WO2014178624A1 - Anode active material for lithium rechargeable battery - Google Patents

Abstract

The present invention relates to an anode active material for a lithium rechargeable battery, and more specifically relates to an anode active material for a lithium rechargeable battery wherein the anode active material comprises a core part exhibiting gradients in nickel, manganese and cobalt concentrations in the core-to-surface direction, and a shell part wherein the nickel, manganese and cobalt concentrations are constant and the nickel concentration is adjusted so as to be in a predetermined range. In the anode active material according to the present invention, because the shell part, wherein the nickel concentration is adjusted so as to be in a predetermined range and the remaining metal concentrations are constant, is formed on the surface of the core part having the gradients in nickel, manganese and cobalt concentrations, it follows that even though the nickel concentration is high the residual lithium is reduced, and the lifespan characteristics and charging and discharging characteristics are outstanding and high capacity is exhibited while even so the crystal structure is stabilised such that structural stability is exhibited even when used at high voltage.

Description

Cathode active material for lithium secondary battery

The present invention relates to a cathode active material for a lithium secondary battery, and more particularly, to a lithium including a core part having a concentration of nickel, manganese and cobalt gradient from the center to a surface direction, and a shell part having a constant concentration of nickel, manganese and cobalt. It relates to a positive electrode active material for a secondary battery.

Lithium secondary batteries have an operating voltage of 3.7 V or more, and have a higher energy density per unit weight than nickel-cadmium batteries or nickel-hydrogen batteries. As a result, the demand for lithium secondary batteries is increasing day by day. Doing.

Recently, research on hybridizing an internal combustion engine and a lithium secondary battery to use it as a power source for an electric vehicle has been actively conducted in the United States, Japan, and Europe. Development of plug-in hybrid (P-HEV) batteries for cars with mileage less than 60 miles per day is actively underway in the United States. The P-HEV battery is a battery having almost the characteristics of an electric vehicle, the development of a high capacity battery is the biggest problem. In particular, the development of a positive electrode material having a high tap density of 2.0 g / cc or more and high capacity of 230 mAh / g or more is a major challenge.

Anode materials currently commercialized or under development include LiCoO 2, LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li _{1 + X} [Mn _2-x M _x ] O ₄ , and LiFePO ₄ . Among these, LiCoO 2 is an excellent material having stable charge and discharge characteristics, excellent electronic conductivity, high battery voltage, high stability, and flat discharge voltage characteristics. However, Co has low reserves, is expensive, and toxic to humans. Therefore, development of other anode materials is desired. In addition, there is a disadvantage in that the crystal structure is unstable due to de-lithography during charging and the thermal characteristics are very poor.

In order to improve this, many attempts have been made to substitute a portion of nickel with a transition metal element to shift the exothermic start temperature to the high temperature side or to broaden the exothermic peak to prevent the rapid exotherm. However, satisfactory results are still not obtained. In other words, LiNi1-xCoxO2 (x = 0.1-0.3) material in which a part of nickel is substituted with cobalt shows excellent charge and discharge characteristics, but thermal safety problems are solved. I couldn't. In addition, European Patent No. 0872450 also discloses Li _a Co _b Mn _c M _d Ni _{1- (b + c + d)} O ₂ (M = B, Al, in which not only Co and Mn are substituted for Ni, but also other metals ₎ Si, Fe, Cr, Cu, Zn, W, Ti, Ga) type, but the thermal stability of the Ni-based still has not been solved.

In order to eliminate this disadvantage, Korean Patent Publication No. 2005-0083869 proposes a lithium transition metal oxide having a concentration gradient of a metal composition. This method is a method of synthesizing the internal material of a certain composition and then applying a material having a different composition to the outside to prepare a double layer, and then mixed with a lithium salt to heat treatment. As the internal material, a commercially available lithium transition metal oxide may be used.

However, this method discontinuously changes the metal composition of the positive electrode active material between the resultant inner and outer material compositions, and does not continuously change gradually. In addition, the powder synthesized by the present invention is not suitable for use as a cathode active material for lithium secondary batteries because the tap density is low because ammonia, which is a chelating agent, is not used.

In order to improve this point, Korean Patent Laid-Open Publication No. 2007-0097923 proposes a cathode active material having an inner bulk portion and an outer bulk portion and having a continuous concentration distribution according to the position of metal components in the outer bulk portion. However, in this method, since the concentration is constant in the inner bulk portion and the metal composition is changed only in the outer bulk portion, there is a need to develop a positive electrode active material having a better structure in terms of stability and capacity.

In addition, as the Ni content increases, the reversible capacity is relatively increased, but the thermal stability is sharply decreased. When the Ni content is relatively low and the Mn content is increased, the thermal stability is improved, but there is no advantage in comparison to LiCoO2 in the past in terms of energy density. You lose. Therefore, in order to completely replace or partially replace the conventional LiCoO ₂ , an optimal Ni: Mn: Co composition and Li / M should be selected in terms of capacity and safety.

Control of the Li / M ratio in the positive electrode active material is related to the Mn content in the composite transition metal, it is possible to insert extra lithium in the transition metal layer by a certain amount of Mn substitution amount or more. In terms of battery characteristics, the extra lithium inserted into the transition metal layer results in relatively high high-rate characteristics and lifespan characteristics. In addition, the composition system having a relatively higher Mn content compared to the ternary composition containing a low Mn content, It is easy to insert lithium to minimize the amount of lithium introduced during synthesis to control the water-soluble base content such as Li ₂ CO ₃ , LiOH remaining on the surface of the active material after firing. The residual lithium component decomposes during charging and discharging or reacts with the electrolytic solution to generate CO 2 gas. As a result, a swelling phenomenon of the battery is generated, thereby lowering the high temperature stability.

In particular, when a ternary cathode active material containing Ni as a main component is exposed to air and moisture, impurities such as LiOH and Li 2 CO 3 are formed on the surface (see Schemes 1 and 2; J. Power Sources, 134, page 293, 2004). ).

Scheme 1 LiNiO ₂ + yH2O → Li _1-y NiO _{2-y / 2} + yLiOH

Scheme 2

LiNi _0.8 Co _0.15 Al _0.05 O ₂ + 4xO ₂ + yH ₂ O → Li _1-y Ni _0.8 Co _0.15 Al _0.05 O ₂ + 2xLi ₂ CO ₃

The residual lithium formed increases the pH when preparing the slurry of the electrode plate, and gelation occurs because the slurry containing NMP (1-methyl-2-pyrrolidinone) and the binder (Binder) starts to polymerize. It causes problems in the manufacturing process. Lithium hydroxide reduces the dispersibility of the positive electrode active material, binder, conductive material, etc. in the solvent, the longer the time required to stabilize the viscosity of the slurry. In addition, when applying to the current collector in the state that the viscosity of the slurry is not stabilized, there is a problem that the uniform coating is not made on the current collector, the smoothness of the electrode surface is lowered, and thus the performance of the battery is lowered.

Therefore, many prior arts focus on improving the properties and manufacturing process of nickel-based positive electrode active materials to reduce residual lithium.

An object of the present invention is to provide a positive electrode active material of a novel structure consisting of a core portion and a shell portion capable of reducing the content of residual lithium while increasing the content of nickel to solve the problems of the prior art as described above. do.

The present invention to solve the above problems

A core portion in which the concentrations of nickel, manganese and cobalt exhibit a gradient from the center to the surface direction; And a shell portion having a constant concentration of nickel, manganese, and cobalt; Including,

The core portion is represented by the concentration of the center of the nickel, manganese and cobalt as CC1-Ni, CC1-Co, CC1-Mn,

The core portion may have a concentration gradient size of each of the first core portion CS1-Ni, CS1-Mn, CS1-Co; And

The second core portion of the concentration gradient size of the nickel, manganese and cobalt is CS2-Ni, CS2-Mn, CS2-Co;

The concentration of CC 1 -Ni in the center is 0.95 or more,

The concentration of nickel, manganese and cobalt in the shell portion is represented by SC-Ni, SC-Mn, SC-Co, and the nickel concentration SC1-Ni in the shell portion provides a positive electrode active material for a lithium secondary battery.

In the cathode active material according to the present invention, the concentration gradient sizes CS1-Ni, CS1-Mn, CS1-Co, and nickel, manganese, and cobalt in the second core portion in the first core portion. Concentration gradient sizes of CS2-Ni, CS2-Mn, CS2-Co are CS1-Ni <0, CS1-Mn> 0, CS1-Co> 0, CS2-Ni <0, CS2-Mn> 0, CS2-Co> It is characterized by being 0.

In the cathode active material according to the present invention, the concentration of nickel, manganese and cobalt in the shell portion is represented by SC1-Ni, SC1-Mn, SC1-Co, and the concentration of nickel, manganese and cobalt in the shell portion is constant. .

 In the cathode active material according to the present invention, the concentrations of SC1-Ni, SC1-Mn, and SC1-Co in the shell portion are the same as the concentrations of nickel, manganese, and cobalt in the outermost portion of the core portion. It is done.

In the cathode active material according to the present invention, the average cobalt concentration of the core part and the shell part may be 6%. In the positive electrode active material according to the present invention, the average cobalt concentration is the average cobalt concentration of the whole positive electrode active material particles prepared according to the present invention. When the average cobalt concentration of the particles as a whole is 6% or less, the rate characteristic and capacity of the lithium secondary battery may decrease.

In the cathode active material according to the present invention, the nickel concentration at the point where the first core portion and the second core portion contact each other may be 0.9. In other words, the minimum value of nickel concentration in the first core portion may be 0.9 and the maximum value of nickel concentration in the second core portion may be 0.9.

In the cathode active material according to the present invention, the shell portion has a volume of 30% or less of the total volume.

The cathode active material according to the present invention forms a shell portion with a constant concentration on the surface of a core portion having a concentration gradient of nickel, manganese, and cobalt, and thus has excellent capacity and charge / discharge characteristics. Structural stability.

Figure 1 shows the results of measuring the concentration of Ni, Mn, Co according to the distance from the center of the particles produced in the embodiment of the present invention by EDX.

2 to 5 show the results of measuring charge and discharge characteristics, life characteristics, and DSC characteristics of a battery including the active material prepared in Example 1 and Comparative Example of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited by the following examples.

<Example>

To prepare particles having a core concentration gradient of two, first, a solution of Ni _X1 Co _y1 Mn _z1 OH ₂ (x1, y1, z1) and Ni _X2 Co were prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate. A second aqueous metal solution of _y2 Mn _z2 OH ₂ (x2, y2, z2) was prepared, and ammonia solution of 25 mol concentration at 0.7 liter / hour was mixed while changing the mixing ratio of the first and second metal aqueous solutions. Was continuously added to the reactor at 0.07 liter / hour to prepare a core having a first concentration gradient.

Thereafter, the concentration of nickel sulfate, cobalt sulfate, and manganese sulfate was adjusted to 0.7 liters / hour while mixing while changing the mixing ratio of the third metal aqueous solution and the second metal aqueous solution having a constant Ni _{X 3} Co _{y 3} Mn _{z 3} OH ₂ to a concentration of 25 mol. Ammonia solution was continuously added to the reactor at 0.07 liter / hour to prepare a core part having a second concentration gradient.

Thereafter, the concentration of nickel sulfate, cobalt sulfate, and manganese sulfate was supplied with an aqueous solution for forming a shell portion having a constant concentration of Ni _{X 4} Co _{y 4} Mn _{z 4} OH ₂ to prepare a shell portion having a concentration different from that of the core portion terminal having a second concentration gradient. .

In Examples 11 to 20 thus prepared, the concentration of the aqueous metal solution is shown in Table 1 below.

Table 1

	First metal aqueous solution			Second metal aqueous solution			Tertiary metal solution			4th metal aqueous solution			Shell thickness
	Ni	Co	Mn	Ni	Co	Mn	Ni	Co	Mn	Ni	Co	Mn
Example 1	98	2	2	90	4	6	69	08	23	60	12	28	0.5 μm
Example 2	98	2	2	90	4	6	70	7	23	60	10	30	0.5 μm

The prepared metal composite hydroxide was filtered, washed with water, and dried in a 110 ° C. hot air dryer for 12 hours. After mixing the metal composite hydroxide and lithium hydroxide (LiOH) in a 1: 1 molar ratio, and heated at a temperature increase rate of 2 ℃ / min and maintained at 450 ℃ for 10 hours, followed by pre-firing at 700 ~ 900 ℃ It baked by time and obtained the positive electrode active material powder.

Comparative Example

Using a metal aqueous solution represented by Ni ₈₀ Co ₆ Mn ₁₄ OH _{2 It} was prepared a composite oxide particle of Comparative Example in which the concentration of nickel, cobalt, manganese is constant throughout the particle.

Experimental Example: EDX Photo Measurement

The concentration of Ni, Mn, Co according to the distance from the center of the particles prepared in Example 1 was measured by EDX and the results are shown in FIG. In the case of the particle according to the embodiment of the present invention in FIG.

Experimental Example Charge and Discharge Characteristics, Life Characteristics and DSC Measurements

Charge and discharge characteristics, life characteristics and DSC characteristics of the battery including the active material prepared in Examples 1 to 2, and Comparative Examples were measured and shown in Table 2 below and FIGS. 2 to 5.

TABLE 2

From Table 2 and FIG. 2 showing charge and discharge characteristics, it can be seen that the capacity of the battery including the cathode active material according to the present invention is 220 mAh / g or more. Thus, the capacity is expressed including high nickel, but in FIG. 5. As can be seen in the DSC characteristics, the ignition temperature is higher than 40 ° C. than the comparative example it can be seen that the thermal stability is greatly improved.

Experimental Example Residual Lithium Measurement

The results of measuring the amount of the residual LiOH and Li ₂ CO ₃ of the active material particles prepared in Example 1, Comparative Example are shown in Table 3 below.

TABLE 3

	Residual LiOH	Li 2 CO 3	Sum
Comparative Example 1	7124	5397	12521
Example 1	3208	3095	6307

In Example 3 of the present invention it can be seen that the residual lithium is reduced to 50% of the comparative example.

Experimental Example Determination of Tap Density and BET Surface Area

The tap density of the active material particles prepared in Example 1 and Comparative Example 1 is shown in Table 4 below.

Table 4

	Tap density
Example 1	2.52
Comparative Example 1	2.62

The positive electrode active material according to the present invention forms a shell portion having a constant concentration on the surface of the core portion having a concentration gradient of nickel, manganese, and cobalt, so that the crystal structure is stabilized while exhibiting high capacity due to excellent life characteristics and charge / discharge characteristics. Structural stability.

Claims (8)

1. A core portion in which the concentrations of nickel, manganese and cobalt exhibit a gradient from the center to the surface direction; And a shell portion having a constant concentration of nickel, manganese, and cobalt; Including,

   The core portion is represented by the concentration of the center of the nickel, manganese and cobalt as CC1-Ni, CC1-Co, CC1-Mn,

   The core portion may have a concentration gradient size of each of the first core portion CS1-Ni, CS1-Mn, CS1-Co; And

   And a second core portion having concentration gradient sizes of nickel, manganese, and cobalt, respectively, CS2-Ni, CS2-Mn, and CS2-Co.

   The concentration of CC 1 -Ni in the center is 0.95 or more,

   Nickel, manganese, and cobalt concentration in the shell portion is represented by SC-Ni, SC-Mn, SC-Co and nickel concentration SC1-Ni in the shell portion is a positive electrode active material for a lithium secondary battery.
2. The method of claim 1,

   Concentration gradient sizes of nickel, manganese and cobalt in the first core portion CS1-Ni, CS1-Mn, CS1-Co, and concentration gradient sizes of nickel, manganese and cobalt in the second core portion CS2-Ni, CS2 -Mn, CS2-Co is

   CS1-Ni <0, CS1-Mn> 0, CS1-Co> 0, CS2-Ni <0, CS2-Mn> 0, CS2-Co> 0, the positive electrode active material for a lithium secondary battery
3. The method of claim 1,

   Nickel, manganese and cobalt concentration in the shell portion is represented by SC1-Ni, SC1-Mn, SC1-Co and the concentration of nickel, manganese and cobalt in the shell portion is a positive electrode active material for lithium secondary battery
4. The method of claim 1,

   Concentrations SC1-Ni, SC1-Mn, and SC1-Co of the shell portion are the same as the concentration of the outermost portion of the core portion.
5. The method of claim 1,

   The average cobalt concentration of the core portion and the shell portion is 6% positive electrode active material for lithium secondary batteries.
6. The method of claim 1,

   The positive electrode active material for lithium secondary batteries whose nickel concentration is 0.9 at the point where the said 1st core part and the 2nd core part contact | connect.
7. The method of claim 1,

   The shell portion has a volume of 30% or less of the total volume of the cathode active material for a lithium secondary battery.
8. A lithium secondary battery comprising the cathode active material for any one of claims 1 to 7

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