KR20130095572A - Preparation method of a positive active for a lithium secondary battery - Google Patents

Abstract

PURPOSE: A manufacturing method of a cathode active material is provided to be able to manufacture a LiMnO2 cathode active material with an improved capacitance and an excellent charge/discharge efficiency by precipitating manganese, vanadium or niobium with reduction. CONSTITUTION: A manufacturing method of a cathode active material comprises a step of producing manganese complex precipitate by precipitating manganese and hetero metal elements with reduction from a mixed solution including a hetero metal compound containing at least one hetero metal element selected from V and Nb, and a manganese compound; and a step of mixing the manganese complex participate and the lithium compound, and plasticizing the mixture to produce a lithium manganese complex oxide represented by Chemical formula 1: Li_(1+a)(Mn_(1-b)M_b)_(1-a)O_2; wherein a is 0<=a<=1/3, b is 0<=b<=0.5, M is at least one metal element selected from V and Nb.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a lithium secondary battery,

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery capable of excellent capacity characteristics and charge / discharge efficiency, and more particularly to a method for producing a positive electrode active material for a lithium secondary battery by reducing and precipitating manganese, vanadium, niobium, will be.

The lithium rechargeable battery which is currently commercialized and used is equivalent to the heart of the digital era in which the average discharge potential is rapidly applied to portable phones, notebook computers, camcorders, and the like, which is referred to as 3C as a 3.7V battery.

Composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- x} Co _x O ₂ , and LiMnO ₂ are used as positive electrode active materials of such lithium secondary batteries. LiCoO ₂ exhibits good electrical conductivity, high battery voltage, and excellent electrode characteristics, and is a representative cathode active material currently commercialized and marketed by SONY, etc., but has a disadvantage of being expensive. LiNiO ₂ is the least expensive of the above-mentioned positive electrode active material, and exhibits the highest discharge capacity of the battery characteristics, but it is difficult to synthesize.

Currently, more than 95% of the batteries in the world use high-priced LiCoO ₂ , and efforts are being made to replace such LiCoO ₂ . Thus, Mn-based cathode active materials such as LiMn ₂ O ₄ , LiMnO ₂ , which are easy to synthesize, relatively inexpensive, and have little pollution to the environment are actively researched. However, such LiMn ₂ O ₄ , LiMnO _2, etc. have a small capacity and are not excellent in charging / discharging efficiency due to repeated use.

Therefore, it is necessary to study the development of a cathode active material and a process for a lithium secondary battery, which have improved capacity when used for a lithium secondary battery, excellent charge / discharge efficiency, and reduced production cost compared to LiCoO ₂ .

The present invention provides a method for producing a cathode active material for a lithium secondary battery, which comprises lithium manganese composite oxide having improved capacity and excellent charge / discharge efficiency through reduction precipitation of manganese and vanadium or niobium.

The present invention also provides a cathode active material for a lithium secondary battery manufactured by the above method.

The present invention also provides a lithium secondary battery comprising the cathode active material.

The present invention provides a process for producing a manganese composite precipitate by reducing and precipitating manganese and a dissimilar metal element from a mixed solution containing a dissimilar metal compound containing at least one dissimilar metal element selected from the group consisting of V and Nb and a manganese compound, And mixing the manganese composite precipitate with a lithium compound to form a lithium manganese composite oxide represented by the following formula (1), followed by calcination at 300 to 800 ° C.

[Formula 1]

Li _{1 + a} (Mn _{1 - b} M _b ) _{1 - a} O ₂

In the formula, a is 0 ≦ a ≦ 1/3, b is 0 ≦ b ≦ 0.5, and M is at least one metal element selected from the group consisting of V and Nb.

The present invention also provides a cathode active material for a lithium secondary battery produced by the above method.

The present invention also provides a lithium secondary battery comprising the cathode active material.

Hereinafter, a method for producing a cathode active material for a lithium secondary battery according to a specific embodiment of the present invention, a cathode active material for a lithium secondary battery produced thereby, and a lithium secondary battery including the same will be described in detail. It will be apparent to those skilled in the art, however, that this is not intended to limit the scope of the invention, which is set forth as an example of the invention, and that various modifications may be made to the embodiments within the scope of the invention.

&Quot; Including "or" containing ", unless the context clearly dictates otherwise throughout the specification, refers to any element (or component) including without limitation, excluding the addition of another component .

In the present invention, the term "lithium secondary battery" refers to a battery capable of continuously performing charging and discharging. Such a lithium secondary battery has a characteristic feature of storing electric energy. However, as described above, since lithium secondary batteries (cathode active materials for lithium secondary batteries) must escape in the form of ions upon desorption, they must have structural stability. In the portion where the transition metal material having such structural stability is mainly used, There are limited disadvantages of process and material.

Accordingly, the present invention provides a lithium secondary battery having improved capacity, excellent charge / discharge efficiency, and low-temperature sintering process which reduces production cost compared with LiCoO ₂ , by producing a cathode active material by reducing and precipitating manganese and vanadium A process improvement effect can be obtained.

In particular, as a result of experiments conducted by the inventors of the present invention, it has been found that excellent characteristics that can maintain a constant discharge capacity can be secured by manufacturing a cathode active material by a reduction precipitation and doping method and applying the cathode active material to a lithium secondary battery.

Generally, Li ₂ MnO ₃ active material is rich in Li. Therefore, it is possible to realize a large capacity when used alone, and since Mn has the most stable form of quadrivalent in the active material, the Mn dissolution occurs in LiMn ₂ O ₄ There is no stability problem. Most of the spinel or layered cathode active material is subject to volume change when repeatedly inserting and desorbing lithium, which causes the structure to collapse and cause a decrease in capacity. However, in the case of Mn 4, the structure is most stable, so structural collapse does not occur easily. In addition, the cathode active material suitable for HEV or EV requires high output, and Mn 4 should be driven at 4.4V or higher in order to be activated. If activated, it can be used at a high voltage of 4.8 ~ 5V.

The disadvantage of the known cathode active material is that the first discharge capacity is large but the capacity tends to decrease as the cycle progresses. This is because Li ₂ O is produced during the sustained cycle, which leads to the continual loss of oxygen in the structure and Mn does not maintain quadrivalent. Accordingly, in the present invention, Mn is doped with a pentavalent element such as vanadium or niobium to induce mixed valency in which Mn has an oxidation number between 4 and 3 and 4, The capacity can be increased or sustained by improving the collapse of the structure. The present cathode active material has a half composition of Li ₂ MnO ₃ in the production of Ni-rich Li [Ni _x Co _y Mn _z ] O ₂ , Production and electrochemical characteristics of Li ₂ MnO ₃ are under investigation.

According to an embodiment of the present invention, there is provided a method for producing a cathode active material for a lithium secondary battery, which comprises subjecting manganese, vanadium (V), niobium (Nb), and the like to reduction precipitation under predetermined process conditions.

The method for producing a cathode active material for a lithium secondary battery includes the steps of subjecting manganese and a dissimilar metal element to reduction precipitation using a mixed solution containing a dissimilar metal compound containing at least one dissimilar metal element selected from the group consisting of V and Nb and a manganese compound Producing a manganese composite precipitate; And mixing the manganese composite precipitate with a lithium compound, followed by calcination at 300 to 800 ° C to produce a lithium manganese composite oxide represented by the following formula (1).

[Formula 1]

Li _{1 + a} (Mn _{1 - b} M _b ) _{1 - a} O ₂

Wherein a may be 0? A? 1/3; b may be 0 ≦ b ≦ 0.5, preferably 0 ≦ b ≦ 0.3, more preferably 0 ≦ b ≦ 0.2; M may be at least one metal element selected from the group consisting of V and Nb.

In particular, in the formula (1), the indexes of a and b are 0 ≦ a ≦ 1/3, 0 ≦ b ≦ 0.5, preferably 0 ≦ a ≦ 1/3, for the vanadium (V) doped lithium manganese composite oxide. 0 ≦ b ≦ 0.3, more preferably 0 ≦ a ≦ 1/3, 0 ≦ b ≦ 0.2, and 0 ≦ a ≦ 1/3, 0 for niobium (Nb) doped lithium manganese composite oxide ≤ b ≤ 0.3, preferably 0 ≤ a ≤ 1/3, 0 ≤ b ≤ 0.25, more preferably 0 ≤ a ≤ 1/3, 0 ≤ b ≤ 0.2.

The lithium manganese complex oxide may be represented by the following general formula (2).

(2)

_{Li 4/3 (Mn 1 -} x M x) 2/3 O 2

Wherein x may be 0 ≦ x ≦ 0.5, preferably 0 ≦ x ≦ 0.3, more preferably 0 ≦ x ≦ 0.2; M is at least one metal element selected from the group consisting of V and Nb.

In the lithium manganese composite oxide is _{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 V 0 .1) 2/3 O 2, Li 4 / _{3 (Mn 0.85 V 0.15) 2/3} O 2, Li 4/3 (Mn 0 .95 Nb 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 Nb 0 .1) 2/3 O _2, it may be mentioned _{Li 4/3 (Mn 0 .995} Nb 0 .05) 1 alone or in combination of two or more, such as _2/3 O _2.

In the present invention, the manganese composite precipitate to be a precursor of the lithium manganese composite oxide is produced by reduction deposition of manganese (Mn) and vanadium (V) or niobium (Nb) together with manganese (Mn) (V), and niobium (Nb). The manganese composite precipitate of the present invention is characterized by showing an amorphous phase. Due to the high enthalpy energy of the amorphous crystal phase, the annealing process (500-600 ° C) is significantly lower than the solid process involving the heat treatment at a temperature higher than 800 ° C ℃) can be obtained through a single crystal phase, such as the final Li ₂ MnO ₃ to be obtained, and it is possible to control, as the particle size is also an object due to the low heating temperature.

In particular, in the case of a conventional wet process, a precursor of a lithium composite oxide is produced in a crystal phase from a hydroxide (NiCoMn-OH) or an oxide compound by a co-precipitation method, There is a problem that needs to be done. However, in the case of the present invention, it is possible to produce an amorphous lithium manganese complex oxide precursor, and even if a calcination process is performed at a remarkably low temperature in a conventional wet process or the like, a final crystalline lithium manganese composite oxide There are advantages to be gained.

In the present invention, the step of subjecting manganese (Mn), vanadium (V), niobium (Nb) and the like to reduction precipitation to produce a manganese composite precipitate is carried out at a pH of 9 to 13, preferably at a pH of 9.5 to 12.5, 12. &Lt; / RTI &gt; The pH range corresponds to a mixed solution in which a dissimilar metal compound including a dissimilar metal element such as vanadium (V) or niobium (Nb) and a manganese compound are dissolved. In order for the dissimilar metal elements such as vanadium (V) and niobium (Nb) to be simultaneously reduced and precipitated together with manganese (Mn) in the mixed solution, the pH value may be 9 or more, and the pH value Can be 13 or less.

Such a pH value can be adjusted by using a reducing agent in the mixed solution. As the reducing agent, one or more selected from the group consisting of KBH ₄ , LiBH ₄ , NaBH ₄ , NaAlH ₄ and LiAlH ₄ can be used. As the reducing agent, NaBH ₄ , KBH ₄ and the like are preferable in terms of producing an amorphous type precipitate. In addition, an acid or a basic compound may be added in addition to the reducing agent to adjust the pH value to the optimum range or to prevent a sharp rise in the pH value. Examples of such acidic compounds include HCl, HClO ₄ , H ₂ SO ₄ and HBr. Examples of basic compounds include ammonia, KOH, LiOH, NaOH, NH ₄ OH, CH ₃ COOH and HCN. However, when a basic compound is added alone without the reducing agent as described above, manganese (Mn), vanadium (V), niobium (Nb) and the like may not be precipitated at the same time and only Mn ₃ O ₄ may precipitate .

On the other hand, a mixed solution containing both a manganese compound and a metal compound including a different metal element such as vanadium or niobium is first prepared by mixing the dissimilar metal compound at a pH of 9 to 13, preferably at a pH of 10 to 12, 10 to 11 in a basic solvent, and then dissolving the manganese compound therein. However, after the manganese compound is adjusted to pH 2 to 6, preferably pH 3 to 5, more preferably pH 4 to 5, of the solution containing the dissimilar metal compound according to the pH range, the manganese compound is added .

The manganese compound may be at least one selected from the group consisting of manganese sulfate, manganese nitrate, manganese nitrate, manganese acetic acid, manganese chloride, manganese dioxide, manganese trioxide, and manganese oxide. Among them, manganese sulfate, manganese nitrate and manganese acetate are preferably used in terms of dissolving the manganese raw material. The vanadium compound may be at least one selected from the group consisting of vanadium metal, vanadium oxide (V ₂ O ₅ , V ₂ O ₄ , V ₂ O ₃ , V ₃ O ₄ ), vanadium oxychloride, vanadium tetrachloride, vanadium trichloride At least one selected from the group consisting of ammonium vanadium oxide, sodium metavanadate and potassium metavanadate, lithium chloride, niobium oxide (NbO, NbO ₂ , Nb ₂ O ₅ ), niobium chloride, and niobium phosphate can be used. Among them, vanadium oxide, sodium metavanadate and niobium oxide are preferably used in terms of dissolving the dissimilar metal element raw material.

The molar ratio of the dissimilar metal elements such as vanadium and niobium to manganese may be 0.01 to 0.50 mol, preferably 0.02 to 0.20 mol, more preferably 0.05 to 0.15 mol. The molar ratio of vanadium to manganese may be 0.01 mol or more in terms of the minimum substitution amount of the dissimilar metal element, and the molar ratio of vanadium to manganese may be 0.50 mol or less in terms of the maximum substitution amount of the dissimilar metal element.

The present invention may further include a step of drying the lithium manganese complex oxide precursor produced from the reduction precipitation step. The drying step may be carried out at a temperature of 40 to 150 ° C, preferably 80 to 130 ° C, more preferably 100 to 120 ° C.

On the other hand, the manganese composite precipitate thus obtained after the drying is mixed with the lithium compound and then subjected to a heat treatment process at a temperature of 300 to 800 ° C, preferably 350 to 700 ° C, more preferably 400 to 620 ° C, . &Lt; / RTI &gt; This firing process can be performed by a two-step heat treatment process including a first heat treatment and a second heat treatment. Here, the primary heat treatment is performed at a temperature of 300 to 700 ° C for 7 to 15 hours, preferably at a temperature of 350 to 600 ° C for 9 to 14 hours, more preferably at a temperature of 400 to 550 ° C, For a period of time. Further, the secondary heat treatment is carried out at a temperature of 300 to 800 ° C for 10 to 20 hours, preferably at a temperature of 400 to 700 ° C for 14 to 18 hours, more preferably at a temperature of 440 to 620 ° C &Lt; / RTI &gt; for 15 to 17 hours.

As the lithium compound in the present invention, at least one selected from the group consisting of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium sulfite, lithium fluoride, lithium nitrate, lithium bromide, lithium iodide and lithium chloride may be used , Preferably lithium hydroxide, lithium carbonate and the like can be used.

The molar ratio of lithium to manganese can be 1.60 to 1.80 mol, preferably 1.65 to 1.78 mol, more preferably 1.70 to 1.75 mol. In terms of single-stage production, the molar ratio of lithium to manganese may be 1.60 mol or more, and the molar ratio of lithium to manganese may be 1.80 mol or less in terms of controlling the intensity ratio of each surface index have.

According to another embodiment of the present invention, there is provided a cathode active material for a lithium secondary battery produced by the above-described method. The cathode active material for a lithium secondary battery may include a lithium manganese composite oxide represented by the following general formula (1).

[Formula 1]

Li _{1 + a} (Mn _{1 - b} M _b ) _{1 - a} O ₂

Wherein a may be 0? A? 1/3; b may be 0 ≦ b ≦ 0.5, preferably 0 ≦ b ≦ 0.3, more preferably 0 ≦ b ≦ 0.2; M may be at least one metal element selected from the group consisting of V and Nb.

In particular, in the formula (1), the indexes of a and b are 0 ≦ a ≦ 1/3, 0 ≦ b ≦ 0.5, preferably 0 ≦ a ≦ 1/3, for the vanadium (V) doped lithium manganese composite oxide. 0 ≦ b ≦ 0.3, more preferably 0 ≦ a ≦ 1/3, 0 ≦ b ≦ 0.2, and 0 ≦ a ≦ 1/3, 0 for niobium (Nb) doped lithium manganese composite oxide ≤ b ≤ 0.3, preferably 0 ≤ a ≤ 1/3, 0 ≤ b ≤ 0.25, more preferably 0 ≤ a ≤ 1/3, 0 ≤ b ≤ 0.2.

The lithium manganese complex oxide may be represented by the following general formula (2).

(2)

_{Li 4/3 (Mn 1 -} x M x) 2/3 O 2

Wherein x may be 0 ≦ x ≦ 0.5, preferably 0 ≦ x ≦ 0.3, more preferably 0 ≦ x ≦ 0.2; M is at least one metal element selected from the group consisting of V and Nb.

In the lithium manganese composite oxide is _{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 V 0 .1) 2/3 O 2, Li 4 / _{3 (Mn 0.85 V 0.15) 2/3} O 2, Li 4/3 (Mn 0 .95 Nb 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 Nb 0 .1) 2/3 O ₂ , Li _4/3 (Mn _0.995 Nb _0.05 ) _2/3 O _2, and the like.

The cathode active material for a lithium secondary battery according to the present invention has a discharge capacity of 140 mAhg ^-1 or more at a cycle number of 2 times or more as measured by a method of evaluating a case of an SUS product as a test cell for evaluating an electrode, To 220 mAhg ^-1 , preferably from 170 to 210 mAhg ^-1 , more preferably from 180 to 200 mAhg ^-1 .

According to another embodiment of the present invention, there is provided a lithium secondary battery comprising the cathode active material for the lithium secondary battery. The lithium secondary battery is characterized in that the electrochemical characteristics of a conventional material are improved by using a cathode active material prepared by reducing and precipitating manganese and vanadium to produce a single phase lithium manganese composite oxide.

In particular, the lithium secondary battery of the present invention comprises a cathode including a cathode active material; An anode including a negative electrode active material; And a separator between the anode and the cathode.

The lithium secondary battery of the present invention may include a wide variety of negative electrode active materials.

In the present invention, matters other than those described above can be added or subtracted as required, and therefore, the present invention is not particularly limited thereto.

According to the present invention, a LiMnO ₂ system cathode active material for lithium secondary batteries having improved capacity and reduced charge / discharge efficiency by reducing and precipitating manganese and vanadium or niobium together can be produced.

In addition, when the cathode active material for a lithium secondary battery according to the present invention is produced, it is possible to produce a lithium secondary battery having a reduced production cost, improved capacity, and excellent charge / discharge efficiency.

1 is a photograph showing a SEM measurement result of a precursor, that is, a manganese composite precipitate obtained by simultaneous reduction precipitation of manganese and vanadium according to Example 1 of the present invention.
FIG. 2 is a graph showing XRD measurement results of a precursor, that is, a manganese composite precipitate obtained by simultaneous reduction precipitation of manganese and vanadium according to Example 1 of the present invention.
FIG. 3 is a graph showing the XRD measurement results of the lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 1 to 6 according to the present invention (Example 1: Li _4/3 (Mn _0.95 V _0.05 ) _2/3 O _2, in example _{2: Li 4/3 (Mn} 0 .9 V 0 .1) 2/3 O 2, in example _{3: Li 4/3 (Mn} 0 .85 V 0 .15) 2 / ₃ O _2, example _{4: Li 4/3 (Mn} 0 .95 Nb 0 .05) 2/3 O 2, example _{5: Li 4/3 (Mn} 0 .9 Nb 0 .1) 2/3 O _2, example _{6: Li 4/3 (Mn 0.85 Nb} 0.15) 2/3 O 2, the control _{group: Li 4/3 Mn 2/} 3 O 2].
4 is a photograph showing the results of SEM measurement of the lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 1 to 3 of the present invention by V doping amount (Example 1: M = V, b? 0.05, 2: M = V, b? 0.10, Example 3: M = V, b? 0.15).
5 is a graph showing the XRD measurement results of the lithium manganese composite oxide prepared by the dry method according to Comparative Examples 1 to 6 according to the present invention. [Comparative Example 1: Li _4/3 (Mn _0.95 V _0.05 ) _{2 / 3} O _2, Comparative example _{2: Li 4/3 (Mn} 0 .9 V 0 .1) 2/3 O 2, Comparative example _{3: Li 4/3 (Mn} 0 .95 Nb 0 .05) 2/3 O _2, Comparative example _{4: Li 4/3 (Mn} 0 .9 Nb 0 .1) 2/3 O 2, Comparative example _{5: Li 4/3 (Mn} 0 .85 V 0 .15) 2/3 O 2, Comparative example _{6: Li 4/3 (Mn 0.85 Nb} 0.15) 2/3 O 2, the control _{group: Li 4/3 Mn 2/} 3 O 2].
6 is a photograph showing the results of SEM measurement of the lithium manganese composite oxide prepared by the dry method according to Comparative Examples 1 to 4 of the present invention by V doping amount (Comparative Example 1: M = V, b? 0.05, Comparative Example 2: M = V, b? 0.10, Comparative Example 3: M = Nb, b? 0.05, and Comparative Example 4: M = Nb, b?
FIG. 7 is a graph showing electrochemical characteristics of a lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 1 to 3 of the present invention. Example 1: M = V, b? 0.05 (wet) Example 2: M = V, b? 0.10 (wet), Example 3: M = V, b? 0.15 (wet).
8 is a graph showing the results of measurement of electrochemical characteristics of a lithium manganese composite oxide prepared by a dry method according to Comparative Examples 1 to 4 of the present invention. Comparative Example 1: M = V, b? 0.05 (dry) 2: M = V, b? 0.10 (dry), Comparative Example 3: M = Nb, b? 0.05 (dry), and Comparative Example 4: M = Nb, b?
9 is a graph showing the results of measurement of lifetime characteristics of the lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 1 to 3 of the present invention and the lithium manganese composite oxide prepared by the dry method according to Comparative Examples 1 to 4 example _{1: Li 4/3 (Mn} 0 .95 V 0 .05) 2/3 O 2 Wet process, example _{2: Li 4/3 (Mn} 0 .9 V 0 .1) 2/3 O 2 Wet process, example _{3: Li 4/3 (Mn} 0 .85 V 0 .15) 2/3 O 2 Wet process, Comparative example _{1: Li 4/3 (Mn} 0 .95 V 0 .05) 2/3 O ₂₃ O ₂ Solid process, Comparative example _{2: Li 4/3 (Mn 0.9 V} 0.1) 2/3 O 2 Solid process, Comparative example _{3: Li 4/3 (Mn} 0 .95 Nb 0 .05) 2/3 O Solid process _2, Comparative example _{4: Li 4/3 (Mn} 0 .9 Nb 0 .1) 2/3 O 2 Solid process].
Figure 10 is an exemplary lithium-manganese composite oxide prepared by the reduction precipitation method according to Example 3 of the present invention _{(Li 4/3 (Mn 0} .85 V 0 .15) 2/3 O 2) Li / M ratio relative to (ratio XRD &lt; / RTI &gt;
11 is a photograph showing SEM measurement results of a lithium manganese composite oxide prepared by the reduction precipitation method according to Example 2 of the present invention and a product using a lithium manganese composite oxide prepared by a dry method according to Comparative Example 2 ) Example 2, (B) Comparative Example 2].
12 is a graph showing the XRD measurement results of the lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 2 and 3 of the present invention and the product using the lithium manganese composite oxide prepared by the dry method according to Comparative Example 2 example _{2: Li 4/3 (Mn 0.9 V} 0.1) 2/3 O 2 Wet process, example _3: Li _4/3 Comparative example (Mn _{0 .85 0 .15} V) _2/3 O ₂ Wet process, _{2: Li 4/3 (Mn} 0 .9 V 0 .1) 2/3 O 2 Solid process].

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

Example  One

3.05 g of LiOH and 2.84 g of KOH were dissolved in 500 mL of distilled water to prepare a basic solvent having a pH of 10.5. Then, a vanadium compound (V ₂ O ₅ , 98%) was dissolved in the basic solvent. After dissolving the manganese compound (MnSO ₄ · 5H ₂ O, 98%) in a basic solution dissolving V ₂ O ₅ by using dilute HCl to a pH of 4, a transparent pale brown solution .

A KBH ₄ solvent was added to the solution of vanadium compound and manganese compound dissolved therein to raise the pH to 10 to 12, and a complex compound in which vanadium and manganese were precipitated together was obtained as a dark brown precipitate. At this time, HCl was used to suppress the rapid increase of pH, and ammonia water was used to raise the pH to 11.5 because the pH was limited to only 9 by the reducing agent alone. The resulting vanadium manganese composite precipitate was washed with water to remove impurities, and then dried at 80 DEG C for 8 hours or more. The vanadium manganese composite precipitate thus obtained was completely amorphous as a result of XRD analysis (see FIG. 2).

The dried vanadium manganese composite precipitate was mixed with the lithium compound (Li ₂ CO ₃ , 98%) such that the molar ratio (Li / Mn ratio) was 1.71. Thereafter, a uniform mixture was obtained by planetary ball milling using a 10 mm ball.

The lithium manganese vanadium complex mixture powder was placed in a tube furnace, and the temperature was raised at a rate of 3 ° C per minute to raise the temperature to 400 to 550 ° C. Then, this state was maintained for 12 hours by adding oxygen gas, Heat treatment was performed. Thereafter, the temperature was raised at a rate of 3 ° C per minute, and the temperature was further raised to about 40 ° C to 70 ° C, that is, to 440 ° C to 620 ° C, as compared with the first heat treatment. Followed by a secondary heat treatment. To produce a dark red color of the lithium-manganese composite oxide according to the present invention by carrying out the process [the formula _{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2] was prepared in the cathode active material for a lithium secondary battery.

The powder obtained by the heat treatment was confirmed by SEM and XRD. As a result of the analysis, the synthesized powder showed uniform particle size and phase and showed a single crystal phase free of impurities.

Example  2

Except that the amorphous reduced precipitate was prepared by varying the content of the vanadium compound (V ₂ O ₅ ) and the manganese compound (MnSO ₄ .5H ₂ O) so that the molar ratio of the metal components was Mn: V = 0.9: 0.1. of example 1, to prepare a cathode active material for a lithium secondary battery _{[Li 4/3 (Mn 0} .9 V 0 .1) 2/3 O 2] in the same manner and using the SEM, XRD in the same manner was confirmed to particle size and structure .

Example  3

Except that the amorphous reduced precipitate was prepared by varying the content of the vanadium compound (V ₂ O ₅ ) and the manganese compound (MnSO ₄ .5H ₂ O) such that the molar ratio of the metal components was Mn: V = 0.85: 0.15. of example 1, to prepare a cathode active material for a lithium secondary battery _{[Li 4/3 (Mn 0} .85 V 0 .15) 2/3 O 2] in the same manner and using the SEM, XRD in the same manner was confirmed to particle size and structure .

Example  4

Vanadium compound (V ₂ O ₅₎ instead of the niobium compound (Nb ₂ O ₅₎ in Example 1, and the cathode active material for a lithium secondary battery in the same manner except that the production of the amorphous phase is reduced sediment using the [Li _4/3 ( _{Mn 0 .95 Nb 0 .05) 2/3} O 2] was prepared to determine the size and structure using the SEM, XRD by the same method.

Example  5

Except that the amorphous phase reduced precipitate was prepared by varying the content of the niobium compound (Nb ₂ O ₅ ) and the manganese compound (MnSO ₄ .5H ₂ O) such that the molar ratio of the metal components was Mn: Nb = 0.9: 0.1. example 4 the same method of producing cathode active material for a lithium secondary battery _{[Li 4/3 (Mn 0} .9 Nb 0 .1) 2/3 O 2] in the and using the SEM, XRD in the same manner was confirmed to particle size and structure .

Example  6

Except that the amorphous-phase reduced precipitate was produced by varying the content of the niobium compound (Nb ₂ O ₅ ) and the manganese compound (MnSO ₄ .5H ₂ O) so that the molar ratio of the metal components was Mn: Nb = 0.85: 0.15. example 4 the same method of producing cathode active material for a lithium secondary battery _{[Li 4/3 (Mn 0} .85 Nb 0 .15) 2/3 O 2] in the and using the SEM, XRD in the same manner was confirmed to particle size and structure .

Comparative Example  One

Cathode active material for a lithium secondary battery having the same composition as in Example 1 with a dry process instead of a wet process to prepare a _{[Li 4/3 (Mn 0} .95 V 0 .05) 2/3 O 2].

First, a lithium compound (Li ₂ CO ₃ ), a vanadium compound (V ₂ O ₅ ), and a manganese compound (Mn ₂ O ₃ ) were mixed. At this time, the molar ratio of lithium to manganese (Li / metal ratio) was 2.04, and 0.05 mol of vanadium was mixed. Then, a planar ball milling was performed using a 10 mm ball to obtain a uniform mixture of lithium manganese vanadium.

The resulting lithium manganese vanadium complex was placed in a tube furnace and heated at a rate of 3 캜 / min to raise the temperature to 650 캜. The state was maintained for 20 hours while oxygen gas was being applied to perform the heat treatment. A cathode active material for a lithium secondary battery of a black red according to the present invention by carrying out the process _{[Li 4/3 (Mn 0} .95 V 0 .05) 2/3 O 2] After producing the dry process, as in Example 1, The particle size and structure were confirmed by SEM and XRD in the same manner.

Comparative Example  2

Except that the content of the vanadium compound (V ₂ O ₅ ) and the manganese compound (Mn ₂ O ₃ ) was varied so that the molar ratio of the metal components was Mn: V = 0.9: 0.1, battery positive electrode active material _{[Li 4/3 (Mn 0} .9 V 0 .1) 2/3 O 2] , and the production by using a SEM, XRD in the same manner was confirmed to particle size and structure.

Comparative Example  3

Vanadium compound (V ₂ O ₅₎ instead of the niobium compound (Nb ₂ O _5), and a is, in Comparative Example 1 and a lithium secondary battery positive electrode active material in the same way except that _{[Li 4/3 (Mn 0} .95 Nb 0. ₀₅ ) _2/3 O ₂ ] was prepared and the particle size and structure were confirmed by SEM and XRD in the same manner.

Comparative Example  4

Except that the content of the niobium compound (Nb ₂ O ₅ ) and the manganese compound (Mn ₂ O ₃ ) was varied so that the molar ratio of the metal components was Mn: Nb = 0.9: 0.1, battery positive electrode active material _{[Li 4/3 (Mn 0} .9 Nb 0 .1) 2/3 O 2] , and the production by using a SEM, XRD in the same manner was confirmed to particle size and structure.

Comparative Example  5

Except that the content of the vanadium compound (V ₂ O ₅ ) and the manganese compound (Mn ₂ O ₃ ) was varied so that the molar ratio of the metal components was Mn: V = 0.85: 0.15, cells produce a positive electrode active material _{[Li 4/3 (Mn 0} .85 V 0 .15) 2/3 O 2] and by using a SEM, XRD in the same manner was confirmed to particle size and structure.

However, the thus prepared cathode active material did not undergo electrochemical characteristics measurement because impurities were present.

Comparative Example  6

Except that the content of the niobium compound (Nb ₂ O ₅ ) and the manganese compound (Mn ₂ O ₃ ) was varied so that the molar ratio of the metal components was Mn: Nb = 0.85: 0.15, battery positive electrode active material _{[Li 4/3 (Mn 0} .85 Nb 0 .15) 2/3 O 2] , and the production by using a SEM, XRD in the same manner was confirmed to particle size and structure.

Test Example

The cell performance was evaluated by preparing a half cell lithium secondary battery using the cathode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 6 in the following manner.

a) lithium secondary battery manufacturing

The cathode active material powders prepared according to Examples 1 to 6 and Comparative Examples 1 to 6 were classified to have an average particle diameter of 20 占 퐉. A slurry was prepared by using 80 wt% of an anode material, 10 wt% of acetylene black as a conductive agent, and 10 wt% of PVdF as a binder, using NMP as a solvent. This slurry was applied to an aluminum foil (Al foil) having a thickness of 20 탆, dried and compacted by a press, and dried in vacuum at 120 캜 for 16 hours to prepare a positive electrode having a disk diameter of 16 mm.

Lithium metal foil punched with a diameter of 16 mm was used as a cathode, and a PP film was used as a separator. As the electrolytic solution, a mixed solution of 1: 2 v / v of EC / EMC of 1M LiPF ₆ was used. After the electrolyte was impregnated into the separator, the separator was sandwiched between the anode and the cathode, and a stainless steel (SUS) product case was covered to prepare a test cell for evaluating an electrode, that is, a half cell of a lithium secondary battery.

b) battery performance evaluation

A half cell lithium secondary battery manufactured by using the cathode active material according to Examples 1 to 6 and Comparative Examples 1 to 6 in the manner as described above was subjected to an experiment to analyze its capacity and efficiency according to repeated charge / . That is, a current of 10 mAg ^-1 was applied using a charge / discharge device to 1.5 ~ 4.8V. Thus, the lithium secondary battery was repeatedly used to fully charge and discharge, and then an experiment was conducted to compare and analyze the capacity according to the number of repeated use.

The results of measurement of lifetime characteristics of the lithium secondary batteries using the cathode active materials according to Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1 below.

division Cycle number One 2 3 4 5 6 7 8 9 10 Example 1
_{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2 charge 150.51 170.12 171.25 205.31 203.57 201.42 202.14 202.31 203.17 202.57 Discharge 116.55 165.42 169.33 196.05 164.03 187.07 182.52 192.00 198.43 200.10 Example 2
_{Li 4/3 (Mn 0 .9} V 0 .10) 2/3 O 2 charge 175.65 192.45 191.87 190.24 190.38 191.25 193.82 185.36 188.62 187.34 Discharge 169.58 187.79 177.74 184.86 185.91 190.25 191.40 188.39 186.58 185.82 Example 3
_{Li 4/3 (Mn 0 .85} V 0 .15) 2/3 O 2 charge 190.27 202.31 220.72 221.45 222.13 221.84 221.64 224.31 225.48 224.92 Discharge 186.21 198.99 216.52 216.73 214.33 217.25 219.28 222.97 225.44 221.27 Comparative Example 1
_{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2 charge 150.36 150.38 150.29 150.28 150.26 150.32 150.31 150.23 150.22 150.19 Discharge 87.65 100.48 107.44 108.29 108.67 114.12 116.68 116.39 118.34 140.20 Comparative Example 2
_{Li 4/3 (Mn 0 .9} V 0 .1) 2/3 O 2 charge 148.25 149.43 149.67 149.36 149.47 149.50 149.52 149.40 149.46 149.49 Discharge 79.82 104.05 103.53 107.24 112.03 113.31 113.76 113.54 113.92 134.05 Comparative Example 3
_{Li 4/3 (Mn 0 .95} Nb 0 .05) 2/3 O 2 charge 150.34 150.21 150.20 150.24 150.26 150.24 150.21 150.22 150.26 150.27 Discharge 99.88 113.16 119.03 130.29 126.14 125.00 129.80 113.87 115.54 138.03 Comparative Example 4
_{Li 4/3 (Mn 0 .9} Nb 0 .1) 2/3 O 2 charge 150.82 150.71 150.93 150.85 150.78 150.83 150.80 150.79 150.80 150.80 Discharge 87.61 103.89 125.13 119.02 125.72 129.14 133.18 136.27 136.53 135.41

As shown in Table 1, it was confirmed that the lithium secondary batteries including the cathode active materials of Examples 1 to 3 prepared using the reduced precipitated precursor had excellent discharge efficiency and had no problems in using the positive active material as a single cathode active material . In particular, in the case of the lithium secondary battery according to Examples 1 to 3, it can be seen that the maintenance rate of the maximum discharge capacity is remarkably improved with an increase in the vanadium doping amount.

On the other hand, it was confirmed that the lithium secondary batteries including the cathode active materials of Comparative Examples 1 to 4 prepared in the discharge capacity measurement results in the past life cycle did not satisfy these characteristics. Particularly, the lithium secondary battery according to Comparative Examples 2 and 4 had a problem in that the discharge capacity due to an increase in the vanadium composition was significantly lowered as in Examples 1 to 3, resulting in a change in oxidation number of manganese . In addition, the lithium secondary batteries according to Comparative Examples 3 and 4 show that the electrochemical characteristics of the lithium secondary battery according to the niobium composition change are not good for improving the discharge capacity, and thus, there is a limit to the use alone.

On the other hand, each of the lithium-manganese composite oxide prepared by the reduction precipitation method according to a second embodiment of the present invention and according to Comparative Example 2 prepared by dry method _{(Li 4/3 (Mn 0} .90 V 0 .10) 2/3 O _The results of SEM measurement of the manufactured product using the above-mentioned ( ₂ ) are shown in Fig. 11 ((A) Example 2, (B) Comparative Example 2]. Here, the heat treatment is maintained at 900 占 폚, and the particle size is not large even at 900 占 폚 in Example 2 produced by the reduction precipitation method as compared with that in Fig. 4. In Comparative Example 2 manufactured by the dry method, 0.0 &gt; C, &lt; / RTI &gt; The XRD measurement results of the lithium manganese composite oxide prepared by the reduction precipitation method according to Examples 2 and 3 of the present invention and the lithium manganese composite oxide prepared by the dry method according to Comparative Example 2 are shown in FIG. From the graph of the XRD measurement results of FIG. 12, it can be seen that when heat treatment was performed at 900 ° C for Examples 2 and 3 and wet and dry V-doped Comparative Examples 2 and 3, impurities were formed in Examples 2 and 3, 3 shows that no impurities are produced by the reduction precipitation method. In other words, the solubility is better in the wet method.

Claims (20)

Generating a manganese complex precipitate by reducing precipitation of manganese and a dissimilar metal element from a mixed solution containing a manganese compound and a dissimilar metal compound including at least one dissimilar metal element selected from the group consisting of V and Nb; And
Mixing the manganese composite precipitate with a lithium compound, and firing the mixture at a temperature of 300 to 800 ° C. to form a lithium manganese composite oxide represented by the following formula (1);
: &Lt; / RTI &gt; a method for producing a cathode active material for a lithium secondary battery comprising:
[Formula 1]
Li _{1 + a} (Mn _{1 - b} M _b ) _{1 - a} O ₂
Wherein a is 0 ≦ a ≦ 1/3, b is 0 ≦ b ≦ 0.5, and M is at least one metal element selected from the group consisting of V and Nb. The method of claim 1,
Wherein the lithium compound is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium sulfite, lithium fluoride, lithium nitrate, lithium bromide, lithium iodide and lithium chloride. . The method of claim 1,
Wherein the manganese compound is at least one selected from the group consisting of manganese sulfate, manganese nitrate, manganese nitrate, manganese acetic acid, manganese chloride, manganese dioxide, manganese trioxide, and manganese oxide. The method of claim 1,
The dissimilar metal compound is composed of vanadium metal, vanadium oxide, vanadium oxychloride, vanadium tetrachloride, vanadium trichloride, ammonium metavanadate, sodium metavanadate and potassium metavanadate, lithium chloride, niobium oxide, niobium chloride, and niobium phosphide Method for producing a positive electrode active material for lithium secondary batteries which is at least one member selected from the group. The method of claim 1,
Wherein the reducing and precipitating is performed under the condition of pH 9 to pH 13. The method for producing a cathode active material for a lithium secondary battery according to claim 1, The method of claim 1,
The reduction precipitation step is _{KBH 4, LiBH 4, NaBH 4} , NaAlH 4, and a method of producing a cathode active material for a lithium secondary battery In performing the addition of more than one kinds of the reducing agent is selected the group consisting of LiAlH ₄ in the mixed solution. The method of claim 1,
Wherein the manganese composite precipitate produced from the reduction precipitation step is an amorphous phase. The method of claim 1,
Wherein the molar ratio of lithium to manganese is from 1.60 to 1.80 mol. The method of claim 1,
Method of producing a positive active material for a lithium secondary battery to react so that the molar ratio of the dissimilar metal element to manganese is 0.01 to 0.50 mol. The method of claim 1,
Wherein the firing step is performed in a two-step heat treatment process including a first heat treatment and a second heat treatment. The method of claim 10,
The first heat treatment is performed by heating at a temperature of 300 to 700 ° C. for 7 to 15 hours, and the second heat treatment is performed by performing the first heat treatment and then heating the mixture at a temperature of 300 to 800 ° C. for 10 to 20 hours A method for producing a cathode active material for a secondary battery. The method of claim 1,
And dissolving the dissimilar metal compound in a basic solvent having a pH of 9 to 13, adjusting the pH to 2 to 6, and dissolving a manganese compound to prepare a mixed solution. The method of claim 1,
And drying the manganese composite precipitate produced from the reduction precipitation step at a temperature of 40 to 150 ° C. 14. A cathode active material for a lithium secondary battery produced by the method according to any one of claims 1 to 13. 15. The method of claim 14,
A cathode active material for a lithium secondary battery including a lithium manganese composite oxide represented by Formula 1 below:
[Formula 1]
Li _{1 + a} (Mn _{1 - b} M _b ) _{1 - a} O ₂
Wherein a is 0 ≦ a ≦ 1/3, b is 0 ≦ b ≦ 0.5, and M is at least one metal element selected from the group consisting of V and Nb. 16. The method of claim 15,
The lithium manganese composite oxide is a cathode active material for a lithium secondary battery that is represented by the following formula (2):
(2)
_{Li 4/3 (Mn 1 -} x M x) 2/3 O 2
Wherein x is 0 ≦ x ≦ 0.5 and M is at least one metal element selected from the group consisting of V and Nb. 17. The method of claim 16,
The lithium manganese composite oxide is _{Li 4/3 (Mn 0 .95} V 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 V 0 .1) 2/3 O 2, Li 4/3 _{(Mn 0.85 V 0.15) 2/3 O} 2, Li 4/3 (Mn 0 .95 Nb 0 .05) 2/3 O 2, Li 4/3 (Mn 0 .9 Nb 0 .1) 2/3 O ₂ , and Li _4/3 (Mn _0.995 Nb _0.05 ) _2/3 O _2, as a cathode active material for a lithium secondary battery. 15. The method of claim 14,
A cathode active material for a lithium secondary battery having a discharge capacity of 140 mAhg ^-1 or more at two or more cycles. A lithium secondary battery comprising the cathode active material according to claim 14. 20. The method of claim 19,
A cathode including a cathode active material;
An anode including a negative electrode active material; And
A separator between the anode and the cathode,
&Lt; / RTI &gt;

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