A method for determining the amount of electrolyte injected into a battery and a lithium ion battery

Abstract

The application relates to a battery electrolyte injection amount determination method and a lithium ion battery. The battery electrolyte injection amount determination method comprises the following steps: obtaining a theoretical electrolyte injection amount according to the positive and negative electrode material area pore volume, the diaphragm pore volume and the battery internal free volume; performing first electrolyte injection on the battery to be injected with a first electrolyte injection amount, and obtaining the coulomb efficiency of the battery, wherein the first electrolyte injection amount is less than the theoretical electrolyte injection amount; performing gradient electrolyte injection on the battery to be injected in a manner that the electrolyte is increased by a preset amount each time, and obtaining the coulomb efficiency of the battery after each injection; and obtaining the optimal electrolyte injection amount of the battery according to the first electrolyte injection amount, the preset amount and the injection times based on the coulomb efficiency. The application also provides a lithium ion battery, and the optimal electrolyte injection amount of the lithium ion battery is obtained by using the method. The application can accurately and quickly determine the electrolyte injection amount of the battery, and reduces the battery performance problems and safety problems caused by excessive or insufficient electrolyte amount.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a method for determining the liquid injection amount of a battery and a lithium ion battery. BACKGROUND

[0002] The electrolyte usage of a lithium ion battery is crucial to the capacity, life, safety and other performances of the battery. Too much electrolyte will not only increase the weight of the battery itself, reduce the energy density and increase the cost, but also cause problems such as softening of the pole core, bulging of the shell, corrosion, leakage and the like, which are prone to cause safety accidents. Too little electrolyte will result in insufficient wetting of the pole piece, which will reduce the battery capacity and increase the internal resistance, affecting the cycle life of the battery; and lithium dendrites are prone to be precipitated, which may even cause safety accidents.

[0003] At the same time, with the industrialization of new material systems such as high-nickel positive electrodes and silicon-carbon negative electrodes, the electrolyte usage of lithium batteries needs to be iteratively designed. In order to ensure the wetting effect of electrolyte injection amount on the positive and negative electrode materials, separators and the like during the whole life cycle of the battery. At present, the design of electrolyte usage in the industry is mainly based on empirical coefficients or experimental verification. The common method is to estimate the electrolyte usage based on the injection coefficient empirical value of different material systems combined with the battery capacity. The test method is mainly to measure the gas production, residual liquid amount and cycle performance of the battery through liquid absorption dissection or battery cycle test to determine the injection amount. The above method based on empirical coefficients is limited by the material system, resulting in large deviation of the injection amount value, which cannot guarantee the accuracy of the battery injection amount, and further cannot guarantee the electrochemical performance and cycle life of the battery; and the dissection or cycle test verification will consume a long time and cause destructive or damaging battery, which increases the development cost, and the dissection or cycle test verification can only be targeted for sampling detection, and cannot achieve full detection of all batteries, so as to guarantee the quality of all batteries.

[0004] A lithium ion battery liquid injection method is disclosed in CN 107046121 A, which comprises liquid injection preparation work before injection, and the preparation work comprises weighing and vacuumizing; a first electrolyte containing vinylene carbonate is injected into a lithium ion secondary battery to be injected to perform first injection, so that the pole piece and the diaphragm are fully infiltrated; after sealing and standing, formation is performed, and 0.04C constant current charging is performed to 3.3V; a second electrolyte containing vinylene carbonate is injected; aging is performed, and 0.07C constant current charging is performed to 3.5V; a third electrolyte containing vinylene carbonate is injected; aging is performed, and 0.2C constant current charging is performed to 3.56V; a fourth electrolyte is injected; aging is performed, and 0.3C constant current charging is performed to 3.78V, and finally, the battery is sealed. The method promotes the formation of a stable and dense SEI film by step-by-step injection and formation, and reasonably selects the injection and formation parameters of each step, but it does not evaluate whether the injection amount of the electrolyte is appropriate, so it cannot confirm whether the total amount of the electrolyte is too much or too little, and thus cannot guarantee the performance of the battery. SUMMARY

[0005] The purpose of the present application is to provide a battery liquid injection amount determination method and a lithium ion battery to accurately and quickly determine the amount of electrolyte for a lithium ion battery, and to reduce the performance and safety problems caused by too much or too little electrolyte.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A battery liquid injection amount determination method comprises the following steps:

[0008] S1, obtaining the theoretical injection amount of electrolyte according to the pore volume of the positive and negative electrode material area, the pore volume of the diaphragm and the free volume inside the battery;

[0009] S2, performing first injection on the battery to be injected with electrolyte in a first injection amount, and obtaining the coulomb efficiency of the battery, wherein the first injection amount is less than the theoretical injection amount;

[0010] S3, performing gradient injection on the battery to be injected with electrolyte in a manner of increasing by a preset amount each time, and obtaining the coulomb efficiency of the battery after each injection;

[0011] S4, obtaining the best injection amount of the battery based on the coulomb efficiency, the first injection amount, the preset amount and the injection times.

[0012] If only the theoretical injection amount of electrolyte is used for injection without considering the coulomb efficiency of the battery, the effect of the designed battery injection amount is not verified in a closed loop, so there is a problem that the electrolyte injection amount is too much or too little, which makes it difficult to guarantee the optimal performance of the battery.

[0013] Preferably, in the S2, the first liquid injection amount is 90% to 95% of the theoretical liquid injection amount.

[0014] Preferably, in the S2, the first liquid injection amount is 94% of the theoretical liquid injection amount.

[0015] Preferably, in the S3, the preset amount is 1% to 5% of the theoretical liquid injection amount.

[0016] Preferably, in the S3, the preset amount is 2% to 3% of the theoretical liquid injection amount.

[0017] Preferably, in the S1, the pore volume of the positive electrode material area of the battery is set as V cp , the pore volume of the negative electrode material area of the battery is set as V ap , the pore volume of the separator is set as V sp , and the free volume inside the battery is set as V free , then the liquid retention and injection volume of the electrolyte is V = V cp + V ap + V sp + V free .

[0018] The density of the electrolyte is set as p, then the liquid retention and injection mass of the electrolyte is M = p*V.

[0019] Preferably, in the S1, the length of the positive electrode sheet material area of the battery is set as L cathode , the width of the positive electrode sheet material area of the battery is set as W cathode , and the thickness of the positive electrode sheet material area of the battery is set as T cathode , then the volume of the positive electrode sheet material area is V cathode = L cathode * W cathode * T cathode , and the porosity of the positive electrode sheet material area is set as P cathode , then the pore volume of the positive electrode material area of the battery is V cp = V cathode * P cathode .

[0020] The length of the negative electrode sheet material area of the battery is set as L anode , the width of the negative electrode sheet material area of the battery is set as W anode , and the thickness of the negative electrode sheet material area of the battery is set as T anode , then the volume of the negative electrode sheet material area is V anode = L anode * W anode * T anode , and the porosity of the negative electrode sheet material area is set as P anode , then the pore volume of the negative electrode material area of the battery is V ap = V anode * P anode .

[0021] The length of the separator of the battery is set as Lseparator , the width of the diaphragm is W separator , the thickness of the diaphragm is T separator , the volume V of the isolation is separator = L separator * W separator * T separator , the porosity P of the diaphragm is set separator , the pore volume V of the diaphragm is sp = V separator * P separator .

[0022] Preferably, the porosity P of the positive electrode sheet material area is determined by using a mercury intrusion method or a gas adsorption method cathode .

[0023] Preferably, the porosity P of the negative electrode sheet material area is determined by using a mercury intrusion method or a gas adsorption method anode .

[0024] Preferably, the porosity P of the diaphragm is determined by the diaphragm material specification separator .

[0025] Preferably, the free volume V inside the battery cell is obtained according to the design size parameters of the battery shell and the components inside the battery shell free .

[0026] Preferably, in S2, after the first liquid injection, the battery is subjected to full charge-full discharge test under the condition of temperature 23-27℃ and 1 / 3C, the charge capacity and discharge capacity of the battery are obtained, and then the coulomb efficiency of the battery is calculated.

[0027] Preferably, in S3, the electrolyte is injected into the battery to be injected in a gradient manner by increasing the preset amount each time, after each injection, the battery is subjected to full charge-full discharge test under the condition of temperature 23-27℃ and 1 / 3C, the charge capacity and discharge capacity of the battery are obtained, then the coulomb efficiency of the battery after each injection is obtained by calculation, and then the electrolyte injection amount and the corresponding coulomb efficiency are fitted to obtain the coulomb efficiency-electrolyte amount curve of the battery.

[0028] Preferably, in S4, according to the coulomb efficiency-electrolyte amount curve of the battery, when the coulomb efficiency tends to be stable, the first injection amount at this time is set as M1, the preset amount is set as M2, and the injection times are set as N, then the optimal injection amount M0 of the battery is M1+M2*N.

[0029] Preferably, the battery includes cylindrical lithium ion batteries, square lithium ion batteries and soft package batteries.

[0030] The application also provides a lithium ion battery, and the optimal injection amount of the lithium ion battery is obtained by the method of the application.

[0031] Advantages of the present application:

[0032] The method for determining the electrolyte injection amount of a battery of the present application effectively ensures the accuracy of the electrolyte injection amount of the battery by calculating the volume space inside the battery and combining the Coulomb efficiency of the battery to obtain the optimal electrolyte injection amount of the battery, thereby reducing the battery performance problems caused by excessive or insufficient electrolyte amount, and effectively improving the electrochemical performance, cycle life, and safety performance of the battery; the method for determining the electrolyte injection amount of a battery of the present application can cover comprehensive detection of all lithium ion batteries, and does not cause any damage to the battery, thereby ensuring the quality and performance of all batteries and reducing the development cost; at the same time, the method for determining the electrolyte injection amount of a battery of the present application is not limited by the material system, size, and structure of the battery, has a wide application range, a short verification period, and has a promotional application value in the field of lithium ion battery technology. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 3 is a ternary battery Coulomb efficiency-electrolyte amount relationship graph (Example 2) of the present application. DETAILED DESCRIPTION

[0034] Other advantages and effects of the present application can be easily understood by those skilled in the art from the content disclosed in the present specification. The present application can also be implemented or applied by means of other different specific embodiments, and the details in the present specification can be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be understood that the preferred embodiments are only for illustrating the present application, and are not intended to limit the protection scope of the present application.

[0035] It should be noted that the diagrams provided in the following examples only schematically illustrate the basic concept of the present application, and only show the components related to the present application in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, number, and proportion of the components in actual implementation can be arbitrarily changed, and the layout type of the components can be more complex.

[0036] In the following description, a large number of details are discussed to provide a more thorough explanation of the embodiments of the present application, however, it is obvious for those skilled in the art to implement the embodiments of the present application without these specific details.

[0037] Example 1

[0038] A method for determining the electrolyte injection amount of a battery, comprising the following steps:

[0039] S1, according to the battery positive and negative electrode material area pore volume, the diaphragm pore volume and the free volume inside the battery, the theoretical injection amount of electrolyte is obtained, specifically including:

[0040] S11, the length of the positive plate material area of the battery is set as L cathode , the width of the positive plate material area is set as W cathode , and the thickness of the positive plate material area is set as T cathode , then the volume of the positive plate material area V cathode = L cathode * W cathode * T cathode , the porosity of the positive plate material area is set as P cathode , then the pore volume of the positive material area of the battery V cp = V cathode * P cathode , unit: ml, wherein the porosity P of the positive plate material area is measured by mercury injection method or gas adsorption method cathode ;

[0041] S12, the length of the negative plate material area of the battery is set as L anode , the width of the negative plate material area is set as W anode , and the thickness of the negative plate material area is set as T anode , then the volume of the negative plate material area V anode = L anode * W anode * T anode , the porosity of the negative plate material area is set as P anode , then the pore volume of the negative material area of the battery V ap = V anode * P anode , unit: ml, wherein the porosity P of the negative plate material area is measured by mercury injection method or gas adsorption method anode ;

[0042] S13, the length of the diaphragm of the battery is set as L separator , the width of the diaphragm is set as W separator , and the thickness of the diaphragm is set as T separator , then the volume of the diaphragm V separator = L separator * W separator * T separator , the porosity of the diaphragm is set as P separator , then the pore volume of the diaphragm V sp = V separator * P separator , unit: ml, wherein the porosity P of the diaphragm is determined by the specification of the diaphragm separator ;

[0043] S14, according to the design size parameters of the battery shell and each component inside it, the free volume inside the battery Vfree ;

[0044] S15, calculate the theoretical injection volume V of the electrolyte through the positive electrode material area pore volume, the negative electrode material area pore volume, the separator pore volume and the free volume inside the battery, V = V cp + V ap + V sp + V free , unit: mL;

[0045] S16, set the density of the electrolyte as p, unit: g / ml, then the theoretical injection mass M of the electrolyte is M = p*V, unit: g;

[0046] S2, first injection of the electrolyte to the battery to be injected at a first injection amount, to obtain the coulomb efficiency of the battery, wherein the first injection amount is less than the theoretical injection amount, specifically comprising:

[0047] S21, first injection of the electrolyte to the battery to be injected at a first injection amount, wherein the first injection amount is 90% to 95% of the theoretical injection amount, that is, set the first injection amount as M1, then M1 = (90% to 95%)*M;

[0048] S22, after the first injection, full charge-full discharge test of the battery under the condition of temperature 23℃-27℃, 1 / 3C, to obtain the charge capacity and discharge capacity of the battery, then calculate the coulomb efficiency of the battery, wherein the coulomb efficiency = discharge capacity / charge capacity;

[0049] S3, gradient injection of the electrolyte to the battery to be injected in a manner of increasing by a preset amount each time, to obtain the coulomb efficiency of the battery after each injection, specifically comprising:

[0050] S31, gradient injection of the electrolyte to the battery to be injected in a manner of increasing by a preset amount each time, wherein the preset amount is 1% to 5% of the theoretical injection amount;

[0051] S32, after each injection, full charge-full discharge test of the battery under the condition of temperature 23℃-27℃, 1 / 3C, to obtain the charge capacity and discharge capacity of the battery, then calculate the coulomb efficiency of the battery, and then fit the electrolyte injection amount and the corresponding coulomb efficiency to obtain the battery coulomb efficiency-electrolyte amount curve;

[0052] S4, based on the coulomb efficiency, obtain the best injection amount of the battery according to the first injection amount, the preset amount and the injection times, specifically comprising:

[0053] According to the battery coulomb efficiency-electrolyte amount curve, when the coulomb efficiency tends to be stable, at this time the first injection amount is M1, the preset amount is M2, and the injection times are N, then the best injection amount M0 of the battery is M1+M2*N.

[0054] Example 2

[0055] Taking a square ternary lithium battery (LP2714897-55Ah) and a square lithium iron phosphate battery (LP214897-42Ah) as examples, the optimal electrolyte injection volume was calculated using the method described in Example 1. Specifically, the first injection volume in S21 was set to 94% of the theoretical injection volume, the preset volume in S31 was set to 1.8% of the theoretical injection volume, and the temperature in S32 was set to 25℃. The calculation results are shown in Table 1, and the coulombic efficiency-electrolyte volume relationship curve of the ternary lithium battery is shown in the figure. Figure 1 As shown.

[0056] Table 1 Results of Optimal Battery Electrolyte Filling Volume

[0057]

[0058]

[0059] From Table 1 and Figure 1 Analysis shows that for a square ternary lithium battery (LP2714897-55Ah), the theoretical electrolyte injection volume is 161.3g, calculated using the pore volumes of the positive and negative electrode regions, the separator pore volume, and the internal free volume of the battery. The optimal electrolyte volume, after iterative optimization based on the battery's coulombic efficiency, is 145g. For a square lithium iron phosphate battery (LP2714897-55Ah), the theoretical electrolyte injection volume is 173.0g, calculated using the same factors. The actual electrolyte volume, after iterative optimization based on the battery's coulombic efficiency, is 155g. This demonstrates a difference between the optimal electrolyte volume and the theoretical electrolyte volume, necessitating iterative optimization based on the battery's coulombic efficiency. The method described in this patent has good applicability to different material systems and different size parameters.

[0060] Table 2 shows a comparative analysis of the optimal electrolyte injection volume calculated by the dissecting battery experiment, the battery cycling experiment, and the coulombic efficiency experiment of this invention.

[0061] Table 2 shows the results of calculating the optimal electrolyte injection volume using three experimental methods.

[0062]

[0063] From the analysis in Table 2, it can be known that the cycle of the dissection battery test is short, but it is a destructive test; the cycle of the battery cycle sample verification is too long, and the performance of the battery after long cycle has been deteriorated, and it is difficult to continue to use. The above two methods can only carry out small sample or sampling test. The coulomb efficiency test not only has a short cycle, but also has no damage to the battery, and can carry out full detection, so as to ensure the quality and cost in the development and manufacturing process of the battery.

[0064] In summary, through many experiments, it is known that the battery liquid injection amount determination method can effectively guarantee the accuracy of the battery liquid injection amount by calculating the volume space inside the battery and combining the coulomb efficiency of the battery to obtain the optimal liquid injection amount of the battery electrolyte, thereby reducing the battery performance problems caused by too much or too little electrolyte, and effectively improving the electrochemical performance, cycle life and safety performance of the battery; the battery liquid injection amount determination method can cover the comprehensive detection of all batteries, and has no damage to the battery, thereby ensuring the quality and quality of all batteries, and reducing the development cost; at the same time, the battery liquid injection amount determination method is not limited by the battery material system, shape size and structure, has a wide application range, has a short verification cycle, and has a popularization and application value in the field of lithium ion battery technology.

[0065] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought of the present application should be covered by the claims of the present application.

Claims

1. A method for determining the electrolyte volume of a battery, characterized in that, Includes the following steps: S1. Based on the pore volumes of the positive and negative electrode regions, the pore volume of the separator, and the internal free volume of the battery, obtain the theoretical electrolyte injection volume; set the pore volume of the positive electrode region as V. cp The pore volume of the negative electrode material region of the battery is V. ap The pore volume of the diaphragm is V sp The free volume inside the battery is V. free Then the theoretical electrolyte injection volume V = V cp +V ap +V sp +V free ; If the density of the electrolyte is set to ρ, then the theoretical mass of the electrolyte injected is M = ρ·V; S2. The electrolyte is injected into the battery with the first injection volume. The battery is then subjected to a full charge-full discharge test at a temperature of 23℃~27℃ and 1 / 3C to obtain the battery's charging capacity and discharging capacity. The coulombic efficiency of the battery is then calculated. The first injection volume is 90%~95% of the theoretical injection volume. S3. Gradually inject electrolyte into the battery by increasing the preset amount each time. After each injection, conduct a full charge-full discharge test on the battery at a temperature of 23℃~27℃ and 1 / 3C to obtain the battery's charging capacity and discharging capacity. Then, calculate the coulombic efficiency of the battery after each injection, and fit the electrolyte injection amount with the corresponding coulombic efficiency to obtain the battery coulombic efficiency-electrolyte amount curve. The preset amount is 1%~5% of the theoretical injection amount. S4. Based on the battery coulombic efficiency-electrolyte volume curve, when the coulombic efficiency tends to stabilize, set the first electrolyte injection volume as M1, the preset volume as M2, and the number of injections as N. Then the optimal electrolyte injection volume of the battery is M0 = M1 + M2·N.

2. The method for determining the battery electrolyte volume according to claim 1, characterized in that, In step S1, the length of the positive electrode material area of ​​the battery is set to L. cathode The width of the positive electrode sheet area is W. cathode The thickness of the positive electrode sheet area is T. cathode The volume V of the positive electrode material region is then... cathode =L cathode ·W cathode ·T cathode The porosity of the positive electrode material region is set to P. cathode The pore volume V in the positive electrode region of the battery is then... cp =V cathode ·P cathode ; The length of the negative electrode material area of ​​the battery is set to L. anode The width of the negative electrode sheet area is W. anode The thickness of the negative electrode sheet area is T. anode The volume V of the negative electrode sheet material region anode =L anode ·W anode ·T anode The porosity of the negative electrode sheet material region is set to P. anode The pore volume V of the negative electrode material region of the battery is then... ap =V anode ·P anode ; The separator length of the battery is set to L. separator The diaphragm width is W separator The diaphragm thickness is T separator Then the isolated volume V separator =L separator ·W separator ·T separator The porosity of the membrane is set to P. separator Then the pore volume of the diaphragm V sp =V separator ·P separator .

3. The method for determining the battery electrolyte volume according to claim 1, characterized in that, The batteries include cylindrical lithium-ion batteries, square lithium-ion batteries, and pouch batteries.

4. A lithium-ion battery, characterized in that, The optimal electrolyte volume for the lithium-ion battery is calculated using the method described in any one of claims 1 to 3.

Images