JP4359977B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, many portable electronic devices have appeared, and their size and weight have been reduced. Accordingly, secondary batteries that can be repeatedly charged and discharged as portable power sources for these electronic devices are also required to be reduced in size and weight. For this reason, research and development for improving the energy density of the secondary battery is being actively promoted.
[0003]
As a high-performance secondary battery, for example, a non-aqueous electrolyte secondary battery using a carbon material that can be doped and dedoped with lithium as a negative electrode is lightweight and has a high capacity. It has been put into practical use for portable electronic devices.
[0004]
[Problems to be solved by the invention]
In addition, in order to realize a battery having a high energy density, development of a negative electrode material that has a high doping / undoping capacity per unit volume or weight and that can effectively use lithium is underway.
[0005]
For example, it is known that metals or metalloids such as Al, Ge, Si, Sn, Zn, and Pb are alloyed with lithium, and a secondary battery using a metal material obtained by alloying these as an anode active material. Has been studied (Japanese Patent Laid-Open No. 10-223221). Further, secondary batteries using iron silicide, nickel silicide, and manganese silicide as negative electrode active materials have been studied (Japanese Patent Laid-Open Nos. 5-159780, 8-153517, and 8-153538). Issue gazette). However, non-aqueous electrolyte secondary batteries using these negative electrode active materials have not been put into practical use because of their poor cycle characteristics.
[0006]
The present invention has been proposed in view of such a conventional situation, and by using a metal material as a negative electrode active material, a non-aqueous electrolyte secondary battery having excellent cycle characteristics and higher performance than the conventional one is provided. The purpose is to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the non-aqueous electrolyte secondary battery according to the present invention is capable of reversibly doping and dedoping Li with a negative electrode having a negative electrode active material capable of reversibly doping and dedoping Li. In a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive active material and a non-aqueous electrolyte, the negative active material is a composite comprising at least an alloy phase that is alloyed with Li and an alloy phase that is difficult to alloy with Li An alloy phase containing a textured metal material and at least alloying with Li contains at least one of CoSn ₂ , Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , and Ni ₃ Sn, and an alloy phase that is difficult to alloy with Li is Co ₃ SnC _0.7 or Ni ₃ C.
[0008]
In the non-aqueous electrolyte secondary battery according to the present invention configured as described above, the negative electrode active material contains a composite structure metal material composed of at least an alloy phase alloyed with Li and an alloy phase difficult to alloy with Li. At least the alloy phase alloyed with Li contains at least one of CoSn ₂ , Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , and Ni ₃ Sn, and the alloy phase that is difficult to alloy with Li is Co ₃ SnC _0.7. Or it contains Ni ₃ C. Thereby, a nonaqueous electrolyte secondary battery has a negative electrode which can utilize lithium effectively.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
[0010]
The nonaqueous electrolyte secondary battery to which the present invention is applied includes a positive electrode, a negative electrode, and an electrolyte as basic components. In the present invention, the negative electrode active material contains at least a composite structure metal material composed of an alloy phase alloyed with Li and an alloy phase difficult to alloy with Li.
[0011]
Here, the alloy phase alloyed with Li preferably contains at least one of CoSn, CoSn ₂ , Co ₃ Sn ₂ , Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , and Ni ₃ Sn. The alloy phase that is difficult to alloy with Li preferably contains at least one of Co ₃ SnC _0.7 , Co ₂ C, Co ₃ C, and Ni ₃ C. Furthermore, Sn, Co, Ni, or C may be contained in a single phase in the composite structure metal material. Further, the composite structure metal material is preferably low crystalline.
[0012]
Conventionally, the negative electrode active material of this type of non-aqueous electrolyte secondary battery has contained a metal material composed of an element alloying with Li. Since an element alloying with Li is accompanied by a large volume change when alloying with Li, a non-aqueous electrolyte secondary battery using this negative electrode active material has a problem of poor cycle characteristics.
[0013]
Therefore, when the negative electrode active material contains a composite structure metal material in which an alloy phase that is alloyed with Li and an alloy phase that is difficult to alloy with Li coexist, a change in volume of the negative electrode active material as a whole is suppressed. Thought. Moreover, since the alloy phase which is difficult to alloy with Li contains a metal, it can also be expected to act as a conductive agent. Thus, it was considered that this negative electrode active material can realize improved load characteristics.
[0014]
Therefore, a non-aqueous electrolyte secondary battery using such a negative electrode active material has a negative electrode that can effectively use lithium.
[0015]
Moreover, it is also possible to use together the composite structure metal material as described above and a conventionally known negative electrode active material usually used in this type of non-aqueous electrolyte secondary battery. Examples of the negative electrode active material that can be used in combination include materials that can be doped / undoped with lithium, such as carbon materials.
[0016]
The non-aqueous electrolyte secondary battery includes constituent elements such as a positive electrode and an electrolyte in addition to the negative electrode having the negative electrode active material described above, and other constituent elements similar to the conventional ones can be used.
[0017]
Hereinafter, the components of the non-aqueous electrolyte secondary battery will be described by taking a button-type battery as an example.
[0018]
As shown in FIG. 1, the button-type nonaqueous electrolyte secondary battery 1 includes a negative electrode 2, a negative electrode can 3 that contains the negative electrode 2, a positive electrode 4, a positive electrode can 5 that contains the positive electrode 4, and a positive electrode 4. When the separator 6 disposed between the negative electrode 2 and the insulating gasket 7 is provided and an electrolytic solution is used as an electrolyte, the negative electrode can 3 and the positive electrode can 5 are filled with a nonaqueous electrolytic solution. When a solid electrolyte or gel electrolyte is used as the electrolyte, a solid electrolyte layer and a gel electrolyte layer are formed on the active material layer of the negative electrode 2 or the positive electrode 4.
[0019]
The negative electrode 2 can be reversibly doped and dedoped with Li on the negative electrode current collector, and the negative electrode mixture containing the negative electrode active material and the binder described above is applied and dried. An active material layer is formed. As the negative electrode current collector, for example, copper foil, nickel foil or the like is used.
[0020]
As a binder contained in a negative electrode active material layer, the well-known resin material etc. which are normally used as a binder of the negative electrode active material layer of this kind of battery can be used. Moreover, it is possible to add the well-known additive etc. which are normally used for this kind of battery to a negative electrode active material layer.
[0021]
The negative electrode can 3 accommodates the negative electrode 2 and serves as the external negative electrode of the nonaqueous electrolyte secondary battery 1.
[0022]
The positive electrode 4 has a positive electrode active material layer formed on a positive electrode current collector by applying and drying a positive electrode mixture containing a positive electrode active material capable of reversibly doping and dedoping Li and a binder. It becomes. For example, an aluminum foil or the like is used as the positive electrode current collector.
[0023]
As the positive electrode active material, a metal oxide, a metal sulfide, or a specific polymer can be used depending on the type of the target battery. For example, a metal sulfide or oxide that does not contain lithium, such as CoS ₂ , MoS ₂ , NbSe _2, and V ₂ O _5, can be used as the positive electrode active material.
[0024]
Further, as the positive electrode active material, a general formula LiM _x O ₂ (wherein M represents at least one transition metal, x is different depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10. .) Can be used. As the transition metal M constituting this lithium composite oxide, Co, Ni, Mn and the like are preferable. Specific examples of these lithium composite oxides include LiCoO ₂ , LiSnO ₂ , Li _x Ni _y Co _1-y O ₂ (where x and y vary depending on the charge / discharge state of the battery, and generally 0 <x <1, 0.7 <y <1.02.), LiMnO _{4 and the} like. These lithium composite oxides can generate a high voltage and become a positive electrode active material excellent in energy density.
[0025]
For the positive electrode 4, these positive electrode active materials may be used singly or in combination.
[0026]
As the binder contained in the positive electrode active material layer, a known resin material or the like that is usually used as a binder for the positive electrode active material layer of this type of battery can be used. When a metal lithium foil is used as the positive electrode active material, no binder is necessary.
[0027]
Moreover, it is possible to add the well-known electrically conductive agent, additive, etc. which are normally used for this kind of battery to a positive electrode active material layer.
[0028]
The positive electrode can 5 accommodates the positive electrode 4 and serves as an external positive electrode of the nonaqueous electrolyte secondary battery 1.
[0029]
The electrolyte may be a liquid so-called electrolyte, or may be a solid electrolyte or a gel electrolyte.
[0030]
When the electrolyte is an electrolytic solution, various nonaqueous solvents that are usually used in a nonaqueous electrolytic solution of this type of battery can be used as the nonaqueous solvent. Specific examples include organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxymethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. These non-aqueous solvents may be used alone or in combination of two or more.
[0031]
In addition, when the electrolyte is a solid electrolyte or a gel electrolyte, the polymer materials used include silicon gel, acrylic gel, acrylonitrile gel, polyphosphazene modified polymer, polyethylene oxide, polypropylene oxide, and composite polymers thereof. As a polymer such as poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), poly (vinylidene fluoride-co-tetrafluoroethylene), poly (vinyl Various kinds of vinylidene fluoride-co-trifluoroethylene) and mixtures thereof can be used, but of course, the present invention is not limited thereto.
[0032]
As the light metal salt dissolved (compatible) in the electrolyte, a salt of a light metal such as lithium, sodium, or aluminum can be used, and can be determined as appropriate according to the type of the battery.
[0033]
For example, when configuring a lithium ion secondary battery, specifically, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB (C ₆ H ₆ ), LiSn (SO ₂ ). A lithium salt such as CF ₃ ) can be used.
[0034]
The separator 6 separates the positive electrode 4 and the negative electrode 2, and a known material that is normally used as a separator for this type of non-aqueous electrolyte secondary battery can be used. For example, a non-woven fabric, a polymer film made of a porous material (specifically, polypropylene or the like) having liquid permeability is used. When a solid electrolyte or gel electrolyte is used as the electrolyte, the separator 6 is not necessarily provided.
[0035]
The insulating gasket 7 is incorporated in and integrated with the negative electrode can 3. The insulating gasket 7 is for preventing leakage of the non-aqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5.
[0036]
In the non-aqueous electrolyte secondary battery 1 configured as described above, the negative electrode active material contains at least a composite structure metal material composed of an element that is alloyed with Li and an element that is difficult to alloy with Li. Accordingly, the nonaqueous electrolyte secondary battery 1 has a very high capacity and excellent cycle characteristics.
[0037]
Further, the alloy phase alloyed with Li contains at least one of CoSn, CoSn ₂ , Co ₃ Sn ₂ , Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , and Ni ₃ Sn. The secondary battery 1 has improved cycle characteristics. Furthermore, the alloy phase that is difficult to alloy with Li contains at least one of Co ₃ SnC _0.7 , Co ₂ C, Co ₃ C, or Ni ₃ C, so that the non-aqueous electrolyte secondary battery 1 has a cycle. The characteristics are further improved.
[0038]
In addition, the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited in shape, such as a cylindrical shape, a square shape, and a button shape, and may be any size such as a thin shape and a large size.
[0039]
【Example】
Hereinafter, a nonaqueous electrolyte secondary battery to which the present invention is applied will be described based on specific experimental results.
[0040]
Here, as a sample, first, a plurality of composite structure metal materials to be a negative electrode active material were produced, and then a plurality of nonaqueous electrolyte secondary batteries using these negative electrode active materials were produced. And the battery characteristic was evaluated with respect to the difference of a composite structure metal material using these samples.
[0041]
Sample 1
The method for producing the negative electrode is as follows. First, the composite structure metal material used as a negative electrode active material was produced. First, Co powder, Sn powder, and graphite powder were weighed so as to have a weight ratio of 6.8: 6.9: 1 to obtain a mixed powder. Next, 5 g of this mixed powder is placed in a ball mill pot, sealed in an argon atmosphere, subjected to ball mill operation for 27 hours using 25 steel balls having a diameter of 10 mm, and classified to a particle size of 75 μm or less. A composite structure metal material was obtained.
[0042]
Next, 75 parts by weight of the composite structure metal material sample prepared as described above as the negative electrode active material, 20 parts by weight of graphite powder as the conductive agent, and 5 parts by weight of polyvinylidene fluoride as the binder A negative electrode mixture was prepared by mixing. Next, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to obtain a negative electrode mixture slurry. And this negative mix slurry was uniformly apply | coated to the SUS mesh form used as a negative electrode collector, and it was made to dry, and the negative electrode active material layer was formed.
[0043]
The SUS mesh on which the negative electrode active material layer was formed was punched into a disk shape with a diameter of 15.5 mm to obtain a negative electrode. One negative electrode carries 50 mg of a negative electrode active material.
[0044]
Further, as the positive electrode, a lithium metal foil having a thickness of 1.85 mm was punched into substantially the same shape as the negative electrode. As the electrolytic solution, a nonaqueous electrolytic solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / l in an equal volume mixed solvent of propylene carbonate and dimethyl carbonate.
[0045]
The positive electrode obtained as described above was accommodated in a positive electrode can, the negative electrode was accommodated in a negative electrode can, and a separator was disposed between the positive electrode and the negative electrode. A coin-type test cell was manufactured by injecting a non-aqueous electrolyte into the positive electrode can and the negative electrode can, and crimping and fixing the positive electrode can and the negative electrode can. A polypropylene microporous membrane was used as the separator.
[0046]
Sample 2
A test cell was produced in the same manner as Sample 1 except that the ball mill operation was performed for 40 hours when producing the composite structure metal material.
[0047]
Sample 3
A test cell was produced in the same manner as Sample 1 except that the ball mill operation was performed for 60 hours when producing the composite structure metal material.
[0048]
Sample 4
As a composite material of the composite structure metal material, a sample is used except that a mixed powder obtained by weighing Ni powder, Sn powder, and graphite carbon powder so that the weight ratio is 16.3: 3.3: 1 is used. A test cell was prepared in the same manner as in Example 1.
[0049]
Sample 5
As a negative electrode active material, a test cell was prepared in the same manner as in Sample 1, except that a composite tissue metal material in which 5 g of mixed powder was placed in an agate mortar and thoroughly mixed with a pestle was used.
[0050]
Sample 6
A test cell was prepared in the same manner as Sample 1, except that a mixed powder obtained by weighing Co powder and Sn powder so as to have an atomic ratio of 1: 2 was used as a composite material of the composite structure metal material.
[0051]
Sample 7
A test cell was prepared in the same manner as Sample 1 except that a mixed powder obtained by weighing Ni powder and Sn powder so as to have a weight ratio of 2: 1 was used as a composite material of the composite structure metal material.
[0052]
Next, the X-ray diffraction pattern was measured for the composite structure metal material of each sample produced as described above. The measurement conditions of powder X-ray diffraction are as follows.
[0053]
X-ray light source: CuKα ray (monochromatized by graphite monochromator)
X-ray output: 40 kV to 100 mA
Divergent slit: 1/2 deg
Confusion slit: 1/2 deg
Receiving slit: 0.15mm
Measurement angle: 30 ° ≦ 2θ ≦ 50 °
[0054]
FIG. 2 shows an X-ray diffraction pattern of the composite structure metal material produced in Sample 3. From FIG. 2, it can be seen that the composite structure metal material produced in Sample 3 contains Co ₃ SnC _0.7 . In this composite structure metal material, in theory, CoSn ₂ , Co ₃ SnC _0.7 and graphite phase are mixed at a weight ratio of 24: 72: 4 by mixing Co powder, Sn powder and graphite powder in the above-described weight ratio. Obtained in proportion. However, in FIG. 2, the diffraction peak due to a phase other than the Co ₃ SnC _0.7 phase was not observed because the composite structure metal material of Sample 3 has a low content of CoSn ₂ and graphite phase. In addition, it was confirmed by X-ray diffraction that the composite structure metal material produced in Samples 1 and 2 contains Co ₃ SnC _0.7 .
[0055]
It was confirmed by X-ray diffraction that the composite structure metal material produced in Sample 4 contains Ni ₃ C. In this composite structure metal material, in theory, Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , Ni ₃ Sn and Ni ₃ C are mixed in a weight ratio by mixing Ni powder, Sn powder and graphite powder in the above-described weight ratio. Is obtained in a ratio of 8.3: 8.3: 8.3: 75.
[0056]
The composite structure metal material produced in Sample 5 includes CoSn, CoSn ₂ , Co ₃ Sn ₂ , Ni ₃ Sn ₄ , Ni ₃ Sn ₂ , Ni ₃ Sn, which are alloy phases alloyed with Li by X-ray diffraction. In addition, it was confirmed that none of Co ₃ SnC _0.7 , Co ₂ C, Co ₃ C, or Ni ₃ C, which are alloy phases difficult to alloy with Li, was contained.
[0057]
FIG. 3 shows the X-ray diffraction pattern of the composite structure metal material produced in Sample 6. From FIG. 3, it can be seen that the composite structure metal material produced in Sample 6 contains CoSn ₂ .
[0058]
It was confirmed by X-ray diffraction that the composite structure metal material produced in Sample 7 contains Ni ₃ Sn ₄ and / or Ni ₃ Sn ₂ .
[0059]
Next, for the test cells of Sample 1 to Sample 7 manufactured as described above, a charge / discharge test was performed to evaluate the battery characteristics, and the battery characteristics were evaluated. The characteristic evaluation method is shown below.
[0060]
<Evaluation of battery characteristics>
First, constant current charging was performed for each test cell at a current value of 0.2 mA / cm ² , and when the inter-terminal voltage reached 0.0 V (Li ⁺ / Li), the current value was narrowed down to a current value of 0. Charging was terminated when it reached 01 mA / cm ² or less. Next, constant current discharge was performed with a current value of 0.2 mA / cm ² , and the discharge was terminated when the battery voltage dropped to 1.5 V (Li ⁺ / Li). This process was defined as one cycle, and a discharge capacity of up to 5 cycles was obtained. Then, the capacity retention rate S = C (N) / C (1) × 100 [%] was obtained. In the capacity retention rate S, C (1) represents the discharge capacity at the first cycle, and C (N) represents the discharge capacity at the Nth cycle. Moreover, all of this measurement was performed at normal temperature (23 degreeC).
[0061]
FIG. 4 shows the relationship between the battery capacity retention rate of each sample obtained as described above and the charge / discharge cycle.
[0062]
As is apparent from FIG. 4, the alloy phase that is difficult to alloy with Li contained in the composite structure metal material contains at least one of Co ₃ SnC _0.7 , Co ₂ C, Co ₃ C, or Ni ₃ C. The non-aqueous electrolyte secondary batteries 1 to 4 have better capacity retention ratios than the non-aqueous electrolyte secondary batteries of Sample 6 and Sample 7 in which no alloy phase that is difficult to alloy with Li exists.
[0063]
Accordingly, in the composite structure metal material, the alloy phase that is difficult to be alloyed preferably contains at least one of Co ₃ SnC _0.7 , Co ₂ C, Co ₃ C, or Ni ₃ C. As a secondary battery, it was found that the cycle characteristics were more excellent.
[0064]
In addition, when synthesizing the composite structure metal material, Samples 1 to 4 mixed by ball mill operation to be surely alloyed have a better capacity retention rate than Sample 5 which is only mixed for 30 minutes in an agate mortar. Therefore, it was found that the cycle characteristics of the non-aqueous electrolyte secondary battery were further improved by reliably alloying when the composite structure metal material was synthesized.
[0065]
【The invention's effect】
As is clear from the above description, the non-aqueous electrolyte secondary battery according to the present invention contains a composite structure metal material in which the negative electrode active material is composed of at least an alloy phase alloyed with Li and an alloy phase difficult to alloy with Li. Therefore, the cycle characteristics are excellent.
[0066]
In particular, the alloy phase of Li alloyed, of the _{C oSn 2, N i 3 Sn} 4, Ni 3 Sn 2, Ni 3 Sn, contain at least one, Li alloyed hard alloy phase, Co ₃ SnC _0.7 or of Ni 3 _C, by containing at least one non-aqueous electrolyte secondary battery, and further improved cycle characteristics, and a high-performance unprecedented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery to which the present invention is applied.
FIG. 2 is a view showing an X-ray diffraction pattern of a composite structure metal material produced in Sample 3. FIG.
FIG. 3 is a view showing an X-ray diffraction pattern of a composite structure metal material produced in Sample 6. FIG.
FIG. 4 is a characteristic diagram showing the relationship between the capacity retention rate and the charge / discharge cycle of the non-aqueous electrolyte secondary batteries of Samples 1-7.
[Explanation of symbols]
1 Nonaqueous electrolyte secondary battery, 2 negative electrode, 3 negative electrode can, 4 positive electrode, 5 positive electrode can, 6 separator, 7 insulating gasket

Claims (3)

A non-aqueous electrolyte comprising a negative electrode having a negative electrode active material capable of reversibly doping and dedoping Li, a positive electrode having a positive electrode active material capable of reversibly doping and dedoping Li, and a non-aqueous electrolyte In secondary batteries,
The negative electrode active material contains a composite structure metal material composed of at least an alloy phase that is alloyed with Li and an alloy phase that is difficult to be alloyed with Li, and the alloy phase that is at least alloyed with Li is CoSn ₂ , Ni ₃ Sn _4. , Ni ₃ Sn ₂ , Ni ₃ Sn, a non-aqueous electrolyte secondary battery containing Co ₃ SnC _0.7 or Ni ₃ C as an alloy phase that is difficult to alloy with Li . The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material contains a single phase of graphite. The non-aqueous electrolyte secondary battery according to claim 1, wherein the composite structure metal material has a particle size of 75 μm or less.

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