Positive electrode additive for lithium secondary battery, method for producing the same, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode additive for a lithium secondary battery, a manufacturing method thereof, a positive electrode for a lithium secondary battery containing the same, and a lithium secondary battery. According to the present invention, a positive electrode additive for a lithium secondary battery exhibiting high initial irreversible capacity and excellent air stability is provided.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application Nos. 10 - 2021 - 0127403 filed on September 27, 2021, 10 - 2022 - 0059705 filed on May 16, 2022, and 10 - 2022 - 0122332 filed on September 27, 2022, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a cathode additive for a lithium secondary battery, a method for manufacturing the same, a cathode for a lithium secondary battery including the same, and a lithium secondary battery.

Background Art

[0003] With the increasing multifunctionality of electronic devices and the accompanying increase in power consumption, many attempts have been made to increase the capacity of lithium secondary batteries and improve their charge - discharge efficiency.

[0004]

[0005] As an example, a technique has been proposed in which a cathode active material of 80% or more Ni is applied as a cathode material to the cathode of a lithium secondary battery, and a metal or metal - based anode active material such as SiO, Si, or SiC is applied to the anode together with a carbon - based anode active material such as natural graphite or artificial graphite.

[0006]

[0006] Therefore, various solutions have been studied to increase the capacity of lithium secondary batteries or reduce irreversible capacity. One of them is prelithiation, which is a concept of replenishing lithium consumed in the formation of the SEI layer (solid electrolyte interphase layer) in the initial state within the battery.

[0007] Various methods for prelithiation within the battery have been proposed.

[0008] As an example, there is a method of electrochemically lithiating the negative electrode in advance before driving the battery. However, the lithiated negative electrode is very unstable in the atmosphere, and it is difficult to scale up the process with the electrochemical lithiation method. As another example, there is a method of coating the negative electrode with lithium metal or lithium silicide (Li x Si) powder. However, since the powder has high reactivity and reduced atmospheric stability, there is a problem that it is difficult to establish suitable solvents and process conditions during negative electrode coating.

[0009] As a method of prelithiation at the positive electrode, there is a method of further coating more positive electrode material by an amount equal to the amount of lithium consumed at the negative electrode. However, since the amount of the added positive electrode material increases due to the low capacity of the positive electrode material itself, the energy density and capacity per weight of the final battery will be reduced by the amount of the increased positive electrode material.

[0010] Therefore, a material suitable for prelithiation of the battery at the positive electrode must have an irreversible characteristic that at least twice as much lithium desorbs during the first charge as the existing positive electrode material and does not react with lithium during subsequent discharge. An additive that satisfies such conditions is called a sacrificial positive electrode material.

[0011] In the case of a commercial battery, after injecting an electrolyte into a case containing a stacked positive electrode, a separator, and a negative electrode, a formation process of first performing a charge / discharge operation is carried out. In this process, an SEI layer formation reaction occurs on the negative electrode, and gas is generated by the decomposition of the electrolyte. In the formation process, the sacrificial positive electrode material releases lithium and reacts with the electrolyte while decomposing, and gases such as N2, O2, and CO2 generated in the process are recovered by a gas pocket removal process.

[0012] As the sacrificial positive electrode material, an over-lithiated positive electrode material of a metal oxide rich in lithium is often used. As the over-lithiated positive electrode material, Li6CoO4, Li5FeO4, and Li6MnO4 having an anti-fluorite structure are well known. The theoretical capacities of these are 977 mAh / g for Li6CoO4, 867 mAh / g for Li5FeO4, and 1001 mAh / g for Li6MnO4, and they have sufficient capacity to be used as a sacrificial positive electrode material. Among them, Li6CoO4 has the best electrical conductivity and has good electrochemical characteristics for use as a sacrificial positive electrode material.

[0013] However, the sacrificial positive electrode material of Li5FeO4 has disadvantages such as poor air stability, a sharp deterioration in performance when exposed to air, low electrical conductivity, and insufficient irreversible capacity. As a result, there is a problem that a considerable amount of Li5FeO4 must be added to compensate for a large irreversible capacity in a high-capacity lithium secondary battery. This is an inhibitory factor in the recent technological development direction of providing a lithium secondary battery with lower weight and improved capacity characteristics. Therefore, the development of a Li5FeO4-based sacrificial positive electrode material having a larger irreversible capacity is continuously required. Summary of the Invention Problems to be Solved by the Invention

[0014] The present invention provides a cathode additive for a lithium secondary battery that exhibits a high initial irreversible capacity and has excellent air stability.

[0015] The present invention provides a method for manufacturing the cathode additive for a lithium secondary battery.

[0016] The present invention provides a cathode for a lithium secondary battery including the cathode additive for a lithium secondary battery.

[0017] The present invention provides a lithium secondary battery including the cathode for the secondary battery.

Means for Solving the Problems

[0018] According to one embodiment of the present invention, Lithium (Li) iron (Fe) oxide particles doped or undoped with a foreign element, and A cathode additive for a lithium secondary battery including a lithium borate-based compound-containing layer formed on the lithium iron oxide particles is provided.

[0019] According to another embodiment of the present invention, Preparing a precursor mixture including a lithium (Li) precursor and an iron (Fe) precursor, Firing the precursor mixture in an inert gas atmosphere to obtain lithium iron oxide particles doped or undoped with a foreign element, and A method for manufacturing a cathode additive for a lithium secondary battery is provided, including heat-treating a mixture including the lithium iron oxide particles and a lithium borate-based compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate-based compound-containing layer.

[0020] According to still another embodiment of the present invention, a cathode for a lithium secondary battery including a cathode active material, a binder, a conductive material, and the cathode additive for a lithium secondary battery is provided.

[0021] According to still another embodiment of the present invention, there is provided a lithium secondary battery including the positive electrode, negative electrode, separator, and electrolyte for the lithium secondary battery.

[0022] Hereinafter, the positive electrode additive for the lithium secondary battery, the method for manufacturing the positive electrode additive, the positive electrode for the lithium secondary battery, and the lithium secondary battery according to the embodiment of the present invention will be described in more detail.

[0023] The terms and words used in this specification and the claims should not be construed as being limited to ordinary or dictionary meanings, but should be construed as meanings and concepts that conform to the technical idea of the present invention based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0024] Unless otherwise specifically defined in this specification, all technical terms and scientific terms have the same meaning as generally understood by those of ordinary skill in the art to which the present invention pertains. The terms used in the description of the present invention are merely for effectively describing specific examples and are not intended to limit the present invention.

[0025] As used in this specification, the singular form also includes the plural form unless the context clearly indicates the contrary meaning.

[0026] As used in this specification, the meaning of "comprising" does not exclude the presence or addition of other specific characteristics, regions, integers, steps, operations, elements, and / or components while embodying specific characteristics, regions, integers, steps, operations, elements, and / or components.

[0027] Since the present invention can be modified in various ways and can have various forms, specific examples will be illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0028] In this specification, for example, when the positional relationship between two parts such as "on ~", "above ~", "below ~", "on the side of ~" is described, unless the expressions "immediately" or "directly" are used, one or more other parts may be located between the two parts.

[0029] In this specification, for example, when the temporal sequence relationship such as "after ~", "subsequent to ~", "next to ~", "before ~" is described, unless the expressions "immediately" or "directly" are used, it may also include cases that are not continuous.

[0030] The term "at least one" in this specification should be understood to include all combinations that can be presented from one or more related items.

[0031] The term "positive electrode additive" used in this specification means a substance having an irreversible property that lithium desorbs at least twice or more as much as the existing positive electrode material during the initial charging of the battery and does not react with lithium during subsequent discharging. The said positive electrode additive can also be called a sacrificial positive electrode material. Since the said positive electrode additive compensates for lithium loss, as a result, the lost capacity of the battery is recovered, the capacity of the battery increases, and by suppressing gas generation, it is possible to prevent the battery from exploding and improve the life characteristics and safety of the battery.

[0032] According to one embodiment of the present invention, lithium (Li) iron (Fe) oxide particles doped with or without a foreign element, and a positive electrode additive for a lithium secondary battery is provided, which includes a lithium borate compound-containing layer formed on the lithium iron oxide particles.

[0033] As a result of the inventors' continuous research, it has been confirmed that a cathode additive (sacrificial cathode material) in which a lithium borate-based compound-containing layer is formed on lithium iron oxide particles enables excellent electrical conductivity and expression of a high irreversible capacity, and in particular, can exhibit excellent stability against moisture, carbon dioxide, etc. even when exposed to air.

[0034] The cathode additive contains lithium (Li) iron (Fe) oxide particles.

[0035] The lithium (Li) iron (Fe) oxide particles may be doped with a different element or may not be doped.

[0036] As an example, the lithium (Li) iron (Fe) oxide particles may be lithium transition metal oxide particles containing a Li5FeO4-based compound doped or not doped with a different element.

[0037] The Li5FeO4-based compound contains lithium in a ratio higher than the stoichiometric ratio. Excess lithium ions can move to the anode during the initial charge-discharge process to compensate for irreversible capacity loss.

[0038] The lithium transition metal oxide particles may consist only of Li5FeO4 doped or not doped with a different element, and may further contain known sacrificial cathode materials or additives such as Li2NiO2 and Li6CoO4. However, considering the manufacturing cost and physical properties of the cathode additive, etc., the lithium transition metal oxide particles preferably contain Li5FeO4 at least 50 mol% or more, or 70 mol% or more, or 90 mol% or more.

[0039] As an example, the lithium (Li)-iron (Fe) oxide may be Li5FeO4 or a compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li5Fe 1-x-y Al x M y O4 In the formula (1), M is at least one Group 2 element selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba); at least one Group 17 element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I); at least one Period 4 transition metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), and zinc (Zn); and at least one element selected from the group consisting of gallium (Ga) and indium (In), and is at least one element selected from the group consisting of elements selected from the above groups, x is from 0.1 to 0.35, and y is from 0 to 0.1.

[0040] Preferably, in the formula (1), M may be at least one element selected from the group consisting of magnesium (Mg), fluorine (F), titanium (Ti), zinc (Zn), and gallium (Ga).

[0041] In the formula (1), x may be 0.10 or more, or 0.15 or more; and 0.35 or less, or 0.30 or less, or 0.25 or less. Preferably, x may be from 0.10 to 0.35, or from 0.15 to 0.35, or from 0.15 to 0.30, or from 0.15 to 0.25.

[0042] In the formula (1), y may be 0 or more, or 0.01 or more, or 0.02 or more, or 0.03 or more; and 0.10 or less, or 0.07 or less, or 0.05 or less. Preferably, y may be from 0 to 0.1, or from 0 to 0.07, or from 0 to 0.05.

[0043] Preferably, the lithium (Li)-iron (Fe) oxide is Li5FeO4, Li5Fe 0.85 Al 0.15 O4, Li5Fe 0.82 Al 0.18 O4, Li5Fe 0.81 Al0.19 O4, Li5Fe 0.8 Al 0.2 O4, Li5Fe 0.77 Al 0.23 O4, Li5Fe 0.76 Al 0.24 O4, Li5Fe 0.75 Al 0.25 O4, Li5Fe 0.72 Al 0.28 O4, Li5Fe 0.71 Al 0.29 O4, Li5Fe 0.7 Al 0.3 O4, Li5Fe 0.82 Al 0.15 Mg 0.03 O4, Li5Fe 0.77 Al 0.2 Mg 0.03 O4, Li5Fe 0.72 Al 0.25 Mg 0.03 O4, Li5Fe 0.81 Al 0.15 Mg 0.04 O4, Li5Fe 0.76 Al 0.2 Mg 0.04 O4, Li5Fe 0.71 Al 0.25 Mg 0.04 O4, Li5Fe 0.82 Al 0.15 F 0.03 O4, Li5Fe 0.77 Al 0.2 F 0.03 O4, Li5Fe 0.72 Al 0.25 F 0.03 O4, Li5Fe 0.81 Al 0.15 F 0.04 O4, Li5Fe 0.76 Al 0.2 F 0.04 O4, Li5Fe 0.71 Al 0.25 F 0.04 O4, Li5Fe 0.82 Al 0.15 Ti 0.03 O4, Li5Fe 0.77 Al 0.2 Ti 0.03 O4, Li5Fe 0.72 Al0.25 Ti 0.03 O4, Li5Fe 0.81 Al 0.15 Ti 0.04 O4, Li5Fe 0.76 Al 0.2 Ti 0.04 O4, Li5Fe 0.71 Al 0.25 Ti 0.04 O4, Li5Fe 0.82 Al 0.15 Zn 0.03 O4, Li5Fe 0.77 Al 0.2 Zn 0.03 O4, Li5Fe 0.72 Al 0.25 Zn 0.03 O4, Li5Fe 0.81 Al 0.15 Zn 0.04 O4, Li5Fe 0.76 Al 0.2 Zn 0.04 O4, Li5Fe 0.71 Al 0.25 Zn 0.04 O4, Li5Fe 0.82 Al 0.15 Ga 0.03 O4, Li5Fe 0.77 Al 0.2 Ga 0.03 O4, Li5Fe 0.72 Al 0.25 Ga 0.03 O4, Li5Fe 0.81 Al 0.15 Ga 0.04 O4, Li5Fe 0.76 Al 0.2 Ga 0.04 O4 and Li5Fe 0.71 Al 0.25 Ga 0.04 It may be one or more compounds selected from the group consisting of O4.

[0044] In the lithium (Li) iron (Fe) oxide, the hetero element can exhibit a stable single phase with iron (Fe). By forming such a single phase, a part of the lithium (Li) iron (Fe) oxide is inactivated to improve its structural stability, and the generation of oxygen gas due to the decomposition of the lithium (Li) iron (Fe) oxide can be suppressed.

[0045] The formation of a single phase in which such a hetero element is alloyed can be confirmed, for example, by analyzing the lithium (Li) iron (Fe) oxide by XRD (X-ray diffraction). Specifically, when the lithium (Li) iron (Fe) oxide is analyzed by XRD, the peak derived from iron (Fe) is shifted by doping and appears as a single peak indicating a stable single phase rather than a secondary phase. In a specific example, the formation of a single phase doped with the hetero element can be confirmed from the fact that a single peak confirmed at 2θ of, for example, 23 degrees to 24 degrees ± 0.1 degree, which is derived from the iron (Fe), is shifted by about 0.10 degree to 0.20 degree compared to the case where the hetero element is not added.

[0046] The lithium (Li) iron (Fe) oxide particles can have a volume average particle diameter (D50) of 0.5 μm to 45 μm, or 1 μm to 25 μm, or 5 μm to 15 μm, and can be in the form of primary particles or secondary particles in which the primary particles are aggregated. In the above particle size range, the positive electrode additive can be uniformly mixed with the positive electrode active material and exhibit appropriate characteristics in the positive electrode.

[0047] In order to have an appropriate particle size distribution and volume average particle diameter, after synthesizing the lithium iron oxide particles, the lithium iron oxide particles can be passed through a standard sieve having a mesh size corresponding to the desired particle size distribution. The particle size distribution and volume average particle diameter (D50) of the lithium iron oxide particles can be measured and calculated using a well-known laser particle size analyzer or the like.

[0048] According to an embodiment of the present invention, the positive electrode additive includes a lithium borate compound-containing layer formed on the lithium iron oxide particles.

[0049] The lithium borate compound-containing layer is a coating layer formed on the lithium iron oxide particles. The lithium borate compound-containing layer is formed on all or part of the surface of the lithium iron oxide particles. The schematic cross-section of the positive electrode additive according to the example can have a structure as shown in FIG. 1.

[0050] The lithium borate compound-containing layer may be a coating layer composed of a lithium borate compound.

[0051] In addition, additives such as lithium hexafluorophosphate, lithium triflate, and lithium difluorophosphate, which are known in the field of lithium secondary batteries, are contained together with the lithium borate compound in the lithium borate compound-containing layer. However, in order to sufficiently exhibit the effect of improving air stability by introducing the lithium borate compound-containing layer, the lithium borate compound-containing layer preferably contains 50 mol% or more, or 70 mol% or more, or 90 mol% or more of the lithium borate compound.

[0052] The lithium borate compound-containing layer formed on the lithium iron oxide particles can be confirmed by an electron microscope or XRD analysis for the positive electrode additive.

[0053] According to an embodiment of the present invention, the lithium borate compound may be one or more compounds selected from the group consisting of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(2-methyl-2-fluoromalonate)borate, and lithium malonate difluoroborate.

[0054] According to an embodiment of the present invention, the lithium borate compound is contained in an amount of 2.0 parts by weight to 25.0 parts by weight, or 2.0 parts by weight to 20.0 parts by weight, or 2.5 parts by weight to 20.0 parts by weight, or 2.5 parts by weight to 15.0 parts by weight, or 2.5 parts by weight to 10.0 parts by weight, or 2.5 parts by weight to 5.0 parts by weight based on 100 parts by weight of the total content of the positive electrode additive.

[0055] In order to sufficiently exhibit the effect of improving the air stability of the positive electrode additive, the content of the lithium borate compound is preferably 2.0 parts by weight or more based on 100 parts by weight of the total content of the positive electrode additive. However, when the content of the lithium borate compound is excessively high, the irreversible capacity and the capacity characteristics during charge and discharge of the positive electrode additive decrease. Therefore, the content of the lithium borate compound-containing layer is preferably 25.0 parts by weight or less based on 100 parts by weight of the total content of the positive electrode additive.

[0056] On the other hand, the positive electrode additive for the lithium secondary battery may further include a carbon coating layer formed on the lithium iron oxide particles.

[0057] As an example, the positive electrode additive for the lithium secondary battery may include the lithium iron oxide particles; a carbon coating layer formed on the lithium iron oxide particles; and a lithium borate compound-containing layer formed on the carbon coating layer.

[0058] And the positive electrode additive for the lithium secondary battery may further include a carbon nanotube-containing layer formed on the carbon coating layer.

[0059] As an example, the positive electrode additive for the lithium secondary battery may include the lithium iron oxide particles; a carbon coating layer formed on the lithium iron oxide particles; a carbon nanotube-containing layer formed on the carbon coating layer; and a lithium borate compound-containing layer formed on the carbon nanotube-containing layer. The schematic cross-section of the positive electrode additive according to the above example can have a structure as shown in FIG. 2.

[0060] The inventors continued research to improve the electrical conductivity and irreversible capacity of the lithium iron oxide-based positive electrode additive and to improve the air stability by a simpler method. As a result of such continuous research, in the manufacturing process of the lithium iron oxide-based positive electrode additive, a dispersion liquid in which carbon nanotubes are dispersed in the presence of a water-soluble polymer dispersant is added, and a carbon coating layer derived from the water-soluble polymer dispersant is formed on the lithium iron oxide particles by firing, and it was confirmed that a positive electrode additive was obtained. Also, it was confirmed that a positive electrode additive in the form of a double coating layer in which the carbon coating layer and the carbon nanotube-containing layer were respectively formed was obtained in the manufacturing process. And a lithium borate compound-containing layer is formed on the carbon coating layer or the carbon nanotube-containing layer.

[0061] In the positive electrode additive, a carbon nanotube-containing layer having an electrical conductivity similar to that of the lithium iron oxide particles is formed thereon, and it can have excellent electrical conductivity and high irreversible capacity compared to the conventionally known lithium iron oxide-based positive electrode additive. Further, a uniform carbon coating layer derived from the water-soluble polymer dispersant is formed on the surface of the lithium iron oxide particles, and carbon nanotubes are uniformly bonded at a relatively high ratio on such a carbon coating layer. Therefore, the positive electrode additive of the above embodiment can have even higher electrical conductivity and irreversible capacity.

[0062] According to one embodiment, in the positive electrode additive for a lithium secondary battery, due to the interaction between the carbon coating layer and the carbon nanotube-containing layer, a high proportion of carbon nanotubes are uniformly bonded onto the lithium iron oxide particles, thereby greatly improving the electrical conductivity, irreversible capacity, and capacity characteristics during charge and discharge. And the lithium borate compound-containing layer formed on the carbon nanotube-containing layer enables improvement of air stability, and the electrical conductivity, irreversible capacity, and capacity characteristics of the positive electrode additive can be stably exhibited.

[0063] In the positive electrode additive, a carbon coating layer is formed on the lithium transition metal oxide particles, and a carbon nanotube-containing layer including carbon nanotubes physically or chemically bonded onto the carbon coating layer is formed. The formation of the carbon coating layer and the carbon nanotube-containing layer can be confirmed by electron microscopy or XRD analysis of the positive electrode additive.

[0064] According to an embodiment of the present invention, the total content of the carbon coating layer and the carbon nanotube-containing layer may be 0.5 parts by weight to 6.0 parts by weight, or 1.0 parts by weight to 6.0 parts by weight, or 1.0 parts by weight to 5.9 parts by weight, or 1.5 parts by weight to 5.9 parts by weight, or 1.5 parts by weight to 5.8 parts by weight, based on 100 parts by weight of the total content of the positive electrode additive.

[0065] And the carbon coating layer: the carbon nanotube-containing layer is included in a weight ratio of 1:4 to 1:50, or 1:8 to 1:50, or 1:8 to 1:30, or 1:10 to 1:30, or 1:10 to 1:20.

[0066] By controlling the total content and weight ratio of the carbon coating layer and the carbon nanotube-containing layer within the above ranges, without inhibiting properties such as the irreversible capacity of the lithium transition metal oxide particles by the carbon coating layer, a high ratio of carbon nanotubes can be uniformly bonded onto the carbon coating layer to further improve the electrical conductivity, irreversible capacity, and capacity characteristics during charge and discharge of the positive electrode additive.

[0067] In a specific embodiment, the carbon coating layer is contained in an amount of 0.05 parts by weight to 2.0 parts by weight, or 0.06 parts by weight to 2.0 parts by weight, or 0.06 parts by weight to 1.9 parts by weight based on 100 parts by weight of the total content of the positive electrode additive; the carbon nanotube-containing layer is contained in an amount of 0.4 parts by weight to 4.0 parts by weight, or 0.8 parts by weight to 4.0 parts by weight, or 0.8 parts by weight to 3.95 parts by weight, or 1.0 parts by weight to 3.95 parts by weight, or 1.0 parts by weight to 3.90 parts by weight based on 100 parts by weight of the total content of the positive electrode additive.

[0068] The ranges of the respective contents of the carbon coating layer and the carbon nanotube-containing layer and the range of their total content can be measured and calculated based on analyzing the carbon content on the surface of the positive electrode additive by well-known elemental analysis or based on the content of the water-soluble polymer dispersant and carbon nanotubes used as raw materials.

[0069] For the positive electrode additive, the carbon coating layer can have a thickness of 10 nm to 300 nm. And on the carbon coating layer, the carbon nanotubes of the carbon nanotube-containing layer are physically uniformly adsorbed or chemically bonded. Due to such a thickness of the carbon coating layer and the bonding form of the carbon nanotubes, the positive electrode additive of one embodiment can exhibit optimized irreversible capacity and capacity characteristics during charge and discharge.

[0070] The thickness of the carbon coating layer is calculated based on the BET specific surface area of the positive electrode additive and the analysis result of the above-described carbon content, or can be measured by analyzing the positive electrode additive with a transmission electron microscope (TEM) or a scanning transmission electron microscope (SEM).

[0071] The above-described positive electrode additive can be mixed with a separate positive electrode active material and act as a sacrificial positive electrode material for compensating the irreversible capacity of the negative electrode during the initial charge and discharge process of the lithium secondary battery. After such irreversible capacity compensation, the positive electrode active material acts. Moreover, since the positive electrode additive also has improved capacity characteristics during charge and discharge, it can also be preferably applied as an additional positive electrode active material.

[0072] According to another embodiment of the present invention, preparing a precursor mixture containing a lithium (Li) precursor and an iron (Fe) precursor; firing the precursor mixture in an inert gas atmosphere to obtain lithium iron oxide particles doped or undoped with a foreign element; and heat-treating a mixture containing the lithium iron oxide particles and a lithium borate-based compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate-based compound-containing layer, thereby providing a method for manufacturing the positive electrode additive for a lithium secondary battery.

[0073] Prepare a precursor mixture containing a lithium (Li) precursor and an iron (Fe) precursor. Preferably, the precursor mixture is prepared by solid-phase mixing a lithium precursor, an iron precursor, and, if necessary, a foreign element precursor in accordance with the stoichiometric ratio of Li5FeO4 or the chemical formula 1.

[0074] As the lithium precursor, an oxide containing lithium such as Li2O can be used without particular limitation.

[0075] As the iron precursor, one or more compounds selected from the group consisting of chlorides, nitrates, sulfates, phosphates, oxides, halides, and hydrates of Fe(III) can be used.

[0076] As the hetero-element precursor, oxides or ammonium salts of the hetero-elements can be used. As non-limiting examples, compounds such as Al2O3, NH4F, TiO2, MgO, ZnO, and Ga2O3 can be used as the hetero-element precursor.

[0077] A step of firing the precursor mixture in an inert gas atmosphere to obtain lithium iron oxide particles doped or undoped with hetero-elements is performed.

[0078] The step can be performed in an inert atmosphere formed using an inert gas such as Ar, N2, Ne, and He.

[0079] The firing in the step of obtaining the lithium (Li) iron (Fe) oxide particles can be performed at a temperature of 500 °C or higher, or 500 °C to 1000 °C, or 550 °C to 800 °C. In order to generate crystal seeds at an appropriate rate, the firing temperature is preferably 500 °C or higher, or 550 °C or higher. However, if the heat treatment temperature is too high, a sintering phenomenon occurs in which the grown crystal particles solidify. Therefore, the firing temperature is preferably 1000 °C or lower, or 800 °C or lower. Specifically, the firing temperature can be 500 °C or higher, or 550 °C or higher, or 600 °C or higher; and 1000 °C or lower, or 800 °C or lower, or 700 °C or lower. Preferably, the firing temperature can be 550 °C to 1000 °C, or 550 °C to 800 °C, or 550 °C to 700 °C, or 600 °C to 700 °C.

[0080] The firing is performed for 2 hours to 12 hours at the firing temperature. The firing time can be adjusted in consideration of the time required for the crystals of lithium iron oxide to be stabilized.

[0081] A step of heat-treating a mixture containing the lithium iron oxide particles and a lithium borate compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate compound-containing layer is performed.

[0082] The step can be performed in an inert atmosphere formed using an inert gas such as Ar, N2, Ne, and He.

[0083] Alternatively, the step can be performed in an oxygen-containing gas atmosphere such as air. Lithium iron oxides such as Li5FeO4 have chemical properties that react with carbon dioxide (CO2) and moisture (H2O) in the air to change to Li2CO3 or LiOH when exposed to air. Therefore, it can be expected that it is not preferable to heat-treat the lithium iron oxide particles in air, which is an oxygen-containing gas, in the step. However, contrary to this expectation, by heat-treating a mixture of the lithium iron oxide particles and a lithium borate compound in an oxygen-containing gas atmosphere and at a temperature of 300 °C or higher, lithium iron oxide excellent in air stability coated with a lithium borate compound-containing layer can be obtained.

[0084] The mixing of the lithium iron oxide particles and the lithium borate compound can be performed by solid-phase mixing using an ordinary mixer.

[0085] The heat treatment in the step of obtaining the lithium iron oxide particles coated with the lithium borate compound-containing layer can be performed for 1 hour to 10 hours at a temperature of 300 °C or higher, or 300 °C to 450 °C, or 310 °C to 450 °C, or 310 °C to 400 °C in an inert gas or an oxygen-containing gas atmosphere.

[0086] Here, the lithium borate compound can be used in an amount of 2.0 parts by weight to 25.0 parts by weight, or 2.0 parts by weight to 20.0 parts by weight, or 2.5 parts by weight to 20.0 parts by weight, or 2.5 parts by weight to 15.0 parts by weight, or 2.5 parts by weight to 10.0 parts by weight, or 2.5 parts by weight to 5.0 parts by weight based on 100 parts by weight of the lithium iron oxide particles.

[0087] Additives such as lithium hexafluorophosphate, lithium triflate, and lithium difluorophosphate can be further mixed with the lithium borate compound. However, in order to sufficiently exhibit the effect of improving air stability by introducing the lithium borate compound-containing layer, it is preferable to apply the additive in a content of 50 mol% or less, or 30 mol% or less, or 10 mol% or less.

[0088] According to another embodiment of the present invention, Mixing and heat-treating a carbon nanotube, a water-soluble polymer dispersant, and an iron (Fe) precursor to form an iron oxide carbon precursor; Firing a mixture containing a lithium precursor and the iron oxide carbon precursor in an inert gas atmosphere to form lithium iron oxide particles; and A method for producing the positive electrode additive for a lithium secondary battery is provided, which includes heat-treating a mixture containing the lithium iron oxide particles and a lithium borate compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate compound-containing layer.

[0089] As an example, the step of forming the iron oxide-carbon precursor may include forming a carbon nanotube dispersion in which the carbon nanotubes are dispersed in an aqueous solvent in the presence of the water-soluble polymer dispersant, mixing the carbon nanotube dispersion and an iron (Fe) precursor in the presence of a base, reacting the carbon nanotube dispersion and the iron (Fe) precursor in the mixture at a temperature of 50°C to 100°C, and filtering and drying the reaction product solution, followed by heat treatment at a temperature of 200°C to 300°C.

[0090] The iron oxide-carbon precursor is mixed with a lithium precursor and fired at a high temperature to form lithium iron oxide particles. At the same time, the water-soluble polymer dispersant is fired on the surface of the lithium iron oxide particles to form a uniform carbon coating layer. Carbon nanotubes are bonded onto the carbon coating layer. Then, the lithium iron oxide particles and a lithium borate-based compound are mixed and fired in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate-based compound-containing layer.

[0091] Any water-soluble polymer can be used as the water-soluble polymer dispersant as long as it can uniformly disperse carbon nanotubes in an aqueous solvent and can form the carbon coating layer by firing. Preferably, the water-soluble polymer dispersant may include one or more compounds selected from the group consisting of polyvinylpyrrolidone-based polymers, polyacrylic acid-based polymers, polyvinyl alcohol-based polymers, and hydroxyalkyl cellulose-based polymers.

[0092] The water-soluble polymer dispersant and the carbon nanotubes can be dispersed and mixed in an aqueous solvent by a method such as ultrasonic injection to form a carbon nanotube dispersion. Then, the carbon nanotube dispersion can be mixed with an iron precursor or its aqueous solution and can be mixed together with a base such as ammonium hydroxide.

[0093] In order to form a carbon coating layer with an appropriate thickness and content, the water-soluble polymer dispersant can be used in an amount of 0.1 to 2 parts by weight, or 0.5 to 2 parts by weight, or 0.5 to 1.5 parts by weight based on the total content of the iron oxide-carbon precursor. And, in order to form a carbon nanotube-containing layer with an appropriate content on the carbon coating layer, the carbon nanotube can be used in an amount of 1 to 10 parts by weight, or 2 to 10 parts by weight, or 2 to 7 parts by weight based on the total content of the iron oxide-carbon precursor.

[0094] The iron (Fe) precursor may contain one or more compounds selected from the group consisting of nitrates, sulfates, phosphates, oxides, halides, and hydrates of Fe(III).

[0095] As described above, after mixing the carbon nanotube dispersion and the iron precursor, the carbon nanotube dispersion and the iron precursor are stirred, a base such as ammonium hydroxide (NH4OH) is added in an equivalent ratio of the iron precursor, and the reaction is carried out at a temperature of 50°C to 100°C, or 70°C to 90°C for 1 hour to 10 hours. After filtering and drying the reaction product solution, heat treatment is further carried out at a temperature of 200°C to 300°C, or 220°C to 280°C for 2 hours to 15 hours or 6 hours to 12 hours to remove impurities. At this time, the drying step can be carried out using a general oven or the like, and an iron oxide-carbon precursor can be formed by such a process.

[0096] After mixing the iron oxide-carbon precursor with the lithium precursor, it can be fired at a temperature of 500°C or higher, or 500°C to 1000°C, or 550°C to 700°C to form lithium iron oxide. At this time, since the reaction between the iron oxide-carbon precursor and the lithium precursor is carried out as an equivalent reaction, for example, when the lithium precursor is a lithium oxide such as Li2O, the iron oxide-carbon precursor: lithium precursor can be mixed at a molar ratio of 1:5 and fired at a high temperature.

[0097] As the lithium precursor, other than the lithium oxide (Li2O), lithium precursors well-known in the technical field to which the present invention pertains can be used.

[0098] On the other hand, the step of heat-treating the mixture containing the lithium iron oxide particles and the lithium borate-based compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate-based compound-containing layer is replaced with the above-described content.

[0099] If necessary, the step of washing and drying the lithium iron oxide particles coated with the lithium borate-based compound-containing layer can be performed.

[0100] As a non-limiting example, the washing step can be performed by mixing the lithium iron oxide particles and the washing liquid at a weight ratio of 1:2 to 1:10 and stirring. As the washing liquid, distilled water, ammonia water, etc. can be used. The drying can be performed by heat-treating at a temperature of 100°C to 200°C or 100°C to 180°C for 1 hour to 10 hours.

[0101] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery is provided.

[0102] The positive electrode for the lithium secondary battery may include a positive electrode active material, a binder, a conductive material, and the positive electrode additive.

[0103] The positive electrode additive has the property of irreversibly releasing lithium during charge and discharge of the lithium secondary battery. Therefore, the positive electrode additive is included in the positive electrode for the lithium secondary battery and can serve as a sacrificial positive electrode material for prelithiation.

[0104] Preferably, the positive electrode for the lithium secondary battery includes a positive electrode material containing a positive electrode active material, a conductive material, the positive electrode additive, and a binder; and a current collector that supports the positive electrode material.

[0105] Here, the matters regarding the positive electrode additive are replaced with the above-described content.

[0106] In order to increase the battery capacity to make it a high-capacity battery, the ratio of the negative electrode active material in the negative electrode must be further increased, and thereby, the amount of lithium consumed in the SEI layer also increases accordingly. Therefore, after calculating the amount of lithium consumed in the SEI layer of the negative electrode, the amount of the sacrificial positive electrode material applied to the positive electrode side can be calculated backward to determine the design capacity of the battery.

[0107] According to one embodiment, the positive electrode additive is contained in an amount of more than 0% by weight and 15% by weight or less based on the total weight of the positive electrode material.

[0108] In order to compensate for the irreversible lithium consumed in the formation of the SEI layer, the content of the positive electrode additive is preferably more than 0% by weight based on the total weight of the positive electrode material.

[0109] However, when the positive electrode additive is contained in excess, the content of the positive electrode active material showing a reversible charge-discharge capacity decreases, the capacity of the battery decreases, and the remaining lithium in the battery is plated on the negative electrode, inducing a short circuit of the battery or inhibiting the safety. Therefore, the content of the positive electrode additive is preferably 15% by weight or less based on the total weight of the positive electrode material.

[0110] Specifically, the content of the positive electrode additive can be more than 0% by weight, or 0.5% by weight or more, or 1% by weight or more, or 2% by weight or more, or 3% by weight or more; and 15% by weight or less, or 12% by weight or less, or 10% by weight or less based on the total weight of the positive electrode material.

[0111] Preferably, the content of the positive electrode additive may be 0.5 wt% to 15 wt%, or 1 wt% to 15 wt%, or 1 wt% to 12 wt%, or 2 wt% to 12 wt%, or 2 wt% to 10 wt%, or 3 wt% to 10 wt% based on the total weight of the positive electrode material.

[0112] As the positive electrode active material, any material that can reversibly intercalate and deintercalate lithium ions can be used without particular limitation. For example, the positive electrode active material can be a composite oxide or phosphate containing cobalt, manganese, nickel, iron, or a combination of these metals and lithium.

[0113] As a non-limiting example, the positive electrode active material can be a compound represented by any one of the following chemical formulas. Li a A 1-b R b D2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5); Li a E 1-b R b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE 2-b R b O 4-c D c (0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b R c D d (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < d ≦ 2); Li a Ni 1-b-c Co b R c O 2-d Z d (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < d < 2); Li a Ni 1-b-c Co b R c O 2-dZ2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < d < 2); Li a Ni 1-b-c Mn b R c D d (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < d ≤ 2); Li a Ni 1-b-c Mn b R c O 2-d Z d (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < d < 2); Li a Ni 1-b-c Mn b R c O 2-d Z2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < d < 2); Li a Ni b E c G d O2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3 (0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3 (0 ≤ f ≤ 2); and LiFePO4.

[0114] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0115] Of course, those having a coating layer on the surface of the positive electrode active material can also be used, or the positive electrode active material and the positive electrode active material having a coating layer can be mixed and used. As the coating element contained in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof can be used.

[0116] According to one embodiment, the positive electrode active material is contained in an amount of 80% to 95% by weight based on the total weight of the positive electrode material.

[0117] Specifically, the content of the positive electrode active material can be 80% by weight or more, or 82% by weight or more, or 85% by weight or more; and 95% by weight or less, or 93% by weight or less, or 90% by weight or less based on the total weight of the positive electrode material.

[0118] Preferably, the content of the positive electrode active material can be 82% to 95% by weight, or 82% to 93% by weight, or 85% to 93% by weight, or 85% to 90% by weight based on the total weight of the positive electrode material.

[0119] The conductive material is used to impart conductivity to the electrode.

[0120] As the conductive material, any material can be used without particular limitation as long as it does not cause chemical changes in the battery and has electron conductivity. As non-limiting examples, the conductive material can be carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; graphite such as natural graphite and artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. As the conductive material, one or a mixture of two or more of the above examples can be used.

[0121] The content of the conductive material is adjusted within a range that does not induce a decrease in the battery capacity while exhibiting an appropriate level of conductivity. Preferably, the content of the conductive material can be 1 wt% to 10 wt% or 1 wt% to 5 wt% based on the total weight of the positive electrode material.

[0122] The binder is used to make the positive electrode material adhere well to the current collector. As non-limiting examples, the binder can be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc. As the binder, one or a mixture of two or more of the above examples can be used.

[0123] The content of the binder is adjusted within a range that does not induce a decrease in the battery capacity while exhibiting an appropriate level of adhesiveness. Preferably, the content of the binder can be 1 wt% to 10 wt% or 1 wt% to 5 wt% based on the total weight of the positive electrode material.

[0124] As the current collector, any material applicable to the positive electrode of a lithium secondary battery in the technical field to which the present invention pertains can be used without particular limitation.

[0125] As non-limiting examples, as the current collector, stainless steel; aluminum; nickel; titanium; fired carbon; or those obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0126] Preferably, the current collector has a thickness of 3 μm to 500 μm. In order to enhance the adhesion of the positive electrode material, the current collector may have fine irregularities formed on its surface. The current collector can have various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0127] The positive electrode for the lithium secondary battery is formed by laminating a positive electrode material containing the positive electrode active material, the conductive material, the positive electrode additive, and the binder on the current collector.

[0128] According to another embodiment of the present invention, a lithium secondary battery including the positive electrode for the lithium secondary battery, a negative electrode, a separator, and an electrolyte is provided.

[0129] The lithium secondary battery includes a positive electrode containing the positive electrode additive. Thereby, the lithium secondary battery can suppress gas generation at the positive electrode during charge and discharge, and can exhibit improved safety and life characteristics. And the lithium secondary battery can exhibit a high discharge capacity, excellent output characteristics, and a capacity retention rate.

[0130] Therefore, the lithium secondary battery is used as an energy supply source having improved performance and safety in the field of portable electronic devices such as mobile phones, notebook computers, tablet computers, mobile batteries, digital cameras, etc.; and in the field of means of transportation such as electric vehicles, electric bicycles, and personal mobility devices.

[0131] The lithium secondary battery includes an electrode assembly wound between a positive electrode and a negative electrode with a separator interposed therebetween, and a case in which the electrode assembly is housed. The positive electrode, the negative electrode, and the separator are impregnated with an electrolyte.

[0132] The lithium secondary battery can have various forms such as square, cylindrical, and pouch types.

[0133] Matters regarding the positive electrode are replaced with the content described in the item of the positive electrode for the lithium secondary battery.

[0134] The negative electrode may include a negative electrode material containing a negative electrode active material, a conductive material, and a binder; and a current collector supporting the negative electrode material.

[0135] Examples of the negative electrode active material include substances capable of reversibly intercalating and deintercalating lithium ions, lithium metal, alloys of lithium metal, substances dopable and dedopable with lithium, and transition metal oxides.

[0136] Examples of the substances capable of reversibly intercalating and deintercalating lithium ions include carbonaceous substances, such as crystalline carbon, amorphous carbon, or mixtures thereof. Specifically, the carbonaceous substance may be natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch-based carbon fibers, meso-carbon microbeads, petroleum or coal tar pitch-derived cokes, soft carbon, and hard carbon.

[0137] The alloy of the lithium metal can be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd.

[0138] The substance capable of doping and undoping the lithium can be Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof; provided that Si is excluded), Sn, SnO2, Sn-R alloy (where R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof; provided that Sn is excluded), etc. And as the substance capable of doping and undoping the lithium, at least one of the above examples and SiO2 can be mixed and used. The Q and R can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, etc.

[0139] And the transition metal oxide can be vanadium oxide, lithium vanadium oxide, lithium titanate, etc.

[0140] Preferably, the negative electrode contains one or more negative electrode active materials selected from the group consisting of a carbonaceous material and a silicon compound.

[0141] That is, according to another embodiment of the present invention, there is provided a lithium secondary battery including the positive electrode for a lithium secondary battery; a negative electrode containing one or more negative electrode active materials selected from the group consisting of a carbonaceous material and a silicon compound; a separator; and an electrolyte.

[0142] Here, the carbonaceous material is at least one substance selected from the group consisting of the natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fiber, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon described above. And the silicon compound is a compound containing Si described above, that is, Si, Si-C composite, SiO x (0 < x < 2), and can be the Si-Q alloy, a mixture thereof, or a mixture of at least one of these and SiO2.

[0143] According to one embodiment, the negative electrode active material is contained in an amount of 85% by weight to 98% by weight based on the total weight of the negative electrode material.

[0144] Specifically, the content of the negative electrode active material can be 85% by weight or more, or 87% by weight or more, or 90% by weight or more; and 98% by weight or less, or 97% by weight or less, or 95% by weight or less based on the total weight of the negative electrode material.

[0145] Preferably, the content of the negative electrode active material can be 85% by weight to 97% by weight, or 87% by weight to 97% by weight, or 87% by weight to 95% by weight, or 90% by weight to 95% by weight based on the total weight of the negative electrode material.

[0146] Regarding the conductive material, the binder, and the current collector contained in the negative electrode material, the content described in the item of the positive electrode for the lithium secondary battery is substituted.

[0147] The separator separates the positive electrode and the negative electrode and provides a migration path for lithium ions. As the separator, any material applicable to the separator of the lithium secondary battery in the technical field to which the present invention pertains can be used without particular limitation. The separator preferably has a low resistance to the ion migration of the electrolyte and excellent wettability to the electrolyte.

[0148] Specifically, the separation membrane can be a porous polymer film made of polyolefin-based polymers such as polyethylene, polypropylene, ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methacrylate copolymer. The separation membrane can be a multilayer film in which two or more layers of the porous polymer film are laminated. The separation membrane can be a nonwoven fabric containing glass fibers, polyethylene terephthalate fibers, and the like. And the separation membrane can be coated with a ceramic component or a polymer substance to ensure heat resistance or mechanical strength.

[0149] On the other hand, as the electrolyte, any electrolyte applicable to lithium secondary batteries in the technical field to which the present invention pertains can be used without particular limitation. For example, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like.

[0150] Specifically, the electrolyte can contain a non-aqueous organic solvent and a lithium salt.

[0151] As the non-aqueous organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move can be used without particular limitation.

[0152] Specifically, the non-aqueous organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether solvent such as dibutyl ether and tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene and fluorobenzene; a carbonate solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol solvent such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and containing a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolane, etc.

[0153] Among the above examples, it is preferable to use a carbonate solvent as the non-aqueous organic solvent.

[0154] In particular, considering the charge-discharge performance of the battery and the compatibility with the sacrificial cathode material, as the non-aqueous organic solvent, it is preferable to use a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant (e.g., ethylene carbonate, propylene carbonate) and a linear carbonate having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate). In this case, it is advantageous for the expression of the above-described performance to mix and use the cyclic carbonate and the linear carbonate at a volume ratio of 1:1 to 1:9. Further, as the non-aqueous organic solvent, it is preferable to use a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1:2 to 1:10; or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) at a volume ratio of 1 to 3:1 to 9:1.

[0155] The lithium salt contained in the electrolyte dissolves in the non-aqueous organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0156] Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiN(SO2F)2, (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, and LiB(C2O4)2, etc. Preferably, the lithium salt can be LiPF6, LiFSI, and mixtures thereof.

[0157] The lithium salt is contained in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt contained in the above concentration range can exhibit excellent electrolyte performance by imparting appropriate conductivity and viscosity to the electrolyte.

[0158] Optionally, the electrolyte contains additives for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, improving the discharge capacity of the battery, and the like.

[0159] For example, the additives may be haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like. The additive is contained in an amount of 0.1% by weight to 5% by weight based on the total weight of the electrolyte.

Advantages of the Invention

[0160] The positive electrode additive for a lithium secondary battery according to the present invention exhibits a high initial irreversible capacity and has excellent air stability. Such a positive electrode additive can compensate for the irreversible capacity loss of a high-capacity lithium secondary battery and can effectively suppress gas generation in the battery and resulting fires and explosions.

Brief Description of the Drawings

[0161]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

BEST MODE FOR CARRYING OUT THE INVENTION

[0162] Hereinafter, the actions and effects of the invention will be specifically described with reference to specific examples of the invention. However, this is presented as an exemplification to assist in the understanding of the invention. It is not intended that the scope of the invention be limited in any way by the following examples, and it is obvious to those of ordinary skill in the art that various changes and modifications are possible within the scope of the present invention and the scope of the technical idea.

[0163] Example 1 (1) Production of lithium iron oxide particles Li2O (manufactured by Ganfeng Lithium) and Fe2O3 (manufactured by Sigma-Aldrich) were solid-phase mixed (molar ratio Li2O:Fe2O3 = 5:1). The mixture was formed into pellets using a press and fired at 750 °C (heating for 6 hours and maintaining for 12 hours) under an Ar atmosphere to obtain lithium iron oxide particles (Li5FeO4).

[0164] (2) Production of cathode additive 4.0 parts by weight of lithium tetrafluoroborate (LiBF4, manufactured by TCI) was solid-phase mixed with 100 parts by weight of the lithium iron oxide particles (Li5FeO4) using a mixer. The mixture was heat-treated in a heat treatment furnace at a temperature of 310 °C in an Ar atmosphere for 1 hour to obtain lithium iron oxide particles coated with a LiBF4-containing layer.

[0165] (3) Manufacture of Lithium Secondary Battery The lithium iron oxide coated with the LiBF4-containing layer, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 95:3:2 in an organic solvent (N-methylpyrrolidone) to produce a positive electrode material slurry. The positive electrode material slurry was applied to one side of a current collector, which was an aluminum foil with a thickness of 15 μm, and rolled and dried to produce a positive electrode (punching size: diameter 14 mm).

[0166] The positive electrode, negative electrode, separator, and electrolyte were prepared to manufacture a coin cell type lithium secondary battery. At this time, Li metal with a thickness of 300 μm (punching size: diameter 15 mm) was used as the negative electrode. As the electrolyte, a non-aqueous organic solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:2:1 and 1.0 M of LiPF6 and 2 wt% of vinylene carbonate (VC) were dissolved was used. And as the separator, a PE resin material separator (manufactured by W-scope, WL20C, 20 μm) was used.

[0167] Example 2 (1) Manufacture of Lithium Iron Oxide Particles When manufacturing the lithium iron oxide particles according to Example 1, Al2O3, which is a heterogeneous element precursor, was further added to obtain lithium transition metal oxide particles having a composition of Li5Fe 0.8 Al 0.2 O4.

[0168] (2) Manufacture of Positive Electrode Additive Instead of Li5FeO4 as the lithium transition metal oxide, Li5Fe0.8 Al 0.2 Lithium transition metal oxide particles coated with a LiBF4-containing layer were obtained in the same manner as in Example 1, except that Al2O4 was used.

[0169] (3) Fabrication of a lithium secondary battery A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0170] Example 3 (1) Fabrication of lithium iron oxide particles During the fabrication of the lithium iron oxide particles according to Example 1, Al2O3, which is a heterogeneous element precursor, was further added to obtain lithium transition metal oxide particles having a Li5Fe 0.8 Al 0.2 O4 composition.

[0171] (2) Fabrication of a cathode additive Lithium transition metal oxide particles (Li5Fe 0.8 Al 0.2 O4) and lithium tetrafluoroborate (LiBF4) were heat-treated in an air atmosphere instead of an Ar atmosphere to obtain lithium transition metal oxide particles coated with a LiBF4-containing layer in the same manner as in Example 1.

[0172] (3) Fabrication of a lithium secondary battery A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0173] Example 4 (1) Fabrication of lithium iron oxide particles During the fabrication of the lithium iron oxide particles according to Example 1, Al2O3, which is a heterogeneous element precursor, was further added to obtain lithium transition metal oxide particles having a Li5Fe 0.75 Al 0.25 O4 composition.

[0174] (2) Manufacturing of positive electrode additives LiFe instead of LiFeO4 as lithium transition metal oxide 0.75 Al 0.25 Lithium transition metal oxide particles coated with a LiBF4-containing layer were obtained in the same manner as in Example 1, except that O4 was used.

[0175] (3) Manufacture of lithium secondary batteries A lithium secondary battery was manufactured in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0176] Example 5 (1) Manufacturing of lithium iron oxide particles In the preparation of the lithium iron oxide particles according to Example 1, Al2O3, a precursor of a different element, was further added to form Li5Fe 0.75 Al 0.25 Lithium transition metal oxide particles with O4 composition were obtained.

[0177] (2) Manufacturing of positive electrode additives The lithium transition metal oxide particles (LiFe 0.75 Al 0.25 100 parts by weight of O4) was mixed with 3.0 parts by weight of lithium tetrafluoroborate (LiBF4, manufactured by TCI) in a solid phase using a mixer. The mixture was heat-treated in an Ar atmosphere at a temperature of 310°C for 1 hour in a heat treatment furnace to obtain lithium transition metal oxide particles coated with a LiBF4-containing layer.

[0178] (3) Manufacture of lithium secondary batteries A lithium secondary battery was manufactured in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0179] Example 6 (1) Manufacturing of lithium iron oxide particles In the preparation of the lithium iron oxide particles according to Example 1, Al2O3, a precursor of a different element, was further added to form Li5Fe 0.75Al 0.25 Lithium transition metal oxide particles with an O4 composition were obtained.

[0180] (2) Production of the positive electrode additive With respect to 100 parts by weight of the lithium transition metal oxide particles (Li5Fe 0.75 Al 0.25 O4), 2.5 parts by weight of lithium tetrafluoroborate (LiBF4, manufactured by TCI) was solid-phase mixed using a mixer. The mixture was heat-treated in a heat treatment furnace at a temperature of 310 °C in an Ar atmosphere for 1 hour to obtain lithium transition metal oxide particles coated with an LiBF4-containing layer.

[0181] (3) Production of the lithium secondary battery A lithium secondary battery was produced in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0182] Example 7 (1) Production of the lithium iron oxide particles When producing the lithium iron oxide particles according to Example 1, Al2O3 and TiO2, which are heterogeneous element precursors, were further added to obtain lithium transition metal oxide particles with an Li5Fe 0.77 Al 0.2 Ti 0.03 O4 composition.

[0183] (2) Production of the positive electrode additive Lithium transition metal oxide particles coated with an LiBF4-containing layer were obtained in the same manner as in Example 1, except that Li5Fe 0.77 Al 0.2 Ti 0.03 O4 was used instead of Li5FeO4 as the lithium transition metal oxide.

[0184] (3) Production of the lithium secondary battery A lithium secondary battery was produced in the same manner as in Example 1, except that the lithium transition metal oxide coated with the LiBF4-containing layer was used.

[0185] Example 8 (1) Production of the positive electrode additive Using a 0.2L reactor and a mechanical stirrer, the positive electrode additive of Example 1 was produced by the following method.

[0186] A carbon nanotube aqueous dispersion manufactured by LG Chem was used. The aqueous dispersion was prepared by setting the contents of carbon nanotubes (CNT) and polyvinylpyrrolidone (Acros organics, Mw50,000 g / mol), which is a water-soluble polymer dispersant, to 5.83 wt% and 1.0 wt%, respectively, putting these into 200 ml of deionized (DI) water, and mixing them with an ultrasonic chip for 10 minutes.

[0187] 0.6 mol (242.328 g) of iron(III) nitrate nonahydrate was dissolved in 600 ml of deionized water, and this was slowly put into a flask containing 28 g of the CNT aqueous dispersion (CNT content with respect to the iron oxide carbon precursor (Fe2O3CNT precursor) formed in the subsequent process = 3.3 wt%), and stirred for 30 minutes. Next, 1.8 mol (252.36 g) of NH4OH was slowly poured into the flask, stirred for 30 minutes, and reacted at 80°C for 6 hours.

[0188] After completion of the reaction, it was allowed to stand for 30 minutes, the upper layer solution was discarded, filtration was performed, and drying was carried out in a convection oven at 120°C for 12 hours. The dried powder was heat-treated at 250°C for 6 hours in an air atmosphere to remove impurities, and an iron oxide carbon precursor (Fe2O3CNT precursor) was obtained.

[0189] Li2O (Ganfeng Lithium) and the Fe2O3CNT precursor were uniformly mixed at a molar ratio of 5:1 and fired in a heat treatment furnace at 600°C (heating for 2 hours, maintaining for 6 hours) in an Ar atmosphere to obtain lithium iron oxide.

[0190] 6.0 parts by weight of lithium difluoro(oxalato)borate (Sigma-Aldrich) was mixed with 100 parts by weight of the lithium iron oxide using a mixer. The mixture was fired in a heat treatment furnace at 350 °C (heating for 2 hours and maintaining for 6 hours) under an Ar atmosphere to obtain the cathode additive of Example 1.

[0191] (2) Fabrication of Lithium Secondary Battery The lithium transition metal oxide, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in an organic solvent (N-methylpyrrolidone) at a weight ratio of 90:4:6 to produce a cathode material slurry. The cathode material slurry was coated on one side of a current collector, which was an aluminum foil with a thickness of 15 μm, and rolled and dried to produce a cathode (punching size: diameter 14 mm).

[0192] The cathode, anode, separator, and electrolyte were prepared to fabricate a coin cell-type lithium secondary battery. At this time, Li metal with a thickness of 300 μm (punching size: diameter 14 mm) was used as the anode. As the electrolyte, a non-aqueous organic solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:2:1 and 1.0 M of LiPF6 and 2 wt% of vinylene carbonate (VC) were dissolved was used. And as the separator, a PE resin material separator (manufactured by W-scope, WL20C, 20 μm) was used.

[0193] Example 9 A cathode additive and a lithium secondary battery containing the same were produced in the same manner as in Example 8, except that the content of the lithium difluoro(oxalato)borate was increased to 9.0 parts by weight with respect to 100 parts by weight of the lithium iron oxide.

[0194] Example 10 A positive electrode additive and a lithium secondary battery containing the same were produced in the same manner as in Example 8, except that the content of the CNT aqueous dispersion was increased to 34 g (CNT content with respect to the Fe2O3CNT precursor formed in the subsequent process = 4.0 wt%).

[0195] Example 11 A positive electrode additive and a lithium secondary battery containing the same were produced in the same manner as in Example 8, except that the content of the CNT aqueous dispersion was increased to 48 g (CNT content with respect to the Fe2O3CNT precursor formed in the subsequent process = 5.5 wt%).

[0196] Example 12 A positive electrode additive and a lithium secondary battery containing the same were produced in the same manner as in Example 8, except that the content of the CNT aqueous dispersion was increased to 72 g (CNT content with respect to the Fe2O3CNT precursor formed in the subsequent process = 8.1 wt%).

[0197] Comparative Example 1 (1) Production of lithium iron oxide particles When producing the lithium iron oxide particles according to Example 1, Al2O3, which is a heterogeneous element precursor, was further added to obtain lithium transition metal oxide particles having a Li5Fe 0.8 Al 0.2 O4 composition.

[0198] (2) Production of lithium secondary battery A lithium secondary battery was produced in the same manner as in Example 1, except that the lithium transition metal oxide (Li5Fe 0.8 Al 0.2 O4) was used instead of the lithium transition metal oxide coated with the LiBF4-containing layer.

[0199] Comparative Example 2 (1) Production of lithium iron oxide particles When producing the lithium iron oxide particles according to Example 1, Al2O3, which is a heterogeneous element precursor, was further added to obtain lithium transition metal oxide particles having a Li5Fe 0.75 Al 0.25Lithium transition metal oxide particles with an O4 composition were obtained.

[0200] (2) Manufacture of a lithium secondary battery A lithium secondary battery was manufactured in the same manner as in Example 1, except that the lithium transition metal oxide (Li5Fe 0.75 Al 0.25 O4) was used instead of the lithium transition metal oxide coated with the LiBF4-containing layer.

[0201] Comparative Example 3 (1) Manufacture of lithium iron oxide particles When manufacturing the lithium iron oxide particles according to Example 1, Al2O3 and MgO, which are heterogeneous element precursors, were further added to obtain lithium transition metal oxide particles with an Li5Fe 0.65 Al 0.25 Mg 0.1 O4 composition.

[0202] (2) Manufacture of a lithium secondary battery A lithium secondary battery was manufactured in the same manner as in Example 1, except that the lithium transition metal oxide (Li5Fe 0.65 Al 0.25 Mg 0.1 O4) was used instead of the lithium transition metal oxide coated with the LiBF4-containing layer.

[0203] Comparative Example 4 1.494 g of Li2O (Ganfeng Lithium) and 1.597 g of Fe2O3 (Sigma-aldrich) were solid-phase mixed (molar ratio Li2O:Fe2O3 = 5:1). The mixture was manufactured in pellet form using a press and heat-treated at 750 °C (heating for 6 hours, maintaining for 12 hours) in an Ar atmosphere to manufacture a cathode additive. A lithium secondary battery was manufactured in the same manner as in Example 8, except that the cathode additive was used.

[0204] Comparative Example 5 1.494 g of Li2O (Ganfeng Lithium) and 1.597 g of Fe2O3 (Sigma-aldrich) were mixed in solid phase (molar ratio Li2O:Fe2O3 = 5:1). 0.4 g of polyvinylpyrrolidone (Acros organics, Mw 50,000 g / mol) was added to the mixture and mixed (4 g of polyvinylpyrrolidone was added based on 0.1 mol of the resulting cathode additive (Li5FeO4)). The mixture was manufactured in pellet form using a press and calcined at 750 °C (heating for 6 hours and maintaining for 12 hours) under an Ar atmosphere to produce a cathode additive. A lithium secondary battery was manufactured in the same manner as Example 8 except that the said cathode additive was used.

[0205] Comparative Example 6 1.494 g of Li2O (Ganfeng Lithium) and 1.597 g of Fe2O3 (Sigma-aldrich) were mixed in solid phase (molar ratio Li2O:Fe2O3 = 5:1). 10 wt% of carbon nanotubes (CNT) was added to the mixture and mixed. The mixture was manufactured in pellet form using a press and calcined at 750 °C (heating for 6 hours and maintaining for 12 hours) under an Ar atmosphere to produce a cathode additive. A lithium secondary battery was manufactured in the same manner as Example 8 except that the said cathode additive was used.

[0206] Comparative Example 7 A cathode additive and a lithium secondary battery containing the same were manufactured in the same manner as Example 8 except that the same content of lithium hexafluorophosphate (LiPF6, Sigma-Aldrich) was used instead of the said lithium difluoro(oxalato)borate and the firing thereof was carried out at 250 °C.

[0207] Comparative Example 8 Instead of the lithium difluoro(oxalato)borate, 2.0 parts by weight of lithium triflate (LiOTf, Tokyo Chemical Industry Co.) was used with respect to 100 parts by weight of the lithium iron oxide, and firing thereof was carried out at 500 °C. A positive electrode additive and a lithium secondary battery including the same were produced in the same manner as in Example 8 except for this.

[0208] Comparative Example 9 (1) Production of lithium iron oxide particles In the same manner as in Example 8, Li2O (Ganfeng Lithium) and the Fe2O3 CNT precursor were uniformly mixed at a molar ratio of 5:1, and fired in a heat treatment furnace at 600 °C (heating for 2 hours, maintaining for 6 hours) under an Ar atmosphere to obtain lithium iron oxide.

[0209] (2) Production of lithium secondary battery When producing the positive electrode material slurry, a lithium secondary battery was produced in the same manner as in Example 8 except that the lithium iron oxide, lithium difluoro(oxalato)borate (Sigma-Aldrich), carbon black, and polyvinylidene fluoride were mixed in an organic solvent (N-methylpyrrolidone) at a weight ratio of 82:8:4:6.

[0210] Experimental Example 1 Scanning electron microscope (SEM) images of the positive electrode additives produced in Example 8 and Comparative Example 6 are shown in FIG. 3 (Example 8) and FIG. 4 (Comparative Example 6).

[0211] Results of X-ray diffraction analysis (D8 Endeavor, Bruker) of the positive electrode additives produced in Example 8, 9 and Comparative Examples 4 to 8 are shown in FIG. 5 (Example 8), FIG. 6 (Example 9), FIG. 7 (Comparative Example 4), FIG. 8 (Comparative Example 5), FIG. 9 (Comparative Example 6), FIG. 10 (Comparative Example 7), and FIG. 11 (Comparative Example 8).

[0212] From the analysis results of the scanning microscope and XRD, it was confirmed that a lithium transition metal oxide of Li5FeO4 was formed as the positive electrode additive in the examples, and a double coating layer of a carbon coating layer derived from polyvinylpyrrolidone (PVP) and a carbon nanotube-containing layer was formed on the lithium transition metal oxide particles with a thickness in the range of 10 to 300 nm. And it was confirmed that a lithium borate compound-containing layer was formed on the surface of the lithium transition metal oxide.

[0213] Experimental Example 2 (1) Irreversible capacity and charge-discharge capacity The lithium secondary batteries manufactured in the above examples and comparative examples were charged at a constant current of 60 mA / g at 45°C and a constant voltage of 30 mA / g until 4.25 V was reached, and then discharged at a constant current of 10 mA / g until 2.5 V to perform charge-discharge experiments. The irreversible capacity, charge capacity, and discharge capacity were calculated respectively by the above charge-discharge experiments.

[0214] (2) Charge capacity retention rate after change over time The lithium secondary batteries manufactured in the above examples and comparative examples were stored in a chamber under an air atmosphere maintained at a temperature of 30°C and a relative humidity of 33% (33RH%) for 18 hours. Then, the charge-discharge experiment was performed on the lithium secondary battery under the same conditions. Based on the charge capacity before storage in the chamber, the ratio (capacity retention rate, %) of the charge capacity after storage in the chamber was calculated.

[0215]

Table 1

[0216] Referring to Table 1 above, it was confirmed that the lithium secondary battery of the example showed a sufficient irreversible capacity of 480 mAh / g or more, and a high capacity retention rate of 60% or more after change over time, maintained a hue level similar to that of the electrode film before change over time, and had excellent air stability.

[0217] In contrast, in the lithium secondary battery of the comparative example, during the experiment of changes over time, the electrode film was distorted, making it impossible to measure the capacity retention rate. And in the comparative example, it was confirmed that the electrode film changed to a color significantly darker than the hue of the electrode film before the change over time, and had extremely poor air stability.

[0218] The lithium secondary batteries of Comparative Examples 7 and 8 had serious changes over time, and no electrochemical experiments were conducted.

[0219] It was confirmed that the lithium secondary battery of Comparative Example 9 contained a lithium borate-based compound as an additive to the positive electrode material, and thus had significantly lower initial charge capacity and charge capacity retention rate after changes over time compared to Example 8.

[0220] As described above, the present invention has been described by limited embodiments and drawings, but the present invention is not limited thereby, and it goes without saying that various modifications and variations are possible within the equivalent scope of the technical idea of the present invention and the scope of the claims described below by those having ordinary knowledge in the technical field to which the present invention pertains.

Explanation of Reference Numerals

[0221] 10 Lithium transition metal oxide particles 20 Lithium difluoro(oxalato)borate-containing layer 13 Carbon coating layer 17 Carbon nanotube-containing layer

Claims

1. Lithium iron oxide particles doped or undoped with different elements, and a lithium borate compound-containing layer formed on the lithium iron oxide particles, wherein the lithium iron oxide particles are Li 5 FeO 4 or a compound represented by the following Chemical Formula 1, 【Chemical Formula 1】 Li 5 Fe 1−x−y Al x M y O 4 In the Chemical Formula 1, M is one or more Group 2 elements selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), one or more Group 17 elements selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), one or more Period 4 transition metals selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), and zinc (Zn), and one or more elements selected from the group consisting of one or more elements selected from the group consisting of gallium (Ga) and indium (In), x is 0.1 to 0.35, y is 0 to 0.1, a positive electrode additive for a lithium secondary battery.

2. The lithium borate compound-containing layer is a coating layer composed of a lithium borate compound, the positive electrode additive for a lithium secondary battery according to Claim 1.

3. The lithium borate compound-containing layer is contained in a content of 2 parts by weight to 25 parts by weight based on 100 parts by weight of the total content of the positive electrode additive for a lithium secondary battery, the positive electrode additive for a lithium secondary battery according to Claim 1.

4. The lithium borate compound in the lithium borate compound-containing layer is one or more compounds selected from the group consisting of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(2-methyl-2-fluoromalonate)borate, and lithium malonate difluoroborate, the positive electrode additive for a lithium secondary battery according to Claim 1.

5. The lithium iron oxide particles have a volume average particle size (D50) of 0.5 μm to 45 μm, the positive electrode additive for a lithium secondary battery according to Claim 1.

6. The lithium iron oxide particles, a carbon coating layer formed on the lithium iron oxide particles, and The positive electrode additive for a lithium secondary battery according to claim 1, comprising a lithium borate compound-containing layer formed on the carbon coating layer.

7. The positive electrode additive for a lithium secondary battery according to claim 6, wherein the carbon coating layer is contained in a content of 0.05 parts by weight to 2.0 parts by weight based on 100 parts by weight of the total content of the positive electrode additive for a lithium secondary battery.

8. The lithium iron oxide particles, A carbon coating layer formed on the lithium iron oxide particles, A carbon nanotube-containing layer formed on the carbon coating layer, and The positive electrode additive for a lithium secondary battery according to claim 1, comprising a lithium borate compound-containing layer formed on the carbon nanotube-containing layer.

9. The positive electrode additive for a lithium secondary battery according to claim 8, wherein the carbon nanotube-containing layer is contained in a content of 0.4 parts by weight to 4.0 parts by weight based on 100 parts by weight of the total content of the positive electrode additive for a lithium secondary battery.

10. The positive electrode additive for a lithium secondary battery according to claim 8, wherein the carbon coating layer and the carbon nanotube-containing layer are contained in a weight ratio of 1:4 to 1:

50.

11. A method for manufacturing the positive electrode additive for a lithium secondary battery according to claim 1, comprising: Preparing a precursor mixture containing a lithium (Li) precursor and an iron (Fe) precursor; Firing the precursor mixture in an inert gas atmosphere to obtain lithium iron oxide particles doped or undoped with a foreign element; and Heat-treating a mixture containing the lithium iron oxide particles and a lithium borate compound in an inert gas or an oxygen-containing gas atmosphere to obtain lithium iron oxide particles coated with a lithium borate compound-containing layer.

12. The firing in the step of obtaining the lithium iron oxide particles is performed at a temperature of 500 °C or higher, The heat treatment in the step of obtaining the lithium iron oxide particles coated with the lithium borate compound-containing layer is performed at a temperature of 300 °C or higher. The method for manufacturing the positive electrode additive for a lithium secondary battery according to claim 11.

13. A positive electrode for a lithium secondary battery, comprising a positive electrode active material, a binder, a conductive material, and the positive electrode additive for a lithium secondary battery according to any one of claims 1 to 10.

14. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte for a lithium secondary battery according to claim 13.

15. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 13, a negative electrode containing one or more negative electrode active materials selected from the group consisting of a carbonaceous material and a silicon compound, a separator, and an electrolyte.

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