The Investigation of Triple-Lithiated Transition Metal Oxides Synthesized from the Spent LiCoO 2

: The environmentally friendly closed cycle of the regeneration process of spent LiCoO 2 was successfully developed and the following synthesis of triple-lithiated transition metal oxides was carried out. A hydrometallurgy recycling route with the usage of 1.5 mol/L of malic acid and 3 vol.% of H 2 O 2 as a leaching solution for cobalt extraction was chosen. The efﬁciency of the cobalt extraction reached 95%. The obtained material was investigated using an X-ray diffraction analysis and the EDX and SEM methods. The electrochemical behavior of the synthesized NCM111 was analyzed and compared to the commercially available material of the same type. The material demonstrated a speciﬁc discharge capacity on the ﬁrst cycle of 163.7 mAh/g. The cyclic resource of the material turned out to be unsatisfactory. In addition, perspective cathode materials, such as NCM622 and NCM811, were obtained. The synthesized materials were analyzed using XRD, SEM, EDX, charge– discharge and cycle life tests, and the CVA and EIS methods. The initial speciﬁc discharge capacities of the NCM622 and NCM811 were 168 and 187 mAh/g, respectively. On the ﬁfth cycle, the NCM622 demonstrated an increasing capacity—to 179 mAh/g, unlike NCM811, as the capacity of this material decreased to 141 mAh/g.


Introduction
The use of lithium-ion batteries has increased significantly in recent years, as, due to their high-energy density, they have found applications in many areas, such as electronic devices, energy storage systems, and electric vehicles.After a thousand charge-discharge cycles, their cycle life comes to an end [1], they become unsuitable for the correct operation of portable devices, and they are then subject to disposal/burial [2].If battery waste is not treated properly, it poses a serious environmental hazard, due to the toxic chemicals such as heavy metals (Co, Ni, and Cu, etc.) contained in the cathode/anode, and organic solvents and fluorinated compounds contained in the electrolyte [3][4][5].In fact, researchers have realized the importance of recycling and seen commercial opportunities in this area.The recycling of spent LIB has attracted a lot of attention in both academic and industrial fields, and the technologies developed over the past years are rapidly transforming [6].In addition, when using LIBs in large quantities with high growth rates of the use of this technology, a significant depletion of the raw materials and limited natural resources of metals (for example, Co) threaten the sustainable manufacturing of batteries [7].The recycling of used batteries can reduce the load from both ecological pollution and the lack of resources in the long term.Due to the limited resources of the materials used in the cell and the environmental problems after the termination of the use of LIB, the post-processing of the valuable metals from spent batteries is essential.
As the most valuable metals are concentrated in the cathode materials, the focus of recycling spent LIBs is the recovery of the metals from the waste cathode materials.

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Cathode materials and aluminum current collectors division using the dissolution method, heat treatment method, dissolution in an alkaline solution method, mechanical method, or separation by ultrasound;

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The separation and extraction of the target metals (e.g., Co, Ni, Mn, Cu, Fe, and Li) from the cathode mass [9]; The synthesis of new cathode material.
However, the established technologies in the industrial sector for processing cathode active materials from battery waste have significant disadvantages [10,11]: There are many complex separation stages and, in general, the processing paths are often complicated; • Some valuable materials may be lost in the recycling process; • Secondary pollution takes place due to the impurities' removal and metal ion precipitation by using various solvents, such as acids and alkalis in most recycling processes;

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The high consumption of chemicals during processing, low extraction efficiency of the valuable metal elements from the end-of-life cathode materials, expensive solvents, and complex processing methods hinder the large-scale application of hydrometallurgical technology in industry;

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In the process of pyrometallurgical processing (i.e., melting), only cobalt, iron, copper, and nickel are extracted in the form of alloys or molten metals, and the main components such as lithium are not extracted, which are lost in the form of slag.Moreover, the recovered alloys require further hydrometallurgical purification; • At the end of the hydrometallurgical recycling process, wastewater is discharged, which must be disposed of.
As is mentioned above, in the description of the established technologies, three main routes [12,13] for LIB recycling exist: pyrometallurgy [14,15], hydrometallurgy [16,17], and biometallurgy [18].For this study, the hydrometallurgy strategy was chosen, which allows for the closed-loop recycling process and final products of a high purity to be obtained.The hydrometallurgical route includes leaching (acid or alkali), purification and separation steps, and product recovery.The comparison table of the already studied usages of inorganic and organic acids for the leaching process is presented in Table 1.Based on the conducted studies with usage of organic acid, it can be concluded that a new cathode material with good electrochemical features can be successfully recovered using the sol-gel method [17,[29][30][31]37], in which organic acid can act as both a chelating agent and leaching agent.
Nevertheless, none of the existing studies on the regeneration of cathode materials from spent batteries has considered the strategy of the «closed cycle», in which valuable metal components are regenerated from spent batteries with a LiCoO 2 cathode, and on the basis of the extracted materials, the synthesis of the triple-lithium oxides of cathode materials (Li(Ni x Co y Mn z )O 2 ) is carried out.
This work aims at the methodological development of cobalt extraction from spent Li-ion batteries using a hydrometallurgical process with an organic acid leaching solution, which allows for the use of a cobalt-containing leachate with additional salts of Li, Ni, and Mn as a precursor for the following synthesis of triple-lithiated transition metals oxide NCM.

Cobalt Extraction and NCM Synthesis
As the initial material, a cathode with an aluminum current collector from a spent lithium-ion battery was used as the cobalt source.The spent battery was fully discharged into a 5% NaCl solution for 24 h, then disassembled, and the cathode was separated from the other parts of the battery.The cathode plates were plunged into an acetone solution for 24 h, washed with distilled water to remove the electrolyte salts, and then dried in a vacuum at 95 • C.
The cathode material was leached in a 1.5 mol/L malic acid solution with 3 vol.% of H 2 O 2 at 90 • C with stirring for 1 h.The reaction involved in the leaching was as follows: The undissolved residue was removed via filtering in order to obtain the leachate solution containing Co 2+ ions.After this, Ni, Mn, and Li acetates were added to the leachate solution in a stoichiometric ratio in order to subsequently obtain the NCM material.The calculation was carried out in the following way: after the end of the leaching process, the filtrated residue was dried for 24 h and weighted.The obtained mass was subtracted from the initial cathode mass-this was the theoretical dissolved cathode mass in the solution.This value was multiplied by 0.92 to obtain the active mass in the solution.The most common ratio of cathode material: binder PVDF: conductive additive is 92:5:3, which is used while coating on a current collector.Afterwards, the active mass was multiplied by 0.59-this was theoretical cobalt mass in the solution.Then, this value was divided by the Co molar mass (59 g/mol) to obtain the amount of Co 2+ ions.Furthermore, to calculate the NCM111 amount, the cobalt amount was multiplied by 3.Then, the masses of Ni(CH 3 COO) 2 •4H 2 O (NiAc), Mn(CH 3 COO) 2 •4H 2 O (MnAc), and CH 3 COOLi•2H 2 O (LiAc) were calculated based on the substance amounts (the NiAc and MnAc amounts were equal to the Co amount, and the LiAc value was equal to the NCM111 amount) and respective molar masses.The next step was water evaporation from the resulting solution with the forced removal of gases.The obtained precipitate was used as the precursor for the following synthesis of the NCM cathode material through heat treatment.The scheme of the process is presented on Figure 1.The heat treatment stages are described in more detail in the Supplementary Materials.

Investigation of the Cobalt Extraction Degree Dependence on the Leaching Time
To analyze the effect of the leaching time on the degree of the cobalt extraction from spent cathode material, 5 samples were taken every 20 min during the leaching and then synthesis was carried out according to the method described in the Section 2.1.Nickel acetate in the amount of 0.5 g was added to the precursors as a comparative element for the following elemental analysis.The graph is presented in the Supplementary Materials.

Investigation of the Cobalt Extraction Degree Dependence on the Leaching Time
To analyze the effect of the leaching time on the degree of the cobalt extractio spent cathode material, 5 samples were taken every 20 min during the leaching an synthesis was carried out according to the method described in the Section 2.1.acetate in the amount of 0.5 g was added to the precursors as a comparative elem the following elemental analysis.The graph is presented in the Supplementary Ma To determine the amount of extracted cobalt, the elemental composition w lyzed using the EDX method.

Elemental Analysis and Material Characterization
The morphology and microstructure of the synthesized sample were studied Mira 3 Tescan scanning electron microscope in the SE (secondary electrons) mod chemical composition of the powder was studied on an electron microscope using spectroscopy with an energy dispersion detector from EDX Oxford Instruments 80.An X-ray phase analysis of the obtained samples was performed on a Bruker vance diffractometer (CuKa = 1.5406Å) in the angle range of 15-85 degrees, with a 0.030 and an exposure of 0.8 s at each step.The identification of the phase comp was carried out using the DIFFRAC.EVA V5.0 program.The structural parameter refined using the Rietveld method using TOPAS5 software.The granulometric co tion of the sample was analyzed using Fritsch Analysette 22 NanoTec equipment.
To determine the electrochemical behavior of the materials, electrodes we pared.The composition of the electrode slurry was: 92% of the cathode active m 3% of PVDF as a binder (trade mark Solef 5130), and 5% of carbon black (Supe methylpyrrolidone was used as a solvent.The obtained suspension was applied to num foil using the film coater MSK-AFA-III, MTI Corp.The clearance height was 2 The next step was drying the electrodes, followed by rolling for compaction.Aft circles with a diameter of 14 mm were cut out of the electrode sheet to assemble co of the CR2032 type.Lithium metal was used as the anode material, TC-E918 (Tinki) is a solution of LiPF6 in a mixture of organic carbonates, was used as an electroly Celgard 2325 was used as a separator.
The electrochemical characteristics during charging and discharging were me using the Netware coin cell-5 V 10 mA Battery Test System.The Cyclic voltammet and electrochemical impedance spectroscopy (EIS) measurements were carried o To determine the amount of extracted cobalt, the elemental composition was analyzed using the EDX method.

Elemental Analysis and Material Characterization
The morphology and microstructure of the synthesized sample were studied using a Mira 3 Tescan scanning electron microscope in the SE (secondary electrons) mode.The chemical composition of the powder was studied on an electron microscope using X-ray spectroscopy with an energy dispersion detector from EDX Oxford Instruments X-Max 80.An X-ray phase analysis of the obtained samples was performed on a Bruker D8 Advance diffractometer (CuKa = 1.5406Å) in the angle range of 15-85 degrees, with a step of 0.030 and an exposure of 0.8 s at each step.The identification of the phase composition was carried out using the DIFFRAC.EVA V5.0 program.The structural parameters were refined using the Rietveld method using TOPAS5 software.The granulometric composition of the sample was analyzed using Fritsch Analysette 22 NanoTec equipment.
To determine the electrochemical behavior of the materials, electrodes were prepared.The composition of the electrode slurry was: 92% of the cathode active material, 3% of PVDF as a binder (trade mark Solef 5130), and 5% of carbon black (SuperP).N-methylpyrrolidone was used as a solvent.The obtained suspension was applied to aluminum foil using the film coater MSK-AFA-III, MTI Corp.The clearance height was 200 µm.The next step was drying the electrodes, followed by rolling for compaction.After that, circles with a diameter of 14 mm were cut out of the electrode sheet to assemble coin cells of the CR2032 type.Lithium metal was used as the anode material, TC-E918 (Tinki), which is a solution of LiPF6 in a mixture of organic carbonates, was used as an electrolyte, and Celgard 2325 was used as a separator.
The electrochemical characteristics during charging and discharging were measured using the Netware coin cell-5 V 10 mA Battery Test System.The Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were carried out on a Cortest CS310 potentiostat.The CV conditions were: scanning speed-0.1 mVs −1 ; potential range-2.5-4.3V; and EIS frequency range-0.01Hz to 100 kHz.range-2.5-4.3V; and EIS frequency range-0.01Hz to 100 kHz.

Characterization of Initial Material
Figure 2 shows a diffractogram of the initial cathode material of the LCO type.Lithium cobalt oxide peaks belonging to the spatial group R3 m are clearly observed.In addition, Co3O4 peaks belonging to the Fd-3m group are observed, which can be explained by the fact that, during the charging process, the Li2O/Co mixture could be oxidized into Co, and then the Li2O/CoO mixture could result in the formation of Co3O4 in the higher-voltage region [38].Table 2 shows the chemical composition in atomic percentages of the starting material obtained using the EDX method.Apparently, 8.21 atomic percent of cobalt was present in the material, which made it possible to use this cathode material as a cobalt source for the subsequent extraction.The SEM image of initial material is presented in the Supplementary Materials.

Analysis of Synthesized Material
Figure 3 shows an X-ray diffractogram of the synthesized cathode material of the NCM111 obtained based on the extracted cobalt, and for comparison, a diffractogram of commercial NCM111 material is also added.The patterns of the synthesized NCM material were indexed to layered oxide with an R-3m space group without any peaks of the impurity phase.The peaks were consistent with the standard card of Li(Ni1/3 Co1/3Mn 1/3)O2 (PDF#01-075-9200).The distinct peak split corresponding to the (006)/(102) planes suggests a well-ordered, layered structure.Table 2 shows the chemical composition in atomic percentages of the starting material obtained using the EDX method.Apparently, 8.21 atomic percent of cobalt was present in the material, which made it possible to use this cathode material as a cobalt source for the subsequent extraction.The SEM image of initial material is presented in the Supplementary Materials.

Analysis of Synthesized Material
Figure 3 shows an X-ray diffractogram of the synthesized cathode material of the NCM111 obtained based on the extracted cobalt, and for comparison, a diffractogram of commercial NCM111 material is also added.The patterns of the synthesized NCM material were indexed to layered oxide with an R-3m space group without any peaks of the impurity phase.The peaks were consistent with the standard card of Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 (PDF#01-075-9200).The distinct peak split corresponding to the (006)/(102) planes suggests a well-ordered, layered structure.
Additionally, it is highly recommended for cathode materials to be analyzed according to the following parameters [39][40][41]: 1.
The split of the peaks I006/I102 (2θ~36 • )-this parameter indicates a good ordering of the hexagonal lattice, and peak separation was present both in the synthesized and commercial NCM111.

2.
R-factor, R = (I006 + I102)/I101-the lower the value of this parameter, the higher the ordering of the structure (for good materials < 0.5); for both materials, this parameter was higher than it should have been: for commercial, it was 0.597, and for synthesized, it was 0.866.

3.
The ratio I003/I104 (2θ 003~20 • , 2θ 104~45 • ).The smaller this ratio, the closer the lattice is to cubic.In the context of these materials, this parameter characterizes cationic mixing and, for good materials, should be >1.2.For the commercial material, it was a little bit higher than that for the obtained (1543 and 1442, respectively).Additionally, it is highly recommended for cathode materials to be analyzed according to the following parameters [39][40][41]: 1.The split of the peaks I006/I102 (2θ~36°)-this parameter indicates a good ordering of the hexagonal lattice, and peak separation was present both in the synthesized and commercial NCM111.2. R-factor, R = (I006 + I102)/I101-the lower the value of this parameter, the higher the ordering of the structure (for good materials < 0.5); for both materials, this parameter was higher than it should have been: for commercial, it was 0.597, and for synthesized, it was 0.866.3. The ratio I003/I104 (2θ 003~20°, 2θ 104~45°).The smaller this ratio, the closer the lattice is to cubic.In the context of these materials, this parameter characterizes cationic mixing and, for good materials, should be > 1.2.For the commercial material, it was a little bit higher than that for the obtained (1543 and 1442, respectively).
Obviously, the R-factor of the obtained NCM materials after the cobalt extraction was extremely high for these types of materials.Probably, this could have been a result of the influence of the sol-gel synthesis on the powder structure.The ratio of the 003 and 104 peaks was lower than the ratio of the commercial material, but still more than 1.2; hence, the crystal lattice was hexagonal.The structural parameters of both materials are presented in the Supplementary Materials.
Figure 4 demonstrates the results of the morphology study of the synthesized sample obtained using scanning electron microscopy in the secondary electron mode.Apparently, the powder had rounded particles with an average particle size of 300 nm −1 microns, with a uniform particle size distribution.In addition, the agglomeration of particles in the sample was quite high.It is well known that a small particle size and uniform size distribution contribute to the rapid migration of Li + ions, which can contribute to obtaining excellent electrochemical characteristics [42].Obviously, the R-factor of the obtained NCM materials after the cobalt extraction was extremely high for these types of materials.Probably, this could have been a result of the influence of the sol-gel synthesis on the powder structure.The ratio of the 003 and 104 peaks was lower than the ratio of the commercial material, but still more than 1.2; hence, the crystal lattice was hexagonal.The structural parameters of both materials are presented in the Supplementary Materials.
Figure 4 demonstrates the results of the morphology study of the synthesized sample obtained using scanning electron microscopy in the secondary electron mode.Apparently, the powder had rounded particles with an average particle size of 300 nm −1 microns, with a uniform particle size distribution.In addition, the agglomeration of particles in the sample was quite high.It is well known that a small particle size and uniform size distribution contribute to the rapid migration of Li + ions, which can contribute to obtaining excellent electrochemical characteristics [42].In Table 3, the particle size distribution is presented.The material was prepared before the analysis of the particle size distribution via grinding in an agate mortar.In Table 3, the particle size distribution is presented.The material was prepared before the analysis of the particle size distribution via grinding in an agate mortar.The chemical composition of the obtained material was analyzed using energy dispersive X-ray spectroscopy.The results are presented in Table 4. Thus, the atomic ratio of the transition metals in the synthesized material was Li(Ni 0.35 Co 0.3 Mn 0.35 )O 2 , which is quite close to the theoretically calculated NCM111.In the synthesized material, the amount of cobalt was slightly less than that theoretically calculated, which resulted in a shift in the atomic ratio towards the added nickel and manganese.The cobalt in the composition of layered cathode materials of the NCM type is responsible for increasing their kinetics, low-temperature properties, initial discharge capacity, and thermal stability [43].A low cobalt content is likely to degrade these characteristics.

Electrochemical Characteristics of Obtained Material
The electrochemical characteristics of the obtained material are illustrated in Figure 5. Figure 5a shows the charge/discharge curves at the 1st and 10th cycles at a current rate of 0.1 C and in the voltage range of 2.8-4.3V for the synthesized (SNCM) and 2.6-4.3V for the commercial (CNCM) materials.The synthesized material at the 1st cycle demonstrated a charging capacity of 164.7 mAh/g, a discharge capacity of 163.7 mAh/g, and the Coulomb efficiency for the 1st cycle was 99%, while the capacities for the 10th cycle were 158.2 and 159.4,respectively.The Coulomb efficiency of the material being close to 100% at all 10 cycles indicated a reversible intercalation/deintercalation of the lithium.A slight drop in the capacity during the cycling indicated a sufficient stability of the structure.The shape of the charge-discharge curves was typical for layered cathode materials and there was no clearly defined discharge area.The commercial material at the 1st cycle demonstrated a charging capacity of 153.0 mAh/g, a discharge capacity of 133.0 mAh/g, and the Coulomb efficiency for the 1st cycle was 87%, while for the 10th cycle, the capacities were 140.9 and 139.6, respectively, and the Coulomb efficiency was 99%.Hence, the synthesized NCM111 was not inferior in terms of its electrochemical characteristics compared to the commercially available material of such a type.
The cyclic resource of the material was also investigated and the results are illustrated in Figure 5b.At the 1st cycle, the charge and discharge capacities were 137.73 and 136.16 mAh/g, and at the 60th cycle, the charging and discharging capacities were 112.21 and 107.0 mAh/g, respectively.The capacity loss over 60 cycles was 21.5%.This drop in capacity during the cycling can be explained by the sufficiently high value of the R-factor (0.866), since this parameter indicates that the structure in the sample was not ordered.
In addition, for the obtained material, a current load study was carried out with subsequent relaxation to determine the stability of the material structure, and the results are demonstrated in Figure 5c.The material was tested with discharge currents corresponding to five-hour, one-hour, and twenty-minute discharges.The discharge was carried out with a current of 0.2 C for the first eight cycles.The drop in capacity relative to the fivehour discharge cycle, for discharge with a current of 1 C, was 61%, and with a current of 3 C, it was 43%.When discharged with a current of 0.2 C after 24 cycles of current load, the material was close to the initial capacity values, which meant that the material was quite stable.
(0.866), since this parameter indicates that the structure in the sample was not ordere In addition, for the obtained material, a current load study was carried out with sequent relaxation to determine the stability of the material structure, and the results demonstrated in Figure 5c.The material was tested with discharge currents correspo ing to five-hour, one-hour, and twenty-minute discharges.The discharge was carried with a current of 0.2 C for the first eight cycles.The drop in capacity relative to the hour discharge cycle, for discharge with a current of 1 C, was 61%, and with a curren 3 C, it was 43%.When discharged with a current of 0.2 C after 24 cycles of current l the material was close to the initial capacity values, which meant that the material quite stable.

Comparison of 2 NCM Materials of Different Chemistry Type, Synthesized Using Developed Methodology
To analyze the possibility of using the developed methodology for the cobalt extraction in a consequent synthesis of perspective NCM material, two comparative iterations were carried out: syntheses of NCM622 and NCM811.The chemical and phase compositions, morphology, structure, and electrochemical characteristics of the obtained materials were investigated.
The synthesis method was the same as that described in Section 2.1, except with regard to NCM811.The heat treatment of this precursor was carried out in a tube furnace in oxygen flow, with a flow rate of 20 mL/min.The necessity of heat treatment in oxygen ambiance is explained by the fact that, with a lack of oxygen (in air atmosphere), nonstoichiometric oxide lithium-nickel is formed (Li (1−z )Ni (1+z) O 2 ) [44].If this phase is present in synthesized material, at the 1st cycle of charge-discharge, the additional Ni 2+ ions (1 + z) will cause structure destruction, which leads to poor electrochemical behavior of the material.The effect of nonstoichiometric lithium-nickel oxide forming was investigated, and it was found that Ni 2+ is formed in a lack of oxygen, instead of Ni 3+ , and the Ni 2+ is stable.Based on this fact, to decrease the forming of such undesired oxides, the synthesis of Ni-rich cathode materials should be carried out in oxygen flow.
The synthesized NCM622 and NCM811 cathodes' powders were analyzed in terms of particle size distribution and the results are presented in Table 5.The materials were prepared before the analysis of the particle size distribution via grinding in an agate mortar.In total, 90% of the particles were less than 35.3 mkm for NCM622 and less than 29.1 mkm for the NCM811 material.These values were greater than those of the commercial materials, but the following treatment, such as milling and granulation, will probably increase the characteristics.A comparative diffractogram of the synthesized materials is presented in Figure 6.Obviously, typical peaks of the phase of triple-lithiated transition metal oxide NCM are observed in the two synthesized materials.All the materials had a separation of peaks 006/102 and 108/110, which indicates a good ordering of the layered structure of the materials.Due to the heat treatment of the precursor for the synthesis of the NCM811 material in oxygen flow, it was possible to obtain a material with a good crystallinity.The values of the R-factor for all the materials turned out to be lower than that of the material described in Section 3.3; for NCM622, it was 0.739, and for NCM811, it was 0.685.At the same time, the ratio of peaks 003/104 in the NCM811 material was significantly lower than that in the other cathode material, at 1.896 vs. 1.372.This phenomenon is explained by the fact that the amount of nickel relative to the amount of lithium in 811 was greater than that in the other cathode materials, as a result of which, the cationic mixing of nickel and lithium ions was more expressed, the layered structure was less ordered, and it could be assumed that the capacitance characteristics of this material would be worse.The structural parameters of both materials are presented in the Supplementary Materials.
The scanning electron microphotographs of the obtained NCM622 and NCM811 materials in the secondary electron mode are illustrated in Figure 7. Figure 7a,b illustrate NCM622.It is apparent that the material consisted of rounded particles with a size of 0.5-1 microns, and also that the particles were agglomerated.The NCM811 microphotographs are presented in Figure 7c,d.The particles of this material were fragmented, and this fact can be explained by the bigger amount of nickel in its composition.At a high magnification, it can be observed that the sintered fragmented particles consisted of small particles The values of the R-factor for all the materials turned out to be lower than that of the material described in Section 3.3; for NCM622, it was 0.739, and for NCM811, it was 0.685.At the same time, the ratio of peaks 003/104 in the NCM811 material was significantly lower than that in the other cathode material, at 1.896 vs. 1.372.This phenomenon is explained by the fact that the amount of nickel relative to the amount of lithium in 811 was greater than that in the other cathode materials, as a result of which, the cationic mixing of nickel and lithium ions was more expressed, the layered structure was less ordered, and it could be assumed that the capacitance characteristics of this material would be worse.The structural parameters of both materials are presented in the Supplementary Materials.
The scanning electron microphotographs of the obtained NCM622 and NCM811 materials in the secondary electron mode are illustrated in Figure 7. Figure 7a,b illustrate NCM622.It is apparent that the material consisted of rounded particles with a size of 0.5-1 microns, and also that the particles were agglomerated.The NCM811 microphotographs are presented in Figure 7c,d.The particles of this material were fragmented, and this fact can be explained by the bigger amount of nickel in its composition.At a high magnification, it can be observed that the sintered fragmented particles consisted of small particles of the same f shape, with sizes ranging from 0.5 to 1 microns.The chemical composition of the synthesized materials in terms of atomic percentage is presented in Table 6.Thus, the atomic ratio of the transition metals in the obtained materials for the calculated NCM622 was LiNi0.60Co0.17Mn0.22O2,and for the calculated NCM811, was LiNi0.80Co0.10Mn0.10O2.The obtained results were close to the theoretically calculated ratios, and there was a slightly reduced cobalt content relative to that theoretically calculated, which was likely to affect the initial capacitance characteristics.There was also the presence of more than 1% aluminum, which probably got into the precursor during the extraction of the cobalt from the aluminum current collector.The introduction of an Al 3+ ion increased the Ni 3+ ratio and limited the mixing of cations.Compared to the unmodified samples, the cathode material NCM811 doped with Al 3+ demonstrated an excellent cycling performance with a capacity retention of 70% at 10 °C after 1000 charge-discharge cycles [45].In addition, doping in the precursor was useful for reducing the energy potential, which led to a more uniform distribution of elements and a reduction in binding deficiencies during the subsequent calcination process.It is noteworthy that the alloying of Al could suppress the effect of cationic mixing and reduce the destruction of the structure of the material during charging [46].

Electrochemical Behavior of NCM622 and NCM811
Figure 8 illustrates the electrochemical behavior of the synthesized NCM622 and NCM811.In Figure 8a, charge-discharge curves at a current rate of 0.1 C and in a voltage range of 2.8-4.3V at the 1st and 5th cycles are presented.The initial charging and discharge capacities of the NCM622 were 169 and 168 mAh/g, and those of the NCM811 were The chemical composition of the synthesized materials in terms of atomic percentage is presented in Table 6.Thus, the atomic ratio of the transition metals in the obtained materials for the calculated NCM622 was LiNi 0.60 Co 0.17 Mn 0.22 O 2 , and for the calculated NCM811, was LiNi 0.80 Co 0.10 Mn 0.10 O 2 .The obtained results were close to the theoretically calculated ratios, and there was a slightly reduced cobalt content relative to that theoretically calculated, which was likely to affect the initial capacitance characteristics.There was also the presence of more than 1% aluminum, which probably got into the precursor during the extraction of the cobalt from the aluminum current collector.The introduction of an Al 3+ ion increased the Ni 3+ ratio and limited the mixing of cations.Compared to the unmodified samples, the cathode material NCM811 doped with Al 3+ demonstrated an excellent cycling performance with a capacity retention of 70% at 10 • C after 1000 charge-discharge cycles [45].In addition, doping in the precursor was useful for reducing the energy potential, which led to a more uniform distribution of elements and a reduction in binding deficiencies during the subsequent calcination process.It is noteworthy that the alloying of Al could suppress the effect of cationic mixing and reduce the destruction of the structure of the material during charging [46].

Electrochemical Behavior of NCM622 and NCM811
Figure 8 illustrates the electrochemical behavior of the synthesized NCM622 and NCM811.In Figure 8a, charge-discharge curves at a current rate of 0.1 C and in a voltage range of 2.8-4.3V at the 1st and 5th cycles are presented.The initial charging and discharge capacities of the NCM622 were 169 and 168 mAh/g, and those of the NCM811 were 235 and 187 mAh/g, respectively.The Coulomb efficiency for 622 was 99%, and for 811, was 80%.At cycle 5, the charging and discharging capacities for NCM622 were 180 and 179, and for NCM811, were 146 and 141 mAh/g, respectively.The Coulomb efficiency for NCM622 was 99.3%, and for NCM811, it was 96.5%.The unsatisfactory capacitance characteristics of material 811 after five cycles were explained by the low ordering of the structure and the high cationic mixing.The increase in capacity on cycle 5 for material 622 may have been because of working out the active mass.
Batteries 2023, 9, x FOR PEER REVIEW 12 was 80%.At cycle 5, the charging and discharging capacities for NCM622 were 18 179, and for NCM811, were 146 and 141 mAh/g, respectively.The Coulomb efficien NCM622 was 99.3%, and for NCM811, it was 96.5%.The unsatisfactory capacitance acteristics of material 811 after five cycles were explained by the low ordering of the s ture and the high cationic mixing.The increase in capacity on cycle 5 for material 622 have been because of working out the active mass.The Coulomb efficiency of the material being close to 100% indicates a reversib tercalation/deintercalation of the lithium, indicating a sufficient stability of the stru The shape of the charge-discharge curves was typical for layered cathode material there was no clearly defined discharge area.The medium-discharge voltage of the rial NCM622 was higher than that of NCM811, which indicates that the materia higher energy intensity values.At the same time, the charging curve of 622 was lower that of 811, which indicates a low internal resistance of the material.
Both synthesized materials were analyzed for a cyclic resource and the resu graph is presented in Figure 8b.The capacity drop in NCM622 for 28 cycles was 13% in NCM811 it was 55%.The large drop in the capacity of the NCM811 was due to the cationic mixing, which had an extremely negative effect on the capacitance character of the material.
The synthesized materials were also investigated using cyclic voltammetry an polarization curves are shown in Figure 8c.This method for analyzing the electroche characteristics of a material allows for the reversibility of the electrode reactions to b alyzed, whether side reactions are present on the electrode to be determined, and allows for the kinetics of the electrode reactions in different materials to be compared The Coulomb efficiency of the material being close to 100% indicates a reversible intercalation/deintercalation of the lithium, indicating a sufficient stability of the structure.The shape of the charge-discharge curves was typical for layered cathode materials and there was no clearly defined discharge area.The medium-discharge voltage of the material NCM622 was higher than that of NCM811, which indicates that the material had higher energy intensity values.At the same time, the charging curve of 622 was lower than that of 811, which indicates a low internal resistance of the material.
Both synthesized materials were analyzed for a cyclic resource and the resulting graph is presented in Figure 8b.The capacity drop in NCM622 for 28 cycles was 13% and in NCM811 it was 55%.The large drop in the capacity of the NCM811 was due to the high cationic mixing, which had an extremely negative effect on the capacitance characteristics of the material.
The synthesized materials were also investigated using cyclic voltammetry and the polarization curves are shown in Figure 8c.This method for analyzing the electrochemical characteristics of a material allows for the reversibility of the electrode reactions to be analyzed, whether side reactions are present on the electrode to be determined, and also allows for the kinetics of the electrode reactions in different materials to be compared.The peak of the cathode potential was 3.94 V, and that of the anode potential was 3.58 V.According to the literature [47], those peaks refer to a reversible intercalation of the Li + ions.In the cathode and anode regions for the NCM622 material, the peaks of the potentials of the reversible process of the deintercalation/intercalation of the lithium ions are clearly observed.The peak of the cathode potential was 3.94 V and that of the anode potential was 3.58 V. Peaks of side electrode reactions were not observed.
Peaks of reversible intercalation/deintercalation potentials were also observed for the material NCM811.The cathode peak was present at 3.79 V, and the anode peak at 3.69 V.In addition to these, there were also less obvious redox peaks at 4.03/3.95V and 4.26/4.18V, which appeared during the charge due to multiphase transitions from hexagonal to monoclinic (H1/M), from monoclinic to hexagonal (M/H2), and from hexagonal to hexagonal (H2/H3) [48].The absence of an H2/H3 phase transition with a lower Ni content in the material NCM622 indicated a good reversibility of the electrode and significantly affected the stability of the material structure, which also explained the lower loss of capacitance during charge/discharge of the material NCM622.

Electrochemical Impedance Spectroscopy Investigation
The impedance of the cathode materials obtained was investigated in a two-electrode cell, which was a CR2032 tablet layout, where lithium foil was used as an antielectrode.The impedance measurement was carried out on the Correct CS310 installation in the frequency range from 1.5 × 105 Hz to 0.01 Hz.The measurements were carried out in the infected state up to a potential of 4.3 V and the amplitude of the oscillations was 10 mV.The modeling of the impedance spectra was carried out using the ZView program.The impedance hodographs of the studied samples are presented in Figure 9.It is worth noting that usually when modeling impedance, an equivalent circuit is used, as shown in Figure 10.In this diagram, R1 is the resistance of the cell elements: the housing, spacers, and other components, R2 is the resistance of the CEI film (cathode electrolyte interface), and R3 is the charge transfer resistance.Each block of elements is characterized by a semicircle on the impedance hodograph.
Batteries 2023, 9, x FOR PEER REVIEW 13 of 17 peak of the cathode potential was 3.94 V, and that of the anode potential was 3.58 V.According to the literature [47], those peaks refer to a reversible intercalation of the Li + ions.
In the cathode and anode regions for the NCM622 material, the peaks of the potentials of the reversible process of the deintercalation/intercalation of the lithium ions are clearly observed.The peak of the cathode potential was 3.94 V and that of the anode potential was 3.58 V. Peaks of side electrode reactions were not observed.Peaks of reversible intercalation/deintercalation potentials were also observed for the material NCM811.The cathode peak was present at 3.79 V, and the anode peak at 3.69 V.In addition to these, there were also less obvious redox peaks at 4.03/3.95V and 4.26/4.18V, which appeared during the charge due to multiphase transitions from hexagonal to monoclinic (H1/M), from monoclinic to hexagonal (M/H2), and from hexagonal to hexagonal (H2/H3) [48].The absence of an H2/H3 phase transition with a lower Ni content in the material NCM622 indicated a good reversibility of the electrode and significantly affected the stability of the material structure, which also explained the lower loss of capacitance during charge/discharge of the material NCM622.

Electrochemical Impedance Spectroscopy Investigation
The impedance of the cathode materials obtained was investigated in a two-electrode cell, which was a CR2032 tablet layout, where lithium foil was used as an antielectrode.The impedance measurement was carried out on the Correct CS310 installation in the frequency range from 1.5 * ×105 Hz to 0.01 Hz.The measurements were carried out in the infected state up to a potential of 4.3 V and the amplitude of the oscillations was 10 mV.The modeling of the impedance spectra was carried out using the ZView program.The impedance hodographs of the studied samples are presented in Figure 9.It is worth noting that usually when modeling impedance, an equivalent circuit is used, as shown in Figure 10.In this diagram, R1 is the resistance of the cell elements: the housing, spacers, and other components, R2 is the resistance of the CEI film (cathode electrolyte interface), and R3 is the charge transfer resistance.Each block of elements is characterized by a semicircle on the impedance hodograph.It is worth noting that, for samples NCM 111 and 622, there was no semicircle in the high-frequency region of the spectrum associated with the CEI response.For NCM 811, three semicircles can be observed, instead of two classic ones.Taking into account the corresponding forms of impedance hodographs, the simulation was carried out according to the schemes shown in Figure 11.It can be assumed that a different shape of the hodograph for NCM 811 is associated with phase transitions, which were also noticeable on the CVA graphs.Since the equivalent circuits were used differently, it is proposed to compare the total resistance of the samples, minus R1, since it did not relate to the material under study (Table 7).From the presented data, the sample NCM622 had the highest total resistance.The other two samples were comparable, but the sample NCM811 had the least resistance.In addition, since the "tail" of diffusion was the largest in this sample, this also indicates better kinetics for this material.Sample modeling parameters are presented in the Supplementary Materials.

Conclusions
This paper described the synthesis of different types of triple-lithiated transition metal oxides from spent LiCoO2, with use of extracted cobalt malate and Ni, Mn, and Li acetates using the sol-gel method, followed by a three-stage thermal treatment.The obtained material was investigated using different methods, such as XRD, SEM, and EDX.The initial capacities of the synthesized NCM111 were equal to 163.7 mAh/g and 159.4 mAh/g at the 10th cycle, under a current rate of 0.1 C. The resulting values corresponded to the requirements of commercial materials of the same type.The cycle life study of the material showed a drop of 21.5% after 60 cycles, which could be explained by the high value of the R-factor and disorder of the layered structure.The different current load study demonstrated that the obtained NCM111 was stable.
To analyze the possibility of using the developed synthesis method for obtaining perspective cathode materials, such as NCM622 and NCM811, two comparative iterations were carried out.The synthesis of NCM811 was carried out in oxygen flow to minimize the formation of nonstoichiometric oxide Li(1−z)Ni(1+z)O2, which could lead to structure destruction and as a result, poor electrochemical behavior of the material.The obtained materials were investigated using different analytical methods, such as XRD, SEM, EDX, CVA, and EIS.The initial discharge capacities of NCM622 and NCM811 were 169 and 187 mAh/g, respectively.The drop of capacity in the cycling tests was 13% for NCM 622 and It is worth noting that, for samples NCM 111 and 622, there was no semicircle in the high-frequency region of the spectrum associated with the CEI response.For NCM 811, three semicircles can be observed, instead of two classic ones.Taking into account the corresponding forms of impedance hodographs, the simulation was carried out according to the schemes shown in Figure 11.It can be assumed that a different shape of the hodograph for NCM 811 is associated with phase transitions, which were also noticeable on the CVA graphs.Since the equivalent circuits were used differently, it is proposed to compare the total resistance of the samples, minus R1, since it did not relate to the material under study (Table 7).It is worth noting that, for samples NCM 111 and 622, there was no semicircle in the high-frequency region of the spectrum associated with the CEI response.For NCM 811, three semicircles can be observed, instead of two classic ones.Taking into account the corresponding forms of impedance hodographs, the simulation was carried out according to the schemes shown in Figure 11.It can be assumed that a different shape of the hodograph for NCM 811 is associated with phase transitions, which were also noticeable on the CVA graphs.Since the equivalent circuits were used differently, it is proposed to compare the total resistance of the samples, minus R1, since it did not relate to the material under study (Table 7).From the presented data, the sample NCM622 had the highest total resistance.The other two samples were comparable, but the sample NCM811 had the least resistance.In addition, since the "tail" of diffusion was the largest in this sample, this also indicates better kinetics for this material.Sample modeling parameters are presented in the Supplementary Materials.

Conclusions
This paper described the synthesis of different types of triple-lithiated transition metal oxides from spent LiCoO2, with use of extracted cobalt malate and Ni, Mn, and Li acetates using the sol-gel method, followed by a three-stage thermal treatment.The obtained material was investigated using different methods, such as XRD, SEM, and EDX.The initial capacities of the synthesized NCM111 were equal to 163.7 mAh/g and 159.4 mAh/g at the 10th cycle, under a current rate of 0.1 C. The resulting values corresponded to the requirements of commercial materials of the same type.The cycle life study of the material showed a drop of 21.5% after 60 cycles, which could be explained by the high value of the R-factor and disorder of the layered structure.The different current load study demonstrated that the obtained NCM111 was stable.
To analyze the possibility of using the developed synthesis method for obtaining perspective cathode materials, such as NCM622 and NCM811, two comparative iterations were carried out.The synthesis of NCM811 was carried out in oxygen flow to minimize the formation of nonstoichiometric oxide Li(1−z)Ni(1+z)O2, which could lead to structure destruction and as a result, poor electrochemical behavior of the material.The obtained materials were investigated using different analytical methods, such as XRD, SEM, EDX, CVA, and EIS.The initial discharge capacities of NCM622 and NCM811 were 169 and 187 mAh/g, respectively.The drop of capacity in the cycling tests was 13% for NCM 622 and  From the presented data, the sample NCM622 had the highest total resistance.The other two samples were comparable, but the sample NCM811 had the least resistance.In addition, since the "tail" of diffusion was the largest in this sample, this also indicates better kinetics for this material.Sample modeling parameters are presented in the Supplementary Materials.

Conclusions
This paper described the synthesis of different types of triple-lithiated transition metal oxides from spent LiCoO 2 , with use of extracted cobalt malate and Ni, Mn, and Li acetates using the sol-gel method, followed by a three-stage thermal treatment.The obtained material was investigated using different methods, such as XRD, SEM, and EDX.The initial capacities of the synthesized NCM111 were equal to 163.7 mAh/g and 159.4 mAh/g at the 10th cycle, under a current rate of 0.1 C. The resulting values corresponded to the requirements of commercial materials of the same type.The cycle life study of the material showed a drop of 21.5% after 60 cycles, which could be explained by the high value of the Rfactor and disorder of the layered structure.The different current load study demonstrated that the obtained NCM111 was stable.
To analyze the possibility of using the developed synthesis method for obtaining perspective cathode materials, such as NCM622 and NCM811, two comparative iterations were carried out.The synthesis of NCM811 was carried out in oxygen flow to minimize the formation of nonstoichiometric oxide Li (1−z) Ni (1+z) O 2 , which could lead to structure destruction and as a result, poor electrochemical behavior of the material.The obtained materials were investigated using different analytical methods, such as XRD, SEM, EDX, CVA, and EIS.The initial discharge capacities of NCM622 and NCM811 were 169 and 187 mAh/g, respectively.The drop of capacity in the cycling tests was 13% for NCM 622 and 55% for 811 after 28 cycles.Such a big drop in the NCM811 capacity could be explained by the layered structure disorder and high cation mixing in the material.On the

Batteries 2023, 9 ,Figure 1 .
Figure 1.The scheme of leaching process and following synthesis of the new cathode mater

Figure 1 .
Figure 1.The scheme of leaching process and following synthesis of the new cathode material.

Figure 2
Figure2shows a diffractogram of the initial cathode material of the LCO type.Lithium cobalt oxide peaks belonging to the spatial group R3 m are clearly observed.In addition, Co 3 O 4 peaks belonging to the Fd-3m group are observed, which can be explained by the

Figure 2 .
Figure 2. The diffractogram of the initial material.

Figure 2 .
Figure 2. The diffractogram of the initial material.

Batteries 2023, 9 , 17 Figure 3 .
Figure 3.The diffractogram of the synthesized material and the comparative diffractogram of the commercial NCM111.

Figure 3 .
Figure 3.The diffractogram of the synthesized material and the comparative diffractogram of the commercial NCM111.

Figure 6 .
Figure 6.The comparative diffractogram of the synthesized materials.

Figure 9 .
Figure 9.The hodographs of the impedance of the studied samples.

Figure 9 .
Figure 9.The hodographs of the impedance of the studied samples.

Figure 10 .
Figure 10.The equivalent scheme used at the impedance modeling.

Figure 10 .
Figure 10.The equivalent scheme used at the impedance modeling.

Figure 10 .
Figure 10.The equivalent scheme used at the impedance modeling.

Table 1 .
Comparison of different acid-leaching methods.

Table 2 .
Chemical composition of the initial material in at.%.

Table 2 .
Chemical composition of the initial material in at.%.

Table 3 .
Particle size distribution of synthesized material.

Table 3 .
Particle size distribution of synthesized material.

Table 4 .
Results of EDX analysis of synthesized NCM.

Table 5 .
The particle size distribution of obtained materials.

Table 6 .
Chemical composition of the synthesized materials in at.%.

Table 6 .
Chemical composition of the synthesized materials in at.%.

Table 7 .
Total resistance of the samples.

Table 7 .
Total resistance of the samples.

Table 7 .
Total resistance of the samples.