Additive for positive electrode of lithium secondary battery, method for producing same and positive electrode of lithium secondary battery including same

Abstract

An additive for a positive electrode of a lithium secondary battery is provided, which includes lithium transition metal oxides, Li3PO4 and Li5AlO4. The lithium transition metal oxide is in a form doped with aluminum. The additive including Li3PO4 and Li5AlO4 together with the lithium transition metal oxide has a functionality of improving the stability of the battery when applied to the positive electrode of a lithium secondary battery. Specifically, when a general lithium transition metal oxide is applied to the positive electrode of a lithium secondary battery, there is a problem that the stability is reduced, such as a side reaction with an electrolyte causing gas generation in the battery. The Li3PO4 and Li5AlO4 are mixed uniformly with the lithium transition metal oxide or partially form a coating layer, and a part of the aluminum is doped into the lithium transition metal oxide to suppress the lithium transition metal oxide from causing a side reaction with the electrolyte.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2021-0060079 filed on May 10, 2021 and Korean Patent Application No. 2022-0056352 filed on May 9, 2022, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated as part of this specification.

[0002] The present invention relates to an additive for a positive electrode of a lithium secondary battery, a method for producing the same, and a positive electrode of a lithium secondary battery including the same. [Background technology]

[0003] The demand for secondary batteries as an energy source is rapidly increasing due to technological development and increasing demand for mobile devices. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium transition metal oxides are used as the positive electrode active material for lithium secondary batteries, and among these, lithium cobalt oxide LiCoO2, which has a high working voltage and excellent capacity characteristics, is mainly used. However, LiCoO2 has very poor thermal properties due to the instability of its crystal structure caused by delithiation, and is expensive, so there are limitations to its large-scale use as a power source in fields such as electric vehicles. Lithium manganese oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), and lithium nickel oxides (LiNiO2, etc.) have been developed as alternative materials to LiCoO2. Among these, much research and development has been done on lithium nickel oxide, which has a high reversible capacity of about 200mAh / g and is easy to realize large-capacity batteries.

[0005] In addition, there has been an increased demand for the use of Si-based anode active materials to realize high-capacity lithium secondary batteries, but since Si-based anode active materials have a large irreversible capacity, the positive electrode also needs to balance the irreversible capacity in order to operate the battery efficiently. As a result, research into positive electrode additives with large irreversible capacity has also been conducted, and in the process, various additives such as Li2NiO2, Li2CuO4, and Li6CoO4 have been used as positive electrode additives with large irreversible capacity.

[0006] Li2NiO2 is synthesized from Li2O and NiO using the solid phase method, but the synthesis rate is low and Li2O and NiO remain as unreacted materials. In the case of Li2O and NiO, it is difficult to express capacity, and Li2O can be converted to LiOH and Li2CO3, which causes gelation during the electrode manufacturing process and gas generation during charge / discharge and high-temperature storage.

[0007] In order to solve these problems, research into positive electrode additives for improving the performance of lithium secondary batteries has been ongoing in the relevant technical field. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 10-2016-002187 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides an additive for a positive electrode of a lithium secondary battery, which can improve the stability of a battery when applied to the lithium secondary battery by including Li3PO4 and Li5AlO4 together with a lithium transition metal oxide in which a part of the transition metal is doped with aluminum, a manufacturing method thereof, and a positive electrode of a lithium secondary battery including the additive. [Means for solving the problem]

[0010] According to a first aspect of the present invention, The present invention provides an additive for a positive electrode of a lithium secondary battery, comprising lithium transition metal oxides, Li3PO4 and Li5AlO4, in which the lithium transition metal oxides are doped with aluminum.

[0011] In one embodiment of the present invention, the lithium transition metal oxide is represented by the following formula 1: [Chemical formula 1] Li2Ni 1‐x Al x O2 (where x is between 0.001 and 0.005.)

[0012] In one embodiment of the present invention, the lithium transition metal oxide comprises 75 to 90 wt % based on the total weight of the additive.

[0013] In one embodiment of the present invention, the Li3PO4 comprises 1 to 10 wt % based on the total weight of the additive.

[0014] In one embodiment of the present invention, the Li5AlO4 comprises 0.5 to 5 wt % based on the total weight of the additive.

[0015] In one embodiment of the present invention, a portion of the Li3PO4 is present in a state coated on a lithium transition metal oxide.

[0016] In one embodiment of the present invention, the additive further comprises NiO.

[0017] In one embodiment of the present invention, the NiO comprises 5 to 15 wt % based on the total weight of the additive.

[0018] According to a second aspect of the present invention, The present invention provides a method for preparing an additive for a positive electrode of a lithium secondary battery, comprising: (1) mixing a transition metal source material, a lithium source material, a phosphorus source material, and an aluminum source material to prepare a mixture; and (2) heat-treating the mixture.

[0019] In one embodiment of the present invention, in step (1), the transition metal source material is NiO, the lithium source material is Li2O, LiOH or Li2CO3, the phosphorus source material is (NH4)2HPO4, and the aluminum source material is Al(OH)3.

[0020] In one embodiment of the present invention, in step (2), the mixture is heat-treated at 300 to 700° C. for 10 to 32 hours.

[0021] According to a third aspect of the present invention, The present invention provides a positive electrode for a lithium secondary battery, comprising the additive and a positive electrode active material, the additive being present in an amount of 10 to 40 parts by weight based on 100 parts by weight of the positive electrode active material. Effect of the Invention

[0022] The additive for the positive electrode of the lithium secondary battery according to the present invention includes lithium transition metal oxides, Li3PO4 and Li5AlO4, and the lithium transition metal oxides are doped with aluminum.

[0023] In addition, the positive electrode additive of the lithium secondary battery may include phosphorus, which may be simply mixed or may be included in the form of being coated on the lithium transition metal oxide. By including phosphorus and aluminum together, aluminum can be doped more effectively, and thus the amount of gas generation can be reduced by the phosphorus, and the amount of nickel precipitation can be reduced by the aluminum.

[0024] When the additive containing Li3PO4 and Li5AlO4 is applied to the positive electrode of a lithium secondary battery together with the lithium transition metal oxide, it has a functionality of improving the stability of the battery. Specifically, when a general lithium transition metal oxide is applied to the positive electrode of a lithium secondary battery, a side reaction occurs with the electrolyte, which may cause a problem of stability deterioration such as gas generation in the battery, and the Li3PO4 and Li5AlO4 are mixed uniformly with the lithium transition metal oxide or form a partial coating layer, and a part of aluminum is doped into the lithium transition metal oxide to suppress the lithium transition metal oxide from causing a side reaction with the electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention will now be described in more detail to aid in understanding the present invention.

[0026] The terms and words used in this specification and claims should not be construed in a limited manner based on their ordinary or dictionary meaning, but should be interpreted in a meaning and concept that corresponds to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his / her invention in the best possible way.

[0027] The embodiments provided by the present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0028] Unless the measurement conditions and methods for any physical property described in this specification are specifically described, the physical property is measured according to the measurement conditions and methods commonly used by those of ordinary skill in the art.

[0029] Additives and positive electrode active materials The present invention provides an additive for the positive electrode of a lithium secondary battery, comprising lithium transition metal oxides, Li3PO4 and Li5AlO4.

[0030] The lithium transition metal oxide is mixed with a positive electrode active material to complement the performance of the positive electrode active material, such as the electrode capacity. In the lithium transition metal oxide, the transition metal is selected from Co, Ni, Cu, Mn, Fe, and combinations thereof. Specifically, the lithium transition metal oxide is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2(0 <a<1、0<b<1、0<c<1、a+b+c=1)、LiNi 1‐y Co y O2(O <y<1)、LiCo 1‐y Mn y O2, LiNi 1‐y Mn y O2(O <y<1)、Li(Ni a Co b Mn c )O4(0 <a<2、0<b<2、0<c<2、a+b+c=2)、LiMn 2‐z Ni z O4(0 <z<2)、LiMn 2‐z Co zO4 (0 < z < 2) and can be selected from this combination, but lithium-transition metal oxides such as Li2NiO2, Li2CuO4, Li6CoO4, etc., which contain an excessive amount of lithium and can be utilized together with Si-based negative electrode active materials having a large irreversible capacity, can be used. According to a specific example of the present invention, the lithium-transition metal oxide is Li2NiO2. In the case of the Li2NiO2, it is synthesized by the solid-phase method of Li2O and NiO, but the synthesis rate is low and basically unreacted Li2O and NiO remain. In such cases of Li2O and NiO, it is difficult to exhibit capacity. In the case of Li2O, it can be converted into LiOH and Li2CO3, which causes a gelling phenomenon during the electrode manufacturing process and problems of gas generation during charge / discharge and high-temperature storage. According to a specific example of the present invention, the lithium-transition metal oxide is in a form doped with aluminum. This is because in the manufacture of the additive, it is affected by aluminum source substances and phosphorus source substances added together, etc. The lithium-transition metal oxide doped with aluminum can be expressed as shown in the following Chemical Formula 1.

[0031] [Chemical Formula 1] Li2Ni 1‐x Al x O2 (Here, x is from 0.001 to 0.005, specifically from 0.0015 to 0.004, more specifically from 0.002 to 0.003.)

[0032] In the present invention, Li3PO4 and Li5AlO4, which are included together with the lithium-transition metal oxide as an additive for the positive electrode of a lithium secondary battery, are particularly excellent in suppressing side reactions with the electrolyte when coated on the lithium-transition metal oxide. Therefore, when used together with Li2NiO2 among the lithium-transition metal oxides, it is possible to expect a more excellent effect of improving battery performance by the addition of Li3PO4 and Li5AlO4.

[0033] According to one embodiment of the present invention, the lithium transition metal oxide is included in 75 to 90 wt%, preferably 77 to 87 wt%, more preferably 80 to 85 wt% based on the total weight of the additive. The lithium transition metal oxide is an additive that functions to complement the performance such as the electrode capacity of the positive electrode active material, and is required to be included in a certain level or more in order to express the performance of the lithium secondary battery. However, since safety problems may occur, the ratio of the additive materials Li3PO4 and Li5AlO4 must be appropriately adjusted. If the lithium transition metal oxide is included in less than 75 wt% based on the total weight of the additive, the basic performance of the lithium secondary battery may be deteriorated, and if the lithium transition metal oxide is included in more than 90 wt% based on the total weight of the additive, problems may occur in the stability of the overall positive electrode.

[0034] The additive according to the present invention contains Li3PO4 by adding a phosphorus source material during the preparation process and reacting it with Li2O, etc. The phosphorus source material will be described in detail in the "Preparation method of additive" below. The Li3PO4 improves the stability of the lithium transition metal oxide, and in particular, can suppress the lithium transition metal oxide from reacting with the electrolyte to generate gas in the battery. In addition, when a phosphorus source material of a certain level or more is included during the preparation process of the additive, it helps to dope and locate some aluminum in the lithium transition metal oxide. According to one embodiment of the present invention, the Li3PO4 is included in an amount of 1 to 10 wt%, preferably 2 to 8 wt%, and more preferably 3 to 6 wt%, based on the total weight of the additive. When the Li3PO4 is included in an amount of less than 1 wt% based on the total weight of the additive, the effect of improving the stability of the lithium secondary battery is insignificant, and when the Li3PO4 is included in an amount of more than 10 wt% based on the total weight of the additive, the content of other components is relatively reduced, which is undesirable in terms of the performance of the lithium secondary battery.

[0035] The additive according to the present invention contains Li5AlO4 by adding an aluminum source material and reacting it with Li2O during the preparation process. The aluminum source material will be described in detail in the "Preparation method of additive" below. A part of the aluminum supplied through the aluminum source material can be doped into the lithium transition metal. When aluminum is doped, the lithium transition metal oxide can be expressed as Chemical Formula 1 above. When aluminum is doped in a plane related to the h index, peak splitting can be generated and Ni overflow can be reduced. According to one embodiment of the present invention, the Li5AlO4 is included in an amount of 0.5 to 5 wt%, preferably 1 to 4 wt%, and more preferably 1.5 to 3 wt%, based on the total weight of the additive. When the Li5AlO4 is included in an amount less than 0.5 wt% based on the total weight of the additive, the effect of improving the stability of the lithium secondary battery is insignificant, and when the Li5AlO4 is included in an amount more than 5 wt% based on the total weight of the additive, the content of other components is relatively reduced, which is undesirable in terms of the performance of the lithium secondary battery.

[0036] The additive materials Li3PO4 and Li5AlO4 contained together with the lithium transition metal oxides do not have a superior effect on the stability of the lithium secondary battery compared to using three materials simultaneously, even if one or two of the additive materials are contained in the same or large amounts. The two additive materials each have their own individual functions, and when used together, a synergistic effect is shown in the stability of the lithium secondary battery.

[0037] The additive according to the present invention may further include NiO together with the lithium transition metal oxides Li3PO4 and Li5AlO4. The NiO is one of the transition metal source materials added during the preparation of the additive, and is a stable compound with low reactivity that may exist in the additive in an unreacted state. Depending on the type of transition metal of the lithium transition metal oxide used in the additive, Ni in NiO may be replaced by materials such as Co, Cu, Mn, and Fe. According to one embodiment of the present invention, the NiO is included in an amount of 5 to 15 wt%, preferably 7 to 13 wt%, and more preferably 8 to 11 wt%, based on the total weight of the additive.

[0038] The positive electrode active material functions as a substantial positive electrode active material that exchanges electrons at the positive electrode of the lithium secondary battery, and may be a material commonly used in the relevant technical field. Specifically, the positive electrode active material may be LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2(0 <a<1、0<b<1、0<c<1、a+b+c=1)、LiNi 1‐y Co y O2(O <y<1)、LiCo 1‐y Mn y O2, LiNi 1‐y Mn y O2(O <y<1)、Li(Ni a Co b Mn c )O4(0 <a<2、0<b<2、0<c<2、a+b+c=2)、LiMn 2‐z Ni z O4(0 <z<2)、LiMn 2‐z Co zO4 (0 < z < 2) and can be selected from this combination. Since the additive serves to complement the electrode capacity of the positive electrode active material, the content can be appropriately adjusted in consideration of its relationship with the positive electrode active material. According to a specific example of the present invention, the additive contains 10 to 40 parts by weight, preferably 10 to 30 parts by weight, more preferably 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. When the additive is added within the above range, the effect of improving the performance of the positive electrode active material is excellent.

[0039] Additive manufacturing method The present invention provides a method for manufacturing an additive for a positive electrode of a lithium secondary battery described above. The manufacturing method includes: (1) a step of mixing a transition metal source material, a lithium source material, a phosphorus source material, and an aluminum source material to produce a mixture; and (2) a step of heat-treating the mixture.

[0040] In the step (1), the transition metal source material is a material that supplies transition metal to lithium transition metal oxides and the like contained in the final positive electrode active material, and is generally a transition metal oxide. According to a specific example of the present invention, the transition metal source material is NiO. The lithium source material is a material that supplies lithium to lithium transition metal oxides, Li3PO4, Li5AlO4, Li3BO3, etc. contained in the final additive, and is generally a lithium oxide. According to a specific example of the present invention, the lithium source material is Li2O, LiOH, or Li2CO3. The phosphorus source material is a material that supplies phosphorus to Li3PO4 and the like contained in the final additive, and is generally ammonium phosphate. According to a specific example of the present invention, the phosphorus source material is (NH4)2HPO4. The aluminum source material is a material that supplies aluminum to Li5AlO4 and the like contained in the final additive, and may generally be aluminum hydroxide. According to a specific example of the present invention, the aluminum source material is Al(OH)3.

[0041] In the step (1), the transition metal source material, the lithium source material, the phosphorus source material and the aluminum source material may be added in appropriate amounts according to the content of the components of the additive. According to one embodiment of the present invention, when the source materials are mixed, the content of NiO and Li2O may be adjusted so that the mole of Li2O / mol of NiO is 1.5 to 2.5, specifically 1.7 to 2.3, more specifically 1.9 to 2.1, according to one embodiment of the present invention, the content of Al(OH)3 may be adjusted so that it is 0.005 to 0.05 mol%, specifically 0.01 to 0.04 mol%, more specifically 0.01 to 0.03 mol% based on the mole of NiO, and the content of (NH4)2HPO4 may be adjusted so that P is 1 to 7 wt%, specifically 1.5 to 6 wt%, more specifically 2 to 5.5 wt%, based on the total weight of NiO and Li2O.

[0042] The mixture prepared in step (1) is heat-treated to prepare the additive. The heat treatment is sufficient if it is sufficient to obtain the components of the additive by firing the mixture. According to one embodiment of the present invention, the mixture in step (2) is heat-treated at 300 to 700° C., preferably 300 to 600° C., more preferably 300 to 500° C., for 10 to 32 hours, preferably 10 to 26 hours, more preferably 10 to 20 hours.

[0043] Lithium secondary battery The present invention provides a lithium secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte. In the lithium secondary battery, the positive electrode and the negative electrode are positioned opposite each other, and the separator is interposed between the positive electrode and the negative electrode. The electrode assembly including the positive electrode, the negative electrode, and the separator is housed in a battery container, and the battery container is filled with the electrolyte.

[0044] 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 additive and the positive electrode active material described above.

[0045] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Also, the positive electrode current collector may have a thickness of typically 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0046] The positive electrode active material layer may include a conductive material and a binder in addition to the additive and the positive electrode active material.

[0047] The conductive material is used to give conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing a chemical change in the battery. Specific examples include graphite such as natural graphite and 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like. Among these, one type alone or a mixture of two or more types can be used. The conductive material can be generally included in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0048] The binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination. 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.

[0049] The additive and the positive electrode active material may be included in an amount of 60 to 95 wt % based on the total weight of the positive electrode active material layer.

[0050] The positive electrode may be manufactured by a typical positive electrode manufacturing method, except for using the additive and positive electrode active material described above. Specifically, the positive electrode may be manufactured by coating a composition for forming a positive electrode active material layer, which includes the additive and positive electrode active material, and optionally a binder and a conductive material, on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the additive, positive electrode active material, binder, and conductive material are as described above.

[0051] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the additives, cathode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for the production of a cathode, taking into consideration the coating thickness of the slurry and the production yield.

[0052] Alternatively, the positive electrode may be manufactured by casting the composition for forming a positive electrode active material layer on a support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0053] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0054] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0055] The negative electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; SiO β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, among which one or a mixture of two or more may be used. Also, a thin film of metallic lithium may be used as the negative electrode active material. Also, the carbon material may be either low crystalline carbon or high crystalline carbon. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0056] The binder, conductive material, and negative electrode current collector may be selected with reference to the above-mentioned configuration of the positive electrode, but are not necessarily limited thereto. In addition, the method of forming the negative electrode active material layer on the negative electrode current collector is a known coating method, similar to the positive electrode, and is not particularly limited thereto.

[0057] In the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ions to move. Any separator generally used in lithium secondary batteries may be used without any particular limitation. In particular, a separator having low resistance to ion movement of the electrolyte and excellent humidification ability of the electrolyte is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. In addition, a separator coated with a ceramic component or a polymer material to ensure heat resistance or mechanical strength may be used, and may be selectively used in a single layer or multilayer structure.

[0058] The electrolyte used in the present invention may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like that can be used in manufacturing a lithium secondary battery.

[0059] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0060] The organic solvent may be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that can be used include carbonate-based solvents such as polycarbonate (PC), alcohol-based solvents such as ethanol and isopropyl alcohol, nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group that may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9 to provide excellent electrolyte performance.

[0061] The lithium salt may be any compound capable of providing lithium ions used in a lithium secondary battery without any particular limitation. Specifically, the lithium salt may be LiN(FSO2)2, LiSCN, LiN(CN)2, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiPF6, LiF, LiCl, LiBr, LiI, LiNO3, LiClO4, LiAlO4, LiAlCl4, LiSbF6, LiAsF6, LiBF2C2O4, LiBC4O8, Li(CF3)2PF4, Li(CF3)3PF3, Li(CF3)4PF2, Li(CF3)5PF, Li(CF3)6P, LiCF3SO3, LiC4F9SO3, LiCF3CF2SO3, LiCF3CF2(CF3)2CO, Li(CF3SO2)2CH, LiCF3(CF2)7SO3, LiCF3CO2, LiCH3CO2, or a combination thereof. The lithium salt is preferably used at a concentration within the range of 0.1 to 2.0 M. If the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0062] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0063] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0064] According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0065] The battery module or the battery pack may be used as a power source for one or more medium- to large-sized devices in a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0066] Hereinafter, preferred examples will be presented to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention. It is natural that such changes and modifications fall within the scope of the accompanying claims.

[0067] [Example] Example 1 NiO, Li2O, Al(OH)3, and (NH4)2HPO4 were mixed, and the mixture was heat-treated at 300℃ for 10 hours to produce the additive. During mixing, the contents of NiO and Li2O were adjusted so that the moles of Li2O / moles of NiO were 2.03. The content of Al(OH)3 was adjusted to 0.03 mol% based on the moles of NiO, and the content of (NH4)2HPO4 was adjusted so that P was 5.5 wt% based on the total weight of NiO and Li2O.

[0068] Comparative example 1 (Al 0.03mol%) The additive was prepared in the same manner as in Example 1, except that (NH4)2HPO4 was not used.

[0069] Comparative example 2 (P 5.5wt%) The additive was prepared in the same manner as in Example 1, except that Al(OH)3 was not used.

[0070] Comparative example 3 (Al 0.01mol% P 5.5wt%) The content of Al(OH)3 was adjusted to be 0.01 mol% based on the moles of NiO, and the content of (NH4)2HPO4 was adjusted to be 5.5 wt% P based on the total weight of NiO and Li2O.

[0071] Comparative example 4 (Al 0.02mol% P 5.5wt%) The content of Al(OH)3 was adjusted to be 0.02 mol% based on the moles of NiO, and the content of (NH4)2HPO4 was adjusted to be 5.5 wt% P based on the total weight of NiO and Li2O.

[0072] Experimental Example Experimental example 1: Analysis of additive components The components of the additives of Example 1 and Comparative Examples 1 to 4 were analyzed by X-ray diffraction analysis using an X-ray diffractometer (manufacturer: BRUKER NANO, product name: Bruker D8 Advance) and are shown in Table 1 below.

[0073] [Table 1]

[0074] Manufacture of lithium secondary batteries Lithium secondary batteries were manufactured to confirm the performance of the additives prepared in Example 1 and Comparative Examples 1 to 4. Specifically, the additives in Example 1 and Comparative Examples 1 to 4 were used in combination with the positive electrode active material LiNi 0.83 Co 0.11 Mn0.06 O2 in a weight ratio of 9:1 (positive active material:additive), then mixed with carbon black conductive material and PVDF binder in N-methylpyrrolidone solvent in a weight ratio of 85:10:5 (additive + positive active material:conductive material:binder) to prepare a positive active material slurry, which was then applied to one side of an aluminum current collector (20μm) (loading amount: 0.2~0.3mg / 25cm). 2 ), dried at 130° C. for 20 minutes or more, and then rolled once or twice to a porosity of 26% to prepare a positive electrode.

[0075] The negative electrode was made of a 5:5 mixture of natural graphite and artificial graphite, and a porous polyethylene separator was placed between the positive and negative electrodes to prepare an electrode assembly. The electrode assembly was placed inside a battery case, and an electrolyte was injected into the case to prepare a lithium secondary battery. The electrolyte was prepared by dissolving 0.7M lithium hexafluorophosphate (LiPF6) and 0.3M lithium bis(fluorosulfonyl)imide (LiFSI) in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate (EC / EMC volume ratio = 3 / 7).

[0076] The manufactured lithium secondary battery was used for performance evaluation of Experimental Examples 2 and 3.

[0077] Experimental example 2: Gas generation rate measurement The fabricated lithium secondary battery was charged in CCCV (constant current, constant voltage) mode at 0.1 C to 4.2 V, and stored in an oven at 60° C. for a total of 4 weeks, and the volume change was measured by the Archimedes method.

[0078] The electrolyte was 250ml, containing 0.7M LiPF6, 0.5M LIFSI, 1.5wt% VC, 0.5wt% PS, and 1wt% Esa in a mixed solvent of EC and EMC (mixed volume ratio of EC and EMC = 3:7, EC: ethyl carbonate, EMC: ethyl methyl carbonate) (PS: 1,3-propanesultone, VC: vinylene carbonate, Esa: ethylene sulfate). The pouch-charged cell was stored at 60℃ for 4 weeks, after which the amount of gas generated by the battery was measured using the Archimedes method, and the results are shown in Table 2.

[0079] Table 2 below shows the amount of gas generated when the battery is 100% charged (SOC (State Of Charge) 100) (formation gas), the amount of gas generated after 50 cycles at high temperature (45°C) (cycle gas, 50th), and the amount of gas generated when stored for 4 weeks at high temperature (60°C) (storage gas, 4w), as well as the amount of Ni precipitation.

[0080] The amount of Ni precipitation was measured using an inductively coupled plasma spectrometer (ICP, PerkinElmer 7100 model) and calculated based on the corresponding value for the amount of Ni precipitation in Comparative Example 2.

[0081] [Table 2]

[0082] As a result, as shown in Table 2, Comparative Example 1, in which the positive electrode active material does not contain P element, shows a significantly high amount of gas generation in all of the charged state, the state during charge / discharge, and the state during storage. Also, Comparative Example 2, in which the positive electrode active material does not contain Al, shows a significantly high amount of Ni precipitation.

[0083] Therefore, it was confirmed that the positive electrode active material containing both Al and P elements can reduce both the amount of gas generation and the amount of Ni deposition.

[0084] This is because, although Comparative Example 1 containing only Al among P and Al, and Example 1 containing both P and Al, contain Al in common, when P and Al are contained together, Al is more effectively doped into the Ni site.

[0085] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is of course possible for a person having ordinary skill in the art to which the present invention pertains to make various modifications and variations within the technical spirit of the present invention and the equivalent scope of the following claims.

Claims

1. Lithium transition metal oxide, Li ３ P.O. ４ , and Li ５ AlO ４ Including, The lithium transition metal oxide is doped with aluminum, The lithium transition metal oxide is represented by the following formula 1: The Li 3 PO 4 is contained in an amount of 1 to 10% by weight based on the total weight of the additive. [Chemical formula 1] Li 2 Ni 1-x Al x O 2 (where x is between 0.001 and 0.005).

2. 2. The additive for a positive electrode of a lithium secondary battery according to claim 1, wherein the lithium transition metal oxide is present in an amount of 75 to 90 wt % based on the total weight of the additive.

3. The Li ５ AlO ４ The additive for a positive electrode of a lithium secondary battery according to claim 1, wherein the additive is present in an amount of 0.5 to 5 wt % based on the total weight of the additive.

4. The Li ３ P.O. ４ The positive electrode additive of claim 1 , wherein a part of said additive is present in a state of being coated on the lithium transition metal oxide.

5. The additive for a positive electrode of a lithium secondary battery according to claim 1 , further comprising NiO.

6. 6. The additive for a positive electrode of a lithium secondary battery according to claim 5, wherein the NiO is present in an amount of 5 to 15 wt % based on the total weight of the additive.

7. A method for producing an additive for a positive electrode of a lithium secondary battery according to claim 1, (1) mixing a transition metal source material, a lithium source material, a phosphorus source material, and an aluminum source material to prepare a mixture; and (2) A method for preparing an additive for a positive electrode of a lithium secondary battery, comprising the step of heat-treating the mixture.

8. In the step (1), the transition metal source material is NiO and the lithium source material is Li ２ O, LiOH or Li ２ CO ３ and the phosphorus source substance is (NH ４ ) ２ H.P.O. ４ The aluminum source material is Al(OH). ３ The method for producing an additive for a positive electrode of a lithium secondary battery according to claim 7,

9. 8. The method of claim 7, wherein in step (2), the mixture is heat-treated at 300 to 700° C. for 10 to 32 hours.

10. The additive according to claim 1 and a positive electrode active material, The additive is included in an amount of 10 to 40 parts by weight based on 100 parts by weight of the positive electrode active material.

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