JP3111791B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in a positive electrode active material thereof.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly advancing, and small and lightweight power sources for driving these devices have high energy densities, and have excellent charge / discharge cycle characteristics and long life. There is a high demand for secondary batteries. In this regard, non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, are expected to have high voltage and high energy density.

In order to develop a positive electrode active material for a lithium secondary battery which satisfies the above-mentioned demand, research and development of materials have been actively conducted in recent years. For example, in relation to nickel compounds, Li _y Ni _2-y O ₂ (JP-A-2-40861)
And Li _1-x NiO ₂ (U.S. Pat. No. 4,302,518), and many more development examples have been reported in relation to other transition metal compounds. is there.

[0004] Among these compounds, lithium nickelate LiNiO ₂ has a large charge / discharge capacity per unit weight and may be used as a positive electrode active material for a high capacity nonaqueous electrolyte secondary battery.

As the electrolyte, those containing esters have been applied to all lithium batteries.

[0006]

However, LiNiO ₂
In a battery using a non-aqueous electrolytic solution containing an ester as a positive electrode active material, a decrease in capacity due to repeated charge and discharge, and deterioration during storage of the battery are caused by other compounds, such as lithium cobaltate LiCoO ₂ and manganese. Lithium oxide L
It was found to be larger than a battery using iMnO ₂ as a positive electrode active material.

[0007] The reaction between an ester and a positive electrode active material has been reported in some systems, for example, Thomas et al. (J. Electrochem. Soc., 132 (1)
985) According to 1521), propylene carbonate and LiC
In the oO ₂ system, a polymer film originating from propylene carbonate is formed on the surface of LiCoO ₂ , and the movement of lithium ions accompanying the charge / discharge reaction is inhibited. In particular, when the battery is left in a charged state in which Co becomes tetravalent and oxidizing power increases, the reaction between the positive electrode active material and the electrolytic solution becomes remarkable. The present inventors have set forth the aforementioned T
Using the same analysis technique as reported by
As a result of studying O ₂ , LiCoO ₂ , and LiMnO ₂ , LiNiO ₂ was found to be LiCoO ₂ or LiMnO ₂
Than with various esters.
Therefore, it is considered that this is the cause of the decrease in capacity due to the repetition of charge and discharge and the large deterioration during storage of the battery.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to achieve a high capacity L.
It is intended to suppress the reaction with a non-aqueous electrolyte solution without impairing the characteristics of iNiO ₂ , and to reduce the capacity reduction due to repeated charge / discharge and the deterioration during storage of the battery.

As a result of intensive studies, the present inventors have found that L
When the surface of the INiO ₂ is coated with at least one LiCoO _2, LiMnO _2, it found knowledge that can achieve the object.

The present invention, which relates to a nonaqueous electrolyte secondary battery, has been achieved based on the above findings, and comprises a nonaqueous electrolyte comprising at least a positive electrode, a negative electrode, and a nonaqueous electrolyte containing esters. In an electrolyte secondary battery, the surface of lithium nickel oxide LiNiO ₂ , which is an active material of the positive electrode, is coated with lithium cobaltate LiCoO ₂ and lithium manganate.
It is characterized by being coated with at least one of LiMnO ₂ .

Here, representative examples of the esters contained in the nonaqueous electrolyte include diethyl carbonate, ethylene carbonate,
Examples thereof include propylene carbonate, methyl propionate, and γ-butyrolactone. However, the reaction with LiNiO ₂ in the battery is a problem common to esters, and is not necessarily limited to these esters.

[0012]

In the present invention, LiNiO is used._TwoWith non-aqueous electrolyte
The effect of suppressing the reaction is LiNiO _TwoThe surface of the ester
LiCoO relatively less reactive to_TwoAnd LiM
nO_TwoBy coating with ester,
Oxidation, which is a surface reaction that occurs between
It is considered that reactions such as disassembly and polymerization are suppressed. Change
In addition, the movement of lithium ions during the charge-discharge reaction
LiCoO_TwoAnd LiMnO_TwoDiffuses smoothly inside
LiNiO_TwoAnd the charge / discharge capacity is LiNiO_Two
Is dominant, and the high capacity that is the feature
available. Reaction with esters is LiCoO_TwoAnd LiM
nO_TwoEven less, but lithium ions do not diffuse
Metal (platinum, gold, etc.) and carbon with LiNiO
_TwoIf the surface is covered, the charge / discharge capacity will decrease significantly.
Was. From this, the material to be coated is LiCoO_TwoAnd L
iMnO_TwoNot only to diffuse lithium ions,
To LiNiO_TwoRelatively less reactive than
LiCoO _TwoAnd LiMnO_TwoSame effect as
It is expected that results will be obtained.
Need further study to find out.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

First, a method of manufacturing a positive electrode active material common to the examples will be described. LiNiO ₂ powder obtained by a known method of mixing nickel hydroxide powder and lithium hydroxide powder and heating in an oxygen atmosphere at 700 ° C. is converted into a water-soluble salt containing a transition metal of a compound covering the LiNiO ₂ powder. For example, by dispersing with stirring in an aqueous solution of cobalt nitrate and / or manganese nitrate, and adding an aqueous solution of an alkali salt such as lithium hydroxide to the suspension, the surface of the LiNiO ₂ powder serving as a nucleus is A compound containing the transition metal of the compound to be coated can be deposited. The precipitate obtained by stopping the stirring is washed with water and dried to obtain an intermediate stage powder.

There are other ways to obtain something similar to this intermediate stage powder. For example, a method of performing sputtering using LiNiO ₂ as a base material and a cobalt salt and / or a manganese salt as a target,
There is a method of mechanochemically coating the O ₂ powder with a cobalt salt and / or manganese salt powder, but from the viewpoint of difficulty in production and imperfect coating, the above-described method of precipitation from a solution is preferable.

Depending on the amount of the compound deposited on the intermediate stage powder, it is heated in air with lithium hydroxide powder corresponding to obtaining LiCoO ₂ and / or LiMnO ₂ . The time at this time may be 2 to 3 hours, and if performed for a long time, Co and / or Mn of the surface layer and Ni inside diffuse, and a solid solution is formed.

The state of the coating of the obtained active material was observed by X-ray microanalysis (XMA). When the active material is mixed with the epoxy resin and cured, and an arbitrary surface thereof is polished, the cross section of the active material can be exposed. FIG. 1 shows a schematic diagram of representative results obtained by XMA surface analysis. This shows how LiCoO ₂ and / or LiMnO ₂ are generated on the surface of LiNiO _{2 serving as} a nucleus. A in the figure
Is the portion where Ni is present, B is Co and / or Mn
Indicates the presence of.

Next, an outline of a method and a configuration of the cylindrical test battery in the embodiment will be described below.

The positive electrode mixture paste is prepared by mixing the positive electrode active material obtained by the above-described method, acetylene black and polyvinylidene fluoride in a weight ratio of 100: 4: 5,
-Methyl-2-pyrrolidone was added as a solvent until it had the appropriate viscosity for application. This positive electrode mixture paste was applied to both surfaces of an aluminum foil, dried and rolled to prepare a positive electrode plate. On the other hand, for the negative electrode plate, a carbon material obtained by firing coke and a fluororesin-based binder were used for one each.
The mixture was mixed at a weight ratio of 00:10, kneaded with an aqueous solution of carboxymethyl cellulose to form a paste, applied to both surfaces of a copper foil, dried and rolled. The electrolyte is
Although studied in various combinations, the results were the same in any case, in order to avoid complications in the specific examples, for convenience, propylene carbonate, in an equal volume mixed solvent of ethylene carbonate, as a supporting electrolyte The case of an electrolyte prepared by dissolving lithium perchlorate at a ratio of 1 mol / 1 will be described.

Leads were attached to both the positive and negative electrodes in the form of a strip, and the whole was spirally wound around a polypropylene separator. After storing this in a stainless steel battery case, a predetermined amount of electrolyte was injected, and other components were mounted to form a battery.

FIG. 2 shows a longitudinal sectional view of the cylindrical battery thus produced. In the figure, reference numeral 1 denotes a battery case accommodating an electrode plate group 2, a positive electrode lead 4 is connected to a sealing plate 3 for sealing the battery case 1, and a negative electrode lead is provided at the bottom of the battery case 1.
5 is connected. Reference numeral 6 denotes a packing, which has a function of keeping airtightness and insulating the sealing plate 3 as a positive electrode terminal from the battery case 1 as a negative electrode terminal. The insulating ring 7 has a positive / negative plate of the electrode plate group 2 and a battery case 1 inside the battery.
And short circuit by contact with the sealing plate 3 is prevented.

(Example 1) In the above-described method for producing a positive electrode active material, cobalt nitrate was used as a water-soluble salt containing a transition metal of a compound to be coated, and LiCoO _{2 was} coated on the surface of LiNiO _2.
A cathode active material coated with O ₂ was synthesized. The production method and configuration of the test cylindrical battery are the same as those described above. This battery is referred to as Battery A of the present invention.

Example 2 In the above-mentioned method for producing a positive electrode active material, manganese nitrate was used as a water-soluble salt containing a transition metal of a compound to be coated, and LiMn _{2 was} applied to the surface of LiNiO _2.
A cathode active material coated with O ₂ was synthesized. The production method and configuration of the test cylindrical battery are the same as those described above. This battery is referred to as Battery B of the invention.

Example 3 In the above-mentioned method for producing a positive electrode active material, an equivalent amount of cobalt nitrate and manganese nitrate was used for the water-soluble salt containing the transition metal of the compound to be coated, and LiN was added.
A positive electrode active material having iO ₂ surface coated with LiCoO ₂ and LiMnO ₂ was synthesized. The production method and configuration of the test cylindrical battery are the same as those described above. This battery is referred to as Battery C of the present invention.

(Comparative Example 1) The same as the above-mentioned Example except that LiNiO ₂ whose surface was not coated at all was used as the positive electrode active material. This battery is referred to as Comparative Battery D.

(Experiment 1) Using these batteries A to D,
The charge / discharge was repeated up to 00 times, and the degree of decrease in the discharge capacity was compared. The test conditions at this time were as follows: each battery placed in an atmosphere of 20 ° C. was charged at a constant current of 140 mA to 3.0
It charges and discharges within a voltage range of V to 4.1V.

FIG. 3 shows the results. From FIG. 3, the batteries A, B, and C of the present invention have a slightly smaller discharge capacity than the comparative battery D at the initial stage of the charge / discharge repetition, but the degree of decrease is small, and after about 30 to 70 repetitions. It can be seen that the discharge capacity is larger than that of the comparative battery D.

(Experiment 2) Batteries A to D placed in an atmosphere of 20 ° C. were charged to 4.1 V at a constant current of 140 mA, and then left in an atmosphere of 60 ° C. for 3 weeks. 3. Return the battery after standing to an atmosphere of 20 ° C. and again at a constant current of 140 mA.
The discharge capacity after charging to 1 V was measured. Thus, the degree of deterioration due to standing was evaluated.

The results are shown in Table 1.

[0030]

[Table 1]

From Table 1, it can be seen that the batteries A, B, and C of the present invention have a larger discharge capacity than the comparative battery D, and have less deterioration when left unattended.

[0032]

As is apparent from the above description, according to the present invention, in the nonaqueous electrolyte secondary battery comprising at least the positive electrode, the negative electrode and the nonaqueous electrolyte containing esters, the positive electrode active LiNiO _{2 as} a substance
By coating at least one of lithium cobaltate LiCoO ₂ and lithium manganate LiMnO ₂ to suppress the reaction with a non-aqueous electrolyte without impairing the high capacity of LiNiO _2. In addition, a non-aqueous electrolyte secondary battery can be provided which has a reduced capacity due to repeated charge and discharge and a small deterioration during storage of the battery.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a coated state of an active material according to an embodiment of the present invention.

FIG. 2 is a schematic view of a longitudinal section of a cylindrical battery in an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a difference in reduction in discharge capacity due to repeated charge and discharge of a battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Electrode group 3 Sealing plate 4 Positive electrode lead 5 Negative lead 6 Packing 7 Insulation ring

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shigeo Kobayashi 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-7-192720 (JP, A) JP-A-5- 174872 (JP, A) JP-A-6-251764 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/00-4/04 H01M 10/40

Claims (1)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte containing esters, wherein an active material of the positive electrode is lithium nickel oxide LiN.
The surface of iO ₂ is coated with at least one of lithium cobaltate LiCoO ₂ and lithium manganate LiMnO ₂
Non-aqueous electrolyte secondary battery coated with seed.