JP3093227B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a positive electrode active material of a non-aqueous electrolyte secondary battery.

<< Conventional Technology >> A non-aqueous electrolyte secondary battery is a battery in which lithium metal or an alloy thereof is used for a negative electrode and an active material made of manganese dioxide or another transition metal sulfide or oxide is used for a positive electrode, In a discharge reaction of a battery using these materials, lithium ions move into the positive electrode material, and conversely, in a charge reaction, lithium ions in the positive electrode material move to the negative electrode side, and each of these reactions occurs reversibly. It can be used as a secondary battery.

However, this type of battery has a disadvantage that the discharge capacity gradually decreases when charge and discharge are repeated as a secondary battery.

This is because the lithium ions that have entered the positive electrode due to the discharge gradually become less likely to go outside, and the amount of lithium ions that return to the negative electrode side also decreases due to the charge reaction.

For the purpose of eliminating this kind of defect and improving the cycle characteristics, conventionally, a positive electrode active material obtained by heat-treating EMD (electrolytic manganese dioxide) together with lithium, for example, as disclosed in
As shown in JP-A-63-148550, a positive electrode active material is used in which manganese dioxide obtained from a manganese compound is doped with lithium ions, and this is further heat-treated.

Such a positive electrode active material has relatively good cycle characteristics because impurities such as potassium ions and ammonium ions and protons contained in the solid phase are removed by, for example, lithium entering the crystal structure of manganese dioxide. It is said that a non-aqueous electrolyte secondary battery can be obtained.

<< Problems to be Solved by the Invention >> However, in practice, even if the above-described positive electrode active material was used, no significant improvement in cycle characteristics was observed, and no large effect was obtained in terms of capacity.

The present invention has been made to solve the above problems, and provides a non-aqueous electrolyte secondary battery that further improves cycle characteristics than a conventional battery using a positive electrode active material and increases capacity. The purpose is.

<< Means for Solving the Problems >> In order to achieve the above object, in the present invention, manganese obtained by reacting manganese dioxide in an acidic solution of a mixture of H ₂ SO ₄ and a salt containing NH ₄ ⁺ ions By heating the compound with a lithium salt, X using Fe (Kα)
In the line diffraction, the diffraction angles 2θ are 22 °, 35 °, 47 °, 53
Manganese having peaks near ゜, 64 ゜, 78 ゜
A positive electrode active material for a non-aqueous electrolyte secondary battery comprising lithium and oxygen is produced.

<Operation> In the above configuration, the electric field manganese dioxide is converted to H ₂ SO ₄
By heating a manganese compound obtained by reacting with a lithium salt together with a lithium salt in an acidic solution in which a salt containing NH ₄ ⁺ ions and a salt containing NH ₄ ⁺ ions are mixed, the lattice spacing is considered to be relatively wide even after the calcination treatment. It is supposed that the lithium ion can freely enter and exit the crystal lattice, which leads to an improvement in cycle characteristics and an increase in capacity.

<< Embodiment >> Next, an embodiment of the present invention will be described.

Example As a treatment for changing all of the tetravalent manganese contained in the EMD to trivalent manganese, baking was performed at 800 ° C. for 24 hours.

On the other hand, as an acidic solution containing NH ₄ ⁺ ions, H ₂ SO ₄ 60 ml
(NH ₄ ) ₂ SO ₄ 90 in a sulfuric acid solution in which
A solution to which g was added was prepared.

EMD calcined in 300 ml of this solution heated to 95-100 ° C
Was added and stirred for 2 hours.

After completion of the stirring, the resultant was washed with a large amount of pure water, and then dried at 105 ° C.

Next, ₂ g of LiOH.H ₂ O as a lithium salt was mixed in a mortar per 10 g of the sample that had been subjected to the above treatment, and baked at 300 ° C. for 12 hours to obtain a positive electrode active material composed of a compound of manganese, lithium, and oxygen.

When this cathode active material was analyzed with an X-ray diffractometer, the diffraction angle 2θ was around 22 °, 35 °, 47 °, 53 °, 64 °, 78 ° in x-ray diffraction using Fe (Kα). Shows a peak.

When this peak was collated with an ASTM card, the crystal structure of manganese dioxide in the obtained compound was determined to be an α-type crystal structure having a relatively large lattice spacing. The analysis results confirmed that the same crystal form was maintained after the NH ₄ ⁺ treatment and the calcination treatment with lithium.

Thereafter, 85 parts by weight of the positive electrode active material, 10 parts by weight of acetylene black, and 5 parts by weight of Teflon powder are mixed until uniform to form a pellet-shaped positive electrode having a diameter of 15 mm and a thickness of 0.7 mm. Built-in type battery.

Comparative Example 1 In the same manner as in the prior art, a positive electrode active material obtained by adding lithium hydroxide to EMD and performing a calcination treatment was used. Thereafter, a positive electrode having the same composition as in Example 1 was formed and incorporated into a battery of the same type.

Comparative Example 2 As manganese dioxide, manganese dioxide was prepared by adding ammonium persulfate to a solution of Mn (NO ₃ ) ₂ and then subjected to the same calcination treatment as in Comparative Example 1 to form a positive electrode. Incorporated. The morphology of the manganese dioxide obtained from the above manganese compound is considered to be the α-form having a relatively large lattice spacing, but as a result of analysis, it did not clearly coincide with the α-form after the calcination treatment.

Comparative Example 3 As manganese dioxide, manganese dioxide precipitated by adding hydrochloric acid to a potassium permanganate solution was used.

The crystal form of manganese dioxide obtained from the manganese compound is δ-form, but the analysis result after the calcination treatment shows that the manganese dioxide becomes α-form contrary to Comparative Example 2.

Thereafter, a positive electrode was prepared in the same procedure as in Comparative Examples 1 and 2, and was incorporated into a battery of the same type.

Next, when the cycle characteristics of the battery of the example and the batteries of Comparative Examples 1 to 3 were compared, the results shown in FIG. 1 were obtained.

As a measurement method, the initial voltage is 3.5V
The time until the cut-off voltage was set at a constant current of 2.4 V was measured, and the time to the cut-off voltage at the time of the first measurement of the product of the present invention was set to 100% and plotted up to 50 cycles.

As is clear from this graph, the battery capacity of the present invention is reduced to about 90% of the initial capacity and then kept in a parallel state. It was confirmed that the volume fell below the volume of the product, and then the volume gradually decreased until 50 cycles.

Also, it is not clear what effect the treatment in an acidic solution containing NH ₄ ⁺ ions itself has, but it is clear that the lattice spacing is relatively wide by performing this kind of treatment. It is considered that the α-type crystal structure is maintained even after the sintering treatment, and as a result, lithium ions can freely enter and exit the crystal lattice, thereby improving cycle characteristics and leading to an increase in capacity. .

<< Effects of the Invention >> As described in detail in the above examples, in the non-aqueous electrolyte secondary battery using the positive electrode active material manufactured according to the present invention, compared with the conventional one using the positive electrode Since the charge / discharge cycle characteristics and capacity are improved, this type of non-aqueous electrolyte secondary battery is useful for practical use.

[Brief description of the drawings]

FIG. 1 is a graph comparing the cycle characteristics of the batteries of the comparative example and the battery using the cathode active material manufactured according to the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuhiro Nakamura 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo (56) References JP-A-63-148550 (JP, A) JP-A-3-74054 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/50 H01M 4/58 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claims] 1. A manganese compound obtained by reacting manganese dioxide in an acidic solution in which a salt containing H ₂ SO ₄ and NH ₄ ⁺ ions are mixed, and heating the manganese compound together with a lithium salt,
In X-ray diffraction using Fe (Kα), the diffraction angle 2θ is
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising manganese, lithium, and oxygen having peaks around 22 °, 35 °, 47 °, 53 °, 64 °, and 78 °.