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Non-aqeous electrolyte secondary battery

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Non-aqeous electrolyte secondary battery


A non-aqueous electrolyte secondary battery has a positive electrode containing a positive electrode active material containing a lithium-containing oxide active material, a negative electrode, and a non-aqueous electrolyte. The lithium-containing oxide active material is represented by the general formula LiaMgbMO2±α where 0.65≦a≦1.05, 0<b≦0.3, 0≦α≦0.3, and M is at least one of manganese and cobalt.
Related Terms: Cobalt Electrode Electrolyte Lithium Manganese

Browse recent Sanyo Electric Co., Ltd. patents - Osaka, JP
Inventors: Motoharu Saito, Sho Tsuruta, Masahisa Fujimoto
USPTO Applicaton #: #20130011741 - Class: 429224 (USPTO) - 01/10/13 - Class 429 
Chemistry: Electrical Current Producing Apparatus, Product, And Process > Current Producing Cell, Elements, Subcombinations And Compositions For Use Therewith And Adjuncts >Electrode >Chemically Specified Inorganic Electrochemically Active Material Containing >Manganese Component Is Active Material

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The Patent Description & Claims data below is from USPTO Patent Application 20130011741, Non-aqeous electrolyte secondary battery.

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CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 12/728,718, filed on Mar. 22, 2010, which claims benefit of priority from the prior Japanese Patent Application No. 2009-069497, filed on Mar. 23, 2009, the entire contents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-aqueous electrolyte secondary battery that achieves high capacity and to a method of manufacturing the battery.

2. Description of Related Art

Mobile information terminal devices such as mobile telephones, notebook computers, and PDAs have become smaller and lighter at a rapid pace in recent years. This has led to a demand for higher capacity batteries as the drive power source for the mobile information terminal devices. With their high energy density and high capacity, non-aqueous electrolyte secondary batteries, which perform charge and discharge by transferring lithium ions between the positive and negative electrodes, have been widely used as a driving power source for the mobile information terminal devices.

As the mobile information terminal devices tend towards having greater numbers of functions, such as moving picture playing functions and gaming functions, the power consumption of the devices tends to increase. It is therefore strongly desired that the non-aqueous electrolyte secondary batteries used for the power sources of such devices have further higher capacities and higher performance to achieve longer battery life and improved output power. In addition, applications of the non-aqueous electrolyte secondary batteries are expected to expand from just the above-described applications but to power tools, power assisted bicycles, and moreover hybrid electric vehicles (HEVs) and electric vehicles (EVs). In order to meet such expectations, it is strongly desired that the capacity and the performance of the battery be improved further.

In order to increase the capacity of the non-aqueous electrolyte secondary battery, it is necessary to increase the capacity of the positive electrode. In particular, layered compounds are viewed as promising materials for positive electrode active materials. To date, many lithium-containing layered compounds have been studied. Among the materials that have been developed are LiCoO2, LiNiO2, LiNi1/3Co1/3Mn1/3O2, and NaxCoyMn1-yO2 where 0.6≦x≦0.8 and 0.4≦y≦0.6 (see Japanese Published Unexamined Patent Application No. 2002-220231).

In addition, a technique for synthesizing a lithium compound from a sodium compound has been studied as a method for synthesizing a novel lithium compound (see Japanese Published Unexamined Patent Application No. 2007-220650). According to this method a layered compound, which is difficult to synthesize with lithium, can be easily obtained. In particular, Na0.7CoO2 and NaCo1/2Mn1/2O2 can be used as positive electrode active materials for lithium-ion batteries by ion-exchanging sodium for lithium. Therefore, much research has been conducted on synthesis methods and ion-exchange methods by chemical techniques using Na0.7CoO2 and NaCo1/2Mn1/2O2.

The positive electrode active materials using sodium-based oxides are promising materials that are expected to yield high capacity, and by adding lithium thereto, further high capacity can be obtained. However, the addition of lithium causes the average discharge potential to decrease. Moreover, it causes formation of an impurity similar to Li2MnO3, resulting in the problem of side reactions during charge and discharge.

BRIEF

SUMMARY

OF THE INVENTION

Accordingly, it is an object of the present invention to provide a non-aqueous electrolyte secondary battery and a manufacturing method of the battery that can inhibit side reactions during charge and discharge by suppressing formation of an impurity similar to Li2MnO3 and that can preventing the discharge potential from decreasing even when lithium is added.

The present inventors studied various materials that may suppress formation of Li2MnO3 impurity and prevent the discharge voltage from decreasing, and as a result found that the foregoing object can be accomplished by using magnesium as an additive metal.

Accordingly, the present invention provides a non-aqueous electrolyte secondary battery comprising: a positive electrode containing a positive electrode active material comprising a lithium-containing oxide active material; a negative electrode; and a non-aqueous electrolyte, wherein: the lithium-containing oxide active material is represented by the general formula LiaMgbMO2±α where 0.65≦a≦1.05, 0<b≦0.3, 0≦α≦0.3, and M is at least one of manganese and cobalt; and the lithium-containing oxide active material has a main peak at 2θ=17.95° to 18.15°, as determined by an X-ray powder crystal diffraction measurement (Cukα).

According to the present invention, formation of a lithium-containing impurity that is caused when adding lithium is suppressed so that side reactions are inhibited during charge and discharge, and at the same time, the discharge potential is prevented from decreasing, because magnesium is added to the positive electrode active material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a test cell used for the embodiments of the present invention;

FIG. 2 is a graph showing the result of an XRD analysis for a present invention oxide a1;

FIG. 3 is a graph showing the result of an XRD analysis for a present invention oxide a2;

FIG. 4 is a graph showing the result of an XRD analysis for a present invention oxide a3;

FIG. 5 is a graph showing the result of an XRD analysis for a comparative reference oxide x;

FIG. 6 is a graph showing the result of an XRD analysis for a comparative oxide z1;

FIG. 7 is a graph showing the result of an XRD analysis for a comparative oxide z2;

FIG. 8 is a graph showing the result of an XRD analysis for a comparative oxide z3;

FIG. 9 is a graph showing the result of an XRD analysis for Li2MnO3;

FIG. 10 is a graph showing the result of an XRD analysis for a present invention active material a1-i;

FIG. 11 is a graph showing the result of an XRD analysis for a present invention active material a2-i;

FIG. 12 is a graph showing the result of an XRD analysis for a present invention active material a3-i;

FIG. 13 is a graph showing the result of an XRD analysis for a comparative reference active material x-i;

FIG. 14 is a graph showing the result of an XRD analysis for a comparative active material z1-i;

FIG. 15 is a graph showing the result of an XRD analysis for a comparative active material z2-i; and

FIG. 16 is a graph showing the result of an XRD analysis for a comparative active material z3-i.

DETAILED DESCRIPTION

OF THE INVENTION

The present invention provides a non-aqueous electrolyte secondary battery comprising: a positive electrode containing a positive electrode active material comprising a lithium-containing oxide active material; a negative electrode; and a non-aqueous electrolyte, wherein: the lithium-containing oxide active material is represented by the general formula LiaMgbMO2±α where 0.65≦a≦1.05, 0<b≦0.3, 0≦α≦0.3, and M is at least one of manganese and cobalt; and the lithium-containing oxide active material has a main peak at 2θ=17.95° to 18.15°, as determined by an X-ray powder crystal diffraction measurement (Cukα).

When magnesium is added to the lithium-containing oxide, a lithium-containing impurity layer (a substance with a structure similar to Li2MnO3) that is formed when adding lithium is not formed. As a result, the side reactions that are caused by the lithium-containing impurity (decomposition of the impurity itself, decomposition of the electrolyte, and so forth) are inhibited.

Moreover, when magnesium is added, the average discharge potential increases. Therefore, it is possible to prevent the decrease of the average discharge potential caused by adding lithium. Therefore, in the battery that has the foregoing configuration, the energy density can be increased.

Note that although almost the whole amount of sodium is ion-exchanged by lithium, a small amount of sodium may remain, as will be described later. However, even if a small amount of sodium remains, the remaining amount will be very small and negligible.

It is desirable that the amount b of magnesium is preferably within the range 0<b≦0.2. The reason is as follows. Addition of a large amount of magnesium may cause substantial structural change or formation of impurity, resulting in more side reactions. Consequently, battery deterioration (such as gas formation, capacity loss, and storage performance deterioration) may occur.

It is desirable that the lithium-containing oxide active material be represented by the general formula LiaMgbMnxCoyO2±α, where 0.65≦a≦1.05, 0<b≦0.3, 0.45≦x≦0.55, 0.45≦y≦0.55, 0.90≦x+y≦1.10, and 0≦α≦0.3. It is also desirable that the lithium-containing oxide active material have a crystal structure belonging to an O2 structure, a T2 structure, an O6 structure, or a mixed structure thereof.

The present invention also provides a method of manufacturing a non-aqueous electrolyte secondary battery, comprising the steps of subjecting a sodium-magnesium-containing oxide represented by the general formula NacMgbMO2±α, where 0.65≦c≦0.75, 0<b≦0.3, 0≦α≦0.3, and M is at lease one of manganese and cobalt, to ion-exchange of sodium for lithium by using a molten salt, an aqueous solution, or an organic solvent, to prepare a positive electrode active material; preparing a positive electrode active material slurry containing the positive electrode active material and a binder, and thereafter applying the positive electrode active material slurry to a positive electrode current collector to prepare a positive electrode; placing a separator between the positive electrode and the negative electrode to prepare a power-generating element; and encasing the power-generating element in a battery case and filling a non-aqueous electrolyte in the battery case.

When ion-exchanging the sodium-magnesium-containing oxide using an organic solvent or the like in the step of preparing the positive electrode active material, almost the whole amount of sodium is ion-exchanged for lithium. As a result, the positive electrode active material comprising the lithium-containing oxide is synthesized. The magnesium may or may not be ion-exchanged for lithium partially or entirely.

It is desirable that the sodium-magnesium-containing oxide be represented by the general formula NacMgbMnxCoyO2±α where 0.65≦c≦0.75, 0<b≦0.3, 0.45≦x≦0.55, 0.45≦y≦0.55, 0.90≦x+y≦1.10, and 0≦α≦0.3.

Other Embodiments

(1) As for the conductive agent used in preparing the electrode, the electrode can function even without adding any conductive agent in the case of using an active material having high electrical conductivity. However, when using an active material having low electrical conductivity, it is desirable to add a conductive agent. The conductive agent may be any material as long as it has electrical conductivity. It is desirable to use at least one substance selected from oxides, carbides, nitrides, and carbon materials that have particularly high conductivity. Examples of such oxides include tin oxide and indium oxide. Examples of such carbides include tungsten carbide and zirconium carbide. Examples of such nitrides include titanium nitride and tantalum nitride. In the case of adding a conductive agent, if the amount of the conductive agent added is too small, the conductivity in the positive electrode cannot be improved sufficiently. On the other hand, if the amount of the conductive agent added is too large, the relative proportion of the active material in the positive electrode will be low, and consequently a high energy density cannot be obtained. For this reason, it is desirable that the amount of the conductive agent be from 0 mass % to 30 mass %, more preferably from 0 mass % to 20 mass %, and still more preferably from 0 mass % to 10 mass %, with respect to the total amount of the positive electrode.

(2) Examples of the binder used for the electrode include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, carboxymethylcellulose, and combinations thereof.

When the amount of the binder is too large, the relative proportion of the active material contained in the positive electrode will be small, so the battery will not have a high energy density. For this reason, it is desirable that the amount of the binder be from 0 mass % to 30 mass %, more preferably from 0 mass % to 20 mass %, and still more preferably from 0 mass % to 10 mass %, with respect to the total amount of the positive electrode.

(3) The material for the negative electrode may be any material that is capable of absorbing and deintercalating lithium. Examples include lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, lithium-containing alloys, lithium-intercalated carbon materials, and lithium-intercalated silicon materials.

(4) Examples of the non-aqueous solvent used in the present invention include cyclic carbonic esters, chain carbonic esters, esters, cyclic ethers, chain ethers, nitriles, and amides.

Examples of the cyclic carbonic esters include ethylene carbonate, propylene carbonate, and butylenes carbonate. It is also possible to use a cyclic carbonic ester in which part or all of the hydrogen groups of the just-mentioned cyclic carbonic esters is/are fluorinated. Examples of such include trifluoropropylene carbonate and fluoroethyl carbonate. Examples of the chain carbonic esters include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate. It is also possible to use a chain carbonic ester in which part or all of the hydrogen groups of one of the foregoing chain carbonic esters is/are fluorinated. Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone. Examples of 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-cineol, 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, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxy ethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Examples of the nitriles include acetonitrile. Examples of the amides include dimethylformamide. These substances may be used either alone or in combination.



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stats Patent Info
Application #
US 20130011741 A1
Publish Date
01/10/2013
Document #
13614425
File Date
09/13/2012
USPTO Class
429224
Other USPTO Classes
4292316
International Class
01M4/131
Drawings
17


Cobalt
Electrode
Electrolyte
Lithium
Manganese


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