Cr8O21 active coated high-nickel NCM811 positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a Cr8O21 active coated high-nickel NCM811 positive electrode material as well as a preparation method and application thereof, and relates to the technical field of new energy battery positive electrode material preparation. The material is formed by taking NCM811 as a core and coating the surface with a Cr8O21 active oxide layer. In the low-temperature calcination process, Cr8O21 reacts with residual alkali on the surface of NCM811 to generate LiCrO2 with high ionic conductivity, and the process not only reduces the content of the residual alkali on the surface, but also strengthens lithium ion interface transport kinetics through LiCrO2. The Cr8O21 forms a rapid lithium ion channel through alternate arrangement of [Cr < 3 + > O6] / [Cr < 6 + > O4] in a three-dimensional framework of the Cr8O21, so that mixed arrangement of cations is synergistically inhibited, interface kinetics is optimized, and oxidation-reduction activity is contributed. Therefore, through the design and optimization of the Cr8O21 active oxide coating layer, the synergistic improvement of the structural stability and the electrochemical performance of the high-nickel NCM811 positive electrode material is successfully realized.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of positive electrode materials for new energy batteries, and in particular to a Cr8O 21 Active coated high nickel NCM811 positive electrode material and its preparation method and application. Background Art

[0002] With the transformation of global energy structure and the rapid development of electric vehicle industry, the research of high energy density lithium-ion batteries (LIBs) has become a core topic in the field of energy storage. As a key component of LIBs, the performance of cathode materials directly affects the energy density and cycle life of batteries. In recent years, nickel-rich layered oxide LiNi x Co y Mn z O2(x+y+z=1) has attracted much attention due to its high specific capacity and cost advantage. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is considered one of the most promising cathode materials for LIBs due to its high energy density (>500Wh / kg) and high reversible specific capacity (>200mAh / g). However, the structural instability caused by high nickel content significantly limits its practical application: On the one hand, Ni 3+ / Ni 4+ During the charge and discharge process, lattice oxygen is easily released, causing the layered structure to transform into spinel or rock salt phase; on the other hand, the side reaction between the material surface and the electrolyte is intensified, forming a thick and uneven positive electrode electrolyte interface (CEI film), which triggers the dissolution of transition metal (TM) and the increase of interfacial impedance, resulting in the degradation of the positive electrode material structure and cycle stability, thereby reducing the service life of the lithium-ion battery.

[0003] To improve the electrochemical stability of NCM811, researchers have proposed a variety of modification strategies, including element doping (such as Mg, Ti, Zr, Nb, Ba, etc.), surface coating (such as SiO2, MgF2C, LiCoPO4, etc.) and structural design (such as core-shell, gradient concentration). Among them, surface coating technology has become the most practical modification method because it can effectively isolate electrolyte corrosion, inhibit TM dissolution and has little effect on the bulk structure. However, the electronic insulation of these traditional oxide coatings may hinder charge transfer, and the insufficient mechanical strength of phosphate coatings can easily lead to the cracking of the coating during the cycle. Therefore, the development of new coating materials with high ionic conductivity, chemical stability and mechanical strength remains a current research difficulty.

[0004] In recent years, chromium-based oxides (such as CrO3, Cr2O5, Cr8O 21Due to its unique physical and chemical properties, it has shown great potential in the field of lithium-ion batteries (LIBs) modification. Among them, non-stoichiometric Cr8O 21 Due to its unique three-dimensional layered framework structure, it has attracted widespread attention and has become a research hotspot for high energy density energy storage systems. 21 The research on the mechanism of coating in high nickel NCM811 system still has the following limitations: (1) Cr8O 21 The synergistic mechanism of the redox activity and structural stability of NCM811 in contributing to its capacity has not yet been clarified; (2) there is a lack of systematic research on the quantitative structure-activity relationship between coating process parameters (such as coating amount and heat treatment temperature) and electrochemical performance (such as rate characteristics and cycle life). Summary of the Invention

[0005] The purpose of the present invention is to provide a Cr8O 21 Active coated high nickel NCM811 positive electrode material and its preparation method and application, the ball milling method combined with low temperature calcination method is used to construct Cr8O on the surface of NCM811 21 The coating layer was also systematically investigated. The influence of the coating material on the structural stability, interfacial reaction kinetics, and long-cycle performance of the NCM811 cathode material was investigated. Characterization techniques such as XRD, SEM, and XPS revealed the morphology and chemical state of the coating material. Cyclic and rate tests were used to evaluate the practical potential of the coating material. CV and EIS analysis were then combined to elucidate the lithium-ion transport behavior and phase transition inhibition mechanism.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A Cr8O 21 Active coated high nickel NCM811 positive electrode material is based on NCM811 as the core and coated with Cr8O 21 Active oxide layer composition; Cr8O 21 The crystal structure of the coating layer is composed of [Cr 3+ O6] octahedron and [Cr 6+ O4] tetrahedrons are arranged alternately, Cr 6+ / Cr 3+ Redox pairs reversibly participate in charge and discharge reactions.

[0008] As the preferred technical solution of the present invention, Cr8O 21 The coating amount of the active oxide layer is 1-5 wt%.

[0009] The present invention also proposes this Cr8O 21 Preparation method of active coated high nickel NCM811 positive electrode material, Cr8O 21It was dry-mixed with commercial NCM811 in a certain mass ratio using a planetary ball mill and then calcined in air to obtain NCM811@Cr8O 21 positive electrode material.

[0010] As a preferred technical solution of the present invention, in the preparation method: Cr8O 21 The mass is preferably 1-5 wt % of the mass of commercial NCM811, more preferably 3 wt %. During dry mixing, the ball milling speed is 200 rpm, the ball milling time is 30 min, the calcination temperature is 270° C., and the calcination time is 6 h.

[0011] The present invention also proposes this Cr8O 21 The application of active coated high nickel NCM811 cathode material in lithium ion batteries is achieved through Cr8O 21 The design and optimization of the active oxide coating layer successfully achieved a synergistic improvement in the structural stability and electrochemical performance of the high-nickel NCM811 positive electrode material.

[0012] The present invention is directed to high nickel layered positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) has insufficient cycle stability due to the mixed arrangement of residual lithium compounds on the surface and bulk cations. It is proposed to construct Cr8O by dry ball milling combined with low temperature calcination process. 21 Innovative strategy for active oxide coating. XRD refinement results show that 3% Cr8O 21 The coating significantly inhibits the mixed discharge of cations, making I 003 / I 104 The ratio increased from 1.490 to 1.976, and the layered structure order parameter (I 006 +I 012 ) / I 101 The electrochemical test shows that the optimized NCM811@3Cr8O 21 The sample exhibited a high first-cycle discharge capacity of 236.4 mAh / g at 0.1C (coulombic efficiency 91.7%), and a capacity retention rate of 84.0% after 200 cycles at 1C. The capacity at 5C was 41.0% higher than that of the uncoated sample. XPS analysis revealed that during the low-temperature calcination process, Cr8O 21 It reacts with the residual alkali (LiOH / Li2CO3) on the surface of NCM811 to generate LiCrO2 with high ionic conductivity. This process not only reduces the residual alkali content on the surface, but also enhances the lithium ion interface transport kinetics through LiCrO2. Mechanism studies show that Cr8O 21 Through its three-dimensional framework [Cr 3+ O6] / [Cr 6+O4] alternately arrange to form fast lithium-ion channels, synergistically inhibiting cation mixing, optimizing interfacial dynamics, and contributing to redox activity, achieving a dual improvement in capacity and stability. This invention provides a theoretical basis and innovative solution for the "active-protective" dual-functional interface engineering of high-nickel cathode materials.

[0013] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0014] (1) Selection of active coating materials: innovative use of non-stoichiometric Cr8O 21 As a cladding layer, its three-dimensional framework structure ([Cr 3+ O6] / [Cr 6+ O4] alternately arranged) has both ion transport channels and redox activity.

[0015] (2) Active capacity contribution mechanism: Different from traditional inert coating materials (such as Al2O3), Cr8O 21 Medium Cr 6+ Oxidized to Cr during the first cycle of charging 3+ (Cr 6+ +3e - →Cr 3+ ), contributing 26.7 mAh / g additional capacity, and the oxidized Cr 3+ Reversible participation in subsequent cycles (capacity attenuation rate <0.05% / cycle after 200 cycles);

[0016] (3) The in-situ reaction temperature (270°C) precisely matches the Cr8O 21 Generate and protect the NCM811 structure to achieve the dual goals of active layer construction and bulk structure stability.

[0017] (4) Synergistic inhibition of structural degradation: Cr8O 21 The coating layer inhibits Ni2+ migration through oxygen vacancies (27.23%) and the cation mixing degree is reduced by 32.6% (I 003 / I 104 =1.976).

[0018] (5) Improved interface dynamics: The LiCrO2 interface layer increases the lithium ion diffusion coefficient by 91.5% (3.81×10-13cm2 / s), and the rate performance test shows a 5C capacity of 189.0mAh / g, which is 42.4% higher than the unmodified sample of 132.7mAh / g.

[0019] (6) Contribution to redox activity: Cr 6+ / Cr 3+ The multi-electron reaction provides additional capacity, with the first-cycle discharge capacity increased by 26.7mAh / g (236.4mAh / g vs. 209.7mAh / g).

[0020] (7) Process compatibility: Low-temperature calcination (270°C) avoids damage to the bulk structure of NCM811 and is suitable for large-scale production.

[0021] (8) Cost saving: Calcination in air can achieve liquid phase and in-situ coating process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 To prepare Cr8O 21 XRD pattern (a) and crystal structure (b).

[0023] Figure 2 XRD patterns of the materials: (a) XRD pattern; (b) (003) peak magnification; (c) (006) / (012) peak magnification; (d) (018) / (110) peak magnification.

[0024] Figure 3 NCM811 and NCM811@3Cr8O 21 XPS spectra: (a) full spectrum; (b) Cr 2p spectrum; (c) C 1s spectrum; (d) O1s spectrum; (e) Ni 2p spectrum; (f) Mn 2p spectrum; (g) Co 2p spectrum.

[0025] Figure 4 SEM images of materials at different magnifications (ah) and NCM811@3Cr8O 21 EDS spectrum analysis (i): (a), (b) NCM811; (c), (d) NCM811@1Cr8O 21 (e), (f) NCM811@3Cr8O 21 (g), (h) NCM811@5Cr8O 21 .

[0026] Figure 5 For different Cr8O 21 Electrochemical performance of the coated NCM811 samples in the voltage range of 2.8-4.3 V: (a) first charge-discharge curve at a current density of 0.1C; (b) first charge-discharge characteristics; (c) 200 cycle curves at a current density of 1C; (d) NCM811 and NCM811@3Cr8O 21 Discharge curves of different cycle numbers at 1C current density; (e) rate performance at different current densities; (f) NCM811 and NCM811@3Cr8O 21 Discharge curves at different current densities.

[0027] Figure 6 For different Cr8O 21Electrochemical performance of the coated NCM811 samples in the voltage range of 2.8-4.5 V: (a) first charge-discharge curve at a current density of 0.1C; (b) first charge-discharge characteristics; (c) 100 cycle curves at a current density of 1C; (d) NCM811 and NCM811@3Cr8O 21 Charge and discharge curves of different cycle numbers at 1C current density; (e) 100 cycle curves at 5C current density; (f) NCM811 and NCM811@3Cr8O 21 Charge and discharge curves of different cycle numbers at 5C current density.

[0028] Figure 7 For different Cr8O 21 dQ / dV curves of NCM811 samples with coating content: (a) NCM811; (b) NCM811@1Cr8O 21 (c) NCM811@3Cr8O 21 (d) NCM811@5Cr8O 21 .

[0029] Figure 8 For different Cr8O 21 Voltammetric cycling curves of NCM811 samples with high coating weight: (a) NCM811; (b) NCM811@1Cr8O 21 (c) NCM811@3Cr8O 21 (d) NCM811@5Cr8O 21 .

[0030] Figure 9 For different Cr8O 21 AC impedance spectrum of NCM811 material with coating content and low-frequency region Z Re and ω -1 / 2 Relationship diagram: (a) 1st AC impedance spectrum; (b) 200th AC impedance spectrum; (c) 1st low frequency region Z Re and ω -1 / 2 (d) 200th low frequency area Z Re and ω -1 / 2 relationship diagram.

[0031] Figure 10 Cr8O 21 Schematic diagram of the coating mechanism of NCM811. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with embodiments and drawings.

[0033] Example 1

[0034] 1. Preparation of positive electrode materials

[0035] 1.1、Cr8O 21 Preparation

[0036] Cr8O was prepared by a two-step pyrolysis method. 21 Sample. Weigh 10g of CrO3 (Xilong Scientific, AR) into a crucible and place it in a vacuum drying oven at 100℃ for 12h. Then, place the sample in a muffle furnace and calcine it at 260℃ for 12h. After cooling to room temperature, grind it into powder with a mortar. Continue to place the sample in a muffle furnace and calcine it at 270℃ for 12h to obtain pure Cr8O 21 .

[0037] 1.2 Cr8O 21 Preparation of coated NCM811 cathode material

[0038] Cr8O was prepared by low-energy ball milling combined with low-temperature calcination. 21 Coated NCM811 positive electrode material. 21 The NCM811@Cr8O was dry-mixed with 5 g of commercial NCM811 (NEWARE, AR) at a certain mass ratio (0%, 1%, 3%, 5%) using a planetary ball mill at 200 rpm for 30 min, and then calcined at 270 °C in air for 6 h to obtain NCM811@Cr8O 21 The positive electrode materials, the sample products obtained by coating with different mass ratios are marked as NCM811, NCM811@1Cr8O 21 、NCM811@3Cr8O 21 、NCM811@5Cr8O 21 .

[0039] 2. Characterization of material structure and morphology

[0040] The crystal structure, purity and related material composition of the material were tested by X-ray diffractometer (XRD, PANalytical BV, Empyrean model), and the lattice parameters of the material were refined using Jade6.5 software; the element valence and content on the surface of the material were tested by X-ray photoelectron spectrometer (XPS, Shimadzu, AXIS SUPRA+ model); the morphology and surface element distribution of the material were tested by scanning electron microscopy (SEM, JEOL Ltd., JSM-7610F model).

[0041] 3. Electrochemical performance test

[0042] 3.1. Preparation of electrodes

[0043] Cr8O 21The NCM811 cathode material, acetylene black, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1:1 and placed in a ball mill. An appropriate amount of N-methylpyrrolidone (NMP) was also added. The mixture was ball-milled at 200 rpm for 30 minutes to form a slurry. The slurry was then coated on the current collector aluminum foil. The prepared electrode was dried at 80°C and cut into 14 mm diameter discs for use as the positive electrode.

[0044] 3.2. Assembly of button battery

[0045] Stainless steel shells were used as the positive and negative battery shells, a polypropylene film (Celgar 2500) was used as the separator, a lithium sheet was used as the negative electrode material, and the electrolyte was 1 mol / L LiPF6 in a mixed solvent of EC:DMC:EMC = 1:1:1 (v / v / v). The battery was assembled in a high-purity argon glove box in the order of positive battery shell, positive electrode sheet, separator, electrolyte, metal lithium sheet, and negative battery shell. After assembly, the button cell was placed in a 25°C constant temperature oven for 12 hours.

[0046] 3.3 Electrochemical performance test

[0047] A Lanbo test system was used to test the battery's electrical properties. The specific capacity, rate capability, and cycle capacity retention of the button cell were measured over a voltage range of 2.8-4.3V / 2.8-4.5V. Cyclic voltammetry and AC impedance testing were performed on the battery using an IVIUM electrochemical workstation.

[0048] 4. Results and Discussion

[0049] 4.1 Cr8O 21 XRD pattern and crystal structure of

[0050] Cr8O was prepared by a two-step pyrolysis method. 21 The XRD spectrum of the obtained product is as follows Figure 1 As shown in (a), all diffraction peaks are attributed to pure phase Cr8O 21 , no characteristic peaks of CrO3 and Cr2O5 were observed.

[0051] like Figure 1 As shown in (b), Cr8O 21 It has a three-dimensional layered framework structure, which is composed of [Cr 3+ O6] octahedron and [Cr 6+ O4] tetrahedrons are arranged alternately, and the open crystal framework is a lithium ion (Li + ) storage provides abundant sites, while Cr 3+ / Cr 6+ The redox couple can realize multi-electron transfer reaction (Cr6+ +3e-→Cr 3+ ).

[0052] 4.2 Cr8O 21 Effect of coating modification on the structure of NCM811

[0053] Figure 2 Is different Cr8O 21 Preparation of NCM811@Cr8O 21 XRD patterns of the samples. Figure 2 From the positions of the diffraction peaks in (a), it can be seen that the sample is 21 Before and after coating, the samples showed R-3m space point group, hexagonal crystal system, α-NaFeO2 type layered structure, and the main diffraction peaks (003) and (104) in the spectrum were sharp, proving that all four samples had high crystallinity. No Cr8O was observed in the XRD spectrum. 21 The characteristic peak may be Cr8O 21 Due to low content. Figure 2 As shown in (b), with the Cr8O 21 With the increase of coating amount, the (003) peak position did not shift significantly, indicating that Cr8O 21 It does not penetrate into the NCM811 lattice structure, but only covers the surface of the positive electrode material. Figure 2 In the magnified images (c) and (d), it can be observed that the two pairs of split peaks (006) / (012) and (018) / (110) are obviously split, which indicates that the sample has a highly ordered layered structure. 21 Modification of the coating amount will not change the basic crystal structure of NCM811 material.

[0054] Table 1 Different Cr8O 21 Effect of coating amount on crystal structure parameters of NCM811

[0055]

[0056] Table 1 shows the different Cr8O 21 The effect of coating amount on the crystal structure parameters of NCM811 can be seen from the different Cr8O 21 The lattice constant a value, c value and volume V value of the sample after coating are almost unchanged. 2+ He Li + The radii are 0.069nm and 0.076nm respectively. Due to their close values, Ni 2+ With Li + The phenomenon of occupying each other's positions leads to the appearance of cation Li + / Ni 2+Mixed arrangement phenomenon, resulting in Li + It cannot be properly deintercalated, thus affecting the capacity. In addition, when Li + / Ni 2+ When the mixing degree is too high, Ni 2+ During the charging process of lithium-ion batteries, it will be oxidized to Ni with a smaller ion radius. 3+ (0.056nm), which causes the collapse of the layered structure and leads to a "dive" in the capacity of high-nickel batteries during the cycle.

[0057] I (003) / I (104) The ratio of represents the Li + / Ni 2+ The larger the ratio, the lower the degree of cation mixing. 21 After coating, I (003) / I (104) The ratios of NCM811 are significantly higher than those of the original samples, indicating that after Cr8O 21 After coating modification, Ni 2+ Occupy Li + The ratio of sites is reduced and the order of the layered structure is enhanced. + / Ni 2+ Low mixing degree means that the transition metals occupying the lithium layer in the ternary material are reduced, thus avoiding the transition metal to Li + The impact of migration has a certain degree of high I (003) / I (104) The ternary positive electrode material with a high ratio will show excellent rate performance.

[0058] [I (006) +I (012) / I(101) ] represents the orderliness of the layered structure of the material. The smaller the ratio, the better the orderliness. 21 After coating, [I (006) +I (012) / I(101) ] are all reduced, indicating that after Cr8O 21 After coating modification, NCM811@Cr8O 21 The layered structure of the sample grows better. 21 The cation Li of the sample + / Ni 2+ The lowest degree of mixing and the best layered structure stability will result in better performance in electrochemical tests.

[0059] The X-ray photoelectron spectroscopy (XPS) was used to characterize the NCM811 and its Cr8O 21Coating material (NCM811@3Cr8O 21 )'s surface chemical characteristics analysis shows that Cr8O 21 The coating layer significantly optimizes material properties through multi-dimensional chemical regulation. Figure 3 (a) In the total spectrum, the coated sample shows a Cr 2p characteristic peak at 576-578eV, while the original material has no Cr signal, confirming that Cr8O 21 The Cr 2p fine spectrum ( Figure 3 b) Display Cr 3+ (576.5eV) and Cr 6+ (579.5eV) coexistence, consistent with Cr8O 21 In the coating layer [Cr 3+ O6] octahedron and [Cr 6+ The three-dimensional framework structure formed by the alternating arrangement of O4] tetrahedrons provides a fast transmission path for lithium ions and inhibits the dissolution of transition metals. 3+ Through oxygen vacancies (V0) and Cr 6+ Forming a charge balance network, this mixed valence structure is shown in the O1s spectrum ( Figure 3 d) is confirmed, the oxygen vacancy ratio increases significantly from 17.68% to 27.23%, and the corresponding surface adsorption oxygen intensity (531.5eV) decreases, indicating that the coating layer is not only through Cr 3+ -V0 defects regulate the charge distribution and also inhibit the side reactions between the material surface and the environment. This interface modification is reflected in the C1s spectrum ( Figure 3 c) is reflected by the weakening of the C=O peak intensity, which proves that the adsorption of oxygen-containing functional groups on the surface is reduced and the purity of the material is improved. The interface reaction mechanism is that when calcined at low temperature, Cr8O 21 It may react with the residual alkali (LiOH and Li2CO3) on the surface of NCM811 to generate LiCrO2 with high ionic conductivity. The reaction formula is formula (1) and (2). This process not only reduces the residual alkali content on the surface (inhibits the decomposition of the electrolyte), but also the formed LiCrO2 acts as a fast ion conductor, further enhancing the lithium ion interface transport kinetics.

[0060] Cr8O 21 +LiOH→LiCrO2+H2O↑ (1)

[0061] Cr8O 21 +Li2CO3→LiCrO2+CO2↑ (2)

[0062] In terms of valence state evolution, Ni 2p spectrum ( Figure 3 e) shows that the Ni2+ ratio decreased from 34.59% to 28.27%, Ni 3+ The proportion of Mn increases accordingly, which together with the enhanced I(003) / I(104) peak intensity ratio (1.490→1.976) in XRD reveals the improvement of the order of the layered structure; Mn 2p spectrum ( Figure 3 f) The main peak binding energy shifts rightward from 641.8 eV to 642.3 eV, and Mn 4+ The ratio increased from 31.55% to 34.51%, indicating that Cr8O 21 Through the oxygen vacancy electron capture mechanism (Mn 3+ →Mn 4+ ) effectively suppresses Jahn-Teller distortion; while the Co 2p spectrum ( Figure 3 g) Maintain stable Co 3+ This multi-element synergistic regulation mechanism, combined with the optimization of layered structure parameters ([I(006)+I(012)] / I(101) decreased from 0.453 to 0.417), makes Cr8O 21 The coating layer improves the cation order while 6+ The redox activity and Cr 3+ The interfacial bonding effect establishes a dynamic balance between ion transmission efficiency and interface stability.

[0063] 4.3 Cr8O 21 Effect of coating modification on the morphology of NCM811

[0064] In order to confirm that Cr8O 21 The coating was effectively applied on the surface of NCM811 material, and SEM was used to observe the samples before and after coating. Figure 4 As shown in (a), (c), (e), and (g), it can be seen from the figure that the samples before and after coating are all composed of submicron-level irregular primary particles piled up to form spherical secondary particles of about 15 μm. 21 As the coating amount increases, the surface of NCM811 particles gradually becomes rougher, but the morphology of secondary particles remains intact. Figure 4 The surface morphology of the sample is magnified in (b), (d), (f), and (h). It can be observed that the surface of the NCM811 material is smooth and free of impurities, with clear grain boundaries. 21 Cr8O can be clearly observed on the surface of the coated sample. 21 particles, and as the coating amount increases, the Cr8O attached to the sample surface 21 The particles also increase. 21As a coating layer, it is tightly attached to the surface of NCM811 particles, which can prevent NCM811 from direct contact with the electrolyte during electrochemical testing, prevent HF decomposed by the electrolyte from corroding the NCM811 material itself, and thus improve the electrochemical properties of the material.

[0065] In order to further observe the 21 The distribution of NCM811@3Cr8O on the surface of NCM811 material was analyzed by EDS Mapping. 21 The samples were tested and the results were as follows Figure 4 As shown in (i), Ni, Co, Mn, and O elements can be detected on the sample surface and are evenly distributed. 21 Cr element was also detected in the sample and was evenly distributed. Since its content was smaller than that of Ni, Co, and Mn, the color of Cr element was lighter. 21 It was coated on the surface of NCM811 particles and evenly distributed, successfully constructing a core-shell structure without affecting the distribution of Ni, Co, and Mn elements.

[0066] 4.4 Cr8O 21 Effect of coating modification on the electrochemical performance of NCM811

[0067] Figure 5 It is the electrochemical performance of the material in the voltage range of 2.8-4.3V. Figure 5 (a) and (b) show different Cr8O 21 The effect of coating amount on the first charge-discharge curve of NCM811 cathode material at 0.1C rate (1C = 200mAh / g). The experimental results show that: 3% Cr8O 21 The coated sample showed the best comprehensive performance, with an initial discharge capacity of 236.4 mAh / g and a coulombic efficiency of 91.7%, which were 26.7 mAh / g and 2.7% higher than those of the unmodified sample, respectively. 21 The coating material can repair the surface of NCM811 and maintain the stability of the material structure. The appropriate coating layer can effectively block the direct contact between the electrolyte and the active material, reduce the loss of irreversible capacity, promote the formation of low-impedance, high-stability CEI film, and improve Li + Reversible deintercalation efficiency reduces active Li loss, improves lithium ion transmission path, and reduces electrochemical polarization. 21 When the coating amount is 5%, the material capacity decays, mainly because the coating amount is too large, which leads to the + The diffusion path is extended, the interface impedance increases, and the utilization rate of active materials decreases.

[0068] To clarify Cr8O 21 The influence of surface modification on the long cycle stability of NCM811 cathode material, the sample voltage range of 2.8-4.3V (vs.Li + / Li) was used to evaluate the cycling performance of the battery at 1C rate for 200 cycles. The cycling curves are shown in Figure 2. Figure 5 (c) NCM811, NCM811@1Cr8O 21 、NCM811@3Cr8O 21 and NCM811@5Cr8O 21 The first discharge specific capacities were 196.8mAh / g, 207.9mAh / g, 215.6mAh / g and 204.4mAh / g, respectively. The 200 discharge specific capacities were 147.8mAh / g, 168.1mAh / g, 181.1mAh / g and 162.9mAh / g, respectively. The 200 discharge specific capacities were 75.1%, 80.9%, 84.0% and 79.7%, respectively. The experimental data show that the discharge specific capacity and capacity retention rate of the modified samples increase with the increase of Cr8O 21 The coating amount shows a non-monotonic change trend. 21 The sample showed the best cycle stability, with a discharge capacity increase of 33.3 mAh / g and a capacity retention rate increase of 8.9% after 200 discharges compared with the unmodified sample. Figure 5 (d) NCM811 and NCM811@3Cr8O 21 The charge and discharge curves of NCM811@3Cr8O at different cycle numbers 21 The charge-discharge curves have good overlap and strong chemical reversibility, while the charge-discharge curves of NCM811 have poor overlap and poor chemical reversibility. This phenomenon can be attributed to the physical barrier effect of moderate coating amount, which inhibits the dissolution loss of transition metal ions (Ni, Co, Mn); excessive coating (5%) causes multi-energy attenuation, which reduces the effective utilization rate of active materials. It is worth noting that the slight fluctuation of the cycle curve is related to the change of ambient temperature in winter. NCM811@3Cr8O 21 A comprehensive comparison of the electrochemical performance of NCM811 modified by coating with other coatings in the literature is shown in Table 2.

[0069] For system evaluation of Cr8O 21 The effect of surface modification on the high rate performance of NCM811 cathode material. In the voltage window of 2.8-4.3V, the charge and discharge characteristics of a series of samples were analyzed using a step current density test method (0.1C→0.2C→0.5C→1C→5C). The rate performance curve is shown in Figure 2. Figure 5(e) and (f) are shown. The experimental results show that the unmodified NCM811 sample exhibits significant electrochemical polarization characteristics, and its specific capacity shows a sharp decline trend with increasing rate: at a discharge rate of 0.1C, the discharge specific capacity is 209.6mAh / g, and at an ultra-high rate of 5C, it only maintains a discharge capacity of 132.7mAh / g, corresponding to a capacity retention rate of 63.3%. Cr8O 21 Surface engineering effectively improves the rate response characteristics of the material, among which NCM811@3Cr8O 21 The sample exhibited the best kinetic performance, with a discharge capacity of 235.5 mAh / g at a rate of 0.1C and a capacity of 189.0 mAh / g at a rate of 5C. The capacity retention rate was increased to 80.3%, and the discharge capacity at 5C was increased by 42.4% compared to the unmodified sample (56.3 mAh / g). 21 The coating significantly improves the rate performance of NCM811 by improving the conductivity of NCM811 materials, inhibiting side reactions, stabilizing the structure and optimizing the interface properties. The coating concentration and performance improvement show a nonlinear relationship. 21 and NCM811@5Cr8O 21 The capacity retention rates of the modified samples at 5C were 65.1% and 64.5%, respectively, indicating that excessive coating (>3%) would induce Li + Diffusion barrier, the effective specific surface area of the active material decreases with the increase of coating amount.

[0070] Figure 6 It is the electrochemical performance of NCM811 and its surface modified composite materials in the voltage window of 2.8-4.5V. Figure 6 (a) and (b) are the first charge and discharge curves and first charge and discharge characteristics of the material at a current density of 0.1C. The modified material shows better first discharge specific capacity and coulombic efficiency than the original NCM811, among which NCM811@3Cr8O 21 The discharge specific capacity reaches 224.6 mAh / g and the coulombic efficiency is 90.1%, which are 16.7 mAh / g and 1.2% higher than NCM811 respectively. Figure 6 (c) is the cycling curve of the material at 1C rate. After 100 cycles, NCM811 and NCM811@1Cr8O 21 、NCM811@3Cr8O 21 、NCM811@5Cr8O 21 The discharge specific capacities are 144.5 mAh / g, 152.4 mAh / g, 173.1 mAh / g, and 157.3 mAh / g, respectively, and the capacity retention rates are 80.40%, 81.8%, 84.90%, and 81.0%, respectively. Figure 6(e) is the cycling curve of the material at 5C high rate. After 100 cycles, NCM811 and NCM811@3Cr8O 21 The discharge specific capacities are 115.8 mAh / g and 147.6 mAh / g, respectively, and the capacity retention rates are 65.9% and 84.3%, respectively. Figure 6 It can be seen from (d) and (f) that the Cr8O 21 The coated and modified material exhibited superior cycling stability compared to the unmodified NCM811 material. These data confirm that the surface modification strategy effectively inhibited side reactions at the electrode / electrolyte interface, reduced interfacial impedance by constructing a stable surface coating, and enhanced lithium-ion diffusion kinetics through the three-dimensional ion conductor framework, thereby significantly improving high-rate performance and long-term cycling stability.

[0071] Table 2 NCM811@3Cr8O 21 Comprehensive comparison of electrochemical performance of NCM811 coated with other coatings in the literature

[0072]

[0073] Note: The sources of the existing coating technologies in Table 2 are:

[0074] [1]Y.Li,D.Zhang,Y.Yan,Y.Wang,Z.Li,X.Tan,M.Zhang, Journal of Alloys and Compounds, 923(2022).

[0075] [2]Z.Li,Y.You,Y.Liu,J.Liu,J.Peng,M.Yuan,Ceramics International,50(2024)30493-30503.

[0076] [3] K. Huang, H. Yang, T. Xie, J. Zhou, T. Lan, S. Ong, H. Jiang, Y. Zeng, L. Wan, H. Guo, Y. Zhang, Journal of Electroanalytical Chemistry, 951 (2023).

[0077] [4] MAMM Al-Samet, E. Burgaz, Electrochimica Acta, 507 (2024).

[0078] [5]T.Kim,M.S.Goh,H.Moon,H.Shin,J.Lee,H.Jeong,S.W.Joo,Y.S.Kim,Y.Im,M.Kang,Journal of Colloid and Interface Science,670(2024)729-741.

[0079] [6]J.Jeyakumar,T.H.Mengesha,Y.B.Hendri,Y.-S.Wu,C.-C.Yang,Q.-T.Pham,C.-S.Chern,B.J.Hwang,Journal of Energy Storage,87(2024).

[0080] [7]M.M.Abdelaal,M.Alkhedher,Next Energy,7(2025).

[0081] [8]P.He,M.Zhang,J.Wu,Y.Li,Y.Wang,Y.Yan,D.Zhang,X.Sun,Journal ofAlloys and Compounds,967(2023).

[0082] [9]Y.Zeng,X.Lu,Q.Mao,Y.Wang,T.Ji,X.Guo,R.Shan,J.Zhou,Y.Xia,Y.Cai,J.Yao,Chemical Engineering Science,281(2023).

[0083]

[10] J.Wang,D.Zhao,G.Zhou,S.Wei,S.Hou,Y.Li,H.Ma,Y.Yuan,X.Yan,X.Hou,Ceramics International,49(2023)15842-15850.

[0084]

[11] L.You,G.Li,B.Huang,B.Chu,T.Huang,A.Yu,Journal of Alloys andCompounds,918(2022).

[0085]

[12] X.Tan,M.Zhang,D.Zhang,Y.Yan,Y.Wang,Z.Li,Ceramics International,47(2021)32710-32719.

[0086] According to NCM811@3Cr8O in Table 2 21 The comparative data of Cr8O1 and other coated modified NCM811 materials were analyzed comprehensively. 21 The active coating strategy shows significant advantages in multiple key performance indicators. In the 2.8-4.3V voltage window and 0.1C rate, its first cycle discharge capacity reaches 236.4mAh / g, which is higher than that of LiNbO3 [2] The coating system (200.1mAh / g) increased by 18.1%, compared with Li4Ti5O 12 -TiO2 [3] The composite coating system (205.2mAh / g) increased by 15.2%. The coulombic efficiency reached 91.7%, which is better than SiO2-Li2SiO3. [1] (87.1%) and other traditional coating systems. In terms of 1C cycle stability, the discharge capacity after 100 cycles reached 204.6mAh / g, and the capacity retention rate reached 94.9%. After 200 cycles, the discharge capacity reached 181.1mAh / g, and the capacity retention rate reached 84.0%. Compared with SiO2 [4] After 100 cycles, the coating system has a discharge specific capacity of 162.8 mAh / g and a capacity retention rate of 87.3%, with better cycle attenuation inhibition efficiency.

[0087] Compared with the existing coating technology, Cr8O 21 The coating layer exhibits unique dual-functional advantages of "activity-protection": its three-dimensional framework structure ([Cr 3+ O6] / [Cr 6+ O4]) not only reduces the cation mixing degree (I003 / I104=1.976) through the charge compensation mechanism mediated by oxygen vacancies, but also 6+ / Cr 3+ The redox couple contributed an additional specific capacity (236.4 vs. 213.0 mAh / g@Co3(PO4)2 [5] It is particularly noteworthy that under 4.5V high voltage conditions and at an ultra-high rate of 5C, the material can still maintain a capacity retention rate of 84.3% (147.6mAh / g). These performance breakthroughs are due to the Cr8O 21 Unique interface regulation mechanism of the coating layer: The LiCrO2 fast ion conductor generated by low-temperature calcination (confirmed by XPS) reduces the charge transfer impedance, while the three-dimensional framework structure improves the lithium ion diffusion coefficient, achieving synergistic optimization of interface dynamics and structural stability.

[0088] 4.5 Cr8O 21 Study on coating modification mechanism

[0089] 4.5.1 dQ / dV Curve Analysis

[0090] Figure 7 Is different Cr8O 21 The dQ / dV curve of the coated NCM811 sample after 200 cycles at a current density of 1C and a voltage window of 2.8-4.3V shows that the phase change characteristics of NCM811 and its coated samples are highly correlated with the electrochemical properties and interface kinetic parameters. The H2-H3 phase transition will cause the unit cell volume of the NCM811 material to shrink, resulting in increased difficulty in lithium ion insertion / extraction and poor structural stability of the NCM811 material, which is the main reason for the decline in the cycle performance of the high-nickel NCM811 material. The voltage peak corresponding to the H2→H3 phase transition of the uncoated NCM811 during the charging process shows a trend of significant broadening and continuous attenuation of the peak intensity after the cycle, indicating that its layered structure undergoes irreversible lattice distortion during high-voltage delithiation, which is consistent with the result that the sample has a capacity retention rate of only 75.1% for 200 cycles under 1C conditions in the cycle test. In contrast, NCM811@3Cr8O 21 The H2→H3 phase transition peak maintains a higher peak intensity and a narrower peak width during the cycle, indicating that Cr8O 21 The coating layer effectively alleviates the structural stress accumulation caused by high-voltage phase transition by inhibiting cation mixing (XRD shows that I003 / I104 increases to 1.976) and optimizing the oxygen vacancy distribution (XPS shows that the oxygen vacancy ratio of the 3% coated sample increases to 27.23%), thus forming a mechanism closed loop with its excellent cycle stability (200 times capacity retention rate of 84.0%).

[0091] For NCM811@5Cr8O 21 Although the H3→H2 discharge phase transition peak of the sample did not show significant splitting, the peak position shifted positively after cycling and the rate of decrease in peak intensity was significantly faster than that of the 3% coated sample. This phenomenon is consistent with the EIS test result that the charge transfer impedance of this sample increased sharply to 97.94Ω after cycling, indicating that the deterioration of the interface dynamics caused by excessive coating is the key factor leading to its capacity decay (200 cycles retention rate of 79.7%). Combined with the XRD refinement results (the c / a ratio of the 5% coated sample increased abnormally to 4.9433), it is speculated that the excessive Cr8O 21 The coating may form a dense physical barrier at the interface, hindering the efficient transfer of lithium ions (5C capacity retention decreased by 15.8% compared to the 3% coated sample), rather than directly destroying structural stability through chemical valence imbalance. This reduction in interfacial lithium ion transfer efficiency manifests as a hysteresis effect in the phase transition dynamics on the dQ / dV curve, revealing the nonlinear regulation of the coating thickness on the dynamic balance between structural relaxation and ion diffusion.

[0092] 4.5.2 Cyclic Voltammetry

[0093] The cyclic voltammetry (CV) method was used to study the 21 Electrochemical kinetic behavior of coated NCM811 material. Figure 8 The CV curves of the first three cycles of the four samples at a scan rate of 0.1mV / s are compared. The study found that the CV curve morphology of all samples is basically the same, but there are significant differences in the first oxidation peak potential of the first cycle, which may be related to the violent parasitic reaction at the cathode / electrolyte interface and the SEI film formation dynamics during the first charge and discharge process. By quantifying the voltage hysteresis value (ΔE) between the first cycle H1→M oxidation peak and the corresponding peak after stable cycling, the electrochemical polarization and the degree of interfacial side reactions can be effectively evaluated. The experimental results show that the original NCM811, NCM811@1Cr8O 21 、NCM811@3Cr8O 21 and NCM811@5Cr8O 21 The ΔE of the coated samples are 0.188, 0.176, 0.174 and 0.213V, respectively, among which NCM811@3Cr8O 21 The sample showed the lowest polarization characteristics, which was 7.4% lower than that of the unmodified sample. This polarization suppression effect is related to the 21 The dual regulation mechanism of the coating layer on the interface stability is closely related: the appropriate amount of coating (3%) can effectively block the corrosion of the electrolyte to the active material and maintain the Li + The diffusion channel is unobstructed; while excessive coating (5%) may lead to increased polarization due to the obstruction of electron conduction. This conclusion is mutually confirmed with the mechanism of the previous rate performance test. 21 The coated sample still maintains a capacity retention rate of 83.2% at a 5C rate, which is significantly better than other samples.

[0094] 4.5.3 AC impedance test

[0095] Table 3 Different Cr8O 21 Electrochemical impedance spectroscopy results and low-frequency Z of NCM811 material after the 1st and 100th cycles Re and ω -1 / 2 relationship

[0096]

[0097] Electrochemical impedance spectroscopy (EIS) analysis revealed that Cr8O 21 The coating system regulates the interface dynamics and lithium ion transport behavior of NCM811. Figure 9 As shown in (a), after the first cycle, the Nyquist plots of all samples showed the characteristics of high-frequency semicircle (charge transfer resistance Rct) and low-frequency oblique line (lithium ion solid phase diffusion). The Rct of the uncoated NCM811 is 19.33Ω, while that of the 3% Cr8O21 The Rct of the coated sample decreased significantly to 13.46Ω (30.2%), which is consistent with the Cr 3+ / Cr 6+ The mixed valence network is directly related to the 27.23% increase in the oxygen vacancy ratio. 21 In the three-dimensional framework [Cr 3+ O6] / [Cr 6+ The ordered channels formed by the alternating arrangement of [O4] provide a fast transmission path for lithium ions, and their effect is calculated by the diffusion coefficient D calculated by formula (3). Li + Verified: 3% coated sample first circle D Li + Up to 3.81×10 -13 cm2 / s, which is 91.5% higher than that of the uncoated sample (1.99×10 - 13 cm2 / s). The Warburg coefficient σ calculated by formula (4) decreases from 5.6 in the first cycle to 4.04Ω·s -1 / 2 , further confirming the significant reduction in interfacial impedance.

[0098]

[0099]

[0100] Among them, D Li + ,R,T,A,n,C,F,σ,Z Re , ω represent the lithium ion diffusion coefficient, gas constant, absolute temperature, electrode area, the number of electrons contained in each molecule of lithium ion battery material, Li + Concentration, Faraday constant, Warburg coefficient, real part of impedance in Nyquist plot, angular frequency.

[0101] After 200 cycles ( Figure 9 b), the Nyquist spectra of all samples evolved into a single compressed semicircle, indicating that the relaxation time constant (τ=R×C) of the interfacial film impedance (Rf) and the charge transfer impedance (Rct) tends to overlap. This phenomenon is due to the 21 Coating-induced interfacial phase reconstruction: Cr8O 21It reacts with the residual LiOH / Li2CO3 on the surface of NCM811 to form LiCrO2 (Formula 1-2). Its high ionic conductivity (σ=4.04→2.64Ω·s-1 / 2) reduces the interfacial polarization, making the dynamic response characteristics of Rf and Rct converge. It is worth noting that the Rct of the 3% coated sample only increases to 40.65Ω (an increase of 201%) after cycling, which is much lower than the 521% increase of the uncoated sample (Rct=120Ω). This difference can be attributed to the Cr 3+ / Cr 6+ The redox couple suppresses Mn by charge compensation 3+ Distortion (XPS shows Mn 4+ The ratio increased by 2.96%), and the physical barrier effect of the LiCrO2 interface layer on HF corrosion reduced the HF erosion rate.

[0102] Excessive coating (5%) leads to deterioration of interface performance. After 200 cycles, Rct surges to 97.94Ω, while σ rebounds to 4.5Ω / s. 1 / 2 , D Li + reduced to 3.07×10 -13 cm 2 / s. This negative effect is due to Cr8O 21 The volume expansion caused by the self-redox side reaction (XRD shows that the c / a ratio increases abnormally to 4.9433) leads to the distortion of the lithium ion diffusion path and the breakage of the electronic conductive network (CV test polarization voltage difference ΔE=0.213V). By comparing the Warburg coefficient σ( Figure 9 cd), it was found that the 3% coated sample had the lowest σ value after cycling (2.64Ω / s 1 / 2 ), and its optimal D Li + (8.93×10 -13 cm 2 / s) formed a synergistic effect, confirming the dual regulatory mechanism of "structural stabilization-interface dynamics optimization".

[0103] The combined application of formula (3) and (4) further reveals the kinetic mechanism: after 200 cycles, the σ value of the 3% coated sample drops to 2.64Ω / s 1 / 2 , D Li + Increased to 8.93×10 -13 cm 2 / s, indicating that the lithium ion diffusion path remains efficient during long-term cycling. In contrast, excessive coating (5%) causes the σ value to rebound to 4.5Ω / s 1 / 2 , D Li + reduced to 3.07×10 -13cm 2 / s, which is consistent with the decreasing trend of capacity retention in CV test (84.33%→72.61%), reflecting that Cr8O 21 Excessive introduction causes blockage of diffusion paths and destruction of the electronic conductive network.

[0104] Cr8O 21 The coating can construct three-dimensional ion channels (XRD verification of interlayer spacing expansion of 0.049%), stabilize the interface chemical environment (XPS oxygen vacancy improvement) and inhibit cation distortion (Mn 4+ The multiple mechanisms of ratio optimization) in improving the intrinsic structural order (I 003 / I 104 =1.976), a dynamic equilibrium interface of "low impedance-high diffusion" was established, in which 3% coating achieved Rct and D Li + provides a regulatory mechanism with both structural stability and kinetic advantages for the interface engineering of high-nickel cathode materials.

[0105] Based on the above XPS, XRD and electrochemical kinetic analysis, the present invention reveals that Cr8O 21 The multi-dimensional synergistic modification mechanism of the active coating layer on the NCM811 cathode material, such as Figure 10 As shown. During the low temperature calcination process, Cr8O 21 It reacts with the residual LiOH / Li2CO3 on the surface of NCM811 to form an in-situ LiCrO2 interface layer with high ionic conductivity. This reaction process not only effectively reduces the residual alkali content on the surface (the C=O peak intensity in XPS decreases), but more importantly, it constructs a fast lithium ion transport channel and significantly optimizes the charge transfer kinetics at the electrode / electrolyte interface (EIS shows a 47.4% reduction in Rct). 21 The unique three-dimensional layered framework is composed of [Cr 3+ O6] octahedron and [Cr 6+ O4] tetrahedrons are arranged alternately, and its periodic open structure provides an isotropic diffusion path for lithium ions. XRD refinement results show that this structure effectively suppresses the Ni 2+ The migration to the Li layer significantly reduces the degree of cation mixing (I003 / I104 increases from 1.490 to 1.976). 3+ / Cr 6+ The mixed valence network promotes the oxidation of Mn3+ to Mn4+ through the electron redistribution effect (XPS shows that the Mn4+ ratio increases by 2.96%), effectively alleviating the damage of Jahn-Teller distortion to the layered structure.

[0106] This structure-interface synergistic optimization mechanism forms a dynamic balance during the cycle: moderate Cr8O 21 The coating layer (3%) acts as a physical barrier to inhibit electrolyte corrosion and transition metal dissolution, and also acts as a barrier to inhibit electrolyte corrosion and transition metal dissolution through active Cr 6+ →Cr 3+ The redox reaction contributes to the additional capacity (the first cycle discharge capacity increases by 26.7 mAh / g). However, excessive coating (5%) will lead to Li + The diffusion path is blocked (5C capacity retention decreases by 15.8%) and causes interfacial stress accumulation, ultimately resulting in a surge in charge transfer impedance (Rct = 97.94Ω). Based on this, the present invention clarifies the triple synergistic mechanism of the active oxide coating through structural stabilization, interface dynamics optimization, and redox activity, providing a new theoretical perspective for improving the performance of high-nickel cathode materials.

[0107] In summary, the present invention uses Cr8O 21 The design and optimization of the active oxide coating layer successfully achieved a synergistic improvement in the structural stability and electrochemical performance of the high-nickel NCM811 cathode material. 21 The coating inhibits the mixing of cations (I 003 / I 104 =1.976) and optimized lamellar order ((I 006 +I 012 ) / I 101 =0.417), significantly enhancing the intrinsic stability of the material. Interface reaction kinetics analysis reveals that Cr8O 21 The LiCrO2 fast ion conductor formed by the surface residual alkali effectively reduces the charge transfer impedance (Rct = 13.49Ω). At the same time, its three-dimensional framework structure provides a fast lithium ion transmission channel, which increases the capacity of the material by 41.0% at 5C rate compared with the unmodified sample. Electrochemical performance tests confirm that NCM811@3Cr8O 21 The first cycle discharge capacity reached 236.4 mAh / g (coulombic efficiency 91.7%), and the discharge specific capacity after 200 cycles at 1C was 181.1 mAh / g, with a capacity retention rate of 84.0%, which is better than most coating systems reported in the literature. The impedance surge (Rct = 97.94Ω) and capacity decay caused by excessive coating (5%) emphasize the importance of controlling the coating concentration. The "active-protective" dual-functional interface engineering strategy proposed in this paper, through Cr8O 21 The synergistic mechanism of redox activity contribution and structural stabilization provides new ideas for the development of high-energy-density lithium-ion batteries and has important scientific value and application potential.

[0108] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A Cr8O 21 Active coated high nickel NCM811 positive electrode material, characterized in that, It is based on NCM811 as the core and coated with Cr8O 21 Active oxide layer composition; Cr8O 21 The crystal structure of the coating layer is composed of [Cr 3+ O6] octahedron and [Cr 6+ O4] tetrahedrons are arranged alternately, Cr 6+ / Cr 3+ Redox pairs reversibly participate in charge and discharge reactions.

2. Cr8O according to claim 1 21 Active coated high nickel NCM811 positive electrode material, characterized in that, Cr8O 21 The coating amount of the active oxide layer is 1-5 wt%.

3. Preparation of Cr8O as claimed in claim 1 or 2 21 The method for active coating of high nickel NCM811 positive electrode material is characterized in that, Cr8O 21 It was dry-mixed with commercial NCM811 in a certain mass ratio using a planetary ball mill and then calcined in air to obtain NCM811@Cr8O 21 positive electrode material.

4. The method according to claim 3, wherein Cr8O 21 The mass accounts for 1-5wt% of the mass of commercial NCM811.

5. The method according to claim 4, wherein Cr8O 21 The mass accounts for 3wt% of the commercial NCM811.

6. The method according to claim 3, wherein During dry mixing, the ball milling speed was 200 rpm and the ball milling time was 30 min.

7. The method according to claim 3, wherein The calcination temperature is 270°C and the calcination time is 6 hours.

8. Cr8O prepared by the method according to any one of claims 3 to 7 21 The application of active coated high nickel NCM811 positive electrode material in lithium ion battery is characterized by: Cr8O during the low temperature calcination process of the preparation method 21 It reacts with the residual alkali (LiOH / Li2CO3) on the surface of NCM811 to generate LiCrO2 with high ionic conductivity. This process not only reduces the residual alkali content on the surface, but also enhances the lithium ion interface transport kinetics through LiCrO2. 21 Through its three-dimensional framework [Cr 3+ O6] / [Cr 6+ O4] are alternately arranged to form fast lithium ion channels, synergistically inhibiting cation mixing, optimizing interfacial dynamics and contributing to redox activity, achieving a dual improvement in capacity and stability.

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