Electrolyte, lithium-ion battery, and gas production prediction method

Abstract

In order to overcome the problems of instability of the positive electrode structure and complex gas production detection of lithium-ion batteries during the cyclic charge and discharge process of lithium-ion batteries in the prior art, the present invention provides an electrolyte, including an organic solvent, a lithium salt and an additive, the additive including 1,3-propane sultone and compound A, and compound A including one or more of the following structural formulas: wherein n is 0 or 1, and X1 to X5 are each independently selected from one or more of substituted or unsubstituted C1 to C6 alkylene groups and substituted or unsubstituted C2 to C6 alkenylene groups. At the same time, the present invention also discloses a lithium-ion battery of the above-mentioned electrolyte and a method for predicting gas production of a lithium-ion battery. Adding 1,3-propane sultone and compound A to the electrolyte provided by the present invention can improve the structural stability of the positive electrode. In addition, the gas production of the lithium-ion battery can be predicted based on the remainder of 1,3-propane sultone and the compound A. This prediction method can also be used to guide the design of the content of electrolyte additives.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte, a lithium ion battery and a method for predicting gas production. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics and power batteries due to their high specific energy, fast charge and discharge capabilities, and low self-discharge. As the operating conditions of electronic products and power batteries become increasingly complex, the requirements for lithium-ion batteries are also increasing, particularly in terms of battery capacity and lifespan. The performance of lithium-ion batteries is a key factor in determining their market acceptance; lithium-ion battery performance is influenced by a combination of multiple indicators, with cycle performance and safety being particularly critical.

[0003] However, as the limiting voltage of the positive electrode material continues to increase, the gram capacity of the battery material increases accordingly, causing the high-temperature performance and cycle performance of the battery to deteriorate seriously. In particular, during long-term cyclic charge and discharge under high voltage, the volume of the positive electrode material will expand and produce cracks, and the solvent in the electrolyte will enter the interior of the positive electrode material and destroy the structure, which is not conducive to the stability of the positive electrode structure; in addition, during continuous charging at high temperature, the positive electrode is continuously dissolved and deposited on the negative electrode. When a certain amount is reached, it will cause the negative electrode SEI film to decompose and produce gas. At this time, it is necessary to detect the gas production situation in time and discharge the gas in time to ensure the safe use of the battery; in the existing technology, the battery gas production detection process is cumbersome and the detection device structure is complex, and the battery's gas production nodes and gas production conditions cannot be predicted in advance during the battery cycle. Summary of the Invention

[0004] Aiming at the problems of instability of positive electrode structure during cyclic charge and discharge process of lithium ion batteries and complex gas production detection of lithium ion batteries in the prior art, an electrolyte, a lithium ion battery and a method for predicting gas production are provided.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] In one aspect, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises 1,3-propane sultone and a compound A, wherein the compound A comprises one or more of the following structural formulas:

[0007]

[0008] Wherein, n is 0 or 1, and X1 to X5 are each independently selected from one or more of substituted or unsubstituted C1 to C6 alkylene groups and substituted or unsubstituted C2 to C6 alkenylene groups.

[0009] Optionally, based on the total mass of the electrolyte being 100%, the mass proportion of the 1,3-propane sultone in the electrolyte is a, and 0.01%≤a≤6%.

[0010] Optionally, based on the total mass of the electrolyte being 100%, the mass proportion of the compound A in the electrolyte is b, and 0.01%≤b≤10%.

[0011] Optionally, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, methyl formate, ethyl formate, propyl propionate, methyl butyrate and tetrahydrofuran.

[0012] Optionally, the lithium salt concentration is 0.5M to 2M; the lithium salt includes one or more of an organic electrolyte salt and an inorganic electrolyte salt.

[0013] Optionally, the compound A includes one or more of the following compounds:

[0014] The compound A includes one or more of the following compounds:

[0015]

[0016]

[0017] On the one hand, the present application provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet to form a battery cell.

[0018] Optionally, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, ternary LiNi x Co y Mn z One or more O2 materials, wherein x+y+z=1, x≥y.

[0019] Optionally, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material is selected from graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Al alloy, Li-Sn-O alloy, Sn, SnO, SnO2 and TiO2-Li4Ti5O 12 One or more of .

[0020] On the other hand, the present application provides a method for predicting gas production of a lithium-ion battery, comprising the following operations:

[0021] Charge and discharge the battery cells and detect the battery cell expansion rate;

[0022] Detect the cobalt content in the negative electrode of the battery cell at different expansion rates;

[0023] Detect the contents of 1,3-propane sultone and compound A in the electrolyte at different expansion rates of the battery cell;

[0024] Draw linear graphs of cobalt content, 1,3-propane sultone, and the sum of compound A to predict the gas production node of the battery cell.

[0025] The additives in the electrolyte provided by the present invention include 1,3-propane sultone and the compound A. The 1,3-propane sultone introduces a sulfonic acid group into an organic molecule. During high-temperature storage, 1,3-propane sultone can inhibit gas generation, form an excellent protective film on the positive electrode, improve the thermal stability of the positive electrode interface, and effectively improve the performance of the battery under high-temperature continuous charging; the cyano functional group in the compound A complexes with the transition metal in the positive electrode, which can greatly improve the structural stability of the positive electrode; in addition, during the high-temperature continuous charging process of the lithium-ion battery, the positive electrode cobalt is continuously dissolved and deposited on the negative electrode, which can easily cause gas production at the negative electrode. When the additives in the electrolyte include insufficient 1,3-propane sultone and the compound A, the protective effect on the positive electrode deteriorates and gas production is also induced. In this case, adding the 1,3-propane sultone and the compound A described in the present application to the electrolyte can not only stabilize the positive electrode interface, but also predict the gas production of the lithium-ion battery based on the remaining amount of 1,3-propane sultone and the compound A in the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the test result of the cobalt content in the negative electrode of the lithium-ion battery of the present invention at 60°C and 4.5V;

[0027] Figure 2 This is the test result of PS and compound A content in the lithium-ion battery of the present invention at 60°C and 4.5V;

[0028] Figure 3 This is the test result of the cobalt content in the negative electrode of the lithium-ion battery of the present invention in an environment of 55°C and 4.5V;

[0029] Figure 4 This is the test result of PS and compound A content in the lithium-ion battery of the present invention at 55°C and 4.5V;

[0030] Figure 5 This is the test result of the cobalt content in the negative electrode of the lithium-ion battery of the present invention in an environment of 55°C and 4.5V;

[0031] Figure 6 This is the test result of PS and compound A content in the lithium-ion battery of the present invention at 45°C and 4.5V;

[0032] Figure 7 This is the test result of the cobalt content in the negative electrode of the lithium-ion battery of the present invention at 35°C and 4.5V;

[0033] Figure 8 This is the test result of PS and compound A content in the lithium-ion battery of the present invention at 35° C. and 4.5V. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The present invention provides an electrolyte comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises 1,3-propane sultone and a compound A, wherein the compound A comprises one or more of the following structural formulas:

[0036]

[0037] Wherein, n is 0 or 1, and X1 to X5 are each independently selected from one or more of substituted or unsubstituted C1 to C6 alkylene groups and substituted or unsubstituted C2 to C6 alkenylene groups.

[0038] It should be noted that 1,3-propane sultone (PS) is an active intermediate that gently and quantitatively introduces sulfonic acid groups into organic molecules. It has an inhibitory effect on gas production on the negative electrode surface. Therefore, 1,3-propane sultone can effectively inhibit gas generation during high-temperature storage and is an effective gas production inhibitor. After the addition of 1,3-propane sultone, it can inhibit the generation of high-resistance LIF on the negative electrode, which is beneficial to reducing the internal resistance of the battery.

[0039] Although additives replaced by other functional groups in 1,3-propane sultone have certain film-forming and gas production inhibition effects, their impedance is greater than that of 1,3-propane sultone, the synthesis process is complex, and the cost is higher. For example, the six-membered ring 1,4-butane sultone (BS) has a high preparation cost and is inferior to 1,3-propane sultone in high-temperature performance. 1,3-propylene sultone, a substance with double bonds, has higher film-forming impedance and higher cost. The effect of methylene disulfonate in inhibiting gas production is lower than that of 1,3-propane sultone, and methylene disulfonate itself has the risk of discoloration. In summary, 1,3-propane sultone has a good gas production inhibition effect, cost advantage, low interfacial impedance, high solubility, and no quality problems such as decomposition and discoloration.

[0040] The additives in the electrolyte provided by the present invention include 1,3-propane sultone and the compound A. The 1,3-propane sultone introduces a sulfonic acid group into an organic molecule. During high-temperature storage, 1,3-propane sultone can inhibit gas generation, form an excellent protective film on the positive electrode, improve the thermal stability of the positive electrode interface, and effectively improve the performance of the battery under high-temperature continuous charging; the cyano functional group in the compound A complexes with the transition metal in the positive electrode, which can greatly improve the structural stability of the positive electrode; in addition, during the high-temperature continuous charging process of the lithium-ion battery, the positive electrode cobalt is continuously dissolved and deposited on the negative electrode, which can easily cause gas production at the negative electrode. When the additives in the electrolyte include insufficient 1,3-propane sultone and the compound A, the protective effect on the positive electrode deteriorates and gas production is also induced. In this case, adding the 1,3-propane sultone and the compound A described in the present application to the electrolyte can not only stabilize the positive electrode interface, but also predict the gas production of the lithium-ion battery based on the remaining amount of 1,3-propane sultone and the compound A in the electrolyte.

[0041] In some embodiments, based on the total mass of the electrolyte being 100%, the mass proportion of the 1,3-propane sultone in the electrolyte is a, and 0.01%≤a≤6%.

[0042] The 1,3-propane sultone can form an excellent protective film on the positive electrode. However, if the content of 1,3-propane sultone is too high, it will increase the electrode interface impedance and the viscosity of the electrolyte, and deteriorate the overall dynamic performance of the electrolyte. When the amount of 1,3-propane sultone in the electrolyte is insufficient, it is not conducive to protecting the positive electrode and may induce gas production.

[0043] Specifically, in a preferred embodiment, the mass proportion of 1,3-propane sultone in the electrolyte is 3%.

[0044] In some embodiments, based on the total mass of the electrolyte being 100%, the mass proportion of the compound A in the electrolyte is b, and 0.01%≤b≤10%.

[0045] Specifically, in a preferred embodiment, the mass proportion of the compound A in the electrolyte is 5%.

[0046] In some embodiments, the additive further comprises a film-forming additive, wherein the film-forming additive comprises one or more of vinylene carbonate and its derivatives, halogen-substituted cyclic carbonates, chelated orthoborates, and chelated orthophosphates.

[0047] In some embodiments, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, methyl formate, ethyl formate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0048] Specifically, in a preferred embodiment, the organic solvent includes two or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and propyl propionate (PP).

[0049] In some embodiments, the lithium salt concentration is 0.5M to 2M.

[0050] It should be noted that when the lithium salt concentration is too low, the conductivity of the electrolyte decreases accordingly, thereby affecting the rate and cycle performance of the entire battery system; when the lithium salt concentration is too high, the viscosity of the electrolyte is too high, which is also not conducive to improving the rate of the battery system. Therefore, in a more preferred embodiment, the lithium salt concentration is 0.9M to 1.3M.

[0051] In some embodiments, the lithium salt includes one or more of an organic electrolyte salt and an inorganic electrolyte salt.

[0052] Specifically, the lithium salt includes LiPF6, LiBF4, LiSbF6, LiAsF6, LiTaF6, LiAlCl4, Li2B 10 Cl 10 、Li2B 10 F 10 , LiClO4, LiCF3SO3 LiB(C2O4)2, LiB(O2CCH2CO2)2, LiB(O2CCF2CO2)2, LiB(C2O4)(O2CCH2CO2), LiB(C2O4)(O2CCF2CO2), LiP(C2O4)3 and LiP(O2CCF2CO2)3.

[0053] In some embodiments, the compound A comprises one or more of the following compounds:

[0054]

[0055] Specifically, the compound A is a nitrile compound, 1-1 is 1,3,6-hexanetricarbonitrile, 1-2 is 1,2,3-propanetricarbonitrile, 1-3 is 1,3,5-pentanetricarbonitrile, 1-4 is tetrakis(cyanoethoxymethyl)methane, 1-5 is 1,2,2,3-tetracyanopropane, and 1-6 is tetracyanoethylene.

[0056] Another embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet to form a battery cell.

[0057] The positive electrode sheet includes a positive electrode current collector, the negative electrode sheet includes a negative electrode current collector, the positive electrode current collector is Al foil, and the negative electrode current collector is Cu foil.

[0058] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, ternary LiNi x Co y Mn z One or more O2 materials, wherein x+y+z=1, x≥y.

[0059] Specifically, in a preferred embodiment, the positive electrode active material is selected from lithium cobalt oxide, and the positive electrode active material is covered on the positive electrode current collector.

[0060] In some embodiments, the negative electrode sheet includes a negative electrode active material selected from graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Al alloy, Li-Sn-O alloy, Sn, SnO, SnO2 and TiO2-Li4Ti5O 12 One or more of .

[0061] The negative electrode active material is selected from graphite, and the negative electrode active material is covered on the negative electrode current collector.

[0062] Another embodiment of the present invention provides a method for predicting gas production of a lithium-ion battery, comprising the following operations:

[0063] Charge and discharge the battery cells and detect the battery cell expansion rate;

[0064] Detect the cobalt content in the negative electrode of the battery cell at different expansion rates;

[0065] Detect the contents of 1,3-propane sultone and compound A in the electrolyte at different expansion rates of the battery cell;

[0066] Draw linear graphs of cobalt content, 1,3-propane sultone, and the sum of compound A to predict the gas production node of the battery cell.

[0067] Specifically, the battery cell is charged and discharged, and the specific operation of detecting the battery cell expansion rate is as follows: at 25°C, the divided battery is discharged to 3.0V at 0.2C, and left for 5 minutes; then charged to 4.5V at 0.2C, and left for 5 minutes; the thickness of the fully charged battery cell is recorded as H0, and the fully charged battery cell is transferred to a high temperature (35°C to 60°C) environment, left for 2 hours, discharged to 3.0V at 0.2C, left for 5 minutes, and continuously charged to 4.5V at 1C without setting the cut-off current; continuously charging, and taking out the battery cell for testing every 3 days to determine the thickness H0. n (n = days), calculate the thickness of the continuously charged battery cell, the battery cell expansion rate W = (Hn -H0) / H0×100%;

[0068] Specifically, when the expansion rate is 2% to 4%, 4% to 6%, 6% to 8%, 8% to 10%, or 10% to 12%, the cobalt content G in the negative electrode of the battery cell is detected. n (n = number of days).

[0069] Specifically, the contents of 1,3-propane sultone and compound A in the electrolyte of the battery cell before expansion are detected, and the contents of 1,3-propane sultone and compound A in the electrolyte at different expansion rates of the battery cell are detected, including the following operations: recording the content of 1,3-propane sultone in the fresh battery cell electrolyte as a0 (g / Ah), testing and recording the content of compound A, recorded as b0 (g / Ah); testing and recording the contents of 1,3-propane sultone and compound A in the electrolyte under five expansion and gas production conditions (2% to 4%, 4% to 6%, 6% to 8%, 8% to 10%, 10% to 12%), and recording 1,3-propane sultone as a n (g / Ah), the content of compound A, recorded as b n (g / Ah);

[0070] Passing time (X axis)-cobalt content G n (Y axis) Linear graph, time (X axis) - sum of 1,3-propane sultone and compound A n +b n (Y-axis) The linear graph can predict the point at which the battery cell will produce gas during the continuous charging test at different temperatures.

[0071] The specific test steps for testing the content of 1,3-propane sultone and compound A are as follows:

[0072] Step 1: Weigh the mass of the processed battery cell and record it as M0. Disassemble the processed battery cell and place it in a beaker (the mass of the beaker is recorded as S0). Add an appropriate amount of acetonitrile (record the mass N0) and soak it in ultrasound for 30min to 60min. After the ultrasound is completed, filter the electrolyte and perform GC-MS testing;

[0073] Step 2: Use the residual acetonitrile in the beaker to rinse the disassembled battery cell and the beaker, place the beaker in an oven to dry (85°C), and record the total weight of the beaker and the disassembled battery cell when the total weight decreases by less than 0.01g. The drying is completed and the mass is recorded as P1;

[0074] Step 3: Calculate the residual amount of electrolyte F n =S0+M0-P1, record the dilution factor of the electrolyte = (N0+F n ) / F n ;

[0075] Step 4: GC-MS test 1,3-propane sultone mass percentage is V n , the mass percentage of compound A is J n , the content of 1,3-propane sultone after high temperature continuous charging n (g / Ah)=V n* F n / cell capacity, b n (g / Ah)=J n* F n / Battery cell capacity.

[0076] The present invention is further described below with reference to the following examples.

[0077] Example 1

[0078] This embodiment is used to illustrate an electrolyte and a lithium-ion battery disclosed in the present invention, and includes the following steps:

[0079] Preparation of electrolyte: EC, PC, DEC, and PP were mixed in a mass ratio of 1:1:1:1, and PS and compound A were added as organic solvents. The amount of each component added was based on the mass percentage shown in Example 1 in Table 1. After mixing, LiPF6 was added to obtain an electrolyte with a LiPF6 concentration of 1.1 mol / L.

[0080] Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent CNT (carbon nanotube), the binder PVDF (polyvinylidene fluoride) and the lithium supplement additive are mixed in N-methylpyrrolidone solvent in a mass ratio of 95:1.5:1.5:2, and stirred thoroughly to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector aluminum foil, dried and cold pressed to obtain the positive electrode sheet.

[0081] Preparation of negative electrode sheet: The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water in a mass ratio of 96:1.2:1.5:1.3 to form a uniform negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, dried and cold pressed to obtain the negative electrode sheet.

[0082] Production of lithium-ion batteries: Use PE porous polymer film as the separator, stack the positive electrode, separator and negative electrode in order, so that the separator is in the middle of the positive and negative electrodes, and wind the stacked electrode and separator to obtain a core. Place the core in an aluminum-plastic film bag that has been punched and formed, inject the electrolyte prepared above, and complete the preparation of the lithium-ion battery through vacuum packaging, standing, and formation processes.

[0083] Examples 2 to 6

[0084] Examples 2 to 6 are used to illustrate an electrolyte and a lithium-ion battery disclosed in the present invention, and include most of the operations in Example 1, except that:

[0085] The components in the electrolyte were added according to the mass percentages shown in Examples 2 to 6 in Table 1.

[0086] Comparative Example 1

[0087] This comparative example is used to illustrate an electrolyte and a lithium-ion battery disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

[0088] No PS added.

[0089] Comparative Example 2

[0090] This comparative example is used to illustrate an electrolyte and a lithium-ion battery disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

[0091] No compound A was added.

[0092] Comparative Example 3

[0093] This comparative example is used to illustrate an electrolyte and a lithium-ion battery disclosed in the present invention, and includes most of the operating steps in Example 1, except that:

[0094] PS and compound A were not added.

[0095] Relevant performance tests were performed on Examples 1 to 6 and Comparative Examples 1 to 3, and the test results are entered in Table 1.

[0096] The contents of cobalt, expansion rate, PS and compound A in the negative electrode sheet of the lithium ion battery prepared in Example 1 were detected, including the following operations:

[0097] The lithium battery was continuously charged at 60°C, 55°C, 45°C, 35°C and 4.5V, and the expansion rate, the cobalt content of the negative electrode, the PS and the content of compound A were detected at 0 days, 3 days, 6 days, 12 days, 15 days and 18 days respectively; G obtained at different charging temperatures according to Example 1 above was n , PS and compound A content as time (X axis) - cobalt content G n (Y axis) Linear graph, plotting time (X axis) versus the sum of the contents of additive PS and compound A. n +b n (Y axis) linear graph, we get Figures 1 to 6 ; Fill in the specific test results in Tables 2 to 6.

[0098] Table 1

[0099]

[0100] As can be seen from the test results in Table 1, the low-temperature cycle and high-temperature cycle performance of Examples 1 to 6 are better than those of Comparative Examples 1 to 3. In addition, the actual gas generation time of the Examples under continuous charging at 35°C-4.5V is later than that of the Comparative Examples, indicating that the lithium-ion batteries using the electrolyte of the present application are better than those of the Comparative Examples in terms of expansion performance.

[0101] Compared with Example 1, Comparative Example 1 does not add PS, and its high and low temperature cycle performance is poor. Comparative Example 2 does not add Compound A, and the test results show that its high and low temperature cycle performance is poor, the gas production occurs early, and the expansion performance is poor. In Comparative Example 3, neither PS nor Compound A is added, and its performance is the worst; that is, the addition of PS and Compound A to the electrolyte provided by the present invention can improve the structural stability of the positive electrode. In addition, the gas production of the lithium-ion battery can be predicted based on the residual amount of 1,3-propane sultone and the compound A; on the other hand, it is concluded from the test data that PS and Compound A are added to the electrolyte at the same time. The two can play a synergistic role, form an excellent protective film on the positive electrode, improve the thermal stability of the positive electrode interface, effectively improve the high-temperature continuous charging performance of the battery, and improve the expansion rate.

[0102] Table 2

[0103]

[0104] It can be seen from the test results in Table 2 that when the cobalt content of the negative electrode sheet is 622ppm, the thickness expansion rate (gas production) is greater than 10%. When the gas production is greater than 10%, the PS+Compound A is basically consumed. When the PS+Compound A is consumed, the positive electrode is insufficiently protected, resulting in a large amount of gas production. The cobalt content of the negative electrode sheet also affects the gas production of the battery. When the cobalt content of the negative electrode sheet reaches a certain value, gas production is triggered. Therefore, a continuous charging acceleration test at 60℃ can be used to predict the gas production nodes of continuous charging at 55℃, 45℃, and 35℃. It is assumed that the negative electrode cobalt content will trigger gas production when it is 622ppm, and gas production will also occur when the PS+Compound A is consumed.

[0105] Figures 1-2 , which are the time-cobalt content and time-PS+Compound A linear graphs of Example 1.

[0106] Table 3

[0107]

[0108] From the test results in Table 3, it can be seen that when the cobalt content of the negative electrode sheet is 248ppm, the PS+ compound A is basically consumed, causing gas production;

[0109] According to the data in Table 2, the linear relationship between time and cobalt content and time and PS+compound A was drawn. Figures 3-4 :

[0110] Depend on Figure 3 The linear formula of cobalt content and time in the negative electrode sheet is y = 10.167x + 53.667. Substituting the cobalt dissolution content of 622ppm with gas generation greater than 10% at 60°C into the formula, we get x = 55.9≈56 days.

[0111] Depend on Figure 4 The linear formula of the remaining amount of PS + compound A and time is y = -0.0024x + 0.149. Assuming that all PS + compound A are consumed, y = 0, x = 62 days. If the battery is continuously charged at 55°C, the gas production time when the gas production is greater than 10% is 56 to 62 days.

[0112] Table 4

[0113]

[0114] From the test results in Table 4, it can be seen that when the cobalt content of the negative electrode sheet is 145ppm, the PS+ compound A is basically consumed, causing gas production;

[0115] Depend on Figure 5 The linear formula of cobalt content and time in the negative electrode sheet is y = 4.8571x + 50.619. Substituting the cobalt dissolution content of 622ppm, which produces more than 10% gas from continuous charging at 60°C, into the formula, we can calculate x = 117.6 ≈ 118 days. Figure 6 The linear formula of the remaining amount of PS + compound A and time is y = -0.0012x + 0.151. Assuming that all PS + compound A are consumed, then y = 0, x = 125.8 ≈ 126 days;

[0116] If the battery is continuously charged at 45°C, the gas production time until the gas production is greater than 10% is 118 to 126 days.

[0117] Table 5

[0118]

[0119] From the test results in Table 5, it can be seen that when the cobalt content of the negative electrode sheet is 103ppm, the PS+ compound A is basically consumed, causing gas production;

[0120] Depend on Figure 7 The linear formula of cobalt content and time in the negative electrode sheet is y = 2.5119x + 54.726. Substituting the cobalt dissolution content of 622ppm, which produces more than 10% gas from continuous charging at 60°C, into the formula, we get x = 225.8≈226 days. Figure 8The linear formula of the remaining amount of PS + compound A and time is y = -0.0007x + 0.1502. Assuming that all PS + compound A are consumed, then y = 0, x = 214.6 ≈ 215 days;

[0121] If the battery is continuously charged at 35°C, the gas production time until the gas production is greater than 10% is 215 to 226 days.

[0122] Table 6

[0123]

[0124] It can be seen from the test results in Table 6 that the test results under each test condition in the actual detection correspond to the predicted gas production results of Examples 1 to 4, that is, the number of days on which gas production occurs in the actual detection time all falls within the predicted gas production time range corresponding to Examples 1 to 4; in summary, PS and the compound A are added to the electrolyte provided in the present application, and the gas production of the lithium-ion battery is predicted based on the addition of PS and the compound A. The prediction method has a high accuracy rate, so the gas production of the lithium-ion battery can be predicted based on the residual amounts of PS and the compound A in the electrolyte, and this prediction method can also be used to guide the design of the electrolyte additive content.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting gas production of a lithium-ion battery, characterized in that: The following operations are included: Charge and discharge the battery cells and detect the battery cell expansion rate; Detect the cobalt content in the negative electrode of the battery cell at different expansion rates; Detect the contents of 1,3-propane sultone and compound A in the electrolyte at different expansion rates of the battery cell; Draw linear graphs of time versus cobalt content and time versus the sum of 1,3-propane sultone and compound A contents, and predict the gas production point of the battery cell based on the cobalt content and the remaining amounts of 1,3-propane sultone and compound A. The compound A includes one or more of the following structural formulas: Wherein, n is 0 or 1, and X1 to X5 are each independently selected from one or more of substituted or unsubstituted C1-C6 alkylene groups and substituted or unsubstituted C2-C6 alkenylene groups.

2. The method for predicting gas production of a lithium-ion battery according to claim 1, wherein: Based on the total mass of the electrolyte being 100%, the mass proportion of the 1,3-propane sultone in the electrolyte is a, and 0.01%≤a≤6%.

3. The method for predicting gas production of a lithium-ion battery according to claim 1, wherein: Taking the total mass of the electrolyte as 100%, the mass proportion of the compound A in the electrolyte is b, and 0.01%≤b≤10%.

4. The method for predicting gas production of a lithium-ion battery according to claim 1, wherein: The compound A includes one or more of the following compounds: 。

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