Positive electrode active material comprising oyster shell for lithium secondary battery and preparing method therefor

Abstract

The present invention relates to a positive electrode active material comprising an oyster shell for a lithium secondary battery and a preparing method therefor and, specifically, to a positive electrode active material for a lithium secondary battery, comprising a positive electrode active material and an oyster shell coating layer on the surface of the positive electrode active material, and to a preparing method for a positive electrode active material for a lithium secondary battery, the method comprising the steps of: mixing a positive electrode active material and an oyster shell powder; and heat-treating the mixture. The positive electrode active material comprising the oyster shell was observed to show a reduced internal resistance due to the suppressed electrolyte decomposition at the interface of a positive electrode, and Ca contained in the oyster shell was found to play an important role in removing F- species.

Description

Cathode active material for lithium secondary batteries containing oyster shells and method for producing the same

[0001] The present invention relates to a cathode active material for a lithium secondary battery including oyster shells and a method for producing the same, and more particularly, to a cathode active material for a lithium secondary battery including a cathode active material and an oyster shell coating layer on the surface of the cathode active material, and a method for producing a cathode active material for a lithium secondary battery including a step of mixing a cathode active material and oyster shell powder and a step of heat-treating the mixture.

[0002] As market demand rapidly evolves from small to large-capacity batteries, the characteristics required for lithium-ion batteries (LIBs) are rapidly increasing. As the LIB market expands, achieving higher energy densities than existing LIBs has become a crucial goal. Accordingly, extensive research is currently underway on ways to increase the energy density of LIBs.

[0003] Although many factors can affect the energy density of LIBs, it is widely known that the energy density of the cell is closely related to the specific capacity and voltage that can be achieved with the electrode materials. In this regard, the search for electrode materials that can provide higher specific capacity at higher voltages than conventional electrode materials has increased exponentially in the past few years. In the field of cathode materials, advanced cathode materials, especially LiNi with a high Ni content, are being developed that can achieve higher specific capacity than conventional layered LiCoO2 (LCO) materials. x Co y Mn zResearch on O2(LN) cathodes is increasing significantly. Ni-rich LNCM cathodes are considered advanced cathodes, where some of the Co component of LCO cathodes is replaced with Ni and Mn due to their desirable electrochemical behavior. Specifically, it has been shown that a higher Ni content leads to a higher specific capacity, due to the relatively lower electrochemical potential of Ni species in the layered sites. Therefore, extensive research has recently been conducted to achieve high energy densities in LIBs by substituting more Ni for Co.

[0004] However, Ni-rich LNCM cathode materials have a significant limitation in that their cell life is rapidly reduced due to their unstable interfacial stability. Typically, LNCM cathode materials are prepared by calcining LNCM-OH using a slightly excess Li source (LiOH or Li2CO3). While excess Li is required to promote complete dehydration of LNCM-OH, the unreacted excess Li remains on the LNCM surface. This residual Li has a potential difference of approximately 4.0 V (vs. Li / Li + ) is decomposed into gaseous components through electrochemical reaction, which reduces cell safety due to rapid expansion of the cell. In addition, when Co is replaced with a large amount of Ni in the LNCM cathode material, unstable Ni is generated during electrochemical charging. 4+ The amount of Ni increases. In particular, Ni 4+ is very unstable as it tends to be easily reduced. Therefore, the electrolyte is Ni 4+ It promotes electron transfer reaction between the LNCM and the electrolyte, which easily decomposes at the LNCM interface and forms unstable cationic intermediates due to electrolyte decomposition. If this parasitic reaction continues, undesirable byproducts accumulate on the LNCM surface, which drastically reduces the cycle maintenance. This is because intracellular Li +This is because mobility is severely hindered. Moreover, as the Ni composition increases, microcracks easily form in Ni-rich LNCM cathodes, and even at high Ni compositions, serious side reactions due to electrolyte decomposition occur in microcracked LNCM cathodes during cycling. Therefore, to improve the performance of advanced LIBs, methods for stabilizing the interfacial performance of LNCM cathodes must be determined in advance.

[0005] An efficient and convenient approach to improve the cycling behavior of LNCM cathode materials is to create cathode-electrolyte interphases (CEI) on the LNCM surface using functional electrolyte additives. SO x Additives composed of functional groups (e.g., divinyl sulfone and p-toluenesulfonyl isocyanate) can form stable CEI layers even at high operating potentials. PO x Functionalizing additives (e.g., methyl diethyl phosphonoacetate and methyl diphenylphosphonate) were considered effective because they provide a reliable artificial CEI layer through electrochemical reactions on the LNCM surface, thereby enhancing the safety of LIBs by increasing the non-flammability of the electrolyte. Borate-based additives (e.g., triethanolamine borate and triphenyl borate) have been used in LNCM cathode materials because they generate a CEI layer with higher ion conductivity on the LNCM surface. In addition to electrolyte additives, embedded inorganic coatings, such as metal oxides (Al2O3, MgO, ZnO, TiO2), metal fluorides (AlF3, ZrF4), and metal phosphates (MnPO4, AlPO4), are being widely developed. This is because these inorganic coatings can reduce the active surface area of ​​the LNCM cathode by physically separating the electrode material from the electrolyte, thereby improving the cycling endurance of LIBs.

[0006] Oyster shell (OS) waste, classified as marine debris, cannot be incinerated and must be landfilled, causing serious environmental pollution. South Korea is the world's second-largest oyster producer, producing over 300,000 tons annually. Even though only a small portion of OS waste is reused, OS is a byproduct that accounts for approximately 90% of the total oyster mass.

[0007] Meanwhile, since the OS used is primarily composed of calcium carbonate (CaCO3), it can be considered a potentially valuable material in various chemical fields. Applications include construction materials, adhesives, pharmaceuticals, and food additives. One inorganic component of the OS used is calcium, which, similar to other inorganic components commonly used in surface modification of LNCM cathodes, can enhance interfacial stability. Therefore, OS-based interfacial modification could potentially provide a Ca-based CEI layer on the LNCM surface through a simple heating process.

[0008] In this invention, we propose an OS-based interfacial modification method for LNCM cathode materials (LN83) with an 83% nickel content (Fig. 1). Electrolyte decomposition frequently occurs on the surface of high-nickel cathode materials. The OS-based CEI layer is expected to reduce the surface area and suppress electrolyte decomposition, ultimately improving cell life. Furthermore, the high mechanical strength of OS provides a more robust CEI layer, effectively alleviating mechanical stress that delays the formation of microcracks in LN83 cathode materials. Therefore, the OS-based CEI layer is integrated into the LN83 interface through a simple heating process, and its electrochemical performance is evaluated along with systematic analysis to clarify the effectiveness of the OS-based CEI layer.

[0009] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery is provided, which includes a cathode active material; and an oyster shell coating layer on the surface of the cathode active material.

[0010] The above positive electrode active material is characterized by being represented by the following [chemical formula 1];

[0011] [Chemical Formula 1]

[0012] LiNi a Co b Mn c O2(0.6≤a≤0.9, a+b+c=1).

[0013] The above positive electrode active material is LiNi 0.83 Co 0.11 Mn 0.06 It is characterized by O2.

[0014] The above oyster shell is characterized by reacting with residual lithium on the surface of the positive electrode active material to reduce the amount of residual lithium. The residual lithium may be, but is not limited to, LiOH or Li2CO3.

[0015] The above oyster shell coating layer is characterized in that it acts as a cathode-electrolyte interphase (CEI) layer.

[0016] The above oyster shell coating layer is characterized by containing CaO or CaCO3.

[0017] It is characterized in that as the amount of the above oyster shell increases, the amount of CaO increases more than the amount of CaCO3.

[0018] As the amount of oyster shell increases, the lithium diffusion coefficient (D Li+ ) is characterized by a decrease.

[0019] The above oyster shell coating layer is characterized by suppressing electrolyte decomposition at the anode interface.

[0020] The above oyster shell coating layer is characterized by suppressing cracking of the anode that may occur during cycling.

[0021] The above oyster shell coating layer is fluorine (F) generated during cycling - ) is characterized by capturing species.

[0022] According to another embodiment of the present invention, a lithium secondary battery is provided, which includes a positive electrode including the positive electrode active material; an electrolyte; and a negative electrode.

[0023] According to another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery is provided, comprising the steps of mixing a positive electrode active material and oyster shell powder and the step of heat-treating the mixture.

[0024] The oyster shell powder is characterized in that it is included in an amount of 0.1 to 10 wt% relative to the weight of the positive electrode active material. Preferably, the oyster shell powder may be included in an amount of 0.1 to 9 wt%, 0.1 to 8 wt%, 0.1 to 7 wt%, 0.1 to 6 wt%, 0.1 to 5 wt%, 0.1 to 4 wt%, 0.1 to 3 wt%, 0.1 to 2 wt%, or 0.1 to 1 wt% relative to the weight of the positive electrode active material.

[0025] The above heat treatment is characterized in that it is performed at a temperature of 300 to 800°C for 1 to 12 hours.

[0026] To overcome the limitations related to the interfacial stability of the LN83 cathode material, a CEI layer was formed through a simple one-step process using an OS-based material as a coating precursor. Incorporating the OS-derived CEI layer into the cathode material resulted in surface modification and D Li+ Although the value decreased slightly, the structure of the LN83 cathode material remained intact, maintaining favorable electrochemical behavior. SEM analysis revealed that the island-like CEI layer was well distributed at the interface. This significantly reduced the internal pressure, as the OS-mediated CEI layer suppressed electrolyte decomposition during the initial charging stage.

[0027] In terms of electrochemical performance, the 1.0 OS cathode showed a significantly increased cycling retention. The cell using the 1.0 OS LN83 cathode showed a retention of 93.8%, which was 31.1% higher than that cycled with the original LN83 cathode after 100 cycles. Further systematic analysis revealed that adding Ca to increase the mechanical strength clearly prevented micro-cracking of the LN83 cathode material, thereby suppressing electrolyte decomposition at the highly active LN83 interface and reducing the internal resistance. In addition, Ca was found to have a positive effect on the F - It has been shown to play a significant role in the removal of species, which rapidly accelerates the corrosion of transition metal components such as Ni, Co, and Mn within the battery. Finally, considering that OS is a marine waste, the proposed strategy based on using OS as a functional precursor for LN83 anodes could facilitate the recycling and management of OS waste in the near future.

[0028] Figure 1. Effect of oyster shell (OS) coating on LN83 anode.

[0029] Figure 2. (a) Scanning electron microscopy (SEM) images and Ca energy-dispersive X-ray spectroscopy mapping of untreated LN83 and (b) 1.0 OS powder samples. (c) Transmission electron microscopy (TEM) images for untreated LN83 and (d) 1.0 OS. (e) X-ray diffraction (XRD) patterns of LN83 cathode powder samples with untreated LN83, 0.5 OS, and 1.0 OS. (f) Comparison of Ca X-ray photoelectron spectroscopy (XPS) data for untreated LN83 and 1.0 OS powder samples.

[0030] Figure 3. (a) Quantification of residual lithium (Li2CO3) in untreated LN83 and 1.0 OS powder samples. (b) Particle hardness of untreated LN83, 0.5 OS, and 1.0 OS powder samples. (c) Inner cell with untreated LN83, 0.5 OS, and 1.0 OS cathodes.

[0031] Fig. 4. XRD patterns of stoichiometric amounts of Li2CO3+ excess OS, Li2CO3+ OS, CaO, CaCO3, and Li2CO3.

[0032] Figure 5. Various scan rates ((0.1-0.4 mV s -1 ) Cyclic voltammetry profiles of (a) untreated LN83, (b) 0.5 OS, and (c) 1.0 OS anodes. (d) Li calculated from the linear slope of the peak current density as a function of the square root of the scan rate. + Diffusion coefficient.

[0033] Figure 6. (a) Potential profile of the cell during the formation cycle and (b) inset data for the Coulombic efficiency and formation Coulombic efficiency of the cell during cycling. (c) Cycling performance of the cell. dQ dV-1 analysis of (d) untreated LN83 and (e) 1.0 OS anodes at every 25th cycle.

[0034] Figure 7. Surface and cross-sectional SEM images of cycled (a) untreated LN83 and (b) 1.0 OS anodes. TEM images and fast Fourier transform patterns of cycled (c) untreated LN83 and (d) 1.0 OS anodes. Electrochemical impedance spectroscopy analysis after (e) formation cycle and (f) 100 cycles.

[0035] Fig. 8. XPS profiles of untreated LN83 (top) and 1.0 OS (bottom) anodes after 100 cycles. (a,d) C 1s, (b,e) F 1s, and (c,f) P 2p.

[0036] Figure 9. (a) XRD pattern of OS powder recovered after reaction with TBAF. (b) Elemental analysis (Ni, Co, and Mn) by inductively coupled plasma mass spectrometry for Li recovered from untreated LN83 and 1.0 OS cells.

[0037] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery is provided, which includes a cathode active material; and an oyster shell coating layer on the surface of the cathode active material.

[0038] The present invention will be described in detail below. Unless otherwise defined, terms used herein should be interpreted as generally understood by those of ordinary skill in the relevant field.

[0039] The drawings and examples of this specification are provided to enable those skilled in the art to easily understand and practice the present invention. Contents that may obscure the gist of the invention may be omitted from the drawings and examples, and the present invention is not limited to the drawings and examples.

[0040]

[0041] <Example>

[0042] 1. Anode manufacturing

[0043] OS-coated LN83 cathode materials were prepared as follows. The collected OS samples were ground using a ball milling machine (MM 400, Retsch) at a vibration frequency of 30 Hz. After ball milling the OS samples, the particle size was measured using a particle size analyzer (PSA; Bettersizer S, Bettersize Inc.). Subsequently, LN83 (LiNi 0.83 Co 0.11 Mn 0.06 O2,D 50 = 8.10 μm) and 0.025 g of OS (0.5 wt% OS) or 0.050 g (1.0 wt% OS) were stirred and heated to 500°C in an O2 atmosphere for 5 hours; the samples are referred to herein as untreated LN83, 0.5 OS, and 1.0 OS, respectively. For comparison, 0.050 g of CaCO3 or CaO (1.0 wt% CaCO3 or CaO) was stirred under the same conditions as the OS coating, and these samples are referred to as 1.0 CaCO3 and 1.0 CaO.

[0044]

[0045] 2. Analysis of physicochemical properties

[0046] The particle size of the OS-coated LN83 cathode was determined using PSA. The surface morphology of the LN83 cathode was observed using scanning electron microscopy (SEM; JSM-7800F and JSM-7001F, JEOL) and transmission electron microscopy (TEM; TALOS F200X, FEI). The crystal structure of the LN83 cathode was analyzed using X-ray diffraction (XRD; Empyrean, PANalytical), and the mechanical strength was analyzed using a microindenter (MCT-W500-E, Shimadzu). After treating the sample with 0.1 N HNO3, the residual lithium species in the LN83 cathode were quantified using a titrator (848 Titrino plus, Metrohm). The chemical composition of the fabricated LN83 cathode was analyzed using X-ray photoelectron spectroscopy (XPS; K-alpha, Thermo Fisher Scientific).

[0047]

[0048] 3. Battery manufacturing and electrochemical property analysis

[0049] The LN83 cathode was prepared as follows. First, 1.8 g of LN83 cathode material, 0.1 g of polyvinylidene fluoride (Kureha), and 0.1 g of carbon conductor (C-NERGY, Super-C) were well dispersed in 1.3 mL of N-methyl pyrrolidone (Ashland). These were thoroughly mixed for 1 h, and the resulting slurry was coated on an Al substrate. After coating, the LN83 cathode was initially dried at 120 °C for 3 h and then in a vacuum oven for 12 h. The loading density of the LN83 cathode was 15.04 ± 0.03 mg cm -2 It was.

[0050] For cyclic voltammetry (CV), the cell was assembled with a LN83 anode (working electrode) and a Li cathode (counter and reference electrode). The cell was tested at 0.1 to 0.4 mV s -1 3.0 to 4.5 V (vs. Li / Li) with varying scan rates +) were swept. To evaluate the cycling performance, coin cells were assembled with LN83 cathode, Li cathode, poly(propylene) / poly(ethylene) / poly(propylene) separator, and electrolyte (EC:EMC = 1:2, 1.0 M LiPF6). The cells were charged at 3.0–4.3 V (vs. Li / Li + ) was cycled at 0.1C (1.0C = 180mA / g) for 2 cycles and at 0.5C for 100 cycles using a cycler (LAND, CT2001A) in the range of 0.1C (1.0C = 180mA / g). The in-situ pressure cell was assembled using LN83 anode, Li cathode, electrolyte and separator and then cycled from 3.0V to 4.3V (Li / Li) at 0.2C at 45C. + (in contrast) was circulated. The internal pressure was up to 4.3 V (Li / Li + (Contrast) was recorded as a function of charging time up to potential.

[0051] The cycled LN83 anode was analyzed using SEM, and cross-sectional images were collected using a cross-section polisher (IB-09020CP, JEOL). The changes in surface structure were analyzed using TEM, and the internal resistance was 4.3 V (Li / Li + The electrochemical impedance spectroscopy (EIS) was performed by applying an alternating current (AC) signal with an amplitude of 10 mV from 1 MHz to 1 mHz at a frequency of 1 MHz to 1 mHz. XPS was used to determine the chemical composition of the LN83 anode surface as the etching time varied from 0 to 270 s. OS and F - To investigate the chemical reactivity between the species, OS and tetrabutylammonium fluoride dissolved in tetrahydrofuran (TBAF; TCI) were added to a bottle at a molar ratio of 1:2 and stirred for 1 h. The sample was then left to stand for 24 h and dried in a vacuum oven at 120°C for 12 h. The precipitated solid was analyzed using XRD.

[0052] The Li anode recovered from the cycled coin cell was dissolved in 100 mL of distilled water, and the resulting solution was analyzed using inductively coupled plasma mass spectrometry (ICP-MS; FluoTime 300 / MicroTime 100, Thermo Fisher Scientific) to quantify the metal components dissolved in the Li anode.

[0053]

[0054] <Experimental Results>

[0055] 1. Surface morphology analysis of OS-coated LN83 cathode material

[0056] The surface morphology of the prepared OS-coated LN83 cathode materials was observed using SEM (Fig. 2a,b). No coating layer was observed on the untreated LN83 material, and EDS analysis did not detect any Ca component. However, an island-like coating layer mainly composed of Ca was observed on the OS-coated LN83 material. Particle size analysis showed that the average particle size (D50) of the LN83 cathode materials was identical for all samples (untreated LN83: 8.10 μm, 0.5 OS: 8.10 μm, 1.0 OS: 8.10 μm), consistent with the SEM analysis. Based on TEM images (Fig. 2c,d), the thickness of the OS-derived layer was found to be approximately 2.5 nm. In contrast, no coating layer was found on the untreated LN83 cathode material, indicating that the OS precursor was effectively coated on the LN83 interface.

[0057] XRD analysis indicates that there were no significant structural changes in the LN83 cathode after OS treatment (Fig. 2e). The pristine LN83 and OS-coated LN83 cathode materials exhibited I(006) / I(012) and I(018) / I(110) peaks, respectively, indicating that the layered structure was maintained even after surface modification. The I(003) / I(104) ratios of all samples were greater than 1.20, indicating that cation mixing was not severe in the LN83 cathode.

[0058] To determine the chemical composition of the LN83 cathode, the OS-coated LN83 cathode material was analyzed using XPS (Fig. 2f). While no Ca was observed in the XPS profile of the untreated LN83 cathode, the OS-coated LN83 exhibited apparent Ca peaks composed of CaO (345.3 eV) and CaCO3 (346.2 eV). This strongly suggests that the CaO- and CaCO3-based CEI layer migrates to the LN83 interface via the thermal decomposition of OS when the OS is heat-treated into the LN83 anode. CaO has a wide band gap (7.7 eV) that can be classified as a general insulator, which can effectively prevent electron transfer reactions between the electrode and the electrolyte.

[0059] To clarify the effect of OS-based surface modification, the residual Li2CO3 at the LN83 interface was analyzed by titration (Fig. 3a). Li2CO3 remained at the LN83 interface because an excess of Li2CO3 was initially used for calcination of the LN83 cathode material. As the amount of OS increased, the residual Li2CO3 at the LN83 interface gradually decreased (2,670.7, 1,163.5, and 966.1 ppm for untreated LN83, 0.5 OS, and 1.0 OS, respectively). This suggests that Li2CO3 can accelerate the thermal decomposition of OS during surface modification.

[0060] To further support this finding, the XRD patterns of the mixture (Li2CO3 and OS) heat-treated at 500°C were investigated (Fig. 4). When the molar ratio of Li2CO3 to OS was 1:1, Li2CO3 and CaCO3 were observed in the XRD patterns. When the molar ratio of OS was increased to 13.8, CaO was predominant in the XRD patterns, with a relatively small amount of CaCO3. These results indicate that the Li2CO3 remaining on the LN83 surface can accelerate the thermal decomposition of the OS precursor, thereby providing an artificial CEI layer based on CaO and CaCO3.

[0061] To clarify the effectiveness of the CaO- and CaCO3-based CEI layers, the mechanical stiffness of LN83 particles was determined using a microindenter (Fig. 3b). LN83 cathode materials are primarily composed of clustered primary particles. Therefore, microcracks in the secondary particles are easily induced by external stress through volume expansion during cycling. Therefore, ensuring adequate stiffness of the LN83 cathode material is a critical challenge for improving cycling performance. The particle hardness of the untreated LN83 cathode material was determined to be 168.7 MPa. However, the particle hardness values ​​of 0.5 OS and 1.0 OS were 174.8 and 181.9 MPa, respectively, which were 3.62% and 7.82% higher than those of the uncoated LN83 cathode material, respectively. CaO and CaCO3 are known to be key components in maintaining shell stiffness due to their significant stiffness. This suggests that the OS-coated LN83 cathode material exhibits less internal microcracks due to the CaO and CaCO3-based CEI. The harder layer suppresses the formation of microcracks during cycling. Accelerated microcracks during cycling simultaneously promote electrolyte decomposition at the newly formed surface, which leads to gas formation and exacerbates cell swelling. In fact, as verified by an in-house fabricated pressure monitoring cell, the untreated LN83 cathode material exhibited a continuous increase in internal pressure during charging (12.15 kPa relative to the initial pressure). In contrast, the 0.5- and 1.0-OS cathodes exhibited lower internal pressures during charging (10.24 and 9.37 kPa relative to the initial pressure for 0.5 and 1.0 OS, respectively), which were proportional to the amount of OS precursor used. Coating the LN83 interface with OS is believed to lower the internal pressure within the cell by reducing the residual Li2CO3 (which can form gaseous components through electrochemical reaction) while suppressing microcracks.

[0062]

[0063] 2. Electrochemical performance analysis of OS-coated LN83 cathode material

[0064] To determine the dependence of Li diffusion on OS-based coatings, the kinetic behavior of the material was analyzed through CV and the diffusion coefficient of Li (D Li+ ) was described by the Randles-Sevcik equation (Fig. 5a-d). All LN83 cathode materials exhibited identical CV profiles, suggesting that the interfacial CEI layer did not change the structure of the LN83 cathode. D Li+ In analysis D Li+ The value gradually decreased with increasing OS amount. D of untreated LN83 anode material Li+ is 8.14 Х 10 -9 cm 2 s -1 But in 1.0 OS 7.05 Х 10 -9 cm 2 s -1 10 -9 cm 2 decreased to s-1. Nevertheless, D Li+ This decrease in value is due to Li within the cell. + It is not important to promote .

[0065] To illustrate the effectiveness of the OS-based CEI layer, the electrochemical performance was investigated (Fig. 6a-e). In addition to the OS-coated LN83 cathode material, the cycling behavior of individual CaO or CaCO3-coated LN83 cathode materials was further investigated and compared with the cycling performance of the OS-coated LN83 cathode material. The initial specific capacity decreased with increasing the amount of OS precursor. The untreated LN83 cathode material had a specific capacity of 201.6 mA hg. -1 While the 0.5 OS and 1.0 OS cathode materials showed specific capacities of 190.8 and 187.9 mA hg, respectively. -1 The specific capacities were 182.3 and 184.0 mA·g for LN83 cathodes coated with CaO and CaCO3, respectively. Similar decreases in specific capacities were observed in LN83 cathodes coated with CaO and CaCO3, respectively. -1, which is slightly lower than that of the OS-coated LN83 cathode material.

[0066] Consistent results were observed with respect to the Coulombic efficiency (CE) in the initial cycle. The untreated LN83 cathode exhibited 88.5% CE, whereas the OS-coated LN83 cathode exhibited lower CE values ​​(0.5 OS: 85.9% and 1.0 OS: 83.0%) than the untreated LN83 cathode. In addition, the CE values ​​of the CaO- and CaCO3-coated LN83 cathodes were 82.7% and 82.0%, respectively. When these coating layers were developed at the LN83 interface, D Li+ As observed in the analysis, Li at the interface + This may slightly impede the movement. Therefore, the initial specific capacity and CE values ​​are lower for the LN83 cathode material coated with CEI.

[0067] In contrast, the cycling retention of the OS-coated LN83 cathode material was significantly improved. The untreated LN83 cathode material exhibited a retention of 62.7% after 100 cycles, indicating that many undesirable reactions occurred during cycling. In comparison, 0.5 OS exhibited a retention of 80.4%, representing a 17.7% increase in retention. When the amount of OS precursor was increased to 1.0, the retention of the cell increased by >90% (93.8%), which was 31.1% higher than that of the cycled uncoated LN83 cathode material. Similar behavior was observed for CaO- and CaCO3-coated LN83 cathode materials. After 100 cycles, the retentions of the CaO- and CaCO3-coated LN83 cathodes were 92.9% and 93.2%, respectively.

[0068] Subsequent dQ dV for untreated and 1.0 OS anode materials -1The analysis revealed that a more irreversible phase transition occurred in the untreated LN83 anode than in the 1.0 OS anode. In the H2-H3 transition, the corresponding H2-H3 peak intensity was significantly reduced in the pristine LN83 anode, whereas a smaller decrease in the corresponding H2-H3 peak intensity was observed in the 1.0 OS anode. In addition, a stronger polarization behavior was observed in the H2-H3 peak transition of the untreated LN83 anode, indicating that coating the anode with a Ca-based artificial CEI layer increased the interfacial stability, resulting in less structural deformation in the 1.0 OS anode.

[0069]

[0070] 3. Surface analysis of the cycled OS-coated LN83 anode

[0071] The cycled LN83 anodes were recovered and analyzed using SEM (Fig. 7a,b). The SEM images of the uncoated LN83 anode showed that many microcracks propagated from the inner space to the outer surface. In contrast, the formation of microcracks in the cycled 1.0 OS anode was suppressed, and the microcracks at the LN83 interface were negligible. These results indicate that the OS coating effectively suppressed microcrack formation during cycling due to the enhanced mechanical stiffness after mixing CaO and CaCO3 into the anode. The structural stability of the OS-coated LN83 anode was enhanced. In particular, while a 19.4 nm rock-salt phase developed in the uncoated LN83 anode based on the FFT pattern, this rock-salt phase was significantly reduced (1.0 nm) in the recovered 1.0 OS anode (Fig. 7c,d). This is consistent with the dQ dV -1 It is consistent with the analysis.

[0072] As can be seen from the EIS results (Fig. 7e,f), this undesirable behavior had a substantial impact on the internal resistance. In the initial cycles, the 1.0 OS anode showed a slight increase in internal resistance according to RCEI and RCT (untreated LN83: RCEI 15.5Ω and RCT 15.8Ω; 1.0 OS: RCEI 15.7Ω and RCT 16.9Ω). As mentioned earlier, the incorporation of an artificial CEI layer significantly increased the internal resistance of the cell. + The distance between the electrodes increases, which increases the internal resistance. The recovered 1.0 OS anode showed a lower internal resistance after cycling, with an RCEI of 64.0Ω and an RCT of 31.0Ω. On the other hand, the recovered uncoated LN83 anode showed an RCEI of 79.0Ω and an RCT of 31.5Ω. When parasitic reactions such as microcracks and irreversible phase transitions of the LN83 anode material occur during cycling, the Li + It seriously impedes movement; therefore, cycling performance is improved as internal resistance is reduced.

[0073] XPS analysis of the recovered LN83 anode also provided valuable insights into the effectiveness of the OS-based CEI layer (Figure 8). The C 1s spectra of all samples showed the formation of CC (285.0 eV), CO (286.7 eV), and C=O (287.9 ​​eV) peaks. Quantitative analysis of each peak revealed that the CC peak was more prominent in the recovered LN83 anode (17.7% for the bare LN83 anode and 56.4% for the 1.0 OS anode). In contrast, the recovered bare LN83 anode exhibited larger CO and C=O peaks (CO and C=O peak areas of the bare LN83 anode: 13.7% and 11.0%, respectively) for the 1.0 OS anode. The CC peaks originate from the conducting agent in the anode. Therefore, a larger CC peak indicates a lower electrolyte decomposition at the anode interface. In contrast, the CO and C=O peaks are attributed to electrolyte decomposition, and a higher ratio of these peaks indicates greater electrolyte decomposition. These results indicate that electrolyte decomposition was reduced in the 1.0 OS anode because the OS-derived CEI layer suppressed electron transfer reactions at the interface. This explanation was supported by additional C 1s analysis.

[0074] For the untreated LN83 cathode, lithium carbonate was observed at 289.6 eV. Lithium carbonate is a decomposed adduct generated from the original electrolyte. The decomposed adduct heavily covered the LN83 cathode after cycling. In contrast, no lithium carbonate peak was detected in the recovered 1.0 OS cathode. Instead, the recovered 1.0 OS cathode exhibited a C 1s peak at 290.3 eV and an F 1s peak at 687.2 eV, which were assigned to the CF moiety derived from the binder. The binder peak remaining in the recovered cathode indicates a decrease in electrolyte decomposition, indicating a higher CF peak intensity after cycling. Similar surface behavior was consistently found in the F 1s and P 2p spectra. The top layer of the cathode (etching time: 0 s) contained a higher amount of LiF (685.0 eV), Li, which can be considered as decomposed adducts of the electrolyte. x PO y F z (686.1 eV in F 1s and 134.6 eV in P 2p) and Li x PF y (688.2 eV in F 1s and 136.8 eV in P 2p) were found in the uncoated LN83 anode than in the recovered 1.0 OS anode. When additional etching analysis was attempted on the recovered LN83 anode, CO, C=O, LiF, Li x PO y F z and Li x PF y The proportion of undesirable adducts such as these was significantly reduced in the recovered 1.0 OS anode. In contrast, a significant portion of these adducts still remained in the recovered original LN83 anode. This indicates that a relatively thick decomposition layer developed on the recovered original LN83 anode due to severe electrolyte decomposition.

[0075] F - The species can corrode the transition metal components of the anode through chemical reactions, so F -The concentration of the species should be controlled as low as possible. To further investigate the role of Ca species, OS was treated with fluoride (F - ) was reacted with TBAF equivalent to the species. When the dried mixture was analyzed using XRD (Fig. 9a), the primary product was found to be CaF2, which means that Ca is F - Indicates binding to a species. Ca is F - It is considered to have a strong binding affinity for the species (592 kJ mol-1), which means that Ca is released through the scavenging reaction. - This suggests that the species can be captured. Consistent results were also observed in the ICP-MS analysis of the recovered Li anode (Fig. 9b). F - The species is effectively dissolved in the electrolyte due to its favorable solubility properties when combined with Ni, Co, and Mn during cycling. Subsequently, the dissolved F-bonded transition metal components are easily precipitated on the Li anode through electrochemical reduction at the Li anode. This allows for comparative quantification of the cycled Li anode with F - This means that it can be helpful in effectively estimating the degree of anode corrosion due to species. The Li anode cycled with the untreated LN83 anode showed Ni, Co, and Mn of 16,921, 2,375, and 2,506 ppm, respectively. The Li anode cycled with the 1.0 OS anode showed Ni, Co, and Mn of 4,707, 314, and 742 ppm, respectively, which were lower than those cycled with the untreated LN83 anode. These results indicate that surface modification using the OS precursor suppresses undesirable reactions, such as microcracking and electrolyte decomposition, and preserves the structure of the LN83 anode material, providing excellent cycling durability.

[0076]

[0077] <National Research and Development Project Supporting This Invention>

[0078] This patent application is the result of a basic research project supported by the National Research Foundation of Korea with funding from the Ministry of Science and ICT (Project No. 2022R1F1A1069039).

[0079] This patent application is the result of a basic research project and a university-focused research institute support project in the field of science and engineering, supported by the National Research Foundation of Korea and funded by the Ministry of Education (Project No. 2017R1A6A1A06015181).

[0080] This patent application is the result of the Electric Vehicle High-Power Battery and Charging System Technology Development Project (Project No. 20011905), which was carried out with the support of the Korea Institute of Industrial Technology Planning and Evaluation and with funding from the Ministry of Trade, Industry and Energy.

Claims

1. A positive electrode active material; and a positive electrode active material for a lithium secondary battery comprising an oyster shell coating layer on the surface of the positive electrode active material.

2. In paragraph 1, The above positive electrode active material is a positive electrode active material for a lithium secondary battery, characterized by being represented by the following [chemical formula 1]; [Chemical Formula 1] LiNi a Co b Mr c O2(0.6≤a≤0.9, a+b+c=1).

3. In paragraph 1, The above positive electrode active material is LiNi 0.83 Co 0.11 Mn 0.06 A cathode active material for a lithium secondary battery characterized by being O2.

4. In paragraph 1, A cathode active material for a lithium secondary battery, characterized in that the oyster shell reacts with residual lithium on the surface of the cathode active material to reduce the amount of residual lithium.

5. In paragraph 1, A cathode active material for a lithium secondary battery, characterized in that the oyster shell coating layer acts as a cathode-electrolyte interphase (CEI) layer.

6. In paragraph 1, A cathode active material for a lithium secondary battery, characterized in that the oyster shell coating layer comprises CaO or CaCO3.

7. In paragraph 5, A cathode active material for a lithium secondary battery, characterized in that as the amount of the oyster shell increases, the amount of CaO increases more than the amount of CaCO3.

8. In paragraph 5, As the amount of oyster shell increases, the lithium diffusion coefficient (D Li+ ) A positive electrode active material for a lithium secondary battery characterized by a decrease in the amount of the positive electrode active material.

9. In paragraph 1, A cathode active material for a lithium secondary battery, characterized in that the oyster shell coating layer suppresses electrolyte decomposition at the cathode interface.

10. In paragraph 1, A cathode active material for a lithium secondary battery, characterized in that the oyster shell coating layer above suppresses cracking of the cathode that may occur during cycling.

11. In paragraph 1, The above oyster shell coating layer is fluorine (F) generated during cycling - ) A cathode active material for a lithium secondary battery characterized by capturing a species.

12. A positive electrode comprising any one of the positive electrode active materials of clauses 1 to 11; electrolyte; and A lithium secondary battery containing a cathode.

13. Step of mixing positive electrode active material and oyster shell powder and A method for producing a positive electrode active material for a lithium secondary battery, comprising a step of heat-treating the above mixture.

14. In paragraph 13, A method for manufacturing a positive electrode active material for a lithium secondary battery, characterized in that the oyster shell powder is contained in an amount of 0.1 to 10 wt% relative to the weight of the positive electrode active material.

15. In paragraph 13, A method for manufacturing a cathode active material for a lithium secondary battery, characterized in that the above heat treatment is performed at a temperature of 300 to 800°C for 1 to 12 hours.

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