Low-temperature high-stability NCM622 positive electrode material, preparation method thereof and lithium ion battery

Abstract

This invention discloses a low-temperature, high-stability NCM622 cathode material and its preparation method, as well as a lithium-ion battery. The preparation method specifically includes the following steps: first, dissolving La(NO3)3·6H2O in anhydrous ethanol, then adding NCM622 bulk powder, stirring and impregnating, then adding H3BO3, drying to obtain a modified precursor powder, and finally performing heat treatment in an oxygen-containing atmosphere. After cooling, a cathode material with a La / B gradient composite modified layer on the surface or near the surface is obtained. This invention, through a process of lanthanum pre-impregnation, boron introduction, and final oxygen-containing heat treatment, can precisely control the spatial distribution and chemical morphology of elements, solving the problems of insufficient capacity release, high interfacial impedance, and Li+ in existing NCM622 cathode materials at low temperatures. + To address issues such as diffusion limitation, a target gradient interface structure is effectively constructed to achieve the same level of improvement in low-temperature capacity, rate performance, and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of cathode materials, specifically to a low-temperature, high-stability NCM622 cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] NCM622 is a nickel-cobalt-manganese ternary lithium-ion battery cathode material with the chemical formula LiNi. 0.6 Co 0.2 Mn 0.2 O2, as a 6-series high-nickel material, has achieved a good balance between specific capacity, cost and safety due to its high discharge specific capacity, excellent energy density and good thermal and cycle stability, making it one of the mainstream choices in the current power battery field.

[0003] However, NCM622 still exhibits significant performance bottlenecks in low-temperature applications. At low temperatures (e.g., -20°C), the electrolyte viscosity increases, and the Li... + The increased solvation / desolvation energy barrier, coupled with a significant increase in the intrinsic charge transfer impedance of the material, leads to Li + Diffusion is severely sluggish at the interface and near-surface lattice, resulting in insufficient capacity release and a sharp deterioration in rate performance; To address the aforementioned issues, elemental doping and surface coating are currently the mainstream modification strategies. Regarding single-element modification, the introduction of lanthanum (La) can anchor the near-surface oxygen framework through high-bond-energy La-O bonds, enhancing near-surface oxygen stability or improving the stability of layered structures. The introduction of boron (B) can form borate or boron oxide interface phases on the particle surface, which is beneficial for residual alkali control, interface protection, or Li... + Transport is improved; however, under low-temperature conditions, single La modification has an effect on the Li interface. + The improvement in transport kinetics is very limited and cannot alleviate the problem of the sharp increase in charge transfer impedance at low temperatures; the interface phase formed by single B modification is beneficial to Li + It can conduct electricity, but its stabilizing effect on the near-surface transition metal-oxygen framework is weak, and it cannot effectively suppress structural degradation and metal ion dissolution during long-term low-temperature cycling. Existing research on La / B composite modification mainly focuses on the structural stability of high-nickel materials under room temperature cycling, high temperature storage, or high voltage. However, if La and B are introduced into the bulk phase randomly or only mechanically mixed on the surface, La struggles to preferentially occupy near-surface transition metal sites to provide framework anchoring, while B is prone to uncontrollable bulk doping, weakening its interfacial function. This mismatch between spatial distribution and function means that the potential of La / B composite modification in low-temperature applications of NCM622 is far from being realized. Therefore, there is an urgent need to develop a method that can precisely construct the spatial distribution of elements at the fabrication process level, simultaneously achieving lattice stabilization, interfacial protection, and low-temperature Li…+ Synergistic enhancement of transmission capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a low-temperature, high-stability NCM622 cathode material. By first pre-impregnating with lanthanum, then introducing boron, and finally performing oxygen-containing heat treatment, the spatial distribution and chemical morphology of elements can be precisely controlled. This solves the problems of insufficient capacity release, high interfacial impedance, limited Li+ diffusion, and insufficient near-surface structural stability of existing NCM622 cathode materials at low temperatures. It effectively constructs a target gradient interfacial structure and achieves the same degree of improvement in low-temperature capacity, rate performance, and cycle stability.

[0005] To achieve the above objectives, a method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve La(NO3)3·6H2O in anhydrous ethanol to obtain a lanthanum salt ethanol solution; S2, LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred to impregnate the powder, so that the lanthanum source is adsorbed or distributed on the particle surface or near the surface of the matrix powder to obtain a lanthanum pre-impregnated dispersion. S3, add H3BO3 to the lanthanum pre-impregnated dispersion in step S2 to obtain the La / B co-modified precursor system; The solvent of the La / B co-modified precursor system was evaporated at 50–90 °C and dried at 80–130 °C for 6–24 h to obtain the modified precursor powder. S4, the modified precursor powder from step S3 is heat-treated in an oxygen-containing atmosphere, and after cooling, LiNi with a La / B gradient composite modified layer on the surface or near the surface is obtained. 0.6 Co 0.2 Mn 0.2 O2 cathode material.

[0006] In some examples of this invention, the amount of La(NO3)3·6H2O added is LiNi 0.6 Co 0.2 Mn 0.2 2-3 wt% of the O2 matrix powder; The amount of H3BO3 added is LiNi 0.6 Co 0.2 Mn 0.2 1–2 wt% of the O2 matrix powder.

[0007] In some examples of this invention, the amount of La(NO3)3·6H2O added is LiNi 0.6 Co0.2 Mn 0.2 3wt% of the O2 matrix powder; The amount of H3BO3 added is LiNi 0.6 Co 0.2 Mn 0.2 2 wt% of the O2 matrix powder.

[0008] In some examples of the present invention, in the heat treatment of step S4, the temperature is increased to 700-750°C at a rate of 3-5°C / min and held for 5-10 hours.

[0009] In some examples of the present invention, in the heat treatment of step S4, the temperature is increased to 730-750°C at a rate of 3-5°C / min and held for 8-10 hours.

[0010] A low-temperature, high-stability NCM622 cathode material is prepared by the above-described method for preparing low-temperature, high-stability NCM622 cathode materials. In the La / B gradient composite modified layer on or near the surface of the cathode material, La is enriched on the particle surface and / or near the surface region, and exists in the form of La-O coordination structure, La-enriched oxide phase, lithium lanthanum oxide phase, or with LiNi. 0.6 Co 0.2 Mn 0.2 O2 exists in the form of near-surface lattice interactions; B is distributed in the particle surface to near-surface region in the form of borate structure.

[0011] In some examples of the present invention, the thickness of the La / B gradient composite modified layer is 8–20 nm.

[0012] A lithium-ion battery comprising the aforementioned low-temperature, high-stability NCM622 cathode material.

[0013] Compared with existing technologies, a method for preparing a low-temperature, high-stability NCM622 cathode material has the following advantages: By employing a process of lanthanum pre-impregnation, boron introduction, and final oxygen-containing heat treatment, the spatial distribution and chemical morphology of elements can be precisely controlled. Lanthanum, due to its larger ionic radius, preferentially adsorbs near the surface of NCM622 particles. After heat treatment, it is partially doped into the transition metal layer. The high-bond-energy La-O bonds anchor the oxygen framework, suppress cation mixing, and reconstruct the layered structure, constructing a stable modified inner layer near the surface lattice. Next, a boron source is added. While the boron source is mainly distributed on the surface due to site occupancy effects, its small ionic radius allows for a concentration gradient within a limited depth on the surface. This gradient then spreads uniformly on the particle surface, forming a limited gradient diffusion, ultimately generating a continuous, amorphous, borate-rich fast-ion conductor interface phase. This phase serves the dual purpose of isolating electrolyte side reactions and accelerating low-temperature Li+ transport. Finally, heat treatment in an oxygen-containing atmosphere provides a driving force for appropriate element diffusion and ensures that La and B form functionalized La-O coordination structures and borate phases, respectively. This preparation method can achieve a synergistic effect on the degradation path of NCM622 at low temperatures, which is characterized by structural degradation and kinetic sluggishness. It can effectively construct the target gradient interface structure and achieve the same degree of improvement in low-temperature capacity, rate performance and cycling stability.

[0014] A low-temperature, high-stability NCM622 cathode material has a gradient composite modification layer with La / B surface fast ion conductors coated in situ constructed on the material surface. This unique structure significantly improves the capacity and cycle stability of the material at -20℃ through multiple synergistic mechanisms such as stabilizing the crystal lattice, inhibiting cation mixing, and reducing interfacial impedance. Attached Figure Description

[0015] Figure 1 These are XRD comparison images of samples from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 in this invention. Figure 2 These are SEM comparison images of samples from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 in this invention. Wherein, (a) is the SEM image of the sample in Comparative Example 1, and (b) is the SEM image of the sample in Comparative Example 2. (c) is a SEM image of the sample in Comparative Example 3; (d) is a SEM image of the sample in Example 1; Figure 3 The TEM, HR-TEM, and EDS surface distribution images of the sample in Example 1 of this invention are shown below. Wherein, (a) and (b) are TEM images of Example 1; (c) is an HR-TEM image of Example 1; (d) is a diagram of the EDS surface distribution in Example 1; Figure 4 These are XPS and depth profile results of samples from Example 1 and Comparative Example 1 in this invention. Among them, (a) is the C 1sXPS spectrum of Example 1 and Comparative Example 1; (b) Ni 2p XPS spectra of Example 1 and Comparative Example 1; (c) are the O 1s XPS spectra of Example 1 and Comparative Example 1; (d) shows the Mn 2p XPS spectra of Example 1 and Comparative Example 1; (e) is the La 3dXPS spectrum of Example 1; (f) is the B 1s XPS spectrum of Example 1; (g) is the La 3dXPS depth etching spectrum of Example 1; (h) is the B 1sXPS depth etching spectrum of Example 1; Figure 5 Synchrotron radiation X-ray absorption spectra characterized for Example 1 and Comparative Example 1 of this invention; Among them, (a) is the normalized Ni K-edge X-ray absorption near-edge structure of Example 1 and Comparative Example 1; (b) is the normalized Mn K-edge X-ray absorption near-edge structure of Example 1 and Comparative Example 1; (c) is the normalized Co K-edge X-ray absorption near-edge structure of Example 1 and Comparative Example 1; (d), (e), and (f) are the EXAFS spectra of the R-space Fourier transform of Ni, Mn, and Co with K-edges, and the corresponding standard reference samples; (g) and (h) are wavelet transform (WT) spectra of the Ni K-edge EXAFS signals of Sample 1 and Comparative Example 1, respectively; Figure 6 These are GITT analysis chromatograms of samples from Example 1 and Comparative Example 1 in this invention; Wherein, (a) is the charge-discharge voltage response curve of the first cycle of Comparative Example 1, and the lithium-ion diffusion coefficient (lg D_Li) within the corresponding charge-discharge range. + The real-time trend of ); (b) is the charge-discharge voltage response curve for the first cycle of Example 1, and the lithium-ion diffusion coefficient (lg D_Li) within the corresponding charge-discharge range. + Real-time trend of changes; (c) shows the charge-discharge voltage response curve for the 200th cycle of Comparative Example 1, and the lithium-ion diffusion coefficient (lg D_Li) within the corresponding charge-discharge range. + Real-time trend of changes; (d) shows the charge-discharge voltage response curve for the 200th cycle of Example 1, and the lithium-ion diffusion coefficient (lg D_Li) within the corresponding charge-discharge range. + The real-time trend of ); (e) and (f) are left-hand bar charts comparing the average lithium-ion diffusion coefficients of the four samples after the 1st and 200th cycles, and the corresponding real-time lg D_Li at each cycle stage. + Evolution curve with charge / discharge time (right); Figure 7 The constant current charge-discharge curves, cyclic voltammetry (CV) curves, rate performance, and long-cycle performance are shown at -20℃. Among them, (a) is the constant current charge-discharge curve of Comparative Example 1; (b) is the constant current charge-discharge curve of Example 1; (c) Cyclic voltammetry (CV) curves of Comparative Example 1 and Example 1 at a scan rate of 0.1 mV s⁻¹; (d) is a comparison chart of the rate performance test results of the samples from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3; (e) Comparison of capacity retention rates of samples from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 after 300 cycles at a 0.2C rate; Figure 8 This is a TOF-SIMS depth distribution map of the first part of the sample in Example 1 and Comparative Example 1 according to the present invention.

[0016] Among them, (a) is the C 1sXPS spectrum of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (b) The O 1s XPS spectra of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (c) The F 1s XPS spectra of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (d) are the P 2pXPS spectra of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (e) Ni 2p XPS spectra of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (f) shows the O 1s XPS 20nm etching spectra of Example 1 and Comparative Example 1 after 300 cycles at low temperature; (g) is the La 3dXPS depth etching spectrum of Example 1 after 300 cycles; (h) is the B 1sXPS depth etching spectrum of Example 1 after 300 cycles; Figure 9 This is a TOF-SIMS depth distribution map of the second part of the sample in Example 1 and Comparative Example 1 according to the present invention.

[0017] (i) and (j) represent the LiF2 after electrode cycling in Comparative Example 1 and Example 1, respectively. - CH - C2F - PO2- Li3F5 - and NiF3 - Three-dimensional reconstructed chemical images (100 μm × 100 μm × 100 μm) of characteristic species by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and corresponding two-dimensional chemical distribution maps (100 μm × 100 μm). (k) is the TOF-SIMS depth profile curve of the above-mentioned characteristic species after two electrode cycles (sputtering time corresponds to etching depth). Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0020] A method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve La(NO3)3·6H2O in anhydrous ethanol to obtain a lanthanum salt ethanol solution; S2, LiNi 0.6 Co 0.2 Mn 0.2O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred and impregnated to allow the lanthanum source to be preferentially adsorbed or distributed on the particle surface or near the surface of the matrix powder, thus obtaining a lanthanum pre-impregnated dispersion. S3, add H3BO3 to the lanthanum pre-impregnated dispersion in step S2 to obtain the La / B co-modified precursor system, and evaporate the solvent of the La / B co-modified precursor system at 50-90℃ and dry it at 80-130℃ for 6-24h to obtain the modified precursor powder. S4, the modified precursor powder from step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 700-750℃ at 3-5℃ / min and held for 5-10h. After cooling, LiNi with a La / B gradient composite modified layer on or near the surface is obtained. 0.6 Co 0.2 Mn 0.2 O2 cathode material; Furthermore, the amount of La(NO3)3·6H2O added is LiNi 0.6 Co 0.2 Mn 0.2 The O2 matrix powder comprises 2-3 wt% of its mass, preferably 3 wt%; The amount of H3BO3 added is LiNi 0.6 Co 0.2 Mn 0.2 The O2 matrix powder comprises 1 to 2 wt% of its mass, preferably 2 wt%. In step S4, the temperature is increased to 730-750℃ at a rate of 3-5℃ / min and held for 8-10 hours. LiNi obtained by the above preparation method 0.6 Co 0.2 Mn 0.2 O2 cathode material, its surface or near-surface layer forms a La / B gradient composite modification layer; The thickness of the La / B gradient composite modified layer is 8–20 nm, preferably 10–15 nm. In this gradient composite modified layer, La is enriched on the particle surface and / or near-surface region, and exists as a La-O coordination structure, La-enriched oxide phase, lithium lanthanum oxide phase, or with LiNi. 0.6 Co 0.2 Mn 0.2 O2 exists in the form of near-surface lattice interactions; B is distributed in the particle surface to near-surface region in the form of borate structure.

[0021] Specifically, La exists mainly as lanthanum oxide when doped into the transition metal layer, while B exists as a continuous, amorphous, borate-rich fast ion conductor interface phase on the surface. This gradient layer is formed in situ through a gradient mechanism of pre-impregnation surface enrichment-thermal treatment diffusion. Large-radius La is mainly enriched in the near-surface layer to exert a lattice pillar effect, enhancing lattice stability, suppressing lithium-nickel mixing, and widening lithium-ion diffusion channels. Small-radius B can more easily penetrate to the outermost layer of the material, stabilizing the oxygen framework through bonding, passivating the interface, and blocking electrolyte erosion. The two are hierarchically distributed and functionally complementary. While retaining the bulk capacity of the material, they synergistically suppress irreversible phase transitions and microcrack initiation under high voltage, reduce interfacial charge transfer impedance, and significantly improve the cycle stability, rate performance, and thermal safety of the material, making it suitable for the application requirements of high-energy-density lithium-ion batteries.

[0022] This method for preparing low-temperature, high-stability NCM622 cathode material first involves LiNi... 0.6 Co 0.2 Mn 0.2 O2-based powder is impregnated in a lanthanum source, then a boron source is added, followed by heat treatment in an oxygen-containing atmosphere. This sequential liquid-phase process allows for precise control of the spatial distribution and chemical speciation of elements. Specifically, when LiNi... 0.6 Co 0.2 Mn 0.2 When O2 matrix powder is impregnated in lanthanum source, the lanthanum source, due to its larger ionic radius, preferentially adsorbs near the surface of NCM622 particles. After heat treatment, it is partially doped into the transition metal layer. The high bond energy La-O bond anchors the oxygen framework, suppresses cation mixing and layered structure reconstruction, and constructs a modified inner layer with a stable near-surface lattice. Then, a boron source is added. Due to the site occupancy effect, the boron source is mainly distributed on the surface. However, due to its small ionic radius, a concentration gradient can be formed within a limited depth of the surface layer. It then spreads uniformly on the particle surface and forms a limited gradient diffusion, ultimately generating a continuous amorphous borate-rich fast ion conductor interface phase, which has the dual function of isolating electrolyte side reactions and accelerating low-temperature Li+ transport. Finally, when heat treatment is performed in an oxygen-containing atmosphere, the heat treatment window of 700-750℃ provides a driving force for moderate element diffusion and ensures that La and B form functionalized La-O coordination structures and borate phases, respectively. The three components of this preparation method, when added in the correct order, can form a synergistic effect on the degradation path of NCM622 at low temperatures, which involves structural decay and kinetic sluggishness. If the feeding order is changed or the oxygen-containing heat treatment environment is removed, the target gradient interface structure cannot be constructed, and it is difficult to achieve the same level of improvement in low-temperature capacity, rate performance, and cycle stability.

[0023] Example 1

[0024] A method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve 0.15g of La(NO3)3·6H2O in 5mL of anhydrous ethanol and stir at 400r / min for 12min to obtain a lanthanum salt ethanol solution; S2, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred for 10 min for impregnation to obtain lanthanum pre-impregnated dispersion; S3, Weigh 0.1g of H3BO3 and add it to the lanthanum pre-impregnated dispersion in step S2, stir at room temperature for 15min to obtain the La / B co-modified precursor system; The above La / B co-modified mixture was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S4, the modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 10h, and cooled to obtain NCM622 cathode material with La / B gradient composite improved layer, denoted as NCM@La+B. like Figure 1 Characterization results show that no obvious impurity phase peaks were observed in the XRD pattern of the sample in this example; Figure 2 As shown, SEM revealed that the secondary particle size of the sample was approximately 10–12 μm; Figure 3 As shown, TEM / HRTEM indicates the presence of a composite modified layer containing La and B on or near the surface of the particles, with a thickness of approximately 12.4 nm.

[0025] XRD Rietveld results showed that the cell parameters of the NCM@La+B sample changed regularly compared to the pure sample, with the I(003) / I(104) peak intensity ratio increasing to 1.16, indicating that cation mixing was suppressed to some extent. Figure 4 As shown, XPS depth profiling and / or TOF-SIMS results indicate that La exists primarily as lanthanum oxide doped into the transition metal layer, while B exists as a continuous, amorphous, borate-rich fast-ion conductor interface phase on the surface. This forms an NCM622 cathode material with a La / B gradient composite improved layer. Figure 5 As shown, XAS results indicate that La / B coating does not disrupt the bulk structure of NCM622. By controlling the Ni valence state and oxygen coordination environment on the surface, it suppresses lithium-nickel mixing, the Jahn-Teller effect, and oxygen loss, stabilizes the surface structure, alleviates cycling phase transitions and structural collapse, and improves the cycling and rate performance of the material.

[0026] The NCM@La+B was used as the positive electrode material in the battery, and charge-discharge tests were conducted at low temperatures. Specifically: An experimental platform was constructed using the CR2032 coin cell as the test subject: 0.08g of the above positive electrode material was taken as sample A, 0.01g of conductive agent acetylene black and 0.01g of binder PVDF were added, 4mL of NMP was added to make a slurry and coated on aluminum foil as the positive electrode, and lithium metal sheet was used as the negative electrode. The voltage window was 2.5-4.5V, the positive electrode active material loading was 1.2-1.8mg / cm2, the electrolyte was a mixed solvent of 1mol / L LiPF6 dissolved in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio 1:1), and the separator was a glass fiber separator (Whatman GF / F). Cyclic performance testing was performed under constant current charge and discharge at a specified rate. The capacity retention rate was the ratio of the capacity after the 300th discharge to the capacity after the first discharge. Rate performance testing was conducted at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C rates, each cycled 5 times. Battery assembly was completed entirely in an argon atmosphere glove box with water and oxygen content both below 0.1ppm. like Figure 6 As shown, the diffusion rate of the La / B coated sample is significantly improved at low temperatures, such as... Figure 7 As shown, sample A has an initial discharge specific capacity of 156 mAh / g at -20℃ and 20 mA / g; an initial reversible discharge specific capacity of 135.2 mAh / g at -20℃ and 40 mA / g; and a discharge specific capacity of 110.2 mAh / g after 300 cycles, with a capacity retention of 81%. Figure 8 , Figure 9 As shown, XPS and TOF-SIMS characterizations revealed that after cycling, the La / B coating suppressed interfacial side reactions and Ni reduction and dissolution in NCM622, maintaining the high-valence Ni state on the surface. The coating elements exhibited a surface gradient distribution, which induced the formation of a thin and stable inorganic-rich CEI film, blocking electrolyte side reactions, enhancing interfacial stability, and improving the long-cycle performance of the material.

[0027] Example 2

[0028] A method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve 0.15g of La(NO3)3·6H2O in 5mL of anhydrous ethanol and stir at 400r / min for 12min to obtain a lanthanum salt ethanol solution; S2, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred for 10 min for impregnation to obtain lanthanum pre-impregnated dispersion; S3, Weigh 0.1g of H3BO3 and add it to the lanthanum pre-impregnated dispersion in step S2, stir at room temperature for 15min to obtain the La / B co-modified precursor system; The above La / B co-modified mixture was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S4. The modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 5h, and then cooled to obtain NCM622 cathode material with La / B gradient composite improved layer. In this embodiment, the same steps as in Example 1 are used, except that in step S4, the temperature is increased to 750°C at 5°C / min and held for 5 hours to finally form the positive electrode material. The same CR2032 coin cell test platform as in Example 1 was constructed. In this example, the positive electrode material was used as sample B. The initial discharge specific capacity of sample B at -20℃ and 20mA / g current density was 150mAh / g, the initial discharge specific capacity at -20℃ and 40mA / g current density was 130.3mAh / g, and the discharge specific capacity after 300 cycles was 101.2mAh / g. The capacity retention rate was calculated to be 77%.

[0029] Example 3

[0030] A method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve 0.1 g of La(NO3)3·6H2O in 5 mL of anhydrous ethanol and stir at 400 r / min for 12 min to obtain a lanthanum salt ethanol solution; S2, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred for 10 min for impregnation to obtain lanthanum pre-impregnated dispersion; S3, Weigh 0.05 g of H3BO3 and add it to the lanthanum pre-impregnated dispersion in step S2, stir at room temperature for 15 min to obtain the La / B co-modified precursor system; The above La / B co-modified mixture was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S4. The modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 5h, and then cooled to obtain NCM622 cathode material with La / B gradient composite improved layer. This embodiment uses the same steps as Example 1, the difference being that the amount of La(NO3)3·6H2O added is LiNi. 0.6 Co 0.2 Mn 0.2 The O2 matrix powder content is 2 wt%, and the H3BO3 content is equal to that of LiNi. 0.6 Co 0.2 Mn 0.2 1 wt% of the O2 matrix powder is used to form the cathode material. The same CR2032 coin cell test platform as in Example 1 was constructed. In this example, the positive electrode material was used as sample C. The initial discharge specific capacity of sample C at -20℃ and 20mA / g current density was 142mAh / g, the initial discharge specific capacity at -20℃ and 40mA / g current density was 126.2mAh / g, and the discharge specific capacity after 300 cycles was 95.2mAh / g. The capacity retention rate was calculated to be 75%.

[0031] Comparative Example 1 In this comparative example, traditional LiNi was selected. 0.6 Co 0.2 Mn 0.2 O2-based powder is used as the positive electrode material and is designated as NCM622. like Figure 1 As shown, NCM622 maintains a complete crystal structure, such as Figure 2 As shown, the original NCM622 surface particles are intact, as... Figure 4 As shown, XPS results indicate that La / B was successfully coated onto the NCM622 surface, significantly improving the surface Ni content. 3+ The proportion of adsorbed oxygen inhibits lithium-nickel mixing and enhances interfacial activity. Furthermore, the La and B elements exhibit a gradient distribution from the surface inwards, allowing for sustained interfacial regulation. Figure 6 As shown, the diffusion rate of NCM622 is not as fast as that of the modified material. The same CR2032 coin cell test platform as in Example 1 was constructed, as follows: Figure 7 As shown, the unmodified comparative example exhibited an initial discharge specific capacity of 100 mAh / g at -20℃ and 20 mA / g in this experiment; an initial discharge specific capacity of 89.6 mAh / g at a current density of -20℃ and 40 mA / g; and a capacity of 57 mAh / g after 300 cycles, with a capacity retention of 63.6%. Figure 8 , Figure 9 As shown, the surface is severely damaged after cycling, making it difficult to maintain cycle stability.

[0032] Comparative Example 2 The preparation method of this comparative example specifically includes the following steps: S1, dissolve 0.1 g of La(NO3)3·6H2O in 5 mL of anhydrous ethanol and stir at 400 r / min for 12 min to obtain a lanthanum salt ethanol solution; S2, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred for 10 min for impregnation to obtain lanthanum pre-impregnated dispersion; The lanthanum pre-impregnated dispersion was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S3, the modified precursor powder from step S2 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 5h, and then cooled to obtain the cathode material, denoted as NCM@La; This comparative example uses the same steps as Example 1, except that a single La is used as the modified sample, and H3BO3 is not added for improvement, ultimately forming a cathode material (NCM@La), which is not the NCM622 cathode material with a La / B gradient composite improvement layer. The specific steps include: like Figure 1 As shown, NCM@La still maintains a complete crystal structure, such as Figure 2 As shown in the SEM image, the NCM622@La sample with intact single-La surface after modification still maintains a complete spherical secondary particle morphology, such as... Figure 7 As shown, the same CR2032 coin cell test platform as in Example 1 was constructed. In the test, the first discharge specific capacity of this comparative sample was 138 mAh / g at -20℃ and 20 mA / g current density, and the first discharge specific capacity was 127.4 mAh / g at -20℃ and 40 mA / g current density. After 300 cycles, the capacity was 90.28 mAh / g, and the capacity retention rate was 70%.

[0033] XRD Rietveld refinement results show that the cell parameters of the NCM@La sample change regularly compared to the pure sample, and the I(003) / I(104) peak intensity ratio increases to 1.14, indicating that cation mixing is suppressed to a certain extent. XPS depth profiling and TOF-SIMS results show that the specific state of La is that it is doped into the transition metal layer and mainly exists as lanthanum oxide.

[0034] Comparative Example 3 The preparation method of this comparative example specifically includes the following steps: S1, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2O2 matrix powder was dissolved in 5 mL of anhydrous ethanol and stirred to obtain a mixture; S2, Weigh 0.1g of H3BO3 and add it to the mixture in step S1. Stir at room temperature for 15min, then continue stirring in a 60℃ water bath until the anhydrous ethanol is completely evaporated. Then dry at 100℃ for 12h to obtain the modified precursor powder. S3, the modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere, heated to 750℃ at 5℃ / min, held for 10h, and cooled to obtain a positive electrode material, denoted as NCM@B; The comparative example uses the same steps as Example 1, except that a single B is used as the modified sample, and La(NO3)3·6H2O is not added for improvement, and the final cathode material (NCM@B) is formed, which is not the NCM622 cathode material with La / B gradient composite improvement layer; like Figure 1 As shown, NCM@B still maintains a complete crystal structure, such as Figure 2 As shown, the B-based coating layer uniformly covers the particle surface, making the originally rough surface formed by the stacking of primary particles smoother and denser. The edges of the primary particles are modified by the coating layer without damaging the original particle microstructure of the material. The same CR2032 coin cell test platform as in Example 1 was constructed, as follows: Figure 7 As shown, in the experiment, the first discharge specific capacity of this comparative sample was 140 mAh / g at -20℃ and 20 mA / g current density; the first discharge specific capacity was 124.4 mAh / g at -20℃ and 40 mA / g current density; and the capacity after 300 cycles was 101.2 mAh / g, with a capacity retention rate of 81.6%.

[0035] XRD Rietveld refinement results showed that the cell parameters of the NCM@B sample changed regularly compared to the pure sample, and the I(003) / I(104) peak intensity ratio increased to 1.12, indicating that cation mixing was suppressed to a certain extent. XPS depth profiling and TOF-SIMS results showed that the specific existence state of B was as a continuous amorphous borate-rich fast ion conductor interface phase formed on the surface.

[0036] Comparative Example 4 The preparation method of this comparative example specifically includes the following steps: S1, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder was dissolved in 5 mL of anhydrous ethanol and stirred to obtain an anhydrous ethanol dispersion system containing NCM622 matrix powder. S2, 0.15g of La(NO3)3·6H2O and 0.1g of H3BO3 were simultaneously added to the anhydrous ethanol dispersion system of step S1, and stirred at room temperature for 15min to obtain the La / B co-modified precursor system. The La / B co-modified mixture was then placed in a 60℃ water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Subsequently, it was dried at 100℃ for 12h to obtain the modified precursor powder. S3, the modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 10h, and cooled to obtain NCM622 cathode material with La / B gradient composite improved layer, denoted as NCM@La&B. In this comparative example, the same steps as in Example 1 were used, except that La(NO3)3·6H2O and H3BO3 were added simultaneously to the anhydrous ethanol dispersion system containing NCM622 matrix powder. As a result, the NCM622 cathode material with the La / B gradient composite improvement layer was not formed. The order of addition will affect the composition of the composite structure. The same CR2032 coin cell test platform as in Example 1 was constructed. In the test, the first discharge specific capacity of this comparative sample was 136 mAh / g at -20℃ and 20 mA / g current density, and the first discharge specific capacity was 118.6 mAh / g at -20℃ and 40 mA / g current density. After 300 cycles, the capacity was 90.2 mAh / g, and the capacity retention rate was 76%.

[0037] The comparative sample was characterized by XRD and SEM. La and B elements were found to be locally aggregated and spatially unevenly distributed. B element exhibited both random phase doping and surface segregation, but did not form a gradient doping structure. The surface modification layer was uneven in thickness and relatively thick overall, approximately 20-50 nm.

[0038] Comparative Example 5 The preparation method of this comparative example specifically includes the following steps: S1, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder was dissolved in 5 mL of anhydrous ethanol and stirred to obtain an anhydrous ethanol dispersion system containing NCM622 matrix powder. S2, Weigh 0.1g of H3BO3 and add it to the anhydrous ethanol dispersion system in step S1, stir at room temperature for 15min to obtain a mixture; S3, add 0.15 g of La(NO3)3·6H2O to the mixture in step S2, and stir at 400 r / min for 12 min to obtain the B / La co-modified precursor system; The above B / La co-modified mixture was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S4, the modified precursor powder in step S3 is heat-treated in an oxygen-containing atmosphere: the temperature is increased to 750℃ at 5℃ / min, held for 10h, and cooled to obtain NCM622 cathode material with La / B gradient composite improved layer, denoted as NCM@B+La. The same steps as in Example 1 were used in this comparative example, except that H3BO3 was first introduced into the anhydrous ethanol dispersion system of NCM622 matrix powder, and then La(NO3)3·6H2O was added to finally form the cathode material (NCM@B+La). The same CR2032 coin cell test platform as in Example 1 was constructed. In the test, the first discharge specific capacity of this comparative sample was 130 mAh / g at -20℃ and 20 mA / g current density; the first discharge specific capacity was 120.4 mAh / g at -20℃ and 40 mA / g current density; and the capacity after 300 cycles was 85.2 mAh / g, with a capacity retention rate of 70.8%.

[0039] The comparative sample was characterized by XRD and SEM. The boron element was severely segregated on the surface and formed a continuous boron-containing glass phase capping layer, but gradient doping into the bulk phase was not achieved. The la element was distributed in island-like agglomerates on the surface of the boron-containing glass phase, and could not form a continuous and uniform coating layer. In addition, local insulating impurities were generated. The thickness of the surface modification layer was extremely uneven, with an overall thickness of about 30-70 nm.

[0040] Comparative Example 6 A method for preparing a low-temperature, high-stability NCM622 cathode material specifically includes the following steps: S1, dissolve 0.15g of La(NO3)3·6H2O in 5mL of anhydrous ethanol and stir at 400r / min for 12min to obtain a lanthanum salt ethanol solution; S2, weigh 5g of LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred for 10 min for impregnation to obtain lanthanum pre-impregnated dispersion; S3, Weigh 0.1g of H3BO3 and add it to the lanthanum pre-impregnated dispersion in step S2, stir at room temperature for 15min to obtain the La / B co-modified precursor system; The above La / B co-modified mixture was placed in a 60°C water bath and stirred continuously until the anhydrous ethanol was completely evaporated. Then it was dried at 100°C for 12 hours to obtain the modified precursor powder. S4. The modified precursor powder from step S3 is heat-treated in an inert atmosphere: the temperature is increased to 550℃ at 5℃ / min, held for 10h, and then cooled to obtain NCM622 cathode material, denoted as NCM@La+B. This comparative example uses the same steps as Example 1, except that an argon inert atmosphere is used instead of an air atmosphere, and a non-preferred heat treatment temperature of 550°C is used to finally form a positive electrode material; experiments have verified that this positive electrode material does not have a composite surface structure.

[0041] The same CR2032 coin cell test platform as in Example 1 was constructed. In the test, the first discharge specific capacity of this comparative sample was 112 mAh / g at -20℃ and 20 mA / g current density; the first discharge specific capacity was 101.4 mAh / g at -20℃ and 40 mA / g current density; the capacity after 300 cycles was 79.2 mAh / g, and the capacity retention rate was 78.4%.

[0042] The comparative sample was characterized by XRD and SEM. The boron element could not be fully oxidized and diffused into the bulk phase, and a large amount of reducing boron-containing impurities were enriched on the surface. At the non-preferred temperature, the diffusion driving force of the La / B element was insufficient at 550℃, and a gradient composite structure could not be formed. At 750℃, the excessive diffusion of the element caused the surface modification layer to disappear and was accompanied by particle sintering and grain boundary cracking.

[0043] From the corresponding test results of Examples 1-3 and Comparative Examples 1-6, it can be seen that: Example 1 (NCM@La+B) achieved the highest discharge specific capacity (156 mAh / g at 20 mA / g) and excellent cycling stability (81% retention after 300 cycles) at -20°C by constructing a gradient composite modification layer of "La bulk doped / B surface fast ion conductor" on the surface of NCM622. This significantly outperformed the unmodified original material (Comparative Example 1) and samples modified with single La (Comparative Example 2) or single B (Comparative Example 3), demonstrating the synergistic effect of La and B in functionality. Example 1, by introducing lanthanum salt impregnation first and then adding boron source, ensures that La element preferentially diffuses into the bulk phase for doping, and B element subsequently enriches on the surface to form a coating layer, thus achieving spatial functional division. In contrast, Comparative Example 4, which adds both La and B sources, suffers from uneven element distribution, agglomeration, excessively thick modified layer without gradient, and reduced capacity. Comparative Example 5, which adds B source first and then La source, suffers from severe surface segregation of B element and extremely uneven modified layer. Therefore, the stepwise impregnation process of lanthanum first and then boron directly affects the modified layer structure, forming an effective gradient structure. In Comparative Example 6, the inert atmosphere prevented element B from being fully oxidized to form an effective fast ion conductor phase. In Example 1, heat treatment was performed in an oxygen-containing atmosphere, which avoided the above problems. In addition, compared with Examples 1, 2, and 3, the amount of La(NO3)3·6H2O and H3BO3 added is relatively less than that of LiNi. 0.6 Co 0.2 Mn 0.2 The quality of the O2 matrix powder and the parameters of the heat treatment need to be adjusted within a certain range to suit different application environments; This invention successfully provides a low-temperature, high-stability NCM622 cathode material and its preparation method. The method involves first pre-impregnating with lanthanum, then introducing boron, and finally performing oxygen-containing heat treatment to construct a gradient composite modification layer on the material surface in situ, which is coated with a fast ion conductor of La / B. This unique structure significantly improves the capacity and cycle stability of the material at -20℃ through multiple synergistic mechanisms such as stabilizing the crystal lattice, inhibiting cation mixing, and reducing interfacial impedance.

[0044] The foregoing description, with reference to preferred embodiments, details an exemplary embodiment of the low-temperature, high-stability NCM622 cathode material proposed by the present invention. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of the present invention, and various combinations can be made to the various technical features and structures proposed by the present invention without exceeding the protection scope of the present invention, which is determined by the appended claims.

Claims

1. A method for preparing a low-temperature, high-stability NCM622 cathode material, characterized in that, Specifically, the following steps are included: S1, dissolve La(NO3)3·6H2O in anhydrous ethanol to obtain a lanthanum salt ethanol solution; S2, LiNi 0.6 Co 0.2 Mn 0.2 O2 matrix powder is added to the lanthanum salt ethanol solution in step S1 and stirred to impregnate the powder, so that the lanthanum source is adsorbed or distributed on the particle surface or near the surface of the matrix powder to obtain a lanthanum pre-impregnated dispersion. S3, add H3BO3 to the lanthanum pre-impregnated dispersion in step S2 to obtain the La / B co-modified precursor system; The solvent of the La / B co-modified precursor system was evaporated at 50–90 °C and dried at 80–130 °C for 6–24 h to obtain the modified precursor powder. S4, the modified precursor powder from step S3 is heat-treated in an oxygen-containing atmosphere, and after cooling, LiNi with a La / B gradient composite modified layer on the surface or near the surface is obtained. 0.6 Co 0.2 Mn 0.2 O2 cathode material.

2. The method for preparing a low-temperature, high-stability NCM622 cathode material according to claim 1, characterized in that, The amount of La(NO3)3·6H2O added is LiNi 0.6 Co 0.2 Mn 0.2 2-3 wt% of the O2 matrix powder; The amount of H3BO3 added is LiNi 0.6 Co 0.2 Mn 0.2 1–2 wt% of the O2 matrix powder.

3. The method for preparing a low-temperature, high-stability NCM622 cathode material according to claim 2, characterized in that, The amount of La(NO3)3·6H2O added is LiNi 0.6 Co 0.2 Mn 0.2 3wt% of the O2 matrix powder; The amount of H3BO3 added is LiNi 0.6 Co 0.2 Mn 0.2 2 wt% of the O2 matrix powder.

4. The method for preparing a low-temperature, high-stability NCM622 cathode material according to claim 1, characterized in that, In step S4, the temperature is increased to 700-750℃ at a rate of 3-5℃ / min and held for 5-10 hours.

5. The method for preparing a low-temperature, high-stability NCM622 cathode material according to claim 4, characterized in that, In step S4, the temperature is increased to 730-750℃ at a rate of 3-5℃ / min and held for 8-10 hours.

6. A low-temperature, high-stability NCM622 cathode material, characterized in that, The low-temperature high-stability NCM622 cathode material was prepared by the preparation method of any one of claims 1 to 5. In the La / B gradient composite modified layer on or near the surface of the cathode material, La is enriched on the particle surface and / or near the surface region, and exists in the form of La-O coordination structure, La-enriched oxide phase, lithium lanthanum oxide phase, or with LiNi. 0.6 Co 0.2 Mn 0.2 O2 exists in the form of near-surface lattice interactions; B is distributed in the particle surface to near-surface region in the form of borate structure.

7. The low-temperature, high-stability NCM622 cathode material according to claim 6, characterized in that, The thickness of the La / B gradient composite modified layer is 8–20 nm.

8. A lithium-ion battery, characterized in that, Including the low-temperature, high-stability NCM622 cathode material as described in claim 6.

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