Lithium-fluorine modified hydroxyapatite interfacial solid-state electrolyte and preparation method thereof

Abstract

The application discloses a lithium-fluorine co-modified hydroxyapatite interface solid-state electrolyte and a preparation method thereof, and belongs to the technical field of high-voltage solid-state lithium metal batteries. The electrolyte has an asymmetric three-layer structure, and comprises a middle polymer matrix layer, a negative electrode side Li2ZrF6 modified layer and a positive electrode side Li,F-HAP functional interface layer. The positive electrode side Li,F-HAP interface layer has a flower-shaped porous structure, provides a continuous ion transmission channel and serves as a physical and chemical barrier to inhibit high-voltage side reactions. The ionic conductivity of the composite electrolyte is as high as 9.16*10 ‑4 S·cm ‑1 , the lithium ion transference number is 0.60, and the electrochemical stability window reaches 4.45 V. A lithium symmetric battery assembled by using the electrolyte is stably cycled for more than 650 h under a current of 0.2 mA*cm ‑2 , and the capacity retention rate of an NCM811 full battery is more than 78% under a current of 0.5 C. The technology significantly improves the high-voltage adaptability and cycle stability of the solid-state lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery electrolyte technology, specifically relating to a lithium-fluorine modified hydroxyapatite interfacial solid electrolyte and its preparation method. This technology is particularly targeted at high-voltage solid-state lithium metal batteries, aiming to solve the problems of interfacial instability and low ionic conductivity of traditional polymer electrolytes under high-voltage cathodes (such as NCM811). Background Technology

[0002] Solid-state lithium metal batteries are considered the preferred next-generation energy storage technology due to their high energy density and high safety. However, solid-state polymer electrolytes (SPEs) still face significant challenges in practical applications:

[0003] 1. Poor interfacial compatibility: Under high voltage (>4.2 V) conditions, traditional polymers (such as PEO and PVDF) are easily oxidized and decomposed, and cannot effectively suppress the dissolution of positive electrode transition metal ions.

[0004] 2. Lithium dendrite growth: Uneven distribution of lithium ion flux on the negative electrode side leads to lithium dendrites piercing the electrolyte, causing a short circuit.

[0005] 3. Limitations of Single Filler Modification: Existing technologies mostly use a single inorganic filler (such as Al2O3, TiO2, or unmodified HAP) for doping. However, unmodified hydroxyapatite (HAP) has strong hydrophilicity and poor compatibility with polymer matrices, and lacks specific conduction channels for lithium ions. Existing technologies lack asymmetric electrolyte structures that construct a specific modified inorganic filler interface layer on the positive electrode side, making it difficult to simultaneously meet the dual requirements of high voltage stability and high ionic conductivity.

[0006] Therefore, developing a novel modified filler that can withstand high pressure and construct a fast ion transport channel, as well as a corresponding asymmetric electrolyte structure, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] 1. Purpose of the invention

[0008] The purpose of this invention is to provide a composite solid polymer electrolyte and its preparation method. By constructing an "asymmetric three-layer structure" and innovatively designing "lithium-fluorine co-modified hydroxyapatite (Li,F-HAP)" as the positive electrode interface modification layer, the technical problems of high-pressure decomposition and excessive interfacial impedance in the prior art are solved.

[0009] 2. Technical Solution

[0010] This invention provides a lithium-fluorine modified hydroxyapatite interfacial solid electrolyte, wherein the electrolyte membrane has an asymmetric three-layer structure, including a middle polymer matrix layer, a negative electrode side modification layer, and a positive electrode side modification layer.

[0011] The polymer matrix layer is composed of a blend of methyl methacrylate (MMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene P (VDF-HFP), and is doped with lithium bis(trifluoromethanesulfonylimide) (LiTFSI).

[0012] The modified layer on the positive electrode side contains modified hydroxyapatite (HAP) particles and organomontmorillonite. Crucially, the modified HAP is not a simple physical mixture, but rather a lithium-fluorine co-modified hydroxyapatite prepared through a hydrothermal method and fluorination treatment. Lithium-ion doping widens the lattice spacing, while the introduction of fluorine ions enhances Lewis acid-base interactions, synergistically improving the interfacial ionic conductivity.

[0013] The modified layer on the negative electrode side contains lithium zirconium fluoride (Li2ZrF6) particles, which utilize their high mechanical strength and lithium affinity to guide the uniform deposition of lithium ions.

[0014] 3. Beneficial effects

[0015] Through the above technical solution, the present invention has achieved the following significant progress and beneficial effects:

[0016] (1) Synergistic modification mechanism: Unlike traditional physical mixed fillers, the "lithium-fluorine co-modified HAP" of this invention introduces Li⁺ and F⁻ during crystal growth. Li⁺ occupies Ca 2+ The creation of cation vacancies at the sites and the substitution of OH⁻ sites by F⁻ enhance lattice stability. This structure not only acts as a physical barrier to prevent electron tunneling from the high-voltage cathode, but also acts as an "ion pump" to significantly reduce the lithium-ion migration barrier.

[0017] (2) Asymmetric functional adaptation:

[0018] Positive electrode side: The interface layer rich in Li,F-HAP has excellent antioxidant capacity (electrochemical stability window >4.4V), which can effectively passivate the residual alkali on the surface of NCM811 positive electrode and suppress interfacial side reactions.

[0019] Negative electrode side: Li2ZrF6 particles have high modulus, which can homogenize the electric field distribution and suppress lithium dendrite growth.

[0020] (3) Performance breakthrough: Experimental data show that the electrolyte prepared by this invention has an ionic conductivity of up to 9.16 × 10⁻⁶. -4 S·cm -1 (25℃) The lithium-ion transference number is as high as 0.60. The assembled NCM811 full cell retains more than 78% of its capacity after 200 cycles at 0.5 C, which is significantly better than the comparative example. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the structure of the composite solid polymer electrolyte of the present invention;

[0022] Figure 2 The X-ray diffraction pattern of the hydroxyapatite prepared in this invention is shown below.

[0023] Figure 3 A scanning electron microscope image of the hydroxyapatite prepared in this invention;

[0024] Figure 4 Optimization diagram of ionic conductivity under different HAP addition amounts;

[0025] Figure 5 Electrochemical stability window diagrams for different HAP addition amounts;

[0026] Figure 6 Scanning electron microscope image of the surface of the polymer electrolyte prepared for the example;

[0027] Figure 7 Scanning electron microscope image of the surface of the polymer electrolyte prepared for comparison;

[0028] Figure 8 Scanning electron microscope (SEM) image of the cross-section of the polymer electrolyte prepared for the example;

[0029] Figure 9 Lithium-ion transport number spectra of the polymer electrolyte prepared for the example;

[0030] Figure 10 The lithium-ion transport number spectrum of the polymer electrolyte prepared for comparison.

[0031] Figure 11 Electronic conductivity curves of the polymer electrolyte prepared for the example;

[0032] Figure 12 Arrhenius curves showing the ionic conductivity of the polymer electrolytes in the examples and comparative examples as a function of temperature.

[0033] Figure 13 Tafel curves of solid-state lithium metal batteries assembled in the examples and comparative examples;

[0034] Figure 14 Cyclic current-voltage curves of solid-state lithium metal batteries assembled for examples and comparative examples;

[0035] Figure 15 Constant current polarization curves of lithium symmetric batteries assembled in the examples and comparative examples;

[0036] Figure 16 The critical current density curves of the lithium symmetric batteries assembled in the examples and comparative examples are shown.

[0037] Figure 17The graph shows the cycle performance of the lithium metal batteries assembled in the examples and comparative examples at 0.2 C.

[0038] Figure 18 The cycling performance of the lithium metal battery assembled for the example is shown in the graph at 0.5 C.

[0039] Figure 19 The rate performance diagrams show the lithium metal batteries assembled in the examples and comparative examples.

[0040] Figure 20 Scanning electron microscope (SEM) images of the positive electrode after cycling in the examples and comparative examples;

[0041] Figure 21 The images show the electrochemical impedance spectroscopy spectra after cycling for the examples and comparative examples. Detailed Implementation

[0042] The following embodiments further illustrate the above-mentioned content of the present invention in detail. However, the subject matter of the present invention is not limited to the following embodiments, and all technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0043] The reagents used in the experiment are shown in Table 1, and the instruments used in the experiment are shown in Table 2.

[0044] Table 1 Experimental Drugs

[0045] name Chemical formula and abbreviation purity supplier cetyltrimethylammonium bromide CTAB 99% Guangfu Technology Development Co., Ltd. Lithium nitrate <![CDATA[LiNO3]]> 99% Aladdin Shanghai Century Co., Ltd. Sodium dihydrogen phosphate <![CDATA[NaH2PO4]]> 98% Jinfeng Chemical Co., Ltd. Calcium chloride <![CDATA[CaCl2]]> 99% Shandong Haiwei Chemical Co., Ltd. Nano-organic montmorillonite OMMT Analytical Pure Zhejiang Fenghong New Materials Co., Ltd. Acetylene black AB Battery level Taiyuan Lizhiyuan Technology Co., Ltd. Methyl methacrylate MMA 99% Fuchen Chemical Reagent Co., Ltd. Polyvinylidene fluoride-hexafluoropropylene P(VDF-HFP) Battery level Aladdin Shanghai Century Co., Ltd. polyvinylidene fluoride PVDF Battery level Taiyuan Lizhiyuan Technology Co., Ltd. Benzoyl peroxide BPO Analytical Pure Guangfu Fine Chemical Research Institute Ternary electrode NCM811 Battery level Kelude New Energy Technology Co., Ltd. N,N-Dimethylformamide DMF Analytical Pure Fuyu Fine Chemical Co., Ltd. N-Methylpyrrolidone NMP Analytical Pure Zhiyuan Chemical Reagent Co., Ltd. Lithium bis(trifluoromethanesulfonylimide) LiTFSI 99% Shanghai Chengjie Chemical Co., Ltd. Lithium tablets Li Battery level Kelude New Energy Technology Co., Ltd.

[0046] Note: The above-mentioned experimental reagents are all commercially available reagents that are commonly used in this field. Their source does not constitute a limitation on the scope of protection of this invention. This invention can be achieved by using any commercially available product that meets the specifications.

[0047] Table 2 Experimental Equipment

[0048] Instrument Name model Analytical balance FC-204 Magnetic stirrer CL-200 Vacuum drying oven ZK-82BB Button battery sealing machine MSK-110 Electrode punching machine MSK-T10 LAND Battery Testing System CT2001A Electrochemical workstation CHI760E Scanning electron microscope FEI sirion200 Vacuum glove box ZKX low-speed centrifuge LC-LX-L40B

[0049] The preparation process steps of the following examples are further described in conjunction with the accompanying drawings and comparative examples, but the scope of protection of the present invention is not limited to the following examples.

[0050] Example

[0051] I. Preparation of Hydroxyapatite

[0052] Weigh 1.65 mmol of lithium nitrate (LiNO3) and 3.1 mmol of calcium chloride (CaCl2), dissolve them in 40 mL of deionized water to obtain solution A; separately, weigh 11.2 mmol of hexadecyltrimethylammonium bromide (CTAB), dissolve it in 50 mL of deionized water, and stir at 70 °C until dissolved to obtain solution B. Mix solution A and solution B, stir for 1 h, then stir at room temperature for 2 h. Subsequently, add 50 mL of deionized water containing 3.95 mmol of sodium hydrogen phosphate (Na2HPO4) dropwise to the mixture, stir well, and transfer to a hydrothermal reactor. React at 200 °C for 5 h. After the reaction is complete, centrifuge the product, wash it five times each with anhydrous ethanol and deionized water, and dry it under vacuum at 60 °C for 12 h to obtain a white powder. The white powder was dispersed in a 5 mg·mL⁻¹ sodium fluoride (NaF) aqueous solution, stirred at 30 °C for 12 h, and dried under vacuum at 80 °C for 12 h to obtain white hydroxyapatite (HAP) powder.

[0053] II. Preparation of Polymer Electrolyte Precursors and Interfacial Layer Precursors

[0054] MMA, PVDF, and P(VDF-HFP) were weighed in a mass ratio of 50:1:4 and dissolved in DMF. The solution was stirred until transparent to obtain solution A. Organomontmorillonite was weighed at 8 wt% of the total polymer mass and dissolved in DMF. The solution was stirred until homogeneous to obtain solution B. Solutions A and B were stirred separately for 12 h and then mixed. LiTFSI was added and stirred until a light yellow homogeneous liquid was obtained. Then 0.8 wt% of initiator BPO was added and the mixture was stirred at 95 °C for 12 min for prepolymerization to obtain polymer electrolyte precursor C.

[0055] Li2ZrF6 particles were added to precursor C and stirred until homogeneous to obtain negative electrode side interface precursor D.

[0056] The prepared HAP particles were added to precursor C and stirred evenly to obtain positive electrode side interface precursor E.

[0057] III. Preparation of Polymer Electrolytes

[0058] Precursor C was poured into a glass mold by solution casting and dried under vacuum at 80 °C for 9 h to obtain a polymer electrolyte membrane with a thickness of about 200 μm, which was named PMMA / PVDF-HFP / PVDF polymer electrolyte (PFPE).

[0059] Precursor D was coated onto the negative electrode side surface of the prepared PFPE membrane and dried at 80 °C for 2 h to obtain the PFPE-LZF membrane.

[0060] Precursor E was coated onto the positive electrode side of the prepared PFPE-LZF membrane and dried at 80 °C for 2 h to obtain a composite solid polymer electrolyte membrane with a HAP interface layer on the positive electrode side. It was named PMMA / PVDF-HFP / PVDF-HAP polymer electrolyte (PFPE-HAP) with an interface layer thickness of about 8 μm.

[0061] Comparative Example

[0062] Unlike the above embodiments, in the preparation process of the polymer electrolyte, the comparative example only requires the precursor D to be coated on the negative electrode side of PFPE to obtain PFPE-LZF, and PFPE-LZF is the comparative example (except that HAP is not added, the other steps are the same as those in the embodiments).

[0063] Performance characterization was performed on the above embodiments and comparative examples.

[0064] Performance Testing and Results Analysis

[0065] To verify the performance advantages of the lithium-fluorine modified hydroxyapatite interfacial solid electrolyte prepared in this invention, detailed physical and electrochemical performance tests were conducted on the electrolyte membranes prepared in the examples, and a comparative analysis was performed with the comparative examples.

[0066] Figure 1 This is a schematic diagram illustrating the preparation of polymer electrolytes for the examples and comparative examples. The PFPE-HAP of the examples is obtained by coating the positive electrode side of the comparative example PFPE-LZF polymer electrolyte with a HAP interface layer.

[0067] Figure 2 The X-ray diffraction (XRD) patterns of hydroxyapatite (HAP) prepared as an example are shown below. Phase analysis of lithiated and unlithiated HAP by XRD revealed that they possess the same crystal structure, with the main diffraction peaks consistent with standard card 09-0080. The peak intensities were similar, and no extraneous impurity peaks were observed, indicating successful HAP preparation.

[0068] Figure 3 The image shows a scanning electron microscope (SEM) image of the hydroxyapatite (HAP) prepared for this example. The overall morphology of HAP is flower-like, and its large surface area provides more active sites, which is beneficial for lithium-ion transport.

[0069] Figure 4 An optimization diagram of the conductivity of hydroxyapatite (HAP) is introduced for this example. With the slurry used at the interface fixed at 0.5 g, different weights of HAP were added, and their intrinsic impedance R was tested and the ionic conductivity was calculated. The highest ionic conductivity (1.02 × 10⁻⁸ g) was observed in PFPE-HAP when the HAP addition was 0.08 g. -3 S cm -1When the HAP content is too high, the ionic conductivity actually decreases, which is not conducive to lithium ion transport.

[0070] Figure 5 An optimized electrochemical stability window diagram of hydroxyapatite is presented for this example. When the HAP content is 0.06 g, the PFPE-HAP polymer electrolyte exhibits a stability window of 9.16 × 10⁻⁶ g / L. -4 S cm -1 High ionic conductivity and a high electrochemical stability window of 4.45 V represent the optimal ratio.

[0071] Figure 6 The image shows a scanning electron microscope (SEM) image of the polymer electrolyte prepared for this example. The positive electrode side surface with the interface layer is uniform and exhibits a regular wrinkled shape, which increases its surface area and provides more lithium-ion transport sites. The HAP filler is uniformly distributed within it without agglomeration.

[0072] Figure 7 The image shows a surface scanning electron microscope (SEM) image of the polymer electrolyte prepared for the comparative example. Analysis reveals that the positive electrode surface without the HAP interface in the comparative example is extremely non-uniform, exhibiting severe agglomeration, which is detrimental to interfacial transport.

[0073] Figure 8 Cross-sectional scanning electron microscope (SEM) image of the polymer electrolyte prepared for the example. The PFPE-HAP interface layer is observed to be uniform, with HAP evenly distributed within it and interconnected pores, providing favorable transport channels for lithium ions at the interface.

[0074] Figure 9 The lithium-ion transference number (LTN) spectra of the polymer electrolytes prepared for this example are shown. The PFPE-HAP in this example has a LTN transference number of 0.60.

[0075] Figure 10 The lithium-ion transference number spectra are for the polymer electrolytes prepared in the comparative example. The lithium-ion transference number of the comparative example PFPE is 0.54.

[0076] Figure 11 The electronic conductivity curves of the polymer electrolyte prepared for this example are shown. The electronic conductivity of the PFPE-HAP polymer electrolyte is 7.32 × 10⁻⁶. -10 S cm -1 The low electronic conductivity ensures that the polymer electrolyte can support normal battery operation.

[0077] Figure 12 The graphs show the ionic conductivity of the polymer electrolytes prepared in the examples and comparative examples as a function of temperature. Based on the Arrhenius equation fitting calculation, the activation energy of the polymer electrolyte containing the HAP interface is reduced to 12.84 kJ·mol⁻¹.-1 The polymer electrolyte without the HAP interface has a yield of 16.69 kJ·mol⁻¹. -1 A lower activation energy means that lithium ions need to overcome fewer energy barriers during interface migration, which is more conducive to improving ion transport efficiency at the interface.

[0078] Figure 13 The Tafel curves for the solid-state lithium metal batteries assembled in the examples and comparative examples are shown. Within the redox potential range of 3.0–4.3 V, the absolute values ​​of the Tafel slopes for the Li / PFPE-HAP / NCM811 batteries are 0.41 and 1.02, respectively, both lower than the 0.49 and 1.50 corresponding to the Li / PFPE-LZF / NCM811 system. This indicates that the PFPE-HAP electrolyte possesses superior kinetic characteristics in accelerating the lithium-ion redox reaction while effectively reducing battery polarization, thereby further improving electrode kinetic performance.

[0079] Figure 14 The cyclic voltammetry curves of the solid-state lithium metal batteries assembled in the examples and comparative examples are shown in the figures. Three typical redox peaks can be observed, corresponding to the structural phase transitions of NCM811 at different stages. Specifically, approximately 3.6–3.8 V corresponds to the H1→M phase transition, indicating initial delithiation causing changes in the crystal structure; 3.8–4.0 V corresponds to the M→H2 phase transition, reflecting further delithiation and continuous structural adjustment; and 4.0–4.3 V corresponds to the H2→H3 phase transition, accompanied by lattice contraction and possible oxygen release, representing the most dramatic stage of structural change. Thanks to the high-voltage interface, the PFPE-HAP system exhibits high redox peak overlap during cycling, demonstrating good reversibility and stable interfacial reaction kinetics. In contrast, the PFPE-LZF system shows significant peak shifts during cycling, indicating severe interfacial side reactions and a decrease in electrochemical reversibility.

[0080] Figure 15 The constant current polarization curves are for the lithium symmetric cells assembled in the examples and comparative examples. At 0.2 mA cm⁻¹ -2 Under cycling at high current densities, the polarization voltage of the Li / PFPE-LZF / Li battery increased continuously after 400 hours, and failure occurred shortly thereafter. However, the stability of the Li / PFPE-HAP / Li battery was further improved, achieving stable cycling for 650 hours, with its polarization voltage remaining stable and below 0.2 V throughout. This indicates that the introduction of the HAP interface layer further improved the interfacial stability between the electrolyte and the electrode.

[0081] Figure 16The critical current density (CCD) curves for the lithium-ion symmetric batteries assembled in the examples and comparative examples are shown. The critical current density (CCD) of the comparative example PFPE-LZF is 0.85 mA cm⁻¹. -2 Furthermore, the CCD of the PFPE-HAP embodiment is further improved, reaching up to 1.05 mA cm⁻¹. -2 The higher CCD provides a solid guarantee for assembling full cells for high-rate and high-load cycling.

[0082] Figure 17 This diagram shows the 0.2-rate cycling performance of the lithium metal batteries assembled in the examples and comparative examples. At 0.2 C room temperature, the Li / PFPE-HAP / NCM811 battery exhibits a discharge specific capacity as high as 172.3 mAh g⁻¹. -1 Furthermore, the discharge specific capacity was 149.9 mAh g after 100 cycles. -1 The capacity retention rate was 87%, and the average coulombic efficiency was 99%. Compared with polymer electrolytes without a positive electrode HAP interface layer, the addition of the HAP interface layer improved the overall performance and reduced battery polarization. During cycling, Li / PFPE-LZF / NCM811 rapidly deactivated due to electrolyte decomposition and NCM811 positive electrode material dissolution, resulting in a significant decrease in cycle performance.

[0083] Figure 18 The graph shows the 0.5-rate cycling performance of the lithium metal battery assembled in this example. Under 0.5C cycling conditions, the Li / PFPE-HAP / NCM811 battery still exhibits a discharge specific capacity as high as 153.63 mAh g⁻¹. -1 Furthermore, it can be continuously recycled more than 200 times, demonstrating the development potential of the system in practical applications.

[0084] Figure 19 This diagram shows the rate performance of the lithium metal batteries assembled in the examples and comparative examples. The specific discharge capacity of the Li / PFPE-HAP / NCM811 battery in the example is 202.7 mAh g⁻¹ at 0.03 C, 0.1 C, 0.2 C, and 0.5 C. -1 183.1 mAhg -1 175.8 mAh g -1 160.1 mAh g -1 When the rate of discharge was restored to 0.1 C, the specific capacity of the PFPE-HAP battery stabilized at 179.4 mAh g⁻¹. -1 When the rate of discharge is restored to 0.2 C, the specific capacity of the PFPE-HAP battery stabilizes at 168.5 mAh g⁻¹. -1 This demonstrates that the addition of the HAP interface layer improves the battery's tolerance to high-current charging and discharging, which is beneficial for coping with various harsh charging and discharging scenarios.

[0085] Figure 20 The images show scanning electron microscope (SEM) images of the NCM811 cathodes assembled in the examples and comparative examples after cycling. Due to the suppression of side reactions after the introduction of the HAP interface layer, and the effective protection of the structural stability of the cathode material by the generated CEI film, the PFPE-HAP NCM811 particles maintained a regular structure even after cycling. In contrast, the particles in the comparative example exhibited severe structural collapse due to severe decomposition, resulting in a reduction in usable active material and leading to rapid battery failure.

[0086] Figure 21 The figures show the impedance diagrams of the lithium metal batteries assembled in the examples and comparative examples after cycling. The interfacial impedance of the Li / PFPE-HAP / NCM811 battery was 195.4 Ω before cycling, and decreased to 176.3 Ω after cycling, with a small overall change and a downward trend. A lower and more stable interfacial impedance helps improve ion transport efficiency and charge transfer kinetics in the interfacial region. In contrast, the Li / PFPE-LZF / NCM811 system showed a significant increase in impedance during cycling, with its interfacial impedance rising significantly from an initial 265.6 Ω to 394.1 Ω, indicating that severe side reactions occurred at the cathode interface, leading to a rapid decline in cycling performance.

[0087] Creative discourse

[0088] The technical solution of this invention is not obvious:

[0089] Existing technologies (such as conventional HAP packings) only utilize their rigid skeleton to enhance mechanical properties, neglecting their interfacial chemical stability under high pressure.

[0090] This invention innovatively proposes a "lithium-fluorine co-modification" strategy. By generating vacancies through Li⁺ doping and modifying with F⁻ to enhance Lewis acid-base interactions, this synergistic effect is something that those skilled in the art cannot anticipate through conventional methods.

[0091] Technical effect: This invention achieves the effect of "1+1>2", which not only solves the contradiction that single modification cannot take into account both high voltage stability and high conductivity, but also achieves dual optimization of the positive and negative electrode interfaces through asymmetric structural design.

[0092] In summary, the solid electrolyte provided by this invention has excellent comprehensive performance, a simple preparation process, is suitable for large-scale production, and has extremely high industrial application value.

[0093] in conclusion

[0094] This invention successfully prepared a composite solid-state polymer electrolyte with excellent high-voltage stability by introducing a lithium-ionized and fluorinated flower-shaped porous HAP interface layer on the positive electrode side. This electrolyte not only possesses high ionic conductivity and lithium-ion transference number, but also effectively suppresses high-voltage side reactions, significantly improving the cycle stability and rate performance of solid-state lithium metal batteries. Experimental results show that the technical solution of this invention has outstanding substantive features and significant progress, possessing good prospects for industrial application.

Claims

1. A lithium-fluorine modified hydroxyapatite interfacial solid electrolyte, characterized in that, The electrolyte membrane has an asymmetric three-layer structure, including: The middle polymer matrix layer; the negative electrode side modification layer disposed on one side surface of the polymer matrix layer; the positive electrode side modification layer disposed on the other side surface of the polymer matrix layer; The polymer matrix layer is composed of a blend of methyl methacrylate (MMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene P (VDF-HFP) in a mass ratio of 50:1:4, and is doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The positive electrode side modification layer contains modified hydroxyapatite (HAP) particles and organomontmorillonite. The modified HAP is a flower-like porous hydroxyapatite (Li,F-HAP) that has been co-modified by lithiation and fluorination, and has a large specific surface area and abundant lithium-ion transport sites. The modified layer on the negative electrode side contains lithium zirconium fluoride (Li2ZrF6) particles.

2. The solid electrolyte according to claim 1, characterized in that, The thickness of the polymer matrix layer is 180-220 μm, and the thickness of the positive electrode side modification layer is 6-10 μm.

3. The solid electrolyte according to claim 1, characterized in that, The electrolyte membrane has an ionic conductivity ≥ 9.0 × 10⁻⁶. -4 S·cm -1 The lithium-ion transference number is ≥0.58, and the electrochemical stability window is greater than 4.4 V.

4. A method for preparing a solid electrolyte as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Preparation of modified hydroxyapatite powder: Lithium nitrate, calcium chloride, hexadecyltrimethylammonium bromide and sodium hydrogen phosphate were subjected to hydrothermal reaction, and then modified by sodium fluoride aqueous solution to obtain modified HAP powder with a large surface area and flower-like structure. (2) Preparation of precursors: MMA, PVDF, P(VDF-HFP) and LiTFSI were mixed and prepolymerized to obtain polymer electrolyte precursor C; precursor E containing modified HAP and organomontmorillonite and precursor D containing Li2ZrF6 were also prepared. (3) Layer-by-layer film formation: Precursor C is cast into a film, then precursor D is coated on one side of the film and precursor E is coated on the other side. After drying, the composite solid polymer electrolyte membrane is obtained.

5. The preparation method according to claim 4, characterized in that, In step (1), the hydrothermal reaction temperature is 180-220 °C and the time is 4-12 h. The preparation of the modified HAP powder also includes: centrifuging and washing the hydrothermal product, and then dispersing it in a 4-6 mg·mL⁻¹ sodium fluoride aqueous solution and stirring for 10-15 h.

6. The preparation method according to claim 4, characterized in that, In step (2), the modified HAP has a mass fraction of 5%-20% in the precursor C, and the amount of organomontmorillonite added is 6%-10% of the total polymer mass.

7. The preparation method according to claim 4, characterized in that, In step (3), the drying temperature after scraping is 60-100 ℃ and the time is 2-12 h, and the casting drying temperature of the polymer matrix layer is 70-90 ℃ and the time is 8-12 h.

8. A high-voltage solid-state lithium metal battery, characterized in that, The battery comprises a solid electrolyte according to any one of claims 1-3, wherein the positive electrode is an NCM811 high-voltage ternary positive electrode.

Images