KR100296877B1 - Positive active material for lithium secondary battery and lithium secondary by using the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, and the cathode active material has the following general formula (1).

[Formula 1]

Li _{1 + a} Mn _2-y M _y O _4-z S _z F _z

(Wherein, -0.1 ≦ a ≦ 0.2, 0 ≦ y ≦ 0.2, −0.1 ≦ z ≦ 0.2, and M is a transition metal)

The lithium secondary battery using the positive electrode active material is excellent in cycle life characteristics at high temperature.

Description

Positive electrode active material for lithium secondary battery and lithium secondary battery using same {POSITIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BY USING THE SAME}

[Industrial use]

The present invention relates to a positive electrode active material for lithium secondary batteries, and more particularly, to a positive electrode active material for lithium secondary batteries having excellent high temperature cycle life characteristics.

[Prior art]

Currently, lithium secondary batteries are rapidly increasing in application to mobile phones, camcorders, and notebook computers. The factor that determines the capacity of these batteries is the positive electrode active material and the electrochemical properties of these materials determine whether they can be used at high rates for a long time or maintain their initial capacity over many charge and discharge cycles. Another important characteristic factor is the rate of capacity reduction at high temperatures. For example, in the case of a mobile phone, the capacity decreases rapidly when left at a high temperature (50 ° C.) for a long time.

Among the materials used as the cathode active material for lithium secondary batteries, manganese-based active materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize, have a relatively low manufacturing cost, and have low environmental pollution. Among them, LiMn ₂ O ₄ is emerging as a cathode active material having the highest applicability to electric vehicles due to the stability of a battery system.

LiMn ₂ O ₄ has excellent cycle life at room temperature, but has a problem in that capacity decreases rapidly during continuous charge and discharge at high temperatures. The valence of Mn in LiMn ₂ O ₄ is 3.5, substantially Mn is present in the form of Mn ³⁺ and Mn ⁴⁺ . At this time, when the temperature is increased, Mn ⁴⁺ is stable, but Mn ³⁺ is unstable, and a disproportionation reaction occurs in which Mn ³⁺ becomes Mn ⁴⁺ and Mn ²⁺ during high temperature charge and discharge, and thus, high temperature charge and discharge It is known that the dose decreases rapidly. In addition, a battery using LiMn ₂ O ₄ has a problem in that a phenomenon in which capacity decreases rapidly within an initial 10 cycle occurs.

The present invention is to solve the above problems, an object of the present invention is to provide a positive electrode active material for manganese-based lithium secondary battery excellent in high temperature cycle life characteristics.

1 is a graph showing the high temperature cycle life characteristics of the lithium secondary battery prepared by the method of the Examples and Comparative Examples of the present invention.

In order to achieve the above object, the present invention provides a cathode active material for a lithium secondary battery of the formula (1).

[Formula 1]

Li _{1 + a} Mn _2-y M _y O _4-z S _z F _z

(In the above formula, -0.1 <a <0.2, 0 <y <0.2, -0.1 <z <0.2, and M is a transition metal.)

In addition, the positive electrode including a positive active material for a lithium secondary battery of Formula 1; A negative electrode including a negative electrode active material capable of deintercalation of lithium ions; A separator present between the anode and the cathode; And it provides a lithium secondary battery comprising the non-aqueous electrolyte.

Hereinafter, the present invention will be described in more detail.

The present inventors provide a positive electrode active material for a manganese-based lithium secondary battery having excellent cycle life at high temperature by replacing a part of O with S and F in LiMn ₂ O ₄ and a part of Mn with a transition metal. It has been found that the present invention has been completed.

The positive electrode active material of the present invention in which a part of O is substituted with S and F and a part of Mn is substituted with a transition metal has the following Formula 1.

[Formula 1]

Li _{1 + a} Mn _2-y M _y O _4-z S _z F _z

(Wherein, -0.1 ≦ a ≦ 0.2, 0 ≦ y ≦ 0.2, −0.1 ≦ z ≦ 0.2, M is a transition metal, for example Sc, Ti, V, Cr, Cu, Zn, Ga, Ge And transition metals such as Ag and Cd.

As shown in Formula 1, the positive electrode active material of the present invention is a positive electrode active material formed by substituting part of O with S and F, substituting part of Mn with a transition metal, and partially controlling the amount of Li.

The positive electrode active material having the above-described structure was able to provide a battery having excellent high temperature cycle life characteristics by replacing part of O with S and F and part of Mn with a transition metal. In addition, by controlling the amount of Li, the valence of Mn can be adjusted, so that a sudden decrease in capacity at high temperatures due to an unbalanced phenomenon in which Mn ³⁺ becomes Mn ⁴⁺ and Mn ²⁺ can be prevented.

The positive electrode active material according to the present invention may be prepared by mixing lithium salt, manganese salt, fluorine salt, sulfide salt and cobalt salt in an appropriate ratio, and then firing it at about 750 to 800 ° C. Lithium carbonate, lithium nitrate, lithium hydroxide, etc. may be used as the lithium salt, and manganese acetate, manganese dioxide, and the like may be used as the manganese salt. In addition, manganese fluoride, lithium fluoride, etc. may be used as the fluoride salt, and manganese sulfide, lithium sulfide, etc. may be used as the sulfide salt, and cobalt hydroxide, cobalt nitrate or the like may be used as the cobalt salt. Cobalt carbonate and the like can be used. The lithium salt, manganese salt, fluoride salt, sulfide salt and cobalt salt are not limited to the above-mentioned compounds.

The lithium secondary battery using the positive electrode active material of the present invention is made of a carbon-based active material that is a material that is generally used as a negative electrode active material of lithium secondary batteries, such as graphite and carbon, which can deintercalation-intercalation of lithium ions as a negative electrode. Can be used. As the electrolyte, a non-aqueous liquid electrolyte, a polymer electrolyte, or the like, which is generally used as an electrolyte of a lithium secondary battery, can be used. As the separator, a polymer film generally used in a lithium secondary battery may be used.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

Li ₂ CO ₃ , MnF, MnS, CoOH, LiF and MnO ₂ are uniformly mixed to a molar ratio of Li _1.03 Mn _1.97 Co _0.03 O _3.99 S _0.005 F _0.005 , and then the mixture is calcined at 750 ° C. for 24 hours and then at room temperature It cooled slowly to and produced the positive electrode active material for lithium secondary batteries.

Polyvinylidene as the active material, binder, and carbon black as the conductive agent were mixed at a weight ratio of 92: 4: 4, followed by mixing until a uniform paste was added while adding a certain amount of N-methyl pyrrolidone. The paste was coated on aluminum foil to a thickness of 300 microns using a doctor-blade machine, and then completely blown off N-methyl pyrrolidone at 150 ° C. and then compressed under constant pressure. As a counter electrode, the lithium foil was also cut to the same size as the positive electrode, and then pressed to Ni foil of the coin battery cap. The separator used was celgard, and the electrolyte used was a mixture of ethylene carbonate / dimethyl carbonate in which LiPF ₆ was dissolved.

(Example 2)

After mixing Li ₂ CO ₃ , MnF, MnS, CoOH, LiF and MnO ₂ homogeneously in a molar ratio of Li _1.03 Mn _1.97 Co _0.03 O _3.98 S _0.001 F _0.01 , the mixture was calcined at 750 ° C. for 24 hours and then at room temperature It cooled slowly to and produced the positive electrode active material for lithium secondary batteries. A coin battery was manufactured as in Example 1 using the active material.

(Comparative Example 1)

After uniformly mixing Li ₂ CO ₃ and MnO ₂ to a molar ratio of LiMn ₂ O ₄ , the mixture was calcined at 790 ° C. for 24 hours, and cooled slowly to room temperature to prepare a cathode active material for a lithium secondary battery. A coin battery was prepared in the same manner as in Example 1 using the cathode active material.

The high temperature (50 ° C) cycle life characteristics of the battery were measured using the batteries of Example 1-2 and Comparative Example 1, and the results are shown in FIG. 1. As shown in FIG. 1, as a result of measuring the initial capacities of the batteries of Examples 1-2 and Comparative Example 1, Example 1 was found to be 110 mAh / g, Example 2 was 103 mAh / g, and Comparative Example 1 was 117 mAh / g. In addition, when the batteries of Examples 1-2 and Comparative Example 1 were charged and discharged at 0.2C 20 times, the capacity retention ratio of the initial capacity was 96% in Example 1 and 99% in Example 2, and Comparative Example 1 Was 70%. That is, although the initial capacity of the battery of Comparative Example 1 is slightly higher, it can be seen that the capacity decreases rapidly as the charge and discharge cycle proceeds. Therefore, although the initial capacity of the battery of Example 1-2 was somewhat lower than that of Comparative Example 1, the capacity retention rate according to the charge / discharge cycle was much higher than that of Comparative Example 1, indicating that the high temperature cycle life was excellent. have.

As described above, the high temperature cycle life characteristics of the cathode active material for lithium secondary batteries of the present invention are improved by 25% or more compared to LiMn ₂ O ₄ .

Claims (2)

A cathode active material for a lithium secondary battery of Formula 1 below. [Formula 1] Li _{1 + a} Mn _2-y M _y O _4-z S _z F _z (Wherein, -0.1 ≦ a ≦ 0.2, 0 ≦ y ≦ 0.2, −0.1 ≦ z ≦ 0.2, and M is a transition metal) A positive electrode including a positive active material for a lithium secondary battery of Formula 1; A negative electrode including a negative electrode active material capable of deintercalation of lithium ions; A separator present between the anode and the cathode; And The non-aqueous electrolyte Lithium secondary battery comprising a. [Formula 1] Li _{1 + a} Mn _2-y M _y O _4-z S _z F _z (Wherein, -0.1 ≦ a ≦ 0.2, 0 ≦ y ≦ 0.2, −0.1 ≦ z ≦ 0.2, and M is a transition metal)