KR100922685B1 - Cathode active material for lithium secondary battery - Google Patents

Abstract

The present invention is a lithium metal composite oxide containing nickel, cobalt, manganese, the content of Ni is more than 75 mol% of the total amount of metal elements excluding lithium, the electrode active material characterized in that the molar content of Mn is more than the molar content of Co It provides a manufacturing method, an electrode and a secondary battery comprising the electrode active material.

The present invention is a lithium metal composite oxide of LiNi _1-xy Co _x Mn _y O ₂ composition, the content of Ni is more than 75 mol% compared to the total amount of metal elements excluding lithium, the composition of Mn is more than the molar content of Co By using the material as a positive electrode active material, the average discharge voltage, high rate characteristics, and discharge capacity of the battery is improved, and in particular, the energy density is improved compared to conventional commercial LiCoO ₂ .

Secondary battery, positive electrode active material, lithium metal composite oxide, nickel, cobalt, manganese

Description

Cathode active material for lithium secondary battery {CATHODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY}

1 is a discharge curve of a coin cell according to Experimental Example 1. FIG.

Figure 2 is a curve showing the depth of discharge (Depth of Discharge, DOD) of the coin cell according to Experimental Example 1.

3 is a discharge curve of the pouch-type battery according to Experimental Example 2. FIG.

FIG. 4 is an enlarged view of FIG. 3 and compares it with commercial LiCoO ₂ (hereinafter referred to as LCO).

The present invention relates to a lithium metal composite oxide that can be used as a cathode active material of a lithium secondary battery, and relates to a lithium transition metal composite oxide including nickel, cobalt, and manganese.

Recently, with the development of portable devices such as mobile phones, notebook computers, camcorders, and the like, demand for small secondary batteries such as Ni-MH (Ni-MH) secondary batteries and lithium secondary batteries is increasing. In particular, lithium secondary batteries using lithium and nonaqueous electrolytes have been actively developed due to the high possibility of realizing small, lightweight and high energy density batteries. Generally, transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used as cathode materials of lithium secondary batteries, and lithium metal or carbon as anode materials. And the like, and a lithium secondary battery is constructed by using an organic solvent containing lithium ions as an electrolyte between two electrodes.

LiCoO ₂ has been reported to be useful as a cathode active material for lithium secondary batteries in 1980, and many studies have been conducted to date, and it has been employed as a cathode active material for commercialized lithium secondary batteries. However, cobalt is expensive, and due to problems of stability during high rate charging and discharging, development of a new positive electrode active material is being developed instead.

Compared to cobalt oxide, nickel oxide is expected to be a next generation high capacity battery due to a high discharge capacity of 20% or more. However, efforts to overcome this problem continue due to a disadvantage of deterioration in cycle characteristics due to structural instability.

On the other hand, LiNi _1-xy Co _x M _y O ₂ (M = Ni, Mn, Co, Al, etc.) as a lithium ion cathode active material is widely known as a high-capacity material. It is showing.

① It has a lower discharge voltage than LiCoO ₂ which is widely used as anode material, which lowers the average discharge voltage of the battery.At the same time, the discharge cut-off voltage is lowered to 2V, which is lower than 3V when using LiCoO ₂ . There is a downside to it.

② At the end of the discharge, the profile of the discharge curve does not fall sharply, resulting in a high rate capacity.

In the present invention, in the lithium metal composite oxide of LiNi _{1 -x- y} Co _x Mn _y O ₂ composition, the content of Ni is more than 75 mol% compared to the total amount of metal elements except lithium, the mole content of Mn is the mole content of Co In the above case, it was found that the average discharge voltage, high rate characteristic, and discharge capacity of the battery are improved, and in particular, the energy density is improved compared with the conventional one.

Accordingly, the present invention is a lithium metal composite oxide containing nickel, cobalt, manganese, the content of Ni is 75 mol% or more of the total amount of metal elements excluding lithium, the electrode characterized in that the molar content of Mn is more than the molar content of Co It is an object to provide an active material, an electrode and a secondary battery including the same.

The present invention is a lithium metal composite oxide containing nickel, cobalt, manganese, the content of Ni is 75 mol% or more relative to the total amount of metal elements excluding lithium, the electrode active material characterized in that the molar content of Mn is more than the molar content of Co The purpose is to provide.

In addition, an object of the present invention is to provide an electrode and a secondary battery containing the electrode active material.

Hereinafter, the present invention will be described in detail.

<Electrode active material>

The electrode active material according to the present invention is a lithium metal composite oxide containing nickel, cobalt, and manganese, and in particular, a material based on lithium nickel oxide (LiNiO ₂ ). Structural instability of lithium nickel oxide can be overcome to some extent by the addition of Mn and / or Co, and the electrochemical properties of the lithium nickel oxide change greatly depending on the molar ratio of Ni: Mn: Co.

In the present invention, the molar content of Ni is 75 mol% or more relative to the total amount of metal elements excluding lithium, and the molar content of Mn is more than the molar content of Co.

As shown in the results of the examples to be described later, even when the molar content of Ni is 70 mol% or more relative to the total amount of metal elements excluding lithium, and the molar content of Mn is greater than or equal to the molar content of Co, discharge voltage and rate characteristics may be improved. , The composition having an excellent energy density compared to the conventional commercial LiCoO ₂ has a molar content of Ni is 75 mol% or more relative to the total amount of metal elements except lithium, and the molar content of Mn is more than the molar content of Co.

The present invention may include a lithium metal composite oxide having the following formula.

[Formula 1]

Li _{1 + a} Ni _1-xyz Co _x Mn _y M _z O _2-b A _b (-0.05≤a≤0.05, x + y + z≤0.25, y + z≥x, 0≤z≤0.05, 0 ≤ b ≤ 0.05, M is at least one element selected from the group consisting of metals and metalloids having a six coordination structure, A is at least one element selected from the group consisting of Group 16, 17 elements)

In the present invention, in addition to the transition metals of Ni, Co, and Mn, metals or metalloids having a six coordination structure, such as Al, Mg, Ti, and the like, may be further doped, and thermal stability and electron conductivity may be achieved by the addition of such elements. And the like can be improved.

In addition, in the present invention, the oxygen atoms in the lithium metal composite oxide may be further substituted to further include group 16 and 17 elements such as F and S, thereby improving cycle characteristics of the battery.

<Method for Producing Electrode Active Material>

In order to prepare the electrode active material of the present invention, a method known to those skilled in the art may be used as a powder synthesis method, and non-limiting examples thereof include a solid phase reaction method, a coprecipitation method, a sol gel method, and a hydrothermal synthesis method.

Electrode active material of the present invention is particularly as follows,

① a first step of dissolving a salt of Ni, a salt of Co, and a salt of Mn in a solvent, followed by coprecipitation to provide a metal complex hydroxide of nickel, cobalt, and manganese;

② a second step of baking by mixing the hydroxide with a salt of lithium; It may be prepared by a method comprising a.

At this time, the ratio of the salt of Ni, the salt of Co, and the salt of Mn can be adjusted so that the molar ratio of Ni / (Ni + Co + Mn) is 0.75 or more, and the molar ratio of Mn ≥ Co is molar. .

Kinds of salts of Ni, salts of Co, salts of Mn, and Li are not particularly limited in the present invention, and non-limiting examples thereof include nitrate, sulfate, carbonate, and hydride. Hydroxide, acetate, oxalate, chloride, and the like.

The kind of solvent is not particularly limited in the present invention such as water or an organic solvent.

After dissolving the salt of the transition metal in a solvent, a coprecipitation can be obtained by adding a neutralizing agent and / or a complex, etc. according to a coprecipitation method known to those skilled in the art, and the coprecipitation at this time is the kind of solvent and the kind of salt used , Metal complex hydroxide and the like according to the type of the additive.

The co-precipitated metal composite hydroxide may be mixed with a salt of lithium and then heat treated to obtain a metal composite oxide, wherein the heat treatment temperature may be in the range of 600 ° C. to 1200 ° C., and the heat treatment time is 5 hours to 72 hours. It can be a range of time.

In addition, the heat treatment does not necessarily have to be a single step, and may include two or more heat treatment processes, which continuously perform two or more heat treatments for the purposes of calcinations and crystallization. Can be one.

In addition, the present invention may further include a salt of a metal or metalloid (M) having a six coordination structure, such as Al, Mg, Ti, in the first step, wherein the salt content is mole of Ni The molar ratio of the ratio / (Ni + Co + Mn + M) is 0.75 or more, it can be adjusted so that the mole ratio of (Mn + M) ≥ Co molar ratio.

In addition, the electrode active material according to the present invention, Li, Ni, Co, Mn, and / or M (M = Al, Mg) during the coprecipitation reaction of the material in order to further contain group 16, 17 elements such as F, S, etc. Or a fluoride or sulfide of a metal having a sixth coordination structure, such as Ti or the like, may be coprecipitated together, or may be prepared by a method of heat treatment together by adding the fluoride or sulfide.

However, the electrode active material of the present invention is not limited by the above-mentioned preparation methods, and may be prepared by a powder synthesis method known to those skilled in the art.

<Production of Electrode and Secondary Battery>

An electrode comprising the material described in the present invention as an electrode active material may be prepared by a method known to those skilled in the art. For example, in addition to using the material as an active material according to the present invention, the electrode may further use a conductive agent for providing electrical conductivity and a binder that enables adhesion between the material and the current collector. However, the binder at the time of manufacturing an electrode is different from the binder used at the time of manufacturing the said granulated electrode active material particle | grains.

The paste was prepared by adding and stirring a conductive agent to 1 to 30 wt% and a binder to 1 to 10 wt% with respect to the electrode active material prepared by the above method, and then adding the mixture to the dispersion solvent and stirring the mixture. After coating, compressing and drying, the laminate electrode is manufactured.

The conducting agent generally uses carbon black. Products currently marketed as conductive agents include acetylene black series (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (Armak Company ), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by MMM).

Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) or copolymers thereof, cellulose, and the like, and representative examples of the dispersant are isopropyl alcohol and N-methylpyrrolidone. (NMP), acetone and the like.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the paste of the material is easily adhered and is not reactive in the voltage range of the battery. Representative examples include meshes, foils, and the like, such as aluminum or stainless steel.

The present invention also provides a secondary battery comprising the electrode of the present invention. The secondary battery of the present invention can be produced using a method known in the art, and is not particularly limited. For example, the separator may be placed between the positive electrode and the negative electrode to add a nonaqueous electrolyte. In addition, the electrode, the separator and the nonaqueous electrolyte and, if necessary, other additives, may be those known in the art.

In addition, a porous separator may be used as a separator in manufacturing a battery of the present invention, and for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

The nonaqueous electrolyte of the secondary battery that can be used in the present invention may include a cyclic carbonate and / or a linear carbonate. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), and the like. Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. In addition, the nonaqueous electrolyte of the secondary battery of the present invention contains a lithium salt together with the carbonate compound. Specific examples of lithium salts include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ .

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

EXAMPLE

Example 1 Preparation of Cathode Active Material of LiNi _0.8 Co _0.1 Mn _0.1 O ₂

Ni-nitrate, Co-nitrate, and Mn-nitrate are weighed so that the molar ratio of Ni: Co: Mn is 8: 1: 1, dissolved in water to form an aqueous solution, and co-precipitated to form (Ni, Mn, Co) composite metal hydroxide. Got it. Li ₂ CO _{3 was added} to the metal hydroxide so that the molar ratio of Li: (Ni + Co + Mn) was 1: 1, and then heat treated at 400 ° C. for 2 hours in an electric furnace in an oxygen atmosphere, and then heat treated at 750 ° C. for 12 hours. To obtain a positive electrode active material having a composition of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

[Comparative Example _{1] LiNi 0 .7 Co 0 .1} Mn 0 .2 O ₂ of the positive electrode active material prepared

A positive electrode active material having a composition of LiNi _0.7 Co _0.1 Mn _0.2 O ₂ was obtained in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn was set to 7: 1: 2.

Comparative Example 2 LiNi _{0 .8} positive electrode active material of Co _{0 .15} Mn _{0 .05} O ₂ production

A positive electrode active material having a composition of LiNi _0.8 Co _0.15 Mn _0.05 O ₂ was obtained in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn was set to 8: 1.5: 0.5.

Comparative Example 3 Preparation of Cathode Active Material of LiNi _0.7 Co _0.25 Mn _0.05 O ₂

A positive electrode active material having a composition of LiNi _0.7 Co _0.25 Mn _0.05 O ₂ was obtained in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn was set to 7: 2.5: 0.5.

Experimental Example 1 Coin Cell Test

The positive electrode active materials obtained by the methods of Example 1, Comparative Examples 1, 2, and 3 were respectively mixed so that the ratio of the active material: conductive agent: binder was 95: 2.5: 2.5, and a slurry was prepared using NMP as a solvent. . The slurry was coated on Al foil to obtain a positive electrode. Li metal was used as a counter electrode, and a solution in which 1 M of LiPF ₆ was dissolved in a solution having a weight ratio of 1: 2 by EC: EMC was used as an electrolyte. This coin was punched out to produce a coin cell, and the discharge curve was obtained by CC / CV charging up to 4.25V and CC discharge up to 3.0V, which is shown in FIG. 1. In addition, the coin cell was charged and discharged at a rate of 0.1C, 0.2C, 0.5C, and 1C in the same voltage range as above to obtain a rate characteristic (%) based on capacity compared to 0.1C, which is shown in Table 1 below. Indicated.

As shown in FIG. 1, in Example 1 and Comparative Example 1, where the Mn content was equal to or greater than Co, the average discharge voltage was higher than that of Comparative Examples 2 and 3, and as shown in FIG. 2. Similarly, it was found that the voltage drop at the end of discharge also showed a tendency to fall sharper in the case of Example 1 and Comparative Example 1.

As shown in Table 1, in the case of Example 1 and Comparative Example 1, the content of Mn is equal to or greater than Co, which is higher than that of Co. Since the average discharge voltage of the sample according to the present invention is high, even if the IR drop (average discharge voltage drop), which is essential when discharging at a high current, the discharge capacity reduction effect can be canceled by that much, and the discharge Since the slope of the voltage drop at the terminal is more steep, it seems that the capacity decrease due to the IR drop becomes smaller.

Experimental Example 2 Full-Cell Test

The positive electrode was prepared and used in the same manner as in Experimental Example 1, and the negative electrode was mixed using artificial graphite as an active material such that the ratio of the active material, the conductive agent, and the binder was 94.3: 0.7: 5, and NMP was added as a solvent to prepare a slurry. The slurry was coated on Cu foil to obtain a cathode electrode. Using the same electrolyte solution as in Experimental Example 1 to the obtained positive electrode and negative electrode, a battery in the form of a pouch was prepared, which was charged at 4.2V CC / CV and discharged at 3V CC to obtain a discharge curve as shown in FIG. 3.

In addition, the battery was charged and discharged at a rate of 0.1C, 0.2C, 0.5C, and 1C under the same charge and discharge conditions as described above to obtain a rate characteristic (%) compared to 0.1C, which is shown in Table 2.

As shown in Figure 3, in the case of Example 1, Comparative Example 1, the content of Mn is equal to or greater than Co, it was found that the average discharge voltage is higher, which can also be confirmed by the voltage value shown in Table 2. In addition, in Example 1 and Comparative Example 1, where the Mn content is equal to or greater than Co, the voltage drop at the end of the discharge tended to be sharper.

Table 2 shows that in Examples 1 and 1, where the Mn content is equal to or greater than Co, the average discharge voltage is higher, whereas in Comparative Examples 2 and 3, which are vice versa, the discharge voltage tends to be lower. When cut-off at 3V, the discharge voltage condition, there was a weak point in the capacity implementation. That is, the capacitance at the cut-off voltage of 3V showed about 3% capacity loss of about 97% of the total capacity. On the other hand, in Example 1 and Comparative Example 1, where the Mn content is equal to or greater than Co, since the capacity at 3V occupies more than 99% of the total capacity, the capacity loss is smaller than that of the conventional material, thereby reducing the existing cut-off. off) it was found that there is an advantage to increase the capacity while maintaining the way.

Looking at the rate characteristics shown in Table 2, in Example 1 and Comparative Example 1, where the Mn content is equal to or greater than Co, the average discharge voltage is relatively improved, and the discharge end profile is relatively sharp. It was found that it showed excellent rate characteristics due to the tendency to fall off, and when the material of the present invention was applied, the 1C-rate capacity was 94% or more, but the existing material showed a capacity of 83% or less. .

On the other hand, Table 3 above shows the discharge capacity and the energy density (area of the hatched portion below the graph in the discharge curve of Figure 4, the discharge voltage × capacity, the electrode active material according to the present invention) compared to the commercial LiCoO ₂ material The results are also shown in FIG. 4.

As shown in FIG. 4, in Comparative Example 1 (that is, when Ni content is 70 mol% or more and Mn content is Co or more), a discharge profile or a discharge voltage is much higher than that of the conventional (Comparative Example 3). Although improved, in terms of the actual energy density, when the Ni content of 70 mol% it can be seen that the energy density is lower than the conventional commercial LiCoO ₂ . Therefore, as in the case of Example 1, it was found that the content of Ni should be at least 75 mol% or more to bring about an increase in capacity as well as energy density in comparison with the conventional.

In the present invention, in the lithium metal composite oxide of LiNi _{1- x- y} Co _x Mn _y O ₂ composition, the content of Ni is 75 mol% or more relative to the total amount of the metal elements excluding lithium, the molar content of Mn is Co By using the material having the above composition as the positive electrode active material, the average discharge voltage, high rate characteristic, and discharge capacity of the battery are improved, and in particular, the energy density is improved compared with the conventional one.

Claims (4)

A lithium metal composite oxide containing nickel, cobalt, and manganese, wherein an Ni content is 75 mol% or more relative to the total amount of metal elements excluding lithium, and an Mn content is greater than a mole content of Co. The compound of claim 1, wherein the formula Li _{1 + a} Ni _1-xyz Co _x Mn _y M _z O _2-b A _b (−0.05 ≦ a ≦ 0.05, x + y + z ≦ 0.25, y + z> x, 0 ≤ z ≤ 0.05, 0 ≤ b ≤ 0.05, M is one or more elements selected from the group consisting of metals and metalloids having a six coordination structure, A is one or more selected from the group consisting of Group 16, 17 elements Element). The electrode containing the electrode active material of Claim 1 or 2. A secondary battery having the electrode of claim 3.

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