A control method for quantitative lithium precipitation of a lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and discloses a control method for quantitative lithium precipitation of a lithium ion battery, comprising the following steps: calibrating an initial capacity CO of the battery, and then discharging the battery to a battery capacity C1 corresponding to a to-be-studied lithium precipitation amount; disassembling the discharged battery, and taking out a negative electrode sheet inside the battery; performing an impurity removal operation on the disassembled negative electrode sheet; assembling the negative electrode sheet after the impurity removal and a newly-made positive electrode sheet to obtain a reassembled lithium ion battery, calculating a capacity C2 of the reassembled lithium ion battery according to the positive electrode sheet; and calculating a lithium precipitation amount m of the negative electrode sheet according to the capacities CO, C1 and C2 of the battery. The lithium ion battery reassembled by the method has a uniform lithium precipitation on the negative electrode surface, and does not have the phenomenon of lithium precipitation aggregation, and can effectively perform qualitative and quantitative analysis on the lithium precipitation, thereby effectively avoiding the safety problem of the battery caused by the lithium precipitation of the negative electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a control method for quantitative lithium precipitation of a lithium ion battery. BACKGROUND

[0002] As a kind of energy storage material, lithium ion battery has been more and more integrated into people's life due to its advantages of high energy density, long cycle life and recyclability, such as new energy vehicles, smart phones, energy storage power stations, unmanned aerial vehicle batteries and other lithium battery energy storage equipment, which represent the convenience and social popularity of lithium ion batteries. According to the data, the shipment of lithium ion batteries in China reached 334GWh in 2021, and the planned lithium ion battery capacity in China reached 1TWh by 2025, with a market space of 100 billion yuan and a very broad development prospect. However, due to the high energy density of lithium ion battery, it heats up very quickly in the process of thermal runaway, and the heat release is huge, which can easily affect people's life and property safety. And because of the wide popularity of lithium ion battery in the society, the phenomenon of battery thermal runaway has become a problem that cannot be ignored, so the industry has carried out a series of research and improvement measures on battery thermal runaway safety, including battery intrinsic safety improvement, battery thermal runaway safety mechanism research, battery failure trigger mechanism research, etc.

[0003] In the process of lithium battery thermal runaway safety research, the internal short circuit thermal runaway caused by lithium precipitation on the negative electrode interface has always been a research hotspot. Due to the charging and discharging characteristics of lithium ion batteries, the deintercalation and intercalation of lithium ions in the positive and negative electrodes, and the influence of the deactivation of the positive and negative electrode materials, the N / P ratio imbalance, the electrolyte loss, and the positive and negative electrode polarization during the cycle process, lithium metal precipitation on the negative electrode surface often occurs during the middle and late life of lithium ion batteries. Serious lithium precipitation phenomenon exists the potential risk of causing internal short circuit of the battery by connecting the positive and negative electrodes, so the study of lithium precipitation of lithium ion battery is of great significance to the safety performance of lithium ion battery. Current industry research on lithium battery lithium precipitation safety usually has the following methods: (1) battery lithium precipitation reproduction: by controlling the intercalation process of lithium ions in the negative electrode through methods such as high-rate charging and discharging, long-term cycling, and low-temperature cycling, lithium precipitation on the negative electrode surface is realized. In general, the capacity loss of the lithium battery caused by this method is assumed to be caused by lithium precipitation. However, due to the deactivation of the electrode material, the decomposition of the electrolyte, and the formation of the SEI film during the normal cycle process of the lithium battery, the battery capacity will also decrease. However, this method does not take into account the influence of the above factors, so the amount of lithium precipitation calculated by the battery lithium precipitation reproduction method is usually smaller than the actual amount of lithium precipitation. In addition, the side reactions during the cycle process often cause the deformation and gas production of the lithium battery, which also affects the reliability of the conclusion of the battery lithium precipitation safety research. Secondly, since the lithium precipitation on the negative electrode surface is a cumulative process, the battery cycle is required to reproduce the lithium precipitation, which requires hundreds of cycles and has a huge time cost. (2) Artificial implantation of metal lithium powder to reproduce lithium precipitation: a certain amount of metal lithium powder corresponding to the lithium precipitation amount is weighed in advance, and the metal lithium powder is implanted into the battery during the assembly process of the lithium battery. A series of tests are performed on the battery implanted with the metal lithium powder to characterize the safety performance of the battery corresponding to the lithium precipitation amount. However, this method also has some shortcomings: first, the molar mass of metal lithium powder is light (6.94 g / mol), so the electronic scale and operation requirements for weighing metal lithium powder are extremely high. Secondly, the metal lithium powder implantation process needs to be carried out in a dry environment, which has strict requirements on the environment and a complicated and difficult operation process. Finally, due to the small particle size of the metal lithium powder, agglomeration often occurs during the implantation process, so the uniformity of the metal lithium powder distribution on the surface of the electrode is poor, and the phenomenon of high metal lithium powder content in some areas and almost no metal lithium powder distribution in other areas often occurs, which has little significance for the lithium precipitation safety research under such conditions. SUMMARY

[0004] Therefore, the present application provides a lithium ion battery quantitative lithium precipitation control method to solve the problems of the prior art, such as the poor accuracy of the lithium precipitation amount, the long time consumption, the high operation requirement, and the poor uniformity of the metal lithium powder distribution.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] A control method for quantitatively analyzing lithium of a lithium ion battery, comprising the following steps:

[0007] (1) calibrating an initial capacity C0 of the battery, and then discharging the battery to a battery capacity C1 corresponding to a lithium analysis amount to be studied;

[0008] (2) disassembling the discharged battery, and taking out a negative electrode sheet inside the battery;

[0009] (3) removing impurities from the disassembled negative electrode sheet;

[0010] (4) assembling the negative electrode sheet after removing impurities with a newly prepared positive electrode sheet to obtain a reassembled lithium ion battery, and calculating a capacity C2 of the reassembled lithium ion battery according to the positive electrode sheet;

[0011] (5) calculating a lithium analysis amount m of the negative electrode sheet according to the capacities C0, C1 and C2 of the battery.

[0012] Preferably, in the control method for quantitatively analyzing lithium of the lithium ion battery, the battery is subjected to at least one cycle of charging and discharging in step (1), and the discharge capacity of the last cycle is calibrated as the initial capacity C0 of the battery.

[0013] Preferably, in the control method for quantitatively analyzing lithium of the lithium ion battery, the lithium analysis amount in step (1) is 0-80%, and the corresponding negative electrode sheet capacity condition is 0-80%.

[0014] Further preferably, the lithium analysis amount is 0-50%, and the corresponding negative electrode sheet capacity condition is 0-50%.

[0015] During the test operation, considering the risk of combustion due to oxidation, the lithium analysis amount should not be too large.

[0016] Preferably, in the control method for quantitatively analyzing lithium of the lithium ion battery, before disassembling in step (2), the battery is placed in an environment of 15-35℃ for sufficient standing for more than 2h.

[0017] Further preferably, the battery is placed in an environment of 20-28℃ for sufficient standing for more than 5h.

[0018] Preferably, in the control method for quantitatively analyzing lithium of the lithium ion battery, the impurity removal operation in step (3) is to soak the disassembled negative electrode sheet in an organic solvent for cleaning and vacuum drying.

[0019] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the negative electrode sheet is soaked in the organic solvent for at least 2 hours, the vacuum drying temperature is at least 40 DEG C, and the drying time is at least 1 hour.

[0020] Further preferably, the organic solvent is a DMC solvent.

[0021] It is found through experimental research that if the soaking time is too short, the drying temperature is too low, and the drying time is too short, the impurities will not be completely removed and the water content will be too large, which seriously affects the accuracy of the results and causes the negative electrode sheet to precipitate lithium unevenly.

[0022] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the capacity C2 of the reassembled lithium ion battery is calculated according to the area of the positive electrode sheet, the active material composition and content in step (4).

[0023] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the new positive electrode sheet in step (4) is an uncharged positive electrode sheet.

[0024] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the lithium precipitation amount m of the negative electrode sheet in step (5) is m=C1*C2 / (C0*m), wherein m is the gram capacity, and m is greater than or equal to 100 mAh / g, and further preferably, m is 3860 mAh / g.

[0025] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, C2=the area of the sheet*the gram capacity of the positive active material*the proportion of the positive active material*the coating area density.

[0026] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the following steps are further included:

[0027] (6) The reassembled lithium ion battery is charged to a capacity of C2, and then the charged battery is disassembled to observe the lithium precipitation on the surface of the negative electrode sheet.

[0028] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the following steps are further included:

[0029] (7) The reassembled lithium ion battery is subjected to mechanical abuse testing, electrical abuse testing, and thermal abuse testing, i.e. the safety performance of the lithium ion battery under the corresponding lithium precipitation condition is obtained.

[0030] Preferably, in the above-mentioned lithium ion battery quantitative lithium precipitation control method, the negative electrode sheet is made and the battery is prepared in a dry environment.

[0031] In addition, the present application also provides a control device which adopts the above-mentioned lithium ion battery quantitative lithium precipitation control method.

[0032] The application provides a lithium ion battery quantitative lithium precipitation control method, which has the beneficial effect that, compared with the prior art,

[0033] The lithium precipitation safety research method for the lithium battery has strong operability and few influencing factors, lithium is uniformly precipitated on the negative electrode surface of the lithium ion battery reassembled through the method, the phenomenon of lithium precipitation aggregation does not occur, qualitative and quantitative analysis of lithium precipitation can be effectively performed, the precision of lithium precipitation in the battery is ensured, and the safety problem of the battery caused by negative electrode lithium precipitation is effectively avoided.

[0034] The method is suitable for lithium precipitation safety research of various types of lithium ion batteries, in particular, is suitable for lithium precipitation safety research of soft package lithium ion batteries, square lithium ion batteries and cylindrical lithium ion batteries, is suitable for lithium precipitation safety research of battery cells, battery packs and battery modules, is suitable for lithium ion battery lithium precipitation safety research of laminating process, winding process and cylindrical process, is suitable for lithium precipitation safety research of lithium iron phosphate system batteries, ternary system batteries, lithium cobaltate system batteries, lithium manganate system batteries and silicon negative electrode system, and is suitable for lithium precipitation safety research of solid-state lithium ion batteries, semi-solid lithium ion batteries and liquid lithium ion batteries.

[0035] The negative electrode sheet is soaked in an organic solvent before the lithium ion battery is reassembled to sufficiently remove impurities, so that the incomplete removal of impurities does not affect the test results, and the negative electrode sheet is completely dried before being reassembled into a new lithium ion battery, so that the influence of quality change on the test results is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0037] Figure 1 It is a schematic diagram of the lithium precipitation on the surface of the negative electrode sheet in the embodiment 1 of the present application.

[0038] Figure 2 It is a schematic diagram of the lithium precipitation on the surface of the negative electrode sheet in the embodiment 2 of the present application.

[0039] Figure 3 It is a schematic diagram of the lithium precipitation on the surface of the negative electrode sheet in the embodiment 3 of the present application. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of them. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.

[0041] The present application provides a method for quantitatively controlling lithium precipitation in a lithium ion battery, and relates to the preparation of a corresponding experimental battery for lithium ion battery safety testing. Specifically, the present application provides a method for controlling the quantitative lithium precipitation in a lithium ion battery by assembling a charged negative electrode and a freshly prepared positive electrode. By adjusting the charge state of the negative electrode of the lithium ion battery, and then combining it with an uncharged positive electrode to form a full battery, the corresponding lithium battery capacity of the positive electrode with the same area, active material composition and content is calculated. Then, the prepared battery is charged to realize the quantitative lithium precipitation in the lithium ion battery. The method of the present application can ensure the accuracy and uniformity of lithium precipitation in the battery.

[0042] Example 1

[0043] In the process of making single batteries for lithium ion battery lithium precipitation 10% safety research, the single battery adopts "two positive three negative" structure, and the initial capacity of the battery is calibrated to 320 mAh. The battery is discharged at a current of 0.33C for 18 min, and the discharge capacity is 288 mAh. The discharged battery is disassembled to take out the internal negative electrode, which is placed in DMC solution in a dry environment for 48 h, then taken out and dried in an 80℃ oven for 24 h. The dried negative electrode is stacked and assembled with a freshly prepared positive electrode of the same system, and a single battery with the same area of "two positive three negative" structure is prepared. The capacity C2 of the single battery is calculated as 320 mAh, wherein the calculation formula of C2 is: C2 = 40 cm 2 (active material gram capacity) * 96.5% (positive active material proportion) * 0.036 g / cm 2 (coating area density), the prepared single battery is charged, and the battery after full charging is disassembled to observe the lithium precipitation on the surface of the negative electrode, as shown in Figure 1 The negative electrode surface appears uniform lithium precipitation, and there is no lithium precipitation aggregation phenomenon.

[0044] Example 2

[0045] In the process of making single battery for lithium ion battery lithium precipitation 30% safety research, the single battery adopts "two positive three negative" structure, the battery is calibrated initial capacity of 600mAh, the battery is discharged with 0.33C current for 54min, the discharge capacity is 420mAh, the discharged battery is disassembled to take out the internal negative electrode sheet, the negative electrode sheet is placed in DMC solution in dry environment for 12h, then taken out, and then dried in 80℃ oven for 24h. The dried negative electrode sheet and the new positive electrode sheet of the same system are laminated and assembled into the same area "two positive three negative" structure single battery, and the capacity C2 of the single battery is calculated as 600mAh, wherein the C2 calculation formula is: C2=90cm 2 (positive electrode active material gram capacity)*95.2%(positive electrode active material proportion)*0.028g / cm 2 (coating area density), the prepared single battery is charged, and the lithium precipitation on the surface of the negative electrode sheet of the charged battery is observed, as shown in Figure 2 , uniform lithium precipitation appears on the negative electrode surface, and no lithium precipitation aggregation phenomenon appears.

[0046] Example 3

[0047] In the process of making single battery for lithium ion battery lithium precipitation 30% safety research, the single battery adopts "two positive three negative" structure, the battery is calibrated initial capacity of 600mAh, the battery is discharged with 0.33C current for 54min, the discharge capacity is 420mAh, the discharged battery is disassembled to take out the internal negative electrode sheet, the negative electrode sheet is placed in DMC solution in dry environment for 12h, then taken out, and then dried in 80℃ oven for 24h. The dried negative electrode sheet and the new positive electrode sheet of the same system are laminated and assembled into the same area "two positive three negative" structure single battery, and the capacity C2 of the single battery is calculated as 600mAh, wherein the C2 calculation formula is: C2=90cm 2 (positive electrode active material gram capacity)*95.2%(positive electrode active material proportion)*0.028g / cm 2 (coating area density), the prepared single battery is charged, and the lithium precipitation on the surface of the negative electrode sheet of the charged battery is observed, as shown in Figure 3 , uniform lithium precipitation appears on the negative electrode surface, and no lithium precipitation aggregation phenomenon appears.

[0048] Example 4

[0049] In the process of making single battery for lithium ion battery lithium precipitation 20% safety research, the single battery adopts "two positive three negative" structure, the battery is calibrated initial capacity is 320mAh, the battery is discharged with 0.33C current, the discharge capacity is 256mAh, the discharged battery is disassembled to take out the internal negative pole piece, the negative pole piece is placed in DMC solution in a dry environment and soaked for 48h, then taken out and dried in an 80 DEG C oven for 24h. The dried negative pole piece is stacked with the new positive pole piece of the same system to form a single battery with the same area of "two positive three negative" structure, and the capacity C2 of the single battery is calculated as 320mAh, wherein the C2 calculation formula is: C2=40cm 2 (Active material coating density), the prepared single battery is charged, the charging capacity is 320mAh, and the battery after charging is disassembled to observe the lithium precipitation on the surface of the negative pole piece: uniform lithium precipitation appears on the surface of the negative pole, and no lithium precipitation aggregation phenomenon appears. 2

[0050] In summary, the present application provides a control method for realizing quantitative lithium precipitation of lithium ion battery, in the process of assembling lithium ion battery, the negative pole piece with a certain amount of electricity is combined with the new positive pole piece to form the lithium ion battery, the capacity of the battery can be calculated by the compaction density, thickness, active material type and content of the active material coated on the positive and negative pole pieces of the lithium ion battery, then the lithium ion battery combined is charged (the charging capacity is the calculated battery capacity), so that the lithium ion battery with uniform lithium precipitation on the surface of the negative pole can be obtained, and the quantitative regulation of the lithium precipitation amount in the battery can be realized by adjusting the amount of electricity of the negative pole piece.

[0051] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts of each embodiment can be referred to each other. For the scheme disclosed by the embodiments, since it corresponds to the method disclosed by the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0052] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications of the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.​

Claims

1. A method for controlling quantitative lithium deposition in a lithium-ion battery, characterized in that, Includes the following steps: (1) The battery is calibrated to an initial capacity C0, and then discharged to the battery capacity C1 corresponding to the amount of lithium plating to be studied; (2) Disassemble the discharged battery and remove the negative electrode plate inside the battery; (3) Remove impurities from the disassembled negative electrode sheet; (4) The negative electrode sheet after removing impurities is assembled with the newly made positive electrode sheet to obtain a reassembled lithium-ion battery. The capacity C2 of the reassembled lithium-ion battery is calculated based on the positive electrode sheet. (5) Calculate the amount of lithium deposited on the negative electrode based on the battery capacities C0, C1, and C2; The amount of lithium deposited in the negative electrode in step (5) is m = C1*C2 / (C0*m), where m is the specific capacity and m ≥ 100 mAh / g.

2. The method for controlling quantitative lithium deposition in a lithium-ion battery according to claim 1, characterized in that, In step (1), the battery is charged and discharged at least once, and the initial capacity C0 of the battery is determined by the discharge capacity of the last cycle. And / or the amount of lithium plating described in step (1) is 0-80%; And / or the disassembly process described in step (2) may also include: placing the battery in an environment of 15-35℃ and allowing it to stand for more than 2 hours.

3. The method for controlling quantitative lithium deposition in a lithium-ion battery according to claim 1, characterized in that, The impurity removal operation in step (3) is as follows: the disassembled negative electrode sheet is immersed in an organic solvent for cleaning and then vacuum dried.

4. The method for controlling quantitative lithium deposition in a lithium-ion battery according to claim 3, characterized in that, The negative electrode sheet is immersed in an organic solvent for at least 2 hours, and the vacuum drying temperature is at least 40°C for at least 1 hour.

5. The method for controlling quantitative lithium deposition in a lithium-ion battery according to claim 1, characterized in that, In step (4), the capacity C2 of the reassembled lithium-ion battery is calculated based on the area of ​​the positive electrode, the composition and content of the active material.

6. The method for controlling quantitative lithium deposition in a lithium-ion battery according to claim 1, characterized in that, The value of m is 3860mAh / g.

7. The method for controlling quantitative lithium deposition in a lithium-ion battery according to any one of claims 1-6, characterized in that, C2 = Electrode area * Positive electrode active material specific capacity * Positive electrode active material percentage * Coating surface density.

8. The method for controlling quantitative lithium deposition in a lithium-ion battery according to any one of claims 1-6, characterized in that, It also includes the following steps: (6) Charge the reassembled lithium-ion battery to a capacity of C2, then disassemble the charged battery and observe the lithium plating on the surface of the negative electrode. And / or (7) conduct mechanical abuse tests, electrical abuse tests, and thermal abuse tests on the reassembled lithium-ion batteries to obtain the safety performance of the lithium-ion batteries under the corresponding lithium plating conditions.

9. A control device, characterized in that, The control device employs the quantitative lithium deposition control method for lithium-ion batteries as described in any one of claims 1-8.

Images