阅读说明：本技术 二次电池用正极活性材料、其制备方法以及包含其的锂二次电池 (Positive electrode active material for secondary battery, method for preparing same, and lithium secondary battery comprising same ) 是由 金元泰 柳淙烈 河昇哲 申先植 于 2019-09-30 设计创作，主要内容包括：本发明提供了一种制备二次电池用正极活性材料的方法,所述方法包括如下步骤：准备包含镍(Ni)、钴(Co)和锰(Mn)的锂复合过渡金属氧化物,其中基于所述过渡金属的总含量,所述镍(Ni)的含量为60mol％以上；以及对所述锂复合过渡金属氧化物、作为氟(F)涂覆源的MgF-2和硼(B)涂覆源进行干混和热处理,以在所述锂复合过渡金属氧化物的粒子表面上形成涂覆部。另外,如上所述地制备的正极活性材料包含：锂复合过渡金属氧化物,所述锂复合过渡金属氧化物包含镍(Ni)、钴(Co)和锰(Mn)；和涂覆部,所述涂覆部形成在所述锂复合过渡金属氧化物的粒子表面上,其中基于所述过渡金属的总含量,所述锂复合过渡金属氧化物具有60mol％以上的所述镍(Ni)的含量,并且所述涂覆部包含氟(F)和硼(B)。(The present invention provides a method for preparing a positive active material for a secondary battery, the method comprising the steps of: preparing a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn), wherein a content of the nickel (Ni) is 60 mol% or more based on a total content of the transition metal; and MgF as a fluorine (F) coating source for the lithium composite transition metal oxide 2 And a boron (B) coating source to form a coating portion on the surface of the particles of the lithium composite transition metal oxide. In addition, the positive electrode active material prepared as described above includes: a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn); and a coating part formed on a particle surface of the lithium composite transition metal oxide, wherein the lithium composite transition metal oxide has a content of the nickel (Ni) of 60 mol% or more based on a total content of the transition metal, and the coating part includes fluorine (F) and boron (B).)

1. A method of preparing a positive electrode active material for a secondary battery, the method comprising the steps of:

preparing a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn), wherein a content of the nickel (Ni) is 60 mol% or more based on a total content of the transition metal; and

MgF as a fluorine (F) coating source to the lithium composite transition metal oxide₂And a boron (B) coating source to form a coating portion on the surface of the particles of the lithium composite transition metal oxide.

2. The method of claim 1, wherein the boron (B) coating source is H₃BO₃。

3. The method of claim 1, wherein the MgF is mixed at 0.002 to 0.08 parts by weight based on 100 parts by weight of the lithium composite transition metal oxide₂。

4. The method of claim 1, wherein the boron (B) coating source is mixed at 0.09 to 0.75 parts by weight based on 100 parts by weight of the lithium composite transition metal oxide.

5. The method of claim 1, wherein the heat treatment is performed at 200 ℃ to 600 ℃.

6. A positive electrode active material for a secondary battery, comprising:

a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn); and

a coating part formed on a particle surface of the lithium composite transition metal oxide,

wherein the lithium composite transition metal oxide has a nickel (Ni) content of 60 mol% or more based on the total content of the transition metals, and

the coating portion contains fluorine (F) and boron (B).

7. The positive electrode active material for a secondary battery according to claim 6, wherein the fluorine (F) is contained in an amount of 100ppm to 300ppm based on the total weight of the positive electrode active material.

8. The positive electrode active material for a secondary battery according to claim 6, wherein the boron (B) is contained in an amount of 300ppm to 700ppm based on the total weight of the positive electrode active material.

9. A positive electrode comprising the positive electrode active material according to any one of claims 6 to 8.

10. A secondary battery comprising the positive electrode according to claim 9.

Technical Field

Cross Reference to Related Applications

This application claims the benefit of korean patent application No. 10-2018-0115731, filed by the korean intellectual property office at 28/9/2018, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a positive electrode active material for a secondary battery, a method of preparing the same, and a lithium secondary battery including the same.

Background

Recently, due to rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, electric vehicles, and the like, demand for small and lightweight secondary batteries having a relatively high capacity is rapidly increasing. In particular, lithium secondary batteries are lightweight and have high energy density, and thus are receiving attention as driving power sources for portable devices. Accordingly, research and development efforts have been actively made to improve the performance of the lithium secondary battery.

When an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalating and deintercalating lithium ions, the lithium secondary battery generates electric energy through oxidation and reduction reactions at the time of intercalation/deintercalation of lithium ions from the positive electrode and the negative electrode.

As a positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO) is used₂) Lithium nickel oxide (LiNiO)₂) Lithium manganese oxide (LiMnO)₂、LiMn₂O₄Etc.), lithium iron phosphate compounds (LiFePO)₄) And the like. Further, LiNiO as an improvement of LiNiO having low thermal stability₂Has been developed, a lithium composite transition metal oxide in which a part of nickel (Ni) is replaced with cobalt (Co) and manganese (Mn) (hereinafter, simply referred to as "NCM-based lithium oxide"). However, typical NCM-based lithium composite transition metal oxides that have been developed do not have sufficient capacity properties, and thus their applications are limited.

In order to solve these problems, in recent years, studies have been made to increase the Ni content in the NCM-based lithium composite transition metal oxide. However, in the case of a nickel-rich cathode active material having a high nickel content, its capacity increases, but depending on the depth of charge, with Ni²⁺To Ni^3+/4+And rapid oxygen de-intercalation occurs. The desorbed oxygen reacts with the electrolyte to change the intrinsic properties of the material, and there is a problem of causing instability of the lattice structure and further structural collapse.

Therefore, in order to ensure the stability of Ni-rich high Ni NCM-based lithium composite transition metal oxides, a great deal of research is being conducted on surface modification in combination with coating techniques. However, there is still a need to develop a high-Ni NCM-based positive electrode active material capable of suppressing degradation of battery performance (such as capacity reduction and output reduction) while improving thermal stability. In particular, there is still a need to develop a high Ni NCM-based positive electrode active material having stability at a high voltage of 4.3V or more.

Disclosure of Invention

Technical problem

An aspect of the present invention provides an NCM-based positive electrode active material containing nickel (Ni) of 60 mol% or more to secure high Ni of high capacity, which is capable of suppressing an increase in resistance and a decrease in output depending on a coating material while remarkably improving stability. In particular, the present invention provides a positive electrode active material for a secondary battery that realizes excellent thermal stability and excellent electrochemical performance even at a high voltage of 4.3V or more.

Technical scheme

According to an aspect of the present invention, there is provided a method of preparing a positive electrode active material for a secondary battery, the method including the steps of: preparing a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn), wherein a content of the nickel (Ni) is 60 mol% or more based on a total content of the transition metal; and MgF as a fluorine (F) coating source for the lithium composite transition metal oxide₂And a boron (B) coating source to form a coating portion on the surface of the particles of the lithium composite transition metal oxide.

According to another aspect of the present invention, there is provided a positive electrode active material for a secondary battery, including: a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn); and a coating part formed on a particle surface of the lithium composite transition metal oxide, wherein the lithium composite transition metal oxide has a content of the nickel (Ni) of 60 mol% or more based on a total content of the transition metal, and the coating part includes fluorine (F) and boron (B).

According to still another aspect of the present invention, there are provided a positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode.

Advantageous effects

The cathode active material for a secondary battery prepared according to the present invention is a high-Ni NCM-based cathode active material containing 60 mol% or more of nickel (Ni), which can secure high capacity and solve the problem of deterioration of structural/chemical stability due to the increase of nickel (Ni) of the high-Ni NCM system. Therefore, excellent thermal stability can be ensured, and an increase in resistance and a decrease in output depending on the coating material can also be suppressed. In particular, excellent thermal stability and excellent electrochemical performance can be achieved even at high voltages of 4.3V or more.

Drawings

Fig. 1 is a graph showing the results of evaluating the low-temperature output performance of lithium secondary batteries manufactured using positive electrode active materials prepared according to examples and comparative examples; and is

Fig. 2 is a graph showing the results of evaluating the amount of gas generated during high-temperature storage of lithium secondary batteries manufactured using the cathode active materials prepared according to examples and comparative examples.

Detailed Description

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. In this case, it should be understood that the words or terms used in the specification and claims should not be construed as having meanings defined in common dictionaries. It is further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the present invention, on the basis of the principle that the inventor may appropriately define the meaning of the words or terms in order to best explain the present invention.

<Method for preparing positive electrode active material>

A positive electrode active material for a secondary battery is prepared by: preparing a lithium composite transition metal oxide including nickel (Ni), cobalt (Co), and manganese (Mn), wherein a content of nickel (Ni) is 60 mol% or more based on a total content of transition metals; and the lithium composite transition metalOxide, MgF as fluorine (F) coating source₂And a boron (B) coating source to form a coating portion on the surface of the particles of the lithium composite transition metal oxide.

The method of preparing the positive electrode active material of the present invention will be described in detail step by step.

First, a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn) is prepared, in which the content of nickel (Ni) is 60 mol% or more based on the total content of transition metals.

The lithium composite transition metal oxide is a high nickel (Ni) NCM system having a nickel (Ni) content of 60 mol% or more based on the total content of transition metals. More preferably, the content of nickel (Ni) may be 65 mol% or more, and still more preferably 80 mol% or more, based on the total content of transition metals. When the content of nickel (Ni) of the lithium composite transition metal oxide satisfies 60 mol% or more based on the total content of the transition metals, a high capacity can be secured.

More specifically, the lithium composite transition metal oxide may be represented by the following formula 1.

[ formula 1]

Li_pNi_1-(x1+y1+z1)Co_x1Mn_y1M^a _z1O_2+δ

In the above formula, M^aIs at least one selected from the following: zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo and Cr, and p is more than or equal to 0.9 and less than or equal to 1.5, and 0<x1≤0.2，0<y1 is not less than 0.2, z1 is not less than 0.1, -0.1 is not less than δ is not less than 1, and 0<x1+y1+z1≤0.4。

In the lithium composite transition metal oxide of the above formula 1, Li may be contained in an amount corresponding to p (i.e., 0.9. ltoreq. p.ltoreq.1.5). If p is less than 0.9, the capacity may deteriorate. If p is greater than 1.5, the particles may be sintered in the firing process, and thus it may be difficult to prepare the positive electrode active material. When considering the significant effect of improving the capacity properties of the positive electrode active material according to the control of the Li content and the balance of sintering in the preparation of the active material, it is more preferable that Li may be contained in an amount of 1.0. ltoreq. p.ltoreq.1.15.

In the lithium composite transition metal oxide of the above formula 1, Ni may be contained in an amount corresponding to 1- (x1+ y1+ z1) (e.g., 0.60. ltoreq. 1- (x1+ y1+ z1) < 1). When the Ni content in the lithium composite transition metal oxide of the above formula 1 is 0.06 or more, an amount of Ni sufficient to contribute to charge and discharge can be secured, so that a high capacity can be realized. More preferably, Ni may be contained in an amount of 0.65. ltoreq.1- (x1+ y1+ z 1). ltoreq.0.99.

In the lithium composite transition metal oxide of formula 1 above, Co may be included in an amount corresponding to x1 (i.e., 0< x1 ≦ 0.2). When the Co content in the lithium composite transition metal oxide of the above formula 1 is more than 0.2, the cost may be increased. When considering the significant effect of improving the capacity performance according to the inclusion of Co, more specifically, Co may be included in an amount of 0.05. ltoreq. x 1. ltoreq.0.2.

In the lithium composite transition metal oxide of the above formula 1, Mn may be included in an amount corresponding to y1 (i.e., 0< y 1. ltoreq.0.2) when the effect of improving the life property is considered. When y1 in the lithium composite transition metal oxide of formula 1 above is greater than 0.2, the output performance and capacity performance of the battery may rather be significantly deteriorated. Thus, more specifically, Mn may be contained in an amount of 0.05. ltoreq. y 1. ltoreq.0.2.

In the lithium composite transition metal oxide of the above formula 1, M^aMay be a doping element contained in the crystal structure of the lithium composite transition metal oxide, and may contain M in an amount corresponding to z1 (i.e., 0. ltoreq. z 1. ltoreq.0.1)^a。

Next, the lithium composite transition metal oxide, MgF as a fluorine (F) coating source, is subjected to₂And a boron (B) coating source to form a coating portion on the surface of the particles of the lithium composite transition metal oxide.

In the present invention, MgF is used₂As a fluorine (F) coating source to coat fluorine (F), and a boron (B) coating source is mixed therewith to coat boron (B). When MgF is used₂Coating with fluorine (F), MgF during heat treatment₂F substitutes for some oxygen on the surfaces of the positive electrode active material and lithium boron oxide (LiBO) to form electron holes, thereby improving electron mobility. Since some of the oxygen is substituted by F, the distance between the transition metal and oxygen becomes closer, thereby allowing oxygen at the transition metal during the electrochemical reactionOxygen de-intercalation that may occur when the number of transformations is changed is minimized. By the above, the generation of gas can be suppressed, the formation of an SEI film can be promoted, and the corrosion of the surface of the positive electrode active material due to HF generated by the decomposition of the electrolytic solution can be prevented. As in the present invention, by using MgF₂As a fluorine (F) coating source, there is a significant effect of suppressing structural deterioration of the positive electrode active material. However, MgF₂Has a high melting point of about 1263 ℃, making it difficult to use as a coating source in the prior art. Even when wet coating is considered, it is difficult to apply wet coating to MgF due to its low solubility₂. In addition, Mg has a disadvantage of lowering charge/discharge capacity even in a small amount.

Therefore, the invention applies MgF in dry coating₂Used with boron (B) coating sources to reduce MgF₂Thereby increasing the ease of coating and significantly improving electrochemical performance. In addition, lithium boron oxide (LiBO) generated from the boron (B) coating material has an effect of improving charge/discharge capacity. The cathode active material prepared as described above can suppress an increase in resistance and a decrease in output depending on a coating material while significantly improving stability, and in particular, can realize excellent thermal stability and excellent electrochemical properties even at a high voltage of 4.3V or more.

The boron (B) coating source may include at least one selected from the group consisting of: b is₄C、B₂O₃And H₃BO₃And preferably may be H₃BO₃。H₃BO₃Has a melting point of about 170 ℃ which is relatively lower than the melting point of other boron (B) coating sources, such as B₄C (about 2,763 ℃ C.) and B₂O₃(about 450 ℃ C.). In use H₃BO₃In the case of performing coating, when heat treatment is performed, hydrogen is easily deintercalated, and Boron Oxide (BO) anions are simply formed, so that coating is easily performed, and the effect of improving electrochemical properties may be more excellent.

Boron (B) coating source (especially H)₃BO₃) Are susceptible to anionization in a relatively low temperature range, which can lead to residualLithium reacts and MgF can be reduced by a driving force generated when lithium boron oxide (LiBO) is formed₂The melting point of (2). That is, by using a boron (B) coating source, in particular by using H₃BO₃And MgF₂Can remarkably improve the ease of coating and can achieve uniform coating, and can effectively improve structural stability and increase charge/discharge capacity.

The MgF may be mixed in an amount of 0.002 to 0.08, more preferably 0.008 to 0.06, and still more preferably 0.01 to 0.04 parts by weight based on 100 parts by weight of the lithium composite transition metal oxide₂. By mixing and using MgF in the above-mentioned weight part range₂Generation of gas can be suppressed, and formation of an SEI film can be promoted, and corrosion of the surface of the positive electrode active material due to HF generated by decomposition of the electrolytic solution can be prevented while deterioration of charge/discharge capacity due to Mg can be minimized.

The boron (B) coating source may be mixed in an amount of 0.09 to 0.75 parts by weight, more preferably 0.1 to 0.6 parts by weight, still more preferably 0.2 to 0.4 parts by weight, based on 100 parts by weight of the lithium composite transition metal oxide. By mixing a boron (B) coating source, especially H, in the above-mentioned weight part range₃BO₃Effectively reduce MgF₂And the charge/discharge capacity can be improved.

MgF₂And a boron (B) coating source and a lithium composite transition metal oxide, and then heat-treating the mixture to form a coated portion. The heat treatment may be carried out at 200 ℃ to 600 ℃, more preferably 300 ℃ to 500 ℃. The heat treatment may be performed in an atmospheric atmosphere, and may be performed for 2 hours to 8 hours, more preferably 3 hours to 6 hours.

<Positive electrode active material>

The positive electrode active material prepared as described above includes: a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co), and manganese (Mn); and a coating part formed on a particle surface of the lithium composite transition metal oxide, wherein the lithium composite transition metal oxide has nickel (Ni) in a content of 60 mol% or more based on a total content of transition metals, and the coating part includes fluorine (F) and boron (B).

The lithium composite transition metal oxide is applied with the same composition and chemical formula as those of the lithium composite transition metal oxide in the above-described method of preparing the positive electrode active material.

The positive electrode active material prepared according to the preparation method of the present invention includes a coating portion formed on the surface of the lithium composite transition metal oxide particle, wherein the coating portion includes fluorine (F) and boron (B). The present invention can solve the problem of deterioration of structural/chemical stability due to increase of nickel (Ni) of the high nickel (Ni) NCM system and can secure excellent thermal stability by forming the coating portion containing fluorine (F) and boron (B) in the high nickel (Ni) NCM system having 60 mol% or more of nickel (Ni) as described above. In addition, the generation of gas can be suppressed, and the formation of an SEI film can be promoted, and corrosion of the surface of the positive electrode active material due to HF generated by decomposition of the electrolytic solution can be prevented, while an increase in resistance and a decrease in output depending on the coating material can be suppressed, and deterioration of charge/discharge capacity can be suppressed. In particular, the cathode active material prepared as described above can achieve excellent thermal stability and excellent electrochemical properties even at a high voltage of 4.3V or more.

The fluorine (F) contained in the coating portion may be contained in an amount of 100 to 300ppm, more preferably 100 to 250ppm, still more preferably 120 to 200ppm, based on the total weight of the cathode active material.

The boron (B) contained in the coating portion may be contained at 300 to 700ppm, more preferably 300 to 650ppm, still more preferably 350 to 600ppm, based on the total weight of the positive electrode active material.

By coating fluorine (F) and boron (B) in amounts satisfying the above ranges, excellent thermal stability can be ensured even in the case of a high nickel (Ni) NCM system having 60 mol% or more of nickel (Ni), and there are effects of reducing room temperature resistance and reducing gas generation.

<Positive electrode and secondary battery>

According to another embodiment of the present invention, there are provided a positive electrode for a lithium secondary battery including the positive electrode active material and a lithium secondary battery including the positive electrode.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, it is possible to use: stainless steel; aluminum; nickel; titanium; firing carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like. In addition, the cathode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the cathode current collector to improve adhesion of the cathode active material. For example, the cathode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like.

In addition, the positive electrode active material layer may include a conductive material and a binder as well as the above-described positive electrode active material.

At this time, the conductive material is used to impart conductivity to the electrode, and any conductive material may be used without particular limitation as long as it has electron conductivity and does not cause chemical changes in the battery to be constructed. Specific examples of the conductive material may include: graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one of the above materials or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the binder may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, Ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, Styrene Butadiene Rubber (SBR), fluororubber, or various copolymers thereof, and any one of the above materials or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

In addition to using the above-described positive electrode active material, the positive electrode may be manufactured according to a typical method for manufacturing a positive electrode. Specifically, the positive electrode can be manufactured by: the composition for forming a positive electrode active material layer, which comprises the above-described positive electrode active material and optionally a binder and a conductive material, is coated on a positive electrode current collector, followed by drying and roll-pressing. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent commonly used in the art. Examples of the solvent may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and any one of the above materials or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient if the solvent can dissolve and disperse the positive electrode active material, the binder, and the conductive material, and then has a viscosity that can exhibit excellent thickness uniformity during coating for manufacturing the positive electrode, in consideration of the coating thickness and the production yield of the slurry.

Alternatively, in another method, the positive electrode may be manufactured by: the composition for forming the positive electrode active material layer is cast on a separate support, and then a film obtained by peeling from the support is laminated on the positive electrode current collector.

According to still another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery includes a positive electrode, a negative electrode disposed facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is the same as described above. In addition, the lithium secondary battery may further optionally include: a battery case for accommodating an electrode assembly composed of a positive electrode, a negative electrode, and a separator; and a sealing member for sealing the battery case.

In the lithium secondary battery, the anode includes an anode current collector and an anode active material layer disposed on the anode current collector.

The anode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it is possible to use: copper; stainless steel; aluminum; nickel; titanium; burning the charcoal; copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like; and aluminum-cadmium alloys, and the like. Further, the anode current collector may typically have a thickness of 3 μm to 500 μm, and as in the case of the cathode current collector, fine irregularities may be formed on the surface of the anode current collector to improve the adhesion of the anode active material. For example, the anode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like.

The anode active material layer selectively contains a binder and a conductive material in addition to the anode active material. As an example, the anode active material layer may be prepared by: the composition for forming an anode, which includes an anode active material and optionally a binder and a conductive material, is coated on an anode current collector and then dried. Alternatively, the anode active material layer may be prepared by casting the composition on a separate support and then laminating a film obtained by peeling from the support on an anode current collector.

As the negative electrode active material, a material capable of making lithium into lithium can be usedReversibly intercalating and deintercalating compounds. Specific examples of the anode active material may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; (semi) metallic materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; metal oxides, e.g. SiO, which may or may not be doped with lithium_α(0<α<2)、SnO₂Vanadium oxide, lithium titanium oxide and lithium vanadium oxide; or a composite material comprising a (semi) metal material and a carbonaceous material, such as a Si-C composite material or a Sn-C composite material, and either one of the above materials or a mixture of two or more thereof may be used. In addition, a metallic lithium thin film may be used as a negative electrode active material. In addition, low crystalline carbon and high crystalline carbon may be used as the carbonaceous material. Typical examples of the low crystalline carbon may include soft carbon and hard carbon, and typical examples of the high crystalline carbon may include irregular, platy, scaly, spherical or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high temperature sintered carbon (such as petroleum coal tar or pitch-derived coke).

In addition, the binder and the conductive material may be the same as those described above in the description of the positive electrode.

On the other hand, in the lithium secondary battery, a separator is used to separate a negative electrode from a positive electrode and provide a moving path for lithium ions. Any separator may be used without particular limitation so long as it is generally used as a separator in a lithium secondary battery. In particular, a separator having a high moisture-retaining ability for an electrolytic solution and a low resistance to movement of electrolyte ions is preferable. Specifically, it is possible to use: porous polymer films, for example, porous polymer films prepared from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer; or a laminated structure having two or more layers of the above porous polymer film. In addition, a typical porous nonwoven fabric, such as a nonwoven fabric formed of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like, may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

The electrolyte used in the present invention may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, or the like, which can be used in the manufacture of a lithium secondary battery, but is not limited thereto.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

Any organic solvent may be used without particular limitation so long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, there can be used: ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone and epsilon-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), and Propylene Carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R — CN (where R is a linear, branched or cyclic hydrocarbyl group having C2 to C20 and may contain double bonds, aromatic rings or ether linkages); amides, such as dimethylformamide; dioxolanes, such as 1, 3-dioxolane; or sulfolane. Among these solvents, preferred is a carbonate-based solvent, and more preferred is a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ion conductivity and high dielectric constant and a linear carbonate-based compound (e.g., ethylene carbonate, dimethyl carbonate, or diethyl carbonate) having low viscosity, which can improve the charge/discharge performance of a battery. In this case, when the cyclic carbonate and chain carbonate are present in a ratio of about 1: 1 to about 1: 9, the electrolyte may be excellent in performance when mixed.

Any compound may be used as the lithium salt without particular limitation so long as it can be provided in a lithium secondary batteryThe lithium ion to be used may be any. Specifically, as the lithium salt, LiPF may be used₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂LiCl, LiI or LiB (C)₂O₄)₂. The lithium salt may be used in a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity to exhibit excellent performance, and lithium ions can be efficiently moved.

In the electrolyte, in order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and increase the discharge capacity of the battery, at least one additive such as a halogenated alkylene carbonate compound (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (glycidyl) glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride may be contained in addition to the electrolyte component. At this time, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

The above-described lithium secondary battery comprising the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output performance, and capacity retention rate, and thus can be used for: portable devices such as mobile phones, notebook computers, and digital cameras; and the field of electric vehicles, such as Hybrid Electric Vehicles (HEVs).

Therefore, according to another embodiment of the present invention, there are provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module.

The battery module or the battery pack may be used as a power source for one or more middle-and large-sized devices, for example: an electric tool; electric vehicles such as Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); or an electrical power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example 1

Adding the mixture into a Ni: co: the molar ratio of Mn is 65: 15: 20 to the precursor was added lithium carbonate (Li)₂CO₃) So that the molar ratio of Li/metal (Ni, Co, Mn) became 1.06, and the mixed powder was introduced into an alumina crucible to perform heat treatment. Thereafter, the mixed powder was heat-treated at 750 ℃ for 5 hours and then at 870 ℃ for 10 hours in an oxygen atmosphere to prepare a lithium composite transition metal oxide.

Thereafter, the heat-treated lithium composite transition metal oxide powder was pulverized using a mortar, and then 0.025 parts by weight of MgF was added based on 100 parts by weight of the lithium composite transition metal oxide₂And 0.3 part by weight of H₃BO₃. The mixture was heat-treated at 380 ℃ for 5 hours in an atmospheric atmosphere to prepare a positive electrode active material having a coated portion (F150 ppm, B500 ppm).

Example 2

Except that 0.025 parts by weight of MgF₂And 0.18 part by weight of H₃BO₃A positive electrode active material having a coated portion (F150 ppm, B300 ppm) was prepared in the same manner as in example 1, except for mixing.

Example 3

Except that 0.025 parts by weight of MgF₂And 0.42 parts by weight of H₃BO₃A cathode active material having a coated portion (F150 ppm, B700 ppm) was prepared in the same manner as in example 1, except for mixing.

Example 4

Except that 0.025 parts by weight of MgF₂And 0.09 parts by weight of H₃BO₃A positive electrode active material having a coated portion (F150 ppm, B700 ppm) was prepared in the same manner as in example 1, except that mixing and heat treatment were performed at 600 ℃ for 5 hours in an atmospheric atmosphere.

Example 5

A cathode active material was prepared in the same manner as in example 1, except that the heat treatment was performed at 420 ℃ for 5 hours.

Comparative example 1

A cathode active material was prepared in the same manner as in example 1, except that the heat treatment was performed without adding a coating source to the lithium composite transition metal oxide.

Comparative example 2

Except that 0.25 parts by weight of AlF was used₃To replace MgF₂Except for this, a positive electrode active material was prepared in the same manner as in example 1.

Comparative example 3

Except that 0.63 part by weight of WO was used₃And 0.42 parts by weight of H₃BO₃To replace MgF₂Except for this, a positive electrode active material was prepared in the same manner as in example 1.

Comparative example 4

Except that 0.32 parts by weight of WO is used₃And 0.42 parts by weight of H₃BO₃Except that, a cathode active material was prepared in the same manner as in comparative example 3.

Comparative example 5

Except that 0.025 parts by weight of MgF₂A cathode active material was prepared in the same manner as in example 1, except that it was mixed as a coating source into the lithium composite transition metal oxide.

[ preparation example: production of lithium secondary battery]

Each of the positive electrode active material, the carbon black conductive material and the PVdF binder prepared in examples 1 to 5 and comparative examples 1 to 5 was mixed at a ratio of 96.5: 1.5: 2 in the solvent of N-methylpyrrolidone to prepare a positive electrode mixture material (viscosity: 5000mPa · s), and the mixture material was coated on one surface of an aluminum current collector, dried at 130 ℃, and roll-pressed to manufacture a positive electrode.

Mixing a natural graphite negative electrode active material, a carbon black conductive material and a PVDF binder in a ratio of 85: 10: 5 in an N-methylpyrrolidone solvent to prepare a composition for forming a negative electrode. Then, the composition was coated on one surface of a copper current collector to manufacture a negative electrode.

A porous polyethylene separator was interposed between the positive and negative electrodes prepared as described above to prepare an electrode assembly, which was then placed in a case. After that, an electrolytic solution is injected into the case to manufacture a lithium secondary battery. At this time, lithium hexafluorophosphate (LiPF) was added at a concentration of 1.0M₆) The electrolyte was prepared by dissolving the above-mentioned compound in an organic solvent composed of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC mixed volume ratio: 3/4/3).

[ Experimental example 1: evaluation of resistance at room temperature]

Lithium secondary batteries manufactured in the same manner as in the preparation examples using each of the positive electrode active materials of examples 1 to 5 and comparative examples 1 to 5 were subjected to measurement of resistance at room temperature (25 ℃) in a state of SOC 50% for 10 seconds of discharge, and the results are shown in table 1.

[ Table 1]

Referring to table 1, examples 1 to 5 formed with the coating portions according to the present invention had improved room temperature output when compared with comparative examples 1 to 5.

[ Experimental example 2: evaluation of Low temperature output Properties]

Lithium secondary batteries manufactured in the same manner as in the preparation examples using each of the cathode active materials of examples 1 to 5 and comparative examples 1 to 5 were discharged at-25 ℃ and SOC 20% up to 3V at 0.6C to evaluate low temperature output using the generated voltage difference, and the results are shown in table 2 below and fig. 1.

[ Table 2]

Referring to table 2 and fig. 1, examples 1 to 5 formed with the coating portions according to the present invention had improved low temperature output when compared with comparative examples 1 to 5.

[ Experimental example 3: evaluation of gas Generation]

Lithium secondary batteries manufactured in the same manner as in the preparation examples using each of the cathode active materials of examples 1 to 5 and comparative examples 1 to 5 were stored at SOC 100% and 90 ℃ for 4 weeks to evaluate gas generation per week, and the results are shown in table 2.

Referring to fig. 2, it can be seen that examples 1 to 5 formed with the coated portions according to the present invention have a reduced amount of gas generation after the second week when compared with comparative examples 1 to 5.

[ Experimental example 4: evaluation of Life Performance]

Lithium secondary batteries manufactured in the same manner as in the preparation examples using each of the cathode active materials of examples 1 to 5 and comparative examples 1 to 5 were charged in the CCCV mode (end current 1/20C) at 45 ℃ until the batteries reached 1.0C and 4.25V, and then discharged at a constant current of 1.0C until the batteries reached 3.0V, to thereby conduct 400 charge/discharge experiments, and the capacity retention rates were measured for life performance evaluation. The results are shown in table 3.

[ Table 3]

Referring to table 3, each of the cathode active materials prepared in examples 1 to 5 had a slightly higher initial capacity than those of comparative examples 1 to 5, but had significantly improved life performance after 400 charges/discharges.