Composite solid electrolyte and preparation method thereof, battery

Abstract

This invention discloses a composite solid-state electrolyte, its preparation method, and a battery. The composite solid-state electrolyte comprises a polymer matrix, a sulfide ceramic filler, a main lithium salt, and a nitrile-based lithium salt additive. The nitrile-based lithium salt additive forms an interfacial passivation layer on the surface of the sulfide ceramic filler to suppress interfacial side reactions between the sulfide ceramic filler and the polymer matrix and / or the main lithium salt. This invention maintains the structural integrity of the sulfide ceramic filler, preserving its inherent high ionic conductivity channels, while reducing the interfacial impedance between the organic and inorganic phases, thereby improving the ionic conductivity and interfacial stability of the composite solid-state electrolyte.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to a composite solid-state electrolyte, its preparation method, and a battery. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage technologies, all-solid-state lithium metal batteries, characterized by high energy density and high safety, have become an important development direction for next-generation battery technology. As the core component of all-solid-state batteries, the performance of the solid electrolyte directly determines the overall performance of the battery. Polymer solid electrolytes (such as polyethylene oxide, PEO) are flexible, easy to process, and have good compatibility with lithium metal, but their room-temperature ionic conductivity is extremely low. Organic-inorganic composite solid electrolytes combine the good interfacial compatibility of polymer electrolytes with the high ionic conductivity of inorganic electrolytes, making them one of the most commercially promising solutions currently available. Ideally, the composite solid electrolyte should form a three-dimensional rapid ion conduction network within the polymer matrix, the inorganic phase, and at the organic / inorganic interface.

[0003] However, existing composite solid-state electrolytes face serious interface problems in practical applications. During the preparation and cycling of composite solid-state electrolytes, solvents, polymer matrices, and inorganic ceramic fillers are prone to interfacial side reactions. For example, functional groups or strongly coordinating lithium salt anions in the polymer matrix may react chemically with sulfide ceramics, leading to filler structure degradation and the generation of polysulfides and other byproducts. These side reactions not only disrupt the rapid ion conduction channels of the inorganic filler but also cause a sharp increase in the interfacial impedance between the polymer matrix and the ceramic filler, severely deteriorating the ionic conductivity of the composite solid-state electrolyte and the long-term cycling stability of the battery. Therefore, how to effectively mitigate interfacial side reactions occurring on the surface of inorganic fillers during preparation, reduce interfacial impedance, and improve interfacial compatibility is a key technical problem that urgently needs to be solved in the field of composite solid-state electrolytes.

[0004] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is: addressing the issue that interfacial side reactions easily occur between sulfide ceramic fillers and polymer matrices and / or main lithium salts in the prior art, leading to increased interfacial impedance and decreased ionic conductivity of composite solid electrolytes, and providing a composite solid electrolyte, its preparation method, and battery that can effectively suppress such interfacial side reactions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A composite solid electrolyte comprises: a polymer matrix, a sulfide ceramic filler, a main lithium salt, and a nitrile-based lithium salt additive; wherein the nitrile-based lithium salt additive is used to form an interface passivation layer on the surface of the sulfide ceramic filler to suppress interfacial side reactions between the sulfide ceramic filler and the polymer matrix and / or the main lithium salt.

[0007] In some embodiments, the sulfide ceramic filler is selected from Li6PS5Cl (LPSC) or has the general formula Li 6-y PS 5-y X 1+y At least one of the sulfide ceramics, wherein X is selected from F, Br or I, 0 <y<1。

[0008] In some embodiments, the polymer matrix is ​​selected from at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF).

[0009] In some embodiments, the primary lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium iodide (LiI).

[0010] In some embodiments, the nitrile-containing lithium salt additive is selected from at least one of lithium dicyandiamide (LiDCA), lithium tricyanomethane (LiTCM), lithium tetracyanoborate (LiTCB), lithium difluoro(1,1,2,2-tetracyano-1,2-dioxoethyl)borate (LiDFTCB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), and lithium 4,5-dicyano-1,2,3-triazole (LiDCTA).

[0011] In some embodiments, the molar ratio of lithium ions in the main lithium salt to complexing groups in the polymer matrix is ​​1:16 to 1:10; the content of the nitrile-containing lithium salt additive accounts for 10% to 30% of the molar amount of the main lithium salt.

[0012] The present invention also provides a method for preparing the composite solid electrolyte as described in any of the preceding claims, comprising the following steps: S1, mixing a polymer matrix, a main lithium salt, a nitrile-containing lithium salt additive and a sulfide ceramic filler in a solvent to form a slurry; S2, molding the slurry into a film; S3, removing the solvent to obtain the composite solid electrolyte.

[0013] In some embodiments, in step S1, before adding the sulfide ceramic filler, the nitrile-containing lithium salt additive is first mixed with the main lithium salt in a solvent.

[0014] In some embodiments, the solvent is selected from acetonitrile or N,N-dimethylformamide.

[0015] The present invention also provides a battery comprising: a positive electrode, a negative electrode, and a composite solid electrolyte as described in any of the preceding claims disposed between the positive electrode and the negative electrode.

[0016] In some embodiments, the negative electrode is a lithium metal negative electrode or a lithium metal alloy negative electrode.

[0017] In some embodiments, the active material of the positive electrode is selected from at least one of sulfur (S), lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4).

[0018] The present invention also provides an all-solid-state lithium metal battery, comprising a composite solid electrolyte as described in any of the preceding claims and a lithium metal anode.

[0019] The beneficial effects of this invention compared to the prior art include: This invention introduces a nitrile-based lithium salt additive, utilizing its cyano group (-CN) to strongly coordinate with lithium ions or Lewis acidic sites on the surface of sulfide ceramic fillers. This preferentially forms a stable, lithium-ion-permeable interfacial passivation layer on the sulfide ceramic filler surface. This passivation layer effectively blocks direct contact between functional groups or main lithium salt anions in the polymer matrix and the sulfide ceramic filler, thereby suppressing interfacial side reactions at their source. This maintains the structural integrity of the sulfide ceramic filler, preserving its inherent high ionic conductivity channels, while simultaneously reducing the interfacial impedance between the organic and inorganic phases, thus improving the ionic conductivity and interfacial stability of the composite solid electrolyte.

[0020] In some embodiments, the present invention also has the following beneficial effects: By selecting specific sulfide ceramic fillers (such as Li6PS5Cl), a better synergistic effect can be achieved with the nitrile-based lithium salt additive system of the present invention, further optimizing the formation of the interface passivation layer and ion transport performance.

[0021] By limiting the molar ratio of the main lithium salt to the polymer matrix and the content of nitrile-based lithium salt additives, the interfacial passivation effect of nitrile-based lithium salt additives can be maximized while ensuring sufficient dissociation of lithium salts and ionic conductivity, thus avoiding the adverse effects of excessive nitrile-based lithium salt additives on bulk ionic conductivity.

[0022] By mixing the nitrile-based lithium salt additive with the main lithium salt before adding the sulfide ceramic filler, the nitrile-based lithium salt additive can be pre-distributed more preferentially and evenly in the system, thereby forming a passivation layer more effectively on the surface of the sulfide ceramic filler when it comes into contact with it later.

[0023] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0024] Figure 1a This is the solid-state nuclear magnetic resonance phosphorus spectrum (ssNMR) of the composite solid electrolyte without the addition of nitrile-based lithium salt additives in Comparative Example 1 of this invention.

[0025] Figure 1b This is the solid-state nuclear magnetic resonance phosphorus spectrum (ssNMR) of the composite solid electrolyte in Example 1 of this invention.

[0026] Figure 2 This is the X-ray photoelectron spectrum of the composite solid electrolyte in Embodiment 1 of the present invention.

[0027] Figure 3 This is a scanning electron microscope (SEM) morphology image of the composite solid electrolyte in Embodiment 1 of the present invention.

[0028] Figure 4 This is an elemental distribution diagram of the composite solid electrolyte in Embodiment 1 of the present invention.

[0029] Figure 5 This is a temperature-dependent ionic conductivity diagram of the composite solid electrolyte without the addition of nitrile-based lithium salt additives in Comparative Example 1 of this invention.

[0030] Figure 6 This is a temperature-dependent ionic conductivity diagram of the composite solid electrolyte in Embodiment 1 of the present invention.

[0031] Figure 7 This is a comparison curve of the cycle performance of the full cell based on the electrolyte membrane of Example 1 assembled in Example 5 of the present invention and the full cell based on the electrolyte membrane of Comparative Example 1 assembled in Comparative Example 3.

[0032] Figure 8 This is a comparison curve of the cycle performance of the symmetrical battery based on the electrolyte membrane of Example 1 assembled in Example 5 of the present invention and the symmetrical battery based on the electrolyte membrane of Comparative Example 1 assembled in Comparative Example 3. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0034] It should be noted that the directional terms such as left, right, up, down, top, and bottom used in this embodiment are only relative concepts or are based on the normal use of the product, and should not be considered as restrictive.

[0035] The root cause of the instability at the interface between sulfide ceramics (such as LPSC) and polymer electrolytes lies in the metathesis reaction between sulfides and lithium salts, particularly the strong destructive power of strongly coordinated lithium salt anions on sulfide ceramics. To address this, this invention proposes an "interface diffusion passivation" concept, which involves introducing a type of nitrile-based lithium salt additive containing a strong electron-donating group (-CN). This additive, through the strong coordination of the -CN group with lithium ions or electron-deficient sulfur / phosphorus atoms on the sulfide ceramic surface, preferentially forms a stable, lithium-conducting interfacial protective layer on the ceramic particle surface. This protective layer avoids structural damage caused by the strong interaction between other strongly coordinated host salt anion pairs and lithium ions in the sulfide ceramic, maintaining the structural integrity and ion conduction channels of the ceramic, while ensuring the smooth passage of lithium ions, thus achieving a synergistic improvement in interfacial compatibility and ionic conductivity.

[0036] The core innovation of this invention lies in utilizing the cyano group (-CN) with strong coordination ability in nitrile-containing lithium salts to preferentially occupy the Lewis acidic active sites on the surface of sulfide ceramics, forming a lithium ion diffusion passivation layer, thereby blocking the damage to the sulfide ceramic structure caused by rapid lithium ion diffusion.

[0037] To address the problem of high interfacial impedance caused by interfacial side reactions between existing polymer matrices and sulfide ceramic fillers, this invention provides a composite solid electrolyte containing nitrile-based lithium salt additives. By introducing nitrile-based lithium salt additives into both the polymer matrix and the sulfide ceramic filler, interfacial side reactions between the sulfide ceramic filler and the polymer matrix are effectively suppressed, resulting in a free interface free of polysulfides (Li2S). x Polyphosphorus compounds P2S7 4- The formation of this process significantly improves the ionic conductivity and electrochemical stability of the composite solid electrolyte, thereby enhancing the battery's cycle performance.

[0038] The composite solid electrolyte provided in this invention includes: a polymer matrix, a sulfide ceramic filler, a main lithium salt, and a nitrile-based lithium salt additive; wherein, the nitrile-based lithium salt additive is used to form an interface passivation layer on the surface of the sulfide ceramic filler to suppress interfacial side reactions between the sulfide ceramic filler and the polymer matrix and / or the main lithium salt.

[0039] It should be noted that the nitrile-containing lithium salt additives selected in the embodiments of the present invention exhibit good chemical stability and compatibility in the selected solvents (such as acetonitrile) and polymer matrices (such as PEO and PVDF). Even for polyacrylonitrile (PAN) matrices containing the same cyano group, the nitrile-containing lithium salt additives can effectively perform interfacial passivation without adversely affecting the main structure of the polymer matrix.

[0040] Sulfide ceramic fillers are selected from Li6PS5Cl or Li 6-y PS5-y X 1+y At least one of the sulfide ceramics, wherein X is selected from F (fluorine), Br (bromine) or I (iodine), 0 <y<1。

[0041] The polymer matrix is ​​selected from at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF).

[0042] The main lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium iodide (LiI).

[0043] The nitrile-containing lithium salt additive is selected from at least one of lithium dicyandiamide (Li[N(CN)2], LiDCA), lithium tricyanomethane (Li[C(CN)3], LiTCM), lithium tetracyanoborate (Li[B(CN)4], LiTCB), lithium difluoro(1,1,2,2-tetracyano-1,2-dioxoethyl)borate (LiDFTCB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), and lithium 4,5-dicyano-1,2,3-triazole (LiDCTA).

[0044] The molar ratio of lithium ions in the main lithium salt to the complexing groups in the polymer matrix is ​​1:16 to 1:10; the content of the nitrile-based lithium salt additive accounts for 10% to 30% of the molar amount of the main lithium salt. The molar content of the main lithium salt is 70% to 90%. The molar ratio of the nitrile-based lithium salt additive to the main lithium salt is less than 1. The mass ratio of the sulfide ceramic filler to the polymer matrix is ​​(1:20) to (1:3), preferably (1:10) to (1:5).

[0045] This invention also provides a method for preparing the composite solid electrolyte as described in any of the preceding claims, comprising the following steps: S1. Mix the polymer matrix, main lithium salt, nitrile-containing lithium salt additive, and sulfide ceramic filler in a solvent to form a slurry. The solvent is selected from acetonitrile or N,N-dimethylformamide. Before adding the sulfide ceramic filler, the nitrile-containing lithium salt additive can be mixed with the main lithium salt in the solvent. Specifically, add the polymer matrix, main lithium salt, and nitrile-containing lithium salt additive to 15-25 mL of solvent, dissolve them completely, and then add the sulfide ceramic powder.

[0046] S2. Form the slurry into a film. Specifically, use magnetic stirring at 900-1500 rpm for more than 24 hours, and cast the resulting slurry into a film.

[0047] S3. Remove the solvent to obtain the composite solid electrolyte. Specifically, the solvent is dried in a high-purity argon glove box (H2O<0.01ppm, O2<0.2ppm) at a temperature range of 30-40°C for more than 24 hours to evaporate the solvent. Then, the composite solid electrolyte is evacuated in a vacuum-sealed chamber at -0.1 MPa for more than 24 hours to completely evaporate the solvent, thus obtaining the composite solid electrolyte.

[0048] By utilizing the interaction between the nitrile functional group (-CN) in nitrile-containing lithium salts and the lithium ion sites on the surface of sulfide ceramics, a stable coordination layer is formed in situ on the surface of ceramic particles. This effectively suppresses interfacial side reactions between sulfide ceramics and other lithium salts, inhibits the formation of harmful byproducts such as polysulfides, and thus improves the ionic conductivity and interfacial stability of the composite solid electrolyte.

[0049] This invention also provides a battery comprising: a positive electrode, a negative electrode, and a composite solid electrolyte as described in any of the preceding embodiments, disposed between the positive electrode and the negative electrode. The negative electrode is a lithium metal negative electrode or a lithium metal-containing alloy negative electrode. The active material of the positive electrode is selected from at least one of sulfur (S), lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4).

[0050] This invention also provides an all-solid-state lithium metal battery, comprising a composite solid-state electrolyte as described in any of the preceding embodiments and a lithium metal anode.

[0051] The following describes specific embodiments of the present invention.

[0052] Example 1: This embodiment provides an LPSC sulfide ceramic-based PEO composite solid electrolyte with LiTCM as an additive, wherein the mass ratio of the polymer matrix PEO to the sulfide ceramic filler LPSC is approximately 7.1:1. It is prepared according to the following steps:

[0053] 1. Dissolve 0.1 mmol LiTCM completely in 15-25 mL of acetonitrile to obtain an acetonitrile solution containing LiTCM.

[0054] 2. Add 0.9 mmol of LiTFSI to an acetonitrile solution containing LiTCM and stir for 2 hours until fully dissolved.

[0055] 3. Add 0.1080 g of LPSC sulfide ceramic to an acetonitrile solution containing LiTCM and stir for 2 hours. Compared with the blue suspension without LiTCM, the addition of LiTCM yields a gray suspension (the intrinsic color of sulfide ceramic).

[0056] 4. Add 0.768 g of PEO matrix to the gray suspension, stir for 24 h, and cast into a film.

[0057] 5. Place the suspension containing the PEO matrix into a polytetrafluoroethylene culture dish, dry it in a high-purity argon glove box (H2O<0.01ppm, O2<0.2ppm) at a temperature range of 30-40 °C for more than 24 hours to allow the solvent to evaporate, and then evacuate it in a vacuum-sealed chamber at -0.1MPa for more than 24 hours to obtain the composite solid electrolyte.

[0058] Example 2: The difference between Example 2 and Example 1 is that the LiTCM substance is replaced with LiDCA lithium salt additive, while the remaining steps are the same as in Example 1.

[0059] Example 3: The difference between Example 3 and Example 1 is that the LiTCM substance is replaced with LiTDI lithium salt additive, and the remaining steps are the same as in Example 1.

[0060] Example 4: The difference between Example 4 and Example 1 is that the LiTCM substance is replaced with a LiDCTA lithium salt additive, while the remaining steps are the same as in Example 1.

[0061] Example 5: This embodiment provides a method for assembling a full battery and a symmetrical battery, which is assembled according to the following steps: 1. Preparation of positive electrode slurry: First, weigh 100 mg of PVDF (binder) and place it in a stirred flask. Add 1 mL of NMP (N-methylpyrrolidone) and stir on a small stirrer for 1 hour until the PVDF is completely dissolved. Then add 100 mg of Super P (conductive carbon black) and 1 mL of NMP, stir at room temperature for 1 hour, add 800 mg of composite sulfur (S) active material and 1.5 mL of NMP, and stir at room temperature for more than 6 hours.

[0062] 2. Preparation of positive electrode: The obtained positive electrode slurry is coated on aluminum foil, dried at 80 ℃ for more than 6 hours, and cut into circular pieces with a diameter of 12 mm to obtain S positive electrode. It is then placed in a vacuum oven at 120 ℃ for 6 hours for storage.

[0063] 3. Prepare a composite solid electrolyte and cut it into discs with a diameter of 19 mm.

[0064] 4. Following the full-cell assembly process, the S positive electrode, the PEO-LPSC-LiTFSI0.9LiTCM0.1 composite solid electrolyte membrane prepared in Example 1, and lithium metal (diameter 15.6 mm) were assembled into a 2032 type full cell.

[0065] 5. According to the symmetric battery assembly process, the PEO-LPSC-LiTFSI0.9LiTCM0.1 composite solid electrolyte membrane prepared in Example 1 was sandwiched between two layers of lithium metal (with diameters of 12.5 and 15.6 mm respectively) to assemble a lithium-lithium symmetric battery.

[0066] Example 6: The difference between Example 6 and Example 1 is that the PEO polymer matrix was replaced by PAN, and N,N-dimethylformamide was used as the solvent during preparation, and the remaining steps were the same as those in Example 1.

[0067] Example 7: The difference between Example 7 and Example 1 is that the PEO polymer matrix was replaced by PVDF, and dimethylformamide was used as the solvent during preparation, and the remaining steps were the same as those in Example 1.

[0068] Example 8: The difference between Example 8 and Example 1 is that the main lithium salt LiTFSI was replaced by LiFSI, and the remaining steps were the same as those in Example 1.

[0069] Example 9: The difference between Example 9 and Example 1 is that the main lithium salt LiTFSI was replaced by LiClO4, and the remaining steps were the same as those in Example 1.

[0070] Example 10: The difference between Example 10 and Example 1 is that the main lithium salt LiTFSI was replaced by LiPF6, and the remaining steps were the same as those in Example 1.

[0071] Example 11: The difference between Example 11 and Example 1 is that the main lithium salt LiTFSI was replaced by LiBF4, and the remaining steps were the same as those in Example 1.

[0072] Example 12: The difference between Example 12 and Example 1 is that the main lithium salt LiTFSI was replaced by xLiTFSI+(1-x)LiI (0<x<1), and the remaining steps were the same as those in Example 1.

[0073] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that no nitrile-containing additive was added, LiTFSI was 1 mmol, and the remaining steps were the same as those in Example 1.

[0074] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that no nitrile-containing additives are added, the main lithium salt LiTFSI is replaced with a mixture of LiTFSI and LiI, the total amount of LiTFSI and LiI is 1 mmol, and the remaining steps are the same as in Example 1.

[0075] Comparative Example 3: The difference between Comparative Example 3 and Example 5 is that the composite solid electrolyte prepared in Comparative Example 1 was used to assemble the full cell and the symmetric cell, while the remaining steps were the same as in Example 5.

[0076] Adding nitrile-based lithium salt additives can reduce the spontaneous diffusion of lithium ions at the interface and the resulting structural evolution, thus ensuring that the structure of the interface and the bulk LPSC remains consistent. Figure 1a This is a solid-state nuclear magnetic resonance phosphorus spectrum (ssNMR) of a composite solid electrolyte without the addition of nitrile-based lithium salt additives, which is not found in existing technologies. Figure 1b This is the solid-state nuclear magnetic resonance phosphorus spectrum (ssNMR) of the composite solid electrolyte in Example 1 of this invention, which effectively reveals that the main component of the interface is PS4. 3- Only a small number of P2S7 2- The structure was improved, and side reactions were greatly suppressed. Figure 2 The X-ray photoelectron spectrum after adding a nitrile-containing lithium salt additive shows that TCM can be detected. – It adsorbs onto the surface of LPSC and forms a stable coordination layer. Figure 3 This is a scanning electron microscope (SEM) morphology image of the composite solid electrolyte in Example 1. Figure 3 It can be observed that PEO-LPSC-LiTFSI0.9LiTCM0.1 is a dense composite solid electrolyte. Figure 4 This is the elemental distribution diagram of the composite solid electrolyte in Example 1, where LPSC is uniformly dispersed in the PEO-LPSC-LiTFSI0.9LiTCM0.1 composite electrolyte. Figure 5 This is a temperature-dependent ionic conductivity diagram of a composite solid electrolyte without the addition of nitrile-based lithium salt additives in the prior art. The ionic conductivity of the PEO-LPSC-LiTFSI composite solid electrolyte membrane is ~10. –5 Scm –1 (60 °C), the activation energies in the high-temperature region and the low-temperature region are 0.306 eV and 0.508 eV, respectively. Figure 6 This is a temperature-dependent ionic conductivity diagram of the composite solid electrolyte in Example 1. The ionic conductivity of the PEO-LPSC-LiTFSI0.9LiTCM0.1 composite solid electrolyte membrane is 5.48 × 10⁻⁶. –4 S cm –1At 60 °C, the activation energies in the high-temperature and low-temperature regions were 0.187 eV and 0.457 eV, respectively. This is attributed to the fact that after LiTCM suppresses interfacial side reactions, the ion conductivity of the LPSC sulfide ceramic is maintained, and the interfacial ion transport resistance is reduced.

[0077] Following the full-cell assembly process, a full cell based on a PEO-LPSC-LiTFSI0.9LiTCM0.1 and a PEO-LPSC-LiTFSI composite solid electrolyte membrane was fabricated. Figure 7 This is a comparison curve of the cycling performance of the full cell assembled in Example 5 based on the electrolyte membrane of Example 1 and the full cell assembled in Comparative Example 3 based on the electrolyte membrane of Comparative Example 1. As can be seen from the figure, the full cell assembled with PEO-LPSC-LiTFSI0.9LiTCM0.1 as the S cathode and lithium metal anode still exhibits a capacity of 1101 mAh / g at room temperature and a current density of 0.2C, which is higher than the 320 mAh / g capacity of PEO-LPSC-LiTFSI. It also exhibits higher discharge capacity and stability than PEO-LPSC-LiTFSI after 300 cycles at room temperature and a current density of 0.2C. This is attributed to the increased conductivity of the composite electrolyte by suppressing interfacial side reactions through LiTCM, thus improving the electrochemical performance of the full cell using PEO-LPSC-LiTFSI0.9LiTCM0.1 as the electrolyte.

[0078] Following the assembly process of symmetric cells, a lithium-lithium symmetric cell based on a PEO-LPSC-LiTFSI0.9LiTCM0.1 and a PEO-LPSC-LiTFSI composite solid electrolyte membrane was fabricated. Figure 8 This is a comparison curve of the cycle performance of the symmetric battery assembled in Example 5 based on the electrolyte membrane of Example 1 and the symmetric battery assembled in Comparative Example 3 based on the electrolyte membrane of Comparative Example 1. The results show that the lithium-lithium symmetric battery assembled with PEO-LPSC-LiTFSI0.9LiTCM0.1 matched lithium metal achieves good cycle performance at 0.1 mA / cm². 2 Current density, 0.1 mAh / cm 2 At the deposition capacity, it can cycle stably for 2500 hours, exhibiting a lower polarization voltage and longer cycle life compared to PEO-LPSC-LiTFSI. Because LiTCM alleviates interfacial side reactions between the two phases within the electrolyte, reduces the formation of products such as Li4P2S7 and Li2S and their side reactions at the lithium metal battery interface, it improves the electrochemical stability of the electrode-electrolyte interface, thereby enhancing the electrochemical performance of the composite electrolyte.

[0079] The embodiments of the present invention have the following beneficial effects: During the preparation of LPSC sulfide ceramic composite electrolyte, the sulfide ceramic undergoes an interfacial reaction, as shown in the following equation:

[0080] Due to the strong interaction between the main lithium salt and lithium ions in LPSC, lithium ions continuously migrate from the LPSC sulfide ceramic into the polymer matrix. 3– The framework structure collapsed and formed a P2S7-containing structure at the interface. 4– At the interface, the ionic conductivity of the composite solid electrolyte decreases. TCM containing nitrile-based lithium salt additives... – The unique planar molecular structure enables -CN to form multidentate coordination with lithium ions on the sulfide ceramic surface, but TCM – The interaction with lithium ions is weaker, reducing spontaneous lithium ion migration and the formation of interfacial byproducts. This results in a more complete structure, effectively regulating the interfacial chemistry between the LPSC sulfide ceramic and the polymer matrix, fundamentally suppressing interfacial side reactions. The structure of the two-phase interface is consistent with the bulk interface structure, both being PS4. 3– The framework structure improves the overall electrochemical stability of the composite solid electrolyte and provides a new solution for the practical application of sulfide ceramic-based composite solid electrolytes.

[0081] The composite solid electrolyte provided in this embodiment has high lithium salt dissociation, high ionic conductivity and ion transference number, as well as excellent interfacial stability. It achieves a synergistic improvement in ion transport performance and long-term cycling stability, effectively overcoming the bottleneck problem of performance in traditional sulfide ceramic-based composite solid electrolytes.

[0082] The preparation method in this embodiment is simple, operates under mild conditions, and is cost-controllable. The raw materials involved are widely available, exhibiting strong scalability and engineering adaptability, which is conducive to promoting the development of solid-state battery technology towards large-scale manufacturing. The nitrile-based lithium salt additives are diverse in type and have a wide range of applications, compatible with various polymer matrices and sulfide ceramic systems, demonstrating good versatility and providing flexible material selection space for the diversified design of composite solid-state electrolytes.

[0083] The composite solid electrolyte in this embodiment has good interfacial compatibility with the lithium metal anode and sulfur cathode. The assembled full cell exhibits stable cycle performance, verifying the reliability and practical value of the electrolyte system in actual battery application scenarios.

[0084] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several equivalent substitutions or obvious modifications can be made without departing from the concept of the present invention, and all such modifications, achieving the same performance or application, should be considered within the scope of protection of the present invention.

Claims

1. A composite solid electrolyte, characterized in that, include: The invention comprises a polymer matrix, a sulfide ceramic filler, a main lithium salt, and a nitrile-based lithium salt additive; wherein the nitrile-based lithium salt additive is used to form an interface passivation layer on the surface of the sulfide ceramic filler to suppress interfacial side reactions between the sulfide ceramic filler and the polymer matrix and / or the main lithium salt.

2. The composite solid electrolyte according to claim 1, characterized in that, The sulfide ceramic filler is selected from Li6PS5Cl or has the general formula Li 6-y PS 5-y X 1+y At least one of the sulfide ceramics, wherein X is selected from F, Br or I, and 0 < y < 1.

3. The composite solid electrolyte according to claim 1 or 2, characterized in that, The polymer matrix is ​​selected from at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF).

4. The composite solid electrolyte according to claim 1 or 2, characterized in that, The main lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium iodide (LiI).

5. The composite solid electrolyte according to claim 1 or 2, characterized in that, The nitrile-containing lithium salt additive is selected from at least one of lithium dicyandiamide (LiDCA), lithium tricyanomethane (LiTCM), lithium tetracyanoborate (LiTCB), lithium difluoro(1,1,2,2-tetracyano-1,2-dioxoethyl)borate (LiDFTCB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), and lithium 4,5-dicyano-1,2,3-triazole (LiDCTA).

6. The composite solid electrolyte according to claim 1, characterized in that, The molar ratio of lithium ions in the main lithium salt to complexing groups in the polymer matrix is ​​1:16 to 1:10; the content of the nitrile-containing lithium salt additive accounts for 10% to 30% of the molar amount of the main lithium salt.

7. A method for preparing a composite solid electrolyte according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix the polymer matrix, main lithium salt, nitrile-containing lithium salt additive and sulfide ceramic filler in a solvent to form a slurry; S2. The slurry is formed into a film; S3. Remove the solvent to obtain the composite solid electrolyte.

8. The preparation method according to claim 7, characterized in that, In step S1, before adding the sulfide ceramic filler, the nitrile-containing lithium salt additive is mixed with the main lithium salt in a solvent.

9. The preparation method according to claim 7 or 8, characterized in that, The solvent is selected from acetonitrile or N,N-dimethylformamide.

10. A battery, characterized in that, It comprises: a positive electrode, a negative electrode, and a composite solid electrolyte as described in any one of claims 1 to 6 disposed between the positive electrode and the negative electrode.

11. The battery according to claim 10, characterized in that, The negative electrode is a lithium metal negative electrode or a lithium metal alloy negative electrode.

12. The battery according to claim 10 or 11, characterized in that, The active material of the positive electrode is selected from at least one of sulfur (S), lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4).

13. An all-solid-state lithium metal battery, characterized in that, It comprises a composite solid electrolyte as described in any one of claims 1 to 6 and a lithium metal anode.

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