Solid-state electrolyte, preparation method and lithium ion battery

Abstract

This invention provides a solid electrolyte, a preparation method, and a lithium-ion battery. The solid electrolyte comprises a deuterated sulfone compound, a lithium salt, and a polymer electrolyte. The lithium salt content is 14-45 wt%, the deuterated sulfone compound content is 4-17 wt%, and the polymer electrolyte content is 38-82 wt%. In this scheme, the polymer electrolyte and the deuterated sulfone compound are connected by deuterated hydrogen bonds. By increasing the ratio between the lithium salt and the sulfone compound, the proportion of unpaired sulfone compounds is reduced, thereby improving compatibility with the electrode. Simultaneously, mixing with a polymer that can form hydrogen bonds forms a lithium salt anion-sulfone compound-deuterated sulfone compound bond structure, which fixes the sulfone compound and improves the damage of the SEI film caused by the sulfone compound, effectively improving the compatibility between the sulfone electrolyte and the negative electrode.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and more particularly to a solid electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the increasing demand for lithium batteries in electric vehicles, effectively balancing energy density and safety has become a key research focus. Ternary cathodes are an effective means to improve energy density, but their high-voltage characteristics place high demands on the stability of the electrolyte.

[0003] While carbonate-based electrolytes currently exhibit excellent overall performance over a wide temperature range, their oxidation potential limits their oxidation stability at high voltages (>4.3V), making them prone to interfacial side reactions. They are also flammable, posing safety hazards. Sulfone compounds possess oxidation stability above 5.5V and high dielectric constants, making them commonly used in low-temperature alkaline ion batteries and Li-O2 batteries. However, sulfones present interfacial compatibility issues when paired with graphite anodes. Experimental data shows that in additive-free sulfolane electrolytes, the capacity of a Li / graphite half-cell after 50 cycles is only approximately 24.54 mAh / g, with a capacity retention rate as low as approximately 19.4%.

[0004] In summary, there is still a lack of electrolytes in the current technology that can simultaneously have good compatibility with graphite anodes and withstand high voltage. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention provides a solid electrolyte comprising a deuterated sulfone compound, a lithium salt, and a polymer electrolyte, wherein the lithium salt content is 14-45 wt%, the deuterated sulfone compound content is 4-17 wt%, and the polymer electrolyte content is 38-82 wt%, and the polymer electrolyte and the deuterated sulfone compound are connected by deuterated hydrogen bonds.

[0006] Preferably, the deuterated sulfone compound is in the form of a chain, and the mass ratio of the lithium salt to the deuterated sulfone compound is 1:(0.2~0.4).

[0007] Preferably, the deuterated sulfone compound is a deuterated cyclic sulfone compound, and the mass ratio of the lithium salt to the deuterated sulfone compound is 1:(0.3~1.4).

[0008] This application improves compatibility with the electrode by increasing the ratio between lithium salt and sulfone compounds and reducing the proportion of unpaired sulfone compounds. Simultaneously, mixing with a polymer capable of forming hydrogen bonds creates a bond structure of lithium salt anion-sulfone compound-deuterated sulfone compound, which immobilizes the sulfone compounds and reduces their destructive effect on the SEI film. This effectively improves the compatibility between the sulfone electrolyte and the negative electrode, while also increasing the lithium-ion transport rate, resulting in a solid-state electrolyte that combines high voltage resistance with good compatibility with graphite negative electrodes.

[0009] On the other hand, the present invention also provides a method for preparing a solid electrolyte, comprising the following steps: mixing a deuterated sulfone compound, a lithium salt, and a polymer electrolyte at a temperature higher than the melting point of the deuterated sulfone compound to obtain mixture A; casting and coating mixture A, and placing it at -80~-10℃ for 10-30 hours to obtain a pretreated electrolyte; and placing the pretreated electrolyte at -20℃~0℃ with a vacuum degree ≤10. -3 Under the Pa environment, excess deuterated sulfone compounds are removed to obtain a solid electrolyte containing the target amount of deuterated sulfone compounds.

[0010] By placing the electrolyte at -80~-10℃ for 10-30h, a low-temperature pre-freezing process is performed, which facilitates the preparation of a solid electrolyte containing the target amount of deuterated sulfone compound.

[0011] Preferably, mixture A is prepared by mixing a deuterated sulfone compound with a lithium salt to form mixture B, mixing a deuterated sulfone compound with a polymer electrolyte to form mixture C, and mixing mixture B and mixture C to obtain mixture A.

[0012] Preferably, the concentration of the lithium salt and deuterated sulfone compound in mixture A is 3-6 mol / L.

[0013] Preferably, the lithium salt and polymer electrolyte are mixed to obtain mixture D; mixture D is then mixed with the deuterated sulfone compound at a temperature above the melting point of the deuterated sulfone compound.

[0014] Preferably, the mass ratio of the mixture D to the deuterated sulfone compound is 1:(1-5).

[0015] On the other hand, the present invention also proposes the application of solid electrolytes in graphite batteries.

[0016] On the other hand, the present invention also proposes the application of solid electrolytes in lithium-ion batteries.

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description and claims. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In this application, deuterated hydrogen bond refers to A–D···B, where A and B are atoms with high electronegativity, including but not limited to O, N, and F. This application uses conventional commercially available raw materials as an example. Polymers containing hydrogen-bonding elements formed by grafting, substitution, blending, or other means are all within the scope of protection of this application. The method for controlling the content of deuterated sulfone compounds in the solid electrolyte in this application is as follows: during the freeze-drying and sublimation process of the electrolyte layer, a low-temperature vacuum oven with a cutting area of ​​5×5cm is opened every 1 hour. 2 The content of deuterated sulfone compounds in the solid electrolyte was detected by thermogravimetric analysis until the content of deuterated sulfone compounds reached the target value.

[0020] To more clearly demonstrate the preparation method of this application, the following examples and comparative examples are provided.

[0021] Example 1 A solid electrolyte is prepared by the following steps: 119g of lithium salt, 119g of polymer electrolyte, and 860g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -20°C for 24 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -5°C for 10 hours. -3 Under the Pa environment, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 12wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated dimethyl sulfoxide.

[0022] Example 2 A solid electrolyte is prepared by the following steps: 140g of lithium salt, 820g of polymer electrolyte, and 860g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -10°C for 36 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -10°C for 10 hours. -5 Under the condition of Pa, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 4wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated dimethyl sulfoxide.

[0023] Example 3 A solid electrolyte is prepared by the following steps: 450g of lithium salt, 380g of polymer electrolyte, and 1000g of deuterated sulfone compound are weighed and mixed uniformly at 45°C to obtain mixture A. Mixture A is cast and coated onto a polytetrafluoroethylene plate and placed at -80°C for 10 hours to obtain a pre-frozen electrolyte layer. The pre-frozen electrolyte layer is then placed at 10°C for 10 hours... -3 Under the condition of Pa, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 17wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated sulfolane.

[0024] Example 4 The difference from Example 1 is that the electrolyte layer was lyophilized and sublimated until the content of deuterated sulfone compound was 9.091 wt%.

[0025] Example 5 The difference from Example 1 is that the electrolyte layer was lyophilized and sublimated until the content of deuterated sulfone compound was 16.667 wt%.

[0026] Example 6 A solid electrolyte is prepared by the following steps: 140g of lithium salt, 820g of polymer electrolyte, and 1500g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -10°C for 36 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -10°C for 10 hours. -3Under the Pa environment, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 4.192 wt%, and the target electrolyte with a thickness of 10 μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated sulfolane.

[0027] Example 7 The difference from Example 6 is that the pre-frozen electrolyte layer is placed at -10°C and 10... -3 The electrolyte layer was lyophilized and sublimated under Pa conditions until the content of deuterated sulfone compounds was 16.955 wt%.

[0028] Example 8 The difference from Example 6 is that the deuterated sulfonate was divided into 219g and 1281g, the lithium salt was mixed with 219g of the deuterated sulfonate compound to obtain a lithium salt solution, the polymer electrolyte was mixed with 1281g of the deuterated sulfonate compound to obtain a polymer electrolyte solution, and the lithium salt solution and the polymer electrolyte solution were mixed to obtain mixture A.

[0029] Example 9 The difference from Example 8 is that 140g of lithium salt and 820g of polymer electrolyte were first dissolved in deuterated sulfone compound to form 3mol / L solutions. Then, the lithium salt solution and polymer electrolyte solution were mixed uniformly to obtain mixture A.

[0030] Example 10 The difference from Example 9 is that 140g of lithium salt was dissolved in a deuterated sulfone compound to form a 6mol / L solution.

[0031] Example 11 The difference from Example 10 is that 140g of lithium salt was dissolved in a deuterated sulfone compound to form a 5mol / L solution.

[0032] Example 12 The difference from Example 10 is that 140g of lithium salt was dissolved in a deuterated sulfone compound to form an 8mol / L solution.

[0033] Example 13 The difference from Example 6 is that the lithium salt and polymer electrolyte are first mixed evenly to obtain mixture D, and mixture D is mixed with 1500g of deuterated sulfone compound to obtain mixture A.

[0034] Example 14 The difference from Example 13 is that the lithium salt and polymer electrolyte are first mixed evenly to obtain mixture D, and mixture D is mixed with 960g of deuterated sulfone compound to obtain mixture A.

[0035] Example 15 The difference from Example 13 is that the lithium salt and polymer electrolyte are first mixed evenly to obtain mixture D, and mixture D is mixed with 2880g of deuterated sulfone compound to obtain mixture A.

[0036] Example 16 The difference from Example 13 is that the lithium salt and polymer electrolyte are first mixed evenly to obtain mixture D, and mixture D is mixed with 4000g of deuterated sulfone compound to obtain mixture A.

[0037] Comparative Example 1 A solid electrolyte is prepared by the following steps: 119g of lithium salt, 119g of polymer electrolyte, and 860g of sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -20°C for 24 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -5°C for 10 hours. -3 Under the condition of Pa, the electrolyte layer is freeze-dried and sublimated until the sulfone compound content is 12wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the sulfone compound is dimethyl sulfoxide.

[0038] Comparative Example 2 A solid electrolyte is prepared by the following steps: 119g of lithium salt, 119g of polymer electrolyte, and 860g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -20°C for 24 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -5°C for 10 hours. -3 Under the condition of Pa, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is less than 1 wt%, and a target electrolyte with a thickness of 10 μm can be obtained. In this comparative example, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated dimethyl sulfoxide.

[0039] Comparative Example 3 A solid electrolyte is prepared by the following steps: 119g of lithium salt, 119g of polymer electrolyte, and 1190g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -20°C for 24 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -5°C for 10 hours. -3 Under the Pa environment, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 12wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this comparative example, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated dimethyl sulfoxide.

[0040] Comparative Example 4 A solid electrolyte is prepared by the following steps: 100g of lithium salt, 820g of polymer electrolyte, and 1500g of deuterated sulfone compound are weighed and mixed at 25°C with stirring at 700 rpm for 8 hours to obtain mixture A; mixture A is cast onto a polytetrafluoroethylene plate and placed at -20°C for 24 hours to obtain a pre-frozen electrolyte layer; then the pre-frozen electrolyte layer is placed at -5°C for 10 hours. -3 Under the Pa environment, the electrolyte layer is freeze-dried and sublimated until the content of deuterated sulfone compound is 8wt%, and the target electrolyte with a thickness of 10μm can be obtained. In this embodiment, the lithium salt is LiTFSI, the polymer electrolyte is PVDF, and the deuterated sulfone compound is deuterated dimethyl sulfoxide.

[0041] Sample preparation The solid electrolyte membranes prepared in the above embodiments and comparative examples were cut into 16mm diameter discs and assembled into steel-steel blocking batteries for testing.

[0042] The solid electrolyte membranes prepared in the above embodiments and comparative examples were cut into discs with a diameter of 16 mm and assembled with positive and negative electrodes to form a half-cell. The positive electrode material was graphite and the negative electrode material was lithium. Specifically, the positive electrode sheet was prepared by mixing graphite, conductive agent SuperP, and binder PVDF in a mass ratio of 90:5:5 to form a slurry, which was then coated onto copper foil, dried, and cut into sheets to obtain a graphite positive electrode sheet. The lithium foil was cut and used as the negative electrode sheet. The solid electrolyte membranes prepared in the above embodiments and comparative examples were placed between the positive and negative electrodes to assemble a graphite-lithium system half-cell for testing.

[0043] The solid electrolyte membranes prepared in the above embodiments and comparative examples were cut into 16mm diameter discs and assembled into lithium-steel system batteries for testing.

[0044] Testing items 1) Room temperature ionic conductivity test The assembled blocking battery was placed in a constant temperature chamber at 25℃±2℃. After the temperature stabilized, AC impedance testing was performed using an electrochemical workstation with a frequency range of 1MHz to 0.1Hz and a perturbation voltage amplitude of 10mV. The intercept of the high-frequency region with the real axis was read from the obtained Nyquist plot, which is the bulk resistance Rb of the electrolyte membrane. The ionic conductivity was calculated using the formula σ=d / (Rb·S), where d is the membrane thickness and S is the effective electrode area.

[0045] 2) Cyclic performance test Cyclic performance tests were conducted on the half-cell at room temperature and 55℃±5℃. The half-cell was charged at a constant current of 0.1C to 4.4V, then charged at a constant voltage until the current dropped below 0.05C, and then discharged at 0.1C to 2.8V. The above charge and discharge process was repeated and the capacity retention rate (nth capacity / initial capacity × 100%) was calculated. The cycle was stopped when the capacity retention rate was lower than 86% of the initial capacity and the number of cycles was recorded.

[0046] 3) Stability test Stability tests were conducted on the lithium-steel battery system at 25°C using an electrochemical workstation to perform a linear potential scan from the open-circuit voltage towards the anode, with an upper limit of 6.0V (relative to Li / Li). + The scan rate was 1 mV / s. The current-voltage curve was recorded, and the potential corresponding to the sharp increase in current was taken as the oxidative decomposition potential of the electrolyte.

[0047] The detection results of the above embodiments and comparative examples are shown in the table below: Example 1 <![CDATA[5.82×10 -4 ]]> 753 759 5.88 Example 2 <![CDATA[5.48×10 -4 ]]> 704 707 5.63 Example 3 <![CDATA[5.73×10 -4 ]]> 1028 1051 5.98 Example 4 <![CDATA[5.71×10 -4 ]]> 722 726 5.79 Example 5 <![CDATA[5.65×10 -4 ]]> 726 700 5.85 Example 6 <![CDATA[5.44×10 -4 ]]> 1038 1045 5.76 Example 7 <![CDATA[5.49×10 -4 ]]> 1051 1058 5.75 Example 8 <![CDATA[5.38×10 -4 ]]> 1062 1134 5.78 Example 9 <![CDATA[5.37×10 -4 ]]> 1054 1130 5.78 Example 10 <![CDATA[5.49×10 -4 ]]> 1121 1163 5.82 Example 11 <![CDATA[5.45×10 -4 ]]> 1108 1146 5.8 Example 12 <![CDATA[5.29×10 -4 ]]> 1005 995 5.77 Example 13 <![CDATA[5.74×10 -4 ]]> 1132 1197 5.94 Example 14 <![CDATA[5.23×10 -4 ]]> 1088 1083 5.8 Example 15 <![CDATA[5.25×10 -4 ]]> 1082 1127 5.92 Example 16 <![CDATA[4.32×10 -4 ]]> 894 648 5.91 Comparative Example 1 <![CDATA[2.75×10 -4 ]]> 589 267 5.12 Comparative Example 2 <![CDATA[3.52×10 -5 ]]> 725 752 4.86 Comparative Example 3 <![CDATA[7.98×10 -4 ]]> 248 16 6.1 Comparative Example 4 <![CDATA[2.55×10 -4 ]]> 618 620 5.64 In addition to the above comparisons, solid electrolytes with LiTFSI content higher than 45 wt% were also prepared. It was found that the obtained electrolyte layer was easy to rub and the powder loss was >5%. The powder loss of Comparative Example 2 of this application was ≈2%, and the powder loss of solid electrolytes obtained by other comparative examples and embodiments was ≤1%.

[0048] In addition, the solid electrolyte layers prepared in Comparative Example 1 and Example 1 were stacked with the same positive and negative electrode sheets to form a full cell. The positive electrode sheet was prepared by mixing NCM811, conductive agent SuperP, and binder PVDF in a mass ratio of 90:5:5 to form a slurry, which was then coated onto aluminum foil, dried, and cut into sheets. The negative electrode sheet was prepared by mixing graphite, conductive agent SuperP, and binder PVDF in a mass ratio of 90:5:5 to form a slurry, which was then coated onto copper foil, dried, and cut into sheets. After 1000 cycles of 1C charge and discharge, the battery was disassembled. The surface of the electrode sheet in Example 1 showed no obvious abnormalities, while the surface of the negative electrode sheet in Comparative Example 1 showed lithium plating.

[0049] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A solid electrolyte, characterized in that, include: The mixture comprises a deuterated sulfone compound, a lithium salt, and a polymer electrolyte, wherein the lithium salt comprises 14-45 wt%, the deuterated sulfone compound comprises 4-17 wt%, and the polymer electrolyte comprises 38-82 wt%, and the polymer electrolyte and the deuterated sulfone compound are linked by deuterated hydrogen bonds.

2. The solid electrolyte according to claim 1, wherein the deuterated sulfone compound is in the form of chains, and the mass ratio of the lithium salt to the deuterated sulfone compound is 1:(0.2~0.4).

3. The solid electrolyte according to claim 1, wherein the deuterated sulfone compound is a deuterated cyclic sulfone compound, and the mass ratio of the lithium salt to the deuterated sulfone compound is 1:(0.3~1.4).

4. The method for preparing the solid electrolyte according to claim 1, characterized in that, Includes the following steps, At a temperature above the melting point of the deuterated sulfone compound, the lithium salt and the polymer electrolyte are mixed to obtain mixture A; Mixture A was cast and coated, and placed at -80~-10℃ for 10-36 hours to obtain a pretreated electrolyte; the pretreated electrolyte was then placed at -10℃~10℃ under a vacuum of ≤10 -3 Under the Pa environment, excess deuterated sulfone compounds are removed to obtain a solid electrolyte containing the target amount of deuterated sulfone compounds.

5. The method for preparing the solid electrolyte according to claim 4, characterized in that, The preparation method of mixture A is as follows: a deuterated sulfone compound is mixed with a lithium salt to form mixture B, a deuterated sulfone compound is mixed with a polymer electrolyte to form mixture C, and mixture B and mixture C are mixed to obtain mixture A.

6. The method for preparing the solid electrolyte according to claim 5, characterized in that, The concentration of the lithium salt in mixture A within the deuterated sulfone compound is 3-6 mol / L.

7. The method for preparing the solid electrolyte according to claim 4, characterized in that, The lithium salt and polymer electrolyte are mixed to obtain mixture D; mixture D is then mixed with the deuterated sulfone compound at a temperature above the melting point of the deuterated sulfone compound to obtain mixture A.

8. The method for preparing a solid electrolyte according to claim 7, characterized in that, The mass ratio of the mixture D to the deuterated sulfone compound is 1:(1-3).

9. The application of the solid electrolyte as described in claims 1-8 in graphite batteries.

10. The application of the solid electrolyte as described in claims 1-8 in lithium-ion batteries.