A Cr8O 21 Active-coated high-nickel NCM811 positive electrode material, and preparation method and application thereof

Abstract

A Cr8O 21 This paper discloses an active-coated high-nickel NCM811 cathode material, its preparation method, and its application, relating to the field of cathode material preparation technology for new energy batteries. The material uses NCM811 as the core and is coated with Cr8O2. 21 Composition of the active oxide layer. Cr8O during low-temperature calcination. 21 The residual alkali on the NCM811 surface reacts 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 interfacial transport kinetics through LiCrO2. Cr8O 21 Through its three-dimensional framework [Cr 3+ O6] / [Cr 6+ The alternating arrangement of O4] forms a fast lithium-ion channel, synergistically suppressing cation mixing, optimizing interfacial kinetics, and contributing redox activity. Therefore, this invention utilizes 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.

Description

Technical Field

[0001] This invention relates to the field of new energy battery cathode material preparation technology, specifically to a Cr8O 21 Active-coated high-nickel NCM811 cathode material, its preparation method and application. Background Technology

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

[0003] To improve the electrochemical stability of NCM811, researchers have proposed various modification strategies, including elemental doping (such as Mg, Ti, Zr, Nb, Ba, etc.), surface coating (such as SiO2, MgF2C, LiCoPO4, etc.), and structural design (such as core-shell and gradient concentration). Among these, surface coating technology has become the most promising modification method due to its ability to effectively isolate electrolyte corrosion, inhibit TM dissolution, and have minimal impact on the bulk structure. However, the electronic insulation of these traditional oxide coatings may hinder charge transfer, while the insufficient mechanical strength of phosphate coatings can easily lead to coating cracking during cycling. Therefore, developing novel coating materials that combine high ionic conductivity, chemical stability, and mechanical strength remains a current research challenge.

[0004] In recent years, chromium-based oxides (such as CrO3, Cr2O5, Cr8O) have been increasingly used. 21Due to their unique physicochemical properties, Cr8O3 (and others) shows significant potential in the modification of lithium-ion batteries (LIBs). Among them, non-stoichiometric Cr8O3... 21 Due to its unique three-dimensional layered framework structure, Cr8O has attracted widespread attention and has become a research hotspot for high-energy-density energy storage systems. However, current research on Cr8O... 21 The study of the role mechanism of the coating layer in the high-nickel NCM811 system still has the following limitations: (1) Cr8O 21 The synergistic mechanism of redox activity and structural stability contributing to the capacity of NCM811 is not yet clear; (2) The quantitative structure-activity relationship between coating process parameters (such as coating amount and heat treatment temperature) and electrochemical performance (such as rate performance and cycle life) lacks systematic research. Summary of the Invention

[0005] The purpose of this invention is to propose a Cr8O 21 Active-coated high-nickel NCM811 cathode material, its preparation method and application: Cr8O is constructed on the surface of NCM811 using a ball milling method combined with low-temperature calcination. 21 The coating layer was investigated, and the influence mechanism of the coating material on the structural stability, interfacial reaction kinetics, and long-cycle performance of the NCM811 cathode material was systematically studied. The morphology and chemical state of the coating material were revealed using XRD, SEM, and XPS characterization methods. The practical application potential of the coating material was evaluated through cycle testing and rate testing. Furthermore, CV and EIS analyses were used to elucidate the lithium-ion transport behavior and phase transition suppression mechanism.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A Cr8O 21 The active-coated high-nickel NCM811 cathode material uses NCM811 as the core and is coated with Cr8O. 21 Composition of active oxide layer; Cr8O 21 The crystal structure of the coating layer consists of [Cr] 3+ O6] Octahedron and [Cr 6+ O4] is composed of alternating tetrahedral arrangements, Cr 6+ / Cr 3+ Redox pairs can reversibly participate in charge-discharge reactions.

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

[0009] This invention also proposes this Cr8O 21 The preparation method of active-coated high-nickel NCM811 cathode material, which involves using Cr8O 21NCM811 was dry-mixed with commercial NCM811 at 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 of the material is preferably 1-5 wt% of the commercial NCM811 mass, more preferably 3 wt%. During dry mixing, the ball milling speed is 200 rpm and the milling time is 30 min. The calcination temperature is 270℃ and the calcination time is 6 h.

[0011] This invention also proposes this Cr8O 21 The application of active-coated high-nickel NCM811 cathode material in lithium-ion batteries, 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 cathode material.

[0012] This invention targets high-nickel layered cathode material LiNi 0.8 Co 0.1 Mn 0.1 Due to the insufficient cycle stability of O2(NCM811) caused by residual lithium compounds on the surface and mixed cations in the bulk phase, a process of dry ball milling combined with low-temperature calcination to construct Cr8O is proposed. 21 An innovative strategy for active oxide coating layers. XRD refinement results show that 3% Cr8O 21 The coating significantly inhibits cation mixing, allowing I 003 / I 104 The ratio increased from 1.490 to 1.976, while the layered structure order parameter (I0) also increased. 006 +I 012 ) / I 101 The value decreased from 0.453 to 0.417. Electrochemical tests showed that the optimized NCM811@3Cr8O 21 It exhibits a high initial discharge capacity of 236.4 mAh / g at 0.1C (coulombic efficiency 91.7%), and a capacity retention of 84.0% after 200 cycles at 1C. At 5C, the capacity is 41.0% higher than the uncoated sample. XPS analysis reveals that Cr8O… 21 The Cr8O2 reacts with the residual alkali (LiOH / Li2CO3) on the NCM811 surface 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 interfacial transport kinetics through LiCrO2. Mechanistic studies show that Cr8O2... 21 Through its three-dimensional framework [Cr 3+ O6] / [Cr 6+The alternating arrangement of O4 forms a fast lithium-ion channel, synergistically suppressing cation mixing, optimizing interface kinetics, and contributing redox activity, thereby 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 material: Innovatively adopting non-stoichiometric Cr8O 21 As a covering layer, its three-dimensional framework structure ([Cr 3+ O6] / [Cr 6+ The alternating arrangement of O4[O4] provides both ion transport channels and redox activity.

[0015] (2) Mechanism of active capacity contribution: Unlike traditional inert coating materials (such as Al2O3), Cr8O 21 Cr 6+ It was oxidized to Cr during the first charge. 3+ (Cr 6+ +3e - →Cr 3+ This contributes an additional 26.7 mAh / g capacity, and the oxidized Cr 3+ It can reversibly participate in subsequent cycles (capacity decay rate <0.05% / cycle after 200 cycles);

[0016] (3) In-situ reaction temperature (270℃) precisely matched to Cr8O 21 The formation and protection of the NCM811 structure achieve the dual goals of active layer construction and bulk structural stability.

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

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

[0019] (6) Contribution to redox activity: Cr 6+ / Cr 3+ The multi-electron reaction provides additional capacity, with an initial discharge capacity increase of 26.7 mAh / g (236.4 mAh / g vs. 209.7 mAh / g).

[0020] (7) Process compatibility: Low-temperature calcination (270℃) avoids damage to the bulk structure of NCM811, making it suitable for large-scale production.

[0021] (8) Cost saving: Liquid phase and in-situ coating process can be achieved by calcining in air. Attached Figure Description

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

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

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

[0025] Figure 4 SEM images (ah) of the material at different magnifications and NCM811@3Cr8O 21 EDS energy dispersive spectroscopy 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 coated NCM811 samples in the voltage range of 2.8–4.3 V: (a) initial charge-discharge curves at 0.1 C current density; (b) initial charge-discharge characteristics; (c) 200-cycle curves at 1 C current density; (d) NCM811 and NCM811@3Cr8O 21 Discharge curves at 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 coated NCM811 samples in the voltage range of 2.8–4.5 V: (a) initial charge-discharge curves at 0.1 C current density; (b) initial charge-discharge characteristics; (c) 100-cycle curves at 1 C current density; (d) NCM811 and NCM811@3Cr8O 21 (e) Charge-discharge curves at 1C current density for different cycle numbers; (f) 100-cycle curves at 5C current density; (c) NCM811 and NCM811@3Cr8O 21 Charge-discharge curves at different cycles under a 5C current density.

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

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

[0031] Figure 10 Cr8O 21 Schematic diagram of the mechanism of NCM811 encapsulation. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0033] Example 1

[0034] 1. Preparation of cathode materials

[0035] 1.1, Cr8O 21 Preparation

[0036] Cr8O prepared by a two-step pyrolysis method 21 Sample preparation. 10g of CrO3 (Xilong Scientific, AR) was weighed and placed in a crucible, then vacuum dried at 100℃ for 12h in a vacuum drying oven. The sample was then calcined in a muffle furnace at 260℃ for 12h. After cooling to room temperature, it was ground into powder using a mortar and pestle. The sample was then calcined again in a muffle furnace at 270℃ for 12h to obtain pure-phase Cr8O3. 21 .

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

[0038] Cr8O prepared by low-energy ball milling combined with low-temperature calcination 21 Coating NCM811 cathode material. The synthesized Cr8O 21 NCM811@Cr8O was dry-mixed with 5g of commercial NCM811 (NEWARE, AR) at a certain mass ratio (0%, 1%, 3%, 5%) using a planetary ball mill at 200rpm for 30min, and then calcined at 270℃ for 6h in air atmosphere to obtain NCM811@Cr8O. 21 The cathode material, with different mass ratios of coating, was labeled as NCM811 and NCM811@1Cr8O, respectively. 21 NCM811@3Cr8O 21 NCM811@5Cr8O 21 .

[0039] 2. Material structure and morphology characterization

[0040] The crystal structure, purity, and related material composition of the material were tested using an X-ray diffractometer (XRD, PANalytical BV, 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).

[0041] 3. Electrochemical performance testing

[0042] 3.1 Electrode Preparation

[0043] Cr8O 21@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 jar. At the same time, an appropriate amount of N-methylpyrrolidone (NMP) was added. The mixture was ball-milled at 200 rpm for 30 minutes to make a slurry, which was then coated onto an aluminum foil current collector. The prepared electrode was dried at 80°C, and the dried electrode was cut into round pieces with a diameter of 14 mm as the cathode.

[0044] 3.2 Assembly of button cells

[0045] Stainless steel casings were used for both positive and negative electrodes. Polypropylene membranes (Celgar 2500) were used as separators, lithium foil as the negative electrode material, and 1 mol / L LiPF6 was used as the electrolyte. The solvent composition was a mixed solvent of EC:DMC:EMC = 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.

[0046] 3.3 Electrochemical performance testing

[0047] The Lamborghini testing system was used to test the electrical performance of the batteries. The specific capacity, rate performance, and cycle capacity retention of the coin cells were tested, with a test voltage range of 2.8–4.3V / 2.8–4.5V. The IVIUM electrochemical workstation was used to perform cyclic voltammetry and AC impedance testing on the batteries.

[0048] 4. Results and Discussion

[0049] 4.1, Cr8O 21 XRD patterns and crystal structures

[0050] Cr8O prepared by a two-step pyrolysis method 21 The XRD pattern of the obtained product is as follows Figure 1 As shown in (a), all diffraction peaks belong to the pure phase Cr8O. 21 No characteristic peaks for 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] is composed of alternating tetrahedral structures, and its open crystal framework is composed of lithium ions (Li). + ) storage provides abundant sites, while Cr 3+ / Cr 6+ The redox pair can achieve multi-electron transfer reactions (Cr6+ +3e-→Cr 3+ ).

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

[0053] Figure 2 It is a different Cr8O 21 Preparation of NCM811@Cr8O with varying coating amounts 21 XRD pattern of the sample. Figure 2 The positions of the diffraction peaks in (a) show that the sample was affected by Cr8O 21 Both before and after coating, all four samples exhibited a hexagonal crystal system, α-NaFeO2-type layered structure with R-3m space group. The sharp peaks of the (003) and (104) main diffraction peaks in the XRD patterns demonstrate that all four samples possess high crystallinity. No Cr8O was observed in the XRD patterns. 21 The characteristic peaks may be Cr8O 21 This is due to the low content. For example... Figure 2 As shown in (b), with Cr8O 21 With the increase in coating amount, the position of the (003) peak did not shift significantly, indicating that Cr8O 21 It did not penetrate the NCM811 crystal lattice structure, but merely coated the surface of the cathode material. Furthermore, from... Figure 2 In the magnified images (c) and (d), two pairs of split peaks, (006) / (012) and (018) / (110), are clearly observed to be split, indicating that the sample has a highly ordered layered structure. The results show that different Cr8O... 21 The coating amount modification does not change the basic crystal structure of NCM811 material.

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

[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 coating amounts. 21 The lattice constants a and c, and the volume V of the coated sample showed almost no change. Ni 2+ and Li + The radii are 0.069 nm and 0.076 nm, respectively. Due to their close values, Ni is prone to occur. 2+ With Li + The phenomenon of mutual site occupation results in the formation of cation Li. + / Ni 2+Mixed arrangement phenomenon leads to Li + The inability to properly insert and remove lithium affects the capacity. Furthermore, when Li... + / Ni 2+ When the mixing degree is too high, the Ni occupying the lithium layer 2+ During the charging process of lithium-ion batteries, it is oxidized into Ni, which has a smaller ionic radius. 3+ (0.056nm), which causes the layered structure to collapse, resulting in a "plummeting" capacity of high-nickel batteries during cycling.

[0057] I (003) / I (104) The ratio represents the Li of the ternary material + / Ni 2+ The higher the ratio of the mixing ratio, the lower the degree of cation mixing. Table 1 shows the samples treated with Cr8O... 21 After coating, I (003) / I (104) The ratios of these components were significantly higher than those of the original NCM811 sample, indicating that after processing with Cr8O... 21 After coating modification, Ni in the sample 2+ Occupy Li + The proportion of sites decreased, and the layered structure became more ordered. Li + / Ni 2+ A low degree of mixing means that there is less transition metal occupying the lithium layer in the ternary material, thus avoiding the influence of transition metal on Li. + The impact of migration has a high degree of influence. (003) / I (104) Ternary cathode materials with a high ratio exhibit superior rate performance.

[0058] [I (006) +I (012) / I(101) The ratio of [] represents the orderliness of the layered structure of the material; the smaller the ratio, the better the orderliness. Table 1 shows the samples treated with Cr8O... 21 After coating, [I (006) +I (012) / I(101) The ratios of all three decreased, indicating that after processing with Cr8O 21 After coating modification, NCM811@Cr8O 21 The layered structure of the sample grew better. Overall, NCM811@3Cr8O 21 The sample's cation Li + / Ni 2+ With the lowest degree of mixing and the best stability of the layered structure, it will have superior performance in electrochemical tests.

[0059] X-ray photoelectron spectroscopy (XPS) was used to study NCM811 and its Cr8O 21Coating material (NCM811@3Cr8O) 21 Analysis of the surface and interfacial chemical properties of Cr8O showed that... 21 The coating layer significantly optimizes the material properties through multi-dimensional chemical regulation. Figure 3 (a) The coated sample in the overall spectrum showed a Cr 2p characteristic peak at 576-578 eV, while the original material showed no Cr signal, confirming that Cr8O 21 Successful introduction, coupled with a decrease in the peak intensities of Ni 2p (854-856 eV), Co 2p (780 eV), and Mn 2p (641-643 eV), directly reflects the physical covering effect of the coating layer on the NCM811 surface. Cr 2p fine spectrum ( Figure 3 b) Display Cr 3+ (576.5eV) and Cr 6+ (579.5eV) coexistence, conforming to Cr8O 21 In the coating layer [Cr 3+ O6] Octahedron and [Cr 6+ The three-dimensional framework structure formed by alternating tetrahedral arrangements of O4 provides a rapid transport path for lithium ions while suppressing the dissolution of transition metals. Among these, Cr... 3+ Through oxygen vacancies (V0) and Cr 6+ A charge balance network is formed, and this mixed valence structure is observed in the O1s spectrum ( Figure 3 This is confirmed in d), where the oxygen vacancy ratio significantly increased from 17.68% to 27.23%, while the corresponding surface adsorbed oxygen intensity (531.5 eV) decreased, indicating that the coating layer not only... 3+ -V0 defects regulate charge distribution and also suppress side reactions between the material surface and the environment. This interface modification effect is reflected in the C1s spectrum ( Figure 3 c) This is reflected in the weakening of the C=O peak intensity, which corroborates the reduced adsorption of oxygen-containing functional groups on the surface, thus improving the material purity. The interfacial reaction mechanism is that during low-temperature calcination, 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 formulas are (1) and (2). This process not only reduces the residual alkali content on the surface (inhibits electrolyte decomposition), but also the LiCrO2 formed 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] Regarding valence state evolution, the Ni 2p spectrum ( Figure 3 e) shows that the Ni2+ ratio decreased from 34.59% to 28.27%, Ni 3+ The corresponding increase in proportion, together with the enhanced I(003) / I(104) peak intensity ratio (1.490→1.976) in XRD, reveals the improved orderliness of the layered structure; Mn 2p spectrum ( Figure 3 f) The binding energy of the main peak shifts to the right from 641.8 eV to 642.3 eV, Mn 4+ The proportion 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+ The coordination environment perpetuates its function as a structural stabilizer. 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), enables Cr8O 21 The coating layer improves the cation ordering while simultaneously enhancing the Cr content. 6+ Redox activity and Cr 3+ The interfacial bonding mechanism establishes a dynamic balance between ion transport efficiency and interfacial stability.

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

[0064] To confirm Cr8O 21 The coating was effectively applied to 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), the samples before and after coating are composed of approximately 15 μm spherical secondary particles formed by the accumulation of irregularly shaped primary particles at the submicron level. With the addition of Cr8O... 21 As the coating amount increases, the surface of NCM811 particles gradually becomes rougher, but the morphology of secondary particles remains intact. Figure 4 Images (b), (d), (f), and (h) magnify the surface morphology of the samples, revealing that the NCM811 material has a smooth, impurity-free surface and clear grain boundaries. (The text then abruptly shifts to a seemingly unrelated topic about Cr8O...) 21 Cr8O can be clearly observed on the surface of the coated sample. 21 Particles, and as the coating amount increases, the Cr8O adhering to the sample surface... 21 The particle size also increases accordingly. Cr8O 21As a coating layer, it adheres tightly to the surface of NCM811 particles, which can prevent NCM811 from directly contacting the electrolyte during electrochemical testing, and prevent HF decomposed from the electrolyte from corroding the NCM811 material itself, thereby improving the electrochemical performance of the material.

[0065] To further observe Cr8O 21 The distribution of NCM811 material on the surface was determined by EDS mapping of NCM811@3Cr8O 21 The sample was tested, and the results are as follows: Figure 4 As shown in (i), Ni, Co, Mn, and O elements can be detected on the sample surface and are uniformly distributed. Similarly, in NCM811@3Cr8O 21 Cr was also detected in the sample and was evenly distributed. Because its content is lower than that of Ni, Co, and Mn, Cr is lighter in color. EDS mapping results confirmed that Cr8O 21 The coating was uniformly distributed on the surface of NCM811 particles, 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 This refers to the electrochemical performance of the material in the voltage range of 2.8-4.3V. Among them... Figure 5 (a) and (b) show different Cr8O 21 The effect of coating amount on the first charge-discharge curves of NCM811 cathode material at 0.1C rate (1C = 200 mAh / g). Experimental results show that 3% Cr8O 21 The coated sample exhibited the best overall performance, with an initial discharge specific capacity of 236.4 mAh / g and a coulombic efficiency of 91.7%, representing improvements of 26.7 mAh / g and 2.7% respectively compared to the unmodified sample. This performance improvement is attributed to Cr8O... 21 The coating material can repair the surface of NCM811, maintain the stability of the material structure, and an appropriate coating layer can effectively block direct contact between the electrolyte and the active material, reduce irreversible capacity loss, promote the formation of a low-impedance, high-stability CEI film, and improve Li... + Reversible insertion / extraction efficiency, reduced active Li loss, improved lithium-ion transport pathways, and lower electrochemical polarization. When Cr8O 21 When the coating amount is 5%, the material capacity decreases, mainly because excessive coating leads to a decrease in Li. + The diffusion path is lengthened, the interfacial 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, and the effect of surface modification on the sample in the 2.8-4.3V voltage range (vs. Li). + / Li) underwent a 200-cycle performance evaluation at a 1C rate, and the cycling curves are as follows. Figure 5 As shown in (c). NCM811, NCM811@1Cr8O 21 NCM811@3Cr8O 21 and NCM811@5Cr8O 21 The initial discharge specific capacities were 196.8 mAh / g, 207.9 mAh / g, 215.6 mAh / g, and 204.4 mAh / g, respectively; the discharge specific capacities after 200 cycles were 147.8 mAh / g, 168.1 mAh / g, 181.1 mAh / g, and 162.9 mAh / g, respectively; and the capacity retention rates after 200 cycles were 75.1%, 80.9%, 84.0%, and 79.7%, respectively. Experimental data show that the discharge specific capacity and capacity retention rate of the modified sample increase with the change in Cr8O content. 21 The coating amount exhibits a non-monotonic variation trend. Specifically, SNCM811@3Cr8O 21 The sample exhibited the best cycle stability, with a discharge specific capacity increase of 33.3 mAh / g and a capacity retention increase of 8.9% after 200 discharges compared to the unmodified sample. Figure 5 (d) is NCM811 and NCM811@3Cr8O 21 Charge-discharge curves of NCM811@3Cr8O at different cycle numbers 21 The charge-discharge curves showed good overlap and strong chemical reversibility, while the charge-discharge curves of NCM811 showed poor overlap and poor chemical reversibility. This phenomenon can be attributed to the physical barrier effect of an appropriate coating amount inhibiting the dissolution loss of transition metal ions (Ni, Co, Mn); excessive coating (5%) induces multi-energy decay, reducing the effective utilization rate of the active material. It is worth noting that the slight fluctuations in the cycling curve are related to changes in ambient temperature during winter. NCM811@3Cr8O 21 Table 2 shows a comprehensive comparison of the electrochemical performance of NCM811 with other coatings modified in the literature.

[0069] To systematically evaluate Cr8O 21 The effect of surface modification on the high-rate performance of NCM811 cathode material was investigated. Within a voltage window of 2.8-4.3V, a stepped current density test method (0.1C→0.2C→0.5C→1C→5C) was used to analyze the charge-discharge characteristics of a series of samples. The rate performance curves are shown below. Figure 5As shown in (e) and (f). Experimental results show that the unmodified NCM811 sample exhibits significant electrochemical polarization characteristics, and its specific capacity decreases sharply with increasing rate: the discharge specific capacity is 209.6 mAh / g at 0.1C, but only 132.7 mAh / g is maintained at an ultra-high rate of 5C, corresponding to a capacity retention of 63.3%. Cr8O 21 Surface engineering effectively improves the rate response characteristics of materials, including NCM811@3Cr8O 21 The sample exhibited superior kinetic performance, with a discharge specific capacity of 235.5 mAh / g at 0.1C and 189.0 mAh / g at 5C, maintaining a capacity retention of 80.3%. The discharge specific capacity at 5C was 42.4% higher than the unmodified sample (56.3 mAh / g). Cr8O 21 Coating significantly improves the rate performance of NCM811 by enhancing its conductivity, suppressing side reactions, stabilizing its structure, and optimizing its interface properties. The coating concentration exhibits a non-linear relationship with performance improvement, particularly for NCM811@1Cr8O. 21 and NCM811@5Cr8O 21 The modified samples retained 65.1% and 64.5% of their capacity at 5C, respectively, indicating that excessive coating (>3%) can trigger Li... + The diffusion barrier reduces the effective specific surface area of ​​the active material as the coating amount increases.

[0070] Figure 6 The electrochemical performance of NCM811 and its surface-modified composites is measured in the voltage window of 2.8-4.5V. Figure 6 (a) and (b) show the first charge-discharge curves and characteristics of the material at a current density of 0.1C. The modified material exhibits superior first-discharge specific capacity and coulombic efficiency compared to the original NCM811. Among them, 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) shows the cycling curves of the material at a 1C expansion rate. After 100 cycles, NCM811 and NCM811@1Cr8O 21 NCM811@3Cr8O 21 NCM811@5Cr8O 21 The discharge specific capacities were 144.5 mAh / g, 152.4 mAh / g, 173.1 mAh / g, and 157.3 mAh / g, respectively, and the capacity retention rates were 80.40%, 81.8%, 84.90%, and 81.0%, respectively. Figure 6(e) shows the cycling curves of the materials at a high magnification of 5C. 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 As can be seen from (d) and (f), after Cr8O 21 The coated and modified material exhibits superior cycling stability compared to the unmodified NCM811 material. These data confirm that the surface modification strategy effectively suppresses side reactions at the electrode / electrolyte interface, reduces interfacial impedance by constructing a stable surface coating layer, and enhances lithium-ion diffusion kinetics through a three-dimensional ion-conducting framework, thereby significantly improving high-rate performance and long-term cycling stability.

[0071] Table 2 NCM811@3Cr8O 21 A comprehensive comparison of the electrochemical performance of NCM811 with other coatings modified in the literature.

[0072]

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

[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 Table 2, NCM811@3Cr8O 21 A comprehensive analysis of comparative data with other coated and modified NCM811 materials shows that the Cr8O proposed in this invention... 21 The active coating strategy demonstrates significant advantages in several key performance indicators. Within a voltage window of 2.8-4.3V and a rate of 0.1C, its first-cycle discharge specific capacity reaches 236.4mAh / g, which is significantly higher than that of LiNbO3. [2] The coating system (200.1 mAh / g) was improved by 18.1%, compared to Li4Ti5O 12 -TiO2 [3] The composite coating system (205.2 mAh / g) improved efficiency by 15.2%. The coulombic efficiency reached 91.7%, superior to SiO2-Li2SiO3. [1] (87.1%) and other traditional coating systems. Regarding 1C cycle stability, after 100 cycles, the discharge specific capacity reached 204.6 mAh / g with a capacity retention of 94.9%, and after 200 cycles, the discharge specific capacity reached 181.1 mAh / g with a capacity retention of 84.0%; compared to SiO2... [4] The coating system exhibits a discharge specific capacity of 162.8 mAh / g and a capacity retention rate of 87.3% after 100 cycles, demonstrating superior cycle decay suppression efficiency.

[0087] Compared with existing coating technologies, Cr8O 21 The coating layer exhibits a unique "active-protective" dual-functional advantage: its three-dimensional framework structure ([Cr 3+ O6] / [Cr 6+ O4] not only reduces cation crossover (I003 / I104 = 1.976) through an oxygen vacancy-mediated charge compensation mechanism, but also Cr 6+ / Cr 3+ Redox pairs contributed additional specific capacity (236.4 vs. 213.0 mAh / g @ Co3(PO4)2). [5] Of particular note is that, under a high voltage of 4.5V and an ultra-high rate of 5C, the material still maintains 84.3% of its capacity retention (147.6 mAh / g). These performance breakthroughs stem from Cr8O 21 The unique interface regulation mechanism of the coating layer: the fast ion conductor LiCrO2 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, thus achieving synergistic optimization of interface dynamics and structural stability.

[0088] 4.5, Cr8O 21 Study on the mechanism of coating modification

[0089] 4.5.1 Analysis of dQ / dV curves

[0090] Figure 7 It is a different Cr8O 21 The dQ / dV curves of coated NCM811 samples after 200 cycles at 1C current density and a voltage window of 2.8-4.3V show a high correlation between the phase transition characteristics of NCM811 and its coated samples and their electrochemical performance and interfacial kinetic parameters. The H2-H3 phase transition causes the shrinkage of the cell volume of NCM811 material, leading to increased difficulty in lithium-ion insertion / extraction and decreased structural stability of NCM811 material. This is the main reason for the decline in cycling performance of high-nickel NCM811 materials. The voltage peak corresponding to the H2→H3 phase transition in uncoated NCM811 during charging shows a significant broadening and continuous attenuation trend after cycling, indicating that its layered structure undergoes irreversible lattice distortion during high-voltage lithium extraction. This is consistent with the result that the sample only retained 75.1% of its capacity after 200 cycles at 1C. In contrast, NCM811@3Cr8O... 21 The H2→H3 phase transition peak maintains a higher peak intensity and a narrower peak width during cycling, indicating that Cr8O 21 The coating effectively alleviates the accumulation of structural stress caused by high-pressure phase transition by suppressing cation mixing (XRD showed that I003 / I104 increased to 1.976) and optimizing oxygen vacancy distribution (XPS showed that the oxygen vacancy ratio of the 3% coated sample increased to 27.23%), thus forming a closed-loop mechanism with its excellent cycling stability (capacity retention of 84.0% after 200 cycles).

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

[0092] 4.5.2 Cyclic Voltmeter-Ammeter Test

[0093] Different Cr8O groups were studied using cyclic voltammetry (CV). 21 Electrochemical kinetics of NCM811 coated materials. Figure 8 The CV curves of four samples at a scan rate of 0.1 mV / s for the first three cycles are compared. The study found that the CV curve morphology of all samples was basically the same, but there were significant differences in the potential of the first oxidation peak in the first cycle. This may be related to the intense parasitic reaction at the cathode / electrolyte interface and the kinetics of SEI film formation during the first charge-discharge process. By quantifying the voltage hysteresis (ΔE) between the H1→M oxidation peak in the first cycle and the corresponding peak after stable cycling, the degree of electrochemical polarization and interfacial side reactions can be effectively assessed. The experimental measurements of the original NCM811 and NCM811@1Cr8O... 21 NCM811@3Cr8O 21 and NCM811@5Cr8O 21 The ΔE values ​​for the coated samples were 0.188, 0.176, 0.174, and 0.213 V, respectively, for NCM811@3Cr8O. 21 The sample exhibited the lowest polarization characteristics, reduced by 7.4% compared to the unmodified sample. This polarization suppression effect is related to Cr8O 21 The coating layer is closely related to the dual regulation mechanism of interfacial stability: an appropriate coating (3%) can effectively block the corrosion of the active material by the electrolyte and maintain Li + The diffusion channel is unobstructed; however, excessive coating (5%) may lead to increased polarization due to impaired electron conduction. This conclusion corroborates the mechanism of previous rate performance tests. NCM811@3Cr8O 21 The coated sample maintained 83.2% capacity retention at 5C magnification, which was significantly better than other samples.

[0094] 4.5.3 AC Impedance Test

[0095] Table 3 Different Cr8O 21 Electrochemical impedance spectroscopy simulation results and low-frequency Z-coating 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 systematic regulation of NCM811 interfacial dynamics and lithium-ion transport behavior by coating. For example... Figure 9 As shown in (a), after the first cycle, the Nyquist plots of all samples exhibited a high-frequency semicircle (charge transfer impedance Rct) and a low-frequency sloping line (lithium-ion solid-phase diffusion). The Rct of the uncoated NCM811 was 19.33 Ω, while that of the 3% Cr8O4 sample was...21 The Rct of the coated sample decreased significantly to 13.46 Ω (a decrease of 30.2%), which is consistent with the Cr detected by XPS. 3+ / Cr 6+ The increase of 27.23% in the mixed valence network and oxygen vacancy ratio is directly related to Cr8O. 21 In the three-dimensional framework [Cr 3+ O6] / [Cr 6+ The ordered channels formed by the alternating arrangement of O4 provide a rapid transport path for lithium ions, and their effect is expressed by the diffusion coefficient D calculated using formula (3). Li + Verification was obtained: the first layer D of the 3% coated sample was... Li + Reaching 3.81×10 -13 cm² / s, an increase of 91.5% (1.99×10⁻⁶) compared to the uncoated sample. - 13 The Warburg coefficient σ calculated by formula (4) decreases from 5.6 in the first cycle to 4.04 Ω·s. -1 / 2 This further confirms the significant reduction in interfacial impedance.

[0098]

[0099]

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

[0101] After 200 cycles ( Figure 9 (b) The Nyquist plots of all samples evolved into a single compressed semicircle, indicating that the relaxation time constants (τ = R × C) of the interfacial film impedance (Rf) and charge transfer impedance (Rct) tend to overlap. This phenomenon originates from Cr8O 21 Coating-induced interfacial phase reconstruction: Cr8O during low-temperature calcination 21The reaction of residual LiOH / Li₂CO₃ on the NCM811 surface to form LiCrO₂ (Equation 1-2) reduces interfacial polarization due to its high ionic conductivity (σ = 4.04 → 2.64 Ω·s⁻¹ / ²), causing the dynamic response characteristics of Rf and Rct to converge. Notably, after cycling, the Rct of the 3% coated sample only increased to 40.65 Ω (an increase of 201%), far lower than the 521% increase of the uncoated sample (Rct = 120 Ω). This difference can be attributed to Cr… 3+ / Cr 6+ Redox pairs inhibit Mn through charge compensation 3+ Distortion (XPS displays Mn) 4+ The proportion 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%) led to interface performance degradation; after 200 cycles, Rct surged to 97.94 Ω, while σ rebounded to 4.5 Ω / s. 1 / 2 D Li + Reduced to 3.07×10 -13 cm 2 / s. This negative effect originates from Cr8O 21 The volume expansion caused by the self-redox side reaction (XRD showed an abnormally high c / a ratio of 4.9433) led to the distortion of the lithium-ion diffusion path and the breakage of the electronic conductivity network (CV test polarization voltage difference ΔE = 0.213V). The Warburg coefficient σ of samples with different coating amounts was compared. Figure 9 (cd) It was found that the 3% coated sample had the lowest σ value after cycling (2.64 Ω / s). 1 / 2 ), and its optimal D Li + (8.93×10 -13 cm 2 The synergistic effect formed by the structure stabilization and interface dynamics optimization confirms the dual regulatory mechanism of "structure stabilization and interface dynamics optimization".

[0103] The combined application of formulas (3) and (4) further reveals the kinetic mechanism: after 200 cycles, the σ value of the 3% coated sample decreased to 2.64 Ω / s. 1 / 2 D Li + Increased to 8.93×10 -13 cm 2 The σ / s value indicates that the lithium-ion diffusion pathway remains highly efficient during long-term cycling. In contrast, overcoating (5%) caused the σ value to rebound to 4.5 Ω / s. 1 / 2 D Li + Reduced to 3.07×10 -13cm 2 The / s value is consistent with the decreasing trend in capacity retention (84.33% → 72.61%) observed in the CV test, providing evidence that Cr8O 21 Excessive introduction leads to diffusion path blockage and disruption of the electronic conductivity network.

[0104] Cr8O 21 The coating enhances the interfacial chemical environment by constructing three-dimensional ion channels (XRD verification showed an interlayer spacing increase of 0.049%), stabilizing the interfacial chemical environment (XPS oxygen vacancy enhancement), and suppressing cation distortion (Mn). 4+ Multiple mechanisms (proportional optimization) enhance the intrinsic structural orderliness (I) 003 / I 104 =1.976) while establishing a dynamic equilibrium interface of "low impedance-high diffusion", in which 3% coating content achieves Rct and D Li The optimal matching of + provides a control mechanism that combines structural stability and kinetic advantages for the interface engineering of high-nickel cathode materials.

[0105] Based on the above XPS, XRD and electrochemical kinetic analyses, this invention reveals Cr8O 21 The multi-dimensional synergistic modification mechanism of the active coating layer on NCM811 cathode material, such as Figure 10 As shown. During the low-temperature calcination process, Cr8O 21 An interfacial chemical reaction occurs with residual LiOH / Li₂CO₃ on the NCM811 surface, generating an in-situ LiCrO₂ interfacial layer with high ionic conductivity. This reaction process not only effectively reduces the residual alkali content on the surface (reduced C=O peak intensity in XPS), but more importantly, it constructs a fast lithium-ion transport channel, significantly optimizing the charge transfer kinetics at the electrode / electrolyte interface (EIS shows a 47.4% reduction in Rct). Cr₈O₂ 21 The unique three-dimensional layered framework structure is composed of [Cr 3+ O6] Octahedron and [Cr 6+ The structure consists of alternating tetrahedral O4, whose periodic open structure provides an isotropic diffusion path for lithium ions. XRD refinement results show that this structure effectively suppresses Ni diffusion through an oxygen vacancy-mediated charge compensation mechanism. 2+ Migration into the Li layer significantly reduced the degree of cation mixing (I003 / I104 increased from 1.490 to 1.976). Meanwhile, Cr... 3+ / Cr 6+ The mixed valence network promotes the oxidation of Mn3+ to Mn4+ through electron redistribution (XPS showed an increase of 2.96% in the proportion of Mn4+), effectively mitigating the damage to the layered structure caused by the Jahn-Teller distortion.

[0106] This structure-interface co-optimization mechanism forms a dynamic equilibrium during the cycle: a moderate amount of Cr8O 21 The coating layer (3%) acts as both a physical barrier to inhibit electrolyte corrosion and transition metal dissolution, and also activates Cr... 6+ →Cr 3+ Redox reactions contribute additional capacity (increased first-cycle discharge capacity by 26.7 mAh / g). However, excessive coating (5%) leads to Li... + The obstructed diffusion path (resulting in a 15.8% decrease in 5C capacity retention) and the resulting accumulation of interfacial stress ultimately led to a surge in charge transport impedance (Rct = 97.94 Ω). Based on this, this invention elucidates a new theoretical perspective for improving the performance of high-nickel cathode materials by demonstrating the triple synergistic mechanism of the active oxide coating layer through structural stabilization, interfacial kinetic optimization, and redox activity contribution.

[0107] In summary, this invention utilizes 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. Experiments show that 3% Cr8O... 21 Coating inhibits cation mixing (I 003 / I 104 =1.976) and optimized layered order ((I 006 +I 012 ) / I 101 =0.417), significantly enhancing the intrinsic stability of the material. Interfacial reaction kinetics analysis reveals that Cr8O 21 The LiCrO2 fast ion conductor formed with residual alkali on the surface effectively reduces charge transfer impedance (Rct = 13.49 Ω), while its three-dimensional framework structure provides a fast lithium-ion transport channel, resulting in a 41.0% increase in capacity at 5C rate compared to the unmodified sample. Electrochemical performance testing confirms that NCM811@3Cr8O 21 The initial 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 of 84.0%, which is superior to most coated systems reported in the literature. The impedance surge (Rct = 97.94 Ω) and capacity decay caused by excessive coating (5%) highlight the importance of controlling the coating concentration. The "active-protective" dual-functional interface engineering strategy proposed in this invention utilizes Cr8O... 21 The synergistic mechanism of redox activity contribution and structural stabilization provides a new approach for the development of high-energy-density lithium-ion batteries, and has significant scientific value and application potential.

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

Claims

1. A Cr8O for use in lithium-ion batteries 21 The active-coated high-nickel NCM811 cathode material is characterized by, It uses NCM811 as the core and is coated with Cr8O. 21 The active oxide layer is composed of Cr8O 21 The coating amount of the active oxide layer is 1-5 wt%; Cr8O 21 The crystal structure of the coating layer consists of [Cr] 3+ O6] Octahedron and [Cr 6+ O4] is composed of alternating tetrahedral arrangements, Cr 6+ / Cr 3+ Redox pairs can reversibly participate in charge-discharge reactions; The Cr8O 21 The preparation method of the active-coated high-nickel NCM811 cathode material is as follows: Cr8O 21 NCM811 was dry-mixed with commercial NCM811 at a certain mass ratio using a planetary ball mill, and then calcined in air to obtain NCM811@Cr8O. 21 The cathode material is prepared by ball milling at 200 rpm for 30 min during dry mixing and calcining at 270℃ for 6 h.

2. The Cr8O as described in claim 1 for use in lithium-ion batteries 21 The active-coated high-nickel NCM811 cathode material is characterized by, Cr8O 21 The coating amount of the active oxide layer is 3wt%.

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