Organic lithium salt containing cyano group as well as preparation method and application of organic lithium salt

Abstract

The invention discloses an organic lithium salt containing a cyano group and a preparation method and application thereof, the organic lithium salt containing the cyano group is used as a composite solid electrolyte additive, and the additive is uniformly dispersed in a polyethylene oxide (PEO) matrix to disturb regular arrangement of a polymer chain, so that the crystallinity of the polymer chain is reduced; the movement capability of a polymer chain segment is enhanced; the cyano group has high charge density and linear structure, can provide strong electrostatic attraction and space accessibility, has strong polarity and coordination ability, can significantly change the coordination environment of lithium ions, promotes dissociation and migration of the lithium ions, and improves the ionic conductivity and migration number of the solid electrolyte. Furthermore, as a lithium-containing additive, active lithium loss caused by a solid electrolyte interface (SEI) film formed on the surface of a negative electrode of the battery during first-cycle charging can be compensated, so that the first coulombic efficiency of the battery is improved; the introduction of cyano group also improves the oxidation resistance of molecules, and is beneficial to improving the cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, specifically to an organic lithium salt containing a cyano group, its preparation method, and its application. Background Technology

[0002] Current lithium-ion batteries primarily use liquid electrolytes as ion migration channels, often referred to as the "blood" of the battery. In practical applications, their energy density approaches the theoretical performance limit, while liquid chemical systems are prone to problems such as separator puncture or electrolyte combustion, leading to short circuits and thermal runaway. The core change in solid-state batteries is that solid electrolytes replace both the separator and the electrolyte. Using solid electrolytes can significantly improve the energy density, intrinsic safety, and low-temperature performance of the battery system. Solid-state batteries are considered the ultimate replacement for liquid batteries and have long-term technological development potential.

[0003] Polyethylene oxide (PEO)-based solid electrolytes have attracted widespread research attention due to their significant flexibility and plasticity, which ensures robust electrode-electrolyte contact. Furthermore, PEO is easy to form and process, facilitating integration with existing conventional battery production lines without additional modification costs. However, despite these advantages, PEO-based solid electrolytes still face significant challenges, such as low ionic conductivity at room temperature and limited electrochemical stability at the solid-solid interface, which hinder their practical application in battery systems. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide an organolithium salt containing a cyano group, its preparation method and application, so as to solve the problems of low ionic conductivity and limited electrochemical stability of PEO-based solid electrolytes at room temperature.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an organolithium salt containing a cyano group, the general structural formula of which is as follows:

[0007] Li-O-(CH2) n -CN, where n is a positive integer from 1 to 5.

[0008] Secondly, the present invention provides a method for preparing an organolithium salt, which specifically includes the following steps:

[0009] Under an inert protective atmosphere, hydroxynitrile raw material was added to anhydrous tetrahydrofuran and stirred until the solution became transparent. LiH was then added and the reaction was stirred for 15 hours. The solid was filtered and collected, and then vacuum dried to obtain the organolithium salt.

[0010] The hydroxynitrile raw material has the general structural formula HO-(CH2). n -CN, where n is a positive integer from 1 to 5; the molar ratio of the hydroxynitrile to LiH is (1 to 1.5):1.

[0011] Thirdly, the present invention provides a composite solid electrolyte, which is composed of a polymer matrix, a lithium salt and an additive; the additive is the above-mentioned organic lithium salt or an organic lithium salt obtained by the above preparation method; the amount of the additive is 1% to 15% of the total mass of the composite solid electrolyte, calculated by mass percentage.

[0012] Preferably, the polymer matrix is ​​polyethylene oxide, and the molecular weight (Mv) of the polyethylene oxide is 500,000 to 700,000.

[0013] Preferably, the lithium salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalate borate, and lithium difluorooxalate phosphate.

[0014] Fourthly, the present invention provides a method for preparing a composite solid electrolyte, which specifically includes the following steps:

[0015] Step 1: Under an inert protective atmosphere, the polymer matrix and lithium salt are added to anhydrous acetonitrile and mixed thoroughly to obtain mixture I; wherein, the amounts of polymer matrix and lithium salt are in the molar ratio [EO]:Li + =10~20, the mass ratio of anhydrous acetonitrile to the total mass of polymer matrix and lithium salt is 6~12;

[0016] Step 2: Add additives to mixture I obtained in step 1, and mix evenly at 40℃~60℃ to obtain mixture II;

[0017] Step 3: Pour the mixture II obtained in Step 2 into a mold and dry it under vacuum or inert protective atmosphere until the anhydrous acetonitrile is completely evaporated to obtain a film-like composite solid electrolyte.

[0018] Preferably, the thickness of the composite solid electrolyte is 0.4 mm to 0.6 mm.

[0019] Preferably, the drying temperature is 50℃~60℃ and the drying time is 12h~24h.

[0020] Fifthly, the present invention provides a lithium battery having the above-described composite solid electrolyte or the composite solid electrolyte prepared by the above-described preparation method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The cyano-containing organic lithium salt additive of the present invention exhibits excellent comprehensive performance enhancement in PEO-based composite solid electrolytes. As a functional filler, this additive achieves uniform dispersion in the polymer matrix, effectively disrupting the regular arrangement of PEO molecular chains, significantly reducing the crystallinity of the polymer, and greatly enhancing the mobility of polymer chain segments. This effectively lowers the migration barrier of lithium ions in the electrolyte, fundamentally optimizing the lithium ion transport kinetics. The cyano group, with its unique high charge density and linear molecular configuration, provides strong electrostatic attraction and excellent spatial accessibility. Its strong polarity and coordination ability can significantly alter the coordination environment of lithium ions in the polymer system, effectively promoting the dissociation process of lithium salts and accelerating the migration rate of lithium ions. In addition, as a lithium-containing functional component, this additive can effectively compensate for the active lithium ions consumed during the formation of the solid electrolyte interface film on the negative electrode surface during the first charge of the battery, thereby significantly improving the first charge-discharge coulombic efficiency of the battery. At the same time, the introduction of cyano groups also significantly enhances the antioxidant stability of the molecular structure, effectively broadens the electrochemical window of the electrolyte, and greatly improves the structural stability and performance retention of the battery during long-term cycling.

[0023] 2. This invention employs a simple one-step substitution reaction to synthesize cyano-containing organic lithium salts. The process is concise and efficient, with mild reaction conditions and low raw material costs. Furthermore, the entire preparation process is environmentally friendly, generating no harmful byproducts. High-quality solid electrolyte membranes can be prepared by combining this additive with a PEO matrix using a solution casting method. The process exhibits strong compatibility and is easily scalable for mass production. This composite solid electrolyte not only possesses excellent ionic conductivity and a wide electrochemical stability window but also demonstrates superior interfacial stability and the ability to suppress lithium dendrite growth, effectively improving the safety performance and cycle life of solid-state batteries. This invention provides an innovative solution to address the key technical bottlenecks of current polymer solid electrolytes in terms of room temperature ionic conductivity, interfacial compatibility, and cycle stability, possessing significant industrial application value and broad market prospects. Attached Figure Description

[0024] Figure 1 The NMR carbon spectrum of lithium 3-hydroxypropionitrile prepared in Example 1 of this invention is shown.

[0025] Figure 2 The image shows the FTIR spectra of lithium 3-hydroxypropionitrile and 3-hydroxypropionitrile prepared in Example 1 of this invention.

[0026] Figure 3 This is a SEM image of lithium 3-hydroxypropionitrile prepared in Example 1 of this invention.

[0027] Figure 4The images show cross-sectional SEM images and elemental distribution images of the PEO-based composite solid electrolyte containing lithium 3-hydroxypropionitrile prepared in Example 1 of this invention.

[0028] Figure 5 The electrochemical impedance spectroscopy of the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention is shown.

[0029] Figure 6 The image shows the linear sweep voltammetry curves of the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention.

[0030] Figure 7 The lithium-ion transference number is the PEO-based composite solid electrolyte containing 3-hydroxypropionitrile lithium salt prepared in Example 1 of this invention.

[0031] Figure 8 The lithium-ion transference number is the PEO-based solid electrolyte prepared in Comparative Example 1 of this invention.

[0032] Figure 9 The Li / / Li symmetric cells assembled using the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention achieve a speed of 0.1 mA / cm². 2 0.1mAh / cm 2 Voltage-time curve under the following conditions.

[0033] Figure 10 The graph shows the cycling performance of lithium batteries assembled with PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention at 0.5C under a voltage range of 2.5V-3.8V at 60℃.

[0034] Figure 11 The graph shows the cycling performance of lithium batteries assembled with PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention at 1.0C under a voltage range of 2.5V-3.8V and a temperature of 60°C. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0036] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0037] I. An organolithium salt containing a cyano group

[0038] The general structural formula of the organolithium salt described in this invention is as follows: Li-O-(CH2) n -CN, where n is a positive integer from 1 to 5.

[0039] This invention innovatively designs Li-O-(CH2) n Organic lithium salts with a -CN (n = 1-5) structure ingeniously integrate cyano groups and lithium-ion transport functionality into a single molecular structure by precisely controlling the methylene chain length. This design fully utilizes the high charge density and linear molecular configuration of the cyano group, enabling it to provide strong electrostatic attraction and excellent spatial accessibility in the polymer matrix. This significantly alters the coordination environment of lithium ions, effectively promoting lithium salt dissociation and ion migration, thereby fundamentally solving the key problem of slow lithium-ion transport kinetics in traditional polymer electrolytes. Therefore, the organic lithium salt described in this invention is selected from one of 3-hydroxypropionitrile lithium salt, 4-hydroxybutyronitrile lithium salt, and 5-hydroxypentanitrile lithium salt.

[0040] II. A method for preparing an organolithium salt

[0041] The preparation of the organic lithium salt of the present invention specifically includes the following steps:

[0042] Under an inert protective atmosphere, hydroxynitrile raw material was added to anhydrous tetrahydrofuran and stirred until the solution became transparent. LiH was then added and the reaction was stirred for 15 hours. The solid was filtered and collected, and then vacuum dried to obtain the organolithium salt.

[0043] The hydroxynitrile raw material has the general structural formula HO-(CH2). n -CN, where n is a positive integer from 1 to 5; the molar ratio of the hydroxynitrile to LiH is (1 to 1.5):1.

[0044] This invention employs a simplified one-step substitution reaction route, achieving efficient synthesis under mild conditions by precisely controlling the molar ratio of hydroxynitriles to lithium hydride in a strictly controlled inert atmosphere. This preparation method eliminates traditional complex processes, avoids toxic reagents and harsh reaction conditions, and only requires conventional stirring, filtration, and vacuum drying steps to obtain high-purity products. This preparation method not only significantly reduces production costs and energy consumption but also ensures the environmental friendliness of the product and the reproducibility of the process, laying a solid foundation for large-scale industrial production. Therefore, the molar ratio of hydroxynitriles to LiH can be 1:1, 1.2:1, 1.3:1, 1.5:1, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in the embodiments, any of the above ranges can be combined with any other range.

[0045] III. A composite solid electrolyte

[0046] The composite solid electrolyte of the present invention is composed of a polymer matrix, a lithium salt and an additive; the additive is the above-mentioned organic lithium salt or the organic lithium salt obtained by the above preparation method; the amount of additive is 1% to 15% of the total mass of the composite solid electrolyte, calculated by mass percentage.

[0047] This invention designs a composite system using polyethylene oxide with a specific molecular weight (Mv = 500,000–700,000) as the matrix, preferably high-performance lithium salts such as lithium bis(fluorosulfonyl)imide, and innovatively introduces 1%–15% of cyano-containing organic lithium salts as multifunctional additives. This invention unexpectedly discovered that the formulation fully considers the synergistic effects between the components, enabling the additives to achieve molecular-level uniform dispersion in the polymer matrix, effectively disrupting the regular arrangement of PEO chains, significantly reducing crystallinity, and enhancing chain segment mobility. This structural design not only optimizes ion transport channels but also regulates lithium-ion migration behavior through the strong coordination effect of cyano groups, achieving a perfect balance between ionic conductivity and mechanical properties. Therefore, the percentage of additives in the total mass of the composite solid electrolyte can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., as well as all ranges and subranges between these values. It should be understood that, in the implementation plan, any of the above scopes can be combined with any other scopes.

[0048] In some embodiments of the present invention, the polymer matrix is ​​polyethylene oxide, and the molecular weight Mv of the polyethylene oxide is 500,000 to 700,000.

[0049] In some embodiments of the present invention, the lithium salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

[0050] IV. A method for preparing a composite solid electrolyte

[0051] The present invention prepares the above-mentioned composite solid electrolyte by means of the following steps:

[0052] Step 1: Under an inert protective atmosphere, the polymer matrix and lithium salt are added to anhydrous acetonitrile and mixed thoroughly to obtain mixture I; wherein, the amounts of polymer matrix and lithium salt are in the molar ratio [EO]:Li + =10~20, the mass of anhydrous acetonitrile: the total mass of the polymer matrix and lithium salt is 6~12;

[0053] Step 2: Add additives to mixture I obtained in step 1, and mix evenly at 40℃~60℃ to obtain mixture II;

[0054] Step 3: Pour the mixture II obtained in Step 2 into a mold and dry it under vacuum or inert protective atmosphere until the anhydrous acetonitrile is completely evaporated to obtain a film-like composite solid electrolyte.

[0055] In some embodiments of the present invention, the thickness of the composite solid electrolyte is 0.4 mm to 0.6 mm.

[0056] In some embodiments of the present invention, the drying temperature is 50°C to 60°C and the drying time is 12h to 24h.

[0057] V. A lithium battery

[0058] The lithium battery of the present invention has the above-described composite solid electrolyte or the composite solid electrolyte prepared by the above-described preparation method.

[0059] VI. Examples and Comparative Examples

[0060] Example 1

[0061] Step 1: Add 1.08 g of 3-hydroxypropionitrile to 30 mL of anhydrous tetrahydrofuran at room temperature, place it in a glove box (H2O<0.1ppm, O2<0.1ppm) under argon atmosphere and stir for 15 min. Add 0.118 g of LiH powder, stir at room temperature for 15 h, filter, and then vacuum dry the obtained solid at 150 °C for 6 h to obtain lithium 3-hydroxypropionitrile.

[0062] Step 2: Mix 0.5g PEO and 0.18g LiTFSI (molar ratio [EO]:Li) + =18:1) Dissolved in 6 mL of anhydrous acetonitrile, stirred thoroughly at 60 °C for 6 h, then 0.0756 g of the 3-hydroxypropionitrile lithium salt prepared in step 1 was added, followed by 3 mL of anhydrous acetonitrile. After stirring at 60 °C for 6 h, it was poured into a shallow polytetrafluoroethylene mold (φ70 mm deep, 0.5 mm deep) and then dried at 60 °C for 12 h under argon atmosphere to obtain a composite solid electrolyte membrane;

[0063] Step 3: Cut the composite solid electrolyte membrane prepared in Step 2 into 18mm round slices using a slicer;

[0064] Step 4: Assemble the positive electrode shell, LFP positive electrode sheet, composite solid electrolyte membrane disc obtained in Step 3, lithium sheet, stainless steel gasket, spring sheet and negative electrode shell into a battery in sequence.

[0065] Example 2

[0066] Step 1: Add 1.33g of 4-hydroxybutyronitrile to 30mL of anhydrous tetrahydrofuran at room temperature, place it in a glove box (H2O<0.1ppm, O2<0.1ppm) under argon atmosphere and stir for 15min. Add 0.118g of LiH powder, stir at room temperature for 15h, filter, and then vacuum dry the obtained solid at 150℃ for 6h to obtain lithium 4-hydroxybutyronitrile.

[0067] Step 2: Mix 0.5g PEO, 0.035g LiFSI and 0.163g LiTFSI (molar ratio [EO]:Li) + =15:1) Dissolved in 6 mL of anhydrous acetonitrile, stirred thoroughly at 40 °C for 7 h, then 0.069 g of the 4-hydroxybutyronitrile lithium salt prepared in step 1 was added, followed by 4 mL of anhydrous acetonitrile. After stirring at 40 °C for 8 h, it was poured into a shallow polytetrafluoroethylene mold (φ80 mm deep, 0.5 mm deep) and then dried at 60 °C for 15 h under argon atmosphere to obtain a composite solid electrolyte membrane;

[0068] Step 3: Cut the composite solid electrolyte membrane prepared in Step 2 into 18mm round slices using a slicer;

[0069] Step 4: Assemble the positive electrode shell, LCO positive electrode sheet, composite solid electrolyte membrane disc obtained in Step 3, lithium sheet, stainless steel gasket, spring sheet and negative electrode shell into a battery in sequence.

[0070] Example 3

[0071] Step 1: Add 1.54 g of 5-hydroxypentanilide to 30 mL of anhydrous tetrahydrofuran at room temperature, place it in a glove box (H2O<0.1ppm, O2<0.1ppm) under argon atmosphere and stir for 15 min. Add 0.118 g of LiH powder, stir at room temperature for 15 h, filter, and then vacuum dry the obtained solid at 150 °C for 6 h to obtain 5-hydroxypentanilide lithium salt.

[0072] Step 2: Add 0.6g PEO, 0.163g LiTFSI, 0.041g LiODFB and 0.0715g LiODFP (molar ratio [EO]:Li) + =12:1) Dissolved in 10mL of anhydrous acetonitrile, stirred thoroughly at 50℃ for 8h, then 0.076g of the 5-hydroxypentanonitrile lithium salt prepared in step 1 was added, followed by 5mL of anhydrous acetonitrile. After stirring at 50℃ for 10h, it was poured into a φ90mm shallow polytetrafluoroethylene mold (0.55mm deep), and then dried at 55℃ for 24h under argon atmosphere to obtain a composite solid electrolyte membrane;

[0073] Step 3: Cut the composite solid electrolyte membrane prepared in Step 2 into 18mm round slices using a slicer;

[0074] Step 4: Assemble the positive electrode shell, NCM811 positive electrode sheet, composite solid electrolyte membrane disc obtained in Step 3, lithium sheet, stainless steel gasket, spring sheet and negative electrode shell into a battery in sequence.

[0075] Comparative Example 1

[0076] Compared with Example 1, Comparative Example 1 lacks the cyano-containing organic lithium salt additive. The specific scheme is as follows:

[0077] Step 1: Mix 0.5g PEO and 0.18g LiTFSI (molar ratio [EO]:Li) + =18:1) Dissolved in 9 mL of anhydrous acetonitrile, stirred thoroughly at 60 °C for 12 h, then poured into a shallow polytetrafluoroethylene mold (0.5 mm deep) with a diameter of 70 mm, and then dried at 60 °C for 12 h under argon atmosphere to obtain a composite solid electrolyte membrane;

[0078] Step 2: Cut the PEO-based solid electrolyte membrane prepared in Step 1 into 18mm round slices using a slicer;

[0079] Step 3: Assemble the positive electrode shell, LFP positive electrode sheet, PEO-based solid electrolyte membrane disc obtained in Step 2, lithium sheet, stainless steel gasket, spring sheet and negative electrode shell into a battery in sequence.

[0080] VII. Performance Testing

[0081] 1. Product Characterization

[0082] The 3-hydroxypropionitrile lithium salt prepared in Example 1 was subjected to nuclear magnetic resonance (NMR) carbon spectrum analysis using deuterated methanol (MeOD) as the solvent. The results are as follows: Figure 1 As shown, the 3-hydroxypropionitrile lithium salt prepared in Example 1 contains three types of carbon, corresponding to the three chemical shift positions of the three types of carbon in 3-hydroxypropionitrile.

[0083] Fourier transform infrared (FTIR) spectroscopy was performed on the 3-hydroxypropionitrile lithium salt prepared in Example 1, and the results are as follows: Figure 2 As shown, the 3-hydroxypropionitrile lithium salt prepared in Example 1 was subjected to a temperature of 2253 cm⁻¹. -1 A distinct vibrational peak of the cyano (-CN) group appears at 1080 cm⁻¹. -1 A vibrational peak for the -CO bond appears at 3200-3600 cm⁻¹, but no peak for the hydroxyl group of an alcohol appears in the 3200-3600 cm⁻¹ range. -1 The broad and strong OH stretching vibration peaks within the range indicate that Li in LiH + Substituting the H in -OH; lithium 3-hydroxypropionitrile in the spectrum at 3625 cm⁻¹. -1The sharp free -OH vibration peak generated is due to the absorption of moisture from the air by the sample during testing. This indicates that the 3-hydroxypropionitrile lithium salt prepared in Example 1 conforms to the general structural formula of the organolithium salts described in this invention; the organolithium salts prepared in Examples 2 and 3, after the above characterization, also conform to the general structural formula of the organolithium salts described in this invention.

[0084] The lithium 3-hydroxypropionitrile prepared in Example 1 was tested by scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown, the 3-hydroxypropionitrile lithium salt prepared in Example 1 has a small particle size, is relatively fluffy, and is easy to disperse.

[0085] The PEO-based composite solid electrolyte membrane containing lithium 3-hydroxypropionitrile salt prepared in Example 1 was subjected to cross-sectional SEM and energy-dispersive X-ray spectroscopy (EDS) mapping tests, and the results are as follows: Figure 4 As shown, the thickness of the composite solid electrolyte membrane is approximately 187.6 μm, and the N element is relatively uniformly distributed, indicating that the 3-hydroxypropionitrile lithium salt is uniformly dispersed in the polymer matrix.

[0086] 2. Electrochemical performance

[0087] Since the electrochemical performance of Examples 2 and 3 is not significantly different from that of Example 1, the electrochemical performance will be explained using Example 1 as an example.

[0088] (1) Electrochemical impedance spectroscopy

[0089] Electrochemical impedance spectroscopy was performed on the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1. The results are as follows: Figure 5 As shown, the impedance of the composite solid electrolyte containing lithium 3-hydroxypropionitrile salt prepared in Example 1 is 8.37 Ω, and its ionic conductivity is calculated to be 1.02 × 10⁻⁶. -3 S / cm, compared to Comparative Example 1 (24.12Ω, 0.401×10 -3 The S / cm ratio was increased by 2.5 times. This significant technological advancement effectively solves the industry problem of low room-temperature ionic conductivity in PEO-based solid electrolytes, demonstrating outstanding practical value and industrialization prospects. Simultaneously, this also proves that the uniform dispersion of cyano-containing organic lithium salts in a PEO matrix effectively disrupts the regular arrangement of polymer chains through steric hindrance, reducing crystallinity, enhancing polymer chain segment mobility, and lowering the lithium-ion migration barrier, thereby optimizing lithium-ion transport kinetics. The high charge density and linear molecular structure of the cyano group significantly alter the coordination environment of lithium ions, lowering the migration barrier and promoting lithium-ion transport. + The dissociation and migration of ions improve ionic conductivity.

[0090] (2) Linear scan voltammetry

[0091] Linear sweep voltammetry was performed on the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1, and the results are as follows: Figure 6 As shown, the electrochemical stability window of Example 1 (a composite solid electrolyte containing lithium 3-hydroxypropionitrile) reaches 5.50V, which is significantly wider than that of Comparative Example 1 (pure PEO solid electrolyte) by 0.85V (4.65V). This effectively solves the technical bottleneck of easy oxidation and decomposition of PEO-based electrolytes at high voltages, enabling the electrolyte to be compatible with high-voltage cathode materials and possessing clear industrial application value. Furthermore, it demonstrates that the addition of cyano-containing organic lithium salt additives significantly improves the oxidation resistance of PEO-based solid electrolytes. The high bond energy characteristics (C≡N bond energy approximately 891kJ / mol) and strong electron-withdrawing effect of the cyano groups effectively suppress the oxidative decomposition reaction of the electrolyte at high potentials.

[0092] (3) Dissociation and migration of lithium salts

[0093] The electrochemical impedance spectroscopy (EIS) and time-current curves during polarization of lithium-symmetric batteries assembled using the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 were measured by potentiostatic polarization method. The results are as follows: Figure 7 , Figure 8 As shown, the lithium-ion transference number of Example 1 (a composite electrolyte containing lithium 3-hydroxypropionitrile salt) reached 0.46, a significant increase of 64% compared to 0.28 in Comparative Example 1 (PEO electrolyte). This effectively solves the technical bottleneck of low lithium-ion transference number and severe concentration polarization in traditional PEO electrolytes, providing a reliable guarantee for high-rate charge-discharge performance. At the same time, it also proves that the cyano-containing organic lithium salt additive, with its strong polarity and coordination ability, effectively weakens the Coulomb attraction between lithium ions and anions, promotes lithium salt dissociation and increases the concentration of free lithium ions. Meanwhile, its uniform dispersion in the PEO matrix optimizes the ion transport path and reduces the migration activation energy.

[0094] (4) Stability

[0095] The lithium stability of the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 was tested. A Li||Li symmetric cell was assembled, and the test current density was 0.1 mA / cm². 2 The result is as follows Figure 7 As shown, by assembling a Li||Li symmetric cell and achieving a current of 0.1 mA / cm 2Constant current cycling tests were conducted at current density. Example 1 (a composite electrolyte containing lithium 3-hydroxypropionitrile) maintained stable cycling for over 800 hours with the overpotential consistently below 50 mV, while Comparative Example 1 (pure PEO solid electrolyte) exhibited a polarization voltage exceeding 60 mV and failed after only 220 hours of cycling. This order-of-magnitude performance improvement effectively solves the major technical problem of safety risks caused by lithium dendrite penetration in solid-state batteries, demonstrating outstanding safety and industrial application value. Furthermore, it was demonstrated that the introduction of cyano-containing organic lithium salts forms a stable interface layer rich in Li3N and LiCN on the lithium metal surface. Its high Young's modulus and uniform ion current distribution effectively suppress lithium dendrite nucleation and growth. Simultaneously, the enhanced polymer chain mobility promoted the release of interfacial stress, thereby improving the interface stability and safety of the solid-state battery.

[0096] (5) Cyclic stability

[0097] The cycle stability of the PEO-based solid electrolytes prepared in Example 1 and Comparative Example 1 was tested. LFP||Li coin cells were assembled, and their cycle performance was tested at 0.5C and 1.0C (theoretical specific capacity of 170 mAh / g) within a voltage range of 2.5–3.8V at 60°C. The results are as follows: Figure 8 , Figure 9As shown, the composite solid electrolyte prepared in Example 1 has an initial discharge specific capacity of 157.0 mAh / g at 0.5C, a first-cycle coulombic efficiency of 93.52%, and a capacity retention of 90% after 250 cycles. At 1C, the initial discharge specific capacity is 159.7 mAh / g, the first-cycle coulombic efficiency is 94.57%, and the capacity retention is 80% after 350 cycles. The coulombic efficiency is relatively stable during cycling, approaching 100%, indicating stable cycle performance. In contrast, the pure PEO solid electrolyte prepared in Comparative Example 1 has an initial discharge specific capacity of 141.7 mAh / g at 0.5C, a first-cycle coulombic efficiency of 90.42%, and its efficiency begins to decrease and fluctuate drastically after 95 cycles. At 1C, the initial discharge specific capacity is 90.3 mAh / g, the first-cycle coulombic efficiency is 64.32%, and its efficiency begins to decrease and fluctuate drastically after 80 cycles. This is due to the poor cycle performance caused by side reactions at the electrolyte-cathode interface. Further analysis reveals that the high initial coulombic efficiency stems from the effective compensation of active lithium consumed in SEI film formation by the lithium-containing additive; the excellent cycle stability is attributed to the high antioxidant properties of the cyano group, which suppresses side reactions at the cathode / electrolyte interface, while the stable interface layer reduces active material loss; more importantly, these effects remain significant even under high-temperature testing conditions of 60°C, demonstrating that this invention solves the two major technical problems of initial active lithium loss and poor long-term cycle stability in existing technologies. Therefore, the addition of cyano-containing organic lithium salt additives improves the antioxidant properties of solid-state electrolytes, significantly enhancing the stability of battery cycle performance.

[0098] In summary, the cyano-containing organolithium salt additive of the present invention, through... Figures 3-9 Systematic experimental data fully demonstrate its multiple synergistic effects in PEO-based composite solid electrolytes: significantly improved ionic conductivity (2.5 times), broadened electrochemical window (5.50V), increased lithium-ion transference number (64%), enhanced lithium stability (800+ h), and optimized cycle performance (94.57% coulombic efficiency in the first cycle at 1.0C, and 80% capacity retention after 350 cycles). These breakthrough improvements not only prove that this invention effectively solves the technical bottlenecks of PEO-based solid electrolytes in terms of ion transport kinetics, electrochemical stability, interfacial compatibility, and cycle life, demonstrating clear industrialization value and engineering applicability, but also indicate that the high charge density, linear structure, and strong coordination ability of the cyano group are the core factors for achieving the above performance improvements, providing a reliable technical path for the commercial development of high-performance solid-state batteries.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An organolithium salt containing a cyano group, characterized in that, The structural general formula of the organic lithium salt is as follows: Li-O-(CH2) n -CN, wherein n is a positive integer from 1 to 5.

2. A method for producing an organic lithium salt, characterized by, The organic lithium salt of claim 1 is prepared, specifically comprising the following steps: Under an inert protective atmosphere, the hydroxyl nitrile raw material is added into anhydrous tetrahydrofuran, and after stirring until the solution is transparent, LiH is added, and the reaction is stirred for 15 h, then the solid is filtered and collected, and the solid is vacuum dried to obtain the organic lithium salt; The hydroxynitrile raw material has the general structural formula HO-(CH2). n -CN, where n is a positive integer from 1 to 5; the molar ratio of the hydroxynitrile to LiH is (1 to 1.5):

1.

3. A composite solid-state electrolyte, characterized by, The composite solid-state electrolyte is composed of a polymer matrix, a lithium salt and an additive; the additive is the organic lithium salt of claim 1 or the organic lithium salt obtained by the preparation method of claim 2; and the additive is used in an amount of 1% to 15% of the total mass of the composite solid-state electrolyte, calculated in terms of mass percentage.

4. The composite solid-state electrolyte of claim 3, wherein the solid-state electrolyte is a lithium-based solid-state electrolyte. The polymer matrix is polyethylene oxide, and the molecular weight Mv of the polyethylene oxide is 0.5 to 7 million.

5. The composite solid electrolyte according to claim 3, characterized in that, The lithium salt is one or a combination of the following: lithium bisfluorosulfonylimide, lithium bis-trifluorosulfonylimide, lithium difluoro(oxalato)borate, and lithium difluoro(oxalato)phosphate.

6. A method of preparing a composite solid-state electrolyte, characterized by, The composite solid-state electrolyte of any one of claims 3 to 5 is prepared, specifically comprising the following steps: Step 1: under inert atmosphere, polymer matrix and lithium salt are added into anhydrous acetonitrile, mixed uniformly to obtain a mixed solution I; wherein, the amount of polymer matrix and lithium salt is according to the molar ratio [EO]:Li + = 10-20, the mass of anhydrous acetonitrile: the total mass of polymer matrix and lithium salt is 6-12; Step 2: The additive is added to the mixed solution I obtained in step 1, and the mixture is uniformly mixed at 40 to 60°C to obtain mixed solution II; Step 3: The mixed solution II obtained in step 2 is poured into a mold, and the mold is dried under vacuum or an inert protective atmosphere until the anhydrous acetonitrile is completely volatilized, to obtain a film-shaped composite solid-state electrolyte.

7. The preparation method according to claim 6, characterized in that, The thickness of the composite solid-state electrolyte is 0.4 to 0.6 mm.

8. The preparation method according to claim 6, characterized in that, The drying temperature is 50 to 60°C, and the drying time is 12 to 24 h.

9. A lithium battery, characterized by The lithium battery has the composite solid-state electrolyte of any one of claims 3 to 5 or the composite solid-state electrolyte prepared by the preparation method of claim 6.

Images