KR100790834B1 - Material for Lithium Secondary Battery of High Performance - Google Patents

Abstract

The present invention has a composition represented by Formula 1 below, lithium ions are occluded and released between the mixed transition metal oxide layers ('MO layer'), the storage and release layer of the lithium ions ('reversible lithium layer') Some Ni derived from layers Provided is a nickel-based lithium mixed transition metal oxide wherein ions are inserted to couple MO layers together.

                            Li_xM_yO₂ (One)

             (Wherein M, x and y are as defined in the specification)

Since the nickel-based lithium mixed transition metal oxide according to the present invention has a stable layered structure, the stability of the crystal structure during charging and discharging is improved, and thus a battery including the cathode active material may exhibit high capacity and high cycle stability. In addition, since there are substantially no water-soluble bases, it has excellent storage stability, reduced gas generation, and thus high temperature safety, and enables mass production at low cost.

Description

Material for high performance lithium secondary battery {Material for Lithium Secondary Battery of High Performance}

1 is a schematic diagram of a crystal structure of a conventional nickel-based lithium mixed transition metal oxide, Figure 2 is a schematic diagram of a nickel-based lithium mixed transition metal oxide crystal structure according to an embodiment of the present invention;

3 and 4 are graphs showing a preferred composition range of the nickel-based lithium mixed transition metal oxide according to the present invention;

5 is a FESEM microscope (x 2000) photograph of LiNiMO ₂ according to Example 1 of the present invention: (A) 850 ° C., (B) 900 ° C., (C) 950 ° C., (D) 1000 ° C .;

6 is a FESEM photomicrograph of commercial LiMO ₂ (M = Ni _0.8 Co _0.2 ) according to Comparative Example 1, wherein (A) is a FESEM micrograph of the sample itself, and (B) after heating to 850 ° C. in air. FESEM micrograph of the sample;

7 is a graph showing the average pH titration of commercially available high-Ni LiNiO ₂ In Comparative Example 2, wherein (A) is the sample itself, (B) is the sample after heating to 850 ℃ in an oxygen atmosphere, (C) Is a copy of (A);

8 is a graph measuring the pH titration of a sample according to Comparative Example 3 during storage in a wet chamber, where (A) is the sample itself, (B) the sample after storage for 17 hours, and (C) is 3 days Sample after preservation;

9 is a graph measuring the pH titration of a sample according to Example 2 during storage in a wet chamber, where (A) is the sample itself, (B) the sample after 17 hours storage, and (C) is preserved for 3 days One sample later;

10 is a SEM photograph of a sample according to Example 3;

11 shows Rietveld refinement of an X-ray diffraction pattern of a sample according to Example 3;

12 is a graph showing the electrochemical characteristics of LiNiMO ₂ according to Example 3 in Experimental Example 1, wherein (A) is a graph showing the voltage profile and the rate characteristic at room temperature (cycles 1 to 7), (B) Is a graph showing cycle stability (3.0 to 4.3 V) at C / 5 speeds at 25 ° C. and 60 ° C., (C) is the discharge profile (C / 10 speeds);

FIG. 13 is a graph showing DCS values of samples of Comparative Examples 3 and 4 in Experimental Example 2, wherein (A) is a commercial Al / Ba-modified LiMO ₂ (M = Ni) of Comparative Example 3, and (B) is Commercially available AlPO ₄ -coated LiMO ₂ (M = Ni) of Comparative Example 4;

14 is a graph showing DCS values of LiNiMO ₂ according to Example 3 in Experimental Example 2;

15 shows the results of the electrophysical properties of a polymer battery according to one embodiment of the present invention in Experimental Example 3;

16 is a graph showing swelling of a polymer cell during storage at high temperature in Experimental Example 3;

FIG. 17 shows the lengths of a and c axes of crystallographic unit cells of samples having different Li: M ratios in Experimental Example 4. FIG.

The present invention relates to a nickel-based lithium mixed transition metal oxide and a cathode active material for a secondary battery including the same. More specifically, the nickel-based lithium mixed transition metal oxide according to the present invention has a predetermined composition, and lithium ions are occluded and released between the mixed transition metal oxide layers ('MO layer'), and the lithium ion is occluded and The emitting layer ('reversible lithium layer') contains some Ni derived from the MO layer. Since ions are inserted to bond the MO layers to each other, thereby improving stability of the crystal structure during charging and discharging, the sintering stability is excellent, and a battery including the cathode active material may exhibit high capacity and high cycle stability. In addition, since there are substantially no water-soluble bases, it exhibits excellent storage stability and chemical resistance, and is capable of mass production at a low cost with excellent gas safety and high temperature safety.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries with high energy density and voltage, long cycle life, and low self discharge rate It is commercially used and widely used.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of a lithium secondary battery. In addition, lithium-containing manganese oxides such as LiMnO _{2 in a} layered crystal structure and LiMn ₂ O _{4 in a} spinel crystal structure, and lithium-containing nickel oxide The use of (LiNiO ₂ ) is also contemplated.

Among the positive electrode active materials, LiCoO ₂ is widely used because of its excellent physical properties such as excellent cycle characteristics. However, it is low in safety, expensive due to the resource limitation of cobalt as a raw material, and is not suitable for mass use as a power source in fields such as electric vehicles. There is a limit.

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantage of using a resource-rich and environmentally friendly manganese as a raw material, attracting a lot of attention as a cathode active material that can replace LiCoO ₂ . However, these lithium manganese oxides have disadvantages of small capacity and poor cycle characteristics.

On the other hand, lithium nickel-based oxides such as LiNiO ₂ have a lower discharge cost than the cobalt-based oxides and exhibit high discharge capacity when charged to 4.3 V. The reversible capacity of doped LiNiO ₂ is equivalent to that of LiCoO ₂ (about 165 mAh). / g) in excess of about 200 mAh / g. Thus, despite slightly lower average discharge voltages and volumetric densities, commercialized cells containing LiNiO ₂ positive electrode active materials have improved energy densities. Research is active. However, the LiNiO ₂ based positive electrode active material is limited in practical use due to the following problems.

First, the LiNiO ₂ -based oxide has a sudden phase transition of the crystal structure according to the volume change accompanying the charge-discharge cycle, and thus voids may occur in the cracks or grain boundaries of the particles. Therefore, since the occlusion and release of lithium ions are disturbed to increase the polarization resistance, there is a problem that the charge and discharge performance is lowered. In order to prevent this, conventionally, LiNiO ₂ based oxides were prepared by excessively adding a Li source and reacting in an oxygen atmosphere in the manufacturing process. The cathode active material prepared in this manner has a structure by repulsive force between oxygen atoms in a charged state. There is a problem in that it becomes unstable while expanding and the cycle characteristics are seriously deteriorated by repetition of charge and discharge.

Secondly, LiNiO ₂ has a problem in that excess gas is generated during storage or cycle, which is a reaction residue because an excessive amount of Li source is added and heat-treated during the production of LiNiO ₂ based oxide to form a crystal structure well. This is because water-soluble bases such as Li ₂ CO ₃ , LiOH and the like remain between the primary particles, and when they are charged, they decompose or react with the electrolyte to generate CO ₂ gas. In addition, since LiNiO ₂ particles have a structure of secondary particles in which primary particles are agglomerated, the area of contact of the electrolyte solution is large, and this phenomenon becomes more serious, thereby causing swelling of the battery. It has a problem of degrading high temperature safety.

Third, LiNiO ₂ has a problem in that the chemical resistance is sharply lowered at the surface when exposed to air and moisture, and gelation of the slurry occurs as the NMP-PVDF slurry starts to polymerize due to high pH. These properties cause serious process problems during cell production.

Fourthly, high quality LiNiO ₂ cannot be produced by simple solid phase reactions such as those used in the production of LiCoO ₂ , and contain LiNiMeO ₂ (Me = Co, Mn) containing cobalt as an essential dopant, manganese as other dopants, and aluminum. , Al) Cathode active materials are generally expensive because they are produced by reacting a lithium raw material such as LiOHH ₂ O and a mixed transition metal hydroxide in an oxygen or syngas atmosphere (ie, a CO ₂ deficient atmosphere). In addition, the production costs are further increased when additional steps such as washing or coating are carried out to remove impurities in the production of LiNiO ₂ .

To solve these problems, the present invention provides some Ni derived from a mixed transition metal oxide layer in a reversible lithium layer with a specific compositional formula, as described below. The ions are inserted to provide oxides in the lithium mixed transition metal of the novel structure which are bonded to each other.

In this regard, Japanese Patent Application Laid-Open Nos. 2004-281253, 2005-150057, and 2005-310744 describe the composition formula Li _a Mn _x Ni _y M _z O ₂ [M = Co, Al], where 1≤a An oxide having a range of? 1.2, 0? X? 0.65, 0.35? Y? 1, 0? Z? 0.65, and x + y + z = 1 is disclosed. The oxide is partially overlapped with the present invention in the composition range, but according to the experiments performed by the present inventors, a structure different from the lithium mixed transition metal oxide of the present invention, that is, a structure in which nickel ions are partially inserted into the reversible lithium layer By including a large amount of impurities such as lithium carbonate without having a high temperature, it was confirmed that not only gas generation at a high temperature was serious but also serious problems in structural stability.

Therefore, while using a lithium nickel-based positive electrode active material suitable for high capacity, the crystal structure is stable, there is a high need for a technology capable of achieving high temperature safety with few impurities.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application, after in-depth study and various experiments, the stability of the crystal structure during charging and discharging when the lithium mixed transition metal oxide has a specific composition and a specific structure of atomic units as described below. As a result, it was found that the thermal stability is excellent and high cycle stability can be obtained with high capacity. In addition, since the lithium mixed transition metal oxide can be prepared in a substantially free state of water-soluble base, it has been confirmed that the excellent storage stability, the reduction of gas generation and the high temperature safety resulting from this, and mass production at low cost is possible. The present invention has been completed.

Accordingly, the lithium mixed transition metal oxide according to the present invention has a composition represented by the following Chemical Formula 1, and lithium ions are occluded and released between the mixed transition metal oxide layers ('MO layer'), and the lithium ions are occluded and released. The layer ('reversible lithium layer') contains some Ni derived from the MO layer. It relates to a lithium mixed transition metal oxide characterized in that the ions are inserted to bond the MO layers to each other.

Li _x M _y O ₂ (1)

Where

M = M ' _{1 - k} A _k , where

M 'is _{Ni 1 -ab (Ni 1/2} Mn 1/2) a a Co _b, 0.65≤a + b≤0.85, and 0.1≤b≤0.4, and;

A is a dopant;

0 ≦ k <0.05; And

As x + y ≒ 2, 0.95 ≦ x ≦ 1.05.

The conventional lithium mixed transition metal oxide has a layered crystal structure as shown in FIG. 1, and performs charging and discharging as lithium is inserted or desorbed between MO layers. However, when an oxide having such a structure is used as the positive electrode active material, when lithium is detached from the reversible lithium layer in a charged state, the crystal structure expands and becomes unstable due to repulsion between oxygen atoms in the MO layer, and thus is determined by charge and discharge repetition. As the structure changes, there is a problem that the capacity and cycle characteristics are drastically reduced.

Accordingly, the inventors of the present application perform in-depth studies and various experiments, and as shown in FIG. 2, when some nickel is lowered into the reversible lithium layer and fixed, the occlusion and release of lithium will be disturbed. On the contrary, it was confirmed that the crystal structure can be stabilized to prevent the problem that the crystal structure collapses due to occlusion and release of lithium. As a result, further structural collapse due to oxygen desorption does not occur, and further generation of Ni ²⁺ is prevented, thereby improving the lifespan characteristics and safety, and thus greatly improving the battery capacity and cycle characteristics. Can exhibit characteristics. This concept of the present invention can be said to be a breakthrough completely overturning the conventional concept.

That is, the lithium mixed transition metal oxide according to the present invention is partially Ni in the reversible lithium layer. Since the ions are inserted, even when lithium is released during the charging process, the oxidation number of the Ni ions inserted into the reversible lithium layer is maintained while the crystal structure is not collapsed, and the well-developed layered structure can be maintained. Therefore, a battery including a lithium mixed transition metal oxide having such a structure as a positive electrode active material can exhibit high capacity and high cycle stability.

Moreover, the lithium mixed transition metal oxide according to the present invention has a very good thermal stability because the crystal structure is stably maintained even during sintering at a relatively high temperature in the manufacturing process.

In general, when the high-temperature sintering of LiMO ₂ having a high nickel content in air containing a small amount of CO ₂ is carried out, Ni ³⁺ decomposes as shown in the following equation, and Li ₂ CO ₃ impurities are increased in this process.

LiM ^{3 +} O ₂ + CO ₂ → a Li _{1 - x} M _{1 + x} ^{3 +, 2 +} O ₂ + b Li ₂ CO ₃ + c O ₂

In addition, there is continuous deterioration of the crystal structure, such as increased cation mixing and lattice constants, and a reduced c: a ratio. The molten Li ₂ CO ₃ separates the particles. Loss of contact causes secondary particles to collapse.

However, the lithium mixed transition metal oxide according to the present invention, due to the stability of the atomic structure, the oxygen deficiency due to the reduction and decomposition of Ni ³⁺ in the air atmosphere as described above even when performing high temperature sintering in the air atmosphere. Li ₂ CO ₃ impurities do not form, and deterioration of the crystal structure does not occur. In addition, since there is no need to make an excessive addition of the lithium source, substantially water-soluble bases are not present. Therefore, excellent storage stability, reduction of gas generation and thereby high temperature safety are excellent and mass production is possible at low cost.

Hereinafter, in this specification, in some cases, the lithium mixed transition metal oxide according to the present invention may be referred to as 'LiNiMO ₂ ', or Ni inserted into the reversible lithium layer may be referred to as 'inserted Ni'. Therefore, NiM in LiNiMO ₂ is a notation expressing the complex composition of Ni, Mn and Co in the formula (1).

In one preferred embodiment, in the lithium mixed transition metal oxide Ni ²⁺ and Ni ³⁺ coexist in the MO layer, some of the Ni ²⁺ may have a structure inserted into the reversible lithium layer. That is, in this structure, the Ni ions inserted into the reversible lithium layer are all Ni ²⁺ and the oxidation number value of the ions does not change during the charging process.

In particular, when the lithium mixed transition metal oxide of nickel over coexist Ni ^{2 +} and Ni ^{3 +,} and to an oxygen atom deficiency exists under a predetermined condition (reaction atmosphere, the amount of Li and the like), the Ni accordingly As the oxidation number value changes, some Ni ²⁺ may be inserted into the reversible lithium layer.

The composition of the lithium mixed transition metal oxide should satisfy certain conditions defined by Chemical Formula 1, which may be expressed as in the following formulas.

(i) Ni _{1- (a + b) (} Ni _1/2 Mn _1/2 ) _a Co _b and 0.65 ≦ a + _b ≦ 0.85

(ii) 0.1 ≦ b ≦ 0.4

(iii) x + y ≒ 2 and 0.95 ≦ x ≦ 1.05

With respect to the condition (i), the Ni _{1- (a + b)} is when the mole fraction of the bar, Ni ^3+, which means the content of Ni ³⁺ exceeds 0.35 (a + b <0.65 in the case), Since Li ₂ CO ₃ as a raw material cannot be manufactured on a mass production scale in air, and LiOH must be used as a raw material in an oxygen atmosphere, production efficiency is lowered and manufacturing costs are increased. On the other hand, when the Ni ³⁺ content is less than 0.15 (a + b> 0.85), the content of LiNiMO ₂ The capacity per volume is not competitive compared to LiCoO ₂ .

On the other hand, considering the above conditions (i) and (ii) together, the total mole fraction of Ni including Ni ²⁺ and Ni ³⁺ in LiNiMO ₂ according to the present invention is preferably nickel excess relative to manganese and cobalt. The composition may be 0.4 to 0.7. When the content of nickel is too small, it is difficult to expect a high capacity, on the contrary, when too much, the safety may be greatly reduced. As a result, the volumetric capacity is large and the raw material cost is lower than that of lithium cobalt oxide.

In addition, if the mole fraction of Ni ²⁺ with respect to the Ni content is too high, the cation mixing is increased to form a rock salt structure that does not locally react electrochemically, thus preventing charging and discharging, and thus discharging capacity. This can be reduced. On the other hand, if the mole fraction of Ni ²⁺ in too low structural instability increases and bars in the cycle stability can be reduced, and can be appropriately adjusted in consideration of this, preferably, in the range shown in Figure 3, the Ni ²⁺ The mole fraction may be 0.05 to 0.4 with respect to the total content of Ni.

Therefore, the inserted Ni ²⁺ is intercalated between the MO layers to serve to support them, so that the Ni ²⁺ may be contained at least enough to stably support the MO layers so that the desired charging and cycle stability can be improved. It is preferable that the rate characteristic is not decreased by being inserted to such an extent that it does not interfere with the occlusion and release of lithium ions in the reversible lithium layer. Considering this point as a whole, the mole fraction of Ni ²⁺ inserted and bonded to the reversible lithium layer may be preferably 0.03 to 0.07 based on the total Ni content.

The content of the content or inserting the Ni ²⁺ of the Ni ²⁺ is, for example, the content of Ni ²⁺ if relatively higher the bar, oxygen concentration in the sintering atmosphere, which may be determined by controlling the sintering atmosphere, the content of lithium, such as Will be less.

In relation to the above condition (ii), the cobalt content (b) is 0.1 to 0.4, and when the cobalt content is too high at b> 0.4, the high content of cobalt increases the overall cost of the raw material and reversible capacity. This decreases somewhat. On the other hand, when the content of cobalt is too low (b <0.1), it is difficult to simultaneously achieve sufficient rate characteristics and high powder density of the battery.

Regarding the above condition (iii), there is a problem when the content of lithium is too high, that is, when x> 1.05, in particular, the stability may be lowered during the cycle at a high voltage (U = 4.35 V) at T = 60 ° C. On the other hand, when the content of lithium is too low, that is, when x <0.95, it shows low rate characteristics, and the reversible capacity can be reduced.

In addition, the LiNiMO ₂ may optionally further include a trace amount of dopant. The dopant may be, for example, aluminum, titanium, magnesium, or the like incorporated in a crystal structure. In addition, other dopants such as B, Ca, Zr, F, P, Bi, Al, Mg, Zn, Sr, Ga, In, Ge, Sn, etc. do not coalesce into the crystal structure and accumulate on its grain boundaries or are coated on the surface. Can be included. Doping values of these dopants should be included to an extent that can increase the safety, capacity and overcharge stability of the cell without significantly lowering the reversible capacity, as defined in Formula 1, below 5% (k <0.05) It is included. Further, the dopants may be preferably added at <1% in a range capable of improving stability without lowering the reversible capacity.

As the ratio of Li to Li (M) to the transition metal (M) is lowered, the amount of Ni inserted into the MO layer is gradually increased. When too much amount is lowered into the reversible lithium layer, There is a problem in that the movement of Li ⁺ is disturbed and the reversible capacity is reduced or the rate characteristic is lowered. On the contrary, when the ratio of Li / M is too high, the amount of Ni inserted in the MO layer is too small to cause structural instability, which may lower the safety of the battery and deteriorate the life characteristics. In addition, when the value of Li / M is too high, the amount of unreacted Li ₂ CO ₃ is increased so that the pH proper value is high. That is, since a large amount of impurities are generated, chemical resistance and high temperature stability may be lowered. Therefore, in one preferred example, the ratio of Li: M in the LiNiMO ₂ may be 0.95 to 1.04: 1.

In one preferred embodiment, the lithium mixed transition metal oxide according to the invention is substantially free of water soluble bases, in particular Li ₂ CO ₃ , as impurities.

In general, nickel-based lithium mixed transition metal oxides contain a large amount of water-soluble bases such as lithium oxide, lithium sulfate, and lithium carbonate. The water-soluble bases may be, for example, bases such as Li ₂ CO ₃ and LiOH present in LiNiMO ₂ . And second, a base produced by ion exchange (H ⁺ (water) ← → Li ⁺ (surface, outer surface of the bulk)) on the LiNiMO ₂ surface. The latter case is usually negligible.

The first water soluble base is mainly formed due to the unreacted lithium raw material upon sintering. In order to prevent the collapse of the layered crystal structure of the conventional nickel-based lithium mixed transition metal oxide, since a relatively large amount of lithium is added and sintered at low temperature, it has a relatively larger grain boundary than cobalt-based oxide. This is because lithium ions do not react sufficiently.

On the other hand, LiNiMO ₂ according to the present invention, as described above, since the layered crystal structure is stably maintained, it is possible to perform a relatively high temperature sintering process in the air atmosphere, and has a relatively small grain boundaries. In addition, since unreacted lithium is prevented from remaining on the particle surface, lithium salts such as lithium carbonate and lithium sulfate are substantially not present on the particle surface. In addition, since the lithium source does not need to be excessively added in the production of LiNiMO ₂ , it is possible to fundamentally prevent a problem that impurities are formed due to the unreacted lithium source remaining in the powder.

Therefore, it is possible to fundamentally solve many problems that may occur when a water-soluble base is present, particularly a problem that impairs the safety of the battery by promoting the decomposition reaction of the electrolyte at a high temperature to generate gas.

In the present invention, "substantially free of water-soluble base" is preferably used to titrate 200 ml of a solution containing a lithium mixed transition metal oxide with 0.1 M HCl to reach pH 5 or less. The HCl solution may be consumed to less than 20 ml, more preferably less than 10 ml. Here, the 200 ml solution contains substantially all of the water soluble bases in the lithium mixed transition metal oxide and is prepared by repeated soaking and decanting on 10 g of the lithium mixed transition metal oxide. .

More specifically, first, 5 g of the positive electrode active material powder is added to 25 ml of water and briefly stirred, and about 20 ml of the transparent solution is separated from the powder by soaking and decanting to collect the transparent solution. Again, about 20 ml of water is added to the powder, stirred, decanted and collected. Repeat soaking and decking at least five more times. In this way, a total of 100 ml of clear solution containing water soluble bases are collected. 0.1 M HCl solution is added to the solution to perform pH titration with stirring and the pH profile is recorded as a function of time. The experiment ends when the value reaches pH = 3 or less, and the flow rate can be selected in the range where the titration takes about 20-30 minutes. The content of water soluble base is given by the amount of acid used until pH 5 or below is reached.

In this way it is possible to determine the content of the water-soluble base contained in the powder, in which case it is not significantly affected by variables such as the total time to put the powder in water.

The method for producing a lithium mixed transition metal oxide according to the present invention may preferably be prepared in an oxygen deficient atmosphere. The oxygen depletion atmosphere may be an atmosphere having an oxygen concentration of preferably 10 to 50%, more preferably 10 to 30%. Preferably, there in air Li ₂ CO ₃ and the mixture transition can be produced by solid state reaction of a metal precursor. Therefore, as in the prior art, it is also possible to solve problems such as the increase in manufacturing cost and the presence of a large number of water-soluble bases, which are produced by mixing and sintering LiOH and the respective transition metal precursors in an oxygen atmosphere. That is, by using a low cost and easy to handle raw material, it is possible to manufacture a nickel-containing lithium-containing transition metal oxide having a predetermined composition through a simple solid phase reaction in the air, thereby greatly reducing manufacturing costs. Therefore, mass production is possible with high production efficiency.

That is, in the prior art, due to thermodynamic limitations, it is not possible to produce a nickel mixed transition metal oxide having a high nickel content in air containing a small amount of carbon dioxide. In addition, the prior art case of using the Li ₂ CO ₃ as a precursor, CO ₂ is generated by decomposition of the Li ₂ CO _3, and which not proceed the reaction more than at low partial pressure to hinder the further decomposition of the Li ₂ CO ₃ thermodynamically Since a problem such as not being generated, Li ₂ CO ₃ was not used as a precursor in the actual manufacturing process.

On the other hand, the lithium mixed transition metal oxide according to the present invention can be produced by using a mixed transition metal precursor and Li ₂ CO ₃ as a reaction raw material, and reacted in an oxygen deficient atmosphere, preferably air, significantly reducing the manufacturing cost Can be produced in a relatively simple manner and the production efficiency can be greatly increased. This is because, since the crystal structure of the lithium mixed transition metal oxide of the present invention is stable, the sintering stability at high temperature, that is, the thermodynamic stability is very excellent.

Furthermore, in the production of the lithium mixed transition metal oxide according to the present invention, the lithium raw material and the mixed transition metal raw material may be preferably added in a ratio of 0.95 to 1.04: 1, so that the lithium raw material does not need to be added excessively and remains The possibility of residual water soluble bases derived from a lithium source can be greatly reduced.

Preferably, at least 2 m ³ (volume at room temperature) per kg of dimetal oxide prior to final lithium mixing, so that the reaction can be performed smoothly through high air circulation when the lithium mixed transition metal oxide is produced in a large scale mass production process. Air may be pumped into or out of the reactor. In this process, a heat exchanger can be used, which further enhances the efficiency of energy use by preheating the incoming air entering the reactor while cooling the exhaust air.

The present invention also provides a cathode active material for a secondary battery comprising the lithium nickel-based oxide.

The positive electrode active material according to the present invention may be composed of only a lithium mixed transition metal oxide having the predetermined composition and the structure of a specific atomic unit, and in some cases, may be composed together with other lithium-containing transition metal oxides.

Examples of the lithium-containing transition metal oxides include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site-type lithium nickel oxide represented by the formula LiNi _1-y M _y O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y = 0.01 to 0.3; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The present invention also provides a lithium secondary battery comprising the cathode active material. A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte, and a method of manufacturing a lithium secondary battery is well known in the art, and thus a detailed description thereof is omitted herein.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder to a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture.

The positive electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, a surface of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material, the conductive material, and the like to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode is manufactured by coating and drying a negative electrode active material on a negative electrode current collector, and if necessary, the components as described above may be further included.

The negative electrode current collector is generally made of a thickness of 3 ~ 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As said negative electrode active material, For example, carbon, such as hardly graphitized carbon and graphite type carbon; Li _y Fe ₂ O ₃ (0 ≦ _y ≦ 1), Li _y WO ₂ (0 ≦ _y ≦ 1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or nonwovens made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte solution consists of an electrolyte solution and a lithium salt, and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used as the electrolyte solution.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxolon , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, in the electrolyte solution, for the purpose of improving the charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. . In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The present invention also relates to a lithium mixed transition metal oxide including a mixed transition metal of Ni, Mn, and Co, wherein lithium ions are occluded and released between mixed transition metal oxide layers ('MO layers'), and the lithium ions are occluded. And in the emitting layer ('reversible lithium layer') some Ni derived from the MO layer Ions are inserted to provide a lithium mixed transition metal oxide that couples MO layers together.

In general, when a nickel-based lithium mixed transition metal oxide is used as the positive electrode active material, the collapse of the crystal structure may occur when lithium is occluded and released, and the lithium mixed transition metal oxide according to the present invention may be added to the reversible lithium layer. The inserted nickel ions stabilize the crystal structure, and thus, lifespan characteristics and safety may be simultaneously improved without additional structure collapse due to oxygen desorption.

The present invention also has a composition of formula (2), wherein the proportion of cation mixing (cation mixing) in which some Ni is located in place of lithium stably supports the layered crystal structure from 0.02 to 0.07 based on the total content of Ni It provides a mixed transition metal oxide.

Li _{x '} M "_y' A '_z' O ₂ (2)

Where

0.95≤x'≤1.05, 0≤z '<0.05, x' + y '≒ 2, y' + z '= 1,

M "is a mixed transition metal of Ni, Mn and Co,

A 'is at least one element selected from the group consisting of B, Ca, Zr, S, F, P, Bi, Al Mg, Zn, Sr, Cu, Fe, Ga, In, Cr, Ge and Sn.

From the inventors' experimental confirmation, the case where the cation mixing ratio is 0.02 to 0.07 is particularly preferable in consideration of both charge stability, cycle stability, and rate characteristics. That is, the cation mixing ratio can not only maintain the crystal structure more stably in the above range, but also maximize the occlusion and release of lithium ions.

In addition, having a composition of the formula (2), the ratio of lithium to the mixed transition metal (M) is 0.95 ~ 1.04, the lithium mixed transition, characterized in that some Ni is inserted into the lithium site to stably support the layered crystal structure Provides metal oxides.

Therefore, the lithium raw material does not need to be added excessively, and the possibility of remaining of the water-soluble base which is an impurity derived from the lithium source can be greatly reduced.

When the ratio of lithium to the mixed transition metal (M) is 0.95 to 1.04, the proper cation mixing can be generated to be more structurally stable, minimizing the disturbance of Li ⁺ migration during the charging and discharging process. Therefore, the lithium mixed transition metal oxide is not only excellent in stability, lifespan characteristics and rate characteristics, but also has a high capacity, substantially free of impurities, and thus has high chemical resistance and high temperature stability.

In one preferred embodiment, the lithium mixed transition metal oxide having the composition of Formula 2, wherein the ratio of lithium to the mixed transition metal (M) is 0.95 to 1.04, the cation mixing ratio in which some Ni is located in the lithium site The lithium mixed transition metal oxide may be stably supporting the layered crystal structure as 0.02 to 0.07 based on the total content of Ni. The cation mixing ratio range is as described above.

The present invention also includes a mixed transition metal oxide layer of Ni, Mn and Co ('MO layer') and a layer in which lithium ions are occluded and released ('reversible lithium layer'), and the MO layer and the reversible lithium layer. A lithium mixed transition metal oxide having a layered crystal structure alternately and repeatedly configured, wherein the MO layer includes Ni ³⁺ and Ni ²⁺ , and some Ni ²⁺ ions derived from the MO layer are inserted into the reversible lithium layer. Provided are lithium mixed transition metal oxides.

Such a structure is a structure which is not known so far, and, as described above, greatly contributes to stability, life characteristics, and the like.

In addition, the composition represented by the formula (1), the lithium ion is occluded and released between the mixed transition metal oxide layer ('MO layer'), is prepared by reacting the raw material in an oxygen deficient atmosphere, Ni ^{3 in} the MO layer ⁺ And Ni ²⁺ are included, and some Ni ²⁺ ions derived from the MO layer are inserted into the reversible lithium layer, thereby providing a lithium mixed transition metal oxide.

Conventional lithium mixed transition metal oxides have a crystal structure in which Ni ²⁺ ions are not inserted into the MO layer by reacting raw materials in an oxygen atmosphere, but the lithium mixed transition metal oxides according to the present invention react in an oxygen deficient atmosphere. Ni ²⁺ ions are generated in a relatively large amount, and some of them are inserted into the reversible lithium layer. Therefore, as described above, the crystal structure is stably maintained, so that the sintering stability is excellent and the secondary battery including the same has excellent cycle stability.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

Mixed hydroxide MOOH (M = Ni _4/15 (Mn _1/2 Ni _1/2 ) _8/15 Co _0.2 ) was used as the mixed transition metal precursor, and the mixed hydroxide and Li ₂ CO ₃ were stoichiometric ratio (Li : M = 1.02: 1) and the mixture was sintered in air at various temperature ranges from 850 to 1000 ° C. for 10 hours to prepare a lithium mixed transition metal oxide. At this time, the secondary particles did not collapse at all and remained intact, and the crystal size increased with increasing sintering temperature.

X-ray analysis confirmed that all samples had a well-developed layered crystal structure. In addition, the unit cell volume did not change significantly with increasing sintering temperature, which means that no significant oxygen deficiency and no significant increase in cation mixing occurred, and essentially no lithium evaporation occurred.

Crystallographic data of the prepared lithium mixed transition metal oxide is shown in Table 1 below, and FESEM micrographs are shown in FIG. 5. From these results, it can be confirmed that the lithium mixed transition metal oxide is a well-developed layered LiNiMO _{2 in} which nickel is inserted into the reversible lithium layer at about 3.9 to 4.5%, and sintered in air using Li ₂ CO ₃ as a raw material. In spite of this, it was confirmed that an appropriate amount of Ni ²⁺ can be inserted into the lithium layer to obtain structural stability.

Particularly, the sample (B) sintered at 900 ° C. has a high c: a ratio, so that the crystallinity is excellent, the unit cell volume is low, and an appropriate cation mixing ratio is exhibited, which shows the best electrochemical properties. It was about 0.4-0.8 m <^2> / g.

TABLE 1

Comparative Example 1

50 g of commercially available samples having a composition of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , represented by LiNi _1-x M _x O ₂ (x = 0.3, M = Mn _1/3 Ni _1/3 Co _1/3 ), each in air Heated to 750 ° C, 850 ° C, 900 ° C and 950 ° C (10 hours).

X-ray analysis was performed to obtain detailed lattice parameters at high resolution. It was observed whether the cation was mixed by Rietveld refinement, morphology was analyzed by FESEM and the results are shown in Table 2 below. Referring to Table 2 below, it was found that all samples heated to T ≧ 750 ° C. showed continuous degradation of crystal structure (increased cation mixing, increased lattice constant, and decreased c: a ratio). FIG. 6 discloses a FESEM photograph of a commercial sample itself and a FESEM photograph of the same sample heated at 850 ° C. in air, indicating that the sample heated at T ≧ 850 ° C. collapsed. This is presumably because Li ₂ CO ₃ formed during heating in air melts to separate the particles.

TABLE 2

Therefore, it can be seen that the conventional lithium mixed transition metal oxide of the composition as described above cannot be prepared in the air containing a trace amount of carbon dioxide due to thermodynamic limitations. Also, accordingly, if you use in the manufacture of a lithium mixed transition metal oxide in accordance with the conventional method of composition as mentioned above, Li ₂ CO ₃ as a raw material, CO ₂ is generated by decomposition of the Li ₂ CO _3, and Li ₂ CO ₃ It can be seen that it can not be applied to the actual process because it is difficult to proceed further reaction because it can thermodynamically prevent further decomposition of.

Comparative Example 2

Commercially available sample with LiNi _0.8 Co _0.2 O ₂ PH titration was performed at a flow rate of> 2 l / min for 400 g and the results are shown in FIG. 7. In FIG. 7 curve (A) shows its own pH titration and curve (B) shows the pH titration after heating to 800 ° C. for 24 hours in a flow of pure oxygen. Analysis of the pH profile shows that the content of Li ₂ CO ₃ before and after the heat treatment is the same, and the Li ₂ CO ₃ impurities do not react at all. That is, when heating in an oxygen atmosphere, additional Li ₂ CO ₃ impurities are not generated, but it can be seen that Li ₂ CO ₃ impurities present in the particles are not decomposed. On the other hand, a small increase in the cation mixing, a small decrease in the c: a ratio, and a small decrease in the unit cell volume from the X-ray analysis resulted in a small decrease in the Li content in the crystal structure of LiNiO ₂ and a small amount of Li ₂ O It was confirmed that it was formed. Therefore, it can be seen that it is not possible to produce a stoichiometric lithium mixed transition metal oxide free of impurities and no lithium deficiency in the flow of oxygen gas or synthetic air.

Comparative Example 3

Commercially available Al / Ba-modified nickel high content LiNiO ₂ , LiAl _0.02 Ni _0.78 Co _0.2 O ₂ containing less than 3% aluminum compound was stored in air in a 90% wet chamber at 60 ° C. before exposure to moisture. PH titration was performed on the samples and samples after wet storage for 17 hours and 3 days, respectively, and the results are shown in FIG. 8. Referring to FIG. 8, the amount of water-soluble base was low before storage, but a considerable amount of water-soluble base, mainly Li ₂ CO ₃ , was continuously formed when exposed to air. Thus, even when the initial amount of Li ₂ CO ₃ impurities is low, commercial nickel high content LiNiO ₂ is not stable in air and decomposes at a considerable rate, showing that a considerable amount of Li ₂ CO ₃ impurities are formed during storage.

Example 2

PH titration was performed on the samples before exposure to moisture of the lithium mixed transition metal oxide according to Example 1 and the samples stored for 17 hours and 3 days in air in a 90% wet chamber at 60 ° C, respectively. The results are shown in FIG. 9. Referring to FIG. 9, when comparing the lithium mixed transition metal oxide of Example 2 with the sample of Comparative Example 3 (see FIG. 8), for the 17-hour storage sample, the sample of Comparative Example 3 consumed approximately 20 ml of HCl. On the other hand, the sample of Example 2 consumed 10 ml of HCl, it can be seen that the amount of water-soluble base generated by about 2 times reduced. In addition, the sample of Comparative Example 3 consumed approximately 110 ml of HCl for the 3-day stored sample, whereas the sample of Example 2 consumed 26 ml of HCl, resulting in a reduction of about 5 times the amount of water-soluble base. , It can be seen that the sample of Example 2 degraded about 5 times slower than the sample of Comparative Example 3. Therefore, it can be seen that the lithium mixed transition metal oxide of Example 2 has excellent chemical resistance when exposed to air and moisture.

[Comparative Example 4]

As a commercial sample coated with AlPO ₄ and subjected to mild heat treatment, a pH titration was performed on nickel high content LiNiO ₂ samples having a composition of LiNi _0.8 Mn _0.05 Co _0.15 O ₂ before and after storage in a wet chamber. . pH titration results, the bar doeeotneun 0.1M HCl in 12 ml per 10 g consumed anode, Li ₂ CO ₃ ateuna the initial content is low, the amount of Li ₂ CO ₃ after storage are slightly lower than the formation rate of Comparative Example 3 Sample (80 to 90%), but it was confirmed that a higher content of Li ₂ CO ₃ was formed than the sample of Example 2. Accordingly, the nickel high content LiNiO ₂ did not improve the air stability even when surface-coated, it was confirmed that the increase in the electrochemical properties such as cycle stability and rate characteristics is insignificant.

Example 3

A mixture of Li ₂ CO ₃ and mixed hydroxide MOOH (M = Ni _4/15 (Mn _1/2 Ni _1/2 ) _8/15 Co _0.2 ) was added to a furnace having a chamber of about 20 liter volume at 920 ° C. Sintering was carried out for 10 hours and at least 10 m ³ of air was pumped into the furnace during sintering to produce approximately 5 kg of LiNiMO ₂ in one batch.

After sintering, the unit cell constant was measured by X-ray analysis, and the unit cell volume was compared with the target value (Sample (B) of Example 1: 33.921 × ³ ). ICP analysis confirmed that the ratio of Li and M was very close to 1.00 and the unit cell volume was within the target area. 10 is a SEM micrograph of the prepared cathode active material, Figure 11 shows the Rietveld refinement results. Referring to these drawings, the sample shows a well-developed layer structure has a high crystallinity, a molar fraction of Ni ^{2 +} inserted into the reversible lithium layer of lithium is 3.97%, it was confirmed that the calculated and measured values substantially equal.

On the other hand, less than 10 ml of 0.1 M HCl was consumed to titrate the 10 g positive electrode below pH 5 by performing pH titration, corresponding to the content of Li ₂ CO ₃ impurities of less than about 0.035% by weight. Therefore, it is shown that LiNiMO ₂ having a stable crystal structure and free of Li ₂ CO ₃ impurities can be produced in large quantities from mixed hydroxide and Li ₂ CO ₃ by solid phase reaction.

Experimental Example 1 Electrochemical Characteristic Test

The oxide of Example 3, LiNiMO ₂ according to Comparative Examples 2 to 4, M = (Ni _1/2 Mn _1/2 ) _1-x Co _x and x = 0.17 (Comparative Example 5) and x, respectively. Coin cells were prepared using commercial LiMO ₂ = 0.33 ('Comparative Example 6') as a positive electrode and lithium metal as the negative electrode, and electrochemical properties were tested. Cycle characteristics were performed between 3 and 4.3 V at 25 ° C. and 60 ° C. with mainly C / 5 charge and C / 5 discharge rates (1 C = 150 mA / g).

The results of the electrochemical experiments for Comparative Examples 2 to 4 are shown in Table 3 below. Referring to Table 3, except for Comparative Example 3 (Sample B), the cycle stability was poor. Comparative Example 4 (Sample C) is believed to exhibit poor cycle stability due to surface lithium deficiency. On the other hand, Comparative Example 2 (Sample A) and Comparative Example 3 (Sample B) are not lithium-deficient, but only Comparative Example 4 (Sample C) has a low content of Li ₂ CO ₃ . This presence of Li ₂ CO ₃ not only leads to gas but also to progressively deteriorate performance (at 4.3 V, Li ₂ CO ₃ slowly decomposes and crystals collapse). That is, since there is no nickel-based active material that satisfies both cycle stability and low impurity content, conventional nickel-based active materials have problems of low cycle stability and air stability, and high Li ₂ CO ₃ impurity levels and manufacturing costs. You can check it.

TABLE 3

On the other hand, in the cells of Comparative Examples 5 and 6, the crystallographic densities were almost identical as 4.7 and 4.76 g / cm ³ , respectively, and exhibited a discharge capacity of 157 to 159 mAh / g at the C / 10 rate (3 to 4.3 V). . Compared to LiCoO ₂ with a crystallographic density of 5.04 g / cm ³ and a discharge capacity of 157 mAh / g, the volumetric capacity of Comparative Example 5 corresponds to 93% of LiCoO ₂ , and the density of Comparative Example 6 is 94 of LiCoO ₂ . That's the equivalent of%. Thus, it can be seen that when the Ni content is low, it has a poor volume capacity.

On the other hand, the crystallographic density of LiNiMO ₂ according to Example 3 was 4.74 g / cm ³ (cf. LiCoO ₂ : 5.05 g / cm ³ ). As the discharge capacity is 170 mAh / g or more (cf. LiCoO ₂ : 157 mAh / g) at C / 20, it can be seen that the volume capacity is much improved compared to LiCoO ₂ .

Table 4 below summarizes the electrochemical results of the coin cell using LiNiMO ₂ as an anode according to Example 3, and FIG. 12 discloses voltage profiles, discharge curves and cycle stability.

TABLE 4

Experimental Example 2 Thermal Safety Measurement

In order to determine the thermal stability of the oxide of Example 3 and LiNiMO ₂ according to Comparative Examples 3 and 4, DSC measurements were performed and the results are shown in FIGS. 13 and 14. For the measurement, the coin cells (cathode: lithium metal) were charged to 4.3 V, disassembled, inserted into a sealed DSC can and injected with electrolyte. The total amount of the positive electrode was about 50 to 60 mg, and the total amount of the electrolyte was about the same. Therefore, the exothermic reaction is very anode-limited. DSC measurements were made at a heating rate of 0.5 K / min.

As a result, Comparative Example 3 (Al / Ba-modified LiNiO ₂ ) and Comparative Example 4 (AlPO ₄ -coated LiNiO ₂ ) exhibited strong exothermic reactions at relatively low temperatures. In particular, in the case of Comparative Example 3, the calorific value exceeded the limit of the device. The total cumulative amount of exotherm is larger than 2000 kJ / g, it can be seen that the thermal stability is low (see Fig. 13).

On the other hand, LiNiMO ₂ of Example 3 according to the present invention has a low total calorific value and an exothermic reaction was started at a relatively high temperature (about 260 ° C.) compared to the comparative examples (about 200 ° C.) (FIG. 14). Reference). Therefore, it can be seen that the thermal stability of the LiNiMO ₂ according to the present invention is very excellent.

Experimental Example 3 Electrochemical Characteristic Experiments when Applied to Polymer Battery

A pilot plant polymer cell of type 383562 was manufactured using the lithium mixed transition metal oxide according to Example 3 as a cathode active material. The positive electrode was mixed with 17% LiCoO ₂ , the positive electrode slurry was NMP / PVDF-based, and no additives were added to prevent gelation. The negative electrode used MCMB and the electrolyte used a standard commercial electrolyte without additives to reduce excess swelling. The experiment was performed at 60 ° C. at a charge and discharge rate of C / 5 and the charge voltage was 3.0-4.3 V.

15 shows the cycle stability (0.8 C charge, 1 C discharge, 3-4 V, 2 V) at 25 ° C. of the cell according to the invention. It can be seen that the cycle stability is very good as 91% at C / 1 speed after 300 cycles. The builder-up of the impedance was low. In addition, gas generation during storage was measured and shown in FIG. 16. Very small amounts of gas were generated during storage for 4 hours at 90 ° C. before buffering (4.2 V) and only a slight increase in thickness was observed. This was below or below the expected value when using a good quality LiCoO ₂ anode tested under similar conditions. Therefore, it can be seen that the stability and chemical resistance of LiNiMO ₂ according to the present invention is very excellent.

Experimental Example 4

MOOH (M = Ni _4/15 (Mn _1/2 Ni _1/2 ) _8/15 Co _0.2 ) and Li ₂ CO ₃ as Lithium source and sintered at 910 ~ 920 ℃ in air Samples were prepared. About 50 g of seven samples each with a Li: M ratio ranging from 0.925 to 1.125 were prepared and tested for electrochemical properties.

Table 5 below discloses crystallographic data, and as shown in Table 5, the unit cell volume slowly changed according to the Li: M ratio. 17 shows its crystallographic map, showing that all the samples are located in a straight line. As a result of the pH titration, the water-soluble base content slightly increased with increasing Li: M ratio. The water soluble base is presumably due to surface basicity (ion exchange) and not by decomposition of Li ₂ CO ₃ as in Comparative Example 1.

It is thus clearly shown that the lithium mixed transition metal oxides produced by the process according to the invention are within the stoichiometric range and that lithium is additionally incorporated into the crystal structure. In addition, it can be seen that even when Li ₂ CO ₃ is used as a precursor and the sintering is performed in air, samples without Li ₂ CO ₃ impurities can be prepared.

That is, as the ratio of Li / M decreases, the amount of Ni ²⁺ inserted into the reversible lithium layer is gradually increased, and when too much Ni ²⁺ is inserted into the reversible lithium layer, the movement of Li ⁺ during charging and discharging is performed. Because of this interference, there is a problem that the capacity is reduced or the rate characteristic is lowered. On the contrary, when the ratio of Li / M is too high, the amount of Ni ²⁺ inserted into the reversible lithium layer may be too small, resulting in structural instability, resulting in deterioration of safety of the battery and deterioration of life characteristics. Moreover, at high Li / M values, the amount of unreacted Li ₂ CO ₃ increases, resulting in a high pH titration value. Therefore, in consideration of the performance and safety, to the value of the Ni ^{2 +} into the lithium layer is 3 to rain 0.95 ~ 1.04 degree of Li / M so that about 7% (sample B, C, D) is particularly preferred.

TABLE 5

Example 4

Mixed hydroxide MOOH (M = Ni _4/15 (Mn _1/2 Ni _1/2 ) _8/15 Co _0.2 ) was used as the mixed transition metal precursor, and the mixed hydroxide and Li ₂ CO ₃ were converted into Li: M = 1.01: sintering the mixture was mixed to 1 900 ℃ in air for 10 hours to LiNi _{0 .53} Co _{0 .2 0 .27} Li-Mn having a composition of O ₂ to give the mixed transition metal oxide, 50 g.

X-ray analysis was performed to obtain detailed lattice parameters at high resolution, and cation mixing was observed by Rietveld refinement, and the results are shown in Table 6 below.

Comparative Example 7

A lithium mixed transition metal oxide was prepared in the same manner as in Example 4 except that the Li: M ratio was 1: 1 and calcined in an O ₂ atmosphere, and X-ray analysis and cation mixing were performed. It observed, and the results are shown in Table 6 below.

TABLE 6

As shown in Table 6, the lithium mixed transition metal oxide of Comparative Example 7 can be seen that the cation mixing ratio is significantly low as the heat treatment in the oxygen atmosphere. In this case, there is a problem that the structural stability is deteriorated, that is, when the heat treatment in the oxygen atmosphere is too small cation mixing to develop a layered structure, but it can be seen that the movement of Ni ²⁺ to the extent that it interferes with the cycle stability of the battery .

Example 5

A mixed hydroxide MOOH (M = Ni _1/10 (Mn _1/2 Ni _1/2 ) _6/10 Co _0.3 ) was used as a mixed transition metal precursor, and the mixed hydroxide and Li ₂ CO ₃ were converted into Li: M = 1: 1: except the mixture had a point 1 in the same manner as in example _{4 LiNi 0 .4 Co 0 .3 Mn} 0 lithium mixed transition having a composition of O _{2 .3} was prepared a metal oxide, X-ray analysis and Rietveld It was observed whether the cation was mixed by refinement, the results are shown in Table 7.

TABLE 7

Example 6

As a mixed transition metal precursor _{(M = Ni 5/10 (} Mn 1/2 Ni 1/2) 3/10 Co 0 .2) the mixed hydroxide MOOH was used, the mixed hydroxide and Li ₂ CO ₃ Li: M = 1 except for the points was mixed in a 1 and the example 4 was the same method to manufacture the lithium mixed transition metal oxide having a composition of LiNi _{0 .65} Co _{0 .2 0 .15} Mn ₂ O and, X-ray analysis And whether the cation was mixed by Rietveld refinement was observed, the results are shown in Table 8.

TABLE 8

As shown in Tables 7 and 8, it can be seen that the lithium mixed transition metal oxide according to the present invention can obtain a desired effect as described above in a predetermined range.

As described above, the lithium mixed transition metal oxide according to the present invention has a predetermined composition, and some Ni derived from the MO layer in the reversible lithium layer. Since the ions are interbonded with each other and the MO layers are stable, the crystal structure can be stably supported, thereby not only reducing cycle characteristics but also having high battery capacity and substantially no impurities such as water-soluble bases. It has good storage stability, reduced gas generation and therefore high temperature safety.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (17)

The composition represented by Formula 1 below, lithium ions are occluded and released between the mixed transition metal oxide layers ('MO layer'), and the occlusion and release layer of the lithium ions ('reversible lithium layer') is derived from the MO layer Ni Lithium mixed transition metal oxide, characterized in that the ions are inserted to bond the MO layers and the mole fraction of Ni ions inserted and bonded to the reversible lithium layer is 0.03 to 0.07 based on the total amount of Ni: Li _x M _y O ₂ (1) Where M = M ' _1-k A _k , where M 'is Ni _1-ab (Ni _1/2 Mn _1/2 ) _a Co _b with 0.65 ≦ a + _b ≦ 0.85 and 0.1 ≦ _b ≦ 0.4; A is a dopant; 0 ≦ k <0.05; And As x + y ≒ 2, 0.95 ≦ x ≦ 1.05. 2. The lithium mixed transition metal oxide according to claim 1, wherein Ni ²⁺ and Ni ³⁺ coexist in the MO layer, and Ni ²⁺ is inserted into a reversible lithium layer. The lithium mixed transition metal oxide of claim 1, wherein the mole fraction of Ni in the oxide is 0.4 to 0.7, the mole fraction of Mn is 0.05 to 0.4, and the mole fraction of Co is 0.1 to 0.4. The lithium mixed transition metal oxide of claim 1, wherein the mole fraction of Ni ²⁺ is 0.05 to 0.4 based on the Ni content. delete The lithium mixed transition metal oxide according to claim 1, wherein the ratio of Li: M is 0.95 to 1.04: 1. The lithium mixed transition metal oxide according to claim 1, wherein the oxide does not contain Li ₂ CO ₃ as impurities. The method of claim 7, wherein the Li ₂ CO ₃ is a pH titration while adding 0.1M HCl to 200 ml of a solution containing a lithium transition metal oxide, until 20 ml or less HCl solution until Included to the extent used, the 200 ml solution contains all of the water soluble bases in solution and is prepared by repeated soaking and decanting of 10 g of lithium transition metal oxide. Lithium mixed transition metal oxide. 9. The lithium mixed transition metal oxide of claim 8, wherein the amount of 0.1 M HCl used until the pH reaches 5 or less is 10 ml or less. 10. A cathode active material for a secondary battery, comprising a lithium mixed transition metal oxide according to any one of claims 1 to 4. A lithium secondary battery comprising the cathode active material according to claim 10. A lithium mixed transition metal oxide comprising a mixed transition metal of Ni, Mn, and Co, wherein lithium ions are occluded and released between mixed transition metal oxide layers ('MO layers'), and the occlusion and release layers of lithium ions (' Reversible Lithium layer ') contains Ni derived from MO layer The ions are inserted to bond the MO layers, and the mole fraction of Ni ions inserted and bonded to the reversible lithium layer is 0.03 to 0.07 based on the total amount of Ni. Lithium mixed transition metal oxide having a composition of the formula (2), characterized in that the cation mixing ratio (Cation mixing) where Ni is located in the lithium site stably supports the layered crystal structure as 0.03 to 0.07 based on the total content of Ni: Li _{x '} M "_y' A '_z' O ₂ (2) Where 0.95≤x'≤1.05, 0≤z '<0.05, x' + y '≒ 2, y' + z '= 1, M "is a mixed transition metal of Ni, Mn and Co, A 'is at least one element selected from the group consisting of B, Ca, Zr, S, F, P, Bi, Al, Mg, Zn, Sr, Cu, Fe, Ga, In, Cr, Ge and Sn. The composition according to Formula 2 of claim 13, wherein the ratio of lithium to the mixed transition metal (M) is 0.95 ~ 1.04, Ni is inserted into the lithium site to stably support the layered crystal structure, is inserted into the lithium site Mole fraction of Ni is a lithium mixed transition metal oxide, characterized in that 0.03 ~ 0.07 based on the total amount of Ni. delete A mixed transition metal oxide layer of Ni, Mn, and Co ('MO layer') and a layer in which lithium ions are occluded and released ('reversible lithium layer'), and the MO layer and the reversible lithium layer are alternately and repeatedly configured. a lithium mixed transition metal oxide having a layered crystal structure, the MO layer comprises an Ni ³⁺ and Ni ^2+, Ni ²⁺ and the derived from the MO layer is inserted into the reversible lithium layers, inserted into the reversible lithium layer And the mole fraction of Ni ²⁺ bonded to each other is 0.03 to 0.07 based on the total amount of Ni. The composition according to claim 1 has a composition according to Formula 1, lithium ions are occluded and released between the mixed transition metal oxide layer ('MO layer'), and is prepared by reacting the raw material in an atmosphere having an oxygen concentration of 10 to 50%, MO layer, containing the Ni ³⁺ and Ni ^2+, Ni ²⁺ and the derived from the MO layer is inserted into the reversible lithium layer, a molar fraction of Ni ²⁺ to be coupled are inserted into the reversible lithium layer is the total amount of Ni Lithium mixed transition metal oxide, characterized in that 0.03 ~ 0.07 on the basis.

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