Precursor solutions of gel electrolytes and their applications

Abstract

The present invention provides a precursor solution for a gel electrolyte and its application. The precursor solution comprises a solvent and a monomer having multiple nitrile and epoxy groups. The precursor solution for the gel electrolyte provided by the present invention can be prepared into a polymeric form and then dissolved in an electrolyte. The monomers in the precursor solution undergo cationic polymerization, forming the electrolyte material into a gel state, thereby preventing battery leakage. Furthermore, the gel electrolyte material contains safety groups, which can enhance the safety performance of the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolyte materials, and in particular relates to a precursor solution of a gel electrolyte and applications thereof. Background Art

[0002] Lithium-ion batteries have attracted widespread attention due to their long cycle life and high output voltage. Furthermore, the increasing popularity of new energy vehicles and the rapid development of energy and power are driving the development of lithium-ion batteries with higher energy density. Currently, commercial lithium-ion batteries have reached an energy density bottleneck, making it difficult to increase their energy density. Solid-state batteries, due to their high R&D complexity and demanding process requirements, are currently difficult to mass-produce.

[0003] Because solid-state batteries lack liquid, they are more compact, smaller, and have higher energy density. Replacing the lithium-ion batteries in electric vehicles with solid-state batteries of the same size could theoretically increase capacity by more than 2 times. Furthermore, solid-state lithium batteries are lighter and do not require the monitoring, cooling, and insulation systems of lithium-ion batteries. This frees up more space in the chassis for the batteries, significantly increasing the electric vehicle's range.

[0004] However, the current application of all-solid-state batteries still has the following problems: First, the density of solid-state electrolyte materials is relatively large: for the same positive and negative active materials, since the actual density of solid-state electrolytes is significantly higher than that of liquid electrolytes, the energy density of solid-state batteries is lower than that of liquid batteries under the same system conditions; second, the synthesis process of solid-state electrolyte materials mostly adopts ball milling + high-temperature sintering synthesis process: the ball milling process is time-consuming, consumes a lot of energy, and has high requirements for ball milling equipment. In addition, the sintering process needs to be carried out in an inert atmosphere throughout the process, and the overall process is difficult; third, the interface contact between solid-state electrolytes and electrode materials is poor: solid-state electrolytes and positive and negative electrode materials are mostly solid-solid contact, and the contact area of ​​the materials is much smaller than the solid-liquid interface contact of the electrolyte, so the battery performance is still far lower than that of liquid batteries; fourth, solid-state electrolytes are sensitive to temperature: the higher the temperature, the greater the conductivity of the solid-state electrolyte, and the lower the temperature, the lower the conductivity of the solid-state electrolyte, so the low-temperature performance of solid-state batteries is poor.

[0005] Currently, the performance improvement of all-solid-state lithium batteries is primarily limited by the inability to simultaneously address the low room-temperature ionic conductivity and high solid-solid interface impedance of solid electrolytes. Therefore, there is an urgent need to develop polymer solid electrolytes that not only exhibit high ionic conductivity and low interface impedance, but also possess a certain strength and prevent the precipitation of transition metal ions. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention provides a precursor solution for a gel electrolyte and its application. The precursor solution for the gel electrolyte provided by the present invention can be prepared into a polymeric form and then dissolved in an electrolyte. The monomers in the precursor solution undergo cationic polymerization, transforming the electrolyte material into a gel state, preventing battery leakage. Furthermore, the gel electrolyte material contains safety groups, which can enhance battery safety.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a precursor solution of a gel electrolyte, wherein the precursor solution of the gel electrolyte comprises a solvent and a monomer having a structure shown in Formula 1:

[0009]

[0010] wherein R1, R2, R3 and R4 are each independently selected from or -H, n is an integer in the range of 1 to 3, and at least one substituent among R1, R2, R3 and R4 is X1, X2, X3 and X4 are each independently selected from cyano or -H, and at least one substituent among X1, X2, X3 and X4 is a cyano group.

[0011] The monomers in the precursor solution of the gel electrolyte provided by the present invention contain nitrile groups and epoxy groups, which can be triggered by hydrogen ions obtained by hydrolysis of lithium salts to undergo cationic polymerization, and a gel electrolyte can be formed without the need for additional initiators. At the same time, the nitrile groups contained therein can complex transition metal ions dissolved in the positive electrode material, thereby improving the safety performance of the battery, and the battery will not leak after the gel is formed. In addition, the precursor solution of the gel electrolyte provided by the present invention is used in a small amount, and only a small amount is needed for the gelation reaction to occur.

[0012] In a second aspect, the present invention provides a gel electrolyte comprising a lithium salt, a non-aqueous solvent, a stabilizer, and a gel electrolyte precursor solution, wherein the gel electrolyte precursor solution comprises the gel electrolyte precursor solution according to the first aspect.

[0013] In a third aspect, the present invention provides a method for preparing the gel electrolyte according to the second aspect, the method comprising the following steps:

[0014] After mixing lithium salt, non-aqueous solvent and stabilizer, gel electrolyte precursor solution is added and reacted to obtain the gel electrolyte.

[0015] In a fourth aspect, the present invention provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte, wherein the solid electrolyte comprises the gel electrolyte according to the second aspect.

[0016] In a fifth aspect, the present invention provides an electronic device comprising the electrochemical device according to the fourth aspect.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The monomers in the precursor solution of the gel electrolyte provided by the present invention contain nitrile groups and multiple epoxy groups. During the preparation process of the electrolyte, a double bond addition reaction occurs, and a cationic polymerization reaction occurs to form a gel electrolyte. The nitrile groups contained therein can complex transition metal ions, thereby improving the safety performance of the battery. After the gel is formed, the battery will not leak. In addition, the amount of the precursor solution of the gel electrolyte provided by the present invention is small, and a content of only 0.5% to 1% is required for the gelation reaction to occur. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0020] The present invention provides a precursor solution of a gel electrolyte, wherein the precursor solution of the gel electrolyte comprises a solvent and a monomer having a structure shown in Formula 1:

[0021]

[0022] wherein R1, R2, R3 and R4 are each independently selected from or -H, n is an integer in the range of 1 to 3, and at least one substituent among R1, R2, R3 and R4 is X1, X2, X3 and X4 are each independently selected from cyano or -H, and at least one substituent among X1, X2, X3 and X4 is a cyano group.

[0023] The monomers in the precursor solution of the gel electrolyte provided by the present invention contain nitrile groups and epoxy groups, which can be triggered by hydrogen ions obtained by hydrolysis of lithium salts to undergo cationic polymerization, and a gel electrolyte can be formed without the need for additional initiators. At the same time, the nitrile groups contained therein can complex transition metal ions dissolved in the positive electrode material, thereby improving the safety performance of the battery, and the battery will not leak after the gel is formed. In addition, the precursor solution of the gel electrolyte provided by the present invention is used in a small amount, and only a small amount is needed for the gelation reaction to occur.

[0024] In the present invention, the solvent in the precursor solution of the gel electrolyte includes an ester solvent or an ether solvent.

[0025] Preferably, the precursor solution of the gel electrolyte comprises a solvent and a monomer having a structure shown in Formula 2:

[0026]

[0027] wherein R1, R2, R3 and R4 are each independently selected from or -H, n is an integer in the range of 1 to 3, and at least one substituent in R1 and R2 is and at least one substituent among R3 and R4 is

[0028] The present invention further optimizes the types of monomers and increases the number of cyano groups to increase the electron-withdrawing ability of epoxy groups, making it easy for cationic polymerization to occur.

[0029] Preferably, the monomer having the structure shown in Formula 1 is any one of the following compounds:

[0030]

[0031]

[0032] Preferably, the mass percentage of the monomer having the structure shown in Formula 1 in the precursor solution satisfies any one of the following conditions (a) to (b):

[0033] (a) the weight percentage of the monomer having the structure represented by Formula 1 in the precursor solution is 0.1% to 50%;

[0034] (b) The mass percentage of the monomer having the structure represented by Formula 1 in the precursor solution is 0.5% to 1%.

[0035] In the present invention, the mass percentage of the monomer having the structure shown in Formula 1 in the precursor solution is 0.1% to 50%, preferably 0.5% to 1%, for example, it can be 0.1%, 0.2%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0036] In the present invention, the mass percentage of the monomer is adjusted to form a gel electrolyte with good kinetics. If the content is too low, the gel state cannot be formed, which is not helpful for the safety performance of the battery cell; if the content is too high, the texture of the formed gel is too hard, which will have an adverse effect on the kinetic performance of the battery cell.

[0037] The present invention further provides a gel electrolyte, which includes a lithium salt, a non-aqueous solvent, a stabilizer, and a gel electrolyte precursor solution. The gel electrolyte precursor solution includes the gel electrolyte precursor solution described above.

[0038] Preferably, the mass percentage of the precursor solution of the gel electrolyte in the gel electrolyte is 0.5% to 1%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0039] In the present invention, only a small amount of gel electrolyte precursor needs to be added to obtain the gel electrolyte.

[0040] Preferably, the lithium salt includes at least one of lithium nitrate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(perfluorobutylsulfonyl)imide, lithium (trifluoromethylsulfonyl)(n-perfluorobutylsulfonyl)imide, lithium (fluorosulfonyl)(n-perfluorobutylsulfonyl)imide or lithium bis(oxalatoborate).

[0041] Preferably, the mass percentage of lithium salt in the gel electrolyte is 11% to 15%.

[0042] Preferably, the mass percentage of the lithium salt in the gel electrolyte is 11% to 15%, for example, 11%, 12%, 13%, 14%, or 15%.

[0043] In the present invention, the gel electrolyte has higher ion conductivity by adjusting the mass percentage of the lithium salt.

[0044] In the present invention, the stabilizer includes any one of N,N'-diisopropylcarbodiimide, triphenyl phosphite, heptamethyldisilazane or hexamethyldisilazane, or a combination of at least two thereof.

[0045] In the present invention, the mass percentage of the stabilizer in the gel electrolyte is 1000 ppm.

[0046] In the present invention, a stabilizer is added to prevent the lithium salt from being excessively hydrolyzed and further consumption is avoided.

[0047] The present invention further provides a method for preparing the gel electrolyte described above, the method comprising the following steps:

[0048] After mixing lithium salt, non-aqueous solvent and stabilizer, gel electrolyte precursor solution is added and reacted to obtain the gel electrolyte.

[0049] In the present invention, the non-aqueous solvent includes but is not limited to ester solvents and ether solvents.

[0050] In the present invention, the reaction temperature is 40°C to 50°C, for example, 40°C, 42°C, 45°C, 48°C, or 50°C.

[0051] In a fourth aspect, the present invention provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte, wherein the solid electrolyte comprises the gel electrolyte.

[0052] In a fifth aspect, the present invention provides an electronic device comprising the electrochemical device.

[0053] Example 1

[0054] This embodiment provides a precursor solution of a gel electrolyte, which includes the monomer of the structure shown in Formula I and ethylene carbonate, wherein the weight percentage of the monomer of the structure shown in Formula I in the precursor solution of the gel electrolyte is 1.5%.

[0055] This embodiment also provides a gel electrolyte comprising a gel electrolyte precursor solution, lithium bis(trifluoromethylsulfonyl)imide, an N,N'-diisopropylcarbodiimide stabilizer, and a non-aqueous solvent. The gel electrolyte comprises 0.7% by weight of the gel electrolyte precursor solution, 13% by weight of the lithium bis(trifluoromethylsulfonyl)imide, 1000 ppm by weight of the N,N'-diisopropylcarbodiimide stabilizer, and the balance being the non-aqueous solvent (the non-aqueous solvent being composed of ethylene carbonate and diethyl carbonate in a 1:1 mass ratio).

[0056] The preparation method of the gel electrolyte and lithium ion battery is as follows:

[0057] Preparation of positive electrode:

[0058] The preparation process of the positive electrode sheet is completed entirely under the dew point condition of -40℃. Before the experimental operation, the positive electrode material and the material need to be dehydrated.

[0059] 1. Preparation of conductive adhesive: 30g of polyvinylidene fluoride material and an appropriate amount of NMP solvent are heated and stirred to dissolve to form an adhesive with a solid content of 7%. Then 50g of Super-P material is added to form a conductive adhesive;

[0060] 2. Preparation of positive electrode slurry: 920g NCM 622 powder was added to the conductive glue with a solid content of 75%. The positive electrode slurry was prepared by double planetary stirring for 120min and degassing for 15min.

[0061] 3. The electrode was coated on both sides of the aluminum foil by doctor blade coating with a gap of 65 μm. After coating, the solvent was allowed to dry naturally, and then transferred to a vacuum drying oven and vacuum dried at 120 ° C for 12 hours. After that, the positive electrode was obtained by roller pressing. The active material loading was 15 mg / cm 2 , thickness is 43μm;

[0062] Preparation of negative electrode sheet:

[0063] The preparation of the negative electrode sheet is completed in the negative electrode slurry coating room.

[0064] 4. Preparation of conductive adhesive: 10g of sodium carboxymethyl cellulose material and an appropriate amount of water as a solvent are heated and stirred to dissolve to form an adhesive with a solid content of 7%. Then 20g of styrene-butadiene rubber is added to disperse and dissolve, and then 50g of Super-P material is added to form a conductive adhesive;

[0065] 5. Preparation of negative electrode slurry: 920 g of graphite was added to the conductive glue with a solid content of 50%. The negative electrode slurry was prepared by double planetary stirring for 120 min and degassing for 15 min.

[0066] 6. The electrode was coated on the aluminum foil by doctor blade coating with a gap of 85 μm. After coating, the solvent was allowed to dry naturally, and then transferred to a vacuum drying oven and vacuum dried at 120 ° C for 12 hours. After that, the negative electrode was obtained by roller pressing. The active material loading was 7.3 mg / cm 2 , thickness of 50 μm;

[0067] Lithium-ion battery preparation: The positive and negative electrodes are cut to a certain size, and then assembled into a soft-pack battery in a stacking manner of 4 positive and 5 negative. The capacity of the soft-pack battery is about 500mAh and it is clamped using an external clamp.

[0068] The precursor solution of the gel electrolyte, lithium salt, stabilizer and non-aqueous solvent obtained above were injected into the battery, immersed for 48 hours, and then in-situ polymerized at 45° C. for 24 hours to obtain the gel electrolyte.

[0069] Other examples and comparative examples are based on the steps of Example 1 with parameter changes. The specific changed parameters are shown in Table 1:

[0070] Table 1

[0071]

[0072]

[0073]

[0074] Test conditions

[0075] The lithium ion batteries provided in Examples 1 to 12 and Comparative Examples 1 to 5 were subjected to performance tests using the following methods:

[0076] (1) Acupuncture test:

[0077] According to GBT 31485-2015 Safety requirements and test methods for power batteries for electric vehicles:

[0078] According to GBT 31485-2015, the battery module should be charged according to the method in 6.1.4;

[0079] use A high-temperature resistant steel needle (the cone angle of the needle tip is 45°) pierces the battery at a speed of 25±5mm / s;

[0080] Observe for 1 hour and record the maximum temperature of the battery.

[0081] (2) Electrical abuse and overcharge test:

[0082] According to GBT 31485-2015 Safety requirements and test methods for power batteries for electric vehicles:

[0083] The overcharge test is carried out as follows:

[0084] The battery module is charged according to the method in 6.1.4;

[0085] Charge at a constant current of 1C to 1.5 times the cut-off voltage of the single battery;

[0086] Observe for 1 hour and record the maximum temperature of the battery.

[0087] (3) Thermal abuse - 150℃ hot box test:

[0088] According to GBT 31485-2015 Safety requirements and test methods for power batteries for electric vehicles:

[0089] The heating test is carried out as follows:

[0090] The battery is charged according to the method in 6.1.4;

[0091] The temperature in the oven is raised from room temperature to 150±2℃ at a rate of 5℃ / min and maintained at this temperature for 30 minutes before stopping heating;

[0092] Observe for 1 hour and record the maximum temperature of the battery.

[0093] (4) First coulombic efficiency test: At 25±2°C, test the room temperature charge capacity / room temperature discharge capacity according to the steps shown in Table 2 below, and calculate the first coulombic efficiency.

[0094] Table 2

[0095] Step Steps Working Mode Ambient temperature Sampling interval 1 Let it sit Rest 5 minutes; 25℃ 30s 2 Constant current and constant voltage charging 1 / 3C CC to 4.85V, CV to 0.05C; 25℃ 5s 3 Let it sit Rest 5 minutes; 25℃ 30s 4 Constant current discharge 1 / 3C DC to 3.5V; 25℃ 5s 5 Let it sit Rest 5 minutes; 25℃ 30s

[0096] (5) Normal temperature cycle test: The capacity retention rate was tested by 200 normal temperature cycles according to the steps shown in Table 3 below.

[0097] Table 3

[0098]

[0099]

[0100] (6) Rate performance test: The room temperature rate performance was tested according to the steps shown in Table 4 below. Battery rate performance = (2C capacity / 0.33C capacity) × 100%.

[0101] Table 4

[0102]

[0103]

[0104] The test results are shown in Table 5:

[0105] Table 5

[0106]

[0107]

[0108] The data in Table 5 demonstrate that the electrolyte prepared from the precursor solution of the gel electrolyte provided by the present invention, when assembled into a lithium-ion battery, exhibits high initial coulombic efficiency, cycle stability, and rate capability. Furthermore, because the monomers in the precursor solution contain nitrile groups, they can complex with transition metal ions dissolved from the positive electrode material, reducing the risk of thermal runaway and thereby improving battery safety.

[0109] Compared with Example 6, Example 4 has a large steric hindrance due to the fact that the monomer of Example 6 has four epoxy groups. Therefore, the initial coulombic efficiency and rate performance of the lithium ion battery prepared from the gel electrolyte obtained by polymerization are worse than those of the lithium ion battery provided by Example 4. In Example 7, the content of the precursor monomer and stabilizer of the added gel electrolyte is low, so the improvement of the battery performance is not as good as that of Example 1. In Example 8, the content of the precursor monomer and stabilizer of the added gel electrolyte is high, the degree of gelation is high, and the lithium ion transmission rate is not as good as that of Example 1. Therefore, the overall performance of the battery is not as good as that of Example 1.

[0110] Compared with Example 1, Examples 9 and 10 are non-preferred monomer types and contain a large number of epoxy groups, which are four-membered rings and five-membered rings, resulting in greater steric hindrance. The capacity retention rate and rate performance of the lithium ion batteries provided by them are lower than those of Example 1, and the corresponding safety performance is also inferior to that of Example 1. Examples 11 and 12 are cases where the monomer and lithium salt content exceeds the range. If the monomer content is too low, a gel state cannot be formed, which does not help the safety performance of the battery cell. If the content is too high, the gel formed is hard and has an adverse effect on the kinetic performance of the battery cell. If the lithium salt content is too low, the ionic conductivity of the electrolyte is reduced. If the lithium salt content is too high, the side reactions that occur increase. Therefore, the performance of the battery in Example 11 is worse than that of the battery in Example 12, and the overall performance of the lithium ion batteries provided by both is also inferior to that of Example 1.

[0111] Compared with Example 1, Comparative Examples 1 and 2 contain a single group. On the one hand, the nitrile group contained in the monomer in Example 1 can complex the transition metal ions dissolved in the positive electrode material, and on the other hand, the epoxy group can undergo cationic polymerization, thereby improving the battery safety performance; the monomer in Comparative Example 3 contains a small number of nitrile groups, so the loss of transition metal ions is large, and the monomer in Comparative Example 4 contains a small number of epoxy groups, so the electrolyte is difficult to completely gel, further illustrating that Comparative Examples 1 to 4 illustrate that monomers with specific structures and group numbers defined in this application are not used, and the performance of the gel electrolyte finally prepared is not as good as the gel electrolyte provided in Example 1; Comparative Example 5 shows that the combination of epoxy compounds and nitrile compounds cannot achieve the ideal technical effect.

[0112] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A precursor solution of a gel electrolyte, characterized in that: The precursor solution of the gel electrolyte comprises a solvent and a monomer having a structure shown in Formula 2: wherein R1, R2, R3 and R4 are each independently selected from or -H, n is an integer in the range of 1 to 3, and at least one substituent in R1 and R2 is and at least one substituent among R3 and R4 is 2. The precursor solution according to claim 1, characterized in that The monomer having the structure shown in Formula 2 is any one of the following compounds:

3. The precursor solution according to claim 1, characterized in that The mass percentage of the monomer having the structure shown in Formula 2 in the precursor solution satisfies any one of the following conditions (a) to (b): (a) the weight percentage of the monomer having the structure represented by Formula 2 in the precursor solution is 0.1% to 50%; (b) The mass percentage of the monomer having the structure represented by Formula 2 in the precursor solution is 0.5% to 1%.

4. A gel electrolyte, characterized in that The gel electrolyte includes a lithium salt, a non-aqueous solvent, a stabilizer, and a precursor solution of a gel electrolyte. The precursor solution of the gel electrolyte includes the precursor solution of the gel electrolyte according to any one of claims 1 to 3.

5. The gel electrolyte according to claim 4, characterized in that The mass percentage of the precursor solution of the gel electrolyte in the gel electrolyte is 0.5% to 1%.

6. The gel electrolyte according to claim 4, characterized in that The lithium salt comprises at least one of lithium nitrate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(perfluorobutylsulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide or lithium bis(oxalatoborate); The mass percentage of lithium salt in the gel electrolyte is 11% to 15%.

7. The gel electrolyte according to claim 4, characterized in that The stabilizer includes any one of N,N'-diisopropylcarbodiimide, triphenyl phosphite, heptamethyldisilazane or hexamethyldisilazane, or a combination of at least two thereof.

8. A method for preparing the gel electrolyte according to any one of claims 4 to 7, characterized in that: The method comprises the following steps: After mixing lithium salt, non-aqueous solvent and stabilizer, gel electrolyte precursor solution is added and reacted to obtain the gel electrolyte.

9. An electrochemical device, characterized in that The electrochemical device includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte, wherein the solid electrolyte includes the gel electrolyte according to any one of claims 4 to 7.

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