JP2007242570A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with true density of a cathode active material (cathode filling density) improved, and capable of performing reversible charging and discharging as well as obtaining high discharge capacity density. <P>SOLUTION: The cathode active material contains lithium (Li), Nickel (Ni), and bismuth (Bi). In order to obtain the cathode active material, lithium, nickel, and bismuth are mixed so that a ratio of their mol number is to satisfy in that order: Li:Ni:Bi=x:4:y(4<x≤10, and 0.2≤y<3) with the use as starting materials of, for instance, lithium carbonate (Li<SB>2</SB>CO<SB>3</SB>), nickel hydroxide (Ni(OH)<SB>2</SB>), and bismuth oxide (Bi<SB>2</SB>O<SB>3</SB>). In order to obtain a cathode active material with higher true density, a composition of each element in the cathode active material is preferred to satisfy a relation of Li:Ni:Bi=6:4:1 (mol). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte.

  Currently, non-aqueous electrolyte secondary batteries that use a non-aqueous electrolyte as a secondary battery with a high energy density, for example, charge and discharge by moving lithium ions between the positive electrode and the negative electrode are widely used. Yes.

In such a non-aqueous electrolyte secondary battery, a lithium transition metal composite oxide having a layered structure such as lithium nickelate (LiNiO ₂ ) or lithium cobaltate (LiCoO ₂ ) is generally used as a positive electrode, and lithium as a negative electrode. A carbon material, lithium metal, or lithium alloy that can be occluded and released is used (see, for example, Patent Document 1).

  By using the non-aqueous electrolyte secondary battery, a discharge capacity density of 150 to 180 mAh / g, a potential of about 4 V, and a theoretical capacity density of about 260 mAh / g can be obtained.

In addition, a non-aqueous electrolyte in which an electrolyte salt such as lithium tetrafluoroborate (LiBF ₄ ) or lithium hexafluorophosphate (LiPF ₆ ) is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate is used. ing.

  In recent years, such non-aqueous electrolyte secondary batteries have been used as power sources for portable devices, etc., and higher energy density can be obtained as the power consumption increases due to multifunctional use of portable devices. Development of a nonaqueous electrolyte secondary battery is desired.

At present, in lithium cobaltate (Li _1-x CoO ₂ ) used as a positive electrode of a nonaqueous electrolyte secondary battery, when lithium ions are released by 0.5 (= x) or more, the crystal structure collapses, Reversibility (occlusion and release) decreases. As a result, the obtained discharge capacity density remains at about 160 mAh / g.

On the other hand, in lithium nickelate (Li _1-y NiO ₂ ) having the same crystal structure as LiCoO ₂ , lithium ions can be released to about 0.7 (= y), and therefore LiCoO _{2 of} about 200 mAh / g. A higher discharge capacity density can be obtained.

  However, as lithium ions are released, the crystal structure (crystal system) of the lithium nickelate changes in the order of hexagonal system, monoclinic system, and hexagonal system. Due to this change, the crystal structure of lithium nickelate gradually collapses as in the case of lithium cobaltate, and the reversibility is lowered.

  When using non-aqueous electrolyte secondary batteries as power sources for portable devices, it is important to improve the energy density per unit volume, so it is necessary to increase the positive electrode packing density (true density) per unit volume. There is.

  In order to increase the positive electrode packing density, a method of controlling the particle size and form of the positive electrode active material (for example, see Patent Document 1) has been proposed. However, in this method, the positive electrode packing density is sufficiently increased. Have difficulty.

LiCoO ₂ , which is a positive electrode active material generally used for nonaqueous electrolyte secondary batteries, has a positive electrode packing density of about 5.0 g / cm ³ , and LiNiO _{2 has} a positive electrode packing density of about 4.8 g / cm ³ . However, there is a strong demand to obtain a higher positive electrode packing density.
JP 2000-133249 A JP 2001-222993 A

  Therefore, it is conceivable to use a high-density positive electrode active material as another method for increasing the positive electrode packing density. However, a positive electrode active material capable of performing high-density and reversible charge / discharge is not known.

  An object of the present invention is to improve the true density (positive electrode packing density) of a positive electrode active material, to perform reversible charge / discharge, and to obtain a high discharge capacity density, and a nonaqueous electrolyte secondary battery Is to provide.

  The nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode including a positive electrode active material, a negative electrode, and a nonaqueous electrolyte, and the positive electrode active material includes lithium, nickel, and bismuth.

  In the nonaqueous electrolyte secondary battery according to the present invention, by using a positive electrode active material containing lithium, nickel, and bismuth, the positive electrode packing density (true density) of the positive electrode active material can be improved. In addition, reversible charging / discharging can be performed, and a high discharge capacity density can be obtained. The following reasons can be considered about this.

Usually, when a starting material containing lithium and nickel is fired in air, LiNiO ₂ having a crystal structure belonging to the space group R-3m is obtained. When a starting material containing lithium, nickel, and bismuth is fired as in the present invention, it is considered that a positive electrode active material having a crystal structure different from the crystal structure belonging to the space group R-3m is obtained. Thereby, the true density of the positive electrode active material is improved, reversible charge / discharge can be performed, and a high discharge capacity density can be obtained.

  The composition of the positive electrode active material is Li: Ni: Bi = x: 4: y, where the molar ratio of lithium (Li), nickel (Ni), and bismuth (Bi) is expressed in this order. x is preferably greater than 4 and less than or equal to 10, and y is preferably greater than or equal to 0.2 and less than 3.

  In this case, the true density of the positive electrode active material can be further improved, reversible charging / discharging can be performed, and a higher discharge capacity density can be obtained.

  The composition of the positive electrode active material is Li: Ni: Bi = 6: 4: 1 when the ratio of the number of moles of lithium (Li), nickel (Ni), and bismuth (Bi) is expressed in this order. Is preferred.

  In this case, the true density of the positive electrode active material can be further improved, reversible charging / discharging can be performed, and a higher discharge capacity density can be obtained.

  The negative electrode may be made of lithium metal, lithium alloy, carbon material, or silicon material.

  By using such a material as the negative electrode, lithium ions are favorably occluded and released from the negative electrode. In particular, a higher energy density can be obtained by using a negative electrode made of a carbon material or a silicon material.

  The non-aqueous electrolyte may contain one or more selected from the group consisting of cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles and amides.

  In this case, the cost can be reduced and the safety is improved.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to improve the true density (positive electrode filling density) of a positive electrode active material, it becomes possible to perform reversible charging / discharging and to obtain a high discharge capacity density.

  Hereinafter, the nonaqueous electrolyte secondary battery according to the present embodiment will be described with reference to the drawings.

  The nonaqueous electrolyte secondary battery according to the present embodiment includes a working electrode (hereinafter referred to as a positive electrode), a counter electrode (hereinafter referred to as a negative electrode), and a nonaqueous electrolyte.

  The various materials described below and the thicknesses and concentrations of the materials are not limited to those described below, and can be set as appropriate.

(1) Production of Positive Electrode The nonaqueous electrolyte secondary battery according to the present embodiment includes a positive electrode active material, a positive electrode capable of occluding and releasing lithium, and a negative electrode capable of occluding and releasing lithium. And a non-aqueous electrolyte.

  In the present embodiment, the positive electrode active material includes lithium (Li), nickel (Ni), and bismuth (Bi).

In order to obtain this positive electrode active material, for example, lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and bismuth oxide (Bi ₂ O ₃ ) are used as starting materials, and lithium, nickel, When the ratio of the number of moles of bismuth is expressed in this order, mixing is performed so that Li: Ni: Bi = x: 4: y (4 <x ≦ 10 and 0.2 ≦ y <3).

  And the powder obtained by mixing is shape | molded in the shape of a pellet (small particle), This is calcined for 10 hours, for example in the air of 700 degreeC, Then, this baking is performed in the air of 750 degreeC for 20 hours.

  A positive electrode material is obtained by mixing, for example, 80% by weight of the positive electrode active material, 10% by weight of acetylene black as a conductive agent, and 10% by weight of polyvinylidene fluoride as a binder obtained by performing the main baking.

  This positive electrode material is mixed with, for example, a 10% by weight N-methyl-2-pyrrolidone solution with respect to the positive electrode material to prepare a slurry as a positive electrode mixture.

  Then, after apply | coating the produced slurry on the aluminum foil of a positive electrode electrical power collector with a doctor blade method, a positive electrode active material layer is formed by making it dry in a 110 degreeC vacuum, for example.

  And a positive electrode is completed by attaching a positive electrode tab on the area | region of the aluminum foil which does not form a positive electrode active material.

  The conductive agent added when preparing the positive electrode containing the positive electrode active material is not particularly necessary when using a positive electrode active material having excellent conductivity, but when using a positive electrode active material with low conductivity, It is preferable to add a conductive agent.

  As the conductive agent, any material having electrical conductivity may be used, and at least one of oxide, carbide, nitride, and carbon material that is particularly excellent in electrical conductivity can be used.

  Examples of oxides excellent in conductivity include tin oxide and indium oxide. Examples of the carbide excellent in conductivity include titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), tungsten carbide (WC), and the like.

  Examples of nitrides having excellent conductivity include titanium nitride (TiN), tantalum nitride (TaN), niobium nitride (NbN), and tungsten nitride (WN). Examples of the carbon material having excellent conductivity include ketjen black, acetylene black, and graphite.

  In addition, when the addition amount of the conductive agent is small, it is difficult to sufficiently improve the conductivity of the positive electrode. On the other hand, when the addition amount of the binder is large, the proportion of the positive electrode active material contained in the positive electrode decreases. High energy density cannot be obtained. Therefore, the addition amount of the conductive agent is in the range of 0 to 30% by weight of the whole positive electrode, preferably in the range of 0 to 20% by weight, and more preferably in the range of 0 to 10% by weight.

  In addition, the binder (binder) added when producing the positive electrode is polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, and At least one selected from the group consisting of carboxymethylcellulose and the like can be used.

  In addition, when there is much addition amount of a binder, since the ratio of the positive electrode active material contained in a positive electrode will decrease, a high energy density will no longer be obtained. Therefore, the addition amount of the binder is in the range of 0 to 30% by weight, preferably in the range of 0 to 20% by weight, and more preferably in the range of 0 to 10% by weight of the whole positive electrode.

Here, when a starting material containing lithium and nickel is usually fired in air, LiNiO ₂ having a crystal structure belonging to the space group R-3m is obtained.

  On the other hand, when the starting material containing lithium, nickel, and bismuth is fired as in the present embodiment, it has a crystal structure different from the crystal structure belonging to the space group R-3m and has a true density (positive electrode). A positive electrode active material having a high packing density can be obtained.

  In this embodiment, in order to obtain a positive electrode active material having a high true density, it is only necessary that lithium, nickel, and bismuth are all contained in the positive electrode active material.

  In order to obtain a positive electrode active material having a higher true density, as described above, when the ratio of the number of moles of lithium, nickel, and bismuth is expressed in this order, the composition of each element in the positive electrode active material is: It is preferable to satisfy the relationship Li: Ni: Bi = x: 4: y (4 <x ≦ 10 and 0.2 ≦ y <3).

  Further, in order to obtain a positive electrode active material having a higher true density, it is more preferable that the composition of each element in the positive electrode active material satisfies the relationship of Li: Ni: Bi = 6: 4: 1 (mol). .

(2) Production of non-aqueous electrolyte As the non-aqueous electrolyte, an electrolyte salt dissolved in a non-aqueous solvent can be used.

  Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, amides, and the like, which are usually used as non-aqueous solvents for batteries. Is mentioned.

  Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and the like, and those in which some or all of these hydrogen groups are fluorinated can be used. For example, trifluoropropylene carbonate, fluoro Examples include ethyl carbonate.

  Examples of chain carbonic acid esters include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, and the like. Some of these hydrogen groups are fluorinated. It is possible to use.

  Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone. Examples of 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-cineol, crown ether and the like.

  Examples of 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, pentyl phenyl. Ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-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, tetraethy Glycol dimethyl and the like.

  Nitriles include acetonitrile and the like, and amides include dimethylformamide and the like.

  As an electrolyte salt in this Embodiment, what is generally used as an electrolyte salt of the conventional nonaqueous electrolyte secondary battery can be used.

Specific examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ A non-peroxide soluble in a non-aqueous solvent selected from the group consisting of LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAsF ₆ and lithium difluoro (oxalato) borate is used. In addition, you may use 1 type in the said electrolyte salt, and may use it in combination of 2 or more type.

  In this embodiment, as a nonaqueous electrolyte, a nonaqueous solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 30:70, and lithium hexafluorophosphate as an electrolyte salt to a concentration of 1 mol / l. What was added so that it may become is used.

(3) Configuration of negative electrode In this embodiment, a material capable of inserting and extracting lithium ions is used. Examples of this material include lithium materials, lithium alloys, carbon materials such as graphite, and silicon (Si).

(4) Production of Nonaqueous Electrolyte Secondary Battery A nonaqueous electrolyte secondary battery is produced using the positive electrode, the negative electrode, and the nonaqueous electrolyte as described below.

  FIG. 1 is a schematic explanatory diagram of a test cell of a nonaqueous electrolyte secondary battery according to the present embodiment.

  As shown in FIG. 1, a lead wire is attached to the negative electrode 1 made of, for example, lithium metal under an inert atmosphere, and the lead wire is attached to the positive electrode 2 manufactured as described above.

  Next, the separator 4 is inserted between the negative electrode 1 and the positive electrode 2, and the negative electrode 1, the positive electrode 2, and the reference electrode 3 made of, for example, lithium metal are disposed in the cell container 10.

  And the nonaqueous electrolyte secondary battery as a test cell is produced by inject | pouring into the cell container 10 the nonaqueous electrolyte 5 produced as mentioned above.

(5) Effects in the present embodiment In the present embodiment, the starting material containing lithium, nickel, and bismuth is fired to have a crystal structure different from the crystal structure belonging to the space group R-3m. A positive active material with a high true density can be obtained. In addition, reversible charging / discharging can be performed, and a high discharge capacity density can be obtained.

(A) Example 1
Lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and bismuth oxide (Bi ₂ O ₃ ) were used as starting materials for the positive electrode active material.

  In this example, lithium carbonate, nickel hydroxide, and bismuth oxide were mixed in this order at a molar ratio of 3: 4: y. As this y, a total of 4 types of 0.1, 0.5, 1.0, and 1.5 mol were set.

  And the powder of four types of positive electrode active materials obtained by mixing said substance each was shape | molded in the shape of a pellet (small particle). Thereafter, each of these positive electrode active materials was temporarily fired in an air atmosphere at 700 ° C. for 10 hours, and then main fired in an air atmosphere at 750 ° C. for 20 hours.

  Each positive electrode material was obtained by mixing 80% by weight of the positive electrode active material thus prepared, 10% by weight of acetylene black as a conductive agent, and 10% by weight of polyvinylidene fluoride as a binder.

  Each of these positive electrode materials was mixed with an N-methyl-2-pyrrolidone solution to prepare a slurry as a positive electrode mixture.

  Then, after apply | coating the produced slurry on a positive electrode electrical power collector by the doctor blade method, the positive electrode active material layer was formed by drying in 110 degreeC vacuum, respectively. And the positive electrode 2 was obtained by attaching a positive electrode tab on the area | region of the positive electrode collector which did not form a positive electrode active material layer, respectively. The negative electrode 1 and the reference electrode 3 were made of lithium metal having a predetermined size.

  Further, as the non-aqueous electrolyte 5, a non-aqueous solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 30:70 so that lithium hexafluorophosphate as an electrolyte salt has a concentration of 1 mol / l. What was added was used.

  Using the negative electrode 1, the positive electrode 2, the reference electrode 3, and the non-aqueous electrolyte 5, non-aqueous electrolyte secondary battery test cells (four types in total) were produced based on the above embodiment (FIG. 1).

  In the prepared four types of nonaqueous electrolyte secondary batteries, after charging until the potential of the positive electrode 2 based on the reference electrode 3 reaches 4.5V, discharging is performed until the potential reaches 2.5V. It was. The results are shown in Table 1.

  As can be seen from the results in Table 1, the molar ratio of lithium carbonate, nickel hydroxide, and bismuth oxide was 3: 4: 0.5 (expressed in the molar ratio of each element (Li, Ni, and Bi). In this case, it was found that the initial discharge capacity density of the nonaqueous electrolyte secondary battery using the positive electrode active material in the case of Li: Ni: Bi = 6: 4: 1) was the largest.

  FIG. 2 is a graph showing charge / discharge characteristics of a nonaqueous electrolyte secondary battery using a positive electrode active material when the molar ratio of lithium carbonate, nickel hydroxide, and bismuth oxide is 3: 4: 0.5. It is.

As shown in FIG. 2, plateaus (potential flat portions) were confirmed in the 3.7 V region and the 2.8 V region in the discharge curve. Since the discharge curve of the nonaqueous electrolyte secondary battery using LiNiO ₂ as the positive electrode active material has only one potential flat part, the positive electrode active material of this example is in the space group R-3m of LiNiO _2. It was presumed to have a crystal structure different from the crystal structure to which it belongs.

  Further, as shown in Table 1, even if the amount of bismuth oxide is increased from 0.5 mol (1.0 and 1.5 mol in this example) or decreased (0.1 mol in this example), Both initial discharge capacity densities decreased.

(B) Example 2
Lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and bismuth oxide (Bi ₂ O ₃ ) were used as starting materials for the positive electrode active material.

  In this example, lithium carbonate, nickel hydroxide, and bismuth oxide were mixed in this order at a molar ratio of x: 4: 0.5. As this x, a total of four types of 2, 3, 4, and 5 mol were set.

  And the powder of four types of positive electrode active materials obtained by mixing said substance each was shape | molded in the shape of a pellet (small particle). Thereafter, each of these positive electrode active materials was temporarily fired in an air atmosphere at 700 ° C. for 10 hours, and then main fired in an air atmosphere at 750 ° C. for 20 hours.

  Using the positive electrode active material thus produced, test cells (4 types in total) of nonaqueous electrolyte secondary batteries were produced in the same manner as in Example 1 described above.

  In the prepared four types of nonaqueous electrolyte secondary batteries, after charging until the potential of the positive electrode 2 based on the reference electrode 3 reaches 4.5V, discharging is performed until the potential reaches 2.5V. It was. The results are shown in Table 2.

  From the results in Table 2, the initial discharge capacity density of the non-aqueous electrolyte secondary battery using the positive electrode active material when the molar ratio of lithium carbonate, nickel hydroxide, and bismuth oxide is 3: 4: 0.5. Was found to be the largest.

  Further, even when the amount of lithium carbonate was increased from 3 mol (4 and 5 mol in this example) or decreased (2 mol in this example), both the initial discharge capacity density were reduced.

(C) Example 3
In Example 1 and Example 2, the largest initial discharge capacity density can be obtained, and the positive electrode active when the ratio of the number of moles of lithium carbonate, nickel hydroxide, and bismuth oxide is 3: 4: 0.5 The substance was measured by XRD (X-ray diffractometer).

  FIG. 3 is a profile showing the measurement result of the XRD measurement of the positive electrode active material that was able to obtain the largest initial discharge capacity density.

  In the measurement result of FIG. 3, a sharp peak intensity occurred at a diffraction angle 2θ in the vicinity of 17 ° to 19 °. Compared to this peak intensity, the peak intensity at the diffraction angle 2θ near 20 ° and the diffraction angle 2θ near 50 ° to 70 ° is small, which is considered to be caused by impurities.

  From this result, it is expected that the positive electrode active material contains a large amount of impurities. By removing these impurities, an improvement in the initial discharge capacity density can be expected.

FIG. 4 is an XRD measurement profile of a positive electrode active material LiNiO ₂ that is generally used in a non-aqueous electrolyte secondary battery.

Comparing FIG. 4 with FIG. 3, it was found that the positive electrode active material of this example had a crystal structure different from the crystal structure belonging to the space group R-3m of LiNiO ₂ .

(D) Example 4
In Example 1 and Example 2, the positive electrode active material (the ratio of the number of moles of lithium carbonate, nickel hydroxide, and bismuth oxide was 3: 4: 0.5) that was able to obtain the largest initial discharge capacity density. The powder density was measured by a gas replacement method.

As a result of measuring the powder density of the positive electrode active material, a true density of 5.4 g / cm ³ could be obtained.

This is because LiCoO ₂ , which is a positive electrode active material generally used for nonaqueous electrolyte secondary batteries, has a true density of 5.0 g / cm ³ , a LiNiO ₂ true density of 4.8 g / cm ³ , and LiMn ₂ O ₄ . The true density is greater than 4.3 g / cm ³ .

(E) Evaluation By firing a starting material containing lithium, nickel, and bismuth, a positive electrode active material having a crystal structure different from the crystal structure belonging to the space group R-3m and having a high true density can be obtained. I understood.

  And it turned out that reversible charging / discharging can be performed and the high discharge capacity density can be obtained by using the obtained positive electrode active material for a non-aqueous electrolyte secondary battery.

  In order to obtain a positive electrode active material having a high true density, lithium, nickel, and bismuth need only be contained in the positive electrode active material. To obtain a positive electrode active material having a higher true density, lithium, When the ratio of the number of moles of nickel and bismuth is expressed in this order, the composition of each element in the positive electrode active material is Li: Ni: Bi = x: 4: y (4 <x ≦ 10, and 0. It is preferable to satisfy the relationship of 2 ≦ y <3).

  Further, in order to obtain a positive electrode active material having a higher true density, it is more preferable that the composition of each element in the positive electrode active material satisfies the relationship of Li: Ni: Bi = 6: 4: 1 (mol). I understood it.

  The nonaqueous electrolyte secondary battery according to the present invention can be used as various power sources such as a portable power source and an automotive power source.

It is a schematic explanatory drawing of the test cell of the nonaqueous electrolyte secondary battery which concerns on this Embodiment. It is a graph which shows the charging / discharging characteristic of the nonaqueous electrolyte secondary battery using the positive electrode active material in case the molar ratio of lithium carbonate, nickel hydroxide, and bismuth oxide is 3: 4: 0.5. It is the profile which showed the measurement result of the XRD measurement of the positive electrode active material which was able to obtain the largest initial discharge capacity density. The non-aqueous electrolyte secondary battery is a profile of generally positive electrode active material LiNiO ₂ of XRD measurement used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Reference electrode 4 Separator 5 Nonaqueous electrolyte 10 Cell container

Claims (5)

A positive electrode containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte secondary battery, wherein the positive electrode active material contains lithium, nickel, and bismuth. The composition of the positive electrode active material is Li: Ni: Bi = x: 4: y, where the molar ratio of lithium (Li), nickel (Ni), and bismuth (Bi) is expressed in this order. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein x is greater than 4 and 10 or less, and y is 0.2 or more and less than 3. 3. The composition of the positive electrode active material is Li: Ni: Bi = 6: 4: 1 when the molar ratio of lithium (Li), nickel (Ni), and bismuth (Bi) is expressed in this order. The nonaqueous electrolyte secondary battery according to claim 1 or 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is made of a lithium metal, a lithium alloy, a carbon material, or a silicon material. The non-aqueous electrolyte includes one or more selected from the group consisting of cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles and amides. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4.

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