KR20050011213A - The lithium secondary battery with the high temperature conservation-property improved - Google Patents

Abstract

PURPOSE: A lithium secondary battery is provided to minimize the capacity reduction and to prevent the impedance increase of battery upon high temperature storage. CONSTITUTION: The lithium secondary battery comprises a positive electrode, a negative electrode and an electrolytic solution, wherein any one or both of the positive electrode and the negative electrode contain a metal hydroxide, and the electrolytic solution contains a first additive represented by the formula 1 and a second additive having a structure represented by the formula 2, the formula 3 or the formula 4, in which R is a C1-C5 alkenyl group or a C1-C5 alkyl group, and each of R1 and R2 is independently selected from the group consisting of hydrogen, a C1-C5 alkenyl group, a C1-C5 alkyl group, a halogen, and a phenyl group or phenoxy group which are non-substituted or substituted by a C1-C5 alkyl group or halogen.

Description

Lithium secondary battery with improved high temperature storage characteristics {THE LITHIUM SECONDARY BATTERY WITH THE HIGH TEMPERATURE CONSERVATION-PROPERTY IMPROVED}

The present invention relates to a lithium secondary battery with improved high temperature storage characteristics.

Lithium ion batteries are used in a high operating voltage range (0 to 5V), so self-discharge and positive electrode reactivity due to the difference in voltage between high and negative electrodes when exposed to high temperature (over 40 ° C) for a long time after full charge The decomposition reaction with the non-aqueous electrolyte solution causes a decrease in the charge capacity and a sudden increase in the impedance of the battery. This is a major problem of lithium secondary batteries.

In order to solve the above problems, there have been attempts to reduce the reactivity with the electrolyte by using a small amount of additives in the negative electrode, the electrolyte or the positive electrode, or coating inorganic or organic materials on the surface of the positive electrode or the negative electrode powder, in particular Japanese Patent Application Publication No. 98 -255839 incorporates some alkaline earth metal hydroxides into the positive electrode active material to improve its high temperature preservation characteristics after charging.

The inventors have found that incorporating a small amount of metal hydroxide in the preparation of the active material slurry for each or both of the positive and negative electrodes, together with the use of two specific additives in the electrolyte, can achieve the maximum effect in minimizing capacity reduction during high temperature storage. .

The present invention is based on the above findings, and an object of the present invention is to mitigate a decrease in capacity after high temperature storage and to prevent an increase in impedance of a battery.

1 is a schematic diagram showing an insertion electrode roll and a square battery can.

Figure 2 is a graph comparing the initial discharge / charge curve of Comparative Example 4 and Example 1 after high temperature storage.

The present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, an electrolyte, the positive electrode, the negative electrode, or both contain a metal hydroxide, the electrolyte is a first additive of formula 1 and formula 2, formula 3 or formula Provided is a lithium secondary battery characterized by containing a second additive having a structure of 4.

In formula (1), R ₁ and R ₂ are independently of each other hydrogen, a C ₁ -C ₅ alkenyl group, a C ₁ -C ₅ alkyl group, a halogen, or a C ₁ -C ₅ alkyl group or a phenyl group unsubstituted or substituted with halogen or Selected from the group consisting of phenoxy groups;

In Formulas 2 to 4, R is C ₁ ~C ₅ alkenyl (alkenyl) group, or a C ₁ ~C ₅ alkyl group, R ₁ and R ₂ are independently from each other hydrogen, C ₁ ~C ₅ alkenyl group, C ₁ ~ Selected from the group consisting of a C ₅ alkyl group, a halogen, or a C ₁ -C ₅ alkyl group or a phenyl group or a phenoxy group unsubstituted or substituted with a halogen.

In the present invention, it is preferable that the anode, the cathode, or both contain at least one metal hydroxide selected from the group consisting of Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, NaOH.

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

The positive electrode active material slurry or the negative electrode active material slurry according to the present invention includes a metal hydroxide. At this time, the metal hydroxide to be added is preferably used by selecting one or more from the group consisting of crystalline Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, NaOH.

Incorporating a small amount of metal hydroxide in the preparation of the active material slurry of each of the positive and negative electrodes prevents an increase in battery impedance, thereby minimizing a decrease in the average discharge potential, thereby preventing a decrease in energy density.

The amount of metal hydroxide added to each positive electrode and the negative electrode or both is preferably more than 0% by weight and 10% by weight or less. Most metal hydroxides are insulators and do not act as large resistors up to a certain amount. However, when the amount of the metal hydroxides is high, such as 10% by weight, the initial resistance increases, and thus the improvement of high temperature storage characteristics does not appear.

The positive electrode mixture slurry or negative electrode mixture slurry according to the present invention includes a positive electrode active material or a negative electrode active material in addition to the metal hydroxide, respectively.

The present invention uses a transition metal oxide containing lithium as the positive electrode active material, non-limiting examples, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNi _1-X Co _X M _Y O ₂ (where M = Al, Ti, Mg, Zr, 0 <X ≤ 1, 0 ≤ Y ≤ 0.2), LiNi _X Co _Y Mn _1-XY O ₂ (where 0 <X ≤ 0.5, 0 <Y ≤ 0.5) and LiM _x M ' _Y Mn _(2-xy) O ₄ (M, M' = V, Cr, Fe, Co, Ni, Cu, 0 <X ≤ 1, 0 <Y ≤ 1) at least one selected from the group consisting of Transition metal oxides and the like.

According to the present invention, carbon, lithium metal, or an alloy capable of occluding and releasing lithium ions may be used as the negative electrode active material, and TiO ₂ , SnO _2, and Li ₄ Ti ₅ may occlude and release other lithium and have a potential for lithium of less than 2V. Metal oxides such as O ₁₂ may also be used.

As the electrode slurry, a binder, a conductive agent, a viscosity modifier, an auxiliary binder, and the like may be added, if necessary.

The electrolyte according to the present invention comprises a lithium salt and one additive selected from the first additive compound group (1) and one additive selected from the second additive compound group (2), respectively, greater than 0 wt% and 10 wt% in the following electrolyte solution. It contains below. Excessive use of the first additive compound may cause excessive gas generation, and excessive use of the second additive compound may cause an increase in resistance due to an increase in viscosity of the electrolyte.

The lithium salt is at least one selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ .

Non-limiting examples of the electrolyte include ethylene co (carbonate), propylene carbonate, butylene carbonate, vinylene carbonate, sulfolane, γ-butylo lactone, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxy ethane , Tetrahydrofuran, and mixtures thereof.

The first additive compound group (1) of the electrolyte is a compound having the structure of Formula 1, wherein in Formula 1, R ₁ and R ₂ are each independently hydrogen, a C ₁ -C ₅ alkenyl group, C ₁ -C ₅ It is selected from the group consisting of an alkyl group, a halogen, or a C _{1 to} C ₅ alkyl group or a phenyl group or phenoxy group which is optionally substituted with halogen.

Non-limiting examples of the first additive include VC (vinylene carbonate), methyl ester, and the like.

The second additive compound group (2) of the electrolyte solution is a compound having the structure of Formula 2, Formula 3 or Formula 4, wherein R is a C ₁ to C ₅ alkenyl group or a C _{1 to} C ₅ alkyl group R ₁ and R ₂ are each independently composed of hydrogen, a C ₁ -C ₅ alkenyl group, a C ₁ -C ₅ alkyl group, a halogen, or a C ₁ -C ₅ alkyl group or a phenyl group or phenoxy group which is unsubstituted or substituted with halogen. Selected from the group.

Non-limiting examples of the second additive include propane sultone (PS) and propene sultone, dimethyl sulfone, diphenyl sulfone, divinyl sulfone, methane sulfonic acid Etc.

[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

The first additive decomposes to form an SEI layer on the surface of the cathode, and the second additive acts on the surface of the anode and the cathode, contributing to the improvement of high temperature properties. At this time, the first additive is a double bond to help the formation of the SEI layer on the surface of the cathode, the second additive is a S and O bond acts on the positive electrode and the negative electrode to perform its role.

The separator may be polyolefin such as polypropylene or polyethylene, and is preferably porous.

The external shape of the battery may be cylindrical, square or pouch type using a can, or coin type. 1 shows rolls and cans inserted into a square battery as an example. (a) is a cathode active material coated on the Al foil (b) is a porous separator, and (c) is a cathode active material coated on the Cu foil. The three parts can be rolled up as shown to make a roll and inserted into a can to produce a square battery.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

EXAMPLE

Example 1

As shown in FIG. 1, a roll was formed by winding a cathode, a porous separator, and a cathode, and a battery inserted into a rectangular can was used. LiCoO ₂ was used as the positive electrode active material, and the mixing ratio was 92.5 wt% of LiCoO ₂ , 2.5 wt% of Al (OH) _3, 2.5 wt% of Super-P (conductor), and 2.5 wt% of PVDF (binder). Phosphorus mixture was added to phosphorus NMP (N-methyl-2-pyrrolidone) to prepare a cathode mixture slurry, and then coated on Al current collector to prepare a cathode. In addition, artificial graphite was used as the negative electrode active material, and the mixing ratio was 92.8 wt% of artificial graphite, 2.5 wt% of Al (OH) ₃ , 0.7 wt% of Super-P (conductive agent), and 4 wt% of PVDF (binder). The negative electrode mixture was prepared by adding NMP, a solvent, to the composition to prepare a negative electrode mixture slurry, and then coating it on a Cu current collector. As an electrolyte, an EC / EMC solution was used in 1M LiPF ₆ , and 2% by weight of VC (vinylene carbonate) and 3% by weight of propane sultone (PS) were added to the electrolyte.

Comparative Example 1

The same procedure as in Example 1 was carried out except that no additives (VC, PS) were used in the electrolyte.

Comparative Example 2

A battery was prepared by the same method as Example 1 except that only 2 wt% of VC (vinylene carbonate) was added to the electrolyte.

Comparative Example 3

The battery cell was prepared in the same manner as in Example 1 except that only 3 wt% of propane sultone (PS) was added to the electrolyte.

Comparative Example 4

The same procedure as in Example 1 was carried out, except that Al (OH) ₃ was not added to the positive electrode and the negative electrode, and the amounts thereof were filled with LiCoO ₂ and artificial graphite, respectively. In this case, 2 wt% VC (vinylene carbonate) and 3 wt% PS (propane sultone) are added to the electrolyte.

[High Temperature Preservation Experiment]

(1) After charging up to 4.2V with 1C charging current and 1C discharge up to 3V, the initial discharge capacity (A) was confirmed. After the cell was charged up to 4.2V in the same way as above, AC impedance was measured. It was. AC impedance is a measure of battery performance and measured for comparison with the amount of change after high temperature storage. Since the AC impedance measurement was before high temperature storage, the values of Example 1 and Comparative Examples 1 to 4 were almost similar, and were about 60 mohm.

Subsequently, after storing at 80 ° C for 10 days, the AC impedance of the battery was measured, discharged at 1 C, and the remaining capacity (B) was measured. After the remaining capacity was measured, charging and discharging were performed three times to confirm the recovery capacity (C).

By measuring the percentage of the remaining capacity (B) and the recovery capacity (C) compared to the initial capacity (A) to calculate the remaining capacity ratio (= B / A) and recovery capacity ratio (= C / A) is shown in Table 1 below . In addition, AC impedance was compared after high temperature storage.

Remaining capacity (%) Recovery capacity rate (%) AC impedance after high temperature storage Example 1 74 79 120 Comparative Example 1 63 68 110 Comparative Example 2 67 68 105 Comparative Example 3 64 70 100 Comparative Example 4 69 73 390

As can be seen from Table 1, when Al (OH) ₃ is contained in the positive electrode and the negative electrode (Example 1, Comparative Examples 1 to 3) it can be seen that the increase in AC impedance after high temperature storage can be prevented. On the other hand, in the case of Comparative Example 4 in which only two types of additives were used in the electrolyte solution without using Al (OH) ₃ , an additive was not used in the electrolyte solution in terms of remaining capacity and recovery capacity (Comparative Example 1) or one type of additive. It can be seen that it is superior to the case of using only (Comparative Examples 2 and 3). In addition, it can be seen that the case of Example 1 using Al (OH) ₃ and two kinds of additives is superior to that of using only two kinds of additives (Comparative Example 4) without Al (OH) ₃ . Therefore, it can be seen that the two additives and Al (OH) ₃ must be used together to produce synergistic effects and show better high temperature storage characteristics than conventional batteries.

(2) Figure 2 shows the charge and discharge curves after preservation of high temperature in Example 1 and Comparative Example 4. In the case of Example 1, the drop of the discharge voltage due to the increase in resistance is much smaller than that of Comparative Example 4, thereby preventing the reduction of energy density (Wh) as well as the recovery capacity (mAh).

The present invention can improve the remaining capacity after high temperature storage by preparing a battery by including a specific two kinds of additives in the electrolyte, and also a small amount of metal hydroxide in the preparation of the active material slurry of each of the positive electrode and negative electrode, and together with the electrolyte solution By using the above specific two kinds of additives, it is possible to achieve the maximum effect in minimizing capacity reduction during high temperature storage.

Claims (4)

In a lithium secondary battery comprising a positive electrode, a negative electrode, an electrolyte solution, The positive electrode, the negative electrode, or both contain a metal hydroxide, The electrolyte solution is characterized by containing a first additive of the formula (1) and a second additive having a structure of formula (2), (3) or (4). [Formula 1] [Formula 2] [Formula 3] [Formula 4] In formula (1), R ₁ and R ₂ are independently of each other hydrogen, a C ₁ -C ₅ alkenyl group, a C ₁ -C ₅ alkyl group, a halogen, or a C ₁ -C ₅ alkyl group or a phenyl group unsubstituted or substituted with halogen or Selected from the group consisting of phenoxy groups In Formulas 2 to 4, R is C ₁ ~C ₅ alkenyl (alkenyl) group, or a C ₁ ~C ₅ alkyl group, R ₁ and R ₂ are independently from each other hydrogen, C ₁ ~C ₅ alkenyl group, C ₁ ~ Selected from the group consisting of a C ₅ alkyl group, a halogen, or a C ₁ -C ₅ alkyl group or a phenyl group or a phenoxy group unsubstituted or substituted with a halogen. The lithium secondary battery of claim 1, wherein the metal hydroxide is selected from the group consisting of Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, and NaOH. The lithium secondary battery according to claim 1 or 2, wherein the first additive is VC (vinylene carbonate) or methyl ester. The method of claim 1 or 2, wherein the second additive is propane sultone (PS), propene sultone, dimethyl sulfone, diphenyl sulfone, divinyl sulfone ( Divinyl sulfone), or a lithium secondary battery, characterized in that methane sulfonic acid.