Investigation of the Physico-Chemical Properties of the Products Obtained after Mixed Organic-Inorganic Leaching of Spent Li-Ion Batteries

: Lithium-ion batteries are currently one of the most important mobile energy storage units for portable electronics such as laptops, tablets, smartphones, etc. Their widespread application leads to the generation of large amounts of waste, so their recycling plays an important role in environmental policy. In this work, the process of leaching with sulfuric acid for the recovery of metals from spent Li-ion batteries in the presence of glutaric acid and hydrogen peroxide as reducing agents is presented. Experimental results indicate that glutaric-acid application improves the leaching performance compared to the use of just hydrogen peroxide under the same conditions. Obtained samples of leaching residues after mixed inorganic-organic leaching were characterized with Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and X-ray di ﬀ raction.


Introduction
Lithium-ion batteries and accumulators are used in a wide variety of devices-mobile phones, laptops, tablets, but also children's toys and medical equipment. In general, batteries made our life easier and revolutionized the world-thanks to the possibility of using cells as an electricity source, many devices have become mobile, making them more attractive. Complex battery packs are also used in the automotive industry-as a power source for modern hybrid or electric cars. Despite their many advantages, the widespread use of batteries has some drawbacks, mainly due to the quite complex composition of the cells. Lithium-ion batteries are made up of a graphite anode and a cathode, made out of a Li x Me y O n type compound-the most commonly used is lithium cobaltate, LiCoO 2 . Lithium-ion cells also contain an organic electrolyte, which is usually lithium salts dissolved in a mixture of organic solvents (e.g., salts-LiClO 4 , LiPF 6 , LiBF 4 ; solvents-dimethylsulfoxide, propylene carbonate, diethyl carbonate). In addition, the electrodes are separated from each other by a synthetic separator-usually a polyolefin membrane, which enables the transfer of lithium ions while at the same time protecting against a short circuit that may occur as a result of direct contact of the anode with the cathode [1][2][3][4][5]. Each component of the Li-ion battery generates large amounts of waste, while the most hazardous ones are compounds containing heavy metals such as cobalt.
Several studies confirm that one of the main components, the lithium cobaltate, has a negative influence on the environment as well as on living organisms. It induces oxidative DNA damage causing mutagenic effect and inflammatory response, mainly caused by the cobalt release [6]. Many data show the role of Co(II) ions released from batteries, which causes the formation of OH-radical species by a

Materials and Methods
In this study, various types of Li-ion batteries were used. They were obtained from numerous sources of commercial origins. They were dedicated for laptops from different manufacturers, such as Lenovo, Toshiba or Hewlett-Packard. Initially, upstream material was dismantled with the manual procedure described widely in literature, including removal of both steel and plastic cases that cover the batteries [29][30][31]. Anode and cathode were crushed carefully and sieved to separate particular elements such as plastic film, scrap paper, outer metallic body and membrane. Obtained battery powder was collected and used for further research. The obtained mass was subjected to XRD and SEM Energies 2020, 13, 6732 3 of 15 analyses as well as a mineralization method. To mineralize, 0.5 g of the tested waste battery powder was spread wet in an open system using the DigiPREP Jr. mineralization system (parameters: 10.00 mL 65% HNO 3 , digestion time: 5 h, temperature: 120 • C). The obtained solution was evaporated to a volume of approximately 0.5 mL, transferred quantitatively to a plastic container and supplemented with deionized water to 50 g. At the same time, a blank sample was prepared and included in the final results. The analyses were performed in parallel in three repetitions. Then the metal concentrations in the solution were determined using ICP-OES (Agilent 720).
The separated powder from spent Li-ion batteries was subjected to the leaching. Acid leaching was performed in 1.5 M sulfuric acid (96% analytical grade, STANLAB), as the reducing agents glutaric acid C 5 H 8 O 4 (5% w/v) and hydrogen peroxide H 2 O 2 (30% analytical grade, STANLAB; 0.9% v/v) were used. An experiment without the addition of reducing agents was also performed in order to compare its results with samples 1, 2 and 3, and to determine the effect of reducers on the obtained recovery degrees of the tested metals. The ratio of the solid phase to the liquid phase was 1/10 in each case. Other assumed leaching parameters were: temperature-90 • C, time-2 h and mixing speed-500 rpm ( Table 1). The methodology of these experiments has also been demonstrated in previous studies where the results of leaching research were compared with different process parameters [32]. After leaching was complete, the samples were vacuum-filtered. The content of metals Al, Ca, Co, Cr, Cu, Fe, Li, Mn, Na, Ni, Si and Zn in the leachates was determined (ICP-OES, Agilent 720) and their percent recovery degrees were determined in relation to the initial concentrations in the tested material. The samples of battery powder after leaching with reducing agents (no. 1, 2 and 3) were dried at 105 • C for 24 h in order to characterize the metal content. Then, the dried material was analyzed with microscopic and spectroscopic techniques. To determine the morphology of powder the FE-SEM Merlin (Zeiss) equipped with a Gemini II column was used. The device worked in low kV value range (0.5-1.5 kV) and low probe current 10-20 µA. EDS was used for elemental analysis of the measured samples. Complementary to the EDS analysis, for determination of the chemical composition of samples the FT-IR analysis was performed with Nicolet 8700 in range 4000-400 cm −1 . The powder X-ray diffraction patterns were recorded with a powder diffraction X-ray diffractometer (PXRD) X'PERT Phillips with PW 1830 generator with CuKα radiation with line λ = 1.5405980 Å and a scan rate of 0.05 • per minute in 0.016 • steps covering the 2θ angle range from 20 • to 130 • . Measurements were performed at room temperature using DHN software.

Mechanical Treatment
As a result of the mechanical processing of individual cells, the following fractions were obtained: ferromagnetic (metals, e.g., steel housing), diamagnetic (plastics, paper) and paramagnetic (anode and cathode-battery powder) constituting the material used for further research. The components of the entire spent cell and a single lithium-ion battery separated as a result of mechanical processing are presented in Figure 1. and paramagnetic (anode and cathode-battery powder) constituting the material used for further research. The components of the entire spent cell and a single lithium-ion battery separated as a result of mechanical processing are presented in Figure 1. From the presented results, it can be concluded that the entire lithium-ion battery forms a package of individual (in this case nine) cells. Both the complete battery and a single cell are composed of many different components, such as plastics, paper or metals. The most valuable raw material is the battery mass (anode and cathode powders), rich in metals that can be successfully recovered. Battery powder constitutes more than 36% of the total mass of a single spent Li-ion cell, and it was used for further laboratory experiments. The obtained results are very similar to those in the literature [33].

Quantitative and Qualitative Analysis of Battery Powder before Leaching
In order to investigate the qualitative composition of the tested material, the battery powder was subjected to XRD analysis, which showed that the main components in the material are carbon and the cathode compound-LiCoO2. Then the powder material was mineralized, as was the content of metal ions: Al, Ca, Co, Cr, Cu, Fe, Li, Mn, Na, Ni, Si and Zn in the obtained solution (ICP-OES, Agilent 720). It was specified that the tested From the presented results, it can be concluded that the entire lithium-ion battery forms a package of individual (in this case nine) cells. Both the complete battery and a single cell are composed of many different components, such as plastics, paper or metals. The most valuable raw material is the battery mass (anode and cathode powders), rich in metals that can be successfully recovered. Battery powder constitutes more than 36% of the total mass of a single spent Li-ion cell, and it was used for further laboratory experiments. The obtained results are very similar to those in the literature [33].

Quantitative and Qualitative Analysis of Battery Powder before Leaching
In order to investigate the qualitative composition of the tested material, the battery powder was subjected to XRD analysis, which showed that the main components in the material are carbon and the cathode compound-LiCoO 2 . Then the powder material was mineralized, as was the content of metal ions: Al, Ca, Co, Cr, Cu, Fe, Li, Mn, Na, Ni, Si and Zn in the obtained solution (ICP-OES, Agilent 720).
It was specified that the tested battery powder contains all the marked metals, mostly cobalt, lithium and nickel (Table 2).

Acidic Reductive Leaching
As a result of the acidic reductive leaching of the tested battery powder, multiple solutions with a similar raspberry color, but different saturation, were obtained. This could already indicate the degrees of leaching of individual metals, especially cobalt responsible for the pink color of the samples. The contents of the metals in the obtained solutions were determined and presented in the form of percent recovery degrees (Table 3). Based on the results, it can be concluded that all tested metals were leached to some extent in each of the samples (see Table 3). In the case of aluminum, the highest degree of recovery was obtained for sample 1 (reducer 30% solution of H 2 O 2 ), i.e., 71.61%; slightly lower-53.66% for sample 3, where two reducing agents were dosed; and 49.76% for sample 4 (an experiment without reducing agents). The lowest Al recovery was noted for sample 2-10.64%. Therefore, it can be concluded that the addition of glutaric acid does not significantly improve the Al leaching effects and when used with hydrogen peroxide, it may even inhibit the action of the inorganic reducing agent. Similar relationships were also obtained for calcium (1-48.73%, 2-24.58%, 3-35.98%, 4-34.09%); and silicon (1-71.68%, 2-43.30%, 3-70.25%, 4-58.52%). Relatively high levels of lithium recovery were achieved in each of the samples. The greatest amount of lithium was leached in sample 1, where the hydrogen peroxide as a reducing agent (84.19%) was used. A slightly lower degree of recovery (79.81%) was obtained in sample 3 (reducing agents-hydrogen peroxide and glutaric acid). The lowest results were recorded in samples 2 and 4 (respectively: 75.86% and 71.21%). For the other metals, i.e., Co, Cr, Cu, Fe, Mn, Ni and Zn, the highest levels of their recovery were determined for sample 3 (H 2 O 2 + C 5 H 8 O 4 ), which confirms the assumed synergistic action of two chemical compounds used as reducers, in the tested reaction environment. Taking into account all the received results of the analyses, it can be seen that the addition of a reducing agent to the leaching process allows for obtaining higher recovery rates for most of the metals contained in the leached waste battery powder. However, the type of reagent used as a reducing agent is important. It is also worth noting that in sample 1 a very low leaching degree of cobalt was recorded (1.95%), while the use of glutaric acid as a reducing agent in sample 2 increased the recovery degree of this metal to 32.30%. Nevertheless, literature data confirm the positive influence of the presence of hydrogen peroxide used as a reducing agent on the obtained degrees of recovery of cobalt ions (reduction of Co (III) to the more easily leached form-Co (II)) [26], which could not be reproduced in the presented laboratory studies. This may be due to differences in the initial preparation of the research material and the assumed parameters of the leaching process, especially the adopted too-low dose of hydrogen peroxide. Such an assumption was made in previously conducted research [32]. The effect of an H 2 O 2 dose on the sulfuric acid leaching process was investigated, where glutaric acid was also used as a reducing agent. By increasing the dose of H 2 O 2 to 15 mL, it was possible to achieve almost 90% cobalt recovery, with about 96% lithium and 91% nickel recovery. Thus, the hypothesis, that increasing the volume of H 2 O 2 contributes to higher Co recovery degrees, was confirmed [32].
As mentioned before, the battery powder contained the most cobalt, lithium and nickel in its composition. The recovery of these metals from spent Li-ion batteries is most commonly studied in the research. Comparing the obtained results for Co and Ni, it can be clearly stated that the highest levels of their recovery (59.37% and 81.75%, respectively) were obtained in sample 3 leached in the presence of two reducing agents. For lithium, the highest result was obtained for sample 1, however, it is not much higher than in sample 3. Therefore, it can be concluded that taking into account the leaching of all three metals, the process parameters for sample 3 are optimal and give the best results-high efficiency of leaching of metals such as Co, Li and Ni. Detailed considerations on this subject are included in the publication [32]. Moreover, the simultaneous use of hydrogen peroxide and glutaric acid as reducing agents also allowed obtaining the highest recovery degrees of most of the tested materials: Cr (84.60%), Cu (97.36%), Fe (100%), Mn (62.39%) and Zn (93.93%). Next, the leaching residues were investigated to determine the morphology of samples, their chemical composition and crystallinity.

Morphological Studies
The morphology of leaching residues was investigated with scanning electron microscopy (SEM). Initially, SEM analysis was performed for waste battery powder before leaching. As can be seen in Figure 2, the sample has uniform morphology that is mainly based on a granulelike structure. The sample has homogeneous morphology within the whole surface.
dose on the sulfuric acid leaching process was investigated, where glutaric acid was also used as a reducing agent. By increasing the dose of H2O2 to 15 mL, it was possible to achieve almost 90% cobalt recovery, with about 96% lithium and 91% nickel recovery. Thus, the hypothesis, that increasing the volume of H2O2 contributes to higher Co recovery degrees, was confirmed [32].
As mentioned before, the battery powder contained the most cobalt, lithium and nickel in its composition. The recovery of these metals from spent Li-ion batteries is most commonly studied in the research. Comparing the obtained results for Co and Ni, it can be clearly stated that the highest levels of their recovery (59.37% and 81.75%, respectively) were obtained in sample 3 leached in the presence of two reducing agents. For lithium, the highest result was obtained for sample 1, however, it is not much higher than in sample 3. Therefore, it can be concluded that taking into account the leaching of all three metals, the process parameters for sample 3 are optimal and give the best results-high efficiency of leaching of metals such as Co, Li and Ni. Detailed considerations on this subject are included in the publication [32]. Moreover, the simultaneous use of hydrogen peroxide and glutaric acid as reducing agents also allowed obtaining the highest recovery degrees of most of the tested materials: Cr (84.60%), Cu (97.36%), Fe (100%), Mn (62.39%) and Zn (93.93%). Next, the leaching residues were investigated to determine the morphology of samples, their chemical composition and crystallinity.

Morphological Studies
The morphology of leaching residues was investigated with scanning electron microscopy (SEM). Initially, SEM analysis was performed for waste battery powder before leaching. As can be seen in Figure 2, the sample has uniform morphology that is mainly based on a granulelike structure. The sample has homogeneous morphology within the whole surface.  Figure 3 shows images obtained for sample 1 consisting of irregular structures having a different shape and size. The morphology of the sample is similar to the whole bulk structure. As can be seen in Figure 3a, small particles having a grainlike structure about 150-200 nm are visible, however some of them tend to agglomerate, forming wirelike objects. Following images show irregular structures that seem to be crystals. They are present in the whole sample. Figure 3c reveals large objects with a round shape that tends to peel onto their surface. Based on the EDS analysis presented at Figure 3d as the map of elements the smallest granulelike objects consist mainly of cobalt or its compounds. The Following crystal-like structures consist of fluorine, while the oxygen accompanies almost  Figure 3 shows images obtained for sample 1 consisting of irregular structures having a different shape and size. The morphology of the sample is similar to the whole bulk structure. As can be seen in Figure 3a, small particles having a grainlike structure about 150-200 nm are visible, however some of them tend to agglomerate, forming wirelike objects. Following images show irregular structures that seem to be crystals. They are present in the whole sample. Figure 3c reveals large objects with a round shape that tends to peel onto their surface. Based on the EDS analysis presented at Figure 3d as the map of elements the smallest granulelike objects consist mainly of cobalt or its compounds. The Following crystal-like structures consist of fluorine, while the oxygen accompanies almost all objects in the sample except the largest ones that are carbon coming from the graphite in the spent battery powder. all objects in the sample except the largest ones that are carbon coming from the graphite in the spent battery powder. Following images recorded for sample 2 are presented in Figure 4. As can be seen in Figures 4a,b, this sample has a completely different shape than sample 1, and the main objects seem to be crystal-like. That sample looks more compact, and grainlike structures are not visible. Figure 4c reveals large objects that are present in the whole morphology. Their size ranges from about 1 μm up to larger than 10 μm. EDS analysis indicates that the sample is heterogeneous. Additionally, in comparison to the previous sample, it also contains manganese or its compounds that were not leaching within the procedure used for sample 2. Following images recorded for sample 2 are presented in Figure 4. As can be seen in Figure 4a,b, this sample has a completely different shape than sample 1, and the main objects seem to be crystal-like. That sample looks more compact, and grainlike structures are not visible. Figure 4c reveals large objects that are present in the whole morphology. Their size ranges from about 1 µm up to larger than 10 µm. EDS analysis indicates that the sample is heterogeneous. Additionally, in comparison to the previous sample, it also contains manganese or its compounds that were not leaching within the procedure used for sample 2.  Following images recorded for sample 2 are presented in Figure 4. As can be seen in Figures 4a,b, this sample has a completely different shape than sample 1, and the main objects seem to be crystal-like. That sample looks more compact, and grainlike structures are not visible. Figure 4c reveals large objects that are present in the whole morphology. Their size ranges from about 1 μm up to larger than 10 μm. EDS analysis indicates that the sample is heterogeneous. Additionally, in comparison to the previous sample, it also contains manganese or its compounds that were not leaching within the procedure used for sample 2.   The SEM images for sample 3 are presented in Figure 5. The morphology is different from samples 1 and 2. As can be seen in Figure 5a-c, the sample seems to be the most uniform, consisting of rough and compact structures. The objects present in the sample have a size from a few μm to more than 10 μm. The EDS map presented in Figure 5d reveals the elemental composition of the sample, showing large areas of carbon, looking like the substrate and objects that contain cobalt, oxygen, fluoride and even some nitrogen or their compounds. As visible, the surface of carbon is covered uniformly with sulfur that comes from the sulfuric acid during the leaching process. Meshram P. et al. [34] investigated leaching residues consisting of LiCoO2, Li2CoMn3O8 and (Li0.85Ni0.05)(NiO2) that were leached with H2SO4, and revealed that the morphology of the final product is very complex. Similarly to our results, the particles of The SEM images for sample 3 are presented in Figure 5. The morphology is different from samples 1 and 2. As can be seen in Figure 5a-c, the sample seems to be the most uniform, consisting of rough and compact structures. The objects present in the sample have a size from a few µm to more than 10 µm. The EDS map presented in Figure 5d reveals the elemental composition of the sample, showing large areas of carbon, looking like the substrate and objects that contain cobalt, oxygen, fluoride and even some nitrogen or their compounds. As visible, the surface of carbon is covered uniformly with sulfur that comes from the sulfuric acid during the leaching process.  The SEM images for sample 3 are presented in Figure 5. The morphology is different from samples 1 and 2. As can be seen in Figure 5a-c, the sample seems to be the most uniform, consisting of rough and compact structures. The objects present in the sample have a size from a few μm to more than 10 μm. The EDS map presented in Figure 5d reveals the elemental composition of the sample, showing large areas of carbon, looking like the substrate and objects that contain cobalt, oxygen, fluoride and even some nitrogen or their compounds. As visible, the surface of carbon is covered uniformly with sulfur that comes from the sulfuric acid during the leaching process. Meshram P. et al. [34] investigated leaching residues consisting of LiCoO2, Li2CoMn3O8 and (Li0.85Ni0.05)(NiO2) that were leached with H2SO4, and revealed that the morphology of the final product is very complex. Similarly to our results, the particles of product is very complex. Similarly to our results, the particles of LiCoO 2 are much smaller after leaching. Additionally, the final cobalt content was smaller, confirming successive recovery of that element. Lv W. et al. [35] additionally used ammonium chloride as a reducer to treat an initial sample of Li(Ni 0.5 Co 0.2 Mn 0.3 )O 2 , showing that after leaching, the morphology is amorphous, and there is a lower content of Co, Ni and Mn, and a higher content of carbon. This corresponds with our experimental results. Chen X. et al. [36] treated waste battery powder consisting mainly of the LiCoO 2 with sulfuric acid and an organic reducer, such as glucose, saccharose and cellulose. Their research indicated that the sample of leaching residue has a more regular structure with well-defined crystallites after leaching. The efficiency of the leaching was better than without the application of organic additives. All the above-mentioned studies showed a heterogeneous product that required deep characterization with spectroscopic techniques. Therefore, to understand the chemical composition of the products obtained within this work, the FT-IR analysis was performed.

FT-IR Analysis
As shown in Figure 6, the FT-IR was employed to characterize the possible chemical composition of the obtained leaching residues. Spectra were recorded in the range of wavenumber from 4000 cm −1 to 400 cm −1 with a resolution of 5 cm −1 . Pure KBr pellets were used as reference material. Spectra were recorded for all three samples. dicated that the sample of leaching residue has a more regular structure with well-defined crystallites after leaching. The efficiency of the leaching was better than without the application of organic additives. All the above-mentioned studies showed a heterogeneous product that required deep characterization with spectroscopic techniques. Therefore, to understand the chemical composition of the products obtained within this work, the FT-IR analysis was performed.

FT-IR Analysis
As shown in Figure 6, the FT-IR was employed to characterize the possible chemical composition of the obtained leaching residues. Spectra were recorded in the range of wavenumber from 4000 cm −1 to 400 cm −1 with a resolution of 5 cm −1 . Pure KBr pellets were used as reference material. Spectra were recorded for all three samples.
The broad bands located around 3440 cm −1 , 3200 cm −1 are characteristic for vibrations of -OH group, which is absorbed onto the surface of the sample and originates from water. The band that can be ascribed to δH2O is visible at 1649 cm −1 [37,38]. The two bands at 2928 cm −1 and 2880 cm −1 are characteristic for CH2 and CH3, respectively [39,40]. The band at 1649 cm −1 can be assigned to C=O stretching vibration [39], while 1745 cm −1 can be ascribed to stretching of -COOH [41]. Two bands at 1518 cm −1 and 1401 cm −1 may correspond to the asymmetric and symmetric vibrations of the -COO - [42,43]. The band located at 1166 cm −1 confirms the presence of asymmetric stretch of S=O in -SO3H groups. This comes from the leaching process with sulfuric acid. The 1105 cm −1 band corresponds to symmetric stretch [44,45]. The band at 1023 cm −1 is characteristic of the C-O vibration [46,47]. Two small bands located at 876 cm −1 and 821 cm −1 can be attributed to -C-H vibration. Following bands at 669 cm −1 and 558 cm −1 can be assigned to νCo-O vibrations that confirm the formation of Co2O2 nanocrystals [48][49][50]. The band at 603 cm −1 is unclear, and it can be ascribed to Co-O stretching or -OH vibration from the water molecule [50,51]. The broad bands located around 3440 cm −1 , 3200 cm −1 are characteristic for vibrations of -OH group, which is absorbed onto the surface of the sample and originates from water. The band that can be ascribed to δH 2 O is visible at 1649 cm −1 [37,38]. The two bands at 2928 cm −1 and 2880 cm −1 are characteristic for CH 2 and CH 3 , respectively [39,40]. The band at 1649 cm −1 can be assigned to C=O stretching vibration [39], while 1745 cm −1 can be ascribed to stretching of -COOH [41]. Two bands at 1518 cm −1 and 1401 cm −1 may correspond to the asymmetric and symmetric vibrations of the -COO - [42,43]. The band located at 1166 cm −1 confirms the presence of asymmetric stretch of S=O in -SO 3 H groups. This comes from the leaching process with sulfuric acid. The 1105 cm −1 band corresponds to symmetric stretch [44,45]. The band at 1023 cm −1 is characteristic of the C-O vibration [46,47]. Two small bands located at 876 cm −1 and 821 cm −1 can be attributed to -C-H vibration.
Following bands at 669 cm −1 and 558 cm −1 can be assigned to νCo-O vibrations that confirm the formation of Co 2 O 2 nanocrystals [48][49][50]. The band at 603 cm −1 is unclear, and it can be ascribed to Co-O stretching or -OH vibration from the water molecule [50,51].
As can be seen in Figure 6, the spectrum recorded for sample 1 (black curve) that was leached with H 2 SO 4 and H 2 O 2 reveals strong bands at 1166 cm −1 and 1105 cm −1 . These two are the most intensive among all samples. Obtained results correspond with previous analyses that indicated the presence of sulfur or its compounds with EDS mapping and formation of Li 2 SO 4 within the XRD studies. The presence of a strong band in the spectra confirms the formation of the chemical reaction of the acid with the substrate and formation of a compound with S=O groups. Following samples also have these bands, while their intensity confirms lower content of sulfur-based compounds. The bands characteristic to the carbon-based compounds have the highest intensity for sample 3, which confirms the most efficient leaching and corresponds with the above-mentioned analyses.
Based on the recorded spectra it is clear that depending on the leaching method, the chemical composition and content of species change. Procedure 2 seems to be the least efficient towards the recovery of metals, while the most efficient one is procedure 3, where both glutaric acid and hydrogen peroxide were used as reducing agents. Following measurements were performed for a deeper understanding of the chemical composition of the species formed in the samples after the leaching process.

Crystallographic Structure
The XRD patterns were recorded in the diffraction angle (2θ) range from 15 • to 85 • , with a scan rate of 1 • /min. The diffractogram that is presented in Figure 7 shows the patterns for the sample before leaching. The observed X-ray reflecting Bragg angle positions of LiCoO 2 for (003) is about 19.5 • [49,52]. The following pattern located at 37.3 • angle can be described as (001), while the next pattern that has high intensity of about 45 • is characteristic to the (104) plane.
Energies 2021, 14, x FOR PEER REVIEW 10 of 16 Figure 6. FT-IR spectra of battery waste powder for sample 1 that was leached with H2SO4 and H2O2, sample 2 that was leached with H2SO4 and C5H8O4, and sample 3 that was leached with H2SO4, C5H8O4 and H2O2.
As can be seen in Figure 6, the spectrum recorded for sample 1 (black curve) that was leached with H2SO4 and H2O2 reveals strong bands at 1166 cm −1 and 1105 cm −1 . These two are the most intensive among all samples. Obtained results correspond with previous analyses that indicated the presence of sulfur or its compounds with EDS mapping and formation of Li2SO4 within the XRD studies. The presence of a strong band in the spectra confirms the formation of the chemical reaction of the acid with the substrate and formation of a compound with S=O groups. Following samples also have these bands, while their intensity confirms lower content of sulfur-based compounds. The bands characteristic to the carbon-based compounds have the highest intensity for sample 3, which confirms the most efficient leaching and corresponds with the above-mentioned analyses.
Based on the recorded spectra it is clear that depending on the leaching method, the chemical composition and content of species change. Procedure 2 seems to be the least efficient towards the recovery of metals, while the most efficient one is procedure 3, where both glutaric acid and hydrogen peroxide were used as reducing agents. Following measurements were performed for a deeper understanding of the chemical composition of the species formed in the samples after the leaching process.

Crystallographic Structure
The XRD patterns were recorded in the diffraction angle (2θ) range from 15° to 85°, with a scan rate of 1°/min. The diffractogram that is presented in Figure 7 shows the patterns for the sample before leaching. The observed X-ray reflecting Bragg angle positions of LiCoO2 for (003) is about 19.5° [49,52]. The following pattern located at 37.3° angle can be described as (001), while the next pattern that has high intensity of about 45° is characteristic to the (104) plane.  Figure 8 shows the reflection patterns recorded for samples after acid treatment. All samples are highly polycrystalline, and the sharp peaks confirm the formation of welldefined crystallites. The highest intensity of the reflection patterns was observed for sample 2, where the leaching agents were sulfuric and glutaric acids. The lowest intensity was observed for sample 3, where the hydrogen peroxide was used additionally. It suggests that without hydrogen peroxide the leaching process is less effective than with it.  Figure 8 shows the reflection patterns recorded for samples after acid treatment. All samples are highly polycrystalline, and the sharp peaks confirm the formation of well-defined crystallites. The highest intensity of the reflection patterns was observed for sample 2, where the leaching agents were sulfuric and glutaric acids. The lowest intensity was observed for sample 3, where the hydrogen peroxide was used additionally. It suggests that without hydrogen peroxide the leaching process is less effective than with it.

Conclusions
In this paper, the influence of the leaching reagent on the metallic component recovery was investigated. Sulfuric acid was used as a leaching agent, while different reducing agents were used: sample 1-treatment with H2SO4 and H2O2, sample 2-treatment with H2SO4 and C5H8O4, and sample 3-treatment with H2SO4, C5H8O4 and H2O2. Application of the ICP-OES technique revealed that procedure 2 was the least effective towards metal recovery. In this procedure H2O2 was used as a reducing agent. The most effective procedure was observed for sample 3, where both hydrogen peroxide and glutaric acid were used.
The results of morphological studies by SEM and elemental analysis with EDS indicated that the samples were highly heterogeneous with large carbon content. A sample that was leached with both inorganic and organic reducer was the most regular, and the leached residue mainly had large objects that were carbon. The smaller crystallites came  XRD data revealed that sample 1 presented in Figure 8 has multiple patterns with predominant peaks at the angles: 18 [53,54]. Based on the literature, this peak could be also attributed to the CoSO 4 [55]; however, based on the EDS analysis it can be also ascribed to the LiF [56][57][58]. As can be seen, the pattern that spears at all samples about 19.5 • is ascribed to LiCoO 2 for (003) [49,52], while 37.3 • angle can be described as (001), 39.1 • as (102) as well as the above mentioned (222) plane for Co 3 O 4 . The peak around the 55 • angle can be ascribed to the presence of carbon in the sample. The peak at 27 • can be ascribed to the carbon [59] or formation of Li 2 SO 4 under the sulfuric acid treatment, which may be also ascribed to the small peak at 42.1 • [60,61].
Application of glutaric acid instead of hydrogen peroxide leads to the changes in the XRD patterns. The main difference for sample 2 is presented in Figure 8. The difference is the lack of the peak at the 19.5 • angle that corresponds to the (003) LiCoO 2. However, other peaks have a higher intensity than for sample 1. Additionally, the presence of the peak corresponding to the C (102) is more visible. The diffractogram also reveals a pattern for carbon at about a 77.5 • angle. XRD patterns obtained for sample 3 reveal similar crystallinity to sample 2, while the intensity of reflection patterns is slightly lower.
Diffractograms confirm that the main components of all samples are LiCoO 2 and Co 3 O 4 . The results are in good agreement with JCPDS data no. 75-0532 that are indexed to the hexagonal structure LiCoO 2 , JCPDS data no. 43-1003 for literature data [62][63][64][65].
All results of XRD analyses were normalized between 0 to 1 values. As can be seen, the peak visible at 26.6 • corresponds to the carbon (JCPDS 98-061-7290). The presence of carbon comes from the graphite-base anode. The high content of LiCoO 2 as well as Co 3 O 4 in all samples suggests that the leaching agents did not completely dissolve inorganic species in the waste battery powders.

Conclusions
In this paper, the influence of the leaching reagent on the metallic component recovery was investigated. Sulfuric acid was used as a leaching agent, while different reducing agents were used: sample 1-treatment with H 2 SO 4 and H 2 O 2 , sample 2-treatment with H 2 SO 4 and C 5 H 8 O 4 , and sample 3-treatment with H 2 SO 4 , C 5 H 8 O 4 and H 2 O 2 . Application of the ICP-OES technique revealed that procedure 2 was the least effective towards metal recovery. In this procedure H 2 O 2 was used as a reducing agent. The most effective procedure was observed for sample 3, where both hydrogen peroxide and glutaric acid were used.
The results of morphological studies by SEM and elemental analysis with EDS indicated that the samples were highly heterogeneous with large carbon content. A sample that was leached with both inorganic and organic reducer was the most regular, and the leached residue mainly had large objects that were carbon. The smaller crystallites came from an inorganic phase containing metals. Moreover, the results of FT-IR and XRD analysis revealed that the main components of the waste Li-ion battery powders and leaching residues were LiCoO 2 , Co 3 O 4 and carbon originating from the graphite in the battery. The content of LiCoO 2 and Co 3 O 4 was the largest in the sample that was leached with use of glutaric acid and hydrogen peroxide in the same bath. Thus, this work presents a successful attempt to use glutaric acid in the presence of hydrogen peroxide towards metal recovery from spent Li-ion batteries.

Data Availability Statement:
The data presented in this study are available on request.