JP2002343437A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery having superior charging/ discharging cycle characteristics. SOLUTION: This nonaqueous electrolyte battery has between a positive electrode and a negative electrode, a composite layer comprising a first polymer layer which contains an electronic conductive substance which does not react with lithium and a second polymer layer which contains a carbonaceous substance reacting with lithium, the composite layer having ionic conduction paths.

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 In recent years, with the development of electronic devices, the appearance of new high-performance batteries is expected. Currently, so-called lithium-ion batteries using graphite or carbon for the negative electrode and lithium cobaltate or lithium nickelate for the positive electrode have been devised and used as high energy density batteries, but with the expansion of applications, Further, batteries with high performance and high energy density have been demanded.
When lithium metal is used for the negative electrode, a high energy density battery is obtained. However, since the discharge capacity decreases due to dendrite deposition of lithium metal, there is a disadvantage that the life is short.

[0003] In order to improve this, by providing a polymer layer containing carbon particles that occlude lithium between the positive electrode and the negative electrode, lithium released from the negative electrode is captured,
It is proposed to contribute to charging and discharging again (Japanese Patent Application No.
000-048344). However, this method cannot prevent the release of lithium from the negative electrode. Therefore, when the charge and discharge cycle is repeated, the amount of lithium not captured by the polymer layer containing carbon particles increases, resulting in a problem that the discharge capacity decreases.

[0004]

In a battery using lithium metal for the negative electrode, when the charge / discharge cycle is repeated, the lithium metal deposited during charging is released from the negative electrode, and fine lithium metal particles which are difficult to discharge are formed in the vicinity of the negative electrode. The problem is that the capacity is reduced and the capacity is reduced. Even when a polymer layer containing carbon particles that occlude lithium is provided between the positive electrode and the negative electrode, release of lithium from the negative electrode cannot be prevented. Lithium that is not captured by
The problem is that the discharge capacity decreases.

Further, even when a lithium alloy or a carbon material capable of inserting and extracting lithium is used as the negative electrode, the utilization rate of the negative electrode active material is increased in order to increase the energy density of the battery. When the battery is charged at a low rate or at a low temperature, metallic lithium in the form of dendrite precipitates on the surface of the negative electrode active material, and the same problem as in the case of the metallic lithium negative electrode may occur.

The present invention has been made in view of the above problems, and provides a nonaqueous electrolyte battery having excellent charge / discharge cycle characteristics.

[0007]

According to a first aspect of the present invention, in a non-aqueous electrolyte battery, a first polymer layer containing an electron conductive material which does not react with lithium is provided between a positive electrode and a negative electrode. A composite layer with a second polymer layer containing a porous material, wherein the composite layer has an ion conduction path.

According to the first aspect of the present invention, the current collecting property of lithium deposited in the first polymer layer at the time of charging is improved due to the electron conductive material, and the release of lithium at the time of discharging is reduced. And excellent charge / discharge cycle characteristics are obtained.
In addition, the carbonaceous material in the second polymer layer reacts with free lithium particles or dendrites, which are difficult to discharge due to charge and discharge, to generate lithium intercalation substances, and the lithium particles and dendrites react. Thus, lithium particles and dendrites as short-circuit factors can be reduced, and a battery with excellent safety can be obtained.

A second aspect of the present invention is the non-aqueous electrolyte battery, wherein the first polymer layer is provided on the surface of the negative electrode.

According to the second aspect of the present invention, since the dendritic lithium can be discharged, a nonaqueous electrolyte battery having a large capacity can be obtained.

A third aspect of the present invention is the non-aqueous electrolyte battery, wherein at least one of the first polymer layer and the second polymer layer is porous.

According to the third aspect of the present invention, by holding the electrolyte in the pores of the polymer layer, the movement of lithium ions is facilitated, and the charge / discharge characteristics of the nonaqueous electrolyte battery are improved.

According to a fourth aspect of the present invention, in the above nonaqueous electrolyte battery, at least one polymer portion of the first polymer layer or the second polymer layer is ion-conductive.

According to the fourth aspect of the present invention, there is provided a non-aqueous electrolyte battery in which ions can move in the polymer portion of the polymer layer, the ionic conductivity of the entire polymer layer including the pores increases, and the high rate discharge characteristics are excellent. can get.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte battery, comprising a first polymer layer containing an electron conductive substance that does not react with lithium and a carbonaceous material that reacts with lithium between a positive electrode and a negative electrode. And a composite layer with the second polymer layer, wherein the composite layer has an ion conduction path.

By providing the first polymer layer containing an electron conductive substance which does not react with lithium, the current collecting property of lithium deposited in the polymer layer at the time of charging is improved. The amount can be reduced.

In addition, by providing the second polymer layer containing a carbonaceous material that reacts with lithium, the carbonaceous material in the second polymer layer and free lithium particles that are difficult to discharge due to charging and discharging can be provided. The dendrite reacts to generate a lithium intercalation substance, and the reactivity of lithium particles and dendrites decreases. In addition, lithium particles and dendrites as short-circuit factors are reduced, and the lithium intercalation material also contributes to electric discharge, so that a decrease in capacity can be suppressed. Thus, the first polymer layer and the second polymer layer
By using the composite layer with the polymer layer of the above, a nonaqueous electrolyte battery exhibiting excellent charge / discharge cycle characteristics and excellent safety can be obtained.

The nonaqueous electrolyte battery of the present invention comprises a composite layer of a first polymer layer and a second polymer layer between a positive electrode and a negative electrode. The composite layer must have an ion conducting path, since the ions must travel through the composite layer. Here, the ion conduction path means an electrolyte solution or a solid electrolyte in which ions can move, or a combination thereof.
In a battery, the positive electrode and the negative electrode must not be short-circuited, and the composite layer has no electronic conductivity.

In the present invention, the relationship between the first polymer layer and the second polymer layer of the composite layer provided between the positive electrode and the negative electrode is not particularly limited. Further, in addition to the first polymer layer and the second polymer layer, a short circuit prevention film (separator) such as a polyolefin film may be used. Therefore, the order of lamination of the positive electrode, the negative electrode, the first polymer layer, the second polymer layer, and the short circuit prevention film is as follows: a: positive electrode—first polymer layer—second polymer layer—negative electrode; No. 2 polymer layer-first polymer layer-negative electrode, c: positive electrode-short prevention film-first polymer layer-second polymer layer-negative electrode, d: positive electrode-first polymer layer-short circuit prevention film-first 2 polymer layer-negative electrode, e: positive electrode-first polymer layer-second polymer layer-short-circuit prevention film-negative electrode, f: positive electrode-short-circuit prevention film-second polymer layer-first polymer layer-negative electrode , G: positive electrode-second
Polymer layer-short circuit prevention film-first polymer layer-negative electrode,
h: There are patterns such as a positive electrode, a second polymer layer, a first polymer layer, a short circuit prevention film, and a negative electrode.

However, in order to discharge the above-mentioned dendritic lithium, it is preferable that the first polymer layer containing the electron conductive particles which do not react with lithium is provided on the surface of the negative electrode.

In the present invention, when a negative electrode containing lithium metal, a lithium alloy or a carbon material is used, a battery having excellent characteristics can be obtained. Here, the nonaqueous electrolyte battery including the metal lithium anode includes a battery in which metal lithium is formed for the first time by charging and which does not include metal lithium in a discharged state. The nonaqueous electrolyte battery provided with a lithium alloy negative electrode also includes a battery including a metal which is not a lithium alloy as a negative electrode in a discharged state after absorbing lithium for the first time by charging.

The present invention is also applicable to a battery using a lithium metal anode, a mixed anode of lithium metal and carbon, and a lithium alloy or a mixed anode of the alloy and carbon. It is.

In the present invention, lithium ions can be easily transferred by making at least one of the first polymer layer and the second polymer layer porous and holding the electrolyte in the pores. And the charge / discharge characteristics of the battery are improved.

Further, in the present invention, by making at least one polymer portion of the first polymer layer or the second polymer layer ion-conductive, ions can move through the polymer portion of the polymer layer and include the pores. The ionic conductivity of the entire polymer layer is increased, and a nonaqueous electrolyte battery having excellent high-rate discharge characteristics is obtained.

As described above, in the nonaqueous electrolyte battery of the present invention, the discharge performance of the generated lithium particles and lithium dendrite is improved, and the amount of metallic lithium released from the negative electrode is reduced. The characteristics are significantly improved.

In order to improve the charge / discharge cycle characteristics, the porosity of the polymer layer is desirably 10% to 90%, and the pore diameter is desirably 0.003 μm to 10 μm. Here, the porosity of the polymer layer means a ratio of a pore volume obtained by subtracting a volume of a solid material such as a polymer and electron conductive particles and carbon particles from an apparent volume of a layer including pores to the apparent volume. .

In the non-aqueous electrolyte battery according to the present invention, acetylene black, iron, nickel, copper, titanium and the like can be used as the electron conductive substance which does not react with lithium contained in the first polymer layer. Also, the second
Coke, MCMB, mesophase pitch-based carbon fiber, natural graphite, artificial graphite, and the like can be used as the carbonaceous material that reacts with lithium contained in the polymer layer.

In the non-aqueous electrolyte battery according to the present invention, the following polymer materials are used for the first polymer layer containing the electron conductive substance and the second polymer layer containing the carbonaceous material. They may be used alone or as a mixture: polyethers such as polyacrylonitrile, polyethylene oxide, and polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, and polymethacryl. Ronitrile, 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. Different polymer materials may be used for the polymer layer containing the electron conductive particles and the polymer layer containing the carbon particles.

In the battery according to the present invention, the following solvents may be used as the electrolyte solution: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl Sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,
Polar solvents such as 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, and mixtures thereof.

[0030] In the battery according to the present invention, as the lithium salt to be contained in the lithium ion conductive polymer and a non-aqueous electrolyte _solution, LiPF _6, LiBF _4, LiAs
F ₆ , LiClO ₄ , LiSCN, LiI, LiCl,
LiBr, LiCF ₃ CO 2, LiCF ₃ SO ₃ , Li
N (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ )
₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂
A salt such as CF ₃ ) ₂ or a mixture thereof may be used.
Different salts may be used in the ion-conductive polymer and the non-aqueous electrolyte.

Further, a short-circuit preventing film may be used. As the short-circuit preventing film, an insulating polyethylene microporous film impregnated with an electrolytic solution, a solid polymer electrolyte, or a solid polymer electrolyte containing an electrolytic solution may be used. A gelled electrolyte or the like 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 layer is used as the solid polymer electrolyte, the electrolyte contained in the polymer and the electrolyte contained in the pores may be different.

Further, as a compound capable of inserting and extracting lithium as a positive electrode material, an inorganic compound is represented by a composition formula L
i _x MO ₂ or _Li y _M 2 _{O 4,} (where M is a transition metal, 0 ≦ x ≦ 1,0 ≦ y ≦ 2) represented by the composite oxide, an oxide having tunnel-like pores, Metal chalcogenides having a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O
₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O
₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , NiOOH, F
eOOH, 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 irrespective of an inorganic compound or an organic compound.

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

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. . As the material of the battery case,
Any of a sheet in which a metal foil and a resin film are bonded, iron, or aluminum may be used.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to preferred embodiments.

By combining the following positive electrode plate, negative electrode plate, polyacrylonitrile (PAN) layer, first polymer layer, second polymer layer, and separator, the batteries of Examples 1 to 7 and the batteries of Comparative Examples 1 and 2 were combined. Was prepared.

The positive electrode plate comprises 91 parts of lithium-cobalt composite oxide as an active material, 6 parts of polyvinylidene fluoride (PVdF) as a binder, and acetylene black 3 as a conductive agent.
And N-methyl-2-pyrrolidone (NM
P) was added to prepare a paste, and then applied to both sides of a 20 μm-thick aluminum foil serving as a current collector, followed by drying.

The negative electrode plate was manufactured by attaching a metal lithium foil having a thickness of 20 μm to both sides of a copper foil having a thickness of 10 μm as a current collector.

First, a paste obtained by dissolving polyacrylonitrile (PAN) having a molecular weight of about 100,000 in NMP is applied on a glass plate in a uniform thickness, dried, and dried.
Was removed to solidify the PAN to form a PAN layer.

Next, polyacrylonitrile (PAN) having a molecular weight of about 100,000 and acetylene black as an electron conductive substance which does not react with lithium have a weight ratio of 9%.
The mixture was mixed at 0:10 and NMP was added.
After stirring for 0 hour, the PAN was dissolved in NMP. The paste prepared in this manner is applied on a glass plate at a uniform thickness, and then dried to remove NMP, thereby obtaining a P
The AN was solidified to produce a non-porous first polymer layer containing acetylene black particles, which was designated as a first polymer layer a. Further, after applying the paste in a uniform thickness on a glass plate, the PAN is solidified by immersion in water to remove NMP, thereby forming a porous first polymer layer containing acetylene black particles. It was manufactured and used as a first polymer layer A.

The weight ratio of PAN and spherical graphite particles as a carbonaceous material for storing lithium is 70:30.
And the mixture with NMP added was stirred for 10 hours to dissolve PAN in NMP. The paste prepared in this manner is applied on a glass plate in a uniform thickness, and then dried to remove NMP, thereby solidifying the PAN to form a second polymer layer having no pores containing graphite particles. This was used as the second polymer layer b. Further, after applying the paste in a uniform thickness on a glass plate, the paste is immersed in water to remove NMP, thereby obtaining PA.
Solidifies N to form a porous second material containing graphite particles.
Was produced, and this was used as the second polymer layer B.

When the porous first polymer layer and the porous second polymer layer are prepared, when the PAN solidifies, the path through which NMP escapes in water is a hole. A porous layer having pores was obtained.
The PAN layer was vacuum dried at 65 ° C. for 10 hours to remove water.

As the short-circuit preventing film (separator), a polyethylene separator having a porosity of 40% and a thickness of 25 μm was used.

The positive electrode, the negative electrode, and the P
The AN layer, the first polymer layer, the second polymer layer, and the separator are combined, and these are sequentially stacked and wound to form a square aluminum case having a height of 47.0 mm, a width of 22.2 mm, and a thickness of 7.0 mm. Was inserted. Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 and an electrolyte to which 1 mol / l of LiPF ₆ was added was injected. The capacity of the completed battery is about 90
It became 0 mAh. Table 1 shows the configuration of the electrode group of the manufactured battery.
Summarized in

[0045]

[Table 1]

Using the two cells of the battery (A) according to the present invention and the comparative battery (B) manufactured as described above, 1
A 00 cycle life test was performed. In the life test, as charging conditions, after constant current charging until reaching 4.3 V at 180 mA, constant voltage charging at 4.3 V was performed for a total of 10 hours.
The discharge conditions were a constant current of 180 mA up to 3.0 V, which was one cycle. Further, each of the batteries after 100 cycles of charging and discharging was disassembled, and the amount of dendritic metallic lithium generated in the battery was investigated.

Table 2 shows the results of the life tests of these batteries. However, in Table 2, the capacity retention rate was defined as the ratio (%) of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle in the cycle test. Table 2
Shows the average value of two cells of each battery.

[0048]

[Table 2]

The following is clear from Table 1. The batteries of Examples 1 to 7 and Comparative Examples 1 and 2 (A
1), the first cycle discharge capacity showed almost the same value. However, the capacity retention ratio was 86% or more for the batteries (A to G) of Examples 1 to 7, whereas it was 82% or less for the batteries (H, I) of Comparative Examples 1 and 2. A great difference was seen between the example and the comparative example. That is, it was found that the battery of the example of the present invention had better charge / discharge cycle characteristics than the battery of the comparative example.

Next, the capacity retention rates of the batteries (A to G) of Examples 1 to 7 were compared. From the comparison between Examples 1 and 3 (Batteries A and C) and the comparison between Examples 2 and 4 (Batteries B and D), the batteries (C and C) of Examples 3 and 4 in which the first polymer layer was provided on the negative electrode surface were used. D) had a slightly higher capacity retention than the batteries of Examples 1 and 2 (A and B) in which the first polymer layer was provided on the positive electrode side. The batteries (E to G) of Examples 5 to 7 in which at least one of the first polymer layer and the second polymer layer was porous were the batteries of Examples 1 to 4 in which the polymer layer was not porous. (A
To D), the capacity retention ratio was large, albeit slightly.

Further, as a result of the disassembly inspection, in the batteries (A to G) of Examples 1 to 7, almost no lithium metal liberated inside the batteries was confirmed, whereas in Comparative Example 1
In the batteries (H and I) of Nos. 2 and 3, a large amount of powdery metallic lithium was attached to the separator.

As described above, the battery according to the present invention comprises, between the positive electrode and the negative electrode, a first polymer layer containing an electron conductive material that does not react with lithium, and a second polymer layer containing a carbonaceous material that reacts with lithium. By providing a composite layer consisting of layers, the current collecting property of metallic lithium deposited on the negative electrode by charging is improved, so that the amount of liberated lithium from the negative electrode is reduced, and as a result, the discharging property of lithium is improved, and It is considered that the obtained charge-discharge cycle characteristics were obtained.

[0053]

As described above, the present invention relates to a non-aqueous electrolyte battery comprising a first polymer layer containing an electron conductive material which does not react with lithium, a carbonaceous material which reacts with lithium, between the positive electrode and the negative electrode. A composite layer with a second polymer layer containing a material is provided, and the composite layer has an ion conduction path.

According to the present invention, the current collecting property of lithium deposited in the first polymer layer at the time of charging is improved due to the electron conductive material, the liberation of lithium at the time of discharging can be reduced, and an excellent charge can be obtained. Discharge cycle characteristics are obtained. In addition, the carbonaceous material in the second polymer layer reacts with free lithium particles or dendrites, which are difficult to discharge due to charge and discharge, to generate lithium intercalation substances, and the lithium particles and dendrites react. Is reduced. Then, lithium particles and dendrite as short-circuit factors are reduced, and a non-aqueous electrolyte battery excellent in safety can be provided.

Continued on the front page F-term (reference) 5H029 AJ05 AJ12 AK02 AK03 AK05 AK16 AK18 AL06 AL07 AL11 AL12 AL18 AM02 AM03 AM04 AM05 AM07 AM16 BJ12 BJ13 CJ08 CJ22 DJ04 DJ08 EJ04 EJ12 HJ12 5H050 AA07 CA07 CB04 CB11 CB12 CB29 DA03 DA09 DA19 EA09 EA10 EA23 FA02 FA04 FA17 GA10 GA22 HA12

Claims (4)

[Claims] 1. A composite layer comprising a first polymer layer containing an electron conductive substance that does not react with lithium and a second polymer layer containing a carbonaceous material that reacts with lithium, between a positive electrode and a negative electrode, The non-aqueous electrolyte battery according to claim 1, wherein the composite layer has an ion conduction path. 2. The non-aqueous electrolyte battery according to claim 1, wherein the first polymer layer is provided on the surface of the negative electrode. 3. The non-aqueous electrolyte battery according to claim 1, wherein at least one of the first polymer layer and the second polymer layer is porous. 4. The non-aqueous electrolyte battery according to claim 1, wherein at least one polymer portion of the first polymer layer or the second polymer layer is ion-conductive.