared with a battery having a higher capacity density. There is a need. For this purpose, it is necessary to increase the thickness of the electrode to relatively reduce the volume occupied by the separator and the electrode current collector. When charging and discharging these batteries, even if the same current value is used, the current density per electrode area becomes larger when thick electrodes are used.
The current distribution becomes non-uniform, and the charge / discharge performance particularly at a high rate decreases.

LiCoO ₂ is used as the positive electrode active material of the current lithium ion battery. In this case, the capacity density of the positive electrode plate is as high as about 350 mAh / cm ² . That is, when the current positive electrode plate is used, the same battery capacity can be obtained by using a thicker electrode plate as compared with the case where the capacity density of the present invention is 400 mAh / cm ² or more. Although possible, the current density increases when charging and discharging with the same current, so that it is difficult to make the electrode reaction proceed more uniformly, and the effect of solving the above various problems is reduced. In order to improve the capacitance density of the electrode while maintaining the same electrode thickness, it is necessary to reduce the amount of the conductive material or the binder added, to reduce the thickness of the current collector, or to reduce the pore volume in the electrode. In addition to the above method, a positive electrode active material having a high capacity density can be used.

The present invention is particularly effective when a solid polymer film (polymer film) containing carbon particles is provided between the positive electrode and the negative electrode, and the polymer film has an ion conduction path. Here, the solid polymer film containing carbon particles (polymer film) refers to a film in which carbon particles are contained in a porous polymer solid electrolyte or a film in which carbon particles are contained in polyolefin having micropores. Can be used. In order to prevent a short circuit between the positive electrode and the negative electrode, it is necessary that the solid polymer film (polymer film) containing carbon particles has no electronic conductivity, but a short circuit prevention film is separately provided. If not, that is not the case.

By providing a solid polymer film (polymer film) containing carbon particles between the positive electrode and the negative electrode, carbon particles contained in the polymer film and lithium particles or dendrites that are difficult to discharge due to charge and discharge are provided. Reacts to generate a lithium intercalation substance, which lowers the reactivity and contributes to the safety of the battery. Here, the ion conduction path refers to an electrolyte solution, a solid electrolyte, or the like, through which ions can move.

When assembling the battery, the majority of the carbon particles contained in the polymer film are charged so that the carbon particles present in the polymer film are not charged in preference to the deposition of metallic lithium on the negative electrode when the battery is charged. It must be separated from the negative electrode in electronic conduction. In addition, the carbon particles contained in the polymer film absorb the metallic lithium released from the negative electrode, thereby preventing an internal short circuit and greatly improving the charge / discharge cycle life characteristics.

In the present invention, a lithium alloy or a carbon material can be used regardless of whether metallic lithium is used for the negative electrode. Is obtained. That is, the nonaqueous electrolyte battery including the negative electrode plate including lithium metal includes a battery in which lithium metal is formed for the first time by charging and which does not include lithium metal in a discharged state. In addition, the nonaqueous electrolyte battery including the negative electrode plate including the lithium alloy includes a battery including a metal which is not lithium alloy in a discharged state as an alloy by absorbing lithium for the first time by charging.

In the battery according to the present invention, the following polymer may be used alone or in combination as a material of the solid polymer electrolyte: polyacrylonitrile,
Polyethylene oxide, polyether such as polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate,
Polyvinyl pyrrolidone, polyethylene imine, polybutadiene, polystyrene, polyisoprene, styrene butadiene rubber, nitrile rubber and derivatives thereof. Further, a polymer obtained by copolymerizing various monomers constituting the above polymer may be used.

The compound capable of inserting and extracting lithium as the positive electrode material of the present invention includes inorganic compounds such as a compound represented by the following formula L
i _x MO ₂ or Li _y M ₂ O _4, (where M is one or more transition metals, 0 ≦ x ≦ 1,0 ≦ y ≦ 2) having a composite oxide represented by the tunnel-like holes Oxides and metal chalcogenides having a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , and LiNi _1-x C
_{o x O 2, LiMn 2 O} 4, Li 2 Mn 2 O 4, MnO 2, Fe
O ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , NiOO
H, FeOOH, FeS, LiMnO _{2 and the} like. Examples of the organic compound include a conductive polymer such as polyaniline. Further, the above-mentioned various active materials may be mixed and used regardless of an inorganic compound or an organic compound.

Examples of the material forming an alloy with lithium as the negative electrode material include Al, Si, Pb, Sn, Zn, and Cd, and a mixture thereof may be used. The carbon material used as the negative electrode material may be either graphite or low-crystalline carbon, and the shape may be spherical, fibrous, or massive.

Examples of the solvent for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethyl carbonate and the like. A polar solvent such as formamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof can be used.

The lithium salts dissolved in the non-aqueous solvent include LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiCF ₃
CO ₂ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , Li
Salts such as N (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂ CF ₃ ) ₂ or a mixture thereof may be used.

The short-circuit preventing film (separator) of the non-aqueous electrolyte battery according to the present invention may be a material obtained by impregnating an insulating solution with a microporous polyethylene film, a solid polymer electrolyte, or a solid polymer electrolyte. A gel electrolyte containing a liquid can also be used. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination. Further, when a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolyte contained in the polymer and the electrolyte contained in the pores may be different. Further, the porous polymer solid electrolyte membrane includes a porous polymer solid electrolyte membrane that covers the inside and surface of the electrode plate and the active material itself.

The power generating element according to the present invention may be either a positive electrode plate or a negative electrode plate formed into a thin sheet or foil, laminated in order, or spirally wound. . Also, as the material of the battery case, a sheet in which a metal foil and a resin film are bonded,
Either iron or aluminum may be used.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below using preferred embodiments. [Example 1] LiNi _0.85 Co _0.15 O ₂ as active material
Was mixed at a ratio of 91 wt%, acetylene black at 3 wt%, polyvinylidene fluoride (PVdF) at 6 wt%, and n-methylpyrrolidone (NMP) at a ratio of 10 wt% on an aluminum foil having a width of 20 mm and a thickness of 20 μm. Coated and dried at 150 ° C. to evaporate NMP.
After the above operation was performed on both surfaces of the aluminum foil, it was pressed to obtain a positive electrode. The capacity density of this positive electrode is about 44
It was 0 mAh / cm ² .

A 15 μm-thick metallic lithium foil was attached to both sides of a copper foil having a thickness of 10 μm and a width of 21 mm to form a negative electrode.

A paste obtained by dissolving a polyacrylonitrile (PAN) having a molecular weight of about 100,000 in NMP is applied on a glass plate in a uniform thickness, and then dipped in water to obtain NMP.
By solidifying the PAN by removing the MP, a porous PAN film having a porosity of 50% was manufactured.
After vacuum drying for a period of time to remove water, it was used as a separator.

A solid polymer film containing carbon powder was manufactured as follows. A mixture of NMP, polyacrylonitrile (PAN) having a molecular weight of about 100,000, and spherical graphite powder having a particle size of 2 μm at a weight ratio of 50: 5: 1 was stirred for 10 hours to dissolve PAN in NMP.

The paste produced in this manner is applied on a glass plate in a uniform thickness, and then immersed in water for NMP.
After removing the water, the PAN was solidified and vacuum-dried at 65 ° C. for 10 hours to remove water, thereby producing a PAN film containing graphite particles and having a porosity of 50%. When the polymer solidifies, the path through which NMP escapes in water becomes pores, so that the resulting PAN film containing the spherical graphite powder becomes a porous film having communication holes.

The positive electrode, the negative electrode, the separator, and the PAN film containing the spherical graphite powder manufactured as described above are stacked in the order of the positive electrode, the separator, the PAN film, the negative electrode, the PAN film, and the separator, and wound in a rectangular aluminum case. Was inserted. Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 1: 1.
Inject the electrolytic solution to which 1 mol / l of LiPF ₆ was added,
A battery A according to the present invention having a capacity of about 980 mAh was manufactured. A groove is formed in the aluminum case (a so-called non-return type safety valve), and when the internal pressure of the battery increases, a crack is generated in the groove and the gas inside the battery is released.

Since the PAN swells in the battery due to the electrolytic solution, the PAN containing the separator and the spherical graphite powder
Not only the electrolyte contained in the pores of the AN film, but also the swollen P
AN itself became a polymer electrolyte membrane showing lithium ion conductivity.

Example 2 Instead of the positive electrode plate of Example 1,
LiNi _0.85 Co _0.15 O ₂ and LiCoO ₂ in a weight ratio of 5
A battery B of the present invention was produced in the same manner as in Example 1 except that a positive electrode plate produced using a mixture of 0:50 as an active material was used. The capacity density of this positive electrode plate is about 404 mAh / c.
m ² , and the capacity of the battery was about 900 mAh.

Example 3 Example 1 was used as a negative electrode active material.
A negative electrode plate was manufactured using graphite particles instead of the metallic lithium foil described in the above section. The negative electrode plate has graphite particles (average particle size of 2) as host materials on both surfaces of the current collector.
μm) 92 parts and polyvinylidene fluoride 8 as a binder
And N-methylpyrrolidone was added as appropriate to prepare a paste, which was applied, dried, and then pressed.

A 10 μm thick copper foil was used as the current collector of the negative electrode plate. The thickness of one side of the negative electrode plate active material layer was 15 μm. A battery C of the present invention having a capacity of about 900 mAh was produced in the same manner as in Example 2 except that this negative electrode plate was used. In the battery C of the present invention, the chargeable and dischargeable capacity of the positive electrode active material was set to be larger than the chargeable and dischargeable capacity of the negative electrode active material, and metallic lithium was deposited on the negative electrode active material by charging.

Example 4 As a negative electrode active material, aluminum powder (average particle size of 3 μm) was used instead of graphite particles.
Battery D of the present invention was produced in the same manner as in Example 3 except that m) was used.

Also in the battery D of the present invention, the chargeable / dischargeable capacity of the positive electrode active material was set to be larger than the chargeable / dischargeable capacity of the negative electrode active material, and metallic lithium was deposited on the negative electrode active material by charging.

Comparative Example 1 A comparative battery E was manufactured in the same manner as in Example 2 except that an iron foil was used instead of the copper foil of the negative electrode current collector of Example 2.

[Comparative Example 2] The separator of Example 2 was used instead of the porous PAN film, that is, a PAN film having no pores was produced without performing a porous treatment, and this was used as a separator. Comparative Battery F was produced in the same manner as in Comparative Example 2.

[Comparative Example 3] Instead of the positive electrode plate of Example 2,
A positive electrode plate manufactured using LiCoO ₂ as an active material was manufactured. The capacity density of this positive electrode plate was about 350 mAh / cm ² , and its thickness was larger than that of the positive electrode plate of Example 2. Otherwise in the same manner as in Example 2, a comparative battery G was manufactured. Battery G had a capacity of about 900 mAh.

The batteries A to A of the present invention produced as described above
A life test of 100 cycles was performed using each of D and comparative batteries EG. In the life test, 45
4.2 after constant current charging until reaching 4.2 V at 0 mA
2 hours constant voltage charging at V and 3.0 at 450 mA
The constant current discharge to V was one cycle.

Table 1 shows the cycle life test results of these batteries. However, the average value is shown in Table 1, and the capacity retention rate in the cycle life test was defined as the ratio (%) of the capacity at the 100th cycle to the capacity at the first cycle.

[0048]

[Table 1]

Table 1 shows that all of the batteries A to D of the present invention exhibited a high capacity retention ratio of about 70%, indicating that the cycle life performance was improved. On the other hand, the capacity retention rates of the comparative batteries E and G were low. It is considered that since iron was used as the current collector of the negative electrode plate of the comparative battery E, an alloy with Li was formed and could not be present as a current collector, and its function was lost. In the comparative battery G, the current density was increased due to the use of the thick positive electrode plate, and the current distribution became non-uniform. Further, in the comparative battery F, the reason why the capacity was smaller than the initial value was that diffusion of Li ⁺ ions was difficult because there were no pores in the solid polymer electrolyte, and it was necessary that the solid polymer electrolyte be porous. Was confirmed.

The same results as those of Battery B of the present invention were obtained in Batteries C and D of the present invention. Therefore, even when lithium was formed by charging using graphite or aluminum as the negative electrode active material, the present invention also showed that Confirmed to be valid.

Next, each of these batteries after 100 cycles of charging and discharging was fully charged by the charging method under the same conditions as the cycle test, and then a 3 mm-diameter nail was pierced by penetrating the battery. A safety test was performed. As a result, it was confirmed that in the batteries A to D of the present invention, no smoke or ignition occurred, and there was no problem in safety.

[0052]

According to the present invention, as in the present invention, a current collector made of copper is used for a negative electrode plate provided with metallic lithium, a porous polymer solid electrolyte is provided in a battery, and a capacity density is 400 mAh / c.
By using the positive electrode plate is m ² or more, a high capacity,
A long-life and highly safe nonaqueous electrolyte battery can be provided. In addition, a polymer film containing carbon particles is provided between the positive electrode and the negative electrode, and the polymer film has an ion-conducting passage, so that not only the life performance is improved but also the safety is greatly improved. Since an electrolyte battery can be provided, the industrial value is great.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H021 EE02 EE21 5H029 AJ05 AJ12 AK02 AK03 AK05 AK16 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 AM16 DJ04 DJ07 EJ01 EJ04 EJ12 HJ08 5H050 AA07 AA15 CA16 CB08 CB09 CB12 CB29 DA04 DA07 DA19 EA08 HA08

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode plate containing a substance that occludes and releases lithium ions and a negative electrode plate provided with metallic lithium, wherein a current collector made of copper is used for the negative electrode plate. A non-aqueous electrolyte battery comprising a porous solid polymer electrolyte and a positive electrode having a capacity density of 400 mAh / cm ² or more. 2. The non-aqueous electrolyte battery according to claim 1, further comprising a solid polymer film containing carbon particles between the positive electrode and the negative electrode, wherein the solid polymer film has an ion conduction path.