A surface configuration entropy-stabilized gradient-doped lithium-rich cathode material, a preparation method and application thereof

Abstract

The present invention discloses a gradient-doped lithium-rich cathode material with surface configurational entropy stabilization, which includes a lithium-rich manganese matrix phase and a high-entropy metal-doped reconstruction layer located on the surface of the lithium-rich manganese matrix phase. The chemical formula of the lithium-rich manganese matrix phase is: xLi2MnO3·(1−x)LiMO2, where 0 < x < 1, and M is at least one of Ni, Co, Mn, and Al. The high-entropy metal-doped reconstruction layer includes metal oxides containing five or more metals. The present invention also discloses a preparation method of the gradient-doped lithium-rich cathode material with surface configurational entropy stabilization, which includes pre-sintering with lithium deficiency to obtain a bulk matrix; adding a high-entropy metal dopant and an activator for secondary sintering to induce surface reconstruction; and finally adopting segmented cooling to freeze the high-entropy state to obtain the lithium-rich doped cathode material. Applying it to a lithium-ion battery solves the problems of irreversible loss of lattice oxygen, serious voltage hysteresis, and poor interfacial stability existing in the existing lithium-rich manganese-based cathode materials.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, specifically to a gradient-doped lithium-rich cathode material with surface configuration entropy stabilization, its preparation method, and its application. Background Technology

[0002] Lithium-rich manganese-based layered oxides (xLi2MnO3·(1 LiMO2 is considered an ideal cathode material for next-generation high-energy-density lithium-ion batteries due to its high reversible specific capacity (>250 mAh / g) and low cost. The high reversible specific capacity of lithium-rich manganese-based layered oxides originates not only from the redox reaction of transition metal cations but also from a unique charge compensation mechanism involving anions (oxygen ions).

[0003] However, lithium-rich manganese-based cathode materials still face severe challenges before commercial application. First, in a deeply delithiated state, anion redox reactions easily lead to irreversible lattice oxygen loss (O2 precipitation), causing structural collapse, battery swelling, and safety hazards. Second, during cycling, transition metal ions easily migrate and occupy lithium layer vacancies, causing cation mixing and irreversible phase transitions (layered to spinel phase transformation), resulting in severe voltage hysteresis and energy density decay. Third, the material has poor interfacial stability; the electrolyte is prone to decomposition under high voltage, and interfacial side reactions further exacerbate performance degradation.

[0004] To address the aforementioned issues, existing technologies primarily employ bulk doping and surface coating for modification. In recent years, researchers have begun to explore incorporating the concept of high entropy into the modification of lithium-rich battery materials. Existing studies have introduced various anions such as S, F, and Cl into the bulk phase, forming high-entropy configurations of anion sites, which to some extent suppresses irreversible precipitation of lattice oxygen. However, this type of bulk anion high-entropy strategy mainly targets oxygen sites, providing insufficient protection for the material surface region directly in contact with the electrolyte. It cannot effectively suppress side reactions between surface lattice oxygen and the electrolyte, nor can it address the structural degradation of the surface transition metal layer during cycling. Furthermore, the volume difference between the conventional surface coating and the substrate during cycling easily leads to coating peeling, failing to fundamentally solve the interfacial instability problem.

[0005] Therefore, developing a new strategy for lithium-rich cathode materials that can stabilize the bulk structure, provide effective physicochemical protection in the surface region, and suppress lattice oxygen loss and voltage hysteresis is of great scientific significance and application value. Summary of the Invention

[0006] The object of the present invention is to provide a gradient-doped lithium-rich cathode material with surface configurational entropy stabilization and a preparation method thereof, and to apply the prepared lithium-rich cathode material to a lithium-ion battery, so as to solve the problems of irreversible loss of lattice oxygen, serious voltage hysteresis and poor interface stability existing in the existing lithium-rich manganese-based cathode materials.

[0007] To achieve the above object, the solution of the present invention is: A gradient-doped lithium-rich cathode material with surface configurational entropy stabilization, comprising a lithium-rich manganese matrix phase and a high-entropy metal-doped reconstruction layer located on the surface of the lithium-rich manganese matrix phase. The chemical formula of the lithium-rich manganese matrix phase is: xLi2MnO3·(1 - x)LiMO2, where 0 < x < 1, and M is at least one of Ni, Co, Mn, and Al. The high-entropy metal-doped reconstruction layer comprises metal oxides of five or more metals; the high-entropy metal-doped reconstruction layer forms a superlattice structure in the surface region of the lithium-rich manganese matrix phase, and its configurational entropy ΔS config > 1.5R, where R is the molar gas constant, so as to form a stable high-entropy solid solution structure. The metal elements of the metal oxides are selected from Mg, Ca, Sr, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Y, and La.

[0008] The thickness of the high-entropy metal-doped reconstruction layer is 2 - 50 nm.

[0009] The concentration of the metal elements in the high-entropy doped reconstruction layer decreases in a gradient from the outside to the inside, forming a gradient structure from high entropy on the surface to medium entropy or low entropy inside.

[0010] In the high-entropy doped reconstruction layer, the molar ratio of the metal oxides of d 0 or d 10 electron-type metal ions is greater than 50% of the molar ratio of all metal oxides.

[0011] The metal oxides of d 0 or d 10 electron-type metal ions are the corresponding oxides of Mg 2+ , Ca 2+ , Sr 2 + , Ti 4+ , Zr 4+ , Zn 2+ , Y 3+ , La 3+ .

[0012] A preparation method of a gradient-doped lithium-rich cathode material with surface configurational entropy stabilization, comprising the following steps: Step 1: First, Ni 0.16 Co 0.16 Mn 0.68 (OH)2 precursor and Li2CO3 are mixed at a lithium ion to transition metal ion molar ratio of 0.5~1:1 and sintered in two stages under air atmosphere: pre-sintering at 300~700℃ for 3~10 h and main sintering at 750~980℃ for 10~24 h. The mixture is then cooled to room temperature in the furnace to obtain a lithium-deficient lithium-rich manganese-based cathode material matrix. Step 2: Then, 100 parts of the lithium-rich manganese-based cathode material matrix obtained in Step 1 are mixed evenly with 1.0~1.2 parts of high-entropy metal dopant and 0.3~0.5 parts of LiOH·H2O in a high-speed mixer. The high-entropy metal dopant is composed of five or more metal oxygen-containing compounds mixed in an equimolar ratio, and 0.1 parts of graphene are added as an activator. The mixed powder is then placed in a tube furnace and heated to 750~800℃ under an oxygen atmosphere and sintered for 2~15 h. Step 3: After sintering, the product is cooled to 600~700℃ in the furnace, and then taken out and rapidly cooled to room temperature in flowing air to obtain the gradient-doped lithium-rich cathode material with surface configuration entropy stabilization.

[0013] In this preparation method, the lithium-deficient design in step 1 aims to create lithium site defects in the transition metal layer, creating conditions for the subsequent entry of high-entropy groups; in step 2, sintering causes the doped metal elements to undergo solid-phase diffusion reactions on the surface and induces the formation of a superlattice structure. At the same time, the residual carbon generated by the decomposition of the activator can create grain boundary / crystal plane defects, reduce the solid-phase diffusion activation energy, and promote the gradient distribution of high-entropy elements; the segmented cooling step in step 3 can effectively prevent the segregation of doped metal elements, lock the high-entropy disordered configuration at high temperature to room temperature, and ensure the stabilizing effect of configuration entropy on the lattice.

[0014] The surface configuration entropy-stabilized gradient-doped lithium-rich cathode material is applied to lithium-ion batteries. The assembly process of the lithium-ion battery is as follows: First, the surface configuration entropy-stabilized gradient-doped lithium-rich cathode material is mixed with conductive carbon black and binder PVDF at a mass ratio of 90:5:5. An appropriate amount of NMP is added to form a slurry, which is then coated on aluminum foil. After drying, it is cut into cathode sheets with a diameter of 12 mm. Finally, in a glove box, a CR2032 coin cell is assembled using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1M lithium hexafluorophosphate as the electrolyte.

[0015] The electrolyte is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

[0016] After adopting the above technical solution, the working mechanism of the gradient-doped lithium-rich cathode material with surface configuration entropy stabilization of the present invention is as follows: 1. Suppressing lattice oxygen loss: The high-entropy metal-doped reconstruction layer on the surface increases the system disorder through the high configurational entropy effect, reduces the free energy, and improves the stability of lattice oxygen. Combined with d... 0 / d 10 The introduction of electronic metal ions enhances the binding energy of the metal-oxygen bond and reduces the loss of oxygen atoms due to decoupling and irreversible oxygen evolution under high pressure. 2. Alleviating voltage hysteresis: The high-entropy metal-doped reconstruction layer supports the interlayer structure through strong electrostatic interaction, inhibits irreversible cation migration, reduces spinel phase transformation, and uses the superlattice structure to lock the surface atomic positions, thereby alleviating voltage hysteresis and voltage decay during the lithium insertion / extraction process. 3. Optimize lithium-ion transport and interface stability: The gradient doping structure of the high-entropy metal-doped reconstruction layer alleviates lattice mismatch during volume expansion and reduces microcrack generation. The superlattice structure and the high-entropy reconstruction layer together construct an ultra-stable interface, suppressing electrolyte side reactions and improving interface charge transfer and lithium-ion diffusion kinetics.

[0017] The application of this surface configuration entropy-stabilized gradient-doped lithium-rich cathode material in lithium-ion batteries exhibits the following advantages: 1. Significantly suppresses voltage decay: Through the energy protection of the high-entropy metal doped layer on the surface, the average discharge voltage decay rate of the battery during cycling is reduced to ≤1.5 mV / cycle, which is far superior to unmodified materials and bulk anionic high-entropy materials; 2. Significantly improved cycle stability: The high-entropy metal doped layer on the surface acts as a stable physical and chemical barrier, effectively suppressing interfacial side reactions. After 100 cycles, the capacity retention rate can reach more than 89%, which is significantly better than existing technologies.

[0018] 3. Suppress gas production and improve safety: Stabilizes surface lattice oxygen, suppresses oxygen and carbon dioxide evolution in the battery under high voltage, and reduces the risk of gas swelling and bulging. 4. Improved rate performance: The superlattice structure and gradient design of the high-entropy metal doped layer on the surface ensure rapid transport of lithium ions, improve interfacial charge transfer, and significantly improve discharge capacity retention at high rates. 5. The process is compatible with existing production lines: Based on solid-state sintering, it does not require complex equipment and is easy to scale up for production. Attached Figure Description

[0019] Figure 1 The charge-discharge curves of the lithium-ion batteries assembled in the examples and comparative examples are shown in the voltage range of 2.0~4.8V. Figure 2Cycling performance (1C, 200 cycles) of the lithium-ion batteries assembled for the examples and comparative examples in the voltage range of 2.0~4.8V. Figure 3 The graph shows a comparison of the median voltage decay curves of the lithium-ion batteries assembled in the examples and comparative examples within the voltage range of 2.0 to 4.8V. Detailed Implementation

[0020] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0021] Example A method for preparing a gradient-doped lithium-rich cathode material with surface configuration entropy stabilization includes the following steps: Step 1: First, the Ni prepared in advance by the co-precipitation method... 0.16 Co 0.16 Mn 0.68 (OH)2 precursor and Li2CO3 were mixed at a molar ratio of lithium ions to transition metal ions (Ni, Co, Mn) of 0.8:1 and sintered in two stages under air atmosphere: pre-sintering at 500℃ for 5 h and main sintering at 900℃ for 12 h. The mixture was then cooled to room temperature in the furnace to obtain a lithium-deficient lithium-rich manganese-based cathode material matrix. Step 2: Then, 100 g of the lithium-rich manganese-based cathode material matrix obtained in Step 1 is mixed evenly with 1.2 g of high-entropy metal dopant and 0.5 g of LiOH·H2O in a high-speed mixer. The high-entropy metal dopant is composed of ZrO2, MoO3, WO3, Y2O3 and SrCO3 in an equimolar ratio, and 0.1 g of graphene is added as an activator. Then, the mixed powder is placed in a tube furnace and heated to 800℃ under an oxygen atmosphere and sintered for 8 h. Step 3: After sintering, the product is cooled to 700°C in the furnace, and then taken out and rapidly cooled to room temperature in flowing air at a rate of 10°C / min to obtain the gradient-doped lithium-rich cathode material with surface configuration entropy stabilization.

[0022] This gradient-doped lithium-rich cathode material with surface configuration entropy stabilization includes a lithium-rich manganese matrix phase and a high-entropy metal-doped reconstructed layer located on the surface of the lithium-rich manganese matrix phase. The chemical formula of the lithium-rich manganese matrix phase is: Li 1.0 Ni 0.16 Co 0.16 Mn 0.68 The high-entropy metal-doped reconstructed layer includes ZrO2, MoO3, WO3, Y2O3, and SrCO3; the high-entropy metal-doped reconstructed layer forms a superlattice structure in the surface region of the lithium-rich manganese matrix phase, and its configuration entropy ΔS configThe entropy is greater than 1.5 R, where R is the molar gas constant, thus forming a stable high-entropy solid solution structure. The thickness of the high-entropy metal-doped reconstructed layer is 50 nm. The concentration of metal elements in the high-entropy doped reconstructed layer decreases gradually from the outside to the inside, forming a gradient structure from high entropy on the surface to medium or low entropy inside.

[0023] In the high-entropy doped reconstructed layer, the electrochemically inert d 0 or d 10 The molar percentage of electronic metal ions containing metal oxygen compounds (ZrO2, Y2O3 and SrCO3) is greater than 50% of the total molar percentage of all metal oxygen compounds.

[0024] Comparative Example Ni prepared in advance by coprecipitation method 0.16 Co 0.16 Mn 0.68 (OH)2 precursor and Li2CO3 were mixed at a molar ratio of lithium ions to transition metal ions (Ni, Co, Mn) of 1.2:1 and sintered in two stages under an air atmosphere: pre-calcination at 500℃ for 5 h and main calcination at 900℃ for 12 h, followed by furnace cooling to room temperature to obtain lithium-rich manganese-based cathode material.

[0025] Application examples The positive electrode materials prepared in the examples and comparative examples were applied to lithium-ion batteries. The assembly process of the lithium-ion batteries was as follows: First, the corresponding positive electrode material was mixed with conductive carbon black and binder PVDF at a mass ratio of 90:5:5. An appropriate amount of NMP was added to make a slurry, which was then coated on aluminum foil. After drying, it was cut into positive electrode sheets with a diameter of 12 mm. Finally, in a glove box, a CR2032 coin cell was assembled with a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1M lithium hexafluorophosphate (with EC and DMC mixed solvent at a volume ratio of 1:1) as the electrolyte.

[0026] The assembled lithium-ion battery was charged and discharged under conditions of 0.1C / 0.1C and 1C / 1C within a voltage range of 2.0~4.8V. The test results are as follows: Figures 1-3 As shown. Compared with the unmodified cathode material (comparative example), the gradient-doped lithium-rich cathode material with surface entropy stabilization prepared in this invention exhibits a first discharge specific capacity ≥300 mAh / g at 0.1 C under voltages of 2.0–4.8 V, a capacity retention rate ≥89% after 100 cycles, and a voltage decay ≤1.5 mV / cycle. The first coulombic efficiency, cycle stability, and voltage retention are all significantly improved. This is attributed to the synergistic effect of the high-entropy metal layer and the superlattice structure, which not only stabilizes surface lattice oxygen and inhibits transition metal (TM) migration but also provides stable interface protection and a rapid lithium-ion diffusion channel.

[0027] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A gradient-doped lithium-rich cathode material with surface configuration entropy stabilization, characterized in that: It includes a lithium-rich manganese matrix phase and a high-entropy metal-doped reconstruction layer located on the surface of the lithium-rich manganese matrix phase. The chemical formula of the lithium-rich manganese matrix phase is: xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M is at least one of Ni, Co, Mn, and Al. The high-entropy metal-doped reconstruction layer includes five or more metal oxides; the high-entropy metal-doped reconstruction layer forms a superlattice structure in the surface region of the lithium-rich manganese matrix phase, and its configurational entropy ΔSconfig > 1.5R, where R is the molar gas constant, thereby forming a stable high-entropy solid solution structure. The metal elements of the metal oxides are selected from Mg, Ca, Sr, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Y, and La.

2. The gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 1, characterized in that: The thickness of the high-entropy metal-doped reconstruction layer is 2 - 50 nm.

3. The gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 1, characterized in that: The concentration of metal elements in the high-entropy doped reconstruction layer decreases in a gradient from the outside to the inside, forming a gradient structure from high entropy on the surface to medium entropy or low entropy inside.

4. The gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 1, characterized in that: In the high-entropy doped restructured layer, d 0 or d 10 The molar proportion of the metal oxygen compound of the electron type metal ion is greater than 50% of the molar ratio of all metal oxygen compounds.

5. The gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 4, characterized in that: d, which is electrochemically inert 0 or d 10 The metal oxygen-containing compound of the electronic metal ion is Mg. 2+ Ca 2+ 、Sr 2+ Ti 4+ Zr 4+ Zn 2+ Y 3+ La 3+ The corresponding oxygen-containing compounds.

6. A method for preparing a gradient-doped lithium-rich cathode material with surface configuration entropy stabilization as described in claim 1, characterized in that: It includes the following steps: Step 1: First, Ni 0.16 Co 0.16 Mn 0.68 (OH)2 precursor and Li2CO3 are mixed at a lithium ion to transition metal ion molar ratio of 0.5~1:1 and sintered in two stages under air atmosphere: pre-sintering at 300~700℃ for 3~10 h and main sintering at 750~980℃ for 10~24 h. The mixture is then cooled to room temperature in the furnace to obtain a lithium-deficient lithium-rich manganese-based cathode material matrix. [[ID=根据上述要求,步骤4的翻译内容如下: Step 2: Then, 100 parts of the lithium-rich manganese-based cathode material matrix obtained in Step 1 are mixed evenly with 1.0 - 1.2 parts of high-entropy metal dopants and 0.3 - 0.5 parts of LiOH·H2O in a high-speed mixer. The high-entropy metal dopants are mixed by five or more of the metal oxides in an equimolar ratio, and 0.1 part of graphene is added as an activator. Then, the mixed powder is placed in a tube furnace and heated to 750 - 800 °C in an oxygen atmosphere and sintered for 2 - 15 h.

7. An application of a gradient-doped lithium-rich cathode material with surface configuration entropy stabilization, characterized in that: Step 3: After the sintering is completed, the product is cooled with the furnace to 600 - 700 °C, and then taken out and rapidly cooled to room temperature in flowing air to obtain the gradient-doped lithium-rich cathode material with surface configurational entropy stabilization.

8. The application of the gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 7, characterized in that: It is to apply the gradient-doped lithium-rich cathode material with surface configurational entropy stabilization as described in Claim 1 to a lithium-ion battery.

9. The application of the gradient-doped lithium-rich cathode material with surface configuration entropy stabilization according to claim 8, characterized in that: The assembly process of the lithium-ion battery is as follows: First, the gradient-doped lithium-rich cathode material with surface configurational entropy stabilization is mixed with conductive carbon black and binder PVDF in a mass ratio of 90:5:5, an appropriate amount of NMP is added to make a slurry, and then it is coated on an aluminum foil. After drying, it is cut into a positive electrode plate with a diameter of 12 mm. Finally, in a glove box, a metal lithium sheet is used as the counter electrode, Celgard 2400 is used as the separator, and 1M lithium hexafluorophosphate is used as the electrolyte to assemble a CR2032 button cell. The solvent of the electrolyte is a mixed solvent of EC and DMC with a volume ratio of 1:1.

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