Lithium ion battery liquid injection amount determination method and liquid injection method

Abstract

The invention belongs to the field of batteries, and particularly relates to a lithium ion battery liquid injection amount determination method and a liquid injection method. The method for determining the liquid injection amount of the lithium ion battery is determined through the actual liquid absorption amount of a core package and a proportionality coefficient; the liquid injection amount of the lithium ion battery is equal to the actual liquid absorption amount of the core package / the proportionality coefficient. According to the method for determining the liquid injection amount, on the basis of the actual liquid absorption amount, it can be guaranteed that the liquid injection amount is sufficient, the electrolyte can be fully infiltrated, the problem of liquid overflow caused by too much electrolyte in the trial-manufacturing process is solved, and meanwhile the cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a method for determining the liquid injection amount of a lithium ion battery and a liquid injection method. Background Art

[0002] The electrolyte plays a key role in lithium-ion batteries, providing a channel for the transfer of lithium ions. The amount of electrolyte used is an important factor in the production process of lithium-ion batteries. It is difficult to reasonably determine the amount of liquid injection. Too much liquid injection will lead to a decrease in the energy density of the battery and increase the cost. There is also a risk of leakage or overflow during the battery production process. Too little liquid injection will not allow the electrolyte to fully penetrate the battery, which will affect the performance of the battery, resulting in low capacity, high internal resistance, and rapid decay of the cycle life. It is also easy to cause lithium precipitation, reducing the safety performance of the battery. The existing methods for determining the amount of liquid injection are: First, through experiments, the disadvantage is that the amount of experiments is large and no clear experimental method has been found; 2. Calculate the theoretical injection volume: There is a large deviation from the actual injection volume.

[0003] The injection amount is mainly calculated based on the theoretical injection amount or determined through experiments. Since the actual electrode porosity deviates greatly from the calculated value, it ultimately leads to too much or too little injection. The experiment also requires several experimental cells, which is costly.

[0004] In the related art, the injection amount is mainly calculated based on the theoretical injection amount or determined through experiments. Since the actual electrode porosity deviates greatly from the calculated value, it ultimately leads to too much or too little injection amount. The experiment also requires several experimental battery cells, which is costly.

[0005] Such as the following related patents: CN106159346A discloses "A method for calculating the injection amount of a lithium-ion battery". This patent calculates the theoretical injection amount of the battery by adding the theoretically calculated pore volume to the residual volume inside the battery cell, multiplying it by the density of the electrolyte, and then multiplying it by a coefficient to determine the final injection amount. The disadvantage is that the theoretically calculated pore volume deviates greatly from the actual pore volume, resulting in too much or too little injection. The same is true for traditional methods for determining the injection amount, such as the method of calculating the injection amount based on the battery cell capacity. This method is consistent with its defects and can only be used as a reference; CN116151051A discloses a method for determining the amount of liquid injected into a lithium-ion battery. This patent determines the amount of liquid injected by considering the SOC variation interval corresponding to the main application conditions of the battery cell. It is highly targeted and not suitable for use in many situations. CN116008840A discloses "A method for determining the optimal injection volume". This patent determines the injection volume by performing an AC impedance test on the battery cell and determining the minimum injection coefficient based on the impedance value. It requires several experimental battery cells and is relatively costly. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for determining the liquid injection amount of a lithium ion battery and a liquid injection method.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A method for determining the liquid injection amount of a lithium-ion battery is provided, which is confirmed by the actual liquid absorption amount of a core package and a proportional coefficient; the liquid injection amount of the lithium-ion battery = the actual liquid absorption amount of the core package / the proportional coefficient.

[0008] The proportionality coefficient is 0.85-0.87, preferably 0.87.

[0009] The test of the actual liquid absorption of the core package adopts the following steps: 1) weighing the dry weight of the battery shell and the core package G1; 2) pouring electrolyte into the battery shell and fully soaking it, then pouring out the residual liquid and weighing it as G2; 3) calculating the actual liquid absorption of the core package as G2-G1.

[0010] The method for determining the amount of liquid injected into a lithium-ion battery comprises the following steps: 1) weighing the dry weight G1 of a battery shell and a core pack; 2) pouring electrolyte into the battery shell and fully soaking it, then pouring out the residual liquid and weighing it as G2; 3) calculating the actual amount of liquid absorbed by the core pack as G2-G1; and 4) confirming that the amount of liquid injected into the lithium-ion battery is (G2-G1) / proportional coefficient.

[0011] The time for sufficient infiltration in step 2) is 12-48 hours, preferably 36 hours.

[0012] The present invention also includes a method for injecting electrolyte into a lithium-ion battery, which uses the method for determining the injection amount to inject electrolyte into the lithium-ion battery; the lithium-ion battery includes a core pack and a battery shell; the core pack includes a positive electrode, a negative electrode and a diaphragm.

[0013] The positive electrode is one of a ternary material positive electrode, a lithium-manganese-rich positive electrode, and a phosphate series positive electrode.

[0014] The active material of the negative electrode is one or a mixture of graphite, silicon-carbon and silicon-oxygen materials.

[0015] The material of the diaphragm is a polyethylene-based film, a polypropylene-based film, or a derivative film thereof.

[0016] The electrolyte comprises lithium salt, organic solvent and additives; Preferably, the lithium salt accounts for 12-15 parts by weight, the solvent accounts for 79.5-83.5 parts by weight, and the additive accounts for 4.5-5.5 parts by weight; The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes one or more of carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate, and dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, propylene carbonate and vinylene carbonate; The additive is one or more of fluoroethylene carbonate, vinyl carbonate, 1,3-propylene sultone, tris(trimethylsilyl)phosphite, triphenyl phosphate, trimethyl phosphate, vinylene carbonate, p-phenylene diisocyanate, phenyl methanesulfonate, triallyl phosphate, succinonitrile, adiponitrile and succinic anhydride.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The method for determining the injection amount of the present invention is based on the actual liquid absorption amount, which can not only ensure that the injection amount is sufficient and the electrolyte can be fully infiltrated, but also solve the overflow problem in the trial production process caused by excessive electrolyte, and also reduce costs. The present invention determines the injection amount by the actual liquid absorption amount / proportional coefficient of the core package without a large number of calculations or experiments. After disassembly, the electrolyte residue is appropriate, there is no risk of leakage, and the cycle performance is good. At the same time, the method for determining the battery injection amount of the present invention is not limited by the battery material system, has a wide range of applications, and a short verification cycle. It has promotion and application value in the field of lithium-ion battery technology. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with embodiments. Example

[0019] A method for determining the amount of liquid injected into a lithium-ion battery comprises the following steps: 1) Actual liquid absorption experiment of the core package: (The core package used in this application is LP54173207-200Ah, the positive electrode is lithium iron phosphate, the negative electrode is graphite, and the diaphragm is a rubber-coated diaphragm; the electrolyte is LiPF6 (13%) / EC / DMC / EMC (25:25:50); the theoretical liquid injection volume is (cell physical space + pore space) * electrolyte density = 930g) To ensure that the core package can be fully infiltrated, the core package liquid absorption experiment is performed, and the core package dry weight is G1; 2) Pour the electrolyte into the battery case, fully immerse the core pack in the electrolyte, and fully soak for a period of time (the same as the soaking time in the battery cell manufacturing process, 36 hours is used as a preferred example in this application), then take out the core pack, wipe off the surface electrolyte, and weigh the core pack G2; 3) Calculate the actual liquid absorption of the core pack as G2-G1; 4) Confirm that the amount of liquid injected into the lithium-ion battery is (G2-G1) / proportional coefficient.

[0020] In order to ensure that there is no overflow during the trial production process, experiments were conducted on the actual liquid absorption volume of the core package / different proportional coefficients (0.8, 0.83, 0.85, 0.87, 0.9) to determine the proportional coefficient and thus the final liquid injection volume. The experimental results are shown in Table 1 below: Table 1 Serial number Actual liquid absorption of core pack (g) Proportional coefficient Experimental injection volume (g) Theoretical injection volume (g) Overflow during trial production Residual liquid volume after formation (g) 1 756 0.9 840 930 no none 2 756 0.87 869 930 no 6.7 3 756 0.85 889 930 no 24 4 756 0.83 911 930 yes 43 5 756 0.8 945 930 / / The results show that when the proportional coefficient is 0.9, the experimental injection volume is 840, and there is no overflow during the trial production, but there is no residual liquid after formation, indicating that the battery lacks electrolyte during formation; when the proportional coefficient is 0.87, the experimental injection volume is 869, which does not exceed the theoretical injection volume, and there is no overflow during the trial production, and there is 6.7g of residual liquid after formation, and the capacity also reaches the designed capacity, and the injection volume is more appropriate; when the proportional coefficient is 0.85, compared with 0.87, the capacity difference is not large, indicating that increasing the injection volume has no obvious advantage in the trial production process, but increases the cost; when the proportional coefficient is 0.83, overflow occurs during the trial production, resulting in a significant reduction in injection efficiency; when the proportional coefficient is 0.8, the experimental injection volume exceeds the theoretical injection volume. Therefore, the proportional coefficient of 0.87 is more appropriate, and it has also been verified in some models of batteries. The injection volume is more appropriate when the proportional coefficient is 0.87.

[0021] Therefore, 0.87 is used as a preferred example for subsequent lithium-ion battery injection.

[0022] The following is described with specific embodiments: 1) Core bag liquid absorption experiment: The core bag dry weight G1 is 4295g. The core bag is taken out after being fully soaked for 36 hours. After wiping off the surface electrolyte, the weight G2 is 5252g. The actual liquid absorption of the core bag is G2-G1=957g. 2) Determination of liquid filling amount: The liquid filling amount of the battery cell (design capacity 300Ah) is determined to be 957 / 0.87=1100g.

[0023] The injection volume determined by this method did not cause overflow during the trial production process, and the residual electrolyte amount was 110g after disassembly after capacity separation. The cycle performance was good, with a capacity retention rate of 87% after 2000 cycles.

[0024] Comparative Example 1: According to the method in patent CN106159346A, the theoretical injection amount × 0.85; the theoretical injection amount of this battery cell is 1161g, and the determined injection amount is 1161×0.85=986.85g. The injection amount determined by the patent did not cause overflow during the trial production process, but the residual amount of electrolyte was small and the cycle performance was poor. Compared with the embodiment, the capacity retention rate was 75% after 2000 cycles.

[0025] Comparative Example 2: Calculated by cell capacity; The injection volume is directly determined by the battery cell capacity and the injection coefficient: the designed battery cell capacity is 300Ah, the positive electrode material used is iron lithium, the injection coefficient is calculated according to 3.8g / Ah, and 10g of the retention amount is added, and the injection volume is determined to be 300×3.8+10=1150g. The injection volume of 1150g caused serious overflow during the trial production process. After disassembly, the electrolyte residue was relatively large, about 160g. The subsequent battery will also have the risk of leakage, and the cycle performance is slightly worse than that of the embodiment. After 2000 cycles, the capacity retention rate is 84%.

[0026] Comparative Example 3: According to the method in patent CN116151051A, the injection volume is determined by the internal volume of the battery cell and the expansion coefficient of the positive and negative electrode material areas; the designed battery cell volume is: 2446140mm 3 ; According to the expansion coefficient, the actual injectable volume is calculated to be 906500mm 3 ; The electrolyte density is 1.24g / cm 3 The actual injection volume is 1124.1g.

[0027] The amount of liquid injection determined by this method caused overflow during the trial production process. After disassembly, the residual amount of electrolyte was 120g, and the capacity retention rate after 2000 cycles was 87%, which was consistent with the example.

[0028] The results of the embodiment and the comparative example are shown in Table 2. Table 2 Injection volume (g) Residual amount of electrolyte after disassembly (g) 2000 cycles capacity retention rate (%) Example 1100 110 87 Comparative Example 1 986.85 40 75 Comparative Example 2 1150 160 84 Comparative Example 3 1124.1 120 87 Similarly, the technical solution of the present application is also applicable to other types of lithium-ion batteries, for example, the lithium-ion battery includes a core pack and a battery shell; the core pack includes a positive electrode, a negative electrode and a separator. The positive electrode is one of a ternary material positive electrode, a lithium manganese-rich positive electrode, and a phosphate series positive electrode. The active material of the negative electrode is one or a mixture of graphite, silicon carbon, and silicon oxygen materials. The material of the separator is one of a polyethylene-based film, a polypropylene-based film, or a derivative film thereof. The electrolyte includes a lithium salt, an organic solvent, and an additive; the lithium salt accounts for 12-15 parts by weight, the solvent accounts for 79.5-83.5 parts by weight, and the additive accounts for 4.5-5.5 parts by weight; The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes one or more of carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate, and dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, propylene carbonate and vinylene carbonate; The additive is one or more of fluoroethylene carbonate, vinyl carbonate, 1,3-propylene sultone, tris(trimethylsilyl)phosphite, triphenyl phosphate, trimethyl phosphate, vinylene carbonate, p-phenylene diisocyanate, phenyl methanesulfonate, triallyl phosphate, succinonitrile, adiponitrile and succinic anhydride.

[0029] In summary, the method for determining the injection amount of the present invention can ensure that the injection amount is sufficient and the electrolyte can be fully infiltrated, and it also solves the overflow problem in the trial production process caused by excessive electrolyte, while also reducing costs. The present invention determines the injection amount by the actual liquid absorption amount of the core package / 0.87 without a large number of calculations or experiments. After disassembly, the electrolyte residue is appropriate, there is no risk of leakage, and the cycle performance is good. At the same time, the method for determining the battery injection amount of the present invention is not limited by the battery material system, has a wide range of applications, and a short verification cycle. It has promotion and application value in the field of lithium-ion battery technology.

[0030] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining the amount of liquid injected into a lithium-ion battery, characterized in that: Confirmed by the actual liquid absorption of the core pack and the proportional coefficient; the amount of liquid injected into the lithium-ion battery = the actual liquid absorption of the core pack / the proportional coefficient.

2. The method for determining the amount of liquid injected into a lithium-ion battery according to claim 1, wherein: The proportionality coefficient is 0.85-0.87, preferably 0.

87.

3. The method for determining the amount of liquid injected into a lithium-ion battery according to claim 1, wherein: The test of the actual liquid absorption of the core package adopts the following steps: 1) weighing the dry weight of the battery shell and the core package G1; 2) pouring electrolyte into the battery shell and fully soaking it, then pouring out the residual liquid and weighing it as G2; 3) calculating the actual liquid absorption of the core package as G2-G1.

4. The method for determining the amount of liquid injected into a lithium-ion battery according to claim 1, wherein: The method comprises the following steps: 1) weighing the dry weight G1 of the battery shell and the core package; 2) pouring electrolyte into the battery shell and fully soaking it, then pouring out the residual liquid and weighing it as G2; 3) calculating the actual liquid absorption amount of the core package as G2-G1; 4) confirming that the liquid injection amount of the lithium-ion battery is (G2-G1) / proportional coefficient.

5. The method for determining the amount of liquid injected into a lithium-ion battery according to claim 3, characterized in that: The time for sufficient soaking in step 2) is the same as the soaking time in the cell manufacturing process, preferably 12-48 hours; preferably 36 hours.

6. A method for injecting liquid into a lithium ion battery, characterized in that: The electrolyte is injected into a lithium-ion battery using the method for determining the injection amount described in any one of claims 1 to 5; the lithium-ion battery comprises a core pack and a battery shell; the core pack comprises a positive electrode, a negative electrode and a diaphragm.

7. The method for injecting liquid into a lithium ion battery according to claim 6, characterized in that: The positive electrode is one of a ternary material positive electrode, a lithium-manganese-rich positive electrode, and a phosphate series positive electrode.

8. The method for injecting liquid into a lithium-ion battery according to claim 7, characterized in that: The active material of the negative electrode is one or a mixture of graphite, silicon-carbon, silicon-oxygen materials.

9. The method for injecting liquid into a lithium ion battery according to claim 8, characterized in that: The material of the diaphragm is a polyethylene-based film, a polypropylene-based film, or a derivative film thereof.

10. The method for injecting liquid into a lithium ion battery according to claim 9, characterized in that: The electrolyte comprises lithium salt, organic solvent and additives; Preferably, the lithium salt accounts for 12-15 parts by weight, the solvent accounts for 79.5-83.5 parts by weight, and the additive accounts for 4.5-5.5 parts by weight; The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes one or more of carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate, and dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, propylene carbonate and vinylene carbonate; The additive is one or more of fluoroethylene carbonate, vinyl carbonate, 1,3-propylene sultone, tris(trimethylsilyl)phosphite, triphenyl phosphate, trimethyl phosphate, vinylene carbonate, p-phenylene diisocyanate, phenyl methanesulfonate, triallyl phosphate, succinonitrile, adiponitrile and succinic anhydride.