Method for determining element film formation completion during lithium-ion battery formation and its application

Abstract

The invention provides a method for determining the completion of element film formation during lithium ion battery formation and its application, and relates to the technical field of lithium ion battery formation. The method of the invention obtains element content by sampling negative electrode sheets of lithium ion batteries at different formation stages and performing energy spectrum analysis, and then uses hypothesis testing to test whether the element content on the negative electrode sheets at different formation stages changes significantly to determine whether the element has completed the film formation reaction. It can simply and accurately determine whether the film formation reaction of the element in the formation has been completed, and further can provide a basis for the reasonable formulation and optimization of the lithium ion battery formation process and the SOC point for determining the end of the formation, thereby helping to improve the performance of the lithium ion battery and reduce the production cost.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery formation, in particular to a method for determining whether element film formation is completed during lithium ion battery formation and its application. Background Art

[0002] The formation of lithium-ion batteries is mainly to form a good SEI film on the surface of the negative electrode. If the formation time is too short, the formation may not be sufficient, resulting in the SEI film not being fully formed, affecting the subsequent performance of the battery. If the formation time is too long, it will affect the battery's production capacity during the formation stage and generate unnecessary energy consumption.

[0003] There are two existing ways to determine whether the formation of a lithium-ion battery is complete. One is to determine whether the formation is complete based on whether the gas production in the formation stage is completed. This method mainly monitors the volume change of the battery or the gas production of the battery. The disadvantage is that the gas production is different under different formation conditions and different electrochemical systems, and the judgment accuracy is low. For example, a slight volume change or a tiny gas production cannot form bubbles and cannot be monitored. The other method is to directly measure the thickness of the SEI film on the negative electrode surface of the lithium-ion battery through an atomic force microscope probe. The disadvantage is that the equipment is expensive and not easy to implement.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for determining the completion of element film formation during lithium ion battery formation, which can simply and accurately determine whether the film formation reaction of the element during formation has been completed.

[0006] The second purpose of the present invention is to provide an application of a method for determining the completion of element film formation during lithium ion battery formation, which can accurately determine whether the formation of the lithium ion battery is completed and whether the formation is completed, with high accuracy and easy operation.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] In a first aspect, a method for determining the completion of element film formation during formation of a lithium-ion battery comprises the following steps:

[0009] A number of identical lithium-ion batteries are formed to different states of charge according to a gradient, and then the negative electrode sheets of the lithium-ion batteries in each gradient are sampled and subjected to energy spectrum analysis to obtain the element content of the negative electrode sheet samples, and the element content of the negative electrode sheet samples in adjacent gradients is subjected to a double-sample t-test to obtain a P value. When the P value is greater than 0.05, it is determined that the film-forming reaction of the element has been completed when the lithium-ion battery is formed to a smaller state of charge in the adjacent gradient.

[0010] Furthermore, the element includes at least one of oxygen, sulfur, boron, nitrogen and phosphorus.

[0011] Furthermore, the lithium-ion battery is a lithium-ion battery that has been filled with electrolyte and has not been charged or discharged.

[0012] Furthermore, the method of forming the battery to different states of charge comprises the following steps:

[0013] Several identical lithium-ion batteries are charged with the same current intensity at the same temperature and reach different states of charge at different charging times.

[0014] Furthermore, the gradient ranges from 1-10%.

[0015] Furthermore, the number of the negative electrode sheet samples is greater than 15.

[0016] Furthermore, the method comprises the following steps:

[0017] (a) A number of identical lithium-ion batteries are charged at the same temperature and with the same current intensity, and then charged to different states of charge according to a gradient at different charging times. The batteries are then numbered and grouped in ascending order of state of charge, and recorded as SOC1, SOC2, and SOC n ;

[0018] (b) SOC1, SOC2, ... SOC n The lithium-ion batteries corresponding to the group were disassembled respectively, and several samples were taken from the negative electrode sheets of each lithium-ion battery. The samples were subjected to energy spectrum analysis to obtain SOC1, SOC2, and SOC n The element content of the negative electrode sheet corresponding to the group;

[0019] (c) SOC n-1 and SOC n The element content of the negative electrode sheet corresponding to the group was tested by double sample t test to obtain the P value, which is recorded as P n -1, when P n-1 >0.05, the lithium-ion battery is judged to be charged to SOC n-1 When the charge state corresponding to the group is reached, the film-forming reaction of the elements has been completed.

[0020] In a second aspect, a method for determining the completion of element film formation during formation of a lithium-ion battery is used in determining the completion of formation of a lithium-ion battery.

[0021] Furthermore, the element is oxygen.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The method for determining the completion of element film formation during the formation of a lithium ion battery provided by the present invention comprises the following steps: sampling the negative electrode sheets of the lithium ion battery at different formation stages and performing energy spectrum analysis to obtain the element content, and then using a double sample t test to test whether the element content on the negative electrode sheets at different formation stages changes significantly to determine whether the element has completed the film formation reaction. The method can simply and accurately determine whether the film formation reaction of the element during the formation has been completed, and further determine the formation SOC interval of a specific component in the SEI film or the reaction SOC interval of a specific electrolyte additive, thereby providing a basis for optimizing the injection strategy or formulating a reasonable formation process, and also providing a basis for determining the SOC point at which the formation ends, providing a process window, and helping to improve the performance of the lithium ion battery and reduce the production cost.

[0024] The method for determining the completion of element film formation during lithium ion battery formation provided by the present invention is applied to determining the completion of lithium ion battery formation, and can accurately determine whether the formation film formation of the lithium ion battery is completed and whether the formation is completed, with high precision and easy operation. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] According to a first aspect of the present invention, there is provided a method for determining the completion of element film formation during formation of a lithium ion battery, comprising the following steps:

[0027] A number of identical lithium-ion batteries are formed to different states of charge according to a gradient, and then the negative electrode sheets of the lithium-ion batteries in each gradient are sampled and subjected to energy spectrum analysis to obtain the element content of the negative electrode sheet samples. The element content of the negative electrode sheet samples in adjacent gradients is subjected to a double-sample t-test to obtain a P value. When the P value is greater than 0.05, it is determined that the film-forming reaction of the element has been completed when the lithium-ion battery is formed to a smaller state of charge in the adjacent gradient.

[0028] The method for determining the completion of element film formation during the formation of a lithium ion battery provided by the present invention comprises the following steps: sampling the negative electrode sheets of the lithium ion battery at different formation stages and performing energy spectrum analysis to obtain the element content, and then using a double sample t test to test whether the element content on the negative electrode sheets at different formation stages changes significantly to determine whether the element has completed the film formation reaction. The method can simply and accurately determine whether the film formation reaction of the element during the formation has been completed, and further determine the formation SOC interval of a specific component in the SEI film or the reaction SOC interval of a specific electrolyte additive, thereby providing a basis for optimizing the injection strategy or formulating a reasonable formation process, and also providing a basis for determining the SOC point at which the formation ends, providing a process window, and helping to improve the performance of the lithium ion battery and reduce the production cost.

[0029] In a preferred embodiment, the lithium-ion battery may be a lithium-ion battery that has been filled with electrolyte, fully soaked, and has not been charged or discharged.

[0030] In the present invention, the type of element to be determined is not particularly limited. For example, it can be at least one of oxygen, sulfur, boron, nitrogen and phosphorus, but is not limited to this. As long as it is an element component present in the electrolyte of a lithium-ion battery, the method provided by the present invention can be used to determine at what charge state the film-forming reaction of the element has been completed.

[0031] Among them, when the element to be determined is oxygen, it is possible to determine whether the film formation (SEI film) of the negative electrode is sufficient under a certain state of charge (SOC point), and then to determine the state of charge (SOC point) at which the formation ends, thereby determining whether the battery formation is complete and providing a process window, which is beneficial to improving battery performance and reducing production costs.

[0032] In a preferred embodiment, the method for gradient charging of lithium-ion batteries to different states of charge comprises the following steps:

[0033] Several identical lithium-ion batteries are charged with the same current intensity at the same temperature and reach different states of charge at different charging times.

[0034] The present invention uses the same current to charge the lithium ion battery for different times at the same temperature, so as to achieve the purpose of charging the lithium ion battery to different charge states.

[0035] In a preferred embodiment, the gradient of the present invention is in the range of 1-10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, but not limited to this. The gradient within this range is more conducive to improving the effect and accuracy of the determination.

[0036] In a preferred embodiment, the number of negative electrode sheet samples in the present invention is more than 15, which is beneficial to improving the accuracy of determination.

[0037] A typical method for determining the completion of element film formation during lithium ion battery formation comprises the following steps:

[0038] S1: Several identical lithium-ion batteries are charged with the same current intensity at the same temperature, and are gradient-charged to different states of charge (SOC) at different charging times. They are then numbered and grouped in sequence (numbered in ascending order of state of charge), which can be recorded as SOC1, SOC2, and SOC n ; Wherein, the gradient range may be 1-10%;

[0039] S2: SOC1, SOC2...SOC n The corresponding lithium-ion batteries are disassembled respectively, and a number of samples (the number of samples taken is more than 15) are sampled from the negative electrode sheet of each lithium-ion battery, and the samples are subjected to energy spectrum analysis to obtain SOC1, SOC2...SOC n The element content on the surface of the corresponding negative electrode;

[0040] S3: Sequentially for adjacent groups, namely SOC n-1 and SOC n The element content of the negative electrode sheet corresponding to the group was tested by double sample t test to obtain the P value, which is recorded as P n-1 , when P n-1 >0.05, the lithium-ion battery is judged to be charged to SOC n-1 When the charge state corresponding to the group is reached, the film-forming reaction of the elements has been completed.

[0041] The method of the present invention obtains the element content by sampling the negative electrode sheets of the lithium ion battery at different formation stages and performing energy spectrum analysis, and then uses hypothesis testing to test whether the element content on the negative electrode sheets at different formation stages changes significantly to determine whether the element has completed the film-forming reaction. It can simply and accurately determine whether the film-forming reaction of the element in the formation has been completed, that is, to determine whether the film formation (SEI film) of this element component has been completed by the change in the content of a certain element on the surface of the negative electrode sheet, and further provide a basis for the reasonable formulation or optimization of the lithium ion battery formation process and the determination of the SOC point at the end of the formation, thereby helping to improve the performance of the lithium ion battery and reduce the production cost.

[0042] According to a second aspect of the present invention, there is provided an application of any of the above methods for determining the completion of element film formation during lithium ion battery formation in determining the completion of lithium ion battery formation, wherein the element to be determined may preferably be oxygen.

[0043] The method for judging the completion of element film formation during the formation of a lithium ion battery provided by the present invention is applied to judging the completion of the formation of a lithium ion battery. A double sample t test is used to test whether there is a significant difference in the oxygen element on the surface of a negative electrode sheet at different formation stages, and whether the film (SEI film) on the negative electrode sheet is sufficient, so as to judge whether the formation of the lithium ion battery is completed. The method can accurately judge whether the formation film (SEI film) of the lithium ion battery is finished and whether the formation is completed, and has high precision and is easy to operate.

[0044] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0045] Example 1

[0046] A method for determining the completion of element film formation during lithium ion battery formation, comprising the following steps:

[0047] After the electrolyte was filled and allowed to stand for a long time, 12 lithium-ion batteries were obtained, wherein the electrolyte solvent was mainly composed of carbonate, the lithium salt contained only lithium hexafluorophosphate, and the additive contained only vinylene carbonate;

[0048] The above 12 lithium-ion batteries were charged and formed at a rate of 0.1C at an ambient temperature of 55°C (two batteries in one group, divided into 6 groups in total), and were formed to a state of charge of 10%, 20%, 30%, 40%, 50%, and 60%, respectively. They were numbered and grouped (numbered in ascending order of the state of charge) as SOC1, SOC2, SOC3, SOC4, SOC5, and SOC6, as shown in Table 1.

[0049] Table 1

[0050] Battery Grouping <![CDATA[SOC1]]> <![CDATA[SOC2]]> <![CDATA[SOC3]]> <![CDATA[SOC4]]> <![CDATA[SOC5]]> <![CDATA[SOC6]]> Charging state of charge 10％ 20％ 30％ 40％ 50％ 60％

[0051] The above 6 groups of lithium-ion batteries were disassembled in a dry environment, and their negative electrode sheets were sampled (8 negative electrode samples were sampled from each lithium-ion battery, so 16 negative electrode samples were sampled from each group of lithium-ion batteries), and they were grouped according to the grouping of the above lithium-ion batteries, and recorded as A1, A2, A3, A4, A5, and A6 in sequence, as shown in Table 2. There were 16 negative electrode samples in each group.

[0052] Table 2

[0053] Battery Grouping <![CDATA[SOC1]]> <![CDATA[SOC2]]> <![CDATA[SOC3]]> <![CDATA[SOC4]]> <![CDATA[SOC5]]> <![CDATA[SOC6]]> Corresponding negative electrode sample grouping <![CDATA[A1]]> <![CDATA[A2]]> <![CDATA[A3]]> <![CDATA[A4]]> <![CDATA[A5]]> <![CDATA[A6]]>

[0054] Energy spectrum analysis was performed on the negative electrode samples of the above groups (before the energy spectrum analysis, the negative electrode samples were repeatedly cleaned with dimethyl carbonate to remove the ions in the electrolyte and ions from other sources remaining on the surface of the negative electrode samples, and to eliminate their influence on the element determination of the negative electrode samples, and then the dimethyl carbonate on the negative electrode samples was dried and removed), wherein the energy spectrum analysis instrument was SEM-EDS, the test conditions were 25℃±2℃, 10kV-15kV high voltage, vacuum <500Pa, a side-mounted electronic detector was used, and then the EDS energy spectrum was started, and the surface scan was performed. The test results are shown in Tables 3, 4 and 5;

[0055] It should be noted that there are inevitable errors in the determination of C and O elements by energy spectrum analysis. For this reason, the energy spectrum analysis in this embodiment is to test more than ten samples in parallel to minimize the impact of errors in the energy spectrum analysis, and then determine whether there is a difference in the element content of the two groups of samples through hypothesis testing.

[0056] In Table 3, AC1, AC2, AC3, AC4, AC5, and AC6 represent the carbon content of the negative electrode samples in the groups A1, A2, A3, A4, A5, and A6, respectively, and the unit is %; in Table 4, AO1, AO2, AO3, AO4, AO5, and AO6 represent the oxygen content of the negative electrode samples in the groups A1, A2, A3, A4, A5, and A6, respectively, and the unit is %; in Table 5, AF1, AF2, AF3, AF4, AF5, and AF6 represent the fluorine content of the negative electrode samples in the groups A1, A2, A3, A4, A5, and A6, respectively, and the unit is %.

[0057] Table 3

[0058] <![CDATA[AC1]]> <![CDATA[AC2]]> <![CDATA[AC3]]> <![CDATA[AC4]]> <![CDATA[AC5]]> <![CDATA[AC6 <!-- 4 -->]]> 1 96.9 87.1 77.2 66.2 62.5 62.3 2 96.3 86.9 78.2 66.9 62.7 63.9 3 97.1 85.6 78.0 67.5 63.1 63.1 4 96.0 86.7 77.9 67.3 64.5 63.1 5 96.1 86.7 77.8 66.6 62.4 63.4 6 96.2 87.3 76.7 66.2 64.0 63.8 7 96.5 87.1 76.6 66.8 63.4 63.8 8 95.9 86.6 78.0 67.1 63.9 63.8 9 95.9 87.0 78.1 67.5 64.3 63.1 10 96.8 86.2 77.2 66.5 64.0 64.6 11 96.9 87.1 76.4 67.7 63.5 64.7 12 96.4 86.5 77.0 66.5 63.2 62.6 13 96.9 87.7 76.9 67.0 63.0 63.2 14 96.7 86.2 77.5 66.4 64.1 63.2 15 96.5 86.7 78.2 66.8 63.0 62.9 16 96.7 87.3 78.3 68.0 62.3 64.2

[0059] Table 4

[0060]

[0061]

[0062] The oxygen content of the negative electrode samples of adjacent groups in Table 4 was subjected to a two-sample t-test to obtain a P value. Specifically, the measured contents of all oxygen elements in group AO1 were 0, so the two-sample t-test of the oxygen content data of groups AO1 and AO2 was skipped, and the two-sample t-test of the oxygen content data of groups AO2 and AO3 was directly performed. The result was that the P value was 0, recorded as P2=0 (less than 0.05), so the two-sample t-test of the oxygen content data of groups AO3 and AO4 was continued, and the P value was 0, recorded as P3=0 (less than 0.05), so the two-sample t-test of the oxygen content data of groups AO4 and AO5 was continued. A double-sample t-test was performed on the data, and the result was a P value of 0, recorded as P4=0 (less than 0.05). Therefore, a double-sample t-test was continued on the oxygen content data of AO5 and AO6 groups, and the result was a P value of 0.655, recorded as P5=0.655. It can be seen that P5>0.05, and it can be considered that when the lithium-ion battery is formed to SOC5 or SOC6, there is no significant difference in the content of oxygen on the surface of the negative electrode sample, and it can be determined that the formation of the SEI film on the negative electrode surface has basically ended at this time, that is, when the lithium-ion battery is formed to a 50% state of charge corresponding to SOC5, the formation has been completed.

[0063] Table 5

[0064]

[0065]

[0066] The fluorine content of the negative electrode samples of adjacent groups in Table 5 was subjected to a two-sample t-test to obtain a P value. Specifically, the fluorine content data of groups AF1 and AF2 were subjected to a two-sample t-test, and the result was a P value of 0, recorded as P1=0 (less than 0.05). Therefore, the fluorine content data of groups AF2 and AF3 were further subjected to a two-sample t-test, and the result was a P value of 0.95, recorded as P2=0.95. It can be seen that P2>0.05, and it can be considered that when the lithium-ion battery is formed to SOC2 and SOC3, there is no significant difference in the content of fluorine on the surface of the negative electrode sample, and the main contribution of fluorine is LiF. It can be determined that when the lithium-ion battery is formed to a charge state of 20% corresponding to SOC2, the film-forming reaction of the LiF component has been completed, that is, the film-forming reaction of the fluorine element has been completed.

[0067] In summary, the method of the present invention obtains the element content by sampling the negative electrode sheets of the lithium-ion battery at different formation stages and performing energy spectrum analysis, and then uses hypothesis testing to test whether the element content on the negative electrode sheets at different formation stages changes significantly to determine whether the element has completed the film-forming reaction. It can simply and accurately determine whether the film-forming reaction of the element in the formation has been completed, and further can provide a basis for the reasonable formulation or optimization of the lithium-ion battery formation process, and determine the SOC point at the end of formation, helping to improve the performance of lithium-ion batteries and reduce production costs.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the completion of element film formation during lithium ion battery formation, characterized in that: The following steps are involved: A number of identical lithium-ion batteries are formed to different states of charge according to a gradient, and then the negative electrode sheets of the lithium-ion batteries of each gradient are sampled and subjected to energy spectrum analysis to obtain the element content of the negative electrode sheet samples, and the element content of the negative electrode sheet samples in adjacent gradients is subjected to a double-sample t-test to obtain a P value. When the P value is greater than 0.05, it is determined that when the lithium-ion battery is formed to a smaller state of charge in the adjacent gradient, the film-forming reaction of the element has been completed; The method of forming to different states of charge comprises the following steps: Several identical lithium-ion batteries are charged with the same current intensity at the same temperature and reach different states of charge at different charging times.

2. The method for determining the completion of element film formation during lithium ion battery formation according to claim 1, characterized in that: The element includes at least one of oxygen, sulfur, boron, nitrogen and phosphorus.

3. The method for determining the completion of element film formation during lithium ion battery formation according to any one of claims 1 or 2, characterized in that: The lithium ion battery is a lithium ion battery that has been filled with electrolyte and has not been charged or discharged.

4. The method for determining the completion of element film formation during lithium ion battery formation according to claim 1, characterized in that: The gradient ranged from 1-10%.

5. The method for determining the completion of element film formation during lithium ion battery formation according to claim 1, characterized in that: The number of the negative electrode sheet samples is greater than 15.

6. The method for determining the completion of element film formation during lithium ion battery formation according to claim 1, characterized in that: The method comprises the following steps: (a) A number of identical lithium-ion batteries are charged at the same temperature and with the same current intensity, and then charged to different states of charge according to a gradient at different charging times. The batteries are then numbered and grouped in ascending order of state of charge, and recorded as SOC1, SOC2, and SOC n ; (b) SOC1, SOC2, ... SOC n The lithium-ion batteries corresponding to the group were disassembled respectively, and several samples were taken from the negative electrode sheets of each lithium-ion battery. The samples were subjected to energy spectrum analysis to obtain SOC1, SOC2, and SOC n The element content of the negative electrode sheet corresponding to the group; (c) SOC n-1 and SOC n The element content of the negative electrode sheet corresponding to the group was tested by double sample t test to obtain the P value, which is recorded as P n-1 , when P n-1 >0.05, the lithium-ion battery is judged to be charged to SOC n-1 When the charge state corresponding to the group is reached, the film-forming reaction of the elements has been completed.

7. Use of the method for determining the completion of element film formation during formation of a lithium ion battery as claimed in any one of claims 1 to 6 in determining the completion of formation of a lithium ion battery.

8. The use according to claim 7, characterized in that: The element is oxygen.

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