A lithium titanate modified polymer solid-state electrolyte and a preparation method thereof

Abstract

The present application relates to a kind of lithium titanate modified polymer solid electrolyte, which is prepared by solution casting method using slurry containing cobalt-doped lithium titanate, PEO and LiTFSI, the cobalt-doped lithium titanate has a cobalt doping percentage of 1.26-2.1%, the mass of cobalt-doped lithium titanate accounts for 5-15% of the mass of PEO, and the mass ratio of PEO and LiTFSI is 15-20:1;The particle size of the cobalt-doped lithium titanate is 400-500 nm.The present application uses cobalt-modified lithium titanate, cobalt is more easily obtained and has lower cost, the modified Co-Li4Ti5O 12 Ti-O bond in the spinel structure Li4Ti5O 12 Ti-O octahedron to Ti-O tetrahedron is weakened, making the structure more stable, and the prepared Co-Li4Ti5O 12 / PEO-LiTFSI composite solid electrolyte has excellent tensile strength, thermal stability, improves electrolytic electrochemical performance and battery safety.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, specifically to a lithium titanate modified polymer solid electrolyte and its preparation method. Background Technology

[0002] Solid-state electrolytes, due to their safety, stability, and ease of assembly, represent an ideal direction for the development of next-generation battery technology. Existing solid-state electrolytes mainly include inorganic ceramic electrolytes, polymer electrolytes, and composite electrolytes. Among them, polymer electrolytes possess good toughness and interfacial compatibility, allowing for flexible battery device fabrication through bending; however, their conductivity at room temperature is too low (≤10). -6 The lithium-ion transport capacity (S / cm) is low, making it difficult to achieve normal charge-discharge at room temperature, which limits its commercial use. PEO-based solid electrolytes are commonly used in existing technologies, but unmodified PEO-based solid electrolytes typically have large crystalline regions, severely limiting lithium-ion transport.

[0003] To address the aforementioned issues, existing technology CN115692836A proposes a solid electrolyte and its preparation method. This method involves doping lithium titanate with lanthanide rare earth elements. Compared to untreated lithium titanate, this increases the specific surface area, resulting in more surface charge, a denser structure, and a larger specific surface area to reduce the crystallinity of PEO. This facilitates the transport of metal cations along the polyethylene oxide chain segments, reduces decomposition during charge and discharge, and allows for the formation of physical cross-linking points, thereby improving the mechanical strength of the solid electrolyte. It also exhibits high room temperature conductivity, a high voltage window, and good lithium stability. However, the following problems still exist in this scheme: (1) It uses lanthanide rare earth elements (including scandium Sc, yttrium Y and lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd, promethium Pm, samarium Sm, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, ytterbium Yb, lutetium Lu, a total of 17 elements) to dope and modify lithium titanate to prepare solid electrolytes, resulting in high raw material costs and making it unsuitable for commercial production; (2) The atomic radius of lanthanide rare earth elements is larger than that of Li4Ti5O 12 In the case of Ti, it is difficult to occupy Ti sites for doping modification, and this method cannot be used for Li4Ti5O. 12Directional doping at Li or Ti sites can lead to random substitution of these sites by lanthanide rare earth elements during modification. This results in lattice and bond instability in the prepared lanthanide-doped lithium titanate, making it difficult to meet the high requirements of solid-state electrolytes in terms of mechanical properties, thermal stability, and resistance to high-pressure oxidative decomposition. Furthermore, Yang L, Zhang H, Xia E, and others proposed a PEO / Li₂ZrO₃ composite electrolyte for solid-state secondary lithium batteries. These technologies use inorganic fillers with larger particle sizes added to the PEO-based solid electrolyte, which are difficult to disperse uniformly in PEO, reducing the efficiency of lithium-ion transitions between two adjacent binding sites. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for preparing lithium titanate modified polymer solid electrolyte, which adopts cobalt-doped lithium titanate modified PEO solid electrolyte, and solves the technical problems such as the large crystallization region of PEO-based solid electrolyte and the high cost, mechanical properties, thermal stability and resistance to high pressure oxidation decomposition of existing lanthanide rare earth element-doped lithium titanate.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a method for preparing a lithium titanate modified polymer solid electrolyte, comprising:

[0008] S1. Preparation of cobalt-doped lithium titanate Co-Li4Ti5O 12 ;

[0009] S2. Preparation of composite solid electrolyte using solution casting method, including: dissolving PEO and LiTFSI in an organic solvent to obtain a slurry, and weighing 5-15 wt% of cobalt-doped lithium titanate Co-Li4Ti5O. 12 Add the powder dispersant to the slurry and stir to obtain a homogeneous solid electrolyte slurry;

[0010] S3. The slurry is evenly coated onto a flat, inert substrate, the solvent is evaporated, and then vacuum dried to obtain Co-Li4Ti5O. 12 / PEO-LiTFSI solid electrolyte.

[0011] According to a preferred embodiment of the present invention, in S1, cobalt-doped lithium titanate Co-Li4Ti5O 12 The preparation method is as follows:

[0012] S101: A mixed solution obtained by mixing anhydrous ethanol and hydrogen peroxide is gradually added to the mixed solution while stirring. After complete dissolution, a divalent soluble cobalt salt is added dropwise to obtain solution B.

[0013] S102: Prepare lithium solution A. While stirring solution A, gradually add solution B to it to produce a dark green suspension. Continue stirring to avoid the formation of flocculation and precipitation.

[0014] S103: Transfer to a high-pressure sealed reactor and react at 175-190℃ for 18-26 hours using a solvothermal method. Filter to obtain the precipitate, wash with deionized water and anhydrous ethanol, and dry to obtain precursor C.

[0015] S104: Precursor C is ball-milled to obtain precursor D with a smaller particle size. Precursor D is then calcined in a vacuum furnace at 500-800℃ for 3-8 hours to obtain cobalt-doped lithium titanate Co-Li4Ti5O. 12 Alternatively, the precursor C can be calcined in a vacuum furnace at 500-800℃ for 3-8 hours, and then ball-milled to obtain cobalt-doped lithium titanate Co-Li4Ti5O. 12 .

[0016] According to a preferred embodiment of the present invention, in S101, anhydrous ethanol and 30% H2O2 solution are prepared in a volume ratio of 1.8-2.2:1.

[0017] The amount of the mixed solution prepared should be sufficient to dissolve tetrabutyl titanate, preferably 2.5-5 mL of mixed solution for every 1 millimole of tetrabutyl titanate.

[0018] According to a preferred embodiment of the present invention, in S101, the molar ratio of divalent soluble cobalt salt to tetrabutyl titanate is 1:30-50, preferably 1:35-45, and more preferably 1:40; the cobalt-doped lithium titanate Co-Li4Ti5O obtained therefrom 12 The cobalt doping ratio is 1.26-2.1%; when the molar ratio of divalent soluble cobalt salt to tetrabutyl titanate is 1:40, the cobalt doping ratio is 1.58%.

[0019] According to a preferred embodiment of the present invention, in S102, the lithium solution A is prepared by dissolving lithium hydroxide in water; the lithium solution A is lithium hydroxide; the molar ratio of lithium hydroxide to tetrabutyl titanate is 4-5.5:5, according to Li4Ti5O 12The theoretical value of Li in the molecular formula can be slightly in excess. Here, if the lithium salt is insoluble, it is difficult to uniformly intercalate into the product to obtain cobalt-doped lithium titanate. Therefore, lithium carbonate cannot be used. In addition, lithium chloride and lithium sulfate are difficult to decompose under high temperature calcination, which will introduce anionic impurities. Lithium hydroxide can provide both water-soluble lithium ions and hydroxide precipitants, and react with tetrabutyl titanate in solution B to generate the lithium titanate precursor.

[0020] According to a preferred embodiment of the present invention, in S103, the product is subjected to a solvothermal reaction at 180°C for 24 hours in a high-pressure sealed reactor. The precipitate is then filtered and washed 2-3 times each with deionized water and anhydrous ethanol, and dried to obtain precursor C. Preferably, the drying is performed in an oven at 60-85°C for 6-12 hours.

[0021] According to a preferred embodiment of the present invention, in S104, a zirconia ball milling jar is used for ball milling, and the ball milling is performed for more than 4 hours to obtain a precursor D with a smaller particle size (about 1 to 2 μm).

[0022] According to a preferred embodiment of the present invention, in S104, calcination is performed in an alumina refractory container in a vacuum tube furnace at 600°C for 6 hours to obtain cobalt-doped lithium titanate Co-Li4Ti5O. 12 .

[0023] According to a preferred embodiment of the present invention, in S2, PEO and LiTFSI are dissolved in an organic solvent (preferably acetonitrile or NMP) at a mass ratio of 15-20:1 to prepare a slurry.

[0024] According to a preferred embodiment of the present invention, in S2, cobalt-doped lithium titanate Co-Li4Ti5O 12 The powder dispersant added to the slurry is preferably Australian powder dispersant AD8085, accounting for 10 wt% of the PEO mass. The electrostatic repulsion generated by the powder dispersant adsorbing onto small particles will cause Co-Li4Ti5O to... 12 The particles are dispersed, resulting in faster dispersion of the prepared slurry and avoiding the formation of Co-Li4Ti5O. 12 The agglomeration phenomenon is eliminated, and the stirring time in S3 is significantly shortened. After stirring for 4-6 hours, a homogeneous solid electrolyte slurry can be obtained, which effectively shortens the process time and speeds up the process.

[0025] According to a preferred embodiment of the present invention, in S3, the flat inert substrate is a polytetrafluoroethylene (PTFE) plate. The solvent is slowly evaporated at room temperature for 10-12 hours to prevent excessively rapid evaporation, which could lead to the electrolyte surface solidifying into a thin film while leaving a large amount of residual organic solvent inside. During oven drying, the evaporation of this organic solvent due to heat would cause defects such as bulging and cracking on the solid electrolyte surface. Preferably, the vacuum drying conditions are: drying at 55-70°C in a vacuum drying oven for 18-24 hours.

[0026] Secondly, the present invention provides a lithium titanate modified polymer solid electrolyte, which is prepared by any of the preparation methods described in the above embodiments.

[0027] Thirdly, the present invention provides a lithium titanate modified polymer solid electrolyte, which is prepared by solution casting using a slurry containing cobalt-doped lithium titanate, PEO and LiTFSI. The cobalt-doped lithium titanate has a cobalt doping percentage of 1.26-2.1%, the mass of cobalt-doped lithium titanate accounts for 5-15% of the mass of PEO, and the mass ratio of PEO to LiTFSI is 15-20:1. The particle size of the cobalt-doped lithium titanate is 400-500 nm.

[0028] Preferably, the cobalt-doped lithium titanate is prepared by a hydrothermal method, and its microstructure is a three-dimensional layered structure rearranged in different directions; wherein, Co affects Li4Ti5O 12 The Ti site is modified by substitution doping.

[0029] Preferably, the solvent used in the slurry is acetonitrile; and during the solution casting process, the slurry is first spread on a polytetrafluoroethylene plate, and the solvent is slowly evaporated to 70-80% at room temperature, and then vacuum dried at 55-70°C.

[0030] (III) Beneficial Effects

[0031] (1) The lithium titanate-modified polymer solid electrolyte prepared in this invention is made from cobalt-doped lithium titanate-modified PEO-based solid electrolyte, which prevents PEO chain segment rearrangement and crystallization, reduces PEO crystallinity, and increases the proportion of amorphous regions in PEO that transport lithium ions, thereby significantly improving the electrochemical performance of the prepared polymer solid electrolyte; the cobalt-doped lithium titanate Co-Li4Ti5O3 after ball milling and calcination 12 With a relatively small particle size (approximately 400-500 nm), Co-Li4Ti5O can be tightly packed within PEO to form a solid-solid conductive interface. 12 Together with PEO, they form a hybrid conductive interface, which improves lithium-ion transport efficiency and enhances the Co-Li4Ti5O content. 12 Being tightly embedded in PEO helps to form a stable lithium-ion interphase between the electrode and the solid electrolyte, enhancing ion transport efficiency and reducing internal energy loss in the battery.

[0032] Lithiumized interphase refers to a special class of compounds in which Li + It is embedded into the layered structure of other materials. This embedding process is called "intercalation," which refers to the phenomenon that an element or molecule can be randomly inserted or embedded in the interlayer of another solid material. Specifically, the solid electrolyte prepared in this invention has a surface covered with Co-Li4Ti5O. 12 During the charging and discharging process, Li + It can be embedded in its layered structure; at the contact points between Co-Li4Ti5O12 and the lithium metal anode, some Co-Li4Ti5O 12 The particles generate electron conduction due to their close contact with metallic lithium. 4+x Ti5O 12 Phase, which makes Li + Lithium can be transported through solid-solid contacts between particles. The electric field can extend across the interface via an electronic conduction path, resulting in increased lithium intercalation capacity.

[0033] (2) Compared with existing technologies for doping lanthanide rare earth elements, this invention uses cobalt-modified lithium titanate, whose atomic radius is close to and slightly smaller than that of Ti, making it easier to occupy Li4Ti5O. 12 In the Ti site, not only is cobalt more readily available and cheaper, but the modified Co-Li4Ti5O 12 The Ti-O bonds are stronger, which weakens the spinel structure of Li4Ti5O. 12 The transformation from Ti-O octahedrons to Ti-O tetrahedra in the prepared Co-Li4Ti5O3 structure results in greater structural stability. 12 The PEO-LiTFSI composite solid electrolyte possesses excellent tensile strength and thermal stability, playing a crucial role in battery safety (e.g., Figure 1 As shown, the lithium metal solid-state pouch battery made with CLP-10 solid electrolyte can still light up LEDs after being bent and cut, without producing smoke, burning, or explosions.

[0034] Compared to the unmodified spinel structure Li4Ti5O 12 This invention uses Co 2+ For Li4Ti5O 12 Ti at position 16d 4 + Targeted substitution was carried out to prepare cobalt-doped Co-Li4Ti5O 12 To enable solid electrolytes to possess excellent lithium-ion transfer numbers, such as Figure 2As shown, the lithium-ion transfer number of the unmodified solid electrolyte (0.65) is significantly lower than that of CLP-10 (0.83). Based on density functional theory calculations, this is due to the increased lattice spacing after doping, which affects the cobalt-doped Co-Li4Ti5O4. 12 At the atomic scale, lattice expansion occurs, creating more channels conducive to lithium-ion diffusion (Co-Li4Ti5O3 after cobalt doping modification). 12 The lattice constant decreases compared to the unmodified form, resulting in a smaller cell volume and a larger lattice spacing. This larger lattice spacing creates more pathways conducive to lithium-ion transport, improving lithium-ion transport efficiency and thus mitigating the inherent defects of low lithium-ion transfer number and poor ionic conductivity in lithium titanate. Simultaneously, the Li-O bond strength is significantly weakened after modification, promoting lithium-ion extraction and insertion, improving lithium-ion transport efficiency, and contributing to enhanced rate performance of solid-state electrolyte lithium batteries.

[0035] (3) Compared with the existing technology that uses solid-state sintering, i.e., the method of preparing lithium titanate by stirring-ball milling-calcination, the Co-Li4Ti5O prepared by hydrothermal method in this invention... 12 The precursor is more uniform and has a good nanosheet structure; therefore, after high-temperature calcination, the nanosheets are stacked and arranged in different directions, resulting in a three-dimensional distributed layered structure Co-Li4Ti5O. 12 It exhibits stronger structural stability, and the experimental method is simpler and more time-saving and labor-saving; Co-Li4Ti5O prepared by hydrothermal method 12 In a hydrothermal medium, the product forms a three-dimensional layered structure rearranged in different directions, which is more stable and has a larger specific surface area. This allows it to couple with more lithium salt anions, enabling more free lithium ions to participate in transport and improving the rate performance of solid-state electrolyte lithium batteries. After preparing precursor C, the preparation method of this invention further obtains a smaller precursor D by ball milling, with a particle size range of 1-2 μm, making Co-Li4Ti5O 12 The ether oxygen segment of PEO is uniformly distributed and closely arranged, which improves the transition efficiency of lithium ions between adjacent binding sites.

[0036] This is because, when adjacent Li in a PEO molecule + The distance between the binding sites (two adjacent oxygen atoms) is the chain length of -O-CH2-CH2-O-, Li + The -O-CH2-CH2-O- chain transitions occur within the molecule. Therefore, the added filler should have a size close to the -O-CH2-CH2-O- chain length (approximately 0.5 nm). In this invention, Co-Li4Ti5O obtained by ball milling and calcination... 12 With a particle size of 400-500 nm, the smaller particle size allows for close packing between adjacent binding sites, thereby improving Li...+ Transition rate. Based on the test results, the Co-Li4Ti5O4 with a particle size of 400-500 nm prepared in this invention... 12 The solid electrolyte exhibits excellent ionic conductivity, lithium-ion transfer number, electrochemical stability window, and cycling stability. In summary, smaller particle size has proven to yield better results.

[0037] (4) In this invention, the preparation process of cobalt-doped lithium titanate and the preparation process of solid electrolyte have no special environmental requirements. No special equipment is needed, and preparation does not require an argon-filled glove box. There are no stringent requirements for the gas environment. The process is simple, time-saving, and labor-saving. Furthermore, this invention has advantages such as adjustable film thickness, low cost, environmental friendliness, good repeatability, and ease of large-scale mass production. When adjusting the film thickness, only the slurry consistency (adjusted by solvent dosage) and slurry spreading thickness need to be adjusted during solution casting to obtain solid electrolytes of different film thicknesses for use in assembling various battery models, such as wearable and bendable batteries. Attached Figure Description

[0038] Figure 1 Safety testing of lithium metal solid-state pouch batteries assembled with the solid electrolyte CLP-10 prepared in Example 2 under extreme conditions.

[0039] Figure 2 The lithium-ion transfer number of the solid electrolyte prepared from unmodified cobalt-doped Li4Ti5O12 and the solid electrolyte CLP-10 of Example 2 at an excitation voltage of 10mV.

[0040] Figure 3 The image shows the microstructure of the cobalt-doped lithium titanate prepared in Example 2 using SEM.

[0041] Figure 4 Electrochemical impedance spectroscopy (EIS) of the solid electrolyte CLP-10 prepared in Example 2 at different temperatures.

[0042] Figure 5 The number of lithium-ion transfers is the solid electrolyte CLP-10 of Example 2 at an excitation voltage of 10mV.

[0043] Figure 6 The tensile strength curves are for the composite solid electrolytes of Examples 2-4 and Comparative Example 2.

[0044] Figure 7 The charge-discharge cycle diagrams are for the composite solid electrolytes of Examples 2-4 and Comparative Example 2. Detailed Implementation

[0045] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] This embodiment uses cobalt-doped lithium titanate Co-Li4Ti5O. 12 The preparation method is as follows:

[0048] Prepare a 35 ml solution by mixing anhydrous ethanol and 30% H2O2 solution in a volume ratio of 2.1:1. Stir the solution rapidly and slowly add 10 mmol Ti(OC4H9)4. After complete dissolution, slowly add a 0.225 mmol CoCl2 solution to form solution B.

[0049] Solution A was prepared by dissolving 8.9 mmol LiOH·H₂O in 25 ml of deionized water and stirring magnetically for 20 min. While stirring solution A, solution B was added dropwise to solution A to obtain a dark green suspension. The suspension was stirred rapidly for 30 min to prevent flocculation and precipitation. The reaction mixture was then transferred to a 100 ml stainless steel high-pressure reactor and solvated at 185 °C for 24 hours. The reactants were washed three times each with deionized water and anhydrous ethanol by centrifugation and dried in an oven at 80 °C for 12 hours to obtain precursor C. Precursor C was placed in an alumina boat and calcined at 600 °C for 6 hours in a vacuum tube furnace to obtain cobalt-doped lithium titanate (Co-Li₄Ti₅O₂). 12 ).

[0050] Comparative Example 1

[0051] This comparative example uses undoped cobalt lithium titanate Li4Ti5O. 12 The preparation method is the same as in Example 1, except that a solution of CoCl2 was not added dropwise when forming solution B to prepare Co-doped Li₄Ti₅O₂. 12 .

[0052] Based on density functional theory calculations, the Co-Li4Ti5O in Example 1 was... 12 Comparative Example 1: Lithium titanate Li4Ti5O 12 The lattice parameters (the lattice parameters of lithium titanate are fixed values) are shown in the table below:

[0053] Table 1:

[0054]

[0055]

[0056] As shown in the table above, cobalt doping of lithium titanate increases the lattice spacing (lattice spacing is the distance between the centers of the two lattice cells). The table also shows that cobalt doping of Co-Li4Ti5O... 12 The lattice constants a, b, and c are all relative to Li₄Ti₅O 12The decrease indicates that the modified Co-Li4Ti5O 12 The cell volume decreases, indicating that the modified Co-Li4Ti5O 12 The increased spacing between adjacent lattices leads to greater lattice spacing, resulting in lattice expansion at the atomic scale. This creates more channels conducive to lithium-ion diffusion, improving the inherent poor ionic conductivity of lithium titanate.

[0057] Based on first-principles density functional theory calculations, the Co-Li4Ti5O in Example 1 12 Comparative Example 1: Lithium titanate Li4Ti5O 12 The average bond lengths are shown in the table below (Table 2):

[0058]

[0059] As can be seen from the results in the table above, this invention uses Co 2+ For Li4Ti5O 12 Ti at position 16d 4+ Targeted replacement was performed, and Li4Ti5O was doped. 12 The average bond length changed, and calculations were performed using first-principles density functional theory to determine the cobalt-doped modified Li4Ti5O. 12 The Li-O bond at position 8a changed from 2.178 to 2.336, the Li-O bond at position 16d changed from 2.126 to 2.311, and the Ti-O bond changed from 2.072 to 2.058. These bond length changes indicate that the addition of Co strengthens the Ti-O bonds and, to some extent, weakens the spinel structure of Li₄Ti₅O. 12 The transformation from Ti-O octahedrons to Ti-O tetrahedra in Co-Li4Ti5O results in a more stable structure. The addition of Co-O bonds further stabilizes the Co-Li4Ti5O structure. 12 The ratio of Li-O bonds in Li4Ti5O 12 The longer length of the Li-O bond weakens its stability, promoting the extraction and insertion of lithium ions in the solid electrolyte. Therefore, using Co-Li4Ti5O... 12 Modified PEO-based solid electrolytes can effectively improve the mechanical strength and thermal stability of solid electrolytes. This is consistent with the test results of the electrochemical performance (impedance spectroscopy, ion transfer capability, cycle capacity) and tensile strength of solid electrolytes described below.

[0060] According to experimental tests, compared with the composite PEO-based solid polymer electrolytes for lithium metal batterie reinforced by inorganic boron nitride (h-BN) nanofibers by Song Q, Zhang Y et al. (Chinese Chemical Letters, 2023:108797), the solid electrolyte prepared in this invention has a tensile strength of up to 3.65 MPa, significantly higher mechanical strength, and better thermal stability.

[0061] Example 2

[0062] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared as follows:

[0063] (1) Preparation of cobalt-doped lithium titanate Co-Li4Ti5O 12 ;

[0064] Prepare a 30 ml solution by mixing anhydrous ethanol and 30% H2O2 solution in a volume ratio of 2:1. Stir the solution rapidly and slowly add 10 mmol Ti(OC4H9)4. After complete dissolution, slowly add a solution containing 0.25 mmol CoCl2 to form solution B.

[0065] 9 mmol LiOH·H₂O was dissolved in 30 ml of deionized water and magnetically stirred for 30 min to form solution A. While stirring solution A, solution B was added dropwise to solution A using a dropper to obtain a dark green suspension. The suspension was rapidly stirred for 30 min to prevent flocculation and precipitation. The reaction mixture was then transferred to a 100 ml stainless steel high-pressure reactor and solvated at 180 °C for 24 hours. The reactants were washed three times each with deionized water and anhydrous ethanol by centrifugation and dried in an oven at 80 °C for 12 hours to obtain precursor C.

[0066] Precursor C was placed in a zirconia ball mill jar and ball-milled at 250 rpm for 6 hours using zirconia balls to obtain precursor D with a smaller particle size of 1–2 μm. Precursor D was then placed in an alumina boat and calcined at 600 °C for 6 hours in a vacuum tube furnace to obtain cobalt-doped lithium titanate (Co-Li4Ti5O). 12 ).

[0067] The microstructure of the cobalt-doped lithium titanate is as follows: Figure 3 As shown, this is a three-dimensional layered structure rearranged in different directions. This unique structure is Co-Li4Ti5O 12Coupling with lithium salt anions provides a larger specific surface area and more active sites, which is beneficial for releasing more free lithium ions and increasing the number of lithium ions that can participate in transfer. Before calcination, precursors C and D are single nanosheets, which are stacked in different directions after high-temperature calcination to obtain... Figure 2 The structure of Co-Li4Ti5O shown 12 .

[0068] (2) The composite solid electrolyte was prepared by solution casting, including: firstly, PEO and LiTFSI were dissolved in 60 mL of acetonitrile at a ratio of EO:Li = 18:1, and 10 wt% Co-Li4Ti5O was weighed according to the mass of PEO. 12 Add the mixture to the slurry, along with Ausnutria powder dispersant AD8085, and mechanically stir for 6 hours to obtain a homogeneous solid electrolyte slurry.

[0069] (3) The solid electrolyte slurry was uniformly coated onto a polytetrafluoroethylene plate, and the solvent was slowly evaporated at room temperature for 12 hours. Then, it was transferred to a vacuum drying oven and dried at 60°C for 24 hours to obtain Co-Li4Ti5O. 12 / PEO-LiTFSI solid electrolyte.

[0070] The prepared solid electrolyte has a cobalt doping percentage of 1.58% in cobalt-doped lithium titanate, and the mass of cobalt-doped lithium titanate accounts for 10% of the mass of PEO. The mass ratio of PEO to LiTFSI is 18:1. The particle size of cobalt-doped lithium titanate is 400-500 nm. The solid electrolyte is designated as CLP-10.

[0071] Electrochemical impedance spectroscopy (EIS) of the solid electrolyte CLP-10 prepared in Example 2 was tested at different temperatures (25℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃). The scanning results are as follows: Figure 4 As shown in the figure. Experimental results show that the solid electrolyte CLP-10 exhibits the lowest electrochemical impedance at 40℃, 50℃, 60℃, and 70℃, especially at 60℃ and 70℃. Furthermore, at 80℃, the electrochemical impedance of the solid electrolyte CLP-10 is close to the value measured at 25℃. This indicates that the Co-Li4Ti5O prepared in this invention... 12 The PEO-LiTFSI solid electrolyte has good thermal stability, which plays a crucial role in battery safety.

[0072] The lithium-ion transfer number of the solid electrolyte CLP-10 prepared in this embodiment was further tested at 60°C, with a test voltage of 10 mV and a polarization time of 1000 s. The test results are shown in the curve below. Figure 5As shown, the initial current of CLP-10 was 0.25 μA. With increasing polarization time, CLP-10 reached stability after 300 s, with a steady-state current of 0.21 μA. The calculated lithium-ion transfer number of CLP-10 reached 0.83. This indicates that in CLP-10, Co-Li4Ti5O... 12 Selective transfer is enhanced by suppressing anion excitation in the system, allowing more transport segments to interact with free Li. + Interactions lead to Li + The transfer efficiency is significantly improved. More importantly, in CLP-10, the lithiation interphase can serve as a mixed conductive phase, providing solid-solid contact conduction for the system and greatly improving the efficiency of lithium-ion transfer.

[0073] Comparative Example 2

[0074] This comparative example uses a solution casting method to prepare a composite solid electrolyte, including: firstly, dissolving PEO and LiTFSI in 60 mL of acetonitrile at a ratio of EO:Li = 18:1, adding AD8085 powder dispersant, but without adding Co-Li4Ti5O. 12 The mixture was mechanically stirred for 6 hours to obtain a homogeneous solid electrolyte slurry. The solid electrolyte slurry was then uniformly coated onto a polytetrafluoroethylene (PTFE) plate, and the solvent was slowly evaporated at room temperature for 12 hours. Subsequently, it was transferred to a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid electrolyte that does not contain Co-Li4Ti5O. 12 It also does not contain Li4Ti5O 12 Solid electrolytes are denoted as CLP.

[0075] Example 3

[0076] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared by the same method as in Example 2; the only difference is in step (2), where 5wt% Co-Li4Ti5O is weighed according to the mass of PEO. 12 When added to the slurry, a solid electrolyte is obtained, denoted as CLP-5.

[0077] In this solid electrolyte, the cobalt doping percentage of lithium titanate is 1.58%, the mass of cobalt doped lithium titanate accounts for 5% of the mass of PEO, the mass ratio of PEO to LiTFSI is 18:1, and the particle size of cobalt doped lithium titanate is 500 nm.

[0078] Example 4

[0079] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared by the same method as in Example 2; the only difference is that in (2), 15wt% Co-Li4Ti5O is weighed according to the mass of PEO. 12 When added to the slurry, a solid electrolyte is obtained, denoted as CLP-15.

[0080] In this solid electrolyte, the cobalt doping percentage of lithium titanate is 1.58%, the mass of cobalt doped lithium titanate accounts for 15% of the mass of PEO, the mass ratio of PEO to LiTFSI is 18:1, and the particle size of cobalt doped lithium titanate is 500 nm.

[0081] Tensile strength tests were conducted on the solid electrolytes of Examples 2-4 and Comparative Example 2, and the test results are as follows: Figure 4 As shown. Figure 6 As shown, the solid electrolyte CLP-10 prepared in Example 2 has the highest tensile strength, followed by the solid electrolyte CLP-15 prepared in Example 4, and then the solid electrolyte CLP-5 prepared in Example 3. Comparative Example 2, however, did not have Co-Li4Ti5O added. 12 The PEO solid electrolyte exhibits the lowest tensile strength. This indicates that in Co-Li4Ti5O... 12 When the content of PEO is 10% by mass, the prepared Co-Li4Ti5O 12 The PEO-LiTFSI composite solid electrolyte exhibits the best tensile strength.

[0082] The above experimental results show that, compared with the use of Co-Li4Ti5O, 12 The cobalt-doped lithium titanate modified PEO-based solid electrolyte prepared in this invention exhibits significantly superior tensile strength. This is mainly due to the cobalt doping modification of the Ti sites in lithium titanate, resulting in a modified Co-Li4Ti5O4 solid electrolyte. 12 The Ti-O bonds are stronger, which weakens the spinel structure of Li4Ti5O. 12 The transformation from Ti-O octahedrons to Ti-O tetrahedra in Co-Li4Ti5O results in a more stable structure. 12 / PEO-LiTFSI composite solid electrolyte exhibits excellent tensile strength and superior thermal stability; however, when Co-Li4Ti5O 12 When the proportion of PEO in the electrolyte is too high, the tensile strength of the electrolyte will decrease again.

[0083] The charge-discharge capacity (Capacity mAh / g) of the batteries assembled with the solid electrolytes of Examples 2-4 and Comparative Example 2 was tested, and a charge-discharge cycle graph was plotted for capacity versus cycle number. The test conditions were: test rate of 0.1C and test temperature of 60°C. The test results are as follows: Figure 7 As shown in the figure, the solid electrolyte CLP-10 of Example 2 exhibits the best charge-discharge cycle performance and the largest charge-discharge capacity, followed by the solid electrolyte CLP-15 prepared in Example 4, and then the solid electrolyte CLP-5 prepared in Example 3. Comparative Example 2, however, did not have the addition of Co-Li4Ti5O. 12The PEO solid electrolyte exhibits the worst charge-discharge cycle performance. This indicates that the Co-Li4Ti5O... 12 When the content of PEO is 10% by mass, the prepared Co-Li4Ti5O 12 The PEO-LiTFSI composite solid electrolyte exhibits the best tensile strength. Compared to the unmodified PEO-based solid electrolyte, the Co-Li4Ti5O of ​​this invention... 12 The electrochemical performance of the / PEO-LiTFSI composite solid electrolyte was significantly improved.

[0084] This is mainly based on: the Co-Li4Ti5O prepared in this invention. 12 It can form a mixed conductive interface with PEO, accelerating the Co-Li4Ti5O 12 Lithium ion transitions in PEO-LiTFSI solid electrolyte, Co-Li4Ti5O 12 The presence of [the substance] helps to form a more stable lithium-ion interphase between the electrode and the electrolyte. Compared to the PEO-based solid electrolyte in Comparative Example 2, which does not contain lithium titanate modification and relies solely on the amorphous region of PEO to conduct lithium ions, the Co-Li4Ti5O [electrolyte] of this invention [is superior]. 12 The stacked nanosheet structure is tightly arranged in PEO to form a solid-solid conductive interface. Simultaneously, the widened lattice spacing allows a large number of lithium ions to pass through in a short time, transforming the lithium ion transport pathway from single polymer chain conduction in the PEO solid electrolyte to polymer chain conduction and Co-Li4Ti5O. 12 The solid-solid conduction dual phase improves the lithium-ion transport efficiency and electrochemical performance of the solid electrolyte, especially the charge-discharge cycle performance.

[0085] Example 5

[0086] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared by the same method as in Example 2; the only difference is that in step (1), “0.25 mmol CoCl2” is changed to “0.20 mmol CoCl2”. In the prepared solid electrolyte, the cobalt doping percentage of the cobalt-doped lithium titanate is 1.26%, the mass of the cobalt-doped lithium titanate accounts for 10% of the mass of PEO, and the mass ratio of PEO to LiTFSI is 17:1.

[0087] Example 6

[0088] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared by the same method as in Example 2; the only difference is that in step (1), “0.25 mmol CoCl2” is changed to “0.34 mmol CoCl2”. In the prepared solid electrolyte, the cobalt doping percentage of the cobalt-doped lithium titanate is 2.1%, the mass of the cobalt-doped lithium titanate accounts for 10% of the mass of PEO, and the mass ratio of PEO to LiTFSI is 19:1.

[0089] Example 7

[0090] The lithium titanate modified polymer solid electrolyte of this embodiment is prepared by the same method as in Example 2; the only difference is that in step (1), “9mmol LiOH·H2O” is changed to “10mmol LiOH·H2O”. In the prepared solid electrolyte, the cobalt doping percentage of the cobalt-doped lithium titanate is 1.58%, the mass of the cobalt-doped lithium titanate accounts for 10% of the mass of PEO, and the mass ratio of PEO to LiTFSI is 20:1.

[0091] Co-Li4Ti5O prepared in Examples 5-7 12 Having the same properties as the Co-Li4Ti5O prepared in Example 2 12 They exhibit similar microstructures, namely, a three-dimensional layered structure rearranged in different directions. The electrochemical impedance spectroscopy (EIS), lithium-ion transfer number, tensile strength, and charge-discharge cycle diagrams of the prepared solid electrolyte at different temperatures are basically consistent with the corresponding test values ​​of the solid electrolyte in Example 2. This indicates that when the mass ratio of cobalt-doped lithium titanate to PEO remains constant at 10%, slight adjustments to the doping amount of Co in lithium titanate or slight adjustments to the mass ratio of PEO to LiTFSI have little impact on the performance of the solid electrolyte. This proves that the method for preparing the solid electrolyte of this invention has good repeatability and the performance of the solid electrolyte is relatively stable.

[0092] Comparative Example 3

[0093] Lithium titanate was prepared according to step (1) of Example 2, without adding CoCl2 during the formation of solution B, thus obtaining Co-doped lithium titanate Li4Ti5O. 12 Using Li4Ti5O 12 In step (2) of the alternative embodiment, “Co-Li4Ti5O” 12 "Add the electrolyte to the slurry and mechanically stir for 6 hours to obtain a homogeneous solid electrolyte slurry. Coat the solid electrolyte slurry evenly onto a polytetrafluoroethylene (PTFE) plate, slowly evaporate the solvent at room temperature for 12 hours, and then dry in a vacuum drying oven at 60°C for 24 hours to obtain the solid electrolyte, thus preparing Li4Ti5O." 12 Modified PEO-based solid electrolyte.

[0094] The ionic conductivity of the two solid electrolytes, Example 2 and Comparative Example 3, was tested. The results showed that the Co-Li4Ti5O prepared in Example 2... 12 The modified PEO-based solid electrolyte exhibits an ionic conductivity as high as 3.06 × 10⁻⁶ at 60 °C. -4 S cm -1 While Comparative Example 3 Li4Ti5O 12 The modified PEO-based solid electrolyte has an ionic conductivity of 2.87 × 10⁻⁶ at the same temperature.-4 S cm -1 .

[0095] Comparative Example 4

[0096] Following step (1) of Example 2, cobalt-doped lithium titanate was prepared. After obtaining the precursor C, it was not ball-milled using a zirconia ball mill jar. Instead, the precursor C was directly placed in an alumina boat and calcined at 600°C for 6 hours in a vacuum tube furnace to obtain cobalt-doped lithium titanate (Co-Li4Ti5O). 12 The cobalt-doped lithium titanate prepared at this time has a particle size of 1.5 μm. Due to the excessively large particle size, when it is added to the PEO-based solid electrolyte, the coarser cobalt-doped lithium titanate is difficult to uniformly adhere between two adjacent ether oxygen segments on the PEO chain, resulting in a decrease in lithium ion transport efficiency compared to Example 2, specifically manifested as higher impedance at the same temperature.

[0097] Therefore, ball milling helps improve the transport efficiency of lithium ions in solid electrolytes and reduce impedance. The ball milling process can also be performed after calcination.

[0098] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lithium titanate modified polymer solid electrolyte, characterized in that, It includes: S1, preparing cobalt-doped lithium titanate Co-Li4Ti5O 12 ; The cobalt-doped lithium titanate has a cobalt doping mass percentage of 1.26-2.1% and a particle size of 400-500 nm. S2. Preparation of composite solid electrolyte using solution casting method, including: dissolving PEO and LiTFSI in an organic solvent to obtain a slurry, and weighing 5-15 wt% of cobalt-doped lithium titanate Co-Li4Ti5O3. 12 Add the powder dispersant to the slurry and stir to obtain a homogeneous solid electrolyte slurry; S3. The slurry is evenly coated onto a flat, inert substrate, the solvent is evaporated, and the substrate is transferred to a vacuum drying oven for vacuum drying to obtain Co-Li4Ti5O. 12 / PEO-LiTFSI solid electrolyte.

2. The preparation method according to claim 1, characterized in that, In S1, cobalt-doped lithium titanate Co-Li4Ti5O 12 The preparation method is as follows: S101: A mixed solution obtained by mixing anhydrous ethanol and hydrogen peroxide is gradually added to the mixed solution while stirring. After complete dissolution, a divalent soluble cobalt salt is added dropwise to obtain solution B. S102: Prepare lithium solution A. While stirring solution A, gradually add solution B to it to produce a dark green suspension. Continue stirring to avoid the formation of flocculation and precipitation. S103: Transfer to a high-pressure sealed reactor and react at 175-190℃ for 18-26 hours using a solvothermal method. Filter to obtain the precipitate, wash with deionized water and anhydrous ethanol, and dry to obtain precursor C. S104: Precursor C is ball-milled to obtain precursor D with a smaller particle size. Precursor D is then calcined in a vacuum furnace at 500-800℃ for 3-8 hours to obtain cobalt-doped lithium titanate Co-Li4Ti5O. 12 Alternatively, the precursor C can be calcined in a vacuum furnace at 500-800℃ for 3-8 hours, and then ball-milled to obtain cobalt-doped lithium titanate Co-Li4Ti5O. 12 .

3. The preparation method according to claim 2, characterized in that, In S101, anhydrous ethanol and 30% H2O2 solution are prepared in a volume ratio of 1.8-2.2:

1.

4. The preparation method according to claim 2, characterized in that, In S101, the molar ratio of divalent soluble cobalt salt to tetrabutyl titanate is 1:30-50.

5. The preparation method according to claim 2, characterized in that, In S102, the lithium solution A is prepared by dissolving lithium hydroxide in water; the molar ratio of lithium hydroxide to tetrabutyl titanate is 4-5.5:

5.

6. The preparation method according to claim 2, characterized in that, In S103, a solvothermal reaction was carried out at 180°C for 24 hours in a high-pressure sealed reactor. The precipitate was filtered and washed 2-3 times each with deionized water and anhydrous ethanol, and then dried to obtain precursor C.

7. The preparation method according to claim 2, characterized in that, In S104, a zirconia ball milling jar is used for ball milling, and the ball milling is carried out for more than 4 hours to obtain precursor D with a particle size of 1~2μm. The calcination is carried out in an alumina refractory container in a vacuum tube furnace at 600°C for 6 hours to obtain cobalt-doped lithium titanate (Co-Li4Ti5O). 12 .

8. The preparation method according to claim 2, characterized in that, In S2, PEO and LiTFSI are dissolved in an organic solvent at a mass ratio of 15-20:1 to prepare a slurry.

9. The preparation method according to claim 2, characterized in that, In S3, the flat inert substrate is a polytetrafluoroethylene plate, and the solvent is slowly evaporated at room temperature for 10-12 hours; the vacuum drying conditions are: drying at 55-70℃ in a vacuum drying oven for 18-24 hours.

10. A lithium titanate modified polymer solid electrolyte, characterized in that, The cobalt-doped lithium titanate is prepared by solution casting using a slurry containing cobalt-doped lithium titanate, PEO, and LiTFSI. The cobalt-doped lithium titanate has a cobalt doping mass percentage of 1.26-2.1%, and the mass of cobalt-doped lithium titanate accounts for 5-15% of the mass of PEO. The mass ratio of PEO to LiTFSI is 15-20:

1. The particle size of the cobalt-doped lithium titanate is 400-500 nm.

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