JP2750731B2 - Positive electrode for lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Conventionally, charging and discharging of a lithium secondary battery involves dissolving and depositing lithium ions in an electrolyte solution using a negative electrode made of lithium.
There is a type in which lithium ions are inserted and removed by oxidation-reduction and proceed by using a positive electrode comprising Ca ₂ Mn ₃ O ₈ as an active material.

[Problems to be solved by the invention]

Conventionally, Ca ₂ Mn ₃ O ₈ , which is a positive electrode active material constituting a positive electrode of a lithium secondary battery of the above type, has a drawback that a large discharge capacity cannot be obtained due to low conductivity.

[Means for solving the problem]

The present invention improves the above-mentioned disadvantages of Ca ₂ Mn ₃ O ₈ used as a positive electrode of such a conventional type lithium secondary battery, and provides a positive electrode for a lithium secondary battery capable of obtaining a large discharge capacity. _{but, L X Ca 2-X Mn} 3 O 8 or _{L X E Y Ca 2-XY} M
n ₃ O ₈ (where L is Y or La and E is Ba or Sr) is used as the positive electrode active material.

[Action]

According to the present invention, a complex oxide obtained by substituting part of Ca ₂ ²⁺ of Ca ₂ Mn ₃ O ₈ among trivalent rare earth ions, particularly, with Y or La has conductivity of Ca ₂ Mn _It increases remarkably compared to ₃ O ₈ . Therefore, this is used as a positive electrode active material of a battery, thereby increasing the discharge capacity.

〔Example〕

 Next, examples of the present invention will be described in detail.

L _X C which is the active material of the positive electrode for a lithium secondary battery of the present invention
a _2-X Mn ₃ O ₈ or L _{X EY} Ca _2-XY Mn ₃ O ₈ (where L is Y or L
a, E is Ba or Sr) is a part of Ca ₂ of Ca ₂ Mn ₃ O _{8 represented} by Y ³⁺ , L
a ³⁺ alone or any of these, and those substituted with Ba ²⁺ or Sr ²⁺ , there is no change in the basic structure of Ca ₂ Mn ₃ O ₈ , but the diffraction strength of the `` 211 '' plane is As it increases, "003"
Diffraction of the surface is broad. By replacing Ca ²⁺ with a metal ion of Y ³⁺ or La ³⁺ , Mn ⁴⁺ is reduced to Mn ³⁺ , so on a surface containing Mn ions such as the “211” surface,
It is considered that the charge density increases and the diffraction strength increases. Also, La ³⁺ , Y having an ionic radius larger than that of Ca ²⁺ ions
When replacing with ³⁺ , it is considered that the arrangement of atoms is disordered in the “003” axis containing Ca ²⁺ ions, and that the diffraction becomes broad. Further, by substituting a part of Ca ²⁺ with La ³⁺ and Y ³⁺ , as a result of generating Mn ³⁺ ions, the resistivity is reduced as shown in Table 1 below, and thus the conductivity is reduced. It was found that the effect of La ³⁺ and Y ³⁺ was large.

In the method for producing the active material of the present invention, an aqueous solution of a nitrate mixture having a target metal ion composition is added to an ammonium carbonate aqueous solution, carbonate is coprecipitated, washed with water, dried, and then thermally decomposed at 650 ° C. in an oxygen stream. And synthesized. The obtained oxide was subjected to XRD, resistance measurement and SEM observation.

As a specific example, in order to produce La _0.2 Ca _1.8 Mn ₃ O ₈ , the metal ion composition is adjusted so that the mixture molar ratio is 0.2: 1.8: 3.
The respective nitrates of (NO ₃ ) ₃ , Ca (NO ₃ ) ₂ and Mn (NO ₃ ) ₃ were mixed, the mixture was added to water, and this was added to an aqueous solution of ammonium carbonate (NH ₄ ) CO ₃ to add carbonate Is coprecipitated, washed with water, dried, and then subjected to thermoelectrolysis in an oxygen stream.

In the same manner as above, La _0.4 Ca _1.6 Mn ₃ O ₈ , Y _0.2 Ca _1.8 Mn
₃ O ₈ , La _0.2 Ba _0.2 Ca _1.6 Mn ₃ O ₈ , La _0.2 Sr _0.2 Ca _1.6 Mn
₃ O ₈ , Y _0.4 Ca _1.6 Mn ₃ O ₈ and La _0.1 Ca _1.9 Mn ₃ O ₈ were produced, respectively. For comparison, Ca ₂ Mn ₃ O ₈ and Sr _0.2 Ca _1.8 Mn ₃ O ₈
Was manufactured respectively. The results of measuring the resistivity of these active materials were as shown in Table 1 above.

Next, each positive electrode plate was manufactured using these active materials. These positive electrode plates are obtained by mixing each of the active materials as a main component, for example, acetylene black, adding a Teflon dispersion and isopropanol to the mixture, kneading the mixture into a gum, and then performing roll molding.

Lithium secondary batteries were manufactured using a 1 M LiClO ₄ solution of propylene carbonate as an electrolyte, and a discharge characteristic of each of the batteries was examined. The discharge current was 0.5 mA / cm ² .

As is apparent from the example shown in FIG. 1, the batteries using the positive electrode of the present invention were all Ca ₂ Mn ₃ O ₈ and Sr of the comparative example.
_It can be seen that the discharge characteristics were significantly improved as compared with the battery using _0.2 Ca _0.8 Mn ₃ O ₈ as the positive electrode. More specifically, Y ³⁺ and La ³⁺
The discharge capacity in which Ca ²⁺ is replaced by is increased as compared with that of Ca ² Mn ₃ O ₈ . In particular, the discharge capacity of the La ³⁺ substituted oxide increased remarkably, which coincides with the result of the decrease in resistivity. Also, La
Oxide substituted with ³⁺ -Ba ²⁺ (-Sr ²⁺ ) also shows an increase in discharge capacity, but only with Sr ²⁺ like Sr _0.2 Ca _1.8 Mn ₃ O ₈ shown as a comparative example. On the contrary, it was found that the discharge capacity was lower than that of Ca ₂ Mn ₃ O ₈ .

FIG. 2 illustrates the charge / discharge cycle characteristics of a lithium secondary battery using a positive electrode plate made of the active material of the present invention. Both charging and discharging were performed at 0.5 mA / cm ^2, and discharging was performed until the battery voltage reached 1.5 V. Charging was performed by an amount equal to the amount of discharge, and thereafter, this operation was repeated. As is clear from FIG. 2, the characteristic curve was substantially flat and stable, and it was found that the characteristic curve could be used for a secondary battery. The other active materials of the present invention also showed similar tendency. In this case, the characteristic curve of the cycle characteristics of the oxide substituted with La ³⁺ -Sr ²⁺ was more flat in the initial cycle than the oxide substituted with only La ³⁺ . Although not shown, similar flat cycle characteristics were observed in the case of substitution with La ³⁺ -Ba ²⁺ .

〔The invention's effect〕

As described above, according to the present invention, any of the composite oxides in which a part of Ca ₂ of Ca ₂ Mn ₃ O ₈ is substituted with Y, La or Y-Ba, Y-Sr, La-Ba, La-Sr Is used as the positive electrode active material of the lithium secondary battery, and when forming the positive electrode, the conventional Ca is used.
Compared to the positive electrode made of ₂ Mn ₃ O ₈ , it has the effects of improving the conductivity and increasing the discharge capacity of the battery.

[Brief description of the drawings]

FIG. 1 is a comparison diagram of the discharge characteristics of a lithium secondary battery using a positive electrode of an embodiment of the present invention and a lithium secondary battery using a conventional positive electrode of a comparative example, and FIG. FIG. 4 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery using the positive electrode of FIG.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 10/40 H01M 10/40 Z // C01F 17/00 C01F 17/00

Claims (1)

(57) [Claims] 1. A _{L X Ca 2-X Mn 3} O 8 or _{L X E Y Ca 2-XY} Mn 3 O 8
(Where L is Y or La and E is Ba or Sr) a positive electrode for a lithium secondary battery using a positive electrode active material.