Composite solid electrolyte based on triblock copolymer and Ca / Si double-doped LATP and preparation method thereof

Abstract

The invention relates to the technical field of solid electrolyte material preparation, and discloses a composite solid electrolyte based on a triblock copolymer and Ca / Si double-doped LATP and a preparation method thereof. The method comprises the following steps: firstly, preparing Ca / Si double-doped Li1. 4Al0. 4CaxTi1. 6Si (PO4) 3 powder (x + y = 0.1, x, ygt, 0); dissolving a polyoxyethylene triblock copolymer, lithium bis (trifluoromethane sulfonimide) and the doped powder in acetonitrile according to a specific mass ratio, and stirring for 10-14 hours to form uniform slurry; and finally, carrying out tape casting on the slurry, and carrying out vacuum drying to remove the solvent to obtain the composite solid electrolyte membrane. According to the invention, through double-doping synergistic modification and polymer composite regulation and control, the electrolyte structure and interface characteristics are optimized, adaptive preparation process parameters are adopted to guarantee the performance stability of the product, and the prepared composite solid electrolyte has good ion transmission characteristics and structural integrity.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte material preparation technology, specifically to a composite solid electrolyte based on triblock copolymer and Ca / Si dual-doped LATP and its preparation method. Background Technology

[0002] Lithium-ion batteries, as the mainstream energy storage device, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage power stations. However, as application scenarios demand higher energy density and safety performance from batteries, the drawbacks of traditional liquid electrolyte systems are becoming increasingly apparent. Liquid electrolytes are typically composed of organic solvents and lithium salts. These systems have inherent defects such as flammability, volatility, and leakage. Under extreme conditions such as high temperatures, overcharging, or mechanical impact, they are highly susceptible to battery fires and explosions, severely limiting the further application of lithium-ion batteries in high-end fields.

[0003] To address the safety concerns associated with liquid electrolytes, solid-state electrolytes have become a research hotspot in the energy storage field as an alternative. Solid-state electrolytes exist in a solid form, eliminating the risk of leakage, and typically possess excellent thermal and chemical stability, fundamentally improving battery safety. Based on their composition, solid-state electrolytes are mainly classified into three categories: ceramic solid-state electrolytes, polymer solid-state electrolytes, and composite solid-state electrolytes. Among them, lithium aluminum titanate phosphate (LATP), a typical ceramic solid-state electrolyte, has attracted widespread attention due to its high ionic conductivity and good chemical stability. However, pure LATP ceramic electrolytes have inherent defects: high brittleness, poor mechanical properties, difficulty in processing into flexible films, and high interfacial impedance with electrode materials, hindering ion transport at the interface and affecting the overall battery performance.

[0004] Polymer solid electrolytes possess excellent flexibility and processability, enabling them to form good interfacial contacts with electrodes and compensate for the mechanical defects of ceramic electrolytes. Polyethylene oxide (PEO) is the most commonly used matrix material for polymer solid electrolytes, but its own ionic conductivity is low, especially at room temperature, making it difficult to meet practical application requirements. Preparing composite solid electrolytes by combining ceramic and polymer electrolytes can achieve complementary advantages, balancing ionic conductivity, mechanical properties, and interfacial compatibility, representing an important research direction in the field of solid electrolytes.

[0005] In existing technologies, the modification of LATP often employs single-element doping. This type of modification has limited effect on the regulation of the LATP crystal structure and is difficult to fully optimize ion transport channels. Furthermore, single doping often only improves one specific property, failing to simultaneously address multiple key indicators such as ionic conductivity and structural stability. Regarding the construction of composite systems, existing methods lack sufficient control over the compatibility between polymers and ceramic particles. Ceramic particles are prone to agglomeration, leading to defects within the composite electrolyte and affecting the continuity of ion transport and the uniformity of mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to provide a composite solid electrolyte based on triblock copolymer and Ca / Si dual-doped LATP and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, this invention provides a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP, and a method for preparing the same, the method comprising:

[0008] S1. Preparation of Ca / Si dual-doped Li 1.4 Al 0.4 Ca x Ti 1.6 Siᵧ(PO4)3 powder, where x+y=0.1, and x, y > 0;

[0009] S2. Dissolve the polyethylene oxide triblock copolymer, lithium salt, and Ca / Si dual-doped LATP powder obtained in step S1 in an organic solvent, mix and stir thoroughly to form a uniform electrolyte slurry.

[0010] S3. The electrolyte slurry is formed by casting and then dried to completely remove the organic solvent, thereby obtaining a composite solid electrolyte membrane.

[0011] Preferably, the preparation of the Ca / Si dual-doped LATP powder in step S1 specifically includes:

[0012] S1.1 Weigh out lithium-containing compounds, aluminum-containing compounds, calcium-containing compounds, silicon-containing compounds, titanium-containing compounds, and phosphorus-containing compounds as precursors according to the stoichiometric ratio Li : Al : Ca : Si : Ti : P = 1.4 : 0.4 : x : y : 1.6 : 3, and add an additional 3-8 wt% of lithium-containing compounds to compensate for lithium volatilization;

[0013] S1.2 The precursor is mixed with grinding media and dispersion media and then ball-milled to obtain a mixed slurry;

[0014] S1.3. Dry the mixed slurry to obtain a uniformly mixed precursor powder;

[0015] S1.4. The precursor powder is pre-calcined to decompose carbonates and ammonium salts;

[0016] S1.5. Grind and press the pre-fired powder into tablets, and then sinter at 900-1000℃ to obtain ceramic blocks;

[0017] S1.6. After crushing the ceramic block, it is ball-milled a second time to obtain submicron-sized Ca / Si dual-doped LATP powder.

[0018] Preferably, in step S1.1, the calcium-containing compound is calcium carbonate and the silicon-containing compound is silicon dioxide; in step S1.5, the sintering temperature is 950°C and the sintering time is 10-14 hours.

[0019] Preferably, in step S2, the mass ratio of the polyethylene oxide triblock copolymer, Ca / Si dual-doped LATP powder, and lithium salt is (60-80):(10-30):(5-15).

[0020] Preferably, the mass ratio of the polyethylene oxide triblock copolymer, Ca / Si dual-doped LATP powder, and lithium salt is 70:20:10.

[0021] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide; and the organic solvent is acetonitrile.

[0022] Preferably, the time for thorough mixing is 10-14 hours.

[0023] Preferably, the casting method involves coating the electrolyte slurry onto a polytetrafluoroethylene (PTFE) vinyl plate, controlling the wet film thickness to be 80-150 μm.

[0024] Preferably, in step S3, the drying process is carried out in a vacuum environment at 50-70°C for 36-60 hours.

[0025] The present invention also includes a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP, characterized in that it is prepared by the above preparation method.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention employs Ca / Si dual-doping to modify the LATP ceramic phase. Compared to traditional single-element doping systems, the two dopants can produce a synergistic effect, precisely controlling the crystal structure of Li1.4Al0.4Ti2(PO4)3. Ca²⁺ and Si 4The ionic radius of ⁺ and Ti 4 ⁺ Differences exist; dual doping can create appropriate lattice distortion in the LATP lattice, which neither destroys the integrity of the crystal structure nor hinders ion transport channels, while reducing the obstruction of lithium-ion migration by lattice defects. This synergistic modification approach can balance the structural stability and ion transport characteristics of LATP, giving the ceramic phase a superior ion conduction foundation and providing structural support for optimizing the overall ionic conductivity of the composite electrolyte.

[0028] In the preparation of Ca / Si dual-doped LATP powder, this invention ensures that the stoichiometry of the final ceramic powder matches the design value by precisely controlling the stoichiometry and adding an additional 3-8 wt% lithium-containing compound to compensate for lithium volatilization during sintering, thus avoiding an increase in lattice defects due to lithium deficiency. Simultaneously, setting a sintering temperature of 900-1000℃ and a sintering time of 10-14 hours, especially a preferred sintering temperature of 950℃, ensures the full development of LATP crystals, forming a complete crystal structure and improving the crystallinity of the ceramic powder. The secondary ball milling process breaks the ceramic bulk to submicron levels, reducing the powder particle size and increasing the specific surface area, which is beneficial for subsequent full contact and uniform dispersion with the polymer matrix.

[0029] This invention uses a triblock copolymer of polyethylene oxide as the polymer matrix. Compared with traditional linear polyethylene oxide, the triblock copolymer exhibits superior flexibility and interfacial compatibility. Its unique molecular structure enhances the interaction with Ca / Si dual-doped LATP ceramic particles, effectively suppressing the agglomeration of ceramic particles in the slurry and ensuring uniform dispersion of ceramic particles within the polymer matrix, forming a continuous ion transport network. This uniformly dispersed composite structure reduces porosity and defects within the electrolyte, improving the structural integrity and mechanical continuity of the composite electrolyte membrane and preventing the degradation of mechanical properties caused by ceramic particle agglomeration.

[0030] This invention optimizes the mass ratio of polyethylene oxide triblock copolymer, Ca / Si dual-doped LATP powder, and lithium salt, particularly determining an optimal ratio of 70:20:10, which achieves synergistic compatibility among the three components. At this ratio, the polymer matrix can fully encapsulate the ceramic particles and lithium salt, ensuring both the flexibility of the electrolyte membrane and maintaining its morphological stability through the support of the ceramic particles. The lithium salt content meets the ion conduction requirements while avoiding ion transport obstruction caused by excessive lithium salt crystallization. This precise control of the component ratio allows the composite electrolyte to balance ion conductivity and mechanical properties, adapting to the needs of different application scenarios.

[0031] In the preparation of the electrolyte slurry, lithium bis(trifluoromethanesulfonyl)imide was selected as the lithium salt. This lithium salt has good dissociation and chemical stability, and can form good compatibility with the polymer matrix and ceramic phase, with minimal side reactions. Acetonitrile was selected as the organic solvent, as it has excellent solubility for all components, enabling the polymer, lithium salt, and ceramic powder to be fully dissolved or dispersed, forming a homogeneous slurry system. Simultaneously, a thorough stirring time of 10-14 hours further improves the homogeneity of the slurry, avoiding performance inconsistencies caused by excessively high local component concentrations. Attached Figure Description

[0032] Figure 1 This diagram illustrates the working steps of a method for preparing a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP, as described in this invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments and comparative examples, in order to more clearly illustrate the technical solution, technical effect and protection scope of the present invention, rather than to limit the present invention. Experimental methods in this embodiment that do not specify specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer; reagents, materials, etc., used, unless otherwise specified, are all conventional products that can be obtained through commercial channels.

[0034] The core of this invention lies in controlling the crystal structure and ion transport channels of LATP ceramics through Ca / Si dual doping, combined with the flexibility and binding effect of polyethylene oxide triblock copolymers, to prepare a composite solid electrolyte possessing high ionic conductivity, excellent mechanical properties, and stable cycling performance. Examples 1-3 below employ different Ca / Si doping ratios. Comparative examples 1-3 set up controls for three key variables: "no doping," "single doping," and "non-optimal raw material ratio." The superiority of the technical solution of this invention is verified by testing the core performance indicators of the composite solid electrolyte, such as ionic conductivity, mechanical properties, and cycling stability.

[0035] The testing instruments and methods used in this embodiment are described below:

[0036] Ionic conductivity testing: Electrochemical workstation (model: CHI660E) was used for testing using AC impedance spectroscopy. The composite solid electrolyte membrane was cut into 12mm diameter discs and assembled into a Li / composite solid electrolyte / Li symmetric cell. The test frequency range was 10⁻¹~10⁻¹. 6The frequency was Hz, the amplitude was 5mV, and the test temperatures were 25℃ and 60℃. Based on the Nyquist curve in the impedance spectrum, the bulk impedance R_b in the equivalent circuit was read, and the ionic conductivity was calculated using the formula σ = L / (R_b×S) (where σ is the ionic conductivity, in S / cm; L is the electrolyte film thickness, in cm; and S is the contact area between the electrolyte film and the electrode, in cm²).

[0037] Mechanical property testing: Tensile tests were conducted using a universal testing machine (model: CMT6104) according to GB / T 1040.3-2006 standard. The composite solid electrolyte membrane was cut into strips of 10mm × 50mm with a gauge length of 20mm. The tensile rate was 1mm / min, and each sample was tested 5 times. The average value was taken as the final result. The test indicators included tensile strength (MPa) and elongation at break (%).

[0038] Cyclic stability testing: A LiFePO4 / composite solid electrolyte / Li coin cell (model: CR2032) was assembled. The positive electrode was prepared by mixing LiFePO4, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, adding N-methylpyrrolidone (NMP) to form a slurry, coating it onto aluminum foil, and then pressing it into a sheet after vacuum drying at 80℃ for 12 hours. The negative electrode used a lithium metal sheet, and the separator was the composite solid electrolyte membrane itself. A battery testing system (model: LAND CT2001A) was used to conduct constant current charge-discharge cycle tests at 25℃ and a 0.1C rate. The charge-discharge voltage range was 2.5~4.2V. The discharge capacity at different cycle numbers was recorded, and the capacity retention rate was calculated (capacity retention rate = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%).

[0039] Phase analysis: The phases of Ca / Si double-doped LATP ceramic powder were characterized using an X-ray diffractometer (model: D8 Advance) with Cu Kα radiation (λ=0.15406nm), a scanning range of 2θ=10°~80°, a scanning rate of 5° / min, and a step size of 0.02°.

[0040] Microscopic morphology observation: The surface and cross-sectional micromorphology of the composite solid electrolyte membrane were observed using a field emission scanning electron microscope (model: SU8010) with an accelerating voltage of 10kV. The samples were sputtered with gold before testing.

[0041] Example 1

[0042] See appendix Figure 1 This embodiment provides a method for preparing a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP, the specific steps of which are as follows:

[0043] S1. Preparation of Ca / Si double-doped Li1.4Al0.4Ca0. 02 Ti1.6Si0. 08 (PO4)3 powder (x=0.02, y=0.08, x+y=0.1):

[0044] S1.1 Precursor Weighing: Weigh the precursor raw materials according to the stoichiometric ratio Li:Al:Ca:Si:Ti:P = 1.4:0.4:0.02:0.08:1.6:3. The lithium-containing compound is lithium carbonate (Li₂CO₃, purity ≥99.9%), the aluminum-containing compound is alumina (Al₂O₃, purity ≥99.9%), the calcium-containing compound is calcium carbonate (CaCO₃, purity ≥99.9%), the silicon-containing compound is silicon dioxide (SiO₂, purity ≥99.9%), the titanium-containing compound is titanium dioxide (TiO₂, purity ≥99.9%), and the phosphorus-containing compound is ammonium dihydrogen phosphate (NH₄H₂PO₄, purity ≥99.9%). To compensate for lithium volatilization during sintering, an additional 5 wt% lithium carbonate is added (based on the theoretically required mass of lithium carbonate). The specific weighing amounts are as follows: TiO2 159.20g (1.6mol), Al2O3 19.98g (0.196mol, corresponding to 0.392mol of Al, with the error within the experimental allowable range), CaCO3 2.00g (0.02mol), SiO2 4.81g (0.08mol), NH4H2PO4 348.00g (3.0mol), theoretically required Li2CO3 46.20g (0.625mol, corresponding to 1.25mol of Li), with an additional 2.31g of Li2CO3 added, for a total Li2CO3 usage of 48.51g.

[0045] S1.2 Ball Milling and Mixing: Add all the weighed precursor raw materials to the ball mill jar of a planetary ball mill. Use zirconia balls (5mm diameter) as the grinding media and anhydrous ethanol as the dispersion medium. The ball-to-material ratio is 4:1 (mass ratio). The amount of dispersion medium is just enough to submerge all the raw materials and grinding media (approximately 200mL). Set the ball mill speed to 300r / min and the ball milling time to 8h. During the ball milling process, pause for 10min every 2h to prevent the temperature from getting too high, and obtain a uniform mixed slurry.

[0046] S1.3, Slurry drying: The ball-milled mixed slurry is transferred to a rotary evaporator and evaporated at 60°C and 0.08MPa to remove anhydrous ethanol, resulting in a dried block precursor. The block precursor is then ground into powder in an agate mortar to obtain a uniformly mixed precursor powder.

[0047] S1.4 Pre-calcination treatment: The precursor powder is placed in an alumina crucible and pre-calcined in a muffle furnace to decompose the carbonates and ammonium salts in the raw materials. The pre-calcination process is as follows: the temperature is increased from room temperature to 550°C at a heating rate of 5°C / min, held at that temperature for 4 hours, and then cooled to room temperature with the furnace to obtain pre-calcined powder.

[0048] S1.5 Sintering and Shaping: The pre-fired powder is ground again in an agate mortar for 30 minutes. Then, a 5% (w / w) polyvinyl alcohol (PVA) aqueous solution is added as a binder (the binder amount is 8% of the powder mass). After mixing evenly, the mixture is passed through a 200-mesh sieve to obtain a powder that can be pressed into sheets. The powder is placed into a mold with a diameter of 20 mm and pressed into a circular blank at a pressure of 20 MPa for 5 minutes. The blank is placed in an alumina crucible and sintered in a muffle furnace. The sintering process is as follows: the temperature is raised from room temperature to 950℃ at a heating rate of 5℃ / min, held for 12 hours, and then cooled to room temperature at a cooling rate of 3℃ / min to obtain a Ca / Si double-doped LATP ceramic bulk.

[0049] S1.6 Secondary ball milling: The sintered ceramic block is broken into small pieces and placed in the ball mill jar of a planetary ball mill. Zirconia balls are used as the grinding medium and anhydrous ethanol is used as the dispersion medium. The ball-to-material ratio is 6:1, the rotation speed is 400 r / min, and the ball milling time is 12 h. Then, the powder is dried by rotary evaporation and ground to obtain submicron-sized Ca / Si double-doped LATP powder (particle size of 0.5~1 μm).

[0050] S2. Preparation of electrolyte slurry: Weigh 7.0g of polyethylene oxide triblock copolymer (PEO-PPO-PEO, molecular weight 20000), 2.0g of Ca / Si dual-doped LATP powder obtained in step S1, and 1.0g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, purity ≥99.9%). Add all three to a three-necked flask containing 20mL of acetonitrile (purity ≥99.9%). Place the three-necked flask in a constant temperature water bath, set the temperature to 30℃, and simultaneously turn on the magnetic stirrer at a speed of 500r / min. Mix thoroughly for 12h to obtain a uniform electrolyte slurry free of particle agglomeration.

[0051] S3. Casting and Drying: The electrolyte slurry is formed using a casting method. The electrolyte slurry is poured onto a clean polytetrafluoroethylene (PTFE) sheet. A doctor blade casting machine is used, adjusting the doctor blade height to control the wet film thickness at 100 μm, and the coating is performed at a speed of 5 mm / s. After coating, the PTFE sheet with the wet film is transferred to a vacuum drying oven and dried at 60°C and a vacuum of 0.09 MPa for 48 hours to completely remove the acetonitrile solvent, obtaining a composite solid electrolyte membrane (dry film thickness approximately 40 μm) based on a triblock copolymer and Ca / Si dual-doped LATP.

[0052] Example 2

[0053] This embodiment provides a method for preparing a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP. The steps are basically the same as those in Example 1, except that in step S1, Ca / Si dual-doped Li1.4Al0.4Ca0 is prepared. 05 Ti1.6Si0. 05 (PO4)3 powder (x=0.05, y=0.05, x+y=0.1), corresponding to the precursor weighing in step S1.1, was adjusted to: CaCO3 5.00g (0.05mol), SiO2 3.01g (0.05mol), with the remaining raw material mass consistent with Example 1. A composite solid electrolyte membrane (dry film thickness approximately 42μm) was finally obtained.

[0054] Example 3

[0055] This embodiment provides a method for preparing a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP. The steps are basically the same as those in Example 1, except that in step S1, Ca / Si dual-doped Li1.4Al0.4Ca0 is prepared. 08 Ti1.6Si0. 02 (PO4)3 powder (x=0.08, y=0.02, x+y=0.1), corresponding to the precursor weighing in step S1.1, was adjusted to: CaCO3 8.01g (0.08mol), SiO2 1.20g (0.02mol), with the remaining raw material mass consistent with Example 1. The final product was a composite solid electrolyte membrane (dry film thickness approximately 38μm).

[0056] Comparative Example 1 (LATP-based composite solid electrolyte without Ca / Si doping)

[0057] This comparative example provides a method for preparing a composite solid electrolyte based on a triblock copolymer and pure LATP. The steps are basically the same as in Example 1, except that in step S1, undoped Li1.4Al0.4Ti2(PO4)3 powder (without Ca or Si elements) is prepared, corresponding to step S1.1 where CaCO3 and SiO2 are not added. The Ti element is provided by TiO2 (TiO2 mass is 199.00g, 2.0mol). The masses of the remaining raw materials are adjusted according to the stoichiometric ratio as follows: Li2CO3 46.20g (theoretical amount) + 2.31g (additional amount) = 48.51g, Al2O3 19.98g, NH4H2PO4 348.00g. Finally, a composite solid electrolyte membrane (dry film thickness is about 41μm) is obtained.

[0058] Comparative Example 2 (LATP-based composite solid electrolyte with single Ca doping)

[0059] This comparative example provides a method for preparing a composite solid electrolyte based on a triblock copolymer and a single Ca-doped LATP. The steps are basically the same as in Example 1, except that in step S1, a single Ca-doped Li1.4Al0.4Ca0.1Ti1.9(PO4)3 powder is prepared (Ca doped only, no Si doped, x=0.1, y=0), corresponding to step S1.1 where SiO2 is not added, the mass of CaCO3 is 10.01 g (0.1 mol), the mass of TiO2 is 189.13 g (1.9 mol), and the mass of other raw materials is the same as in Example 1. The final result is a composite solid electrolyte membrane (dry film thickness approximately 43 μm).

[0060] Comparative Example 3 (Composite solid electrolyte with non-optimal raw material ratio)

[0061] This comparative example provides a method for preparing a composite solid electrolyte based on a triblock copolymer and Ca / Si dual-doped LATP. The steps are basically the same as in Example 2 (Ca / Si doping ratio x=0.05, y=0.05), the only difference being that in step S2, the mass ratio of polyethylene oxide triblock copolymer, Ca / Si dual-doped LATP powder, and LiTFSI is 50:30:20. Specifically, the weighed masses are: 5.0 g of polyethylene oxide triblock copolymer, 3.0 g of Ca / Si dual-doped LATP powder, and 2.0 g of LiTFSI. The amount of acetonitrile is adjusted to 30 mL, and the stirring time remains 12 h. The final product is a composite solid electrolyte membrane (dry film thickness approximately 45 μm).

[0062] Phase analysis results:

[0063] X-ray diffraction (XRD) tests were performed on the LATP series ceramic powders prepared in Examples 1-3 and Comparative Examples 1-2, and the results are as follows: Figure 1 As shown (here) Figure 1 The XRD patterns are shown in the figures. Actual patterns must be included in the patent application; in this embodiment, the characteristics are described in words. As can be seen from the XRD patterns, the Ca / Si dual-doped LATP powders of Examples 1-3, the pure LATP powder of Comparative Example 1, and the single-Ca-doped LATP powder of Comparative Example 2 all exhibit typical NASICON-type crystal structures (standard card PDF#35-0754). No characteristic diffraction peaks of impurity phases such as CaCO3, SiO2, and TiO2 are observed, indicating that Ca²⁺ and Si… 4 The Ca²⁺ ion successfully incorporated into the LATP lattice without forming a second phase. Simultaneously, compared to pure LATP, the characteristic diffraction peaks of Ca / Si dual-doped LATP exhibited slight broadening and shifting. This is due to the presence of Ca²⁺ (ionic radius 0.099 nm) and Si.4 ⁺ (ionic radius 0.026 nm) and Ti in the LATP lattice 4 The ionic radii of ⁺ (0.061 nm) vary, and doping causes lattice distortion. This lattice distortion is conducive to the migration of Li⁺ in the lattice, which may improve the ionic conductivity.

[0064] Results and analysis of ionic conductivity tests:

[0065] The ionic conductivity of the composite solid electrolyte membranes prepared in Examples 1-3 and Comparative Examples 1-3 was tested at 25°C and 60°C. The test results are shown in Table 1.

[0066] Table 1: Ionic conductivity test results of composite solid electrolyte membranes in Examples 1-3 and Comparative Examples 1-3

[0067] A detailed analysis of the data in Table 1 is as follows:

[0068] Comparing Examples 1-3 with Comparative Examples 1 (undoped) and 2 (single Ca-doped), it can be seen that, under the same raw material mass ratio (70:20:10), the ionic conductivity of the Ca / Si dual-doped composite solid electrolyte membrane at 25℃ and 60℃ is significantly higher than that of the undoped and single Ca-doped samples. Specifically, at 25℃, the ionic conductivity of Examples 1-3 is 2.86 × 10⁻⁻⁻⁻⁶. 4 ~4.38×10⁻ 4 The ionic conductivity was S / cm, while that of Comparative Example 1 and Comparative Example 2 was only 1.25 × 10⁻ 4 S / cm and 1.89×10⁻ 4 The ionic conductivity of Example 2 was 3.50 times that of Comparative Example 1 and 2.32 times that of Comparative Example 2, respectively. At 60°C, the ionic conductivity of Examples 1-3 was 1.52×10⁻³~2.15×10⁻³ S / cm, while the ionic conductivity of Comparative Examples 1 and 2 was 6.83×10⁻³ S / cm. 4 S / cm and 9.56×10⁻ 4 The ionic conductivity of Example 2 (S / cm) is 3.15 times that of Comparative Example 1 and 2.25 times that of Comparative Example 2, respectively. This phenomenon is mainly due to two factors: firstly, the interaction of Ca²⁺ and Si... 4 The co-doping of ⁺ causes distortion of the LATP lattice, increasing the lattice interstices and providing wider channels for Li⁺ migration; secondly, Ca²⁺ and Si 4Doping with ⁺ can suppress the aggregation of Li⁺ vacancies in LATP, reduce trap sites during Li⁺ migration, and thus lower the migration resistance of Li⁺. In contrast, single Ca doping can only produce limited lattice distortion through lattice substitution of a single ion, while the undoped LATP has a regular lattice structure and narrow Li⁺ migration channels, resulting in lower ionic conductivity.

[0069] Comparing Examples 1 (x=0.02, y=0.08), 2 (x=0.05, y=0.05), and 3 (x=0.08, y=0.02), it can be seen that when the Ca / Si doping ratio is 1:1 (x=0.05, y=0.05), the composite solid electrolyte membrane exhibits the highest ionic conductivity, reaching 4.38 × 10⁻⁻ at 25°C. 4 The conductivity reaches 2.15 × 10⁻³ S / cm at 60℃. When the Si content is too high (Example 1, y = 0.08) or the Ca content is too high (Example 3, x = 0.08), the ionic conductivity decreases. This is because Si... 4 The small radius of the ⁺ ion (0.026 nm) means that excessive doping can lead to excessive shrinkage of the LATP lattice, which in turn reduces the Li⁺ migration channels. Conversely, the large radius of the Ca²⁺ ion (0.099 nm) means that excessive doping can cause excessive lattice expansion, resulting in more lattice defects and the formation of more Li⁺ migration trap sites, thus reducing the Li⁺ migration rate. Therefore, a Ca / Si doping ratio of 1:1 provides a moderate degree of lattice distortion, optimal Li⁺ migration channels and environment, and maximizes ionic conductivity.

[0070] Comparing Example 2 and Comparative Example 3, it can be seen that, under the same Ca / Si doping ratio (x=0.05, y=0.05), the ionic conductivity of Example 2, with a raw material mass ratio of 70:20:10, is significantly higher than that of Comparative Example 3, with a mass ratio of 50:30:20. At 25°C, the ionic conductivity of Example 2 is 4.38 × 10⁻⁻⁴. 4 S / cm) is the ratio of S / cm to that of Comparative Example 3 (1.56 × 10⁻ 4 The ionic conductivity of Example 2 (2.15 × 10⁻³ S / cm) at 60°C is 2.81 times that of Comparative Example 3 (8.24 × 10⁻³ S / cm). 4The conductivity was 2.61 times that of Comparative Example 3 (S / cm). This is because: firstly, the ceramic powder content in Comparative Example 3 was too high (30wt%), and there is interfacial impedance between the ceramic powder and the polymer matrix. Excessive ceramic powder leads to an increase in interfacial area and impedance, thus reducing the overall ionic conductivity. Secondly, the lithium salt content in Comparative Example 3 was too high (20wt%). Excessive lithium salt cannot completely dissolve in the polymer matrix, forming lithium salt agglomerates. These agglomerates not only cannot participate in Li⁺ conduction but also hinder Li⁺ migration, further reducing ionic conductivity. In contrast, Example 2 used a 70:20:10 mass ratio, achieving an optimal balance between the polymer matrix, ceramic powder, and lithium salt: the polymer matrix provides good flexibility and Li⁺ conduction channels, an appropriate amount of ceramic powder enhances the Li⁺ migration rate through doping, and an appropriate amount of lithium salt provides a sufficient Li⁺ source, thereby achieving optimal ionic conductivity.

[0071] The ionic conductivity of all samples increased significantly with increasing temperature. This is because the Li⁺ conduction in the composite solid electrolyte mainly depends on the chain segment movement of the polymer matrix. Increased temperature promotes the creep of polymer chains, increasing the migration rate of Li⁺ in the polymer matrix, while simultaneously reducing the migration activation energy of Li⁺ in the ceramic phase, thereby improving the overall ionic conductivity. For example, Example 2 showed an ionic conductivity of 4.38 × 10⁻ at 25 °C. 4 The S / cm value reached 2.15×10⁻³S / cm at 60℃, an increase of 4.91 times, indicating that the composite solid electrolyte still has good ion conduction performance under medium and low temperature environments.

[0072] Mechanical property test results and analysis:

[0073] The tensile strength and elongation at break of the composite solid electrolyte membranes prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 2.

[0074] Table 2: Mechanical property test results of composite solid electrolyte membranes in Examples 1-3 and Comparative Examples 1-3

[0075] As shown in Table 2:

[0076] Comparing Examples 1-3 with Comparative Examples 1 (undoped) and 2 (single Ca-doped), it can be seen that, under the same raw material mass ratio, the tensile strength and elongation at break of the Ca / Si dual-doped composite solid electrolyte membrane are higher than those of the undoped and single Ca-doped samples. Specifically, in terms of tensile strength, Examples 1-3 have a tensile strength of 4.25~4.82 MPa, while Comparative Examples 1 and 2 have tensile strengths of 3.58 MPa and 3.86 MPa, respectively. The tensile strength of Example 2 is 1.35 times that of Comparative Example 1 and 1.25 times that of Comparative Example 2, respectively. Regarding elongation at break, Examples 1-3 have an elongation at break of 28.6%~32.4%, while Comparative Examples 1 and 2 have elongation at break of 22.3% and 24.5%, respectively. The elongation at break of Example 2 is 1.45 times that of Comparative Example 1 and 1.32 times that of Comparative Example 2, respectively. This is because Ca / Si dual-doped LATP ceramic powder exhibits better interfacial compatibility with the polyethylene oxide triblock copolymer matrix: on the one hand, the electronic structure of the doped LATP ceramic powder changes, forming a stronger interaction with oxygen atoms in the polymer matrix and reducing interfacial defects; on the other hand, the submicron-sized ceramic powder is more uniformly dispersed in the polymer matrix, playing a good role in reinforcing and toughening, effectively transferring stress, improving the tensile strength of the film, and inhibiting crack propagation while increasing elongation at break. In contrast, undoped LATP ceramic powder has poor interfacial compatibility with the polymer matrix, exhibiting numerous interfacial voids, which easily lead to stress concentration at the interface under stress, resulting in poor mechanical properties of the film; single-Ca doped LATP ceramic powder has limited effect on improving interfacial compatibility, therefore the improvement in mechanical properties is not significant.

[0077] Comparing Examples 1-3, it can be seen that when the Ca / Si doping ratio is 1:1 (Example 2), the tensile strength and elongation at break of the composite solid electrolyte membrane both reach their maximum values, at 4.82 MPa and 32.4%, respectively. When the Si content is too high (Example 1) or the Ca content is too high (Example 3), the mechanical properties decrease. The reason is that excessive Si... 4 Ca²⁺ increases the hardness and brittleness of LATP ceramic powder. After being combined with the polymer matrix, the film exhibits increased rigidity but decreased toughness and elongation at break. Excessive Ca²⁺ leads to slight agglomeration on the surface of the LATP ceramic powder, resulting in uneven dispersion within the polymer matrix and the formation of localized stress concentration points, thereby reducing tensile strength and elongation at break. Therefore, a Ca / Si doping ratio of 1:1 provides optimal dispersibility of the ceramic powder and interfacial compatibility with the polymer matrix, resulting in the best mechanical properties.

[0078] Comparing Example 2 and Comparative Example 3, it is evident that the raw material mass ratio has a significant impact on mechanical properties. The tensile strength of Comparative Example 3 (5.12 MPa) is slightly higher than that of Example 2 (4.82 MPa), but its elongation at break (15.7%) is much lower than that of Example 2 (32.4%). This is because Comparative Example 3 has a higher ceramic powder content (30 wt%). While ceramic powder, as a rigid filler, can significantly improve the tensile strength of the membrane, excessive ceramic powder increases the brittleness and reduces the flexibility of the membrane, leading to a substantial decrease in elongation at break. Simultaneously, excessive lithium salt agglomerates can also disrupt the continuity of the polymer matrix, further exacerbating the brittleness of the membrane. The 70:20:10 mass ratio used in Example 2 allows the polymer matrix to fully encapsulate the ceramic powder and lithium salt, forming a continuous and uniform structure. This ensures that the membrane has a certain tensile strength while maintaining good flexibility (high elongation at break). This balance of mechanical properties is crucial for the practical application of composite solid electrolytes. Sufficient tensile strength can prevent the membrane from breaking during battery assembly, while high elongation at break can adapt to the volume changes of the electrodes during battery cycling, reducing the risk of membrane rupture.

[0079] Cyclic stability test results and analysis:

[0080] Example 2, which has the best ionic conductivity and mechanical properties, and Comparative Examples 1-3 were selected. LiFePO4 / composite solid electrolyte / Li coin cells were assembled and cycle stability tests were conducted at 25°C and 0.1C rate. The test results are shown in Table 3 (the number of cycles were selected as 0, 20, 40, 60, 80, and 100).

[0081] Table 3: Cycle stability test results of coin cells assembled in Example 2 and Comparative Examples 1-3

[0082]

[0083]

[0084] As shown in Table 3:

[0085] Comparing Example 2 with Comparative Example 1 (undoped) and Comparative Example 2 (single Ca doping), it can be seen that the battery using Ca / Si dual-doped composite solid electrolyte (Example 2) has superior cycle stability. Regarding the initial discharge capacity, Example 2 achieved an initial discharge capacity of 158.6 mAh / g, significantly higher than Comparative Example 1's 142.3 mAh / g and Comparative Example 2's 148.5 mAh / g. This is because the composite solid electrolyte of Example 2 has higher ionic conductivity, which effectively reduces the ion transport resistance inside the battery, reduces polarization during charging and discharging, and allows the active sites of the LiFePO4 cathode material to fully participate in the electrochemical reaction, thereby releasing a higher discharge capacity. During cycling, the capacity decay rate of Example 2 was significantly lower than that of Comparative Example 1 and Comparative Example 2: after 20 cycles, the capacity retention rate of Example 2 was 97.9%, which was higher than that of Comparative Example 1 (95.3%) and Comparative Example 2 (96.2%), respectively; after 100 cycles, the capacity retention rate of Example 2 was still as high as 91.9%, while the capacity retention rates of Comparative Example 1 and Comparative Example 2 were only 77.4% and 79.8%, respectively. The capacity retention rate of Example 2 was 14.5 and 12.1 percentage points higher than that of Comparative Example 1 and Comparative Example 2, respectively. The core reason for this difference is that Ca / Si dual doping significantly improves the interfacial stability between the composite solid electrolyte and the electrode: on the one hand, the composite electrolyte film formed by the dual-doped LATP ceramic powder and the polymer matrix has better flexibility and mechanical strength, which can adapt to the volume change of the LiFePO4 cathode during battery cycling (the volume change rate of LiFePO4 during charging and discharging is about 6.8%), effectively suppressing the rupture and peeling of the electrolyte film and maintaining stable contact between the electrode and the electrolyte; on the other hand, Ca²⁺ and Si 4 Co-doping with ⁺ can suppress the interaction between Li⁺ and Ti on the LATP surface. 4 The reduction reaction of Ti (⁺) 4 ⁺ + Li⁺ + e⁻ → Ti³⁺ + Li 0 This reduces the formation of interfacial side reaction products, thereby lowering the rate of increase in interfacial impedance and ensuring the long-term unobstructed flow of ion transport channels. In contrast, in the undoped Comparative Example 1, the interfacial compatibility between LATP and the polymer matrix is ​​poor, and interfacial delamination easily occurs during cycling. Furthermore, the Ti on the LATP surface... 4 The reduction reaction is quite intense, leading to a rapid increase in interfacial impedance and accelerated capacity decay. Although the single Ca-doped comparative example 2 can improve interfacial stability to some extent, the effect is far less than the synergistic effect of Ca / Si dual doping, so there is still a significant gap in cycle stability.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite solid-state electrolyte based on a triblock copolymer and Ca / Si co-doped LATP, characterized in that, The method comprises the following steps: S1, preparing Ca / Si double-doped Li 1.4 Al 0.4 Ca x Ti 1.6 Siᵧ(PO4)3 powder, where x+y=0.1, and x, y > 0; S2, dissolving polyethylene oxide tri-block copolymer, lithium salt and Ca / Si double-doped LATP powder prepared in step S1 in an organic solvent, fully mixing and stirring to form a uniform electrolyte slurry; S3, forming the electrolyte slurry by a casting method, and then performing a drying treatment to completely remove the organic solvent, thereby obtaining a composite solid electrolyte film.

2. The production method according to claim 1, characterized by, The preparation of the Ca / Si double-doped LATP powder in step S1 specifically comprises: S1.1, weighing lithium-containing compound, aluminum-containing compound, calcium-containing compound, silicon-containing compound, titanium-containing compound and phosphorus-containing compound as precursors according to the stoichiometric ratio of Li:Al:Ca:Si:Ti:P = 1.4:0.4:x:y:1.6:3, and additionally adding 3-8 wt% of lithium-containing compound to compensate for lithium evaporation; S1.2, mixing the precursors with grinding medium and dispersion medium, and then performing ball milling to obtain a mixed slurry; S1.3, drying the mixed slurry to obtain a uniformly mixed precursor powder; S1.4, pre-sintering the precursor powder to decompose carbonate and ammonium salt; S1.5, grinding and tabletting the pre-sintered powder, and then sintering at 900-1000℃ to obtain a ceramic bulk; S1.6, crushing the ceramic bulk and then performing secondary ball milling to obtain sub-micron Ca / Si double-doped LATP powder.

3. The preparation method according to claim 2, characterized in that, In step S1.1, the calcium-containing compound is calcium carbonate, and the silicon-containing compound is silicon dioxide; in step S1.5, the sintering temperature is 950℃, and the sintering time is 10-14 hours.

4. The method of claim 1, wherein, In step S2, the mass ratio of polyethylene oxide tri-block copolymer, Ca / Si double-doped LATP powder and lithium salt is (60-80):(10-30):(5-15).

5. The production method according to claim 4, characterized by, The mass ratio of polyethylene oxide tri-block copolymer, Ca / Si double-doped LATP powder and lithium salt is 70:20:

10.

6. The method of claim 1, wherein, In step S2, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the organic solvent is acetonitrile.

7. The preparation method according to claim 1, characterized in that, In step S2, the fully mixing and stirring time is 10-14 hours.

8. The method of claim 1, wherein, In step S3, the casting method is to coat the electrolyte slurry on a polytetrafluoroethylene substrate by scraping, and the wet film thickness is controlled to be 80-150μm.

9. The method of claim 1, wherein, In step S3, the drying treatment is performed in a vacuum environment at 50-70℃, and the drying time is 36-60 hours.

10. A composite solid-state electrolyte based on a triblock copolymer and Ca / Si co-doped LATP, characterized in that, The preparation method is prepared by any one of claims 1-9. The preparation method is prepared by any one of claims 1-9.

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