JP2798991B2 - Manufacturing method of non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a non-aqueous electrolyte secondary battery,
In particular, the present invention relates to a method in which cycle characteristics and capacity are improved by discharge treatment in an initial stage of manufacturing a positive electrode.

<< Prior Art >> Manganese dioxide is known as a positive electrode active material in a lithium secondary battery.

This manganese dioxide is widely used because of its excellent preservability (stability), abundant resources and low cost. However, since lithium as the negative electrode active material is highly reactive with moisture, In practical use, heat treatment must be performed to remove water.

However, it is said that the crystal form of manganese dioxide changes from γ-type to β-γ-type or β-type by performing this kind of heat treatment.

Manganese dioxide having a γ-type crystal structure has a small collapse of the crystal after discharge, whereas β-γ or β-type has a large collapse of the crystal structure at the time of discharge. Accordingly, there is a disadvantage that the capacity is reduced and the cycle characteristics are reduced.

For this reason, it has been proposed to use, as a positive electrode active material, one obtained by heat-treating lithium-doped electrolytic manganese dioxide as disclosed in, for example, JP-A-62-108455.

Manganese dioxide of this structure suppresses the change in crystal structure even when heat-treated, indicating that the manganese dioxide has better cycle characteristics than batteries using a positive electrode active material obtained by heat-treating conventional manganese dioxide alone. .

《Problems to be solved by the invention》 As a result of various studies for the purpose of further improving the superior cycle characteristics of the fired body of manganese dioxide and metal as described above, the present invention is to perform discharge control in the initial stage of production. As a result, the inventors have found that a positive electrode active material having further improved cycle characteristics and capacity can be obtained by doping alkali metal ions into the positive electrode active material once and then charging the same, and have completed the present invention.

<< Means for Solving the Problems >> In order to achieve the above object, the present invention relates to a method of adding at least one kind of alkali metal, alkaline earth metal, transition metal, or rare earth metal compound to manganese dioxide and heating the mixture. The positive electrode thus obtained is opposed to an alkali metal in the presence of a non-aqueous electrolyte, and the recovery open circuit voltage after 24 hours is 1.5 to 2.7.
By discharging to V, the inside of the positive electrode is doped with an alkali metal ion.

More specifically, the above-described discharge treatment is performed immediately after the production of the completed non-aqueous electrolyte secondary battery by laminating a positive electrode and an alkali negative electrode having the above-described composition via a separator, and adding a non-aqueous electrolyte. Alternatively, the same discharge treatment may be performed on the positive electrode before assembling, and then the battery may be assembled using the positive electrode.

Lithium is added as an alkali metal added to the manganese dioxide, calcium and magnesium are used as alkaline earth metals, and chromium and magnesium are used as transition metals.
Iron, cobalt, vanadium, molybdenum, titanium and tungsten can be used, and lanthanum and cesium can be used as rare earth metal compounds.

<Operation> According to the non-aqueous electrolyte secondary battery using the positive electrode subjected to the above-described discharge treatment, the cycle characteristics are higher than those using the conventional positive electrode in which alkali metal ions are simply doped into manganese dioxide. And the capacity is also improved.

And, as mentioned above, it is confirmed that the morphology of manganese dioxide changes when a fired body of manganese dioxide and a metal compound is produced. Is presumed to be modified to a structure that is more advantageous for the reversibility of the entrance and exit of alkali metal ions during subsequent charge and discharge.

<< Effects of the Invention >> In the method of the present invention, in the positive electrode made of manganese dioxide to which the same metal compound is added, the cycle characteristics can be improved and the capacity can be increased as compared with the related art.

In addition, since the above-described effects can be obtained only by adding the initial discharge process and the recharging process at the final stage of the manufacturing process, the main portion of the existing non-aqueous electrolyte secondary battery manufacturing process is performed without any modification. And can be easily implemented.

<< Embodiment >> An embodiment of the present invention will be described below.

The non-aqueous electrolyte secondary battery of the present invention has the following (a) to
It is made through the manufacturing process of (e).

(B) LiOH respect manganese dioxide 1 mol obtained by _{electrolysis, Ca (OH) 2, Mg} (OH) 2, Cr 2 O 3, FeO 3, CoO, V 2 O 3, M
0.1 mol of each of nO ₃ , TiO ₂ , WO ₃ , La ₂ O ₃ , and Ce ₂ O ₃ were added, and the mixture was thoroughly mixed in a mortar, heated at 400 ° C., cooled, and further mixed at 400 ° C. Heat treatment was performed for 72 hours to obtain a positive electrode active material.

(B) 8 parts by weight of the obtained positive electrode active material was mixed with 1 part by weight of acetylene black and 1 part by weight of PTFE powder as a binder to form a pellet-shaped positive electrode having a diameter of 13 mm and a thickness of 1.2 mm.

(C) Next, a CR2016 type coin-type battery was assembled using these positive electrodes by the same method as the conventional method except for the above.

Note that metallic lithium was used as the negative electrode active material, a polypropylene porous film was used as the separator, and PC: DME = 1: 1, LiClO ₄ 1 mol / was used as the nonaqueous electrolyte.

(D) Immediately after the assembly, a resistance of 500Ω was connected to each battery, and an initial discharge treatment was performed until the recovery open circuit voltage after 24 hours became 2.5V.

(E) Each battery was subsequently charged at 1 mA up to 3.5 V to produce a product.

Next, the charge / discharge cycle of each battery manufactured through the above manufacturing process was performed up to 50 times, and as a result, the characteristic of capacity (mA) with respect to the cycle shown in FIG. 1 was obtained. The charge / discharge current was 1 mA, the minimum voltage was 2.2 V, and the maximum voltage was 3.5 V.

In addition, as a reference, charge / discharge cycle characteristics of a battery using a positive electrode active material composed of manganese dioxide alone and a battery in which initial discharge treatment was not performed with a positive electrode active material obtained by adding lithium to manganese dioxide were also measured.

From the figure, it can be seen that the cycle characteristics of the respective additive substances vary, but for example, when comparing the initial discharge treatment with the lithium-added positive electrode and the one without the initial discharge treatment, the initial difference is large. However, it is understood that a significant difference occurs at the 20th cycle, and an extremely large capacity difference occurs at the 50th cycle.

Further, an extreme difference has been confirmed between a battery using a positive electrode of manganese dioxide alone and a battery containing another metal compound.

Next, as a result of investigating the discharge capacity in 10 charge / discharge cycles when the addition ratio of each metal substance to manganese dioxide was changed from 10 to 70 mol%, the results shown in FIG. 2 were obtained. In addition, Li, C
a, Cr, La were selected.

According to this result, the discharge capacity is gradually reduced up to the addition amount of about 50 mol%, but when it exceeds this, the capacity is extremely reduced.

Therefore, it was found that the upper limit of the amount of various metals to be added to manganese dioxide was 50 mol%, and it was desirable that the addition ratio be less than that.

Next, in the heat treatment step of the production step (a), the influence of the treatment temperature on the discharge capacity was measured for the discharge capacity at the 20th cycle for Li and La, and the results shown in FIG. 3 were obtained.

From this result, it was found that the heat treatment temperature in the range of 200 to 450 ° C. had a small decrease in capacity, and that the heat treatment at 300 ° C. particularly had a favorable effect on the crystal structure.

Next, when the influence of the discharge treatment conditions in the initial discharge treatment step (d) was measured for Li, La, and manganese dioxide without addition, the measurement results shown in FIG. 4 were obtained.

From this result, it is desirable to discharge to the recovery open-circuit voltage between 1.5 and 2.7 V, which is within the range of the hatched area in the figure, as the initial discharge processing, and in any other case, the discharge capacity is reduced.

 In particular, about 2.2 V gives a good result in the capacitance characteristics.

As a result, the amounts of the various metal compounds added to manganese dioxide were within 50 mol%, the heat treatment conditions were 200 to 450 ° C., and the recovery open circuit voltage in the initial discharge treatment step was 1.5%. By setting the voltage to ~ 2.7 V, it is estimated that the repetition of the charge / discharge cycle of the positive electrode results in a crystal structure that is difficult to collapse.As a result, it is thought that the cycle characteristics can be improved and the capacity can be increased. .

[Brief description of the drawings]

FIG. 1 is a graph showing the discharge capacity characteristics with respect to the charge / discharge cycle of each battery obtained by the method of the present invention, and FIG. 2 is a relation between the addition ratio of each metal compound to manganese dioxide constituting the cathode active material and the discharge capacity. FIG. 3 is a graph showing the relationship between the heat treatment temperature of the positive electrode active material and the discharge capacity, and FIG. 4 is a graph showing the relationship between the open circuit voltage and the discharge capacity in the initial discharge process.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Nakanishi 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 4/00-4/04 H01M 4/36-4/62 H01M 10/36-10/40

Claims (2)

(57) [Claims] 1. A positive electrode obtained by adding at least one kind of an alkali metal, alkaline earth metal, transition metal or rare earth metal compound to manganese dioxide and heating the resultant to form an alkali in the presence of a non-aqueous electrolyte. A method for producing a non-aqueous electrolyte secondary battery, comprising: doping alkali metal ions into a positive electrode by facing the metal and discharging until a recovery open circuit voltage after 24 hours becomes 1.5 to 2.7 V. 2. An alkali metal added to the positive electrode is lithium, an alkaline earth metal is calcium, magnesium, a transition metal is chromium, iron, cobalt, vanadium, molybdenum, titanium, tungsten, a rare earth metal compound is lanthanum or cesium. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein: