KR100274235B1 - Cathode active material for lithium ion secondary battery - Google Patents

Abstract

PURPOSE: Provided is a cathode active material for lithium ion secondary battery, which has a low irreversible capacity, and low reduction of capacity in continuous charging/discharging. CONSTITUTION: The cathode active material for lithium ion secondary battery, is represented by formula LiwNi1-x-y-zCoxM'yM"zO2(wherein, M' is selected from the group consisting of Al, B, Mn and Mg, M" is selected from the group consisting of Al, B, Mn and Mg, 0.97 <= w <= 1.05, 0.80 <= 1-x-y-z <= 0.85, 0.11 <= x <= 0.18, 0.02 <= y+z <= 0.04). The cathode active material has an average diameter of 0.5-50 micron, specific surface area of 0.2-5 g/m¬2, and tap density of 1.7-3 g/cc.

Description

Cathode active material for lithium ion secondary battery

Industrial use field

The present invention relates to a cathode active material for lithium ion secondary batteries, and more particularly to a cathode active material for nickel-based lithium ion secondary batteries.

Prior art

Representative lithium ion secondary battery positive electrode active material may include a cobalt-based positive electrode active material LiCoO ₂ , which has excellent conductivity at room temperature, excellent life characteristics, but has the disadvantage of small capacity.

In order to solve this problem, there have been attempts to improve capacity through a modification of a cell design, and alternatively, there has been an attempt to develop a new high capacity cathode active material. Examples of such active materials include nickel-based cathode active materials such as LiNiO _{2 having a} capacity of about 20% larger than that of LiCoO ₂ , which is a cobalt-based cathode active material. However, LiNiO ₂ exhibits an initial capacity of 180 mAh / g, but has a large irreversible capacity, and the capacity of the active material collapses during continuous charging and discharging, thereby rapidly decreasing the capacity.

To solve this problem, US Patent No. 5,631,105 discloses an active material in which a part of nickel or lithium in LiNiO ₂ is replaced with magnesium, calcium, strontium, barium, aluminum, chromium, boron or cobalt, and US Patent No. 5,626,635 Discloses an active material in which a part of nickel is substituted with cobalt or manganese in LiNiO ₂ , but its effect is not sufficient.

In order to solve the above problems, an object of the present invention is to provide a nickel-based active material having a small irreversible capacity and a small capacity decrease even during continuous charging and discharging.

1 is a charge and discharge graph according to a first embodiment of the present invention.

2 is a charge and discharge graph according to a second embodiment of the present invention.

3 is a charge and discharge graph according to a third embodiment of the present invention.

4 is a charge and discharge graph according to a fourth embodiment of the present invention.

In order to achieve the above object, the present invention has the following general formula (1), has an average particle diameter of 0.5-50 microns, a specific surface area of 0.2-5 g / m 2, and a tap density of 1.7-3 g / kPa. It provides an active material.

Formula 1

Li _w Ni _1-xyz Co _x M ′ _y M ″ _z O ₂

Wherein M 'is Al, B, Mn or Mg, M' 'is Al, B, Mn or Mg, 0.97≤w≤1.05, 0.80≤1-xyz≤0.85, 0.11≤x≤0.18, 0.02≤y + z≤0.04.

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

A part of nickel of LiNiO ₂ used as an active material of a lithium ion secondary battery is substituted with cobalt having high electron conductivity and stabilizing the active material structure, and a part of the cobalt is again replaced with aluminum, boron, manganese, magnesium or a mixture thereof. By substituting with, it is stable even during continuous charging and discharging to prepare an active material having a small irreversible capacity. Preferably magnesium alone or at the same time magnesium and aluminum are used to displace a portion of cobalt. At this time, the composition ratio of the elements constituting the active material preferably satisfies the following formula (1).

Formula 1

Li _w Ni _1-xyz Co _x M ′ _y M ″ _z O ₂

Wherein M 'is Al, B, Mn or Mg, M' 'is Al, B, Mn or Mg, 0.97≤w≤1.05, 0.80≤1-xyz≤0.85, 0.11≤x≤0.18, 0.02≤y + z≤0.04.

In the case of the active material that deviates from the composition ratio, the irreversible capacity is large and does not exhibit a desirable cycle life.

In order to prepare the active material according to the present invention, the raw materials capable of providing the respective elements constituting the active material are mixed at an appropriate ratio, followed by primary sintering at 350-450 ° C. for 5-7 hours, and then at 650-750 ° C. Second sintering for 14-16 hours. Preferably, primary sintering is carried out at 400 ° C. for 6 hours, and secondary sintering is carried out at 700 ° C. for 15 hours. At this time, LiOH, NiOH as nickel source, CoOH as cobalt source, CoOH as manganese source, MnOOH as magnesium source, MgOH as magnesium source, Al (OH) ₃ as aluminum source, H ₃ BO ₃ as boron source can be used. .

It is preferable that the average particle diameter of the finally prepared active material is 0.5-50 micron. If the average particle diameter is less than 0.5 microns, there is a possibility that side reactions with the electrolyte may occur, and if the average particle diameter exceeds 50 microns, the packing density may be lowered during manufacturing of the electrode plate.

Moreover, it is preferable that the specific surface area of an active material is 0.2-5 g / m <2>. If the specific surface area is less than 0.2 g / m 2, the charge and discharge efficiency of the battery may decrease, and if the specific surface area exceeds 5 g / m 2, there is a possibility that side reactions with the electrolyte occur.

In addition, it is preferable that the tap density of the active material is 1.7-3 g / ㏄, and the active material outside this range is difficult to exhibit a desirable packing density in manufacturing the electrode plate.

Those skilled in the art will be able to easily manufacture a lithium ion secondary battery according to a known battery manufacturing method using the cathode active material of the present invention.

In the lithium ion secondary battery, tin oxide, amorphous carbon, graphite, lithium metal, organic sulfur, etc. may be used as a negative electrode active material, and lithium salts such as LiPF ₆ and LiClO ₄ may be dissolved as an electrolyte. Nonnaquaous electrolytes such as propylene carbonate, ethylene carbonate and dimethyl carbonate can be used.

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.

Example 1-25

Using LiOH as the lithium source, NiOH as the nickel source, CoOH as the cobalt source, MnOOH as the manganese source, MgOH as the magnesium source, Al (OH) ₃ as the aluminum source, H ₃ BO ₃ as the boron source The mixture was mixed so as to have an active material composition ratio according to the formula of, and first sintered at 400 ° C. Subsequently, after secondary sintering at 700 ° C. for 15 hours, the mixture was slowly cooled to room temperature.

92 wt% of the prepared active material, 4 wt% of the conductive agent, and 4 wt% of polyvinylidene fluoride as a binder were mixed with N-methyl pyrrolidone as a solvent to prepare a slurry, and then applied to a current collector to prepare a positive electrode plate.

The battery was assembled using a mixture of ethylene carbonate and dimethyl carbonate in which lithium metal, a separator, and LiPF ₆ were dissolved as electrolytes, and then charged and discharged at 0.1 C. Is shown in Table 1. At this time, the final charging voltage was 4.1V, the final discharge voltage was 2.75V, and the charge and discharge graphs of the batteries according to Examples 1, 2, 3, and 4 are respectively 1, 2, and FIG. 3 and FIG. 4. The irreversible capacity is calculated from the initial charge capacity and the discharge capacity value, and is expressed as a percentage. The cycle life is the capacity after 80 cycles of charge and discharge at 1C.

Chemical formula Charge capacity (h / g) Discharge capacity (h / g) Irreversible capacity (%) Cycle life (%) Example 1 LiNi _0.8 Co _0.16 Mn _0.04 O ₂ 150 97 35 70 Example 2 LiNi _0.8 Co _0.16 Mg _0.04 O ₂ 168 128 24 85 Example 3 LiNi _0.8 Co _0.16 Al _0.04 O ₂ 164 118 28 81 Example 4 LiNi _0.8 Co _0.16 B _0.04 O ₂ 134 84 36 75 Example 5 LiNi _0.8 Co _0.18 Mn _0.02 O ₂ 160 110 32 65 Example 6 LiNi _0.8 Co _0.18 Mg _0.02 O ₂ 195 156 20 70 Example 7 LiNi _0.8 Co _0.18 Al _0.02 O ₂ 184 140 24 65 Example 8 LiNi _0.8 Co _0.18 B _0.02 O ₂ 150 102 32 62 Example 9 LiNi _0.85 Co _0.11 Mn _0.04 O ₂ 155 101 35 70 Example 10 LiNi _0.85 Co _0.11 Mg _0.04 O ₂ 181 138 24 82 Example 11 LiNi _0.85 Co _0.11 Al _0.04 O ₂ 175 126 28 76 Example 12 LiNi _0.85 Co _0.11 B _0.04 O ₂ 145 90 38 72 Example 13 LiNi _0.8 Co _0.16 Mg _0.02 O ₂ 140 98 30 65 Example 14 LiNi _0.8 Co _0.16 Mg _0.02 Al _0.02 O ₂ 163 124 24 65 Example 15 LiNi _0.8 Co _0.16 Mg _0.02 B _0.02 O ₂ 162 115 29 62 Example 16 LiNi _0.85 Co _0.11 Mn _0.02 Mg _0.02 O ₂ 153 103 33 70 Example 17 LiNi _0.85 Co _0.11 Al _0.02 Mg _0.02 O ₂ 175 131 25 76 Example 18 LiNi _0.85 Co _0.11 B _0.02 Mg _0.02 O ₂ 145 94 35 72 Example 19 LiNi _0.85 Co _0.11 Mn _0.01 Al _0.03 O ₂ 155 101 35 70 Example 20 LiNi _0.85 Co _0.11 Al _0.03 B _0.01 O ₂ 175 126 28 76 Example 21 LiNi _0.85 Co _0.11 B _0.02 Al _0.02 O ₂ 145 90 38 72 Example 22 LiNi _0.85 Co _0.11 Mn _0.02 Al _0.02 O ₂ 155 101 35 70 Example 23 Li _1.05 Ni _0.8 Co _0.18 Mg _0.02 O ₂ 185 143 23 Example 24 LiNi _0.8 Co _0.18 Mg _0.02 O ₂ 195 156 20 Example 25 Li _0.97 Ni _0.8 Co _0.18 Mg _0.02 O ₂ 176 147 16

As shown in FIGS. 1, 2, 3, 4 and Table 1, it can be seen that Example 2 using magnesium and Example 3 using aluminum exhibit relatively high capacity characteristics. In addition, when the irreversible capacity is 25% or less, it can be seen that a part of cobalt is substituted by using magnesium alone or magnesium and aluminum at the same time, and a cycle life of 80% or more can be used to remove part of cobalt using magnesium or aluminum. It can be seen that the case of substitution. As a result, it can be seen that it is preferable to replace a part of cobalt added to the nickel-based positive electrode active material using magnesium or aluminum or a mixture thereof.

As described above, the lithium ion secondary battery manufactured using the nickel-based positive electrode active material according to the present invention has a small irreversible capacity and a small capacity decrease even during continuous charging and discharging. In addition, by assembling the battery using the positive electrode active material according to the present invention and the negative electrode active material having the same amount of irreversible capacity as the positive electrode active material, it is possible to provide a battery having efficient use of the active material.

Claims (2)

The positive electrode active material for lithium ion secondary batteries which has the following general formula (1), has an average particle diameter of 0.5-50 microns, a specific surface area of 0.2-5 g / m 2, and a tap density of 1.7-3 g / m 3. Formula 1 Li _w Ni _1-xyz Co _x M ′ _y M ″ _z O ₂ Wherein M ′ is selected from the group consisting of Al, B, Mn and Mg, M ″ is selected from the group consisting of Al, B, Mn and Mg, and 0.97 ≦ w ≦ 1.05, 0.80 ≦ 1-xyz ≦ 0.85 , 0.11 ≦ x ≦ 0.18, 0.02 ≦ y + z ≦ 0.04. The positive active material for a lithium ion secondary battery of claim 1, wherein M ′ is Mg and M ″ is Al or Mg.