Rare earth gradient modified high-nickel ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a rare earth gradient modified high-nickel ternary positive electrode material and a preparation method and application thereof. A preparation method of a rare earth gradient modified high-nickel ternary positive electrode material comprises the following steps: bulk phase light rare earth doping: mixing a lithium source, a high-nickel ternary precursor and a light rare earth source, and carrying out first sintering treatment to obtain a bulk phase doped material; carrying out near-surface co-doping, mixing the bulk phase doping material with a medium rare earth source and a doping agent, and then carrying out secondary sintering treatment to obtain the rare earth gradient modified high-nickel ternary positive electrode material, the dopant comprises at least one of a zirconium source and a phosphorus source. According to the invention, a gradient functional structure combining bulk phase light rare earth doping and near-surface medium rare earth-electrolyte affinity element co-doping is adopted, so that the defect of poor cycle performance of the existing high-nickel ternary positive electrode material in a lithium ion battery due to bulk phase structure degradation and interface impedance sharp increase is effectively overcome.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a rare-earth gradient modified high-nickel ternary cathode material, its preparation method, and its application. Background Technology

[0002] Solid-state batteries are considered a core direction for next-generation power batteries, and their advantages in safety and high energy density promise to significantly improve the range and safety of electric vehicles. The performance of these batteries is highly dependent on the interfacial compatibility and structural stability between the cathode material and the solid electrolyte. High-nickel ternary cathode materials, especially systems with a nickel content of over 90%, possess very high theoretical specific capacity and are ideal cathode choices for achieving high-energy-density solid-state batteries. However, these materials face significant challenges in the solid-state battery environment.

[0003] In terms of bulk structure, high-nickel materials undergo drastic lattice contraction and phase transitions during lithium-ion insertion / extraction, generating significant internal stress. This easily leads to microcracks in the particles, disrupting ion transport channels and causing continuous capacity decay. Regarding the interface, the surface of high-nickel materials contains various chemically highly reactive residues. When in contact with oxide or sulfide solid electrolytes, these residues undergo side reactions, generating a high-resistivity interface layer that severely hinders ion migration and causes a sharp increase in interfacial charge transfer resistance, far exceeding the allowable range for practical solid-state battery applications. While conventional bulk doping can stabilize the structure to some extent, it cannot effectively suppress drastic lattice changes and is ineffective against interface problems. Surface coatings, although able to mitigate interfacial reactions, often fail to alleviate bulk crack formation due to high lattice mismatch with the electrolyte. Existing rare-earth doping methods are mostly designed for liquid batteries, but in solid-state batteries, the synergistic optimization of bulk crack resistance and interface stability is difficult, ultimately resulting in poor cycle performance of the material in solid-state batteries. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor cycle performance of existing high-nickel ternary cathode materials in solid-state battery applications due to the deterioration of bulk structure and the surge in interface impedance. The present invention provides a rare earth gradient modified high-nickel ternary cathode material, its preparation method and application, which solves the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a rare-earth gradient modified high-nickel ternary cathode material, comprising: Bulk phase light rare earth doping: After mixing lithium source, high nickel ternary precursor and light rare earth source, the first sintering treatment is performed to obtain bulk doped material; Near-surface co-doping: After mixing the bulk dopant with a medium rare earth source and a dopant (electrolyte affinity element), a second sintering process is performed to obtain a rare earth gradient modified high-nickel ternary cathode material; The dopant includes at least one of a zirconium source (e.g., ZrO2, suitable for oxide solid electrolytes) and a phosphorus source (e.g., (NH4)2HPO4, suitable for sulfide solid electrolytes).

[0006] Furthermore, the general chemical formula of the high-nickel ternary precursor is Ni x Co y Mn z (OH)₂, where x ≥ 0.9, y > 0, z > 0, and x + y + z = 1; for example, Ni 0.9 Co 0.05 Mn 0.05 (OH)2; And / or, the light rare earth element in the light rare earth source includes at least one of lanthanum (La), neodymium (Nd), praseodymium (Pr), and cerium (Ce); preferably a light rare earth element with an ionic radius of 1.03~1.16 Å; And / or, the medium rare earth elements in the medium rare earth source include at least one of gadolinium (Gd), dysprosium (Dy), samarium (Sm), europium (Eu), and terbium (Tb).

[0007] Furthermore, the lithium source includes at least one of lithium hydroxide (LiOH·H2O) and lithium carbonate; And / or, the zirconium source includes at least one of zirconium oxide (ZrO2), zirconium nitrate (Zr(NO3)4·5H2O), zirconium oxychloride (ZrOCl2·8H2O), zirconium hydroxide (Zr(OH)4), zirconium acetate (Zr(CH3COO)4), and zirconium sulfate (Zr(SO4)2·4H2O); And / or, the phosphorus source includes at least one of diammonium hydrogen phosphate ((NH4)2HPO4), ammonium dihydrogen phosphate (NH4H2PO4), ammonium phosphate ((NH4)3PO4), lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4), and ammonium phosphite ((NH4)2HPO3).

[0008] Furthermore, based on the percentage of light rare earth element molars in the total molar amount of transition metals in the high-nickel ternary precursor, the doping amount of light rare earth elements is 0.2~0.4 mol%; And / or, based on the percentage of the molar amount of medium rare earth elements to the total molar amount of transition metals in the high-nickel ternary precursor, the doping amount of medium rare earth elements is 0.2~0.3 mol.

[0009] Furthermore, based on the percentage of the total molar amount of phosphorus and zirconium elements in the dopant relative to the total molar amount of transition metals in the high-nickel ternary precursor, the total doping amount of phosphorus and zirconium elements is 0.1~0.3 mol%; And / or, the molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor is (1.05~1.10):1.

[0010] Furthermore, the temperature of the first sintering treatment is 800~950℃, which is higher than the conventional temperature to enhance the bulk lattice stability; And / or, the holding time for the first sintering treatment is 10~12h; And / or, the heating rate of the first sintering treatment is 5~10℃ / min; And / or, the sintering atmosphere of the first sintering treatment is an oxygen-containing atmosphere, preferably an oxygen atmosphere (oxygen partial pressure ≥ 95%).

[0011] Furthermore, the temperature of the second sintering treatment is 450~600℃, preferably 450~550℃, with medium-temperature diffusion to control the doping depth in the near-surface region; And / or, the holding time for the second sintering treatment is 4~6 hours; And / or, the heating rate of the second sintering treatment is 2~5℃ / min; And / or, the sintering atmosphere of the second sintering treatment is an inert atmosphere, preferably an argon atmosphere.

[0012] Furthermore, after the first sintering treatment and the second sintering treatment, the corresponding sintering products are crushed, pulverized and sieved (200~300 mesh). And / or, in the steps of bulk light rare earth doping and near-surface co-doping, the mixing method independently includes at least one of ball milling (300~400 r / min, ball-to-material ratio 10:1, time 2~4 h) and stirring (2000~3000 r / min, time 30~60 min).

[0013] Secondly, the present invention also provides a rare earth gradient modified high-nickel ternary cathode material, which is prepared by the above-mentioned method for preparing rare earth gradient modified high-nickel ternary cathode material.

[0014] Thirdly, the present invention also provides a solid-state battery, wherein the positive electrode comprises the above-mentioned rare-earth gradient modified high-nickel ternary positive electrode material.

[0015] In this invention, apart from promethium and scandium, rare earth minerals are divided into three groups according to the requirements of the separation process (extraction separation), which is common knowledge in the field: Light rare earth elements (P204 weak acidity extraction) — lanthanum, cerium, praseodymium, neodymium; Medium rare earth elements (P204 low acidity extraction) — samarium, europium, gadolinium, terbium and dysprosium; Heavy rare earth elements (P204 medium acidity extraction) — holmium, europium, erbium, thulium, ytterbium, lutetium, yttrium.

[0016] The technical solution of this invention has the following advantages: 1. A method for preparing a rare-earth gradient modified high-nickel ternary cathode material, comprising: bulk light rare-earth doping, wherein a lithium source, a high-nickel ternary precursor, and a light rare-earth source are mixed and subjected to a first sintering treatment to obtain a bulk doped material; and near-surface co-doping, wherein the bulk doped material is mixed with a medium rare-earth source and a dopant and subjected to a second sintering treatment to obtain a rare-earth gradient modified high-nickel ternary cathode material; wherein the dopant includes at least one of a zirconium source and a phosphorus source. This invention employs a gradient functional structure combining "bulk light rare-earth doping" and "near-surface medium rare-earth-electrolyte affinity element co-doping," utilizing light rare-earth elements with large ionic radii (such as La) 3+ 、Nd 3+ Doping at the bulk Li sites effectively widens the interlayer spacing, suppressing harmful phase transitions and drastic lattice contraction during charging and discharging, thereby enhancing the bulk structural stability and preventing particle breakage. In the near-surface region, doping with medium rare earth elements (such as Gd)... 3+ Dy 3+ ) and compatibility dopant (Zr 4+ For oxide electrolytes, P 5+ Co-doping with sulfide electrolytes quenches surface active oxygen, significantly reduces lattice mismatch with solid electrolytes, and suppresses the formation of high-resistivity interface byproducts, thereby greatly reducing interface impedance. This overcomes the defect of poor cycle performance caused by bulk structure deterioration and interface impedance surge in existing high-nickel ternary cathode materials in lithium-ion batteries.

[0017] 2. In the preparation method of the rare-earth gradient modified high-nickel ternary cathode material of the present invention, the first step is to perform bulk doping sintering in a high-temperature oxygen atmosphere at 800~950℃, which ensures the uniform solid solution of light rare earth ions deep in the crystal lattice and lays the foundation for the stability of the bulk structure; the second step is to fully mix the obtained bulk dopant with a medium rare earth source and an affinity element source, and then perform low-temperature diffusion sintering in an inert atmosphere at 450~550℃. This process controls the enrichment of modified elements only in the near-surface region of the particles, optimizes the designed concentration gradient distribution, and further avoids functional interference caused by uniform doping. Detailed Implementation

[0018] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0019] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0020] Example 1 This embodiment provides a method for preparing a rare-earth gradient modified high-nickel ternary cathode material, the specific steps of which are as follows: (1) Bulk light rare earth doping: Based on the molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor of 1.07:1, and the doping amount of La element of 0.3 mol% (calculated as the percentage of the molar amount of La element to the total molar amount of transition metal in the high-nickel ternary precursor), weigh out lithium hydroxide (LiOH·H2O) and high-nickel ternary precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2 was mixed with lanthanum oxide (La2O3) (dry mixing for 40 minutes at 2500 r / min). The mixture was then subjected to a first sintering treatment at 880℃ for 11 hours in an oxygen atmosphere (oxygen partial pressure ≥95%) at a heating rate of 8℃ / min. After furnace cooling, the mixture was crushed, pulverized, and passed through a 250-mesh sieve to obtain a bulk doped material. (2) Near-surface co-doping: Based on the total molar amount of transition metals in the high-nickel ternary precursor being 100%, gadolinium oxide (Gd2O3) and zirconium oxide (ZrO2) were weighed out according to the ratio of 0.25 mol% Gd element doping and 0.2 mol% Zr element doping, and mixed with the bulk dopant obtained in step (1) (added to a planetary ball mill (ball-to-material ratio 10:1) and ball-milled at 350 r / min for 3 h). The ball-milled material was heated to 500 °C in an argon atmosphere at a heating rate of 3 °C / min for a second sintering treatment for 5 h. After being cooled in the furnace, it was crushed, pulverized, and passed through a 250-mesh sieve to obtain rare earth gradient modified high-nickel ternary cathode material.

[0021] Example 2 This embodiment provides a rare-earth gradient modified high-nickel ternary cathode material, the preparation method of which includes the following steps: (1) Bulk light rare earth doping: Based on a molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor of 1.05:1 and an Nd element doping amount of 0.2 mol% (calculated as the percentage of Nd element molar amount to the total molar amount of transition metal in the high-nickel ternary precursor), weigh out lithium carbonate and Ni from the high-nickel ternary precursor respectively. 0.92 Co 0.04 Mn 0.04 (OH)2 and neodymium oxide (Nd2O3) were mixed (dry mixing at 2000 r / min for 60 minutes). The mixture was then subjected to a first sintering treatment at 800℃ for 12 hours in an oxygen atmosphere at a heating rate of 5℃ / min. After furnace cooling, the mixture was crushed, pulverized, and passed through a 200-mesh sieve to obtain the bulk doped material. (2) Near-surface co-doping: Based on the total molar amount of transition metals in the high-nickel ternary precursor being 100%, dysprosium oxide (Dy2O3) and diammonium hydrogen phosphate ((NH4)2HPO4) were weighed out according to the ratio of 0.2 mol% Dy element doping and 0.1 mol% P element doping, and mixed with the bulk dopant obtained in step (1) (added to a planetary ball mill (ball-to-material ratio 8:1) and ball-milled at 300 r / min for 4 h). The ball-milled material was heated to 450 °C in an argon atmosphere at a heating rate of 2 °C / min for a second sintering treatment for 6 h. After being cooled in the furnace, it was crushed, pulverized, and passed through a 200-mesh sieve to obtain rare earth gradient modified high-nickel ternary cathode material.

[0022] Example 3 This embodiment provides a method for preparing a rare-earth gradient modified high-nickel ternary cathode material, the specific steps of which are as follows: (1) Bulk light rare earth doping: Based on the molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor of 1.10:1, and the doping amount of La element of 0.4 mol% (calculated as the percentage of the molar amount of La element to the total molar amount of transition metal in the high-nickel ternary precursor), weigh out lithium hydroxide (LiOH·H2O) and high-nickel ternary precursor Ni 0.95 Co 0.03 Mn 0.02 (OH)2 was mixed with lanthanum oxide (La2O3) (dry mixing for 30 minutes at 3000 r / min). The mixture was then subjected to a first sintering treatment at 950°C for 10 hours in an oxygen atmosphere at a heating rate of 10°C / min. After furnace cooling, the mixture was crushed, pulverized, and passed through a 300-mesh sieve to obtain a bulk doped material. (2) Near-surface co-doping: Based on the total molar amount of transition metals in the high-nickel ternary precursor being 100%, gadolinium oxide (Gd2O3) and lithium phosphate (Li3PO4) were weighed out according to the ratio of 0.3 mol% Gd element doping and 0.3 mol% P element doping, and mixed with the bulk dopant obtained in step (1) (added to a planetary ball mill (ball-to-material ratio 12:1) and ball-milled at 400 r / min for 2 h). The ball-milled material was heated to 550 °C in an argon atmosphere at a heating rate of 5 °C / min for a second sintering treatment for 4 h. After being cooled in the furnace, it was crushed, pulverized, and passed through a 300-mesh sieve to obtain rare earth gradient modified high-nickel ternary cathode material.

[0023] Example 4 This embodiment provides a method for preparing a rare-earth gradient modified high-nickel ternary cathode material, the specific steps of which are as follows: (1) Bulk light rare earth doping: Based on a molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor of 1.06:1, and a Pr element doping amount of 0.25 mol% (calculated as the percentage of Pr element molar amount to the total molar amount of transition metal in the high-nickel ternary precursor), weigh out lithium hydroxide (LiOH·H2O) and high-nickel ternary precursor Ni 0.91 Co 0.06 Mn 0.03 (OH)2 and praseodymium oxide (Pr6O) 11 The mixture was then dry-mixed for 35 minutes at 2800 r / min. The mixture was then subjected to a first sintering treatment at 850°C for 11.5 h in an oxygen atmosphere at a heating rate of 7°C / min. After cooling in the furnace, the mixture was crushed, pulverized, and passed through a 280-mesh sieve to obtain the bulk doped material. (2) Near-surface co-doping: Based on the total molar amount of transition metals in the high-nickel ternary precursor being 100%, europium oxide (Eu2O3) and zirconium nitrate (Zr(NO3)4·5H2O) were weighed out according to the ratio of Eu element doping amount of 0.22mol% and Zr element doping amount of 0.15mol%, and mixed with the bulk dopant obtained in step (1) (added to a planetary ball mill (ball-to-material ratio 9:1) and ball-milled at 320r / min for 3.5h). The ball-milled material was heated to 480℃ in an argon atmosphere at a heating rate of 4℃ / min for a second sintering treatment for 5.5h. After being cooled in the furnace, it was crushed, pulverized, and passed through a 280-mesh sieve to obtain rare earth gradient modified high-nickel ternary cathode material.

[0024] Example 5 This embodiment provides a method for preparing a rare-earth gradient modified high-nickel ternary cathode material, the specific steps of which are as follows: (1) Bulk light rare earth doping: Based on a molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor of 1.08:1 and a Ce element doping amount of 0.35 mol% (calculated as the percentage of Ce element molar amount to the total molar amount of transition metal in the high-nickel ternary precursor), weigh out lithium carbonate and Ni from the high-nickel ternary precursor respectively. 0.93 Co 0.05 Mn 0.02 (OH)2 was mixed with cerium oxide (CeO2) (dry mixing for 50 minutes at 2200 r / min). The mixture was then subjected to a first sintering treatment at 920°C for 10.5 h in an oxygen atmosphere at a heating rate of 6°C / min. After furnace cooling, the mixture was crushed, pulverized, and passed through a 220-mesh sieve to obtain the bulk doped material. (2) Near-surface co-doping: Based on the total molar amount of transition metals in the high-nickel ternary precursor being 100%, samarium oxide (Sm2O3) and ammonium dihydrogen phosphate (NH4H2PO4) were weighed out according to the ratio of Sm element doping amount of 0.28 mol% and P element doping amount of 0.25 mol%, and mixed with the bulk dopant obtained in step (1) (added to a planetary ball mill (ball-to-material ratio 11:1) and ball-milled at 380 r / min for 2.5 h). The material obtained after ball milling was heated to 520 °C in an argon atmosphere at a heating rate of 3.5 °C / min for a second sintering treatment of 4.5 h. After being cooled in the furnace, it was crushed, pulverized, and passed through a 220 mesh sieve to obtain rare earth gradient modified high-nickel ternary cathode material.

[0025] Example 6 This embodiment provides a method for preparing rare earth gradient modified high-nickel ternary cathode material. The only difference between this method and Example 1 is that the second sintering temperature in the bulk light rare earth doping is adjusted to 600℃, while all other conditions are exactly the same as in Example 1.

[0026] Comparative Example 1 This comparative example provides a method for preparing a high-nickel ternary cathode material. The only difference between this method and Example 1 is that near-surface co-doping is not performed. That is, the bulk doped material is used as the final product after the bulk light rare earth doping is completed. All other conditions are exactly the same as in Example 1.

[0027] Comparative Example 2 This comparative example provides a method for preparing a high-nickel ternary cathode material. The only difference between this method and Example 1 is that the light rare earth source used in the bulk light rare earth doping step is replaced with an equimolar amount of medium rare earth source (gadolinium oxide), and then a near-surface co-doping step is performed. All other conditions are exactly the same as in Example 1.

[0028] Comparative Example 3 This comparative example provides a method for preparing a high-nickel ternary cathode material. The only difference between this method and Example 1 is that a medium rare earth source (gadolinium oxide) is not added in the near-surface co-doping step. All other conditions are exactly the same as in Example 1.

[0029] Comparative Example 4 This comparative example provides a method for preparing a high-nickel ternary cathode material. The only difference between this method and Example 1 is that no dopant (zirconia) is added in the near-surface co-doping step. All other conditions are exactly the same as in Example 1.

[0030] Test case The positive electrode materials prepared using the above examples and comparative examples were assembled with corresponding solid electrolytes into CR2032 type solid-state button half-cells. The specific methods are as follows: In an argon glove box (water and oxygen content ≤0.1 ppm), the prepared positive electrode material was used as the active material and mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent to prepare a slurry, which was then uniformly coated onto an aluminum foil current collector. After vacuum drying at 120°C for 12 hours, the slurry was cut into positive electrode sheets (active material surface loading of 10 mg / cm²). 2 Using lithium metal sheets as the negative electrode and corresponding solid electrolyte sheets (LLZO with a thickness of 200 μm for oxide systems; Li7P3S for sulfide systems)... 11 A membrane with a thickness of 500 μm (500 μm) is used as both the separator and the electrolyte. The layers are stacked in the following order: negative electrode shell, lithium sheet, solid electrolyte sheet, positive electrode sheet, spring sheet, and positive electrode shell. The electrolyte is subjected to a pressure of 300 MPa (for sulfide electrolyte Li7P3S). 11 Solid-state batteries are produced by cold pressing and encapsulation under a pressure of 600 MPa (for oxide electrolytes LLZO, when the dopant is a phosphorus source, an oxide electrolyte is used) or 600 MPa (for zirconium source, an oxide electrolyte is used) and then encapsulating them.

[0031] The test was conducted at a constant temperature of 25°C. The assembled solid-state battery was placed in the Blue Electric testing system for electrochemical performance testing. Interfacial impedance testing: Before any charge-discharge test, the electrochemical impedance spectroscopy (EIS) of the battery is tested using an electrochemical workstation with a test frequency range of 0.01 Hz and a perturbation voltage of 5 mV to obtain the interfacial charge transfer resistance (Rct) value.

[0032] Charge / discharge performance testing: After completing the EIS test, charge / discharge tests were performed. First, the battery was charged at a constant current rate of 0.1C (1C = 200 mA / g) to 4.3V, then charged at a constant voltage until the current dropped to 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 0.1C to 2.8V. This constitutes one cycle. The initial charge / discharge specific capacity and the first-cycle coulombic efficiency (first-cycle discharge specific capacity / first-cycle charge specific capacity) were recorded. Subsequently, cycle performance tests were continued at a charge rate of 0.5C and a discharge rate of 1C within a voltage window of 2.8-4.3V. A capacity calibration cycle at 0.1C was inserted after every 10 cycles. The discharge specific capacity at the 100th cycle was recorded, and its ratio to the initial 0.1C discharge specific capacity was calculated as the 100-cycle capacity retention rate. The test results are shown in Table 1.

[0033] Table 1

[0034] Based on the above test results, it can be seen that the overall electrochemical performance of Examples 1 to 6 of the present invention is significantly better than that of the comparative examples. Among them, the interfacial impedance of Example 6 (with a higher second sintering temperature) is 31.5 Ω·cm. 2 The ionization rate (90.2%) was significantly higher than that of Examples 1-5 (≥92.9%), indicating that the optimized two-step sintering process is the key control step for achieving elemental gradient distribution and synergistic effects of bulk enhancement and interface stabilization. Comparative Example 1 (only bulk light rare earth doping but lacking near-surface modification) had a higher interface impedance (82.0 Ω·cm). 2 Although the cycle retention rate (75.8%) of Comparative Example 2 (without bulk structure) was better than that of Comparative Examples 2-4, it was still much lower than that of Examples 1-6. This proves that although bulk doping can partially improve structural stability, it cannot solve the serious interfacial side reactions and impedance surge problems caused by highly active surfaces. The interfacial impedance of Comparative Example 2 (with medium rare earth elements replacing light rare earth elements in the bulk phase) was 65.1 Ω·cm. 2 The poorer cycle performance (80.5%) indicates that light rare earth elements (LREEs) are significantly better than medium rare earth elements (MRREEs) in improving bulk structural stability. The interfacial impedance of Comparative Example 3 (near-surface lack of MRREEs) is 57.3 Ω·cm. 2 Although lower than Comparative Examples 1 and 2, its cycle retention rate (82.2%) remained relatively low, confirming the irreplaceable key role of rare earth elements in improving interfacial chemical stability. Comparative Example 4 (near-surface lacking electrolyte affinity elements) had an interfacial impedance of 73.1 Ω·cm. 2 The high 0.5% and poor cycling performance (78.5%) demonstrate that the introduction of zirconium or phosphorus sources is crucial for reducing lattice mismatch with solid electrolytes and constructing low-impedance ion transport channels. Their absence will directly lead to interface compatibility failure.

[0035] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a rare-earth gradient modified high-nickel ternary cathode material, characterized in that, include: Bulk phase light rare earth doping: After mixing lithium source, high nickel ternary precursor and light rare earth source, the first sintering treatment is performed to obtain bulk doped material; Near-surface co-doping: After mixing the bulk dopant with a medium rare earth source and dopant, a second sintering process is performed to obtain a rare earth gradient modified high-nickel ternary cathode material. The dopant includes at least one of zirconium source and phosphorus source.

2. The preparation method according to claim 1, characterized in that, The general chemical formula of the high-nickel ternary precursor is Ni x Co y Mn z (OH)2, where, x≥0.9, y>0, z>0, x+y+z=1; And / or, the light rare earth elements in the light rare earth source include at least one of lanthanum, neodymium, praseodymium, and cerium; And / or, the medium rare earth elements in the medium rare earth source include at least one of gadolinium, dysprosium, samarium, europium, and terbium.

3. The preparation method according to claim 1 or 2, characterized in that, The lithium source includes at least one of lithium hydroxide and lithium carbonate; And / or, the zirconium source includes at least one of zirconium oxide, zirconium nitrate, zirconium oxychloride, zirconium hydroxide, zirconium acetate, and zirconium sulfate; And / or, the phosphorus source includes at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, lithium phosphate, dilithium hydrogen phosphate, and ammonium phosphite.

4. The preparation method according to claim 1 or 2, characterized in that, The doping amount of light rare earth elements is 0.2~0.4 mol% based on the percentage of light rare earth element molars relative to the total molar amount of transition metals in the high-nickel ternary precursor. And / or, based on the percentage of the molar amount of medium rare earth elements to the total molar amount of transition metals in the high-nickel ternary precursor, the doping amount of medium rare earth elements is 0.2~0.3 mol.

5. The preparation method according to claim 1 or 2, characterized in that, The total doping amount of phosphorus and zirconium is 0.1~0.3 mol%, calculated as the percentage of the total molar amount of phosphorus and zirconium in the dopant relative to the total molar amount of transition metals in the high-nickel ternary precursor. And / or, the molar ratio of lithium element in the lithium source to transition metal element in the high-nickel ternary precursor is (1.05~1.10):

1.

6. The preparation method according to claim 1 or 2, characterized in that, The temperature of the first sintering treatment is 800~950℃; And / or, the holding time for the first sintering treatment is 10~12h; And / or, the heating rate of the first sintering treatment is 5~10℃ / min; And / or, the sintering atmosphere of the first sintering treatment is an oxygen-containing atmosphere, preferably an oxygen atmosphere.

7. The preparation method according to claim 1 or 2, characterized in that, The temperature of the second sintering treatment is 450~600℃, preferably 450~550℃; And / or, the holding time for the second sintering treatment is 4~6 hours; And / or, the heating rate of the second sintering treatment is 2~5℃ / min; And / or, the sintering atmosphere of the second sintering treatment is an inert atmosphere, preferably an argon atmosphere.

8. The preparation method according to claim 1 or 2, characterized in that, After the first sintering treatment and the second sintering treatment, the corresponding sintering products are crushed, pulverized and sieved. And / or, in the steps of bulk light rare earth doping and near-surface co-doping, the mixing method independently includes at least one of ball milling and stirring.

9. A rare-earth gradient modified high-nickel ternary cathode material, characterized in that, It is prepared by the method for preparing rare earth gradient modified high-nickel ternary cathode material according to any one of claims 1 to 8.

10. A solid-state battery, characterized in that, Its positive electrode comprises the rare earth gradient modified high-nickel ternary positive electrode material as described in claim 9.

Images