Title of Invention: Method for manufacturing positive electrode additive for lithium secondary battery and positive electrode additive for lithium secondary battery prepared therefrom Technical field [One] Cross-reference with related application(s) [2] This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0124564 filed on October 18, 2018, and all contents disclosed in the documents of the Korean patent application are incorporated as part of this specification. [3] The present invention relates to a method of manufacturing a positive electrode additive for a lithium secondary battery having a high irreversible capacity, preventing gelation and reducing gas generation, and to a positive electrode additive prepared therefrom. Background [4] As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used. [5] Although graphite is mainly used as a negative electrode material for a lithium secondary battery, since graphite has a small capacity per unit mass of 372 mAh/g, it is difficult to increase the capacity of a lithium secondary battery. Accordingly, materials for forming lithium and intermetallic compounds, such as silicon, tin, and oxides thereof, have been developed and used as non-carbon-based negative electrode materials that exhibit higher capacity than graphite. There is a problem that the irreversible capacity loss is large. [6] On the other hand, a lithium ion source or storage can be provided to the cathode material, and a method to overcome the irreversible capacity loss of the anode by using a material that is electrochemically active after the first cycle so as not to degrade the overall performance of the battery is studied. , Was suggested. Specifically, there is a method of using a lithium nickel-based oxide containing an excess of lithium, such as Li 2 NiO 2 , as a sacrificial cathode material or an irreversible additive (or an overdischarge inhibitor) for a cathode. [7] However, the lithium nickel-based oxide is mainly produced by reacting nickel oxide such as NiO with an excess of lithium oxide, and the yield of this reaction is low, so that unreacted residues or by-products are inevitably irreversible additives including the lithium nickel-based oxide. Will remain within. [8] Such unreacted residues or by-products may include, for example, lithium oxide such as Li 2 O, nickel oxide such as NiO, and by- products such as LiOH and Li 2 CO 3 derived from the lithium oxide . [9] These residues or by-products are decomposed during the initial battery cycle to generate excessive gases such as O 2 and CO 2 . In addition, in the case of by-products such as LiOH, it reacts with the binder component during the preparation of the composition for manufacturing the electrode, resulting in an increase in viscosity or gelation of the composition, which makes it difficult to uniformly apply the electrode composition for forming the active material layer. As a result, there is a problem that the characteristics of the battery are deteriorated. [10] Further, it is possible to reduce the cycle efficiency of a positive electrode such as free LiOH and/or free Li derived from LiOH, and the lithium oxide or nickel oxide has difficulty in expressing a basic capacity, thereby reducing the capacity of the irreversible additive. Detailed description of the invention Technical challenge [11] Accordingly, the present invention reduces the amount of residual by-products/unreacted in the positive electrode additive, has a high irreversible capacity, suppresses gelation in the electrode manufacturing process, and produces a positive electrode additive for a lithium secondary battery that can reduce gas generation in the battery use process. Is to provide a way. [12] The present invention provides a positive electrode additive for a lithium secondary battery having a reduced by-product/unreacted residual amount and having a high irreversible capacity. Means of solving the task [13] Accordingly, the present invention includes a step of preparing a lithium nickel oxide of Formula 1 by mixing a lithium raw material, a nickel raw material, and a raw material optionally including element M, followed by heat treatment, [14] The lithium raw material contains Li 2 O and LiOH, and the LiOH is used in an amount of 3 to 25% by weight based on the total weight of the lithium raw material. [15] It provides a method of preparing a positive electrode additive for a lithium secondary battery containing the lithium nickel oxide: [16] [Formula 1] [17] [18] In Chemical Formula 1, [19] M is selected from the group consisting of transition metals, amphoteric elements, P, F, and B, provided that M is not nickel, [20] 0≤x<1. [21] The present invention also contains 95 to 99.5% by weight of the lithium nickel oxide represented by the following formula (1); And 0.5 to 5% by weight of NiO, [22] Based on 100 parts by weight of the total weight of the lithium nickel oxide and NiO, [23] To provide a positive electrode additive for a lithium secondary battery comprising less than 5 parts by weight of LiOH and less than 0.6 parts by weight of Li 2 CO 3 : [24] [Formula 1] [25] [26] In Chemical Formula 1, [27] M is selected from the group consisting of transition metals, amphoteric elements, P, F, and B, provided that M is not nickel, [28] 0≤x<1. [29] In addition, the present invention is the positive electrode additive; It provides a positive electrode mixture comprising; and a positive electrode active material. [30] The present invention also includes a positive electrode comprising the positive electrode mixture; Electrolytes; It provides a lithium secondary battery including; and a negative electrode. Effects of the Invention [31] The positive electrode additive for a lithium secondary battery prepared by the method according to the present invention may contain a higher fraction of lithium nickel oxide of Formula 1, which is a major component that exhibits irreversible capacity, and a reduced fraction of unreacted residues/byproducts. Can include. [32] As a result, the positive electrode additive may exhibit a higher irreversible capacity, and due to the reduced content of unreacted residues/by-products, gelation in the electrode manufacturing process or gas generation in the electrode operation process can be significantly reduced. [33] Accordingly, the positive electrode and lithium secondary battery manufactured using the positive electrode additive may exhibit more excellent electrochemical characteristics and lifespan characteristics. Mode for carrying out the invention [34] Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. [35] The terms or words used in the specification and claims are not to be construed as limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention, based on the principle of [36] Hereinafter, a method of manufacturing a positive electrode additive for a lithium secondary battery according to an embodiment of the present invention, a positive electrode additive prepared according to the method, and a lithium secondary battery including the same will be described. [37] According to an embodiment of the present invention, a lithium raw material material, a nickel raw material material, and a raw material material containing optionally element M are mixed and then heat treated to prepare a lithium nickel oxide represented by the following formula (1), [38] The lithium raw material contains Li 2 O and LiOH, and the LiOH is used in an amount of 3 to 25% by weight based on the total weight of the lithium raw material. [39] A method of preparing a positive electrode additive for a lithium secondary battery containing the lithium nickel oxide is provided: [40] [Formula 1] [41] [42] In Chemical Formula 1, [43] M is selected from the group consisting of transition metals, amphoteric elements, P, F, and B, provided that M is not nickel, [44] 0≤x<1. [45] As a result of continued experiments of the present inventors, in addition to Li 2 O previously used in the lithium raw material , a predetermined amount of LiOH is used together as a lithium raw material. It was found that it was possible to obtain a positive electrode additive for a lithium secondary battery, more specifically an irreversible additive containing an unreacted residue/by-product as a higher fraction and a lower fraction of lithium nickel oxide, and completed the invention. The technical principle by which this effect is achieved can be expected as follows. [46] When a predetermined amount of LiOH is used together as a lithium raw material, these components have a melting point of about 462° C., which may exhibit a lower melting point than the Li 2 O (melting point: about 1438° C.), and in particular, the lithium raw material And, it may exhibit a melting point lower than the heat treatment (calcination) temperature for reaction of the nickel raw material. As a result, such LiOH can be dissolved during the reaction to wrap the remaining lithium and nickel raw materials, and the remaining lithium and nickel raw materials, and the like can be uniformly dispersed. Accordingly, the reaction rate between the lithium raw material such as Li 2 O and the nickel raw material is improved, and according to the above manufacturing method, a positive electrode additive containing a higher proportion of lithium nickel oxide of Formula 1 can be prepared. . [47] In addition, with the improvement of the fraction of Formula 1, the fraction of unreacted residues such as Li 2 O or NiO or by- products such as LiOH and Li 2 CO 3 derived from lithium oxides such as Li 2 O may be significantly reduced. I can. [48] Accordingly, the positive electrode additive prepared by the method of one embodiment may exhibit an improved irreversible capacity due to a higher fraction of Formula 1, and due to the reduced content of unreacted residues/by-products, gelation in the electrode manufacturing process or, The amount of gas generated during electrode operation can be significantly reduced. [49] Meanwhile, in the method of the embodiment, the LiOH included in the lithium raw material may be included in an amount of 3 to 25% by weight, or 5 to 23% by weight, or 8 to 22% by weight of the total lithium raw material. [50] In addition, a specific embodiment of a lithium raw material containing such an amount of LiOH is 70 to 95 mol%, or 80 to 92 mol% of Li 2 O, and 5 to 30 mol%, or 8 to 20 mol% of LiOH May consist of %. [51] In the composition of the lithium raw material, if the content of LiOH is too large, it may act as an impurity and remain in the positive electrode additive that is finally formed, which may promote gelation during electrode formation or increase gas generation. have. Conversely, if the content of LiOH is too small, the effect of increasing the fraction of Formula 1 or lowering the fraction of unreacted residue/by-product may not be properly achieved depending on the addition thereof. [52] On the other hand, as the nickel raw material reacting with the lithium raw material, an oxide or hydroxide containing nickel such as , for example, nickel oxide (NiO) or nickel hydroxide (Ni(OH) 2 ) may be used. Nickel (NiO) can be used. [53] In addition, when the lithium nickel oxide of Formula 1 further includes a raw material M in the form of doping or a composite, the raw material containing the element M may be further used in the method of one embodiment. As the raw material containing the element M, oxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides or oxyhydroxides, phosphates and the like may be used, and phosphates may be used among them. At this time, the M is to improve thermal stability and structural stability by substituting a part of nickel in the finally prepared lithium nickel oxide, and specifically, Co, Mn, W, Fe, Mg, Ti, Cu, or A transition metal element having a divalent, trivalent or pentavalent oxidation number such as Zr; An amphoteric element having 3 and an oxidation number such as Al; And it may be selected from the group consisting of P, F, and B, among which M may be selected from the group consisting of W, Ti, Al, Zr, P, F, and B, and more specifically Is excellent in reactivity with lithium, and may be Al, P, or B capable of forming a more stable compound . [54] The lithium raw material, nickel raw material, and raw material containing element M as described above may be used in an amount that satisfies the composition ratio of metal elements including lithium and nickel in the lithium nickel oxide represented by Formula 1 to be finally prepared. [55] In addition, when mixing the above-described raw materials, a sintering agent may be optionally further added. The sintering agent is specifically a compound containing ammonium ions such as NH 4 F, NH 4 NO 3 , or (NH 4 ) 2 SO 4 ; Metal oxides such as B 2 O 3 or Bi 2 O 3 ; Alternatively , it may be a metal halide such as NiCl 2 or CaCl 2, and any one or a mixture of two or more of them may be used. The sintering agent may be used in an amount of 0.01 mol to 0.2 mol per 1 mol of the nickel raw material. When used within the above content range, the effect of improving sintering characteristics is excellent, so that the performance of the positive electrode material can be improved and a decrease in initial capacity of the battery can be prevented during charging and discharging. [56] In addition, when mixing the above-described raw materials, a moisture removing agent may be optionally further added. Specifically, the moisture removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more of them may be used. The moisture remover may be used in an amount of 0.01 mol to 0.2 mol per 1 mol of the nickel raw material. [57] On the other hand, the heat treatment step for reacting each of the above-described raw materials may be specifically performed at a temperature of 500 to 900°C, or 550 to 800°C, or 600 to 800°C, for 5 to 25 hours, or 10 to 20 hours. have. [58] If the heat treatment (calcination) temperature is too low, the fraction of unreacted residues/by-products in the finally formed positive electrode additive may increase. Conversely, if the heat treatment temperature is too high, it is not easy to control the reaction rate of each raw material, As a result, there is a concern about generation of side-reactants. [59] The heat treatment, specifically, the firing step including the step of raising and maintaining the temperature may be performed under an inert gas atmosphere such as nitrogen, helium, or argon to suppress the generation of side reactions. Among these, it may be carried out in a nitrogen gas atmosphere in consideration of the excellent effect of increasing the reaction efficiency and suppressing the generation of side reactions. [60] In addition, after the heat treatment process, a cooling process may be optionally further performed. The cooling process may be performed according to a conventional method, and specifically, may be performed by a method such as natural cooling or hot air cooling in an atmospheric atmosphere. [61] By the heat treatment process as described above, a positive electrode additive for a lithium secondary battery having an improved fraction of Formula 1 and a reduced fraction of unreacted residue/by-product may be prepared. Accordingly, according to another embodiment of the present invention, 95 to 99.5% by weight, or 95 to 97% by weight of the lithium nickel oxide of Formula 1; And 0.5 to 5% by weight, or 3 to 5% by weight of NiO, and less than 5 parts by weight, or 3 to 5 parts by weight of LiOH based on 100 parts by weight of the total weight of the lithium nickel oxide and NiO, and 0.6 weight There is provided a positive electrode additive for a lithium secondary battery containing less than part, or 0.1 to 0.55 parts by weight of Li 2 CO 3 : [62] [Formula 1] [63] [64] In Chemical Formula 1, [65] M is selected from the group consisting of transition metals, amphoteric elements, P, F, and B, provided that M is not nickel, [66] 0≤x<1. [67] The positive electrode additive of this other embodiment contains the main component of Formula 1 in a higher proportion than previously known, for example, 95% by weight or more, and the proportion of the remaining unreacted residue/by-product may be reduced. In the composition of the positive electrode additive, the LiOH and Li 2 CO 3 may be derived from the lithium raw material, more specifically, Li 2 O and/or LiOH. [68] Due to the high fraction of Formula 1 and the low fraction of unreacted residues/by-products, the positive electrode additive of another embodiment may exhibit a higher irreversible capacity, and significantly reduce the amount of gas generated during gelation or operation of the electrode. Can be reduced. [69] The positive electrode additive may typically be used as a sacrificial positive electrode material or an irreversible additive (or an overdischarge inhibitor) that can compensate for the irreversible capacity loss of the negative electrode as it contains an excessive amount of lithium, but itself can also be used as an active material of the positive electrode. have. [70] Accordingly, according to another embodiment of the present invention, the positive electrode additive is applied as an irreversible additive, the positive electrode additive; And a positive electrode active material; [71] In this positive electrode mixture, the weight ratio of the positive electrode additive to the positive electrode active material may be 1:99 to 35:65, or 2:98 to 20:80, thereby exhibiting excellent irreversible capacity and high capacity characteristics. [72] Such a positive electrode mixture may be formed on a positive electrode current collector to form a positive electrode, such a positive electrode; Electrolytes; And a lithium secondary battery including a negative electrode. [73] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed from the positive electrode mixture formed on the positive electrode current collector. [74] The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , Silver, or the like may be used. In addition, the positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwovens. [75] In addition, the positive electrode active material layer may be formed from the positive electrode mixture described above, and the positive electrode mixture and the positive electrode active material layer may include the positive electrode additive, the positive electrode active material, a conductive material, and a binder. [76] At this time, the conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it does not cause chemical changes and has electronic conductivity. Specific examples include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; Graphite such as natural graphite or artificial graphite; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, a conductive polymer such as a polyphenylene derivative may be used, and one of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer. [77] In addition, the binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC). ), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer. [78] In addition, lithium transition metal oxide may be typically used as the positive electrode active material. [79] Specifically, the lithium transition metal compound includes a metal of cobalt, manganese, nickel, iron, or a combination thereof; And lithium; may be used a composite oxide, specific examples thereof, LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 2 , Li(Ni a Co b Mn c )O 2 (0