In-situ growth of NiZn-PBA@NiZn-LDH heterostructure lithium ion battery negative electrode material and preparation method thereof

Abstract

Hierarchical structure is considered as an effective strategy to improve the electrochemical energy storage performance. In this work, a NiZn-PBA@NiZn-LDH heterostructure with three-dimensional core and two-dimensional shell structure was constructed by hydrothermal growth and alkaline etching process. NiZn-PBA nanocubes as the structural framework, in situ growth of vertical interlaced NiZn-LDH nanosheets on its surface, thus forming a three-dimensional network with hierarchical porous structure. The structure can significantly increase the electrochemically active surface area, promote the rapid penetration of electrolyte, and accelerate the ion and electron transmission kinetics. Structural characterization results show that the heterostructure is successfully constructed, accompanied by abundant oxygen vacancies and multi-metallic redox active centers. Benefiting from the synergistic effect between PBA core and LDH nanosheet, the electrode shows high specific capacity, good rate performance and excellent cycle stability. At the same time, the hierarchical structure can effectively relieve the volume change and maintain the structural stability during charging and discharging. This study provides an effective strategy for designing PBA-based heterostructure energy storage materials.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, specifically relating to a cobalt-free and carbon-free gradient heterostructure anode material, and a method for preparing the material through a self-templating induction and alkaline etching synergistic strategy, particularly relating to the application of the material in high-performance lithium-ion battery anodes. Background Technology

[0002] Layered bimetallic hydroxide (LDH) and Prussian blue analogue (PBA) derivatives are considered promising candidates for lithium-ion battery anodes due to their considerable theoretical capacity, tunable composition, and mild preparation process. However, traditional PBA / LDH composites generally suffer from problems such as easy agglomeration and stacking of layers, insufficient exposure of active sites, and sluggish electron and ion transport kinetics. These issues lead to structural collapse during lithium-ion insertion / extraction, resulting in rapid capacity decay and poor rate performance. Existing technologies often optimize performance through external modification and composite conductive additives, but these methods fail to address the fundamental structural problems of layer agglomeration and high interfacial transport resistance. Furthermore, the material's structural stability and energy storage kinetics are difficult to improve synergistically, failing to meet the practical application requirements of long-cycle, high-rate lithium-ion batteries. Therefore, developing a novel PBA@LDH heterostructure anode material with stable structure, abundant active sites, and efficient charge transport has become an urgent technical challenge in this field. Summary of the Invention

[0003] 1. Materials Design

[0004] This invention employs a 3D core-2D shell gradient heterostructure design, using nickel foam (NF) as the in-situ growth substrate, a 3D cubic NiZn-PBA as the structural core, and vertically oriented 2DNiZn-LDH nanosheets as the shell to construct a gradient heterostructure electrode material.

[0005] This invention employs a 3D core-2D shell gradient heterostructure design, using nickel foam (NF) as the in-situ growth substrate, a 3D cubic NiZn-PBA as the structural core, and vertically oriented 2DNiZn-LDH nanosheets as the shell to construct a gradient heterostructure electrode material.

[0006] The material exhibits a porous nanosheet array morphology with nanosheet thicknesses ranging from 30 to 200 nm and pore sizes from 10 to 80 nm. The crystal phase is a pure NiZn-PBA and NiZn-LDH composite crystal form, without any impurity phases. The heterojunction interface can form an internal electric field, effectively shortening the ion diffusion path and improving electron transport efficiency. High-efficiency charge transport is achieved based on the intrinsic structure design. Ni element provides abundant redox active sites, significantly improving lithium-ion storage capacity and cycle stability.

[0007] 2. Preparation method

[0008] Nickel foam pretreatment: After cutting the nickel foam, it is immersed in HCl solution for ultrasonic cleaning, then cleaned alternately with deionized water and anhydrous ethanol, and then vacuum dried to remove the surface oxide layer and impurities.

[0009] NiZn-PBA core preparation: 3D cubic NiZn-PBA nanoparticles were synthesized by co-precipitation method and used as self-templates and structural support cores;

[0010] In-situ hydrothermal growth: Using DMF / methanol / deionized water as a mixed solvent, a NiZn-MOF buffer layer was grown in-situ on the surface of NiZn-PBA, and in-situ loading of nickel foam was achieved simultaneously.

[0011] Alkali etching conversion: The MOF layer is converted in situ into vertically oriented NiZn-LDH nanosheets by etching with a mixed alkaline solution of NaOH / Na2CO3, resulting in NiZn-PBA@NiZn-LDH composite anode material.

[0012] 3. Performance advantages

[0013] Structural advantages: The 3D core layer effectively inhibits the aggregation of 2D LDH nanosheets, and the porous structure significantly increases the electrode / electrolyte contact area, thus significantly shortening the lithium-ion diffusion path; Kinetic characteristics: The lithium-ion diffusion coefficient is 1.212 × 10⁻⁶. -12 cm²s -1 Compared to the air-annealed sample (4.303×10), -13 cm²s -1 The efficiency was improved by 181.6%; Electrochemical performance: As a negative electrode of lithium-ion batteries, it exhibits typical pseudocapacitive redox behavior in the voltage window of 0.01 to 3.0V, with excellent rate reversibility, and the capacity can be fully recovered after the current density drops back to the initial value.

[0014] Kinetic characteristics: Low interfacial charge transfer resistance, significantly improved ion diffusion kinetics, coulombic efficiency remains close to 100% during long cycles, and excellent structural stability;

[0015] Process advantages: The preparation process is simple, the reaction conditions are mild, no complicated post-processing is required, and it is suitable for large-scale preparation. Attached Figure Description

[0016] Figure 1 The XRD analysis of the material provided in the embodiments of the present invention confirms the composition of the material and the characteristic peaks of the NiZn-LDH layered crystal phase.

[0017] Figure 2 The XPS analysis of the material provided in the embodiments of the present invention is shown. The material contains Ni, Zn, Fe, O, N and C elements.

[0018] Figure 3These are TEM, SAED, HAADF-STEM, and SAED images of the material provided in the embodiments of the present invention, illustrating that the material is a well-crystallized composite pure phase crystal with uniform distribution of each constituent element.

[0019] Figure 4 The SEM images of the material provided in the embodiments of the present invention confirm the structural transformation of the material from the cubic PBA core phase to the layered LDH shell phase.

[0020] Figure 5 The electrochemical analysis diagram of the material provided in the embodiments of the present invention confirms that the NiZn-PBA@NiZn-LDH anode material has fast charge transport kinetics, excellent rate reversibility and long cycle structural stability, and exhibits efficient pseudocapacitive energy storage characteristics in lithium-ion storage.

[0021] Figure 6 The material work function, diffusion barrier, and differential charge diagram provided in the embodiments of the present invention illustrate that heterostructure interfaces can induce significant charge rearrangement and form a built-in electric field, thereby optimizing the interface electronic structure and promoting the charge transport process.

[0022] Figure 7 The material density of states and band diagram provided by the embodiments of the present invention illustrate that the construction of heterostructures significantly increases the electronic density of states near the Fermi level and enhances the degree of electron delocalization. Detailed Implementation

[0023] Example 1: Material Preparation

[0024] Nickel foam pretreatment: Immerse 4 cm² of nickel foam in 2.5 mol / L HCl solution and ultrasonically clean for 30 min, then ultrasonically clean with deionized water and anhydrous ethanol for 15 min each, and vacuum dry at 60℃ for 2 h.

[0025] Preparation of NiZn-PBA: 218.1 mg nickel nitrate hexahydrate, 535.7 mg zinc nitrate hexahydrate, and 975.0 mg sodium citrate were dissolved in 75 mL of deionized water to obtain solution A; 725.9 mg potassium ferricyanide was dissolved in 75 mL of deionized water to obtain solution B; solution B was added dropwise to solution A, stirred for 1 h, allowed to stand at 25 °C for 24 h, centrifuged, washed, and dried to obtain NiZn-PBA;

[0026] Preparation of P@M precursor: 150 mg of NiZn-PBA and 15 mg of SDS were dispersed in 90 mL of DMF / methanol / water (1:1:1) mixed solvent, 1308.6 mg of zinc nitrate hexahydrate, 337.7 mg of nickel nitrate hexahydrate and 948.6 mg of 1,3,5-pyromellitic acid were added, and pretreated nickel foam was placed in the solution. The mixture was hydrothermally heated at 120 °C for 10 h, and then washed and dried to obtain P@M.

[0027] Preparation of P@L material: 150 mg P@M was dispersed in 60 mL of deionized water, and 3 mL of a mixed alkaline solution of 1 M NaOH and 0.1 M Na2CO3 was slowly added dropwise. The mixture was stirred at room temperature for 60 min, washed until neutral, and dried under vacuum at 60 °C for 8 h to obtain NiZn-PBA@NiZn-LDH anode material.

[0028] Example 2: Performance Verification XRD Test: The material simultaneously exhibits characteristic peaks of both the cubic NiZn-PBA and layered NiZn-LDH phases, with no impurities and a pure crystal structure. XPS Test: The material contains Ni, Zn, Fe, O, N, and C elements. Ni exists as Ni2+, and Fe is in a mixed valence state of Fe2+ / Fe3+, with lattice oxygen and oxygen vacancies coexisting. SEM / TEM Test: NiZn-PBA consists of uniform cubic particles with vertically grown ultrathin LDH nanosheets on the surface, forming a 3D core-2D shell gradient heterostructure with uniform elemental distribution. Electrochemical Test: Obvious redox peaks are observed at different scan rates, indicating rapid kinetic response and excellent electrochemical reversibility. The charge transfer resistance is significantly lower than that of traditional single-component materials, and the ion diffusion rate is fast. The capacity reversibility is excellent in the 0.1–1.2 Ag-1 rate range, with a long-cycle coulombic efficiency of nearly 100% and outstanding structural stability.

Claims

1. A biomimetic gradient heterostructure NiZn-PBA@NiZn-LDH composite electrode material, characterized in that: Using nickel foam (NF) as the in-situ growth substrate, the core is a 3D cubic NiZn-PBA structure, and the shell is a vertically oriented 2D corrugated NiZn-LDH nanosheet, forming a 3D core-2D channel gradient heterostructure. The crystal is a pure-phase NiZn-PBA and NiZn-LDH composite crystal, without impurities. The material exhibits a porous nanosheet array morphology, with nanosheet thickness of 30–200 nm and pore size of 10–80 nm, and Ni element is present. 2+ / Ni 3+ Mixed valence state.

2. The material as described in claim 1, wherein the preparation method comprises: a. Immerse the nickel foam (NF) in 1.0–5.0 mol / L HCl solution for 10–30 min, then clean it with alternating ultrasonic cleaning with deionized water and anhydrous ethanol, and finally dry it. b. Dissolve nickel nitrate hexahydrate (0.75 mmol), zinc nitrate hexahydrate (1.8 mmol), and sodium citrate (3.3 mmol) in 75 mL of deionized water to obtain solution A. Dissolve potassium ferricyanide (2.25 mmol) in 75 mL of deionized water to obtain solution B. Add solution B dropwise to solution A and stir continuously until fully mixed. Allow the mixture to stand at 25 °C to precipitate. Centrifuge, wash, and dry to obtain NiZn-PBA powder. c. Mix N,N-dimethylformamide, methanol, and deionized water in a volume ratio of 1:1:1 (30 mL of each solvent), add NiZn-PBA (150 mg), sodium dodecyl sulfate (15 mg), zinc nitrate hexahydrate (1308.6 mg), nickel nitrate hexahydrate (337.7 mg), and 1,3,5-pyromellitic acid (948.6 mg), stir well, then add pretreated nickel foam, and hydrothermally react at 120 °C for 10–12 h. Wash and dry to obtain NiZn-PBA@NiZn-MOF; d. Mix N,N-dimethylformamide, methanol, and deionized water in a volume ratio of 1:1:1 (30 mL of each solvent), add NiZn-PBA (150 mg), sodium dodecyl sulfate (15 mg), zinc nitrate hexahydrate (1308.6 mg), nickel nitrate hexahydrate (337.7 mg), and 1,3,5-pyromellitic acid (948.6 mg), stir well, and then add pretreated nickel foam. React hydrothermally at 120 °C for 10–12 h, wash and dry to obtain NiZn-PBA@NiZn-MOF.

3. The application of the material as described in claim 1 in the negative electrode of a lithium-ion battery.

4. The material as described in claim 1, at 0.1 A g -1 It exhibits a distinct pseudocapacitive redox peak at current densities, with a rapid kinetic response; within the range of 0.1–1.2 A g. -1 It exhibits excellent capacity reversibility across the rate range, with current density dropping back to 0.1 A g. -1 The capacity can be fully recovered, and the coulombic efficiency remains close to 100% throughout the long cycle.

5. The material as described in claim 1 has low charge transfer resistance at the electrode / electrolyte interface, significantly improving ion diffusion kinetics; the heterojunction interface forms a built-in electric field, which is a narrow bandgap semiconductor of 0.3 to 1.2 eV, which can efficiently control electronic states and accelerate lithium-ion and electron transport, achieving efficient energy storage without the need for external carbon-based conductive agents.

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