JP2006073369A - Non-aqueous electrolyte secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery in which charge and discharge capacity density can be increased, while charge and discharge cycle characteristics can be enhanced. <P>SOLUTION: This is the non-aqueous electrolyte secondary battery which is equipped with a cathode 1 that contains a cathode active material having reflecting angles 2θ of peak positions of diffraction pattern by X-ray diffraction method at least at 40±2°, 47±2°, and 68±2°, a cathode 2 that contains a material that stores and releases lithium ions, and a non-aqueous electrolyte 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nonaqueous electrolyte secondary battery and a method for manufacturing the same, and more particularly to a nonaqueous electrolyte secondary battery including a positive electrode including a positive electrode active material and a method for manufacturing the same.

Conventionally, as a high energy density secondary battery, a nonaqueous electrolyte secondary battery that charges and discharges by moving lithium ions between a positive electrode and a negative electrode using a nonaqueous electrolyte is known. In this conventional non-aqueous electrolyte secondary battery, a lithium-containing transition metal oxide such as LiCoO ₂ is used for the positive electrode, and a metal containing lithium or a carbon material capable of inserting and extracting lithium is used for the negative electrode. As the non-aqueous electrolyte, a non-aqueous electrolyte is used in which an electrolyte made of a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate. In recent years, the non-aqueous electrolyte secondary battery has been used as a power source for various portable devices. Along with the increase in power consumption due to the multifunctional use of portable devices, a non-aqueous electrolyte secondary battery having a higher energy density is demanded.

  In patent document 1, in order to improve energy density, using the aluminum alloy by which lithium was doped beforehand as a metal containing lithium used for a negative electrode is proposed.

JP-A-7-105934

However, in the conventional non-aqueous electrolyte secondary battery disclosed in Patent Document 1, the lithium-containing transition metal oxide such as LiCoO ₂ used for the positive electrode has a large mass and a small number of reaction electrons. There is a problem that it is difficult to sufficiently increase the capacity (capacity density) per mass. In addition, since LiCoO ₂ having a layered structure is used for the positive electrode, there is an inconvenience that when a large amount of lithium contained in the positive electrode is extracted during charging, the crystal structure (layered structure) of LiCoO ₂ is destroyed. . For this reason, there arises a disadvantage that the amount of lithium available for charging and discharging is limited. As a result, the charge / discharge capacity density is reduced, and it is difficult to improve the charge / discharge cycle characteristics.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to increase the charge / discharge capacity density and to improve the charge / discharge cycle characteristics. And providing a non-aqueous electrolyte secondary battery.

  Another object of the present invention is to provide a non-aqueous electrolyte secondary battery that can easily produce a non-aqueous electrolyte secondary battery that can increase charge / discharge capacity density and improve charge / discharge cycle characteristics. It is to provide a manufacturing method.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, a nonaqueous electrolyte secondary battery according to a first aspect of the present invention has a reflection angle 2θ at the peak position of a diffraction pattern by an X-ray diffraction method of at least 40 ± 2 degrees and 47 ±. A positive electrode including a positive electrode active material at 2 degrees and 68 ± 2 degrees, a negative electrode including a material that absorbs and releases lithium ions, and a nonaqueous electrolyte are provided.

In the non-aqueous electrolyte secondary battery according to the first aspect, as described above, the reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method is at least 40 ± 2 degrees, 47 ± 2 degrees, 68 When the positive electrode contains the positive electrode active material having ± 2 degrees, the reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method is at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. The number of reaction electrons when the positive electrode active material has occlusion and release of lithium is larger than the number of reaction electrons when the positive electrode active material containing a lithium-containing transition metal oxide such as LiCoO ₂ occludes and releases lithium. The positive electrode contains a positive electrode active material having a reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. In the case, Richiu The positive electrode can occlude and release more lithium compared to the case where the positive electrode contains a positive electrode active material containing a platinum-containing transition metal oxide. As a result, when the positive electrode contains a positive electrode active material having a reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. The capacity per unit mass (capacity density) can be increased as compared with the case where the positive electrode contains a positive electrode active material containing a lithium-containing transition metal oxide such as LiCoO ₂ . In addition, the positive electrode includes a positive electrode active material having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. Since the peak position of the diffraction pattern by the X-ray diffraction method of the active material is different from the peak position of the diffraction pattern by the X-ray diffraction method of the lithium-containing transition metal oxide such as LiCoO ₂ , the positive electrode active material has a layered structure such as LiCoO ₂ It is considered that the lithium-containing transition metal oxide is not contained. As a result, even if a large amount of lithium contained in the positive electrode is extracted during charging, the structure of the positive electrode active material does not collapse, so there is no need to limit the amount of lithium that can be used for charging and discharging. As a result, the charge / discharge capacity density can be increased and the charge / discharge cycle characteristics can be improved.

  In the nonaqueous electrolyte secondary battery according to the first aspect, preferably, the positive electrode active material contains lithium and at least one material selected from the group consisting of cobalt, oxygen, and sulfur. If comprised in this way, the positive electrode active material which has easily the reflection angle 2theta of the peak position of the diffraction pattern by X-ray diffraction method to at least 40 +/- 2 degree, 47 +/- 2 degree, and 68 +/- 2 degree Can be formed.

In this case, preferably, the positive electrode active material includes a lithium-containing transition metal sulfide. If comprised in this way, lithium containing transition metal sulfide is accompanied by the oxidation-reduction of sulfur in which two electrons can be taken in and out when inserting and extracting lithium, whereas lithium containing transition such as LiCoO ₂ Since the metal oxide accompanies redox of a transition metal such as cobalt (Co) capable of taking in and out only one electron when inserting and extracting lithium, the number of reaction electrons of the lithium-containing transition metal sulfide (2 Is greater than the number of reaction electrons (one) of the lithium-containing transition metal oxide. Thereby, the positive electrode active material containing lithium-containing transition metal sulfide can occlude and release more lithium than the positive electrode active material containing lithium-containing transition metal oxide. As a result, the positive electrode active material contains a lithium-containing transition metal sulfide, whereby the capacity per unit mass (capacity density) can be increased. In addition, since the positive electrode active material contains a lithium-containing transition metal sulfide, the positive electrode active material does not contain a lithium-containing transition metal oxide such as LiCoO ₂ having a layered structure, so that the lithium contained in the positive electrode during charging Even if many are extracted, the structure of the positive electrode active material does not collapse. This eliminates the need to limit the amount of lithium available for charge / discharge. As a result, the charge / discharge capacity density can be increased and the charge / discharge cycle characteristics can be improved.

  In the non-aqueous electrolyte secondary battery according to the first aspect, preferably, the negative electrode includes one of a carbon material and a silicon material. If a negative electrode made of such a material is used, unlike the case where lithium or the like is used for the negative electrode, a negative electrode active material constituting the negative electrode falls off due to the formation of dendritic (dendritic) precipitates on the negative electrode surface. Can be suppressed. Thereby, it can suppress that charging / discharging capacity density falls.

  A method for manufacturing a nonaqueous electrolyte secondary battery according to a second aspect of the present invention includes lithium in at least one of an oxide and a sulfide, and a transition metal in the oxide and the sulfide. The step of forming a mixture of oxide and sulfide in the state of being contained in at least one of the above, and heat-treating the mixture, the reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method is at least 40 A step of forming a positive electrode active material having ± 2 °, 47 ± 2 °, and 68 ± 2 °, and a step of forming a negative electrode containing a material that absorbs and releases lithium ions.

In the method for manufacturing a nonaqueous electrolyte secondary battery according to the second aspect, as described above, lithium is contained in at least one of an oxide and a sulfide, and a transition metal is contained in the oxide and the sulfide. When the oxide and sulfide mixture is heat-treated in the state of being contained in at least one of the materials, the reflection angle 2θ at the peak position of the diffraction pattern by the X-ray diffraction method is at least 40 ± 2 degrees, Reflection of the peak position of the diffraction pattern by the X-ray diffraction method formed by heat-treating the mixture of oxide and sulfide by forming a positive electrode active material having 47 ± 2 degrees and 68 ± 2 degrees the angle 2 [Theta], at least a 40 ± 2 °, and 47 ± 2 degrees, the number of reaction electrons when the cathode active material absorbing and releasing lithium with a and 68 ± 2 degrees, LiCoO ₂ Since the positive electrode active material containing any lithium-containing transition metal oxide is considered to have a larger number of reaction electrons at the time of occlusion and release of lithium, X formed by heat-treating a mixture of oxide and sulfide When the positive electrode contains a positive electrode active material having a reflection angle 2θ at the peak position of the diffraction pattern by the line diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees, a lithium-containing transition Compared with the case where the positive electrode contains a positive electrode active material containing a metal oxide, the positive electrode can occlude and release more lithium. As a result, lithium is contained in at least one of the oxide and sulfide, and the transition metal is contained in at least one of the oxide and sulfide. A positive electrode active material having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method formed by heat-treating the mixture at least at 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees When the positive electrode includes, the capacity (capacity density) per unit mass can be increased as compared with the case where the positive electrode includes a positive electrode active material containing a lithium-containing transition metal oxide such as LiCoO ₂ . A mixture of oxide and sulfide in a state where lithium is contained in at least one of oxide and sulfide and transition metal is contained in at least one of those oxide and sulfide. To form a positive electrode active material having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. Therefore, the positive electrode active material has a layered structure because the peak position of the diffraction pattern of the positive electrode active material by the X-ray diffraction method differs from the peak position of the diffraction pattern of the lithium-containing transition metal oxide such as LiCoO ₂ by the X-ray diffraction method. It is considered that no lithium-containing transition metal oxide such as LiCoO ₂ is contained. As a result, even if a large amount of lithium contained in the positive electrode is extracted during charging, the structure of the positive electrode active material does not collapse, so there is no need to limit the amount of lithium that can be used for charging and discharging. As a result, the charge / discharge capacity density can be increased and the charge / discharge cycle characteristics can be improved.

  In the nonaqueous electrolyte secondary battery manufacturing method according to the second aspect, preferably, the step of forming the positive electrode active material is performed by heat-treating a mixture of lithium cobaltate and lithium sulfide in an inert atmosphere. Forming a material. If constituted in this way, sulfide (lithium-containing transition metal sulfide) is generated by heat-treating a mixture of oxide (lithium cobaltate) and sulfide (lithium sulfide) under an inert atmosphere. Unlike a case where a mixture of lithium cobaltate and lithium sulfide is heat-treated in the air, a positive electrode active material containing a lithium-containing transition metal sulfide can be easily obtained.

  In this case, preferably, the step of forming the positive electrode active material includes a step of mixing lithium cobaltate and lithium sulfide at substantially the same ratio. If comprised in this way, the reflection angle 2theta of the peak position of the diffraction pattern by X-ray diffraction method will be easily made at least 40 ± by heat-treating a mixture of lithium cobaltate and lithium sulfide in an inert atmosphere. A positive electrode active material having 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees can be obtained.

  Examples of the present invention will be specifically described below.

  In this application, while producing the positive electrode active material of the nonaqueous electrolyte secondary battery by the Example corresponding to this invention, the positive electrode active of the nonaqueous electrolyte secondary battery by the following comparative examples 1 and 2 as a comparative example A material was prepared, and the composition of each positive electrode active material was examined by an X-ray diffraction method. In addition, non-aqueous electrolyte secondary batteries including a positive electrode active material according to an example of the present invention were manufactured and characteristics were examined.

[Preparation of positive electrode active material]
(Example)
Lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) were mixed at a molar ratio of 1: 1 and then molded into pellets. And in the Example, the positive electrode active material was produced by heat-processing a pellet at 800 degreeC for 5 hours by argon (Ar) atmosphere.

(Comparative Example 1)
After mixing lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) at a molar ratio of 1: 1, a positive electrode active material was produced by molding into pellets. That is, in Comparative Example 1, no heat treatment was performed.

(Comparative Example 2)
Lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) were mixed at a molar ratio of 1: 1 and then molded into pellets. And in this comparative example 2, the positive electrode active material was produced by heat-processing a pellet in air | atmosphere at 800 degreeC for 5 hours.

[Composition analysis by X-ray diffraction method]
Next, the results of measurement by XRD (X-Ray Diffraction: X-ray diffraction method) of the positive electrode active materials according to Examples, Comparative Examples 1 and 2 will be described with reference to FIGS. 1 to 3, the horizontal axis represents the reflection angle 2θ (degrees), and the vertical axis represents the X-ray reflection intensity (cps (count per second)). cps is the number of X-ray counts per second. First, as shown in FIGS. 1 and 2, the positive electrode active material according to the example manufactured by heat treatment in an argon (Ar) atmosphere is the positive electrode active material according to the comparative example 1 manufactured without performing the heat treatment. It was found to have a different composition (crystalline phase). Specifically, in the positive electrode active material according to Comparative Example 1 manufactured without heat treatment, peaks of lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) appeared as shown in FIG. On the other hand, in the positive electrode active material according to the example manufactured by heat treatment in an argon (Ar) atmosphere, as shown in FIG. 1, the peaks of lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) (Refer to FIG. 2) hardly appeared. In the positive electrode active material according to the example, new peaks that did not exist before the heat treatment appeared at positions where the reflection angle 2θ was 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. These new peaks are considered to be peaks of a positive electrode active material generated by heat-treating lithium cobalt oxide (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere. Thus, when lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) are heat-treated in an argon (Ar) atmosphere, a mixture of lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) Were found to produce substances with different new compositions (crystalline phases).

Further, as shown in FIGS. 2 and 3, the positive electrode active material according to Comparative Example 2 manufactured by heat treatment in the atmosphere has a composition different from that of the positive electrode active material according to Comparative Example 1 manufactured without performing heat treatment. It turned out to have. Specifically, as described above, in the positive electrode active material according to Comparative Example 1 manufactured without performing the heat treatment, as shown in FIG. 2, lithium cobalt oxide (LiCoO ₂ ) and lithium sulfide (Li ₂ S) A peak appeared. In contrast, in the cathode active material according to Comparative Example 2 which is manufactured is heat-treated in the atmosphere, as shown in FIG. 3, lithium sulfate obtained by lithium sulfide (Li 2 _S) is oxidized (Li ₂ A SO ₄ ) peak appeared. Further, the cathode active material according to Comparative Example 2, similarly to the cathode active material according to Comparative Example 1, the peak of the lithium cobalt oxide (LiCoO ₂₎ appeared. Thus, when lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) are heat-treated in the atmosphere, lithium sulfide (Li ₂ S) is oxidized to produce lithium sulfate (Li ₂ SO ₄ ). On the other hand, it was found that no change occurred in lithium cobalt oxide (LiCoO ₂ ).

Further, as shown in FIGS. 1 and 3, the positive electrode active material according to the example generated by heat-treating lithium cobalt oxide (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere is It can be seen that the positive electrode active material of Comparative Example 2 produced by heat treating lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in the air is also different. That is, in the positive electrode active material according to the example, peaks appeared at the reflection angles 2θ of 40 ± 2 °, 47 ± 2 °, and 68 ± 2 °, whereas in the positive electrode active material according to Comparative Example 2, Then, a peak of lithium sulfate (Li ₂ SO ₄ ) obtained by oxidizing lithium sulfide (Li ₂ S) and a peak of lithium cobaltate (LiCoO ₂ ) appeared.

Here, in the examples, a lithium-containing transition metal sulfide that is a sulfide is generated by heat-treating an oxide (lithium cobaltate) and a sulfide (lithium sulfide) in an inert (Ar) atmosphere. it is conceivable that. That is, the positive electrode active material having a new crystal phase according to the example generated by heat-treating lithium cobalt oxide (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere includes lithium cobalt oxide ( Unlike the positive electrode active material according to Comparative Example 2 produced by heat-treating LiCoO ₂ ) and lithium sulfide (Li ₂ S) in the air, it is considered to be a lithium-containing transition metal sulfide.

[Production of positive electrode]
Lithium-containing transition metal sulfide (80% by mass) as a positive electrode active material according to the example produced as described above, acetylene black (10% by mass) as a conductive agent, and polytetrafluoroethylene as a binder (10% by mass) was mixed and molded by pressing. Then, the positive electrode was produced by making it dry at 110 degreeC under vacuum.

[Preparation of non-aqueous electrolyte]
By adding lithium hexafluorophosphate (LiPF ₆ ) as a solute to a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 3: 7 to a concentration of 1.0 mol / l, A non-aqueous electrolyte was prepared.

[Production of test cell]
FIG. 4 is a perspective view showing a test cell prepared for examining the characteristics of the positive electrode of the nonaqueous electrolyte secondary battery according to the example. Referring to FIG. 4, in the test cell, positive electrode 1 and negative electrode 2 were placed in glass test cell container 10 such that positive electrode 1 and negative electrode 2 were opposed to each other with separator 3 interposed therebetween. The reference electrode 4 was also disposed in the test cell container 10. And the test cell was produced by inject | pouring the nonaqueous electrolyte 5 in the test cell container 10. FIG. In addition, while using the positive electrode by the Example produced as mentioned above as the positive electrode 1, the negative electrode 2 and the reference electrode 3 used lithium metal. Further, as the non-aqueous electrolyte 5, the non-aqueous electrolyte according to the example manufactured as described above was used.

[Charge / discharge test]
A charge / discharge test was performed on the test cell produced as described above. The charging / discharging conditions were as follows: a charging current of 0.5 mA / cm ^{2 and} a charging current of 4.0 V (vs. Li / Li ⁺ ) were charged to a charging end potential of 0.5 mA / cm ^2. The battery was discharged to a discharge end potential of 1.0 V (vs. Li ^/ Li ⁺ ). And this charge / discharge was made into 1 cycle, and the capacity density of the charge / discharge of the 1st cycle was measured. The result is shown in FIG. The capacity density is determined by the following formula.

  Capacity density (mAh / g) = Current flowed (mAh) / Mass of positive electrode active material (g)

As shown in FIG. 5, in the example in which the discharge end potential was set to 1.0 V (vs. Li ^/ Li ⁺ ), the charge capacity density in the first cycle was 250 mAh / g, and the discharge capacity in the first cycle. The density was 278 mAh / g. The average discharge potential in the first cycle was 1.76 V (vs. Li / Li ⁺ ). Thus, it was found that a relatively high initial (first cycle) charge / discharge capacity density can be obtained in the examples. It was also found that reversible charging / discharging can be performed.

As described above, 40 ± 2 °, 47 ± 2 °, and 68 ± produced by heat-treating lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere. In the example using the positive electrode active material having the reflection angle 2θ at the peak position of the diffraction pattern twice, a relatively high initial (first cycle) charge / discharge capacity density can be obtained, and charge / discharge cycle characteristics can be obtained. Can be improved. This is considered to be due to the following reason. That is, in the example, lithium-containing transition metal sulfide having a new crystal phase is generated by heat-treating lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere. it is conceivable that. This lithium-containing transition metal sulfide is accompanied by redox of sulfur capable of taking in and out two electrons when inserting and extracting lithium, whereas a lithium-containing transition metal oxide such as LiCoO ₂ is lithium Occlusion and release are accompanied by redox of a transition metal such as cobalt (Co) capable of taking in and out only one electron. For this reason, it is considered that the number of reaction electrons (two) of the lithium-containing transition metal sulfide is larger than the number of reaction electrons (one) of the lithium-containing transition metal oxide. Thereby, it is considered that the positive electrode active material containing lithium-containing transition metal sulfide can occlude and release more lithium than the positive electrode active material containing lithium-containing transition metal oxide. As a result, an example using a positive electrode active material containing a lithium-containing transition metal sulfide produced by heat-treating lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere Then, it is thought that the capacity | capacitance per unit mass (capacity density) was able to be raised.

In the example, the positive electrode active material manufactured by heat-treating lithium cobalt oxide (LiCoO ₂ ) and lithium sulfide (Li ₂ S) in an argon (Ar) atmosphere has a layered structure of lithium cobalt oxide ( Since it does not contain LiCoO ₂ ), it is considered that the structure of the positive electrode active material does not collapse even if a large amount of lithium contained in the positive electrode is extracted during charging. This eliminates the need to limit the amount of lithium that can be used for charging and discharging, so it is considered that reversible charging and discharging can be performed efficiently. As a result, it was considered that the charge / discharge capacity density was increased and the charge / discharge cycle characteristics could be improved.

  In addition, it should be thought that the Example disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes meanings equivalent to the scope of claims for patent and all modifications within the scope.

  For example, in the above embodiment, an example of producing a lithium-containing transition metal sulfide using lithium cobaltate and lithium sulfide as starting materials has been shown. However, the present invention is not limited thereto, and a lithium-containing transition metal sulfide can be produced. Any material other than lithium cobaltate and lithium sulfide may be used. If lithium and a transition metal are contained in at least one of an oxide and a sulfide as a starting material, a lithium-containing transition metal sulfide is produced using the method for producing a positive electrode active material according to the above example. be able to. Examples of the oxide as a starting material include titanium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, and molybdenum oxide as oxides that do not contain lithium. Examples of the oxide containing lithium include lithium oxide, lithium cobaltate, lithium nickelate, and lithium manganate. Moreover, the sulfide as a starting material includes, for example, titanium sulfide, manganese sulfide, iron sulfide, cobalt sulfide, nickel sulfide, copper sulfide, and molybdenum sulfide as sulfides that do not contain lithium. Moreover, lithium sulfide is mentioned as a sulfide containing lithium.

  Further, in the above embodiment, acetylene black, which is a carbon material, is used as the conductive agent added to the positive electrode. However, the present invention is not limited to this, and a conductive carbon material other than acetylene black is added to the positive electrode. It may be used as an agent. In this case, when the amount of the conductive agent added to the positive electrode is increased, the ratio of the active material in the positive electrode is decreased, so that it is difficult to obtain a high energy density. For this reason, it is preferable that the ratio of the electrically conductive agent added to a positive electrode is 0 to 30 mass%. In addition, the ratio of the conductive agent is more preferably 0% by mass or more and 20% by mass or less, and further preferably 0% by mass or more and 10% by mass or less.

  Further, in the above embodiment, polytetrafluoroethylene was used as the binder to be added to the positive electrode. However, the present invention is not limited to this, and polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polymethacrylate. The same effect can be obtained when at least one material selected from the group consisting of polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, and carboxymethylcellulose is used.

  Moreover, in the said Example, although polytetrafluoroethylene as a binder added to a positive electrode was mixed in the ratio of 10 mass%, this invention is not limited to this, The polytetrafluoroethylene as a binder added to a positive electrode is mixed. The ratio of fluoroethylene should just be 0.1 to 30 mass%. In addition, the ratio of polytetrafluoroethylene is more preferably 0.1% by mass or more and 20% by mass or less, and further preferably 0.1% by mass or more and 10% by mass or less.

  Further, in the above examples, a non-aqueous electrolyte containing a mixed solvent of ethylene carbonate and diethyl carbonate was used. However, the present invention is not limited to this, and if it can be used as a solvent for a non-aqueous electrolyte battery, ethylene carbonate and A solvent other than a mixed solvent with diethyl carbonate may be used. Examples of the solvent other than the mixed solvent of ethylene carbonate and diethyl carbonate include cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, and amides. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Moreover, what fluorinated a part or all of the hydrogen group of cyclic carbonate can also be used, for example, trifluoropropylene carbonate, fluoroethyl carbonate, etc. are mentioned. Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate. Further, those in which some or all of the hydrogen groups of the chain carbonate ester are fluorinated can also be used.

  Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone. The cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3. , 5-trioxane, furan, 2-methylfuran, 1,8-cineole and crown ether. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, Benzyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 0-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether Such fine tetraethylene glycol dimethyl and the like. Examples of nitriles include acetonitrile. Examples of amides include dimethylformamide.

In the above embodiment, the solute is used a non-aqueous electrolyte lithium hexafluorophosphate (LiPF ₆₎ was dissolved in a (electrolyte salt), the present invention is not limited thereto, lithium hexafluorophosphate A nonaqueous electrolyte in which a solute other than the above is dissolved may be used. Examples of solutes other than lithium hexafluorophosphate include, for example, lithium difluoro (oxalato) borate (a substance represented by the chemical formula of Chemical Formula 1 below), LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiC ₄ F. ₉ SO ₃ , LiN (CF ₃ SO ₂ ) _2, LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like. Moreover, you may use the mixture which combined 2 or more selected from the group which consists of an above-described solute as a solute.

  In the above-described embodiments, lithium metal is used as the negative electrode. However, the present invention is not limited to this, and any material other than lithium metal may be used as the negative electrode active material as long as lithium can be occluded and released. Good. Examples of materials that can be used as the negative electrode active material include lithium materials, carbon materials such as graphite, and silicon. Here, since silicon (Si) has a high capacity, a non-aqueous electrolyte battery having a high energy density can be obtained by using a negative electrode including a negative electrode active material made of silicon.

In the above embodiment, lithium sulfide and lithium cobaltate _{(LiCoO 2) (Li 2 S} ) and the molar ratio of 1: After mixing in a ratio of 1, an example of manufacturing a positive electrode active material by heat treatment However, the present invention is not limited to this, and a positive electrode having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method is at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees. If it is possible to produce an active material, after mixing lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S) at a ratio other than 1: 1, a positive electrode active material is produced by heat treatment. May be. In this case, it is preferable to mix as the percentage of lithium sulfide _(Li 2 S) is smaller than the ratio of lithium cobaltate (LiCoO _2).

In the above embodiment, after mixing the lithium cobalt oxide (LiCoO ₂₎ and lithium sulfide _(Li 2 S), under argon (Ar) atmosphere, by heat treatment at 800 ° C., 5 h, the positive electrode active material However, the present invention is not limited to this, and an inert gas other than argon (Ar) is used when heat-treating a mixture of lithium cobaltate (LiCoO ₂ ) and lithium sulfide (Li ₂ S). May be used. Moreover, you may produce a positive electrode active material by heat-processing on conditions other than 800 degreeC or 5 hours.

It is the graph which showed the XRD spectrum of the positive electrode active material produced by heat-processing in argon (Ar) atmosphere by an Example. 6 is a graph showing an XRD spectrum of a positive electrode active material produced without performing heat treatment according to Comparative Example 1. 5 is a graph showing an XRD spectrum of a positive electrode active material produced by heat treatment in the atmosphere according to Comparative Example 2. It is the perspective view which showed the test cell produced in order to investigate the characteristic of the positive electrode of the nonaqueous electrolyte secondary battery by an Example. It is the graph which showed the result of the charging / discharging test done about the test cell corresponding to an Example.

Explanation of symbols

1 Positive electrode 2 Negative electrode 5 Nonaqueous electrolyte

Claims (7)

A positive electrode including a positive electrode active material having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees;
A negative electrode comprising a material that occludes and releases lithium ions;
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte. The positive electrode active material is
With lithium,
The nonaqueous electrolyte secondary battery according to claim 1, comprising at least one material selected from the group consisting of cobalt, oxygen, and sulfur.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the positive electrode active material includes a lithium-containing transition metal sulfide.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode includes any one of a carbon material and a silicon material. A mixture of the oxide and the sulfide in a state where lithium is contained in at least one of the oxide and the sulfide and a transition metal is contained in at least one of the oxide and the sulfide. Forming a step;
By heat-treating the mixture, a positive electrode active material having a reflection angle 2θ at a peak position of a diffraction pattern by an X-ray diffraction method of at least 40 ± 2 degrees, 47 ± 2 degrees, and 68 ± 2 degrees is formed. And a process of
Forming a negative electrode containing a material that occludes and releases lithium ions. A method for manufacturing a non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary according to claim 5, wherein the step of forming the positive electrode active material includes a step of forming a positive electrode active material by heat-treating a mixture of lithium cobalt oxide and lithium sulfide in an inert atmosphere. Battery manufacturing method.   The method for producing a non-aqueous electrolyte secondary battery according to claim 6, wherein the step of forming the positive electrode active material includes a step of mixing lithium cobaltate and lithium sulfide at substantially the same ratio.

Images