Electrolyte of lithium iron phosphate battery and lithium iron phosphate battery

Abstract

The invention discloses an electrolyte of a lithium iron phosphate battery and the lithium iron phosphate battery, belongs to the technical field of power batteries, and overcomes the defect that the lithium iron phosphate battery in the prior art is relatively poor in multiplying power and rapid charging performance. The electrolyte of the lithium iron phosphate battery comprises an electrolyte, a solvent and a first additive, the solvent comprises an organic solvent I; and based on the total mass of the electrolyte, the content of the organic solvent I is more than 30%. According to the electrolyte, the rate capability and the cycle performance of the lithium iron phosphate battery can be remarkably improved, and meanwhile, the lithium iron phosphate battery has good high-temperature performance and low-temperature performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of power batteries, and in particular relates to an electrolyte of a lithium iron phosphate battery and a lithium iron phosphate battery. Background Art

[0002] Lithium iron phosphate batteries have low cost and good safety, but compared with ternary batteries, the rate performance of lithium iron phosphate batteries is poor, which makes the fast charging performance of lithium iron phosphate batteries poor.

[0003] The market competition for lithium iron phosphate power batteries is becoming increasingly fierce. How to improve the fast charging capability of lithium iron phosphate batteries while ensuring energy density is an urgent problem to be solved. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor rate fast charging performance of lithium iron phosphate batteries in the prior art, thereby providing an electrolyte for a lithium iron phosphate battery and a lithium iron phosphate battery.

[0005] To this end, the present invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides an electrolyte for a lithium iron phosphate battery, comprising an electrolyte, a solvent and a first additive;

[0007] The solvent includes an organic solvent I; based on the total mass of the electrolyte, the content of the organic solvent I is greater than 30%;

[0008] The structural formula of the organic solvent I is as follows:

[0009]

[0010] In Formula I, R 1 , R 2 Each independently selected from a C1-C7 saturated alkylene group or a C1-C7 unsaturated alkylene group;

[0011] The first additive includes a maleic anhydride additive, and the structure of the maleic anhydride additive is as shown in Formula II:

[0012]

[0013] In formula II, R 3 , R 4 Each of them is independently selected from H, a C1-C7 saturated hydrocarbon group, a C1-C7 unsaturated hydrocarbon group, an aromatic group or a halogen element.

[0014] The voltages of ternary batteries and iron-lithium batteries are different. The voltage of ternary batteries is above 4.0V, while the voltage upper limit of iron-lithium batteries is 3.65V. A large amount of organic solvent I added may cause the ternary battery to produce a large amount of gas when working at high voltage; therefore, the electrolyte of the present invention is more suitable for iron-lithium batteries.

[0015] The term "C1-C7 saturated alkylene" refers to an alkylene group containing 1 to 7 carbon atoms, suitable examples of which are methylene (-CH 2 -), ethylene (-CH 2 CH 2 - or -CH(CH 3 )-), propylene (-CH 2 CH 2 CH 2 -、-CH 2 CH(CH 3 )- or -C(CH 3 ) 2 -).

[0016] The term "C1-C7 unsaturated alkylene" refers to an alkenylene or alkynylene group containing 1 to 7 carbon atoms, suitable examples of which are vinylene -CH=CH-, propenylene -CH=CH-CH 2 -.

[0017] The term "aryl" refers to a carbon ring system having aromatic properties, and its structure can be monocyclic, polycyclic or condensed ring. Examples of aryl include, but are not limited to, phenyl.

[0018] The term "hydrocarbyl" refers to a monovalent group composed of two elements, carbon and hydrogen. The hydrocarbyl group may be in the form of an alkyl, alkenyl, alkynyl, etc.

[0019] In a possible embodiment, the organic solvent I comprises One or more of .

[0020] In a possible implementation, based on the total mass of the electrolyte, the content of the maleic anhydride additive is 0.5% to 5%.

[0021] In a possible implementation manner, the mass ratio of the organic solvent I to the maleic anhydride additive is (10-50):(0.5-5).

[0022] In a possible implementation, the solvent further includes carbonate, and the mass ratio of the carbonate to the organic solvent I is (30-48): (30-50).

[0023] In a possible implementation, the carbonate includes ethylene carbonate and ethyl methyl carbonate.

[0024] In a possible implementation, the mass ratio of ethylene carbonate, ethyl methyl carbonate and organic solvent I is (20-38): (10-20): (30-45).

[0025] In a possible implementation manner, the electrolyte further includes a second additive.

[0026] In a possible implementation, the second additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and lithium bifluorooxalatoborate.

[0027] In a possible implementation manner, based on the total mass of the electrolyte, the content of the second additive is 0.5% to 5%.

[0028] In a possible implementation, the electrolyte includes one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide;

[0029] Optionally, the content of the electrolyte is 10% to 20% based on the total mass of the electrolyte.

[0030] In a second aspect, the present invention provides a lithium iron phosphate battery, comprising the above-mentioned electrolyte.

[0031] The technical solution of the present invention has the following advantages:

[0032] 1. The electrolyte of the lithium iron phosphate battery of the present invention comprises an electrolyte, a solvent and a maleic anhydride additive; the solvent comprises an organic solvent I; based on the total mass of the electrolyte, the content of the organic solvent I is more than 30%; the structural formula of the organic solvent I is as follows:

[0033] In Formula I, R 1 , R 2 Each independently selected from a saturated alkylene group of C1 to C7 or an unsaturated alkylene group of C1 to C7; the structure of the maleic anhydride additive is as shown in Formula II:

[0034] In formula II, R 3 , R 4 Each of them is independently selected from H, a C1-C7 saturated hydrocarbon group, a C1-C7 unsaturated hydrocarbon group, an aromatic group or a halogen element.

[0035] The solvent of the electrolyte of the present invention introduces a large amount of organic solvent I with a specific structure containing both cyano and fluorine-containing groups. The cyano group can combine with transition metal ions, improve the surface of the positive electrode material, and inhibit the battery from flatulence during high-rate fast charging; the fluorine-containing group can form a good SEI film, which improves the performance stability of the electrode material. In addition, the organic solvent I replaces a part of the carbonate solvent, which can reduce the viscosity of the electrolyte and accelerate the mass transfer capacity of the electrolyte at low temperatures. The electrolyte of the present invention can significantly improve the rate performance and cycle performance of the lithium iron phosphate battery, and at the same time make the lithium iron phosphate battery have good high temperature performance and low temperature performance.

[0036] The electrolyte of the lithium iron phosphate battery of the present invention also includes maleic anhydride additives. Maleic anhydride additives participate in the formation of the SEI film, further improving the rate performance of the battery while maintaining good high temperature performance. At the same time, the cyanide group of the organic solvent I and the maleic anhydride additive act synergistically, and the cyanide group acts as a nucleophilic reagent to attack the carbonyl carbon of the anhydride to form an amide intermediate, which can improve the electrochemical performance of the battery. By adsorbing on the electrode surface to form a protective film, isolating the electrolyte and inhibiting side reactions, it is beneficial to further improve the ultra-low temperature (-20°C) discharge performance of the battery and maintain good stability in a low temperature environment. The usable temperature range of the battery is improved. DETAILED DESCRIPTION

[0037] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0038] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0039] The preparation method of organic solvent I comprises:

[0040] (1) Add Br under light or heating conditions 2 Substitution reaction to obtain

[0041] (2) Dissolve in DMF solvent, add NaCN, stir in ethanol for 2-6h to obtain

[0042] The synthetic reaction formula of steps (1) and (2) is

[0043] In a glove box, the electrolyte, additives and solvent are fully mixed in proportion to obtain an electrolyte solution.

[0044] Example 1

[0045] The present embodiment provides an electrolyte for a lithium iron phosphate battery, which includes, based on the total mass of the electrolyte, 45% of an organic solvent I-, 25% of ethylene carbonate, 11% of ethyl methyl carbonate, 14% of lithium hexafluorophosphate, 0.5% of a maleic anhydride additive, 3.5% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium difluorooxalate borate.

[0046] The structural formula of the organic solvent I in this embodiment is:

[0047] The structural formula of the maleic anhydride additive in this embodiment is:

[0048] Example 2

[0049] The present embodiment provides an electrolyte for a lithium iron phosphate battery, which includes, based on the total mass of the electrolyte, 45% of an organic solvent I-, 25% of ethylene carbonate, 10% of ethyl methyl carbonate, 14% of lithium hexafluorophosphate, 2% of a maleic anhydride additive, 3% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium difluorooxalate borate.

[0050] The structural formulas of the organic solvent I and the maleic anhydride additive in this embodiment are the same as those in Example 1.

[0051] Example 3

[0052] The present embodiment provides an electrolyte for a lithium iron phosphate battery, which includes, based on the total mass of the electrolyte, 45% of an organic solvent I-, 23% of ethylene carbonate, 10% of ethyl methyl carbonate, 14% of lithium hexafluorophosphate, 4% of a maleic anhydride additive, 3% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium difluorooxalate borate.

[0053] The structural formulas of the organic solvent I and the maleic anhydride additive in this embodiment are the same as those in Example 1.

[0054] Example 4

[0055] The present embodiment provides an electrolyte for a lithium iron phosphate battery, which includes, based on the total mass of the electrolyte, 30% of an organic solvent I-, 38% of ethylene carbonate, 10% of ethyl methyl carbonate, 14% of lithium hexafluorophosphate, 4% of a maleic anhydride additive, 3% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium difluorooxalate borate.

[0056] The structural formulas of the organic solvent I and the maleic anhydride additive in this embodiment are the same as those in Example 1.

[0057] Example 5

[0058] This embodiment is basically the same as embodiment 1, except that the structural formula of the organic solvent I in this embodiment is:

[0059] Example 6

[0060] This embodiment is basically the same as embodiment 1, except that the first additive in this embodiment is:

[0061]

[0062] Example 7

[0063] This embodiment is basically the same as embodiment 1, except that the first additive in this embodiment is:

[0064]

[0065] Example 8

[0066] This embodiment is basically the same as embodiment 1, except that the first additive in this embodiment is:

[0067]

[0068] Example 9

[0069] This embodiment is basically the same as embodiment 1, except that the first additive in this embodiment is:

[0070]

[0071] Example 10

[0072] The present embodiment provides an electrolyte for a lithium iron phosphate battery, which includes, based on the total mass of the electrolyte, 45% of an organic solvent I-, 25% of ethylene carbonate, 10% of ethyl methyl carbonate, 11% of lithium hexafluorophosphate, 3% of lithium bis(fluorosulfonyl)imide, 2% of maleic anhydride, 3% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium bis(fluorooxalyl)borate.

[0073] The structural formula of the organic solvent I in this embodiment is the same as that in Example 1.

[0074] Comparative Example 1

[0075] This comparative example provides an electrolyte for a lithium iron phosphate battery, which comprises, based on the total mass of the electrolyte, 45% of an organic solvent I-, 25% of ethylene carbonate, 12% of ethyl methyl carbonate, 14% of lithium hexafluorophosphate, 3% of vinylene carbonate, 0.5% of fluoroethylene carbonate, and 0.5% of lithium difluorooxalate borate.

[0076] The structural formula of the organic solvent I in this comparative example is the same as that in Example 1.

[0077] Comparative Example 2

[0078] This comparative example is substantially the same as Example 1, except that in this comparative example, organic solvent I is not added, and an equal amount of dimethyl carbonate is used to replace organic solvent I.

[0079] Comparative Example 3

[0080] This comparative example provides an electrolyte for a lithium iron phosphate battery, which comprises, based on the total mass of the electrolyte, 45% dimethyl carbonate, 25% ethylene carbonate, 11.5% ethyl methyl carbonate, 14% lithium hexafluorophosphate, 3.5% vinylene carbonate, 0.5% fluoroethylene carbonate, and 0.5% lithium difluorooxalatoborate.

[0081] This comparative example is basically the same as Example 1, except that, in this comparative example, organic solvent I and maleic anhydride additives are not added, that is, an equal amount of dimethyl carbonate is used to replace organic solvent I, and an equal amount of ethyl methyl carbonate is used to replace maleic anhydride additives.

[0082] Comparative Example 4

[0083] This comparative example provides an electrolyte for a lithium iron phosphate battery, which comprises, based on the total mass of the electrolyte, 35% dimethyl carbonate, 10% organic solvent I-1, 25% ethylene carbonate, 11% ethyl methyl carbonate, 14% lithium hexafluorophosphate, 0.5% maleic anhydride additives, 3.5% vinylene carbonate, 0.5% fluoroethylene carbonate, and 0.5% lithium difluorooxalate borate.

[0084] The structural formulas of the organic solvent I and the maleic anhydride additive in this comparative example are the same as those in Example 1.

[0085] Test example

[0086] Batteries were prepared using the electrolytes of the embodiment and the comparative example respectively:

[0087] Positive electrode: lithium iron phosphate (LFP), Super-P, CNT and poly (vinylidene fluoride) (PVDF) are mixed and stirred in a mass ratio of 97:0.6:0.6:1.8, and then evenly coated on the surface of aluminum foil, dried at 100°C in vacuum for 12 hours, and sliced ​​to obtain the positive electrode sheet.

[0088] Negative electrode: Artificial graphite (AG), Super-P, styrene-butadiene latex (SBR) and carboxymethyl cellulose (CMC) are mixed and stirred in a mass ratio of 96:0.7:2:1.3, and then evenly coated on the surface of copper foil, dried at 120°C in vacuum for 12 hours, and sliced ​​to obtain the negative electrode sheet.

[0089] Battery assembly: According to the order of positive electrode, separator and negative electrode, the laminated soft-pack battery is assembled with PP separator. The electrolyte injection coefficient of each battery is 4g / Ah. The soft-pack battery is fully dried after baking. After high-temperature aging, formation, secondary sealing, capacity division and other processes, the battery performance is tested respectively.

[0090] The electrochemical performance of the battery is tested by:

[0091] Room temperature rate performance: At room temperature 25°C, the above lithium-ion battery is charged to 3.65V using a 4C constant current, charged to a current of 0.05C using a constant voltage, and then discharged to 2.0V using a 1C constant current. Calculate the constant current charging ratio at a 4C rate.

[0092] -20℃ discharge performance: At 25℃, the above lithium-ion batteries were charged to 3.65V using 1C constant current, charged to 0.05C using constant voltage, and then discharged to 2.0V using 1C constant current, and the capacity released at room temperature was calculated. Subsequently, the battery was charged to 3.65V using 1C constant current, charged to 0.05C using constant voltage, and the battery was left at -20℃ for 7h, and discharged to 2.0V using 1C constant current, and the capacity released at low temperature was calculated. The capacity discharged at low temperature was divided by the capacity discharged at room temperature to compare the low temperature discharge performance.

[0093] Room temperature fast charge cycle performance: At room temperature 25°C, the above lithium-ion battery is discharged at 1C constant current to 10% SOC, then charged at 4C constant current to 80% SOC, then charged at 1C constant current and constant voltage to 100% SOC, and finally discharged at 1C constant current to 2.0V. This is taken as one cycle to calculate the capacity retention rate after the 500th cycle.

[0094] High temperature cycle performance: At a high temperature of 45°C, the lithium-ion battery is charged to 3.65V at 1C constant current and constant voltage, and then discharged to 2.0V at 1C constant current. This is taken as one cycle to calculate the capacity retention rate after the 500th cycle.

[0095] The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] It can be seen from Table 1 that the electrolyte of the present invention can significantly improve the rate performance and cycle performance of the lithium iron phosphate battery, and at the same time make the lithium iron phosphate battery have good high temperature performance and low temperature performance.

[0099] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. An electrolyte for a lithium iron phosphate battery, characterized in that: comprising an electrolyte, a solvent and a first additive; The solvent includes an organic solvent I; based on the total mass of the electrolyte, the content of the organic solvent I is greater than 30%; The structural formula of the organic solvent I is as follows: In Formula I, R1 and R2 are independently selected from a C1-C7 saturated alkylene group or a C1-C7 unsaturated alkylene group; The first additive includes a maleic anhydride additive, and the structure of the maleic anhydride additive is as shown in Formula II: In formula II, R3 and R4 are independently selected from H, a C1-C7 saturated hydrocarbon group, a C1-C7 unsaturated hydrocarbon group, an aromatic group or a halogen element.

2. The electrolyte of the lithium iron phosphate battery according to claim 1, characterized in that: The organic solvent I comprises One or more of .

3. The electrolyte of the lithium iron phosphate battery according to claim 1, characterized in that: Based on the total mass of the electrolyte, the content of the maleic anhydride additive is 0.5% to 5%.

4. The electrolyte of the lithium iron phosphate battery according to claim 1, characterized in that: The mass ratio of the organic solvent I to the maleic anhydride additive is (10-50):(0.5-5).

5. The electrolyte of the lithium iron phosphate battery according to claim 1, characterized in that: The solvent further comprises carbonate, and the mass ratio of the carbonate to the organic solvent I is (30-48): (30-50).

6. The electrolyte of the lithium iron phosphate battery according to claim 5, characterized in that: The carbonates include ethylene carbonate and ethyl methyl carbonate.

7. The electrolyte of the lithium iron phosphate battery according to claim 6, characterized in that: The mass ratio of ethylene carbonate, ethyl methyl carbonate and organic solvent I is (20-38): (10-20): (30-45).

8. The electrolyte of the lithium iron phosphate battery according to any one of claims 1 to 7, characterized in that: The electrolyte further includes a second additive; The second additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and lithium bifluorooxalate borate; Optionally, based on the total mass of the electrolyte, the content of the second additive is 0.5% to 5%.

9. The electrolyte of the lithium iron phosphate battery according to any one of claims 1 to 5, characterized in that: The electrolyte includes one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; Optionally, the content of the electrolyte is 10% to 20% based on the total mass of the electrolyte.

10. A lithium iron phosphate battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 9.

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