TECHNICAL FIELD The present disclosure relates to a method for reusing resources in the fabrication of a lithium secondary battery. More particularly, the present disclosure relates to a method for collecting and reusing positive electrode scrap generated in the lithium 10 secondary battery fabrication process or positive electrode active materials of lithium secondary batteries discarded after use. The present application claims the benefit of Korean Patent Application No. 10-2020-0062371 filed on May 25, 2020 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 15 BACKGROUND ART Lithium secondary batteries that can be recharged repeatedly are gaining attention as an alternative to fossil energy. They have been primarily used in traditional handheld devices such as mobile phones, video cameras and electric power tools. Recently, the 20 range of applications tends to gradually extend to vehicles which are powered by electricity (EVs, HEVs, PHEVs), large-capacity energy storage systems (ESSs) and uninterruptible power systems (UPSs). A lithium secondary battery includes an electrode assembly including unit cells, 3 each unit cell including a positive electrode plate and a negative electrode plate including a current collector and an active material coated on the current collector with a separator interposed between the positive electrode plate and the negative electrode plate, and a packaging or a battery case in which the electrode assembly is hermetically received 5 together with an electrolyte solution. The lithium secondary battery primarily includes lithium-based oxide as the positive electrode active material and a carbon-based material as the negative electrode active material. The lithium-based oxide contains a metal such as cobalt, nickel or manganese. In particular, cobalt, nickel and manganese are very expensive invaluable metals. Among them, cobalt is a strategic metal, and its supply is 10 the focus of attention all over the world. Due to the limited number of cobalt producing countries, the global supply of cobalt is unstable. When a supply and demand imbalance of strategic metal occurs, there is a very high possibility that the cost of the raw material will rise. Studies have been made to collect and recycle invaluable metals from lithium 15 secondary batteries (waste batteries) discarded after the expiration date. In addition to waste batteries, resources may be more preferably collected from waste materials discarded after punching the positive electrode plate or the positive electrode in which defects or failures occurred during the process. Currently, the lithium secondary battery is fabricated, as shown in FIG. 1, by 20 coating a positive electrode slurry including a positive electrode active material, a conductive material, a binder and a solvent on a long sheet-type positive electrode current collector 10 such as an aluminum (Al) foil to form a positive electrode active material layer 20, manufacturing a positive electrode sheet 30, and punching a positive electrode 4 plate 40 to a predetermined size. The leftover after punching is discarded as positive electrode scrap 50. If the positive electrode active material is collected and reused from the positive electrode scrap 50, it will be very desirable in the industrial-economic and environmental aspects. 5 Most of the existing methods of collecting the positive electrode active material include dissolving the positive electrode with hydrochloric acid, sulfuric acid, nitric acid or the like, extracting the active material elements such as cobalt, nickel and manganese and using them as raw materials for the positive electrode active material synthesis. However, the active material element extraction using acids uses a non-eco-friendly 10 process to collect pure raw materials, and needs a neutralization process and a waste water treatment process, resulting in the increased process cost. Additionally, it is impossible to collect lithium, one of the key positive electrode active material elements. To overcome these disadvantages, there is a need for a direct reuse method that does not dissolve the positive electrode active material and does not extract the active material in 15 the form of an element. DISCLOSURE Technical Problem The present disclosure is directed to providing a method for collecting and reusing 20 active materials from positive electrode scrap. Technical Solution To achieve the above-described problem, a positive electrode active material reuse 5 method of the present disclosure includes (a) thermally treating positive electrode scrap comprising a lithium composite transition metal oxide positive electrode active material layer comprising nickel, cobalt and manganese on a current collector in air for thermal decomposition of a binder and a conductive material in the active material layer, to 5 separate the current collector from the active material layer, and collecting an active material in the active material layer, (b) washing the collected active material with a lithium compound solution which is basic in an aqueous solution and drying, and (c) annealing the washed active material with an addition of a lithium precursor to obtain a reusable active material. 10 In the present disclosure, the positive electrode active material reuse method may further include (d) surface-coating the annealed active material. The thermal treatment may be performed at 300 to 650℃. The thermal treatment may be performed at 550℃ for 30 min at the temperature rise rate of 5℃/min. 15 The lithium compound solution contains a lithium compound, preferably LiOH, in an amount of more than 0% and 15% or less. The washing may be performed within 1 hour. The washing may be performed by stirring the collected active material at the same time with immersing in the lithium compound solution. 20 The lithium precursor may be at least one of LiOH, Li2CO3, LiNO3 or Li2O. The lithium precursor may be added in an amount for adding lithium at a ratio of lost lithium to a ratio between lithium and other metal in a raw active material used in the active material layer. 6 For example, the lithium precursor may be added in an amount for adding lithium at a molar ratio of 0.001 to 0.4. Further, the lithium precursor is preferably added in an amount for adding more lithium at a molar ratio of 0.0001 to 0.1 based on a 1 : 1 molar ratio of lithium : other 5 metal. The annealing may be performed in air at 400 to 1000℃. A temperature of the annealing step may exceed a melting point of the lithium precursor. The active material in the active material layer may be collected in a form of 10 powder, and carbon produced by carbonization of the binder or the conductive material may not remain on a surface. The surface-coating step may include coating at least one of a metal, an organic metal or a carbon material on the surface by a solid or liquid phase process, and thermally treating at 100 to 1200℃. 15 The reusable active material may be represented by the following Formula 1: [Formula 1] LiaNixMnyCozMwO2+δ where M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, 1 The electrochemical performance is evaluated using each of the positive electrode 20 active materials prepared by the method of examples and comparative examples as described below. Example 1: Reusable active material is collected by the active material reuse method of the present disclosure as described above. Positive electrode scrap discarded 23 after punching the positive electrode plate having NCM-based lithium composite transition metal oxide as the active material is prepared and the thermal treatment of S30 is performed at 550℃ for 30 minutes. The washing of S40 is performed for 10 minutes using LiOH. In S50, annealing is performed at 750℃ for 15 hours with an addition of 5 the lithium precursor (Li2CO3) in an amount for adding more lithium at the molar ratio of 0.09 during the process based on the molar ratio (Inductively Coupled Plasma (ICP) analysis) of lithium and other metal in the raw active material. Theoretically, in the case of fresh active material, the molar ratio of lithium : other metal is 1 : 1, but since an average error of ICP equipment for measuring the molar ratio is ±0.05, and preferably 10 about ±0.02, the molar ratio of lithium : other metal in the raw active material may be 1 ± 0.05 : 1 through ICP measurement. In this experiment, the lithium precursor is added based on the analysis ratio through ICP analysis. Example 2: In addition to example 1, the active material surface protection layer recovery process of S60 is performed. 15 Comparative example 1: Fresh NCM-based lithium composite transition metal oxide, not reusable active material, is used. Comparative example 2: Only thermal treatment of S30 in the active material reuse method of the present disclosure as described above is performed to remove the binder and the conductive material and separate the Al current collector, and NCM-based 20 lithium composite transition metal oxide active material is collected. S30 is performed in the same condition as example 1. In the active material reuse method of the present disclosure, surface modification of S40, crystal structure recovery of S50 and surface coating of S60 are not performed. 24 Comparative example 3: Further to comparative example 2, active material is collected by performing the surface modification of S40 of the active material reuse method of the present disclosure. That is, surface modification is performed, but in the active material reuse method of the present disclosure, crystal structure recovery of S50 5 and surface coating of S60 are not performed. S40 is performed in the same condition as example 1. Comparative example 4: Further to comparative example 2, NCM-based lithium composite transition metal oxide active material is collected by performing the crystal structure recovery of S50 of the active material reuse method of the present disclosure 10 without the surface modification of S40. As opposed to example 1, annealing for crystal structure recovery is performed without lithium precursor addition. Comparative example 5: S30, S40 and S50 of the active material reuse method are performed in the same way as example 1. However, as opposed to example 1, annealing for crystal structure recovery is performed without lithium precursor addition. 15 ICP analysis is performed on the positive electrode active material collected or prepared in each of the examples and comparative examples to analyze an amount of remaining LiF, a ratio of lithium and other metal in the active material, and an amount of a specific element such as B or W. Additionally, the electrochemical performance is evaluated using cells (Coin Half 20 Cell, CHC) manufactured by metering 96.25 wt% of the positive electrode active material collected or prepared in each of the examples and comparative examples, 1.5 wt% of carbon black as the conductive material and 2.25 wt% of PVdF as the binder, mixing with NMP to prepare a slurry and manufacturing the positive electrode. 25 To determine an amount of LiF remaining in the active material collected in comparative examples 2 and 3, F detection and analysis is performed by ICP. The result is shown in the following Table 1. [Table 1] Comparative example 2 Comparative example 3 F content (mg/kg) 1450 ND 5 ND indicates 30 ppm or less as measured. Referring to Table 1, a significant reduction in the F content in the collected positive electrode active material is found in comparative example 3 compared to comparative example 2. That is, it can be seen that LiF is completely dissolved in the lithium compound solution by washing, and thus 10 removed so thoroughly that it cannot be detected by ICP. Accordingly, it can be seen that LiF removal is performed remarkably well by S40. To identify if there is a change of lithium in the positive electrode active material during S30 and S40 of the present disclosure, a ratio of lithium/other metal in the active material is analyzed by ICP. The result is shown in the following Table 2. 15 [Table 2] Comparative example 1 Comparative example 2 Comparative example 3 Ratio of lithium and other metal in active material 0.99 0.95 0.91 Referring to Table 2, it can be seen that comparative example 2 has a reduction in the ratio of lithium/other metal by approximately 0.2 to 0.5 through thermal treatment of S30 compared to comparative example 1, and comparative example 3 has a reduction in 20 the ratio of lithium/other metal by approximately 0.2 to 0.5 through washing and drying of 26 S40 compared to comparative example 2. It seems that NCM-based lithium composite transition metal oxide has a significant reduction in the ratio of lithium to other metal due to a relatively large specific surface area of particles and transformation to the spinel structure. Accordingly, it can be seen that it is necessary to compensate for the deficient 5 lithium. Table 2 shows the values measured by ICP analysis, and ICP analysis has an error value of about ±0.02 as mentioned above. Accordingly, in comparative example 1 of fresh active material, the ratio of lithium and other metal may be smaller than 1. Accordingly, an amount of lithium precursor added to compensate for lithium loss is a 10 reduced amount of lithium based on the ratio (the molar ratio analyzed by ICP) of lithium and other metal in the raw active material (i.e., fresh active material) used in the active material layer. FIGS. 3 and 4 show the results of cell evaluation using the active materials of example and comparative examples. At different currents, the rate performance is 15 evaluated by evaluating the capacity as a function of cycle number. The equipment used for evaluation is a charge/discharge tester commonly used in the lab. There is no difference depending on the measuring device or method. In the graphs of FIGS. 3 and 4, the horizontal axis indicates the cycle number and the vertical axis indicates capacity. Voltage is 3 to 4.3V, and initial formation charge/discharge is performed at 20 0.1C/0.1C. The electrolyte solution for the cell is a carbonate based electrolyte solution and includes Ethylene carbonate (EC):Ethyl methyl carbonate (EMC)=3:7 with an addition of additives. WHAT IS CLAIMED IS: 1. A positive electrode active material reuse method, comprising: (a) thermally treating positive electrode scrap comprising a lithium composite 5 transition metal oxide positive electrode active material layer comprising nickel, cobalt and manganese on a current collector in air for thermal decomposition of a binder and a conductive material in the active material layer, to separate the current collector from the active material layer, and collecting an active material in the active material layer; (b) washing the collected active material with a lithium compound solution which 10 is basic in an aqueous solution and drying; and (c) annealing the washed active material with an addition of a lithium precursor to obtain a reusable active material. 2. The positive electrode active material reuse method according to claim 1, 15 further comprising: (d) surface-coating the annealed active material. 3. The positive electrode active material reuse method according to claim 1, wherein the thermal treatment is performed at 300 to 650℃. 20 4. The positive electrode active material reuse method according to claim 1, wherein the lithium compound solution contains a lithium compound in an amount of more than 0% and 15% or less, and the washing is performed within 1 hour. 34 5. The positive electrode active material reuse method according to claim 1, wherein the washing is performed by stirring the collected active material at the same time with immersing in the lithium compound solution. 5 6. The positive electrode active material reuse method according to claim 1, wherein the lithium precursor used in the annealing is at least one of LiOH, Li2CO3, LiNO3 or Li2O. 10 7. The positive electrode active material reuse method according to claim 1, wherein the lithium precursor is added in an amount for adding lithium at a ratio of lost lithium to a ratio between lithium and other metal in a raw active material used in the active material layer. 15 8. The positive electrode active material reuse method according to claim 7, wherein the lithium precursor is added in an amount for adding lithium at a molar ratio of 0.001 to 0.4. 9. The positive electrode active material reuse method according to claim 7, 20 wherein the lithium precursor is added in an amount for adding more lithium at a molar ratio of 0.0001 to 0.1 based on a 1 : 1 molar ratio of lithium : other metal. 10. The positive electrode active material reuse method according to claim 1, 35 wherein the annealing is performed in air at 400 to 1000℃. 11. The positive electrode active material reuse method according to claim 1, wherein a temperature of the annealing step exceeds a melting point of the lithium 5 precursor. 12. The positive electrode active material reuse method according to claim 1, wherein the active material in the active material layer is collected in a form of powder, and carbon produced by carbonization of the binder or the conductive material does not 10 remain on a surface. 13. The positive electrode active material reuse method according to claim 2, wherein the surface-coating step includes coating at least one of a metal, an organic metal or a carbon material on the surface by a solid or liquid phase process, and thermally 15 treating at 100 to 1200℃. 14. The positive electrode active material reuse method according to claim 1, wherein the reusable active material is represented by the following Formula 1: [Formula 1] 20 LiaNixMnyCozMwO2+δ where M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, 1