Modified pEO-based solid-state electrolytes, preparation thereof and use in solid-state batteries

Abstract

The application belongs to the field of solid electrolyte materials, and particularly relates to a preparation method of a modified oxidized polyolefin-based solid electrolyte, which comprises synthesis of a solid electrolyte and a vacuum film forming process at T. The solid electrolyte comprises an epoxy polymer base and components A and lithium salt dispersed in the epoxy polymer base; the component A is a modified organic high-molecular polymer rich in hydroxyl groups; 0.5T0<=T<T0, and T0 is the melting temperature of the epoxy polymer. The method can reduce the crystallinity of the oxidized polyolefin-based solid electrolyte to a certain extent, limit the movement of polyanion groups, and improve the cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more specifically to the field of electrolyte technology for solid-state batteries. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage devices, are widely used in mobile phones, computers, and electric vehicles. While pursuing high specific energy and long lifespan, lithium-ion batteries also present significant safety hazards such as occasional combustion and explosion. Using solid-state electrolytes instead of liquid electrolytes can fundamentally solve these safety issues and effectively improve battery energy density and cycle life. Among these, polyethylene oxide (PEO)-based solid-state electrolytes exhibit good chemical stability, strong lithium salt dissolution ability, and are also environmentally friendly materials, currently being widely researched and used in solid-state batteries. For example, Chinese patent document CN113394464A discloses a PEO solid-state electrolyte.

[0003] While PEO-based electrolytes exhibit good stability, they also face some unique challenges, such as easy crystallization and difficulty in lithium-ion migration. To address these issues, the industry has offered several improvement solutions. For example, patent document CN115863745A discloses a polymer / graphene composite solid electrolyte membrane and its preparation method, specifically reporting the improvement of PEO crystallization through the addition of graphene. Another example is Chinese patent document CN113471520A, which discloses a solid electrolyte using cyclodextrin as a filler, its preparation method, and its application, specifically describing the reduction of polymer crystallinity using organic supramolecular cyclodextrin.

[0004] While existing improvement methods can alleviate the crystallization problem of PEO to some extent, the improvement effect is limited. Moreover, it is difficult to simultaneously solve problems such as the low lithium-ion transference number that plague PEO-based solid electrolytes. Some processes reduce the mechanical strength of the solid electrolyte while reducing the crystallinity of the polymer, resulting in severe polarization of lithium ions during electroplating deposition, which is very detrimental to the cycle life of the battery. Summary of the Invention

[0005] To address the issues of high crystallinity and relatively difficult lithium ion migration in PEO-based solid electrolytes, this invention provides a method for preparing a modified PEO-based solid electrolyte, aiming to solve the problems of high crystallinity and difficult lithium ion migration in PEO-based solid electrolytes.

[0006] The second objective of this invention is to provide a modified PEO-based solid electrolyte prepared by the aforementioned method and its application in lithium-ion batteries.

[0007] A third object of the present invention is to provide a lithium-ion battery comprising the modified PEO-based solid electrolyte.

[0008] Due to the differences in the polymer matrices of solid electrolytes, different technical problems need to be overcome. For example, for PEO-based solid electrolytes, problems such as the easy formation of spherulitic phases in PEO and the difficulty of lithium-ion migration need to be overcome. In view of this problem, the present invention provides the following improvement solutions:

[0009] A preparation method of a modified PEO-based solid electrolyte, in which PEO, CMC-Li, and LiFSI are slurried and then coated on a mold, and then first-stage heat treatment is carried out under the conditions of pressure P1 and temperature T1, and then second-stage heat treatment is carried out under the conditions of pressure P2 and temperature T2 to obtain the modified PEO-based solid electrolyte;

[0010] Wherein, P1 and P2 are less than 0.1 MPa; 0.5T0 ≤ T1 < T2 < T0, and the T0 is the melting point temperature of PEO.

[0011] The present invention innovatively combines PEO, CMC-Li, and LiFSI synergistically to perform the two-stage gradient negative pressure controlled temperature heat treatment. In this way, problems such as the easy crystallization of PEO-based solid electrolytes and the difficulty of lithium-ion migration can be synergistically solved unexpectedly, and the lithium-ion migration and high-temperature cycle stability of PEO-based solid electrolytes can be significantly improved.

[0012] In the present invention, the synergy of the components of PEO, CMC-Li, and LiFSI and the combination of the two-stage gradient negative pressure treatment process are the key to synergistically solving the problems of easy crystallization and difficult lithium-ion migration of PEO-based solid electrolytes.

[0013] In the present invention, there is no special requirement for the type of PEO, as long as it can meet the application requirements of solid electrolytes. For example, its molecular weight is 1 million to 4 million, and further it can be 1 million to 600,000.

[0014] In the present invention, the melting point of the PEO can be, for example, 60 to 100 °C, and further it can be 60 to 70 °C.

[0015] In the present invention, the molecular weight of the CMC-Li is 1000 to 5000, and further it can be 4000 to 5000.

[0016] In the present invention, the Li content of the CMC-Li can be adjusted as needed. For example, it can be 1 to 5 wt.%, and further it can be 2 to 4 wt.%.

[0017] In this invention, the weight ratio of PEO, CMC-Li, and LiFSI is 1:0.03-0.06:0.1-0.4; preferably 1:0.04-0.05:0.2-0.3.

[0018] In this invention, the solvent used in the pulping process includes at least one of ACN, DMF, or NMP;

[0019] In this invention, the slurry preparation method can be conventional, and the solid content of the slurry after slurry preparation only needs to be suitable for the coating requirements. For example, the solid content of the slurry after slurry preparation is 0.05 to 0.1 g / mL; the solid content refers to the ratio of the total weight to the volume of PEO, CMC-Li, and LiFSI.

[0020] In this invention, the mold can be any mold known in the industry suitable for the preparation of solid electrolytes; for example, it can be a mold with a smooth and flat surface. Further, the mold is a smooth, flat mold without adhesive properties.

[0021] In this invention, thanks to the synergistic combination of PEO, CMC-Li, and LiFSI, and further coordinated with the subsequent two-stage gradient temperature-controlled heat treatment process, as well as the temperature and pressure during the treatment process, the PEO crystallization problem and the difficulty of lithium migration can be suppressed in a synergistic way, thereby improving the overall performance of the obtained solid electrolyte.

[0022] In this invention, 0.5T0≤T1≤0.8T0, 0.8T0<T2≤0.95T0;

[0023] Preferably, the temperature of T1 can be 40-50°C, and the temperature of T2 can be 55-60°C.

[0024] The present invention also shows that, based on the two-stage gradient temperature control, further gradient pressure control helps to synergistically suppress PEO crystallization and synergistically improve the overall performance of the prepared solid electrolyte.

[0025] In this invention, P1 > P2;

[0026] Preferably, P1 is -0.06 to -0.04 MPa;

[0027] Preferably, P2 ≤ -0.1MPa, and considering processing costs, it can be further -0.5MPa to -0.1MPa.

[0028] The study unexpectedly showed that by controlling the pressure P1, temperature T1, pressure P2, and temperature T2 together, the problems of easy crystallization of PEO matrix and difficulty in lithium ion migration could be further suppressed, and the electrochemical performance of the prepared solid electrolyte could be further synergistically improved.

[0029] In this invention, the heat treatment and pressure holding time t1 of the first stage of heat treatment is 5 to 20 hours, preferably 10 to 15 hours;

[0030] Preferably, the heat treatment and pressure holding time t2 of the second stage is 5 to 20 hours, and more preferably 10 to 15 hours.

[0031] The present invention also provides a modified PEO-based solid electrolyte prepared by the preparation method described above.

[0032] In this invention, the preparation method can endow the prepared solid electrolyte with special physicochemical characteristics, and the solid electrolyte with the characteristics obtained by the preparation method can unexpectedly exhibit better electrochemical performance.

[0033] The present invention also provides a solid-state lithium-ion battery, comprising a positive electrode, a solid electrolyte and a negative electrode sequentially composited, wherein the solid electrolyte is a modified PEO-based solid electrolyte prepared by the preparation method described in the present invention.

[0034] The solid-state lithium-ion battery of the present invention, except for the modified PEO-based solid electrolyte described in the present invention, can have other conventional components and parts.

[0035] For example, the positive electrode described in this invention can be conventional, for example, its active material is at least one of lithium iron phosphate, lithium manganese iron phosphate, and nickel-cobalt-manganese ternary materials.

[0036] For example, the negative electrode is lithium metal or a negative electrode containing at least one negative electrode active material, such as graphite or silicon.

[0037] In this invention, the solid-state lithium-ion battery is an all-solid-state lithium battery.

[0038] Beneficial effects

[0039] This invention innovatively combines PEO, CMC-Li, and LiFSI, and further incorporates gradient temperature-controlled heat treatment in the first and second stages. This unexpectedly and synergistically solves problems such as easy crystallization and difficulty in lithium ion migration in PEO-based solid electrolytes, and can significantly improve lithium ion migration and cycle stability of PEO-based solid electrolytes.

[0040] In this invention, based on the combined components of PEO, CMC-Li, and LiFSI, the combination of gradient temperature control and gradient pressure control processes can further solve the problems of easy crystallization of PEO and difficulty in lithium migration, which helps to further improve the performance of the prepared solid electrolyte. Attached Figure Description

[0041] Figure 1 SEM images of the unmodified membrane (Comparative Example 1) and the membrane modified in Example 1 are shown, where (a and c are the corresponding test images of the unmodified membrane; b and d are the corresponding test images of the modified membrane).

[0042] Figure 2 XRD patterns of the unmodified membrane (Comparative Example 1) and the modified membrane of Example 1;

[0043] Figure 3 Impedance diagrams of the unmodified membrane (Comparative Example 1) and the modified membrane of Example 1;

[0044] Figure 4 This is a graph showing the ion transport number test results for Example 1;

[0045] Figure 5 Cycling diagrams of the unmodified membrane (Comparative Example 1) and the modified membrane of Example 1; Detailed Implementation

[0046] The specific steps of the present invention are illustrated below through embodiments, but the present invention is not limited to the following embodiments. Various processes and methods not described in detail in the present invention are conventional methods known in the art.

[0047] As an example of typical implementation, in the following cases, unless otherwise stated, the PEO used has a MW~600000 rating from Aladdin and a melting point (T0) of 65°C.

[0048] The CMC-Li used has a molecular weight of 4000-5000, comes from Green Energy Fiber Materials Co., Ltd., and has a lithium content of 3±0.5wt%.

[0049] In this invention, solid electrolyte membranes can be assembled into energy storage devices using known methods, and their electrochemical performance can be tested. For example, in the following cases, the electrochemical testing method is as follows:

[0050] EIS impedance testing: The impedance diagram of the electrolyte is measured using an electrochemical workstation, and then analyzed using the formula... The ionic conductivity was calculated.

[0051] Cycle performance testing of lithium iron phosphate solid-state batteries: Lithium metal was used as the negative electrode, and an electrode sheet coated with LFP (lithium iron phosphate):PVDF:conductive carbon black in a 7:2:1 ratio was used as the positive electrode. A button cell was assembled with a solid electrolyte, and the cycle performance of the battery was tested using a battery testing system. The test temperature was 60℃.

[0052] Example 1

[0053] 0.142 g LiFSI was weighed into a 20 mL serum bottle in a glove box. 12 mL of acetonitrile solution was added dropwise to the bottle, and the mixture was stirred on a stirring table. 0.0264 g CMC-Li was weighed and added to the bottle, and the mixture was stirred for 1 h to ensure uniform dispersion. Then, 0.66 g PEO was weighed and added uniformly to the solution being stirred. The mixture was stirred thoroughly at room temperature for 24 h to obtain a homogeneous solid electrolyte slurry. After stirring, the slurry was uniformly dispersed in a smooth, flat mold made of polytetrafluoroethylene (PTFE). It was first subjected to a heat treatment at 45℃ (T1) and P1 (-0.05 MPa) for 12 h (t1), and then subjected to a heat treatment at 60℃ (T2) and P2 (-0.1 MPa) for 12 h (t2) to obtain a modified PEO-based solid electrolyte membrane (modified membrane). The microstructure is shown in the figure. Figure 1 (b and 1d).

[0054] X-ray diffraction analysis (XRD) is shown in the figure. Figure 2 The results show that the degree of crystallinity of the polymer changed significantly before and after the treatment.

[0055] EIS impedance testing, using the formula The calculated ionic conductivity is 1.04 × 10⁻⁶. -4 S / cm.

[0056] Ion mobility number testing, using the formula The calculated ion transport number is 0.46.

[0057] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 160 mAh·g. -1 After 100 cycles, the specific capacity retention rate was 95%, and after 200 cycles, the specific capacity retention rate was 86%.

[0058] Example 2

[0059] Compared to Example 1, the only difference is that P1 and P2 were changed to not form gradient voltage control. The experimental groups were as follows:

[0060] Group A: P1 and P2 are the same, both are -0.05MPa;

[0061] Group B: P1 and P2 are the same, both are -0.1MPa;

[0062] The results were obtained by measuring according to the method in Example 1:

[0063] Group A: EIS impedance test, ionic conductivity 8.32 × 10⁻⁶ -5 S / cm. Ion transport number is 0.44.

[0064] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 152 mAh / g. -1 After 200 cycles, the specific capacity retention rate was 82%.

[0065] Group B: EIS impedance test, ionic conductivity 7.92 × 10⁻⁶ -5 S / cm. Ion transport number is 0.43.

[0066] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 150 mAh·g. -1 After 200 cycles, the specific capacity retention rate was 81%.

[0067] As can be seen from Examples 1 and 2, on the basis of two-stage gradient heating heat treatment, further combined with two-stage gradient pressure control, can unexpectedly achieve a synergistic effect, which helps to further solve the problems of easy crystallization of PEO and difficulty in lithium ion migration, improve the lithium migration effect of the prepared solid electrolyte, and improve its capacity retention.

[0068] Example 3

[0069] Compared with Example 1, the only difference is that the mass ratio of CMC-Li and LiFSI added was changed, and the experimental groups were as follows:

[0070] Group A: The weight ratio of PEO, CMC-Li, and LiFSI is 1:0.02:0.25.

[0071] Group B: The weight ratio of PEO, CMC-Li, and LiFSI is 1:0.06:0.15.

[0072] The results were obtained by measuring according to the method in Example 1:

[0073] Group A: EIS impedance test, ionic conductivity 7.56 × 10⁻⁶ -5 S / cm. Ion transport number is 0.41.

[0074] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 145 mAh / g. -1 After 200 cycles, the specific capacity retention rate was 78%.

[0075] Group B: EIS impedance test, ionic conductivity 7.92 × 10⁻⁶-5 S / cm. Ion transport number is 0.42.

[0076] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 148 mAh·g. -1 After 200 cycles, the specific capacity retention rate is 80%.

[0077] Example 4

[0078] Compared with Example 1, the only difference is that T1 / T2 / P1 / P2 / t1 / t2 are changed, and the experimental groups are as follows:

[0079] Group A: T1 is 40℃, P1 is -0.06MPa, t1 is 15h, T2 is 55℃, P2 is -0.2MPa, t2 is 15h;

[0080] Group B: T1 is 50℃, P1 is -0.04MPa, t1 is 10h, T2 is 60℃, P2 is -0.15MPa, t2 is 10h;

[0081] The results were obtained by measuring according to the method in Example 1:

[0082] Group A: EIS impedance test, ionic conductivity 8.63 × 10⁻⁶ -5 S / cm. Ion transport number is 0.40.

[0083] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 149 mAh·g. -1 After 200 cycles, the specific capacity retention rate is 80%.

[0084] Group B: EIS impedance test, ionic conductivity 7.37 × 10⁻⁶ -5 S / cm. Ion transport number is 0.42.

[0085] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 151 mAh·g. -1 After 200 cycles, the specific capacity retention rate was 81%.

[0086] Comparative Example 1

[0087] 0.142 g LiFSI was weighed into a 20 mL serum bottle in a glove box. 12 mL acetonitrile solution was added dropwise to the bottle, and the mixture was stirred on a stirring table for 0.5 h to ensure uniform dispersion. Then, 0.66 g PEO was weighed and added uniformly to the solution being stirred. The mixture was stirred thoroughly at room temperature for 24 h to obtain a homogeneous solid electrolyte slurry. After stirring, the slurry was uniformly dispersed in a smooth polytetrafluoroethylene (PTFE) mold and vacuum dried at 60 °C for 24 h. The solvent was evaporated, and the film was dried to obtain a PEO-based solid electrolyte membrane (unmodified membrane). The microstructure is shown in [Figure showing microstructure]. Figure 1 a and 1c).

[0088] Comparative Example 2

[0089] Compared to Example 1, the only difference is that gradient temperature control was not performed, and the experimental groups were as follows:

[0090] Group A: T1 and T2 are the same, both at 45℃;

[0091] Group B: T1 and T2 are the same, both at 60℃;

[0092] The results were obtained by measuring according to the method in Example 1:

[0093] Group A: Ionic conductivity 5.86 × 10⁻⁶ -5 S / cm.

[0094] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 142 mAh / g. -1 After 200 cycles, the specific capacity retention rate was 71%.

[0095] Group B: Ionic conductivity 6.93 × 10⁻⁶ -5 S / cm. Cycling at 0.2C, the first cycle was 144 mAh·g. -1 After 200 cycles, the specific capacity retention rate was 73%.

[0096] As can be seen from Example 1, the gradient temperature control treatment of the present invention can unexpectedly further solve the problems of PEO crystallization and lithium migration difficulties, and can achieve better results.

[0097] Comparative Example 3

[0098] Compared with Example 1, the only difference is that the lithium salt is replaced with LITFSI, while the other processes and testing conditions are the same as in Example 1.

[0099] EIS impedance testing showed an ionic conductivity of 2.36 × 10⁻⁶. -5 S / cm. Ion transport number is 0.31.

[0100] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 144 mAh·g. -1 After 200 cycles, the specific capacity retention rate was 51%.

[0101] Comparative Example 4

[0102] Compared with Example 1, the only difference is that an equal amount of CMC is used to replace CMC-Li, while other processes and testing conditions are the same as in Example 1.

[0103] EIS impedance testing showed an ionic conductivity of 4.59 × 10⁻⁶. -5 S / cm. Ion transport number is 0.34.

[0104] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 139 mAh·g. -1 After 200 cycles, the specific capacity retention rate was 37%.

[0105] Comparative Example 5

[0106] Compared with Example 1, the only difference is that an equal amount of CMC-Na is used to replace CMC-Li, while other processes and testing conditions are the same as in Example 1.

[0107] EIS impedance testing showed an ionic conductivity of 5.23 × 10⁻⁶. -5 S / cm. Ion transport number is 0.35.

[0108] Lithium iron phosphate solid-state battery cycle test: Cycling at 0.2C rate, the first cycle yielded 142 mAh / g. -1 After 200 cycles, the specific capacity retention rate was 42%.

Claims

1. A preparation method of a modified PEO-based solid electrolyte, which comprises slurrying PEO, CMC-Li, and LiFSI and then coating the slurry on a mold, followed by first-stage heat treatment under the conditions of pressure P1 and temperature T1, and then second-stage heat treatment under the conditions of pressure P2 and temperature T2 to obtain the modified PEO-based solid electrolyte; in, P1 and P2 are less than 0.1 MPa; 0.5T0 ≤ T1 < T2 < T0, where T0 is the melting point temperature of PEO; P1 > P2; The weight ratio of PEO, CMC-Li, and LiFSI is 1:0.03 - 0.06:0.1 - 0.

4.

2. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The molecular weight of the PEO is 1 million - 4 million.

3. The method for preparing the modified PEO-based solid electrolyte as described in claim 2, characterized in that, The molecular weight of the PEO is 1 million - 600,000.

4. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The molecular weight of the CMC-Li is 1000 - 5000.

5. The method for preparing the modified PEO-based solid electrolyte as described in claim 4, characterized in that, The molecular weight of the CMC-Li is 3000 - 5000.

6. The method for preparing the modified PEO-based solid electrolyte as described in claim 4, characterized in that, The Li content of the CMC-Li is 1 - 5 wt.%.

7. The method for preparing the modified PEO-based solid electrolyte as described in claim 6, characterized in that, The Li content of the CMC-Li is 2 - 4 wt.%.

8. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The weight ratio of PEO, CMC-Li, and LiFSI is 1:0.04 - 0.05:0.2 - 0.

3.

9. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The solvent used in the slurrying process includes at least one of ACN, DMF, or NMP; In the slurried slurry, the solid content is 0.05 - 0.1 g / mL.

10. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The mold has a smooth and flat surface.

11. The method for preparing the modified PEO-based solid electrolyte as described in claim 10, characterized in that, The mold is a smooth and flat mold without adhesion.

12. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, 0.5T0 ≤ T1 ≤ 0.8T0, 0.8T0 < T2 ≤ 0.95T0.

13. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, characterized in that, The temperature of T1 is 40 - 50 °C, and the temperature of T2 is 55 - 60 °C.

14. The preparation method of the modified PEO-based solid electrolyte according to claim 1, wherein, P1 is -0.06 - -0.04 MPa; P2 ≤ -0.1 MPa.

15. The method for preparing the modified PEO-based solid electrolyte as described in claim 1, 12, 13, or 14, characterized in that, The heat preservation and pressure maintenance treatment time t1 of the first-stage heat treatment is 5 - 20 h; The heat preservation and pressure maintenance treatment time t2 of the second-stage heat treatment is 5 - 20 h.

16. The method for preparing the modified PEO-based solid electrolyte as described in claim 15, characterized in that, The heat preservation and pressure maintenance treatment time t1 of the first-stage heat treatment is 10 - 15 h; The heat preservation and pressure maintenance treatment time t2 of the second-stage heat treatment is 10 - 15 h.

17. A modified PEO-based solid electrolyte prepared by the preparation method according to any one of claims ១ - ១៦.

18. A solid-state lithium-ion battery, comprising a positive electrode, a solid electrolyte, and a negative electrode sequentially combined, characterized in that, The solid electrolyte is a modified PEO-based solid electrolyte prepared by the preparation method according to any one of claims ១ - ១៦.

19. The solid-state lithium-ion battery as described in claim 18, characterized in that, The active material in the positive electrode is at least one of lithium iron phosphate, lithium manganese iron phosphate, and nickel cobalt manganese ternary.

20. The solid-state lithium-ion battery as described in claim 18, characterized in that, The negative electrode is lithium metal or a negative electrode containing at least one of graphite or silicon as the negative electrode active material.

21. The solid-state lithium-ion battery according to any one of claims 18 to 20, characterized in that, The solid-state lithium-ion battery is an all-solid-state lithium battery.

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