Semi-solid electrolyte and lithium ion battery and preparation method thereof

Abstract

The present invention relates to a semi-solid electrolyte and a lithium-ion battery and a preparation method thereof. In order to solve the problem in the prior art that when a compound containing a sulfate ester functional group is added to the semi-solid electrolyte, the compound containing the sulfate ester functional group will undergo a strong side reaction during the in-situ thermal curing process, resulting in deterioration of battery performance, the present invention provides a semi-solid electrolyte comprising a polymerizable monomer, an initiator, a solvent, a lithium salt, and an additive, wherein the additive comprises a compound having a structural formula as shown in formula (I). The semi-solid electrolyte of the present invention can significantly reduce the occurrence of side reactions during the curing process, has good stability, and when applied to a lithium-ion battery, can improve the battery's room temperature and high temperature cycle performance, significantly suppressing the increase in the DCR.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a semi-solid electrolyte and a lithium ion battery and a preparation method thereof. Background Art

[0002] In-situ solidification technology converts liquid electrolytes into semi-solid electrolytes within the battery. This semi-solid electrolyte can effectively reduce interfacial impedance, improve battery safety, and increase battery energy density, while also being fully compatible with existing battery production equipment.

[0003] Sulfate-containing substances are commonly used as negative electrode film-forming additives in liquid electrolytes, effectively improving battery high-temperature storage and cycling performance. However, these substances themselves have poor stability and decompose at high temperatures, producing large amounts of hydrofluoric acid, which exacerbates the deterioration of electrolyte quality. Thermal curing is a commonly used and effective method for preparing semi-solid electrolytes in in-situ curing technology. However, the prolonged high-temperature environment during the curing process accelerates the decomposition of sulfate esters, deteriorating battery performance.

[0004] Therefore, it is urgent to develop an electrolyte with good stability, good cycling performance at both room and high temperatures, and suitable for in-situ curing technology. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a semi-solid electrolyte with few side reactions and good stability during the in-situ curing process, and the room temperature and high temperature cycle performance of the lithium ion battery using the semi-solid electrolyte is improved.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The first object of the present invention is to provide a semi-solid electrolyte comprising a polymer monomer, an initiator, a solvent, a lithium salt and an additive, wherein the additive comprises one or more compounds represented by formula (I).

[0008]

[0009] Wherein, R1 and R2 are independently selected from one of alkyl, fluoroalkyl, alkoxy, fluoroalkoxy or olefin groups.

[0010] Preferably, R1 and R2 are independently selected from C 1～3 Alkyl, C 1～3 Fluorinated alkyl, C 1～3 Alkoxy, C 1～3 Fluoroalkoxy and C 2～3 A type of olefin group.

[0011] Preferably, the compound represented by formula (I) is selected from one or more substances represented by the following structural formulas:

[0012]

[0013] Preferably, the added amount of the compound represented by formula (I) is 0.01 to 5% of the total mass of the semi-solid electrolyte, for example, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, etc.

[0014] More preferably, the added amount of the compound represented by formula (I) is 0.1 to 4% of the total mass of the semi-solid electrolyte.

[0015] More preferably, the added amount of the compound represented by formula (I) is 0.5 to 3% of the total mass of the semi-solid electrolyte.

[0016] Preferably, the additives further include other additives, and the other additives are selected from one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide, and the addition amount of the other additives is 0.01 to 20% of the total mass of the semi-solid electrolyte, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc.

[0017] More preferably, the other additives are selected from one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and vinylene carbonate.

[0018] According to a specific and preferred embodiment, the other additives are one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and vinylene carbonate.

[0019] Further preferably, the addition amount of the other additives is 0.1 to 20% of the total mass of the semi-solid electrolyte.

[0020] More preferably, the amount of the other additives added is 2 to 13% of the total mass of the semi-solid electrolyte.

[0021] Still further preferably, the amount of the other additives added is 2-5% of the total mass of the semi-solid electrolyte.

[0022] Preferably, the polymerizable monomer is selected from one or more of pentaerythritol tetraacrylate, pentaerythritol triacrylate, polydipentaerythritol pentaacrylate, polydipentaerythritol hexaacrylate and vinylene carbonate.

[0023] Further preferably, the polymerizable monomer is selected from pentaerythritol tetraacrylate and / or pentaerythritol triacrylate.

[0024] Preferably, the added amount of the polymerized monomer is 1 to 10% of the total mass of the semi-solid electrolyte, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, etc.

[0025] Further preferably, the added amount of the polymerized monomer is 1.5-7% of the total mass of the semi-solid electrolyte.

[0026] More preferably, the added amount of the polymerized monomer is 2-6% of the total mass of the semi-solid electrolyte.

[0027] Preferably, the initiator is a thermal initiator.

[0028] More preferably, the initiator is selected from one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate and di-tert-butyl azodicarboxylate.

[0029] More preferably, the initiator is selected from dimethyl azobisisobutyrate.

[0030] Preferably, the added amount of the initiator is 0.1-5% of the mass of the polymerization monomer, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.

[0031] More preferably, the added amount of the initiator is 0.3-4% of the mass of the polymerization monomer.

[0032] More preferably, the added amount of the initiator is 0.5-3% of the mass of the polymerization monomer.

[0033] Still more preferably, the added amount of the initiator is 0.5-2% of the mass of the polymerization monomer.

[0034] Preferably, the solvent is selected from one or more of cyclic carbonates and chain carbonates, the cyclic carbonate is ethylene carbonate (EC) and / or propylene carbonate (PC), and the chain carbonate is selected from one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

[0035] More preferably, the solvent is a mixed solvent of diethyl carbonate, ethylene carbonate and ethyl methyl carbonate.

[0036] More preferably, the volume ratio of diethyl carbonate, ethylene carbonate and ethyl methyl carbonate is 1:1 to 2:2 to 4, for example, 1:1:2, 1:1.5:2, 1:2:2, 1:1:3, 1:1.5:3, 1:2:3, 1:1:4, 1:1.5:4, 1:2:4, etc.

[0037] Still more preferably, the volume ratio of diethyl carbonate, ethylene carbonate and ethyl methyl carbonate is 1:1-2:2-3.

[0038] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt is 1 to 1.5 mol / L, for example, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc.

[0039] A second object of the present invention is to provide a lithium-ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is a semi-solid electrolyte as described in any one of the above items.

[0040] A third object of the present invention is to provide a method for preparing a lithium ion battery, comprising: uniformly mixing the initiator, the solvent, the lithium salt, and the additive as described above, injecting the mixture into a battery containing a positive electrode, a negative electrode, and a separator, encapsulating the mixture, and allowing the mixture to stand at 30-40° C. (e.g., 32° C., 34° C., 36° C., 38° C., etc.) for 12-48 hours (e.g., 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, etc.), and then in-situ curing at 50-80° C. (e.g., 55° C., 60° C., 65° C., 70° C., 75° C., etc.) to obtain the lithium ion battery, wherein the in-situ curing time is 3-24 hours (e.g., 5 hours, 10 hours, 15 hours, 20 hours, etc.), and during the in-situ curing process, applying 0.5 kg / cm 2 ~3Kg / cm 2 (e.g. 1Kg / cm 2 , 1.5Kg / cm 2 , 2Kg / cm 2 , 2.5Kg / cm 2 etc.) pressure.

[0041] Preferably, the battery is placed at 32-37° C. for 20-40 hours after packaging.

[0042] Preferably, the in-situ curing is carried out at 55-70° C., and the time of the in-situ curing is 5-15 hours.

[0043] Preferably, the battery is subjected to a pressure of 0.5 kg / cm 2~2Kg / cm 2 pressure.

[0044] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0045] The semi-solid electrolyte provided by the present invention has few side reactions during the in-situ solidification process and good stability. When used in lithium-ion batteries, it can improve the battery's cycle performance at room temperature and high temperature and significantly inhibit the increase of DCR. DETAILED DESCRIPTION

[0046] The present invention is further described below with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples may be further adjusted according to the specific requirements of the application. Unspecified implementation conditions are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other. Unless otherwise specified herein, "%" represents mass percentage.

[0047] In view of the fact that existing compounds containing sulfate functional groups have poor stability and are prone to side reactions when used in semi-solid electrolytes, and that when used in lithium-ion batteries, the room temperature and high temperature cycle performance of lithium-ion batteries are poor, the inventors of the present invention have conducted in-depth research and a large number of experiments, and finally proposed a solid electrolyte and a lithium-ion battery using the semi-solid electrolyte. The semi-solid electrolyte of the present invention contains a compound as shown in formula (I), specifically compound A, compound B or compound C. The above three compounds not only have cyclic sulfate functional groups, which help to form a negative electrode film and can improve the room temperature and high temperature cycle performance of the battery, but also have nitrogen-containing groups, are Lewis basic, and can adsorb free H in the electrolyte. + , HF and PF5, inhibit a series of side reactions in the semi-solid electrolyte and improve the thermal stability of the semi-solid electrolyte.

[0048] In the present invention, the preparation methods of compound A, compound B and compound C are as follows:

[0049] Preparation of compound A

[0050] 125 g of 3-amino-1,2-benzenediol was dissolved in 600 mL of tetrahydrofuran, and then 138 g of potassium carbonate was added in batches. The mixed solution was cooled to 0°C and stirred for 1 hour. Then, 142 g of iodomethane was added dropwise. The temperature was then raised to 25°C and reacted for 5 hours. After the reaction was completed, the product was filtered, and the filtrate was dried, concentrated and distilled to obtain the first step product.

[0051] 1 mol of the first-step product and 2.5 mol of imidazole were dissolved in 1 liter of dichloromethane, and the mixed solution was cooled to -10°C. Subsequently, 1 mol of sulfonyl chloride was added dropwise to the mixed solution. After the addition was completed, the temperature was raised to room temperature and the reaction was carried out for 1 hour. After the reaction was completed, the product was filtered, and the filtrate was washed with 10% hydrochloric acid, 2% sodium bicarbonate aqueous solution and ultrapure water, and then concentrated and distilled to obtain compound A.

[0052] Preparation of compound B

[0053] 125 g of 3-amino-1,2-benzenediol was dissolved in 600 mL of tetrahydrofuran, and then 138 g of potassium carbonate was added in batches. The mixed solution was cooled to 0°C and stirred for 1 hour. Then, 142 g of iodoethane was added dropwise. The temperature was then raised to 25°C and reacted for 5 hours. After the reaction was completed, the product was filtered, and the filtrate was dried, concentrated and distilled to obtain the first step product.

[0054] 1 mol of the first-step product and 2.5 mol of imidazole were dissolved in 1 liter of dichloromethane, and the mixed solution was cooled to -10°C. Subsequently, 1 mol of sulfonyl chloride was added dropwise to the mixed solution. After the addition was completed, the temperature was raised to room temperature and the reaction was carried out for 1 hour. After the reaction was completed, the product was filtered, and the filtrate was washed with 10% hydrochloric acid, 2% sodium bicarbonate aqueous solution and ultrapure water, and then concentrated and distilled to obtain compound B.

[0055] Preparation of compound C

[0056] 125 g of 3-amino-1,2-benzenediol was dissolved in 600 mL of tetrahydrofuran, and then 138 g of potassium carbonate was added in batches. The mixed solution was cooled to 0°C and stirred for 1 hour. Then, 142 g of vinyl iodide was added dropwise, and then the temperature was raised to 25°C and reacted for 5 hours. After the reaction was completed, the product was filtered, and the filtrate was dried, concentrated and distilled to obtain the first step product.

[0057] 1 mol of the first-step product and 2.5 mol of imidazole were dissolved in 1 liter of dichloromethane, and the mixed solution was cooled to -10°C. Subsequently, 1 mol of sulfonyl chloride was added dropwise to the mixed solution. After the addition was completed, the temperature was raised to room temperature and the reaction was carried out for 1 hour. After the reaction was completed, the product was filtered, and the filtrate was washed with 10% hydrochloric acid, 2% sodium bicarbonate aqueous solution and ultrapure water, and then concentrated and distilled to obtain compound C.

[0058] In the present invention, catechol sulfate is a compound shown in the following structural formula:

[0059]

[0060] Example 1

[0061] Cathode preparation

[0062] Weigh the positive electrode material lithium nickel manganese cobalt oxide, the conductive agent acetylene black, and the binder PVDF in a mass ratio of 95:2.5:2.5, add an appropriate amount of N-methylpyrrolidone, and mix thoroughly to prepare the positive electrode slurry. The positive electrode slurry is coated on aluminum foil, dried, and then rolled and cut to obtain positive electrode sheets. The positive electrode compaction density is 4.15g / cm 3 .

[0063] Anode preparation

[0064] Graphite, conductive agent acetylene black, carboxymethyl cellulose, and styrene-butadiene rubber were weighed in a mass ratio of 95:2.5:2:0.5, and an appropriate amount of deionized water was added and stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry was coated on copper foil, dried, and then rolled and cut to obtain negative electrode sheets. The negative electrode compaction density was 1.65 g / cm 3 .

[0065] Preparation of electrolyte

[0066] A mixed solvent with a volume ratio of DEC:EC:EMC=2:3:5 was weighed to fully dissolve 1.2 mol / L of lithium hexafluorophosphate, and then 2% of lithium bis(fluorosulfonyl)imide, 0.6% of lithium difluorophosphate, 1% of vinylene carbonate and 1% of compound A were added to the above solution respectively, accounting for 2% of the total mass of the electrolyte, and finally 3% of the polymer monomer pentaerythritol tetraacrylate and 0.045% of the initiator dimethyl azobisisobutyrate were added to the total mass of the electrolyte.

[0067] Battery manufacturing

[0068] Using the above-mentioned positive electrode, negative electrode and electrolyte, a PE separator with a thickness of 12 microns is selected, and a lamination process is adopted to manufacture soft-pack batteries with a designed capacity of 5000 mAh.

[0069] After the battery is filled and sealed, it is placed at 35°C for 36 hours to ensure that the electrolyte completely penetrates the positive and negative electrode materials. It is then placed in a 60°C environment for 10 hours and subjected to a 1Kg / cm 2 The liquid electrolyte is converted into a semi-solid electrolyte in situ under the pressure of

[0070] Example 2

[0071] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that the amount of compound A added in the preparation of the electrolyte was 2%.

[0072] Example 3

[0073] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that the amount of compound A added in the preparation of the electrolyte was 3%.

[0074] Example 4

[0075] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that the amount of compound A added in the preparation of the electrolyte was 5%.

[0076] Example 5

[0077] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that Compound A was replaced with Compound B in the electrolyte preparation, and the added amount was 1%.

[0078] Example 6

[0079] A semi-solid electrolyte was produced in the same manner as in Example 5, except that the amount of compound B added in the electrolyte production was 2%.

[0080] Example 7

[0081] A semi-solid electrolyte was produced in the same manner as in Example 5, except that the amount of compound B added in the electrolyte production was 3%.

[0082] Example 8

[0083] A semi-solid electrolyte was produced in the same manner as in Example 5, except that the amount of compound B added in the electrolyte production was 5%.

[0084] Example 9

[0085] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that Compound A was replaced with Compound C in the electrolyte preparation, and the added amount was 1%.

[0086] Example 10

[0087] A semi-solid electrolyte was produced in the same manner as in Example 9, except that the amount of compound C added in the electrolyte production was 2%.

[0088] Example 11

[0089] A semi-solid electrolyte was produced in the same manner as in Example 9, except that the amount of compound C added in the electrolyte production was 3%.

[0090] Example 12

[0091] A semi-solid electrolyte was produced in the same manner as in Example 9, except that the amount of compound C added in the electrolyte production was 5%.

[0092] Comparative Example 1

[0093] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that compound A was replaced with catechol sulfate in an amount of 1%.

[0094] Comparative Example 2

[0095] A semi-solid electrolyte was prepared in the same manner as in Comparative Example 1, except that the amount of catechol sulfate added in the electrolyte preparation was 2%.

[0096] Comparative Example 3

[0097] A semi-solid electrolyte was prepared in the same manner as in Comparative Example 1, except that the amount of catechol sulfate added in the electrolyte preparation was 3%.

[0098] Comparative Example 4

[0099] A semi-solid electrolyte was prepared in the same manner as in Comparative Example 1, except that the amount of catechol sulfate added in the electrolyte preparation was 5%.

[0100] Comparative Example 5

[0101] A semi-solid electrolyte was prepared in the same manner as in Example 1, except that Compound A was not added during the preparation of the electrolyte.

[0102] The electrolytes obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were placed in 60° C. for 24 hours and observed for color change. They were then injected into batteries and observed for solidification. The results are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] The batteries obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were subjected to the following tests respectively.

[0107] Battery charge and discharge tests were conducted at 25°C and 45°C, with a voltage range of 2.75 to 4.25V. The battery was cycled at a 1C rate, and the capacity retention after 1000 cycles was tested. The battery's DC internal resistance (DCR) was obtained by discharging the battery to 50% state of charge at 1C for 30s every 50 cycles. The 1000-cycle DCR growth rate (%) = (DCR after 1000 cycles - DCR after the first cycle) / DCR after the first cycle × 100%; the capacity retention rate (%) = (discharge capacity after 1000 cycles / discharge capacity after the first cycle) × 100%. The cycling performance results of the battery at 25°C are shown in Table 2, and the cycling performance of the battery at 45°C is shown in Table 3.

[0108] Table 2

[0109]

[0110]

[0111] Table 3

[0112]

[0113]

[0114] Comparison of Comparative Examples 1 to 4 and Comparative Example 5 shows that after adding different proportions of catechol sulfate, the capacity retention rate of the semi-solid electrolyte at room temperature and high temperature is significantly improved, and the DCR growth is suppressed. However, when catechol sulfate is added to the semi-solid electrolyte, the color changes from milky white to light yellow after in-situ thermal curing, which indicates that catechol sulfate has undergone obvious side reactions. As can be seen from Examples 1 to 12 in Tables 1 to 3, after the introduction of the three compounds of the present invention, the semi-solid electrolyte still remains milky white, which indicates that the three substances of the present invention do not undergo side reactions similar to catechol sulfate, and the room temperature and high temperature performance of the battery are improved compared to the battery with catechol sulfate added. In particular, after adding 1% of the three compounds of the present invention respectively, the room temperature and high temperature capacity retention rates of the battery are improved, and at the same time, the DCR growth of the lithium-ion battery is significantly suppressed.

[0115] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A semi-solid electrolyte comprising a polymer monomer, an initiator, a solvent, a lithium salt and an additive, characterized in that: The additive includes one or more compounds as shown in formula (I), Formula (I); Wherein, R1 and R2 are independently selected from C 1~3 Alkyl, C 1~3 Fluorinated alkyl, C 1~3 Alkoxy, C 1~3 Fluoroalkoxy and C 2~3 A type of olefin group.

2. The semi-solid electrolyte according to claim 1, characterized in that The compound represented by formula (I) is selected from one or more substances represented by the following structural formulas: 。 3. The semi-solid electrolyte according to any one of claims 1 to 2, characterized in that The added amount of the compound represented by formula (I) is 0.01-5% of the total mass of the semi-solid electrolyte.

4. The semi-solid electrolyte according to claim 1, characterized in that The additives also include other additives, which are selected from one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide, and the addition amount of the other additives is 0.01-20% of the total mass of the semi-solid electrolyte.

5. The semi-solid electrolyte according to claim 1, characterized in that The polymerizable monomer is selected from one or more of pentaerythritol tetraacrylate, pentaerythritol triacrylate, polydipentaerythritol pentaacrylate, polydipentaerythritol hexaacrylate and vinylene carbonate; and / or, the added amount of the polymerizable monomer is 1-10% of the total mass of the semi-solid electrolyte.

6. The semi-solid electrolyte according to claim 1, characterized in that The initiator is a thermal initiator; and / or, the initiator is selected from one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate and di-tert-butyl azodicarboxylate; and / or, the added amount of the initiator is 0.1-5% of the mass of the polymerization monomer.

7. The semi-solid electrolyte according to claim 1, characterized in that The solvent is selected from one or more of cyclic carbonates and chain carbonates, the cyclic carbonate is ethylene carbonate and / or propylene carbonate, and the chain carbonate is selected from one or more of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate; and / or the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt is 1-1.5 mol / L.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is a semi-solid electrolyte according to any one of claims 1 to 7.

9. A method for preparing a lithium ion battery, characterized in that: The initiator according to any one of claims 1 to 7, the solvent, the lithium salt, and the additive are uniformly mixed and injected into a battery containing a positive electrode, a negative electrode, and a separator, and then packaged and placed at 30-40° C. for 12-48 hours, and then in-situ cured at 50-80° C. to obtain the lithium ion battery, wherein the in-situ curing time is 3-24 hours, and during the in-situ curing process, 0.5 kg / cm 2 ~3Kg / cm 2 pressure.

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