Method for testing ratio of positive and negative reaction amounts of organic element-containing additive and electrolyte reversing method

Abstract

The invention belongs to the field of batteries, and particularly relates to a method for testing the ratio of positive and negative reaction amounts of an organic element-containing additive and an electrolyte reversing method. The invention discloses a method for testing the ratio of the positive and negative reaction amounts of an organic element additive. The method comprises the following steps: analyzing a pole piece of a disassembled battery to obtain the consumption of the organic element additive on a positive pole piece and a negative pole piece; the ratio of the consumption of the organic element additive of the negative plate to the consumption of the organic element additive of the positive plate is the ratio of the reaction amounts of the organic element additive at the positive electrode and the negative electrode. The invention provides a method for reverse analysis of a lithium ion battery electrolyte formula. The consumption condition of the organic element additive, especially the S-containing additive, at the positive electrode and the negative electrode is explored, so that the type of the S-containing additive is judged, and the addition amount of the S-containing additive in the original electrolyte is further calculated.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to a test method for the ratio of the reaction amounts of an organic element additive at the positive and negative electrodes and an electrolyte reverse method. Background Art

[0002] Lithium-ion batteries have higher energy density, longer cycle life, no memory effect, etc. compared with other chemical energy storage devices, and are widely used in mobile phones, laptop computers, fuel vehicles, new energy vehicles, industrial energy storage and other fields. As a carrier for ion transport, the electrolyte is the guarantee for lithium-ion batteries to obtain advantages such as high voltage and high specific energy. The electrolyte of lithium-ion batteries mainly consists of three major parts: lithium salt, solvent and additive. Among them, a small amount of additive is used in the electrolyte, which is a functional product for improving the overall ionic conductivity, flame retardancy, rate performance, overcharge safety and other properties of the electrolyte. In particular, the addition of S element-containing additives (sulfates and sulfonates) can effectively promote the formation of the SEI film, form a thin film on the electrode surface, reduce the contact resistance between the electrodes, and improve the energy density of the battery. Thereby improving the high-temperature cycle, high-temperature storage and low-temperature discharge performance of the battery. Generally, the addition amount of S element-containing additives does not exceed 1%, and excessive addition is likely to cause the rupture and pulverization of the negative electrode interface, bringing a series of performance deterioration and safety problems. Therefore, it is very necessary to clarify the S-containing additive and its reaction degree at the positive and negative electrodes and determine its addition amount in the electrolyte.

[0003] Currently, for the electrolyte after charge and discharge of lithium-ion batteries, GC-MS (gas chromatography-mass spectrometry) can be used to analyze the components of its solvent and additives, and IC (ion chromatography) can be used to analyze the content of its lithium salt components. However, the component contents obtained by this method are all the remaining amounts of the additives after the charge and discharge reaction. Since the products formed by the additives at the positive and negative electrodes are very complex, it is impossible to clarify their reaction amounts at the positive and negative electrodes through existing test means, and thus it is impossible to know their initial addition amounts. As a result, it is impossible to clarify the reasonable addition amount of the additives at the initial design stage of lithium-ion batteries to ensure excellent subsequent electrical performance of the batteries. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings in the prior art and provide a test method for the ratio of the reaction amounts of an organic element additive at the positive and negative electrodes and an electrolyte reverse method.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A test method for the ratio of the reaction amounts of an organic element additive at the positive and negative electrodes, comprising the following steps:

[0007] 1) Prepare electrolytes with different organic element additives; and inject the electrolytes into the same battery;

[0008] 2) Discharge and disassemble the battery after injection of the electrolyte solution;

[0009] 3) Analyze the electrode sheets of the disassembled battery to obtain the consumption amounts of the organic element additive in the positive electrode sheet and the negative electrode sheet;

[0010] 4) The ratio of the consumption amount of the organic element additive in the negative electrode sheet to the consumption amount of the organic element additive in the positive electrode sheet is the ratio of the reaction amounts of the organic element additive between the positive and negative electrodes.

[0011] The organic element additive is an S element additive, a boron element additive or a nitrile additive; preferably, the S element additive is one or a mixture of methylene methane disulfonate (MMDS), vinylene sulfate (DTD), or propylene sulfite (PS).

[0012] The consumption amount C1 of the organic element additive in step 3) can be calculated by the following formula: C1 = (d * W1 * M * 10 -6 ) / M0;

[0013] wherein, C1 is the mass (g) of the organic element additive; d is the total mass (g) of the electrode powder in the electrode sheet; M is the relative molecular mass (g / mol) of the organic element additive; M0 is the relative molecular mass (g / mol) of the organic element, and W1 is the content of the organic element obtained by testing (ppm); preferably, it is the content of the organic element obtained by ICP testing (ppm).

[0014] The electrolyte solution in step 1) includes a lithium salt, a solvent, a conventional additive and an organic element additive;

[0015] Preferably, the lithium salt is LiPF6; the mass content of the lithium salt is 10% - 20%; preferably 15%;

[0016] Preferably, the solvent is one or a mixture of ethylene carbonate (EC), N-ethyl-N-methylpyrrolidone (EMC), and dimethyl carbonate (DMC);

[0017] Preferably, the conventional additive is one or a mixture of fluoroethylene carbonate (FEC) and vinylene carbonate (VC);

[0018] Preferably, the mass content of the conventional additive is 5% - 8%; preferably 7%;

[0019] Preferably, the mass content of the organic element additive is 0.5% - 2%; preferably 1%;

[0020] Preferably, the specific steps of step 2) are as follows: the battery is charged at 0.1C and then rests for 30 min; discharged at 0.1C and repeated twice; then the battery is fully discharged: first discharged at a large current of 1C to the cut-off voltage and rested for 15 min; then discharged at 0.2C to the cut-off voltage and rested for 15 min; then discharged at 0.1C to the cut-off voltage and rested for 15 min; then discharged at 0.05C to the cut-off voltage and rested for 15 min.

[0021] The present invention also includes a reverse analysis method for an electrolyte, which combines the ratio of the reaction amounts of the organic element additives at the positive and negative electrodes to determine the type and / or content of the organic element additives.

[0022] The method for determining the type of the organic element additive is as follows: analyze the electrolyte after disassembling the battery to be tested, and determine the type of the organic element additive by the types of organic elements in the electrolyte. Specifically:

[0023] When the electrolyte does not contain organic elements, the type of the organic element additive is determined by comparing the content of the organic element additive in the positive electrode plate and the negative electrode plate with the ratio of the reaction amounts of the organic element additive at the positive and negative electrodes.

[0024] When the electrolyte contains organic elements, the type of the organic element additive is determined by elemental analysis.

[0025] The method for determining the content of the organic element additive includes the following steps:

[0026] S1) Analyze the electrolyte obtained after disassembling the battery to be tested to obtain the remaining amount of the organic element additive in the electrolyte.

[0027] S2) Analyze the electrode plates obtained after disassembling the battery to be tested respectively, and calculate the consumption amount of the organic element additive in the electrode plates through the organic element content of the tested electrode plates; preferably, ICP testing is used.

[0028] S3) The initial amount of the organic element additive is the sum of the consumption amount of the organic element additive in the electrode plates in step S2) and the remaining amount of the organic element additive in the electrolyte in step S1).

[0029] The method for determining the content of the organic element additive is particularly applicable to the case where the types of the organic element additives do not exceed two.

[0030] The test method for the remaining amount of the organic element additive in the electrolyte in step S1) is as follows: Weigh the battery, and record the mass as M1; Disassemble the battery and pour out the free electrolyte; After drying the disassembled positive electrode plate, negative electrode plate, separator and mechanical parts, weigh them, and record the mass as M2; The mass of the electrolyte is a1 = M1 - M2; Use IC to test the concentration of inorganic substances in the free electrolyte, and obtain the mass of inorganic substances as M3 according to the concentration of inorganic substances and the mass of the electrolyte; The mass of the organic matter in the electrolyte is b1 = a1 - M3; Use GC to test the content of the organic element additive in the free electrolyte; Obtain the remaining amount of the organic element additive in the electrolyte through the mass of the organic matter.

[0031] The test method for the consumption amount of the organic element additive in step S2) is as follows:

[0032] When there is only one organic element additive in the electrolyte, directly calculate the consumption amount of the organic element additive through the organic element content of the electrode plate obtained by ICP test;

[0033] When there are two organic element additives in the electrolyte, calculate the consumption amount of the organic element additive through the ratio K of the reaction amounts of the organic element additives at the positive and negative electrodes and the organic element content of the electrode plate obtained by ICP test; Specifically, it includes the following steps: Set the organic element content after the positive electrode reaction of the first organic element additive as X1, then the organic element content after the negative electrode reaction of the first organic element additive is K1X1; The organic element content after the positive electrode reaction of the second organic element additive is X2, then the organic element content after the negative electrode reaction of the second organic element additive is K2X2; Among them, K1 is the ratio of the reaction amounts of the first organic element additive at the positive and negative electrodes; K2 is the ratio of the reaction amounts of the second organic element additive at the positive and negative electrodes;

[0034] Obtain the total organic element content Y1 of the positive electrode plate and Y2 of the negative electrode plate through ICP test; X1 + X2 = Y1; K1X1 + K2X2 = Y2; K1, K2, Y1, and Y2 are known quantities obtained by testing or calculation. By solving the simultaneous equations, the organic element content X1 after the positive electrode reaction of the first organic element additive, the organic element content X2 after the positive electrode reaction of the second organic element additive, the organic element content Y1 after the negative electrode reaction of the first organic element additive, and the organic element content X2 after the positive electrode reaction of the second organic element additive can be obtained. Calculate the consumption amount of the organic element additive according to the organic element content;

[0035] The consumption amount C1 of the organic element additive can be calculated by the following formula: C1 = (d * W1 * M * 10 -6) / M0; where C1 is the mass of the organic element additive (g), d is the total mass of the electrode powder in the electrode (g), M is the relative molecular mass of the organic element additive (g / mol), M0 is the relative molecular mass of the organic element (g / mol), and W1 is the content of the organic element obtained by ICP test or the calculated content of the organic element (ppm).

[0036] The total mass of the electrode powder in the electrode (g) is obtained by the following method: Measure the length and width of the electrode after disassembly and drying, and calculate the areas to be Sj respectively; Cut the dried electrodes with the same length and width and an area of S, and weigh their masses as Nj respectively. Immerse the cut electrodes in water and perform ultrasonic treatment until the electrode powder completely falls off; Take out the foil, dry it, and obtain the foil masses as Nb respectively. Then the total mass of the electrode powder is d = Sj * (Nj - Nb) / S; where: Sj and S are in the unit of cm 2 , and d, Nj, and Nb are in the unit of g.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The present invention provides a test method for the ratio of the reaction amounts of an organic element additive in the positive and negative electrodes. By this test method, the reaction amounts of the organic element additive in the positive and negative electrodes are clarified, so as to obtain its initial addition type or addition amount, which is convenient for reverse analysis of the lithium-ion battery electrolyte formula.

[0039] The electrolyte reverse method of the present invention explores the consumption of organic element additives, especially S-containing additives, in the positive and negative electrodes, thereby determining the types of S-containing additives, and further calculating the addition amount of S-containing additives in the original electrolyte. It solves the problem of inaccurate measurement of the content of lithium-ion battery additives after charge and discharge.

[0040] Based on the idea of the present invention, corresponding test methods can be developed for the original addition amounts of other additives. Specific embodiments

[0041] In order to enable those skilled in the art of the present technology to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0042] Example 1

[0043] Taking a 21700 cylindrical lithium-ion battery as an example, the substantial features of the present invention will be described below. The organic element additive can be an S element additive, a boron element additive, or a nitrile additive. In this application, the additive with S as the organic element is used for test description.

[0044] The test method for the ratio of the reaction amounts of the S-containing additive in the positive and negative electrodes includes the following steps:

[0045] 1) Prepare electrolytes containing different organic element additives; and inject the same batteries with the electrolytes.

[0046] The electrolyte includes a lithium salt, a solvent, a conventional additive, and an organic element additive; preferably, the lithium salt is LiPF6; the mass content of the lithium salt is 10%-20%; preferably 15%; preferably, the solvent is one or a mixture of ethyl carbonate (EC), ethylene methyl carbonate (EMC), and dimethyl carbonate (DMC); preferably, the conventional additive is one or a mixture of fluoroethylene carbonate (FEC) and vinylene carbonate (VC); preferably, the mass content of the conventional additive is 5%-8%; preferably 7%; preferably, the mass content of the organic element additive is 0.5%-2%; preferably 1%.

[0047] This is shown in Table 1 in this embodiment.

[0048] Table 1 Electrolyte formula for injection

[0049] Component Blank Formulation 1 Formulation 2 Formulation 3 <![CDATA[LiPF6]]> 15 15 15 15 EC 20 20 20 20 EMC 10 7 7 7 DMC 55 50 50 50 FEC 6 5 4 VC 1 2 3 PS 1 DTD 1 MMDS 1 Total 100 100 100 100

[0050] Inject the electrolytes with the following four formulation schemes, with 2 electrode groups for each scheme. The injection volume refers to the designed injection volume of this type of battery, and the total mass of the positive electrode powder and the negative electrode powder is known, as shown in Table 2; let it stand for 24h - 48h.

[0051] 2) Charge and discharge the injected batteries obtained in step 1) and then disassemble them; (it is known that the S-containing additive can react during the first charge and discharge of the battery and participate in the formation of the SEI film). Charge the above batteries with 0.1C using UHPC and let them rest for 30 min. Discharge with 0.1C, and repeat 2 times. Discharge the battery fully: first discharge at a large current of 1C to the cut-off voltage and let it rest for 15 min; then discharge at 0.2C to the cut-off voltage and let it rest for 15 min; then discharge at 0.1C to the cut-off voltage and let it rest for 15 min; then discharge at 0.05C to the cut-off voltage and let it rest for 15 min.

[0052] 3) Analyze the electrodes of the disassembled batteries to obtain the consumption of the organic element additive in the positive electrode and the negative electrode.

[0053] Disassemble the battery, take out the electrolyte and seal it for storage. Take out the internal electrode assembly and separate the positive electrode, negative electrode, separator, and mechanical parts. Immerse and clean the positive electrode, negative electrode, separator, and mechanical parts with DMC solvent for 24h - 48h, and soak repeatedly for more than 3 times. Place the aforementioned positive electrode, negative electrode, separator, and mechanical parts in an oven at 60°C for more than 24h until completely dried.

[0054] The S element contents in the positive electrode powder and the negative electrode powder are measured by ICP respectively as shown in Table 2; the total mass of the positive electrode powder and the total mass of the negative electrode powder are known, which are 18.62 g and 12.86 g respectively; then the consumption C1 of the organic element additive can be calculated by the following formula: C1 = (d * W1 * M * 10 -6 ) / M0; where C1 is the mass (g) of the organic element additive; d is the total mass (g) of the electrode powder in the electrode; M is the relative molecular mass (g / mol) of the organic element additive; M0 is the relative molecular mass (g / mol) of the organic element, and W1 is the organic element content (ppm) obtained by ICP test.

[0055] 4) The ratio of the consumption of the organic element additive in the negative electrode sheet to the consumption of the organic element additive in the positive electrode sheet is the ratio of the reaction amounts of the organic element additive in the positive and negative electrodes (negative / positive reaction ratio of the S additive) as shown in Table 2.

[0056] Table 2 Content of S additive in positive and negative electrode sheets

[0057]

[0058] Combined with the above ratio of the reaction amounts of the organic element additive in the positive and negative electrodes, the type and / or content of the organic element additive can be judged.

[0059] Example 2

[0060] The reverse analysis method of the electrolyte includes the following steps:

[0061] 1) Analyze the electrolyte obtained after disassembling the battery to be tested; obtain the remaining amount of the organic element additive in the electrolyte;

[0062] Specifically, it includes the following steps: Weigh a fully discharged 21700 cylindrical lithium-ion battery to be tested, M1 = 64.96 g. Disassemble the battery to be tested, take out the electrolyte and seal it for storage. Take out the internal electrode assembly and separate the positive electrode sheet, negative electrode sheet, separator and mechanical parts. Immerse and clean the positive electrode sheet, negative electrode sheet, separator and mechanical parts with DMC solvent for 24 h to 48 h, and immerse repeatedly for more than 3 times. Place the above-mentioned positive electrode sheet, negative electrode sheet, separator and mechanical parts in an oven at 60 °C for more than 24 h until completely dried. Weigh the above-mentioned dried positive electrode sheet, negative electrode sheet, separator and mechanical parts, which is M2 = 58.73 g. Thus, the mass of the electrolyte in the lithium-ion battery is a1 = M1 - M2 = 6.230 g.

[0063] Use IC to test the inorganic matter content in the electrolyte. Take 1.00 g of the above electrolyte and make it up to 50 mL in a volumetric flask for testing. The results are shown in Table 3, M3 = 0.698 g:

[0064] Table 3 Inorganic Content in the Electrolyte

[0065] Lithium salt component Absolute content / % Mass / g LiODFB 0.350 0.022 <![CDATA[LiPF6]]> 10.85 0.676 Total 11.20 0.698

[0066] Given that the mass of the inorganic substance is M3 = 0.698 g, then the mass of the organic substance is b1 = a1 - M3 = 6.230 - 0.698 = 5.532 g.

[0067] The components and contents of the organic substances were tested by GC-MS as shown in Table 4:

[0068] Table 4 Organic Content in the Electrolyte

[0069] Organic component Relative content / % Mass / g DMC 30.03 1.661 EMC 37.69 2.085 EC 29.16 1.613 VC 2.72 0.150 PS 0.30 0.017 MMDS 0.10 0.006 Total 100.00 5.532

[0070] S2) Analyze the electrode sheets obtained after disassembling the battery to be tested respectively, and calculate the consumption of the organic element additives in the electrode sheets based on the organic element content of the electrode sheets obtained by ICP testing;

[0071] As can be seen from step S1), there are two organic element additives PS and MMDS in the electrolyte; calculate the consumption of the organic element additives based on the ratio K of the reaction amounts of the organic element additives at the positive and negative electrodes and the organic element content of the electrode sheets obtained by ICP testing;

[0072] Specifically, it includes the following steps: Set the content of organic element S after the positive electrode reaction of the first organic element additive PS as X1, then the content of organic element S after the negative electrode reaction of the first organic element additive PS is K1X1; Set the content of organic element S after the positive electrode reaction of the second organic element additive MMDS as X2, then the content of organic element S after the negative electrode reaction of the second organic element additive MMDS is K2X2; where, K1 is the ratio of the reaction amounts of the first organic element additive at the positive and negative electrodes; K2 is the ratio of the reaction amounts of the second organic element additive at the positive and negative electrodes; As can be seen from Table 2, K1 = 3.4, K2 = 2.2; Obtain the total organic element content Y1 of the positive electrode sheet and the total organic element content Y2 of the negative electrode sheet by ICP testing;

[0073] X1 + X2 = Y1; K1X1 + K2X2 = Y2; By solving the simultaneous equations, the content of organic element X1 after the positive electrode reaction of the first organic element additive, the content of organic element X2 after the positive electrode reaction of the second organic element additive, the content of organic element Y1 after the negative electrode reaction of the first organic element additive, and the content of organic element X2 after the positive electrode reaction of the second organic element additive can be obtained, and calculate the consumption of the organic element additives based on the organic element content;

[0074] Specifically in this embodiment, the S element contents in the positive electrode powder and the negative electrode powder are measured by ICP to be Y1 = 109 ppm and Y2 = 349 ppm respectively. It can be seen from Table 2 that K1 = 3.4 and K2 = 2.2. X1 + X2 = 109; 3.4X1 + 2.2X2 = 109; X1 = 91 ppm, X2 = 18 ppm;

[0075] The consumption C1 of the organic element additive can be calculated by the following formula: C1 = (d * W1 * M * 10 -6 ) / M0; where, c1 is the mass (g) of the organic element additive; d is the total mass (g) of the electrode powder in the electrode; M is the relative molecular mass (g / mol) of the organic element additive; M0 is the relative molecular mass (g / mol) of the organic element, and W1 is the organic element content (ppm) obtained by ICP test.

[0076] It can be calculated that the reaction amount of PS in the positive electrode is 0.0069 g, and the reaction amount in the negative electrode is 0.0235 g. The reaction amount of MMDS in the positive electrode is 0.0014 g, and in the negative electrode is 0.0032 g.

[0077] Among them, the total mass (g) of the electrode powder is obtained in the following way. Measure the length and width of the electrode after disassembly and drying, and calculate the areas to be Sj respectively; cut the dried electrodes with the same length and width and an area of S, and weigh their masses as Nj respectively; soak the cut electrodes in water and perform ultrasonic treatment until the electrode powder completely falls off; take out the foil, dry it, and obtain the foil masses as Nb respectively; then the total mass of the electrode powder in the electrode is d = Sj *

[0078] (Nj - Nb / ) / S; measure and calculate the areas of the dried positive and negative electrodes to be S1 = 776.53 cm 2 、S2 = 828.94 cm 2 . Cut a positive electrode with an area S = 42.0 cm 2 . Weigh it as N1 = 1.50 g. Cut a negative electrode with S = 43.4 cm 2 . Weigh it as N2 = 1.04 g. After completely removing the electrode powder, measure the mass of the positive electrode aluminum foil as N3 = 0.42 g and the mass of the negative electrode copper foil as N4 = 0.33 g respectively. The total mass of the electrode powder in the positive electrode is d1 = S1 * (N1 - N3) / S = 776.53 * (1.50 - 0.42) / 42 = 19.97 g; the total mass of the electrode powder in the negative electrode is d2 = S2 * (N2 - N4) / S = 828.94 * (1.04 - 0.33) / 43.4 = 13.56 g;

[0079] 3): Combining the remaining amount of S-containing additives in the electrolyte in Table 4, the calculation process shows that the original addition amount of PS is 0.0069 (consumption at the positive electrode) + 0.0235 (consumption at the negative electrode) + 0.017 (remaining amount of PS in the electrolyte) = 0.047 g, and the original addition amount of MMDS is 0.011 g. The two S-containing additives account for approximately 1.05% of the total electrolyte volume.

[0080] Example 3:

[0081] Different from Example 2, in step 1), the mass of the battery under test is measured as M1 = 64.42 g. The mass of each component after drying is M2 = 58.28 g. Thus, the mass of the electrolyte in the lithium-ion battery is a1 = M1 - M2 = 64.42 - 58.28 = 6.14 g. The measured inorganic substance contents are shown in Table 5:

[0082] Table 5 Inorganic Substance Contents in the Electrolyte

[0083]

[0084]

[0085] Then the mass of the organic substances is b1 = a1 - M3 = 6.14 - 0.701 = 5.439 g. Using GC-MS testing, there is only one S-containing additive as shown in Table 6. The relative content of DTD in the electrolyte is 0.36%, and the mass is 0.020 g.

[0086] Table 6 Organic Substance Contents in the Electrolyte

[0087] Organic component Relative content / % Mass / g DMC 31.17 1.695 EMC 35.98 1.957 EC 29.46 1.602 VC 3.03 0.165 DTD 0.36 0.020 Total 100.00 5.439

[0088] The testing method for the consumption of the organic element additive in the electrode in step S2) is as follows: The total mass of the positive electrode powder is 19.97 g; the total mass of the negative electrode powder is 13.56 g (for the same batch of batteries in production, the positive and negative electrode schemes are the same, and the total masses of the positive and negative electrode powders are the same). By using ICP to measure the S element contents in the positive electrode powder and the negative electrode powder respectively, they are 129 ppm and 610 ppm. C1 = (d * W1 * M * 10 -6 ) / M0; where c1 is the mass of the organic element additive (g); d is the total mass of the electrode powder in the electrode (g); M is the relative molecular mass of the organic element additive (g / mol); M0 is the relative molecular mass of the organic element (g / mol), and W1 is the organic element content obtained by ICP testing (ppm). Through calculation, the consumption of DTD at the positive electrode is 0.010 g, and the consumption at the negative electrode is 0.032 g.

[0089] 4): By combining the remaining amount of DTD measured in Table 6, the initial addition amount of the S-containing additive DTD in the electrolyte was obtained as 0.062 g, accounting for approximately 1.14% of the total amount of the electrolyte.

[0090] Example 4:

[0091] Different from Example 2, the mass of the battery under test was measured as M1 = 63.58 g. The mass of each component after drying was M2 = 57.43 g. Thus, the mass of the electrolyte in the lithium-ion battery was 6.42 g. The measured inorganic contents are shown in Table 7:

[0092] Table 7 Inorganic Contents in the Electrolyte

[0093]

[0094]

[0095] The inorganic content was 0.971 g, and the mass of the organic matter was 5.449 g. Different from Examples 1 and 2, the presence of the S-containing additive was not detected by GC-MS. (It shows that the S-containing additive was completely consumed during the reaction and only existed in the positive and negative electrode plates, and was not present in the electrolyte.) By ICP, the content of S element in the positive electrode was measured as 953.87 ppm, and in the negative electrode was 277.24 ppm.

[0096] Furthermore, the reaction ratio of the S-containing additive in the negative / positive electrode was obtained as 3.4. Combining with Table 2, the type of the S-containing additive was determined to be PS. Furthermore, the consumption amount of PS in the positive electrode was calculated as 0.017 g, and in the negative electrode was 0.057 g. Then the initial addition amount of PS in the electrolyte was 0.074 g, accounting for approximately 1.36% of the total amount of the electrolyte.

[0097] The deviations between the measured contents of the S-containing additives in the above examples and the actual values are shown in Table 8 below:

[0098] Table 8 Deviations between the Test Values and the Actual Values

[0099] Example Test content Actual content Test error Example 1 1.05％ 1.00％ 5.00％ Example 2 1.14％ 1.20％ -5.00％ Example 3 1.36％ 1.50％ -9.30％

[0100] Generally, the allowable error range for the electrolyte component test is within 10%. Thus, it can be seen that it is feasible to inversely analyze the content of the S-containing additive by the above method.

[0101] In summary, the present invention provides a test method for the ratio of the reaction amounts of an organic element additive in the positive and negative electrodes. By this test method, the reaction amounts of the organic element additive in the positive and negative electrodes are clarified, so as to obtain its initial addition type or addition amount, which is convenient for inversely analyzing the electrolyte formula of the lithium-ion battery.

[0102] The reverse method of the electrolyte of the present invention explores the consumption of organic element additives, especially S-containing additives, at the positive and negative electrodes, thereby determining the types of S-containing additives and further calculating the addition amount of S-containing additives in the original electrolyte. It solves the problem of inaccurate measurement of the content of additives in lithium-ion batteries after charge and discharge.

[0103] Based on the idea of the present invention, corresponding development of test methods for the original addition amounts of other additives can be carried out accordingly.

[0104] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A test method for the ratio of the reaction amounts of an organic element additive in the positive and negative electrodes, characterized in that, It includes the following steps: 1) Prepare electrolytes with different organic element additives; and inject the electrolytes into the same batteries. 2) Charge and discharge the batteries after injection and then disassemble them. 3) Analyze the electrodes of the disassembled batteries to obtain the consumption amounts of the organic element additives in the positive electrode and the negative electrode. 4) The ratio of the consumption amount of the organic element additive in the negative electrode to the consumption amount of the organic element additive in the positive electrode is the ratio of the reaction amounts of the organic element additive in the positive and negative electrodes.

2. The test method for the ratio of the reaction amounts of the organic element additive at the positive and negative electrodes according to claim 1, characterized in that, The organic element additive is an S element additive, a boron element additive, or a nitrile additive. Preferably, the S element additive is one or a mixture of methylene methanedisulfonate (MMDS), divinyl sulfite (DTD), or propylene sulfite (PS).

3. The test method for the ratio of the reaction amounts of the organic element additive at the positive and negative electrodes according to claim 1, characterized in that In step 3), the consumption C1 of the organic element additive can be calculated by the following formula: C1 = (d * W1 * M * 10 -6 ) / M0; Wherein, C1 is the mass (g) of the organic element additive; d is the total mass (g) of the electrode powder in the electrode; M is the relative molecular mass (g / mol) of the organic element additive; M0 is the relative molecular mass (g / mol) of the organic element, and W1 is the organic element content (ppm) obtained by testing.

4. The test method for the ratio of the reaction amounts of the organic elemental additive at the positive and negative electrodes according to claim 1, characterized in that, The electrolyte in step 1) includes a lithium salt, a solvent, a conventional additive, and an organic element additive. Preferably, the lithium salt is LiPF6; the mass content of the lithium salt is 10% - 20%; preferably 15%. Preferably, the solvent is one or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC). Preferably, the conventional additive is one or a mixture of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Preferably, the mass content of the conventional additive is 5% - 8%; preferably 7%. Preferably, the mass content of the organic element additive is 0.5% - 2%; preferably 1%. Preferably, the specific steps of step 2) are: charge the battery at 0.1C, and rest for 30 min; discharge at 0.1C, and repeat 2 times; then fully discharge the battery: first discharge at a large current of 1C to the cut-off voltage, and rest for 15 min; then discharge at 0.2C to the cut-off voltage, and rest for 15 min; then discharge at 0.1C to the cut-off voltage, and rest for 15 min; then discharge at 0.05C to the cut-off voltage, and rest for 15 min.

5. A reverse analysis method for an electrolyte, characterized in that, Judge the type and / or content of the organic element additive based on the ratio of the reaction amounts of the organic element additive in the positive and negative electrodes as described in any one of claims 1 - 4.

6. The reverse analysis method of the electrolyte according to claim 5, wherein, The method for judging the type of the organic element additive is: analyze the electrolyte after disassembling the battery to be tested, and judge the type of the organic element additive by the type of the organic element in the electrolyte. Specifically: When there is no organic element in the electrolyte, judge the type of the organic element additive by comparing the content of the organic element additive in the positive electrode and the negative electrode with the ratio of the reaction amounts of the organic element additive in the positive and negative electrodes. When there is an organic element in the electrolyte, judge the type of the organic element additive by elemental analysis.

7. The reverse analysis method of the electrolyte according to claim 5, characterized in that The method for judging the content of the organic element additive includes the following steps: S1) Analyze the electrolyte obtained after disassembling the battery to be tested to obtain the remaining amount of the organic element additive in the electrolyte. S2) analyzing the pole pieces obtained after disassembling the battery to be tested, and calculating the consumption of the organic element additive in the pole piece by measuring the organic element content of the pole piece obtained by the test; preferably, ICP test; S3) The initial amount of the organic element additive is the sum of the consumption of the electrode organic element additive in step S2) and the remaining amount of the electrolyte organic element additive in step S1).

8. The reverse analysis method of the electrolyte according to claim 7, characterized in that, The test method for the residual amount of the organic element additive in the electrolyte in step S1) is: Weigh the battery and record its mass as M1; disassemble the battery and pour out the free electrolyte; dry the disassembled positive electrode sheet, negative electrode sheet, diaphragm and mechanical parts and weigh them, record their mass as M2; the mass of the electrolyte is a1=M1-M2; IC is used to test the inorganic concentration in the free electrolyte. According to the inorganic concentration and the mass of the electrolyte, the mass of the inorganic is obtained as M3; The mass of organic matter in the electrolyte is b1 = a1-M3; The content of organic element additives in the free electrolyte was tested by GC; the remaining amount of organic element additives in the electrolyte was obtained by the mass of organic matter.

9. The reverse analysis method of the electrolyte according to claim 8, characterized in that, The test method for the consumption of the organic element additive in step S2) is: When there is only one organic element additive in the electrolyte, the organic element content of the electrode obtained by ICP test is directly used to calculate the consumption of the organic element additive; When there are two organic element additives in the electrolyte, the consumption of the organic element additives is calculated by the ratio K of the organic element additives in the positive and negative electrode reactions and the organic element content of the electrode obtained by ICP testing; specifically, the following steps are included: Suppose the organic element content of the first organic element additive after the positive electrode reaction is X1, then the organic element content of the first organic element additive after the negative electrode reaction is K1X1; the organic element content of the second organic element additive after the positive electrode reaction is X2, then the organic element content of the second organic element additive after the negative electrode reaction is K2X2; wherein K1 is the ratio of the positive electrode reaction amount of the first organic element additive; K2 is the ratio of the positive electrode reaction amount of the second organic element additive; The total organic element content Y1 of the positive electrode sheet and the total organic element content Y2 of the negative electrode sheet obtained by ICP test; X1+X2=Y1; K1X1+K2X2=Y2; K1, K2, Y1, and Y2 are known quantities obtained by test or calculation, and the simultaneous equations can obtain the organic element content X1 of the first organic element additive after the positive electrode reaction, the organic element content X2 of the second organic element additive after the positive electrode reaction, the organic element content Y1 of the first organic element additive after the negative electrode reaction, and the organic element content X2 of the second organic element additive after the positive electrode reaction, and the consumption of the organic element additive is calculated according to the organic element content; The consumption C1 of the organic element additive can be calculated by the following formula: C1 = (d * W1 * M * 10 -6 ) / M0; where C1 is the mass (g) of the organic element additive; d is the total mass (g) of the electrode powder in the electrode; M is the relative molecular mass (g / mol) of the organic element additive; M0 is the relative molecular mass (g / mol) of the organic element, and W1 is the content of the organic element obtained by ICP test or the content of the organic element calculated (ppm).

10. The reverse analysis method of the electrolyte according to claim 9, characterized in that, The total mass (g) of the pole powder in the pole piece is obtained by the following method: Measure the length and width of the dried electrode sheet after disassembly, and calculate that their areas are Sj respectively; cut dried electrode sheets with the same length and width and an area of S respectively, and weigh their masses as Nj respectively. Immerse the cut electrode sheets in water and perform ultrasonic treatment until the electrode powder completely falls off; take out the foil material, dry it, and obtain the foil material masses as Nb respectively. Then the total mass of the electrode powder is d = Sj * (Nj - Nb) / S; Where: Sj and S are in cm 2 , d, Nj, and Nb are in g

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