Al-Y co-doped ZrO2 coated NCM811 positive electrode material and preparation method and application thereof

Abstract

The invention discloses an Al-Y co-doped ZrO2 coated NCM811 positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion battery positive electrode materials. The positive electrode material is composed of NCM811 and a coating layer which coats the surface of the NCM811 and is composed of Al-YSZ nanoparticles. The Al-YSZ coating layer can induce NCM811 lattice parameter optimization, the unit cell volume is increased by 0.00026 nm < 3 >, meanwhile, the interface stability is enhanced through the chemical anchoring effect, the occurrence of H2-to-H3 irreversible phase change in high-pressure circulation is effectively inhibited, the dissolution of transition metal ions is reduced, and the lithium ion transmission kinetics is optimized. The preparation process of the material is green and efficient, and a new scheme is provided for interface engineering design of the high-nickel positive electrode material under extreme working conditions.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to an Al-Y co-doped ZrO2-coated NCM811 cathode material and its preparation method, as well as its application in lithium-ion batteries under extreme conditions such as high voltage, high temperature and high rate. Background Technology

[0002] As a core component of new energy storage and power systems, the improvement of lithium-ion batteries' energy density and cycle life plays a decisive role in the development of electric vehicles and smart grids. High-nickel layered oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) has become the preferred cathode material for achieving high energy density batteries due to its ultra-high specific capacity (>200 mAh / g) and cost advantage.

[0003] However, this material faces severe challenges under extreme conditions such as high voltage (>4.3 V), high temperature (>45℃), and high rate (>3 C): Experimental data show that the capacity retention rate of traditional NCM811 is less than 65% after 100 cycles at 4.5 V, the capacity decay rate is more than 20% after 200 cycles at 45℃, and the capacity loss exceeds 40% after 200 cycles at 5 C. These performance degradations are mainly due to three mechanisms: (1) the irreversible phase transition H2→H3 induced by high voltage leads to lattice distortion; (2) high temperature exacerbates the dissolution of transition metal ions and triggers electrolyte decomposition; (3) lithium ion diffusion retardation and particle microcrack propagation caused by high rate charge and discharge. Therefore, developing modification strategies that can improve the comprehensive performance of NCM811 under extreme conditions is of great research value.

[0004] Surface coating technology, by constructing stable physical / chemical barriers, has become an effective means to improve the stability of electrode interfaces. Among them, ZrO2-based ceramic materials exhibit unique advantages due to their outstanding mechanical properties and high thermal stability. While traditional wet chemical methods (such as sol-gel, chemical precipitation, and atomic layer deposition) can obtain uniform coatings, they suffer from complex processes (requiring precise control of pH / temperature) and high equipment costs (ALD equipment investment > 10). 6 Bottlenecks include the US dollar and difficulties in large-scale production.

[0005] In view of this, the present invention employs a dry ball milling combined with calcination process to successfully construct an Al-YSZ (Al-doped Y2O3-stabilized ZrO2) coating system on the surface of NCM811. The prepared cathode material exhibits excellent electrochemical performance under extreme operating conditions. Summary of the Invention

[0006] The purpose of this invention is to propose an Al-Y co-doped ZrO2-coated NCM811 cathode material, its preparation method and application, in order to solve the problem of performance degradation of traditional NCM811 under extreme conditions such as high voltage, high temperature and high rate.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An Al-Y co-doped ZrO2-coated NCM811 cathode material, made from LiNi 0.8 Co 0.1 Mn 0.1 The system consists of O2 (NCM811) and a coating layer on its surface composed of Al-Y co-doped ZrO2 (Al-YSZ) nanoparticles, wherein the Al-YSZ particles have a size of 50–150 nm and are coated on the NCM811 surface at a mass of 0.5%–2% of NCM811.

[0009] Furthermore, this invention also proposes a method for preparing the Al-Y co-doped ZrO2-coated NCM811 cathode material. The method is simple, low-cost, and suitable for large-scale production. Specifically, it includes the following steps:

[0010] Step (1) Preparation of Al-Y co-doped ZrO2 (Al-YSZ) powder: ZrOCl2·8H2O, Y(NO3)3·6H2O and Al(NO3)3·6H2O were dissolved in an appropriate amount of deionized water at a stoichiometric ratio of n(Zr):n(Y):n(Al): = 100:5:2 to obtain a mixed solution; ammonia was added to the mixed solution as a precipitant to adjust the pH value to 9 and a precipitate was obtained; the precipitate was filtered, washed until neutral, dried at 80℃ for 12 h, and then calcined at 1000℃ for 2 h. After pulverization and grinding, Al-Y co-doped ZrO2 (Al-YSZ) powder was obtained.

[0011] Step (2) Raw material mixing: 1 wt% Al-Y co-doped ZrO2 and NCM811 material were dry-mixed using a planetary ball mill at 200 rpm for 30 min;

[0012] Step (3) Calcination treatment: The dry-mixed material is calcined at 600℃ for 4 h in an oxygen atmosphere in a tube furnace, and after cooling, Al-Y co-doped ZrO2 coated NCM811 cathode material is obtained.

[0013] Furthermore, this invention also proposes the application of this Al-Y co-doped ZrO2-coated NCM811 cathode material in lithium-ion batteries, especially its application under extreme operating conditions. Specifically, the cathode material is used to prepare a lithium-ion battery cathode sheet, and the preparation method includes the following steps:

[0014] Step (1) Slurry preparation: Weigh Al-Y co-doped ZrO2-coated NCM811 cathode material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and put them into a ball mill jar. At the same time, add an appropriate amount of N-methylpyrrolidone (NMP) and ball mill at 200 rpm for 30 min to prepare a slurry.

[0015] Step (2) Electrode preparation: The slurry is coated on the current collector aluminum foil, dried at 80°C and cut into round pieces as positive electrodes.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. Process Advantages: The innovative dry ball milling combined with calcination process overcomes the complexity and high cost bottlenecks of traditional wet processes. Solvent-free preparation avoids organic residue contamination of the electrode interface, meeting green manufacturing requirements. The mechanochemical effect generated by high-energy ball milling enhances the interfacial bonding energy between the coating material and the matrix. 600℃ heat treatment induces stable chemical bonds between the coating layer and the NCM811 matrix material, enhancing interfacial stability and preventing coating peeling during cycling. Although the ball-milled coating exhibits uneven thickness and discontinuous particles, its significant improvement in electrode performance indicates that a rationally designed functionalized coating with uniform morphology plays a more decisive role.

[0018] 2. Structural optimization: The Al-Y co-doped ZrO2 coating can induce optimization of the NCM811 lattice parameters, increasing the cell volume by 0.00026 nm. 3 Meanwhile, by enhancing interfacial stability through chemical anchoring effect, it effectively suppresses the occurrence of irreversible phase transition from H2 to H3 during high-pressure cycling, reduces the dissolution of transition metal ions, and optimizes lithium-ion transport kinetics.

[0019] 3. Performance enhancement: The coated and modified materials exhibit superior electrochemical performance under extreme conditions.

[0020] (1) Performance in the 2.8-4.3 V voltage window: At a 0.1 C rate, the initial discharge specific capacity of NCM811@Al-YSZ reached 212.5 mAh / g, an improvement of 18.6% compared to the unmodified NCM811 (179.2 mAh / g); at a high 5 C rate, it could still release a reversible capacity of 168.5 mAh / g, with a capacity retention of 79.3%, which was significantly improved compared to the original sample (140.6 mAh / g, retention of 78.4%). After 200 cycles at a 1 C current density, the discharge capacity remained at 161.5 mAh / g, with a capacity retention of 81.3%, which was further optimized compared to the unmodified sample (136.3 mAh / g, retention of 82.6%). In addition, after 200 cycles at 2.8-4.3 V, the lithium-ion diffusion coefficient of this material increased to 1.82×10⁻⁶. -12 cm 2 / s, with a charge transfer impedance of only 21.50 Ω, resulting in significantly improved dynamic performance.

[0021] (2) Triple extreme operating conditions: Under the conditions of 4.5 V high voltage, 45℃ high temperature and 5 C high rate, the capacity retention rate after 200 cycles increased by 65.17%, 64.47% and 85.99% respectively, which is 0.88%, 8.32% and 6.57% higher than the unmodified sample respectively. Among them, the discharge specific capacity under high voltage cycling reached 137.28 mAh / g, effectively inhibited the dissolution of transition metals in high temperature environment, and maintained excellent ion transport efficiency at high rate.

[0022] 4. In-depth mechanistic analysis reveals that the performance improvement stems from multiple synergistic effects: First, the coating layer effectively suppresses the excessive growth of the SEI film at high temperatures; second, it optimizes the interfacial lithium-ion transport kinetics, significantly reducing charge transfer impedance; finally, the physical barrier effect of the coating layer reduces the electrolyte penetration depth, thereby significantly mitigating irreversible phase transitions during high-voltage cycling. These findings provide important theoretical basis and practical guidance for optimizing the performance of high-nickel cathode materials under extreme operating conditions. Attached Figure Description

[0023] Figure 1 The structures and morphologies of zirconium-based oxides are shown in the following figures: (a) XRD pattern of ZrO2; (b) SEM pattern of ZrO2; (c) XRD pattern of YSZ; (d) SEM pattern of YSZ; (e) XRD pattern of Al-YSZ; (f) SEM pattern of Al-YSZ.

[0024] Figure 2XRD patterns of NCM811 materials coated with different zirconium-based oxides: (a) XRD pattern; (b) magnified view of (003) peak; (c) magnified view of (104) peak; (d) magnified view of (006) / (012) peak; (e) magnified view of (018) / (110) peak.

[0025] Figure 3 XPS spectra of NCM811 materials coated with different zirconium-based oxides: (a) full spectrum; (b) Zr 3d, Y 3d and Al 2p spectra; (c) O 1s spectrum; (d) Ni 2p spectrum; (e) Mn 2p spectrum; (f) Co 2p spectrum.

[0026] Figure 4 SEM images of NCM811 materials coated with different zirconium-based oxides (at different magnifications): (a), (b) NCM811; (c), (d) NCM811@Z; (e), (f) NCM811@YSZ; (g), (h) NCM811@Al-YSZ.

[0027] Figure 5 EDS images of NCM811 materials coated with different zirconium-based oxides: (a) NCM811; (b) NCM811@Z; (c) NCM811@YSZ; (d) NCM811@Al-YSZ.

[0028] Figure 6 TEM (a, b) and HRTEM (c, d) images of NCM811@Al-YSZ.

[0029] Figure 7 Electrochemical performance of NCM811 and its modified materials at room temperature in a voltage window of 2.8–4.3 V: (a) initial charge-discharge curves at a current density of 0.1 C; (b) initial charge-discharge characteristics; (c) rate performance at different current densities; (d) discharge curves at different current densities; (e) 200-cycle curves at a current density of 1 C; (f) charge-discharge curves at different cycle numbers at a current density of 1 C.

[0030] Figure 8Electrochemical performance of NCM811 and its modified materials under extreme conditions: (a) 200-cycle performance at a voltage window of 2.8–4.5 V, room temperature, and a current density of 1 C; (b) charge-discharge curves at different cycle numbers at a voltage window of 2.8–4.5 V, room temperature, and a current density of 1 C; (c) 200-cycle performance at a high temperature of 45 °C at a current density of 1 C and a voltage window of 2.8–4.5 V; (d) charge-discharge curves at a high temperature of 45 °C at a current density of 1 C and a voltage window of 2.8–4.3 V, with different cycle numbers; (e) 200-cycle performance at a high rate of 5 C, room temperature, and a voltage window of 2.8–4.3 V; (f) charge-discharge curves at a high rate of 5 C, room temperature, and a voltage window of 2.8–4.3 V, with different cycle numbers.

[0031] Figure 9 dQ / dV curves for NCM811 materials coated with different zirconium-based oxides: (a) NCM811; (b) NCM811@Z; (c) NCM811@YSZ; (d) NCM811@Al-YSZ.

[0032] Figure 10 CV curves for NCM811 materials coated with different zirconium-based oxides: (a) NCM811; (b) NCM811@Z; (c) NCM811@YSZ; (d) NCM811@Al-YSZ.

[0033] Figure 11 EIS impedance spectra and low-frequency Z'-ω curves of NCM811 materials coated with different zirconium-based oxides −1 / 2 Fitted curves: (a) AC impedance spectrum at 1st; (b) AC impedance spectrum at 200th; (c) Low-frequency region Z' and ω at 1st. −1 / 2 Relationship diagram; (d) Low-frequency region Z' and ω at 200 th −1 / 2 Relationship diagram.

[0034] Figure 12 GITT tests for NCM811 materials coated with different zirconium-based oxides: (a) Comparison of GITT test curves; (b) Detailed GITT test curves for NCM811; (c) Relationship between lithium-ion diffusion rate and potential during charging; (d) Relationship between lithium-ion diffusion rate and potential during discharging. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0036] Example 1

[0037] Preparation of NCM811@Al-YSZ material, and its use in fabricating cathode sheets and battery assembly:

[0038] 1. Material preparation

[0039] Preparation of Al-Y co-doped ZrO2 (Al-YSZ) powder: ZrOCl2·8H2O, Y(NO3)3·6H2O, and Al(NO3)3·6H2O were dissolved in an appropriate amount of deionized water at a stoichiometric ratio of n(Zr):n(Y):n(Al): = 100:5:2 to obtain a mixed solution; ammonia was added to the mixed solution as a precipitant to adjust the pH value to 9, and a precipitate was obtained; the precipitate was filtered, washed until neutral, dried at 80℃ for 12 h, and then calcined at 1000℃ for 2 h. After pulverization and grinding, Al-Y co-doped ZrO2 (Al-YSZ) powder was obtained.

[0040] Preparation of NCM811@Al-YSZ: 1 wt% Al-Y co-doped ZrO2 was dry-mixed with NCM811 material using a planetary ball mill at 200 rpm for 30 min; the dry-mixed material was calcined at 600℃ for 4 h in an oxygen atmosphere in a tube furnace, and after cooling, Al-Y co-doped ZrO2-coated NCM811 cathode material (abbreviated as NCM811@Al-YSZ) was obtained.

[0041] 2. Cathode preparation and battery assembly

[0042] Preparation of the positive electrode: Al-Y co-doped ZrO2-coated NCM811 positive electrode material, acetylene black, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1:1 and placed in a ball mill jar. At the same time, an appropriate amount of N-methylpyrrolidone (NMP) was added. The mixture was ball-milled at 200 rpm for 30 min to prepare a slurry. The slurry was coated on a current collector aluminum foil, dried at 80℃, and then cut into round pieces with a diameter of 14 mm as the positive electrode.

[0043] Battery Assembly: Stainless steel casings were used for both positive and negative electrodes. Polypropylene membrane (Celgar 2500) was used as the separator, lithium metal sheets were used as the negative electrode material, and a 1 mol / L LiPF6 electrolyte was used. The electrolyte solution was a mixed solvent with EC:DMC:EMC ratio of 1:1:1 (v / v / v). The batteries were assembled in a glove box under high-purity argon gas, following the order of positive electrode casing, positive electrode sheet, separator, electrolyte, lithium metal sheet, and negative electrode casing. After assembly, the coin cells were placed in a constant temperature chamber at 25°C for 12 hours.

[0044] Comparative Example 1

[0045] Using NCM811 to prepare positive electrode sheets and assemble batteries:

[0046] The battery assembly process is the same as in Example 1, where commercially available NCM811 is used directly to prepare the positive electrode sheet.

[0047] Comparative Example 2

[0048] Preparation of ZrO2-coated NCM811 (NCM811@Z) material, and its use in preparing cathode sheets and assembling batteries:

[0049] Preparation of ZrO2-coated NCM811: 1 wt% ZrO2 and NCM811 material were dry-mixed using a planetary ball mill at 200 rpm for 30 min; the dry-mixed material was calcined at 600℃ for 4 h in an oxygen atmosphere in a tube furnace, and after cooling, ZrO2-coated NCM811 material was obtained.

[0050] The battery assembly process after preparing the positive electrode sheet by coating NCM811 material with ZrO2 is the same as in Example 1.

[0051] Comparative Example 3

[0052] Preparation of YSZ-coated NCM811 (NCM811@YSZ) material, and its use in preparing cathode sheets and assembling batteries:

[0053] Preparation of YSZ-coated NCM811: 1 wt% of YSZ and NCM811 material were dry-mixed using a planetary ball mill at 200 rpm for 30 min; the dry-mixed material was calcined at 600℃ for 4 h in an oxygen atmosphere in a tube furnace, and after cooling, YSZ-coated NCM811 material was obtained.

[0054] The battery assembly process after preparing the positive electrode sheet using YSZ-coated NCM811 material is the same as in Example 1.

[0055] Characterization of materials prepared in Examples 1, 2, and 3, and electrochemical performance testing of assembled batteries:

[0056] The crystal structure, purity, and related material composition of the material were tested using an X-ray diffractometer (XRD, PANalytical B.V., Empyrean model), and the lattice parameters of the material were refined using Jade 6.5 software. The valence state and content of elements on the material surface were tested using an X-ray photoelectron spectroscopy (XPS, Shimadzu, AXIS SUPRA+ model). The morphology and surface elemental distribution of the material were tested using a scanning electron microscope (SEM, NEC Corporation, JSM-7610F model).

[0057] The LANBTS testing system was used to test the electrical performance of the batteries. The specific capacity, rate performance, cycle capacity retention, and constant current intermittent titration of the coin cells were tested, with a test voltage range of 2.8–4.3 V. The IVIUM electrochemical workstation was used to perform cyclic voltammetry and AC impedance testing on the batteries.

[0058] The characterization and test results are as follows:

[0059] 1. Structure and morphology of the coating material, zirconium-based oxide

[0060] Figure 1 The XRD and SEM spectra of zirconium-based oxides are shown. Analysis indicates that all three materials exhibit nanoparticle structures, but their crystallographic characteristics differ. Figure (a) shows the XRD pattern of ZrO2, which matches the standard card of monoclinic zirconium oxide (M-ZrO2, PDF#86-1450). The peaks are sharp and free of impurities, indicating high crystallinity. Figures (b) and (c) show the XRD patterns of YSZ and Al-YSZ, both corresponding to tetragonal zirconium oxide (T-ZrO2, PDF#49-1642), indicating that the doping of yttrium and aluminum induced the transformation of the crystal structure from monoclinic to tetragonal. SEM images show that the particle size of ZrO2(b) and YSZ(d) is about 200 nm, with a near-spherical distribution and uniform morphology, indicating that the doping of Y2O3 did not significantly change the macroscopic morphology of the particles; while the particles of Al-YSZ(f) are significantly refined to about 100 nm, indicating that the introduction of Al further inhibits grain growth.

[0061] 2. Effect of zirconium-based oxide coating modification on the structure of NCM811

[0062] Figure 2 XRD analysis revealed a significant regulatory effect of zirconium-based oxide coating on the crystal structure of NCM811. The main diffraction pattern (a) shows that all modified samples retain the α-NaFeO2 type layered structure characteristics (space group R-3m), confirming that the coating treatment did not change the basic crystal configuration of the matrix material. The magnified pattern (b) shows that the (003) diffraction peak of the modified samples systematically shifts to a lower angle, which can be attributed to three synergistic mechanisms: (1) Zr 4+ During high-temperature calcination, some of the Li sites are occupied, leading to an expansion of the lithium-oxygen interlayer spacing; (2) interfacial stress between the coating layer and the substrate induces lattice expansion; (3) large-radius Al 3+ (0.535Å) and Y 3+ (0.90 Å) Ni substitution 2+The (0.69 Å) transition metal sites induce local distortion of the lithium-oxygen layer. The simultaneous left shift of the (104) peak (Fig. (c)) indicates an increase in the interlayer spacing of the transition metal layers and a decrease in cation mixing, confirming a significant improvement in interlayer order. Notably, the (006) / (012) and (018) / (110) characteristic peaks (Fig. de) retain their sharp splitting morphology after coating, and their peak spacing is basically consistent with that of the original sample, proving that the coating modification does not destroy the intrinsic long-range order of the layered structure. This multi-scale lattice regulation forms a synergistic effect: the lithium interlayer spacing expands to Li + Diffusion provides optimized pathways, while the ordering of the transition metal layer suppresses cation mixing; together, these two factors enhance the structural stability during cycling.

[0063] The XRD refinement data in Table 1 show that the zirconium-based oxide coating system (especially NCM811@Al-YSZ) synergistically optimizes the NCM811 structure through a triple mechanism: First, the synergistic growth of lattice constants a (+0.000283 nm) and c (+0.000835 nm) induces cell volume expansion (ΔV = +0.00026 nm). 3 This is related to the leftward shift of the (003) diffraction peak. Figure 2 (b) jointly confirms high electricity prices. 3+ Doping-induced lattice distortion effect, its ionic radius difference (Al 3+ 0.535 Å vs Ni 2+ (0.69 Å) leads to widening of interlayer channels; secondly, I (003) / I (104) The increase in intensity ratio to a peak of 1.621 (a 2.1% increase compared to the original sample) confirms that Al 3+ / Y 3+ Co-doping stabilizes the transition metal layer through strong Al-O bonds, significantly suppressing cation mixing; finally, [I (006) + I (012) ] / I (101) The ratio decreased from 0.431 to 0.420 (theoretically, this decrease corresponds to enhanced long-range order of the layered structure), and combined with the slight decrease in the c / a axis ratio (4.945934 → 4.943969), both indicate that the coating layer optimizes structural regularity through interfacial stress reconstruction. These structural evolutions are directly related to electrochemical performance: the synergistic expansion of a / c widens the lithium-ion transport channels, while the improved cation order enhances cycle stability, ultimately achieving a synergistic improvement in kinetic performance and structural stability.

[0064] Table 1. Effect of zirconium-based oxide coating on the lattice parameters of NCM811

[0065] sample a (nm) c (nm) c / a <![CDATA[I (003) / I (104) ]]> <![CDATA[[I (006) +I (012) ] / I (101) ]]> <![CDATA[V(nm 3 ) <!-- 5 -->]]> NCM811 0.287056 1.419760 4.945934 1.587 0.431 0.10132 NCM811@Z 0.287224 1.419869 4.94342 1.600 0.429 0.10144 NCM811@YSZ 0.287243 1.420124 4.943981 1.595 0.423 0.10147 NCM811@Al-YSZ 0.287339 1.420595 4.943969 1.621 0.420 0.10158

[0066] To investigate the effect of zirconium-based oxide coating on the elemental composition and chemical state of NCM811 cathode material, XPS analysis revealed the following: Figure 3 (a) Significant Zr 3p and Zr 3d characteristic peaks were observed in all coated samples in the full spectrum, confirming the successful introduction of zirconium. Figure 3 (b) Fine spectral analysis: 3d-dimer of Zr in the NCM811@Z sample 5 / 2 (181.43 eV) and 3d 3 / 2 The binding energy (183.82 eV) all points towards Zr. 4+ Valence state; NCM811@YSZ sample except Zr 4+ Signal (3d) 5 / 2 181.14 eV, 3d 3 / 2 In addition to 183.49 eV, Y 3d 5 / 2 The binding energy of 157.19 eV confirms Y 3+ Zr is present in the NCM811@Al-YSZ sample; Zr is retained. 4+ Price state (3d) 5 / 2 181.11 eV, 3d 3 / 2 : 183.51 eV), Y 3+ The binding energy shifted to 155.70 eV, and an Al 2p characteristic peak was detected at 67.8 eV, confirming successful aluminum doping. Figure 3 (c) The O 1s spectrum shows that the proportion of lattice oxygen (Metal-O, 528.77 eV) in the coated material is significantly increased, while the content of surface adsorbed oxygen (Li2CO3 / LiOH, 531.47 eV) is reduced, indicating that the zirconium-based coating layer effectively suppresses surface side reactions and enhances structural stability. Figure 3 (d) In the Ni 2p spectrum, the Ni coating sample 2+ / Ni 3+ The ratios (NCM811@Z: 0.35, NCM811@YSZ: 0.33, NCM811@Al-YSZ: 0.21) are all lower than those of the original NCM811 material (0.50). Combined with XRD refinement results, this confirms that zirconium-based coating significantly reduces the Ni content of the lithium layer. 2+ The proportion, thereby effectively alleviating Li + / Ni 2+ Cation mixing. It is worth noting that... Figure 3 The peak fitting results of the Co 2p and Mn 2p spectra in (e, f) are basically consistent before and after coating, indicating that the modification of zirconium-based oxide did not change the chemical state of cobalt and manganese.

[0067] 3. Effect of zirconium-based oxide coating modification on the morphology of NCM811

[0068] Figure 4 The microstructure evolution of NCM811 and its zirconium-based oxide-coated samples is shown. Low-magnification SEM images (a, c, e, g) reveal that both the original NCM811 and the ZrO2, YSZ, and Al-YSZ-coated samples exhibit a spherical secondary particle structure formed by the accumulation of irregular submicron-sized primary particles. The particle size distribution is uniform (approximately 15 μm), and the coating process did not significantly alter the morphology of the secondary particles. However, compared to the original NCM811 (a), the surface roughness of the zirconium-based oxide-coated samples (c, e, g) is significantly increased, indicating that the coating layer has been successfully loaded onto the substrate surface.

[0069] Further observation of the high-magnification images (b, d, f, h) revealed that the uncoated NCM811 (b) surface was smooth and clean with clear grain boundaries; while the NCM811@Z (d) coated with ZrO2 had approximately 200 nm spherical ZrO2 nanoparticles distributed on its surface, attached in a discrete manner, consistent with the spherical morphology characteristic of the highly crystalline ZrO2 itself; the NCM811@YSZ (f) surface also had approximately 200 nm spherical YSZ particles distributed on its surface, with uniform morphology, reflecting the characteristic that Y2O3 doping did not significantly change the macroscopic morphology of zirconium oxide; the Al-YSZ particles on the NCM811@Al-YSZ (h) surface were significantly refined to approximately 100 nm, which is directly related to the characteristic of Al introduction inhibiting grain growth.

[0070] In all three coated samples, the zirconium-based oxide particles adhered to the substrate surface in a discontinuous manner, failing to form a completely closed coating structure. Nevertheless, these coated particles with specific morphologies could still partially prevent direct contact between NCM811 and the electrolyte, thereby mitigating the erosion of the active material by corrosive substances such as HF. Notably, the Al-YSZ coated sample (h) exhibited a higher particle density than the other systems, and due to the particle size refinement to 100 nm, its grain size distribution was more uniform than the undoped system, further confirming the superior properties of Al-YSZ. 3+ The regulatory effect on zirconia crystal growth. This discontinuous coating strategy, while maintaining ion transport channels, provides a possible physical barrier for suppressing interfacial side reactions by relying on the specific morphological characteristics of different zirconium-based oxides.

[0071] Figure 5EDS surface scanning analysis revealed the elemental distribution characteristics of NCM811 and its modified materials. In the original NCM811(i), Ni, Co, and Mn elements (labeled cyan, green, and red, respectively) exhibited a continuous and uniform dispersed distribution on the secondary particle surface, and the O element signal (purple) completely covered the matrix, indicating that the coordination structure of the ternary active components with oxygen atoms was intact in the uncoated material. In the zirconia-coated NCM811@Z(j), while retaining the uniform distribution of Ni / Co / Mn, the newly added Zr element (bright yellow) adhered to the particle surface in a discrete island structure, and its distribution area partially overlapped with the O signal, confirming that ZrO2 exists in the form of discontinuous nanoparticles. For the yttrium-stabilized zirconia-coated NCM811@YSZ(k), the Y element (blue) and Zr element formed a highly overlapping continuous distribution band at the particle edge, and the O signal was significantly enhanced in this region, indicating that the YSZ coating layer achieved near-complete coverage of the matrix in the form of a (Y,Zr)O2 solid solution. In the aluminum-doped yttrium-stabilized zirconia-coated sample NCM811@Al-YSZ(l), the Al element (orange) exhibits a uniform distribution within the coating layer, highly overlapping with the Y / Zr element coverage area. Simultaneously, the Ni / Co / Mn signal intensity gradually decreases with increasing coating layer integrity. The elemental distribution maps of all samples strictly match the spatial contours of their corresponding grayscale images, verifying the stability of the matrix morphology during the coating modification process.

[0072] Figure 6 TEM and HRTEM image analysis revealed that a layer of Al-YSZ coated particles with a thickness of approximately 100 nm formed on the surface of the NCM811@Al-YSZ sample prepared by dry ball milling combined with calcination. These nanoparticles exhibited an irregular spherical structure, indicating that the coated material retained its original crystal framework after high-temperature treatment and did not undergo significant phase transformation or structural degradation. This phenomenon directly confirms the successful implementation of the coating process, effectively isolating the electrolyte from erosion of the substrate through a physical barrier effect, inhibiting transition metal dissolution and interfacial side reactions, and providing microscopic mechanism support for improved capacity retention in subsequent electrochemical performance testing.

[0073] 4. Effect of zirconium-based oxide coating modification on the electrochemical performance of NCM811

[0074] Figure 7(a) and (b) compare the initial charge-discharge behavior of NCM811 and its coated modified materials, revealing the regulatory mechanism of surface engineering strategies on the reversible capacity and electrochemical stability of the materials. This mechanism is directly related to the crystal structure and morphology of zirconium-based oxides. NCM811@Z coated with monoclinic zirconium oxide (M-ZrO2) exhibits significantly improved charging specific capacity (228.6 mAh / g) and discharging specific capacity (188.8 mAh / g) compared to the original NCM811 (218.4 / 179.8 mAh / g) due to the approximately 200 nm spherical nanoparticles and high crystallinity of ZrO2. The coulombic efficiency also slightly increased from 82.3% to 82.6%. This result stems from the physical barrier effect of monoclinic ZrO2, which inhibits electrolyte decomposition and allows for deeper lithium extraction. However, the intrinsically low ionic conductivity due to high crystallinity causes some extracted lithium ions to be irreversibly retained at the interface, thus limiting the efficiency improvement. Yttrium-stabilized zirconium oxide (YSZ)-coated NCM811@YSZ, due to the tetragonal phase (T-ZrO2) and particle size of approximately 200 nm (Y2O3 doping did not significantly alter the macroscopic morphology), showed further improvements of 2.2% and 2.0% in charge specific capacity (233.7 mAh / g) and discharge specific capacity (192.6 mAh / g) compared to NCM811@Z, but the coulombic efficiency slightly decreased to 82.4%. This is because tetragonal YSZ is more conducive to ion transport than monoclinic ZrO2 (the lattice openness of the tetragonal structure is superior to that of the monoclinic phase), but the 200 nm particle size may still present grain boundary transport resistance, resulting in no significant improvement in efficiency. Notably, the aluminum-doped yttrium-stabilized zirconium oxide NCM811@Al-YSZ exhibits breakthrough electrochemical performance due to the introduction of Al, which results in a tetragonal (T-ZrO2) coating layer with finer particles (approximately 100 nm) (Al inhibits grain growth). Its charge specific capacity (258.9 mAh / g) and discharge specific capacity (218.9 mAh / g) are increased by 18.5% and 21.7% respectively compared to the original material, and its coulombic efficiency is improved to 84.6%. This is attributed to two synergistic effects: firstly, the 100 nm finer particles increase the interfacial contact area between the coating layer and the substrate, reducing the ion transport distance; secondly, Al… 3+ Doping-induced YSZ lattice distortion creates high-density oxygen vacancy defects, widening the lithium-ion diffusion channels and suppressing irreversible oxygen loss at high potentials by anchoring surface lattice oxygen. Data patterns indicate that the transformation of the crystal structure from monoclinic to tetragonal can improve ion transport capability, while the combination of grain refinement and doping engineering can further optimize the defect state density, achieving a rebalancing of lithium-ion transport efficiency and electrochemical reversibility.

[0075] Figure 7(c) and (d) reveal the synergistic regulation mechanism of the zirconium-based oxide coating strategy on the lithium-ion transport kinetics and structural stability of NCM811 material through systematic rate performance testing. The original NCM811 exhibits an initial specific capacity of 179.2 mAh / g at a low rate of 0.1C. However, the NCM811@Z coated with monoclinic ZrO2 (M-ZrO2, PDF#86-1450) shows an increased capacity of 181.14 mAh / g due to the physical barrier effect of the 200 nm near-spherical particles suppressing electrolyte interfacial side reactions. However, the intrinsic characteristics of its monoclinic structure limit ion transport, resulting in a limited improvement in capacity. It is worth noting that the yttrium-doped YSZ-coated system (NCM811@YSZ), due to the tetragonal phase of YSZ (T-ZrO2, PDF#49-1642) and a particle size of approximately 200 nm, exhibits a further increase in capacity to 182.9 mAh / g at 0.1C. This increase is attributed to the YSZ content. 3+ The induced monoclinic-to-tetragonal phase transition passivates lattice defects, effectively reducing the diffusion barrier of lithium ions at the coating / matrix interface. Yttrium aluminum co-doped NCM811@Al-YSZ, due to its tetragonal coating (T-ZrO2, PDF#49-1642) and particle refinement to approximately 100 nm (Al inhibits grain growth), exhibits a breakthrough 0.1C capacity (212.5 mAh / g), an improvement of 18.6% compared to the original material. This is attributed to the increased interfacial contact area resulting from the refined particle size, combined with the tetragonal structure and Al... 3+ The induced surface oxygen vacancies optimized the cation mixing degree of the layered structure, significantly enhancing the reversibility of lithium-ion insertion / extraction. When the rate capability was increased to 5C, the original NCM811 capacity decayed to 140.6 mAh / g (78.4% retention); NCM811@Z, due to the limitation of rapid ion transport by the monoclinic ZrO2 phase, achieved a 5C capacity of 143.1 mAh / g (79.0% retention); NCM811@YSZ, thanks to the stability of its tetragonal phase structure, achieved a 5C capacity of 146.1 mAh / g (79.8% retention); while NCM811@Al-YSZ, due to the three-dimensional ion permeation channels synergistically constructed by the 100 nm refined particles and the tetragonal phase structure, achieved a 5C capacity of 168.5 mAh / g (79.3% retention), representing a 19.8% increase in absolute capacity compared to the original material and significantly mitigating concentration polarization effects. Data patterns confirm that yttrium doping stabilizes the zirconium oxide lattice by inducing a tetragonal phase transformation, thereby improving interfacial stability. The introduction of aluminum, on the other hand, refines the particles and modulates the chemical properties of defects in the coating layer and the interfacial contact. Together, they break through the optimization limits of single-component coating.

[0076] Figure 7(e) and (f) compare the cycling performance and capacity evolution of NCM811 materials with different coating modifications, revealing the differentiated regulation mechanism of surface engineering strategies on high-nickel cathode materials. The original NCM811 had an initial discharge specific capacity of 165.0 mAh / g in the 2.8–4.3 V voltage window, which decreased to 136.3 mAh / g after 200 cycles (capacity retention of 82.6%). This capacity decay was related to interfacial side reactions caused by electrolyte penetration and particle structure degradation. The zirconium oxide-coated NCM811@Z, due to the physical barrier effect of approximately 200 nm monoclinic ZrO2 (M-ZrO2, PDF#86-1450) particles, saw an initial discharge capacity increase to 171.8 mAh / g, which remained at 144.4 mAh / g after cycling (retention of 84.1%). However, the limited increase in capacity retention was due to the intrinsically low lithium-ion conductivity of the monoclinic coating layer. Yttrium-stabilized zirconia-coated NCM811@YSZ exhibits superior cycling stability due to the tetragonal phase (T-ZrO2, PDF#49-1642) and particle size of approximately 200 nm. The initial capacity of 171.4 mAh / g is maintained at 138.3 mAh / g after 200 cycles (86.5% retention). This is attributed to the high thermal stability and chemical inertness of the tetragonal phase structure. Y doping enhances lattice oxygen stability, effectively suppressing irreversible phase transitions and transition metal dissolution under high voltage. The aluminum-doped yttrium-stabilized zirconium oxide NCM811@Al-YSZ exhibits significant capacity advantages due to its tetragonal coating layer (T-ZrO2, PDF#49-1642) and finely refined particles (approximately 100 nm) (Al inhibits grain growth). It achieves an initial discharge capacity of 198.7 mAh / g (a 20.4% increase over the original material) and retains an absolute capacity of 161.5 mAh / g after 200 cycles, although the capacity retention (81.3%) is relatively low. This is due to the Al... 3+ Doping significantly improves initial capacity by widening lithium-ion transport channels and increasing active site density through the modulation of defect states in the coating layer. However, particle refinement and the local lattice distortion or interfacial stress accumulation introduced by doping may accelerate structural degradation in the later stages of cycling, resulting in a slightly higher capacity decay rate than the YSZ system. These results highlight the dual effect of surface coating design: the YSZ system extends cycle life through tetragonal phase structure stability optimization, while the Al-YSZ strategy overcomes capacity limits through defect engineering and particle refinement. The performance difference between the two provides an important reference for the modification of high-nickel cathode materials.

[0077] Figure 8Table 2 presents the cycling performance and capacity evolution of NCM811 and its zirconium-based oxide-coated modified materials under triple extreme conditions of high pressure (2.8 - 4.5 V, room temperature, 1 C), high temperature (45 °C, 1 C), and high rate (5 C, room temperature), revealing the differentiated regulation mechanism of the material's tolerance to extreme conditions by different coating strategies. In high-voltage cycling tests, the original NCM811 exhibited lattice distortion due to the irreversible H2→H3 phase transition, resulting in a discharge capacity of only 110.4 mAh / g after 200 cycles, with a capacity retention of 64.3%. NCM811@Z achieved a capacity retention of 70.1% thanks to the physical barrier effect of the monoclinic ZrO2 phase, but the low ionic conductivity of the monoclinic phase limited the absolute capacity. NCM811@YSZ effectively suppressed the phase transition by relying on the stable tetragonal phase structure of Y, achieving a maximum capacity retention of 71.6%. NCM811@Al-YSZ, due to the c-axis expansion (+0.000835 nm) induced by Al-Y co-doping, broadened the lithium-ion transport channel, achieving an absolute discharge capacity of 137.3 mAh / g. Although the capacity retention (65.2%) was slightly lower, this was due to the local lattice distortion introduced by doping, which may accelerate long-term structural degradation. In high-temperature testing, the original NCM811 experienced a sharp drop in capacity retention to 56.2% due to transition metal dissolution and electrolyte decomposition. NCM811@Z and NCM811@YSZ, thanks to the barrier effect of the coating layer, saw their retention rates increase to 60.0% and 60.6%, respectively. NCM811@Al-YSZ, however, achieved a retention rate of 64.5% and a discharge capacity of 124.7 mAh / g, demonstrating its advantage in suppressing high-temperature side reactions, thanks to the physical barrier of its approximately 100 nm coating layer and the stabilizing effect of Y / Al on surface oxygen vacancies (XPS analysis showed an increased lattice oxygen ratio). In high-rate testing, the original NCM811 exhibited a capacity of only 119.4 mAh / g after 200 cycles due to sluggish lithium-ion diffusion. While NCM811@Z and NCM811@YSZ showed improvement, NCM811@Al-YSZ benefited from Al doping, which refined the particles (approximately 100 nm), increased interfacial contact, and optimized oxygen vacancy kinetics (diffusion coefficient 1.82 × 10⁻⁶). -12 cm 2 The catalyst exhibits a high capacity of 144.8 mAh / g with a retention rate of 86.0%, highlighting its unique role in mitigating concentration polarization. These results demonstrate that the YSZ system optimizes cycle life through structural stability, while Al-YSZ overcomes the capacity bottleneck under extreme conditions through defect engineering and lattice manipulation, providing practical evidence for the "stability-kinetics" balance in the design of high-nickel materials adapted to extreme conditions.

[0078] Table 2 Comparison of electrochemical performance of NCM811 and its modified materials under extreme conditions

[0079] sample 2.8 - 4.5 V, RT, 1 C, 200-cycle discharge specific capacity (mAh / g) Capacity retention (%) at 2.8 - 4.5 V, RT, 1 C, 200 weeks 2.8 - 4.3 V, 45℃, 1 C, 200-cycle discharge specific capacity (mAh / g) Capacity retention (%) at 2.8 - 4.3 V, 45℃, 1 C, for 200 weeks 2.8 - 4.3 V, RT, 5 C, 200-cycle discharge specific capacity (mAh / g) Capacity retention (%) at 2.8 - 4.3 V, RT, 5 C, 200 weeks NCM811 110.4 64.3 99.2 56.2 119.4 82.2 NCM811@Z 117.1 70.1 108.4 60.0 125.4 85.4 NCM811@YSZ 124.0 71.6 113.8 60.6 130.3 89.7 NCM811@Al-YSZ 137.3 65.2 124.7 64.5 144.8 86.0

[0080] Table 3 compares the electrochemical performance of NCM811 cathode materials modified with different coating systems. The results show that, compared with mesoporous SiO2, CeO2 / LiCeO2, and TiO2 / Li4Ti5O2 prepared by traditional wet chemical or physical methods such as hydrolysis, liquid-phase mixing, and magnetron sputtering, the NCM811 cathode materials modified with different coating systems have significantly better performance. 12 With the same coating layer, the Al-doped YSZ (Al-YSZ) coating system prepared by the dry ball milling process of this invention exhibits superior comprehensive electrochemical performance. Within a voltage window of 2.8–4.3 V, this system retains a discharge specific capacity of 188.3 mAh / g after 100 cycles at a current density of 1 C, with a capacity retention rate as high as 94.8%. Even after 200 cycles, its discharge specific capacity still reaches 161.5 mAh / g. Simultaneously, its discharge capacity at a high rate of 5 C reaches 168.5 mAh / g, significantly better than most comparative systems (such as mesoporous SiO2 (123.0 mAh / g), CeO2 / LiCeO2 (136.0 mAh / g), and Li2ZrO3 (120.0–135.0 mAh / g)). This performance advantage stems from the unique interfacial characteristics imparted by the dry ball milling process: solvent-free preparation avoids contamination of the electrode interface by organic residues, high-energy mechanochemical effects enhance the interfacial bonding energy between the coating layer and the substrate, and stable chemical bonds induced by calcination at 600℃ effectively suppress the peeling off of the coating layer during cycling; at the same time, the co-doping of Al and Y induces the expansion of the NCM811 cell volume to broaden the lithium-ion transport channels by regulating the YSZ lattice structure, reducing the cation mixing degree to enhance structural stability, and optimizing the interfacial lithium-ion transport kinetics by introducing oxygen vacancy defects. Thus, while improving the cycling stability of the material, it significantly improves its high-rate performance, providing a more efficient and green technical path for the coating modification of high-nickel cathode materials.

[0081] Table 3 Comparative Study of Electrochemical Performance of Different Coating Systems on NCM811 Cathode Material

[0082] Covering material Synthesis method Voltage window (V) Capacity @ CR @ Rate @ Cycles @ Celsius Ratecapability at 5C <![CDATA[mesoporousSiO2 layer [1] ]]> Hydrolysis 2.7 -4.3 162.8 mAh / g @ 87.3 % @ 1 C @ 100th @ RT 123.0 mAh / g <![CDATA[CeO2 / LiCeO2 [2] ]]> Liquid phase mixing method / - 4.3 ~ 160.0 mAh / g @ 90.9 % @ 0.5 C @ 100 th @ RT 136.0 mAh / g <![CDATA[SiO2 / Li2SiO3 [3] ]]> Hydrolysis-Condensation Method 2.7 -4.3 174.3 mAh / g @ 92.0 % @ 1 C @ 100th @ RT 155.0 mAh / g <![CDATA[WO3 / Li2WO4 [4] ]]> Liquid phase method 3.0 -4.3 177.3 mAh / g @ 97.36 % @ 0.5 C @ 100th @ RT Between 120.0 and 130.0 mAh / g <![CDATA[TiO2 / Li4Ti5O 12 [5] ]]> Magnetron sputtering 2.8 -4.3 169.8 mAh / g @ 93.2 % @ 1 C @ 100th @ RT 149.7 mAh / g <![CDATA[Li 0.34 La 0.55 MnO3 -x [6] ]]> coprecipitation method 2.7 -4.3 137.5 mAh / g @ 82.5 % @ 1 C @ 100th @ RT Between 100.0 and 120.0 mAh / g <![CDATA[Al2O3 / LiAlO2 [7] ]]> wet ball milling 2.5 -4.3 162.7 mAh / g @ 90.1 % @ 1 C @ 100th @ RT 139.2 mAh / g <![CDATA[Al2O3 [8] ]]> Atomic deposition method 2.7 -4.3 143.9 mAh / g @ 93.8 % @ 1 C @ 100th @ RT Between 125.0 and 150.0 mAh / g <![CDATA[Ti-doped V2O5 [9] ]]> Liquid phase method 2.8 -4.3 139.7 mAh / g @ 82.0 % @ 1 C @ 100th @ RT 151.1 mAh / g <![CDATA[Li2ZrO3

[10] ]]> Sol-gel method 3.0 -4.3 162.9 mAh / g @ 87.6 % @ 1 C @ 200th @ RT Between 120.0 and 135.0 mAh / g <![CDATA[LiNbO3

[11] ]]> coprecipitation method 2.7 -4.3 168.0 mAh / g @ 87.1 % @ 1 C @ 200th @ RT 160.0 mAh / g Al-doped YSZ (This invention) Dry ball milling 2.8 -4.3 188.3 mAh / g @ 94.8 % @ 1 C @ 100 th @ RT; 161.5mAh / g @ 81.3 % @ 1 C @ 200 th @ RT 168.5 mAh / g

[0083] References for the sources of each coating material in Table 3:

[0084] [1]DU P, PAN YL, GAO XR, et al. Stabilizing LiNi 0.8 Co 0.1 Mn 0.1 O2cathodes with a mixed ionic-electronic conducting Li0.34 La 0.55 MnO3-xmultifunctional coating formed via in-situ conversion of surface Li residual[J]. Journal of Alloys and Compounds, 2024, 979.

[0085] [2]WANG L M, SU Q M, SHI W H, et al. Optimized structure stabilityand cycling performance of LiNiCoMnO through homogeneous nano-thickness AlOcoating br [J]. Electrochimica Acta, 2022, 435.

[0086] [3]AL-SAMET M A M M, BURGAZ E. A novel coating layer of mesoporoussilica on LiNiCoMnO (NCM811a) cathode material for advanced lithium-ionbatteries [J]. Electrochimica Acta, 2024, 507.

[0087] [4]WANG D, JIANG H N, FENG M, et al. A universal multifunctional rareearth oxide coating strategy to stabilize high-nickel lithium layered oxidecathode [J]. Journal of Alloys and Compounds, 2024, 976.

[0088] [5]LI Y J, ZHANG D Y, YAN Y X, et al. Enhanced electrochemicalproperties of SiO-LiSiO-coated NCM811 cathodes by reducing surface residuallithium [J]. Journal of Alloys and Compounds, 2022, 923.

[0089] [6]YOU L Z, LI G X, HUANG B, et al. Surface-reinforced NCM811 withenhanced electrochemical performance for Li-ion batteries [J]. Journal ofAlloys and Compounds, 2022, 918.

[0090] [7]HUANG K, YANG H L, XIE T Z, et al. Li4Ti5O 12 -TiO2 composite coatinglayer enabling LiNi 0.8 Co 0.1 Mn 0.1 O2 electrodes with superior cycling performance[J]. Journal of Electroanalytical Chemistry, 2023, 951.

[0091] [8]WANG J T, ZHAO D, ZHOU G, et al. Effects of Al2O3 and LiAlO2 Co-coating on electrochemical properties of LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode materials[J]. Ceramics International, 2023, 49(10): 15842-50.

[0092] [9]KANG W, JIANG A, CHEN S H, et al. High-performance Ti-doped V2O5coating on the Ni-rich layered cathode: Construction and theoreticalcalculation [J]. Journal of Alloys and Compounds, 2024, 970.

[0093]

[10] ZENG Y H, LU X X, MAO Q Z, et al. Effect of annealing temperatureon the microstructure and electrochemical performance of Li2ZrO3-modified Ni-rich NCM811 [J]. Chemical Engineering Science, 2023, 281.

[0094]

[11] LI Z, YOU Y, LIU Y, et al. Analyzing the mechanism of performanceimprovement in LiNi 0.8 Co 0.1 Mn 0.1 O2 through coating with LiNbO3 fast ion conductor[J]. Ceramics International, 2024, 50(17): 30493-503.

[0095] 5. Analysis of Modification Mechanism

[0096] Figure 9The evolution of differential capacity (dQ / dV) curves for four cathode materials (a) NCM811, (b) NCM811@Z, (c) NCM811@YSZ, and (d) NCM811@Al-YSZ at different cycle numbers during 1C cycling in a voltage window of 2.8–4.3 V is shown. All systems exhibit a significant H2 / H3 phase transition peak shift near 4.2 V. The original NCM811 shows a 0.042 V shift in the H2 / H3 phase transition peak towards higher voltages during charging, while the samples coated with ZrO2, YSZ, and Al-YSZ show shifts of only 0.018 V, 0.015 V, and 0.021 V, respectively. The reverse phase transition peak shift during discharge is more pronounced. The H2 / H3 peak of the unmodified NCM811 shifts towards lower voltage by 0.060 V, while the peak shift of the coated and modified systems decreases sequentially to 0.031 V (ZrO2), 0.024 V (YSZ), and 0.043 V (Al-YSZ). Notably, the differential capacity curves of the zirconium-based oxide-coated samples exhibit higher overlap during cycling, indicating better electrochemical reversibility of their phase transition process. Quantitative analysis shows that after 200 cycles, the charge-discharge H2 / H3 phase transition peak voltage difference of the original NCM811 reaches 0.144 V, significantly higher than the 0.102 V (ZrO2), 0.098 V (YSZ), and 0.106 V (Al-YSZ) of the coated systems. This significant difference in polarization behavior reveals a fundamental difference in the stability of the material interface: the unmodified sample experiences a sharp increase in charge transport impedance due to the accumulation of irreversible phase transitions during cycling, while the zirconium-based oxide coating effectively alleviates the aggravation of polarization by suppressing structural distortion and optimizing the interfacial lithium-ion transport kinetics, thus explaining the significant differences in the electrochemical cycling performance of different systems.

[0097] To systematically reveal the synergistic regulatory effect of zirconium-based oxide coating on the interfacial dynamics and structural stability of NCM811 electrodes, cyclic voltammetry tests were performed on the samples within a voltage window of 2.8–4.3 V and a scan rate of 0.1 mV / s. The results are as follows: Figure 10 As shown, the original NCM811 exhibits the largest potential difference between the first redox peaks (ΔE = 0.125 V), which is consistent with... Figure 7 (e) its high-rate capacity decay (5C capacity is 19.8% lower than Al-YSZ) and Figure 8The significant phase transition peak shift observed in (a) is related to its formation mechanism. This polarization effect originates from the lattice distortion caused by transition metal migration during lithium insertion / extraction in the unmodified material, and the accumulation of interfacial impedance due to continuous electrolyte erosion. After coating with ZrO2, YSZ, and Al-YSZ, the redox peak potential differences decreased to 0.108 V, 0.107 V, and 0.101 V, respectively. Among them, the Al-YSZ system exhibited the lowest polarization difference. Figure 7 (e) shows a significant increase in its 5C capacity (168.5 mAh / g), which confirms that Al / Y co-doping induces lithium interlayer spacing expansion (Δc = +0.000835 nm) and reduces cation mixing degree (Ic). 003 / I 104 The performance improvement was 2.1%, effectively optimizing the lithium-ion transport path at the interface. Notably, although the Al-YSZ system exhibited lower capacity retention (81.3%) during long-term cycling compared to the YSZ system (86.5%), its initial discharge capacity (198.7 mAh / g) was 20.4% higher than the original material. Furthermore, the lowest polarization difference in the CV curve revealed the dynamic equilibrium mechanism of the surface modification strategy: Al doping broadened the lithium-ion transport channels through structural defect engineering in short-term cycling, while the stable cubic Y phase maintained the structural anchoring effect in long-term cycling. This performance differentiation indicates that the functional design of the surface coating layer needs to consider both the dynamic optimization of electrochemical active sites and the long-range stability of the lattice, providing a new approach to the synergistic regulation of "kinetics-stability" in the interface engineering of high-nickel cathode materials.

[0098] To gain a deeper understanding of the kinetic mechanisms of electrode processes and elucidate the underlying reasons for the differences in electrochemical performance among different samples, this invention employs electrochemical impedance spectroscopy (EIS) for systematic analysis. Typical EIS spectra of electrode materials usually exhibit two consecutive semicircles and a low-frequency straight line, corresponding to ohmic impedance (R0). s ), interface impedance (R) f ), charge transfer impedance (R) ct ) and Warburg impedance (Z w ), where R s The intercept point in the high-frequency region along the Z' axis represents the total impedance of the electrolyte, diaphragm, and electrical contacts, with relatively small differences between samples. The small semicircle in the high-frequency region starting from this intercept point reflects the interfacial impedance R. f This is mainly caused by the SEI film formed on the electrode surface or coating layer; the diameter of the large semicircle in the adjacent mid-to-low frequency region characterizes the charge transfer impedance R. ct Its size directly affects the efficiency of the charge transfer process; generally, R ct The smaller the value, the faster the electrode reaction kinetics, which is more conducive to improving electrochemical performance; while the linear Z-value in the low-frequency region... w This is related to the diffusion ability of lithium ions in the electrode material.

[0099] against Figure 11 The EIS spectra shown in (a) and (b) (NCM811, NCM811@Z, NCM811@YSZ, and NCM811@Al-YSZ charged to 4.3V after 1 week and 200 weeks of cycling, respectively) combined with the electrochemical impedance fitting results in Table 4 (analyzed using ZView software), clearly demonstrate the significant effect of coating modification on impedance evolution. After cycling, the R0 of the original NCM811 sample... ct The Rct value surged from 10.94 Ω (1 week) to 65.34 Ω (200 weeks), while the increase in Rct for the zirconium-based oxide-coated samples slowed significantly: NCM811@Z increased from 9.53 Ω to 46.32 Ω, NCM811@YSZ from 8.61 Ω to 33.11 Ω, and NCM811@Al-YSZ from 8.07 Ω to 21.50 Ω. This indicates that zirconium-based oxide coating effectively suppressed the side reactions between the cathode material and the electrolyte, reduced the accumulation rate of charge transfer resistance, and thus improved cycle stability. Notably, the Rct value of NCM811@Al-YSZ... ct The value was the lowest among all samples, indicating that Al-YSZ composite oxide coating is more conducive to lithium-ion intercalation into the material than single ZrO2 or YSZ. The lower R value... ct This ensures that the material can still release high capacity and maintain excellent cycling performance at high rates.

[0100] The lithium-ion diffusion coefficient (D) was further calculated using formulas (1) and (2). Li + ), where the relevant parameters include: D Li + (Lithium-ion diffusion coefficient), R (gas constant), T (absolute temperature), A (electrode area), n (number of electrons per molecule of lithium-ion battery material), C (Li + Concentration), F (Faraday constant), σ (Warburg coefficient), Z' (real part of impedance in the Nyquist plot), ω (angular frequency). After 200 cycles, the DLi coating of the sample... + The value was significantly higher than that of the original NCM811 (3.58 × 10⁻⁶). -13 cm 2 / s): NCM811@Z is 6.08×10 -13 cm 2 / s, NCM811@YSZ is 1.60×10 -12 cm 2 / s, NCM811@Al-YSZ is 1.82×10 -12 cm 2 / s. Meanwhile, its σ values ​​(NCM811@Z: 3.20, NCM811@YSZ: 1.97, NCM811@Al-YSZ: 1.85) are all higher than NCM811's 4.86 × 10⁻⁶. -13 This phenomenon further confirms that zirconium-based oxide coating effectively maintains the high-speed lithium-ion transport dynamics by enhancing interfacial stability, providing a key mechanism to support the performance improvement of materials under extreme conditions.

[0101]

[0102]

[0103] Table 4. Electrochemical impedance spectroscopy (EIS) simulation results and low-frequency Z' and ω values ​​of different zirconium-based oxide-coated NCM811 materials after the 1st and 200th cycles. −1 / 2 Relationship

[0104]

[0105] To further deepen the understanding of lithium-ion transport kinetics in electrode materials, this invention, based on electrochemical impedance spectroscopy (EIS) analysis, combines intermittent galvanostatic titration (GITT) to systematically characterize the lithium-ion transport properties of zirconium oxide-coated NCM811 materials. The tests were conducted under standard conditions: a pulse current density of 0.1C (1C = 200 mA / g), a pulse duration of 10 minutes, and a relaxation time of 40 minutes. The results were obtained from the GITT test curves (…). Figure 12 (a) The differences in polarization behavior of each sample during the lithium-ion intercalation / deintercalation process can be clearly observed, among which the relationship curve of potential (E) versus time (τ) is shown in the figure. Figure 12 (b) is for calculating D Li + It provides key data support. D is analyzed using formula (3). Li + Perform the calculation:

[0106]

[0107] This formula comprehensively considers the constant current pulse time τ, the mass of the active material m, the molar mass of the material M, and the molar volume of lithium ions V. m Electrode geometric area A, voltage change ΔE during the pulse phase τ Voltage change ΔE during relaxation phase s And key parameters such as electrode thickness L.

[0108] Analysis of D during charging and discharging Li + Evolution of voltage ( Figure 12(c,d) It was found that all samples exhibited the lowest diffusion coefficients near 4.2 V. This is mainly due to the structural rearrangement and cell volume changes accompanying the H2 → H3 phase transition, which become the limiting steps for electrode reaction kinetics. Notably, during discharge, when the voltage is below 3.6 V, the diffusion coefficients of all samples... Li + Both showed a continuous downward trend, which may be due to Li + The concentration polarization effect caused by continuous ion intercalation suppressed the lithium-ion diffusion rate. Compared with the original NCM811 material, the zirconium-based oxide-coated modified material exhibited a higher lithium-ion diffusion coefficient throughout the charge and discharge process. Among them, the NCM811@Al-YSZ sample showed the best diffusion performance. This result is highly consistent with its excellent performance in cycle performance and rate performance tests, confirming the significant improvement effect of the surface modification strategy on the intrinsic kinetic properties of the electrode material.

[0109] The multiple modification mechanisms of Al-Y co-doped ZrO2 coatings on NCM811 cathode materials can be attributed to the synergistic effect of structural regulation and interface optimization. From a structural perspective, Al... 3+ and Y 3+ Co-doping induces significant changes in the lattice parameters of NCM811, with the cell volume increasing by 0.00026 nm. 3 The increase in the c-axis (+0.000835 nm) effectively broadened the lithium-ion transport channel, while I (003) / I (104) The intensity ratio increased to 1.621, confirming a decrease in cation mixing and enhanced layered structural order. This lattice optimization not only suppressed the irreversible H2 → H3 phase transition during high-voltage cycling (the phase transition peak voltage difference decreased from 0.144 V to 0.106 V), but also provided a smoother pathway for lithium-ion diffusion, with the diffusion coefficient increasing to 1.82 × 10⁻⁶. -12 cm 2 / s. Regarding interface control, the Al-YSZ coating layer formed by dry ball milling combined with calcination forms a stable chemical bond with the matrix through a chemical anchoring effect. This dual effect of physical barrier and chemical stabilization effectively inhibits electrolyte penetration and transition metal dissolution. XPS characterization shows that the lattice oxygen ratio of the coated material is significantly increased, and the surface adsorbed oxygen content is reduced, confirming that interfacial side reactions are suppressed. TEM observation reveals that the approximately 100 nm physical barrier of the coating layer directly blocks the contact between the electrolyte and the active material, resulting in a reduction in transition metal dissolution under 45°C high-temperature cycling and an increase in capacity retention from 56.15% to 64.47%. Furthermore, Al... 3+The oxygen vacancy defects introduced by doping optimized the ion conduction properties of the coating layer. EIS testing showed that its charge transfer impedance (Rct) was only 21.50 Ω after 200 cycles, significantly lower than the 65.34 Ω of the uncoated sample. This characteristic, together with lattice modulation, synergistically improved the material's kinetic performance at high rates (5 C), achieving a capacity retention of 85.99%. In summary, the Al-Y co-doped ZrO2 coating layer achieved synergistic optimization of the structural stability and electrochemical performance of NCM811 under extreme conditions of high pressure, high temperature, and high rate through a triple mechanism of "lattice expansion - interface stabilization - defect engineering".

[0110] In summary, this invention successfully constructed an Al-Y co-doped ZrO2 (Al-YSZ) coating layer on the surface of NCM811 cathode material using a dry ball milling combined with calcination process, and systematically revealed the performance optimization mechanism of this modification strategy under the triple extreme conditions of 4.5 V high voltage, 45℃ high temperature, and 5 C high rate. XRD refinement results show that Al… 3+ / Y 3+ Co-doping can induce a cell volume expansion of 0.00026 nm in NCM811. 3 (c-axis extension 0.000835 nm), while I (003) / I (104) The strength ratio was improved by 2.1%, effectively mitigating the lattice distortion caused by the H2→H3 phase transition during high-pressure cycling, laying the foundation for structural stability. TEM and XPS analyses confirmed that the approximately 100 nm thick Al-YSZ coating layer formed a stable chemical bond with the matrix through a chemical anchoring effect. This not only suppressed the dissolution of transition metals (increasing the capacity retention rate from 56.15% to 64.47% after 200 cycles at 45°C), but also reduced the surface adsorbed oxygen content, significantly delaying interfacial side reactions.

[0111] Electrochemical performance tests showed that after 200 cycles at 4.5 V, the Al-YSZ-coated sample retained 65.17% of its capacity, an increase of 0.88% compared to the unmodified sample, demonstrating effective suppression of high-voltage phase transition. After 200 cycles at 5 C, its capacity retention reached 85.99%, an increase of 6.57% compared to the unmodified sample, exhibiting excellent high-rate performance. Kinetic tests showed that within a voltage window of 2.8–4.3 V and after 200 cycles at 1 C, the lithium-ion diffusion coefficient of the modified material reached 1.82 × 10⁻⁶. -12 cm 2 / s, with a charge transfer impedance of only 21.50 Ω, significantly optimizing lithium-ion transport kinetics; while the improvement in high-rate performance stems from Al3+ The oxygen vacancy defects introduced by doping and the three-dimensional ion permeation network constructed by refined particles synergistically enhance the reaction kinetics at high rates.

[0112] Al-Y co-doped ZrO2 coating achieves synergistic optimization of structural stability and electrochemical performance of NCM811 under extreme conditions through a triple mechanism of "lattice expansion - interface stabilization - defect engineering". This provides new ideas and theoretical support for the green and large-scale preparation of high-nickel cathode materials and the development of energy storage devices adapted to extreme conditions.

Claims

1. An Al-Y co-doped ZrO2-coated NCM811 cathode material, characterized in that, By LiNi 0.8 Co 0.1 Mn 0.1 The system consists of O2 (NCM811) and a coating layer on its surface composed of Al-Y co-doped ZrO2 (Al-YSZ) nanoparticles, wherein the Al-YSZ particles have a size of 50–150 nm and are coated on the NCM811 surface at a mass of 0.5%–2% of NCM811.

2. A method for preparing the Al-Y co-doped ZrO2-coated NCM811 cathode material as described in claim 1, characterized in that, Includes the following steps: Step (1) Preparation of Al-Y co-doped ZrO2 (Al-YSZ) powder: ZrOCl2·8H2O, Y(NO3)3·6H2O, and Al(NO3)3·6H2O were dissolved in an appropriate amount of deionized water at a stoichiometric ratio of n(Zr):n(Y):n(Al): = 100:5:2 to obtain a mixed solution; ammonia was added to the mixed solution as a precipitant, and the pH was adjusted to 9 to obtain a precipitate; The precipitate was filtered, washed until neutral, dried at 80℃ for 12 h, then calcined at 1000℃ for 2 h, and after pulverization and grinding, Al-Y co-doped ZrO2 (Al-YSZ) powder was obtained. Step (2) Raw material mixing: 1 wt% Al-Y co-doped ZrO2 and NCM811 material were dry-mixed using a planetary ball mill at 200 rpm for 30 min; Step (3) Calcination treatment: The dry-mixed material is calcined at 600℃ for 4 h in an oxygen atmosphere in a tube furnace, and after cooling, Al-Y co-doped ZrO2 coated NCM811 cathode material is obtained.

3. The application of the Al-Y co-doped ZrO2-coated NCM811 cathode material as described in claim 1 in lithium-ion batteries, characterized in that, The method for preparing a lithium-ion battery cathode sheet using the aforementioned cathode material includes the following steps: Step (1) Slurry preparation: Weigh Al-Y co-doped ZrO2-coated NCM811 cathode material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and put them into a ball mill jar. At the same time, add an appropriate amount of N-methylpyrrolidone (NMP) and ball mill at 200 rpm for 30 min to prepare a slurry. Step (2) Electrode preparation: The slurry is coated on the current collector aluminum foil, dried at 80°C and cut into round pieces as positive electrodes.

Images