KR20010035700A - A positive electrode plate for a lithium secondary battery - Google Patents

Abstract

PURPOSE: An anode plate for a lithium secondary battery is provided which has excellent heat-stability and high temperature life property. CONSTITUTION: The anode plate for a lithium secondary battery is prepared by adding metallic oxide powder selected from oxides of Ca, Mg, Sr, Ba and mixtures thereof to lithium complex metallic oxide selected from the group consisting of LixCoO2, LixCoS2, LixMnF2, LixMnF2, LixMnS2, LixMn2O4, LixMn2S4, LixMn2F4, LixCoO2-yFy, LixCoO2-ySy, LixCo1-yMyO2, LixCo1-yMyS2, LixCo1-yMyF2, LixCo1-yMyP2, LixCo1-yMyO2-zSz, LixCo1-yMyO2-zFz, LixNi1-y-zCoyMzO2, LixNi1-y-zCoyMzS2 and LixNi1-y-zCoyMzF2, wherein M is a metal selected from the group consisting of Mg, Al, Cr, Fe, Mn, Sr, La and Ce and each x, y and z is above 0 and under 1.

Description

Positive electrode plate for lithium secondary battery {A POSITIVE ELECTRODE PLATE FOR A LITHIUM SECONDARY BATTERY}

Field of invention

The present invention relates to a positive electrode plate for lithium secondary batteries having improved thermal stability and high temperature life characteristics, and more particularly, to a positive electrode plate for lithium secondary batteries having excellent thermal stability and high temperature life characteristics by mixing a small amount of metal oxide powder with a positive electrode active material. will be.

Prior art

Recently, with the development of the high-tech electronic industry, it is possible to reduce the weight and weight of electronic equipment, and thus the use of portable electronic devices is increasing. As a power source for such portable electronic devices, the necessity of a battery having a high energy density has been increased, and research on lithium secondary batteries has been actively conducted.

Li-metal or carbon material is used as a cathode material of a lithium secondary battery, and a chalcogenide compound is used as a cathode material. When Li-metal is used as a negative electrode material, there is a risk of explosion due to short circuit due to the formation of dendrite (dentrite), which is being replaced by carbon material instead of Li-metal as negative electrode material.

In general, composite metal oxides used as a cathode active material are synthesized by a solid phase method. Matsushita is a method for synthesizing a composite metal oxide using a two-step continuous sintering process in which a mixture of metal oxides is first reacted at 400 to 580 ° C. to form an initial oxide, and a complete crystalline material is synthesized at 600 to 780 ° C. Was used. As such, the method of manufacturing a conventional composite metal oxide electrode is quite complicated and has a disadvantage of undergoing many facilities and processes.

In addition, the conventional composite metal oxide synthesis method has a relatively high synthesis temperature and a large particle size of the reactants, so it is very difficult to control physical properties such as surface area and pore size, particle morphology, and the like. Since is an important factor affecting the electrochemical properties of the battery, efforts are being made to control the physical properties through the diversification of the synthesis method. However, in the conventional solid state method, it is difficult to achieve a change in the surface structure and shape of the shape, and there is an urgent need for a study on improving the electrochemical characteristics of the battery through the surface change.

A material that is currently widely used as a positive electrode active material may include a composite metal oxide of _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LiMnO 2, such as _{LiNi 1-x Co x O 2} (0 <x <1). LiCoO ₂ has good electrical conductivity, high battery voltage, and excellent electrode characteristics, and is a representative anode electrode material commercialized and sold by SONY, and has a disadvantage of being expensive. LiNiO ₂ is relatively inexpensive among the above-mentioned cathode electrode materials and exhibits the highest discharge capacity of battery characteristics, but is difficult to synthesize.

Mn-based electrode materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize, inexpensive, have good electrochemical discharge characteristics, and are less polluted to the environment. In particular, LiMn ₂ O ₄ is emerging as the most promising cathode active material of next-generation large secondary batteries such as electric vehicles and EV power sources due to its excellent stability of the battery system. Discharge capacity is drastically reduced.

In addition, the Mn-based active material also has a problem in that manganese ions spontaneously separate from the internal structure into an electrolyte solution regardless of electrochemical charge / discharge at high temperatures. The manganese ions are eluted by an acidic substance such as HF produced by reacting an electrolytic salt such as LiPF ₆ with water present in the electrolyte and the electrode plate. The eluted manganese ions act as a factor that degrades battery performance, such as a decrease in battery capacity and lifetime.

As a method for solving this problem, a method of synthesizing a lithium equivalent greater than 1 or recently replacing a part of oxygen having a spinel structure with fluorine is known to improve high temperature life characteristics.

An object of the present invention is to provide a positive electrode plate for a lithium secondary battery that improves thermal safety and high temperature life characteristics.

Another object of the present invention is to provide a positive electrode plate for a lithium secondary battery which improves the high temperature life characteristics and safety of the battery by not reacting with an acid material that elutes manganese ions, thereby producing gas in the battery.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the DSC measurement result about the electrode plate for battery manufacture of Example 4 and the comparative example 2. FIG.

Figure 2 is a graph showing the life characteristics at room temperature (20 ℃) and high temperature (50 ℃) for a coin type half-cell prepared according to Example 3.

Figure 3 is a graph showing the high temperature life characteristics at 50 ℃ for coin type half-cell prepared according to Examples 3 and 4 and Comparative Example 2.

In order to achieve the object of the present invention, a metal oxide powder is added to a lithium composite metal oxide to prepare a positive electrode plate.

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

In the present invention, to improve the thermal stability and high temperature life characteristics of the lithium secondary battery, a positive electrode plate is prepared by adding a metal oxide powder to a lithium composite metal oxide as a positive electrode active material.

Examples of the lithium composite metal oxide used as the cathode active material include Li _x CoO ₂ , Li _x CoS ₂ , Li _x CoF ₂ , Li _x MnO ₂ , Li _x MnF ₂ , Li _x MnS ₂ , Li _x Mn ₂ O ₄ , Li _x Mn ₂ S ₄ , Li _x Mn ₂ F ₄ , Li _x CoO _2-y F _y , Li _x CoO _2-y S _y , Li _x Co _1-y M _y O ₂ , Li _x Co _1-y M _y S ₂ , Li _x Co _1-y M _y F ₂ , Li _x Co _1-y M _y P ₂ , Li _x Co _1-y M _y O _2-z S _z , Li _x Co _1-y M _y O _{2 -z} F _z , Li _x Ni _1-yz Co _y M _z O ₂ , Li _x Ni _1-yz Co _y M _z S ₂ , Li _x Ni _1-yz Co _y M _z F _2, and the like may be used. Wherein M is a metal of any one of Mg, Al, Cr, Fe, Mn, Sr, La, Ce and x, y and z are numbers in the range of greater than 0 and less than 1.

As the metal oxide, an oxide of Ca, Mg, Sr, Ba, or a mixture thereof may be used. The metal oxide may be added in powder form and uniformly dispersed in the positive electrode plate. It is preferable that the addition amount of a metal oxide is 0.01 to 10 weight% with respect to a positive electrode active material. If the addition amount of the metal oxide is less than 0.01% by weight, the effect of addition is insignificant, and if it exceeds 10% by weight, there is a problem of deteriorating battery performance due to the progress of side reactions.

The metal oxide, one of CaO, MgO, SrO or BaO of which is to produce a fluoride compound such as by reaction with HF respectively, CaF _2, MgF _2, SrF _2, or BaF _2. Since these fluoride compounds are solid compounds, they do not increase the internal pressure of the battery. In addition, CaF ₂ is excellent in electrical conductivity and is also used as an electrode material, thereby improving battery performance.

The electrode plate for a lithium secondary battery of the present invention is manufactured in the following steps. A slurry is prepared by adding a metal oxide selected from the group consisting of Ca, Mg, Sr, Ba, or a mixture of oxides to the lithium composite metal oxide of the present invention, and then dissolving the mixture in which a binder and a conductive agent are added to a solvent. The prepared slurry is poured on Al-foil, and then manufactured into a thin electrode plate using a doctor blade, and dried and rolled to prepare a electrode plate.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

Examples and Comparative Examples

Example 1

0.1 wt% of CaO powder in a cathode plate component in which 3 parts by weight of polyvinylidene fluoride (PVDF) and 3 parts by weight of a conductive agent (Super P) are mixed with 94 parts by weight of LiCoO ₂ powder (C-10 from Nippon Chemical) (-325mesh) was added. The mixture was placed in an N-methyl pyrrolidone (NMP) solvent to prepare a slurry for preparing a plate. The prepared slurry was poured onto Al-foil and then manufactured into a thin electrode plate using a doctor blade. The pole plate was dried in an oven at 120 ° C. for 3 hours, and then rolled to prepare a pole plate for battery manufacture. A coin-type half cell comprising the electrode plate and lithium metal as a counter electrode and containing 1 M LiPF ₆ and ethylene carbonate / dimethyl carbonate (EC / DMC) (1/1) as a nonaqueous electrolyte was constructed. .

Example 2

A half cell was prepared in the same manner as in Example 1, except that CaO powder was added in an amount of 0.5% by weight.

Example 3

A _half cell was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ powder (LM4 manufactured by Nikki) was used as the positive electrode active material and CaO powder was added in an amount of 1.0% by weight.

Example 4

A _half cell was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ powder (LM4 manufactured by Nikki) was used as the positive electrode active material and CaO powder was added in an amount of 0.5% by weight.

Example 5

A _half cell was prepared in the same manner as in Example 1, except that LiNi _0.9 Co _0.1 Sr _0.002 0 ₂ powder (manufactured by Honjo) was used as the cathode active material.

Example 6

A _half cell was prepared in the same manner as in Example 1, except that LiNi _0.9 Co _0.1 Sr _0.002 0 ₂ powder (manufactured by Honjo) was used as the cathode active material and CaO powder was added in an amount of 0.5% by weight.

Comparative Example 1

A half cell was prepared in the same manner as in Example 1, except that CaO, which is a metal oxide, was not added.

Comparative Example 2

A half cell was prepared in the same manner as in Example 3, except that CaO, which is a metal oxide, was not added.

Comparative Example 3

A half cell was prepared in the same manner as in Example 5 except that CaO, which is a metal oxide, was not added.

Thermal Stability Evaluation of the Plate

The battery plates of Example 4 and Comparative Example 2 were charged at 4.3 V, and then impregnated in the same amount of EC / DMC electrolyte to evaluate thermal stability using DSC. This result is shown in FIG. In the case of the electrode plate of Example 4, it can be confirmed that a two-step reaction was performed. First, an endothermic peak appears due to the reaction between the CaO and the electrolyte solution in the electrode plate, and the remaining electrolyte solution and the charged electrode which did not participate in the reaction with CaO successively. The exothermic peak by reaction with LiMn ₂ O ₄ which is an active material was shown. In contrast, in the case of the electrode plate of Comparative Example 2, only an exothermic peak was observed at around 250 ° C. due to the reaction between O ₂ generated from the charged anode and the electrolyte solution.

Investigation of battery life characteristics

The coin-type half cell of Example 4 was charged and discharged 100 times at room temperature (20 ° C) and high temperature (50 ° C) while varying the amount of current at 0.1C, 0.2C, 0.5C and 1C in the range of 4.3 to 3.0V. It was shown in Figure 2 by measuring the discharge capacity.

Investigation of high temperature life characteristics

The coin-type half-cells of Examples 3 and 4 and Comparative Example 2 were charged and discharged 100 times at 50 ° C. while varying the amount of current at 0.1 C, 0.2 C, 0.5 C and 1 C in the range of 4.3 to 3.0 V. Discharge capacity was measured and shown in FIG. 3.

The positive electrode plate prepared by adding a metal oxide powder to a lithium composite metal oxide prepared according to the present invention has excellent thermal stability. The lithium secondary battery to which the positive electrode plate is applied has improved life characteristics and stability of the battery. In particular, when the electrode plate to which the metal oxide powder is added to the Mn-based cathode active material is applied to a lithium secondary battery, it exhibits excellent high temperature life characteristics.

Claims (4)

The positive electrode plate for lithium secondary batteries manufactured by adding metal oxide powder to the lithium composite metal oxide which is a positive electrode active material. The method of claim 1, wherein the lithium composite metal oxide is Li _x CoO ₂ , Li _x CoS ₂ , Li _x CoF ₂ , Li _x MnO ₂ , Li _x MnF ₂ , Li _x MnS ₂ , Li _x Mn ₂ O ₄ , Li _x Mn ₂ S ₄ , Li _x Mn ₂ F ₄ , Li _x CoO _2-y F _y , Li _x CoO _2-y S _y , Li _x Co _1-y M _y O ₂ , Li _x Co _1-y M _y S ₂ , Li _x Co _1-y M _y F ₂ , Li _x Co _1-y M _y P ₂ , Li _x Co _1-y M _y O _2-z S _z , Li _x Co _1-y M _y O _{2 -z} F _z , Li _x Ni _1-yz Co _y M _z O ₂ , Li _x Ni _1-yz Co _y M _z S ₂ , and Li _x Ni _1-yz Co _y M _z F ₂ (wherein M is Mg , Al, Cr, Fe, Mn, Sr, La, and Ce, any one metal selected from the group consisting of x, y and z is a number in the range of greater than 0 and less than 1) Pole plate. The positive electrode plate of claim 1, wherein the metal oxide powder is selected from the group consisting of Ca, Mg, Sr, Ba, and oxides thereof. The positive electrode plate for lithium secondary battery according to claim 3, wherein the amount of the metal oxide powder added is 0.01 to 10 wt% based on the positive electrode active material.