Method for determining type and content of positive electrode lithium supplement agent

Abstract

The invention belongs to the field of battery testing, and particularly relates to a method for measuring the type and content of a positive electrode lithium supplementing agent. The method for determining the type of the positive electrode lithium supplement agent comprises the following steps: carrying out morphology observation and Mapping test on a to-be-tested sample by using a scanning electron microscope-energy disperse spectroscopy, finding out the positions of particles of the lithium supplement agent through characteristic elements of the lithium supplement agent, carrying out point analysis on the particles of the lithium supplement agent through the scanning electron microscope-energy disperse spectroscopy, and determining the type of the positive electrode lithium supplement agent. And analyzing the element content data of the point analysis to determine the type of the lithium supplement agent in the sample to be detected. According to the technical scheme, the type of the positive electrode lithium supplement agent can be judged, in addition, the content of the lithium supplement agent in the positive electrode plate can be obtained by establishing the standard curve, and finally corresponding data support can be provided for reverse analysis of the formula of the electrode plate in the lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of battery testing, and in particular relates to a method for determining the type and content of a positive electrode lithium replenisher. Background Art

[0002] During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode and embedded in the negative electrode, causing some lithium to be lost on the surface of the negative electrode. At the same time, a layer of SEI film (solid electrolyte interface film) will be formed on the surface of the negative electrode. The formation of the SEI film causes irreversible lithium loss, thereby reducing the active lithium ions inside the battery, the battery capacity will decay, and the cycle life will also be reduced.

[0003] The reduction of active lithium ions is mainly manifested in the formation of SEI film, which mainly occurs in the initial stage of lithium-ion battery cycle. Based on the reduction of the initial efficiency caused by the loss of active lithium, positive electrode lithium supplements came into being. They can provide irreversible lithium ions during the first charge and improve the initial efficiency. At present, there is no good method to characterize the content of lithium supplements. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a positive electrode lithium supplement and a method for determining the content thereof.

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

[0006] A method for determining the type of positive electrode lithium supplement comprises the following steps:

[0007] The morphology of the sample to be tested is observed and mapped using a scanning electron microscope-energy spectrometer (ESD), and the location of the lithium supplement particles is found through the characteristic elements of the lithium supplement.

[0008] The particles of the lithium supplement agent are point analyzed by a scanning electron microscope-energy spectrometer, and the type of the lithium supplement agent in the sample to be tested is determined by analyzing the element content data of the point analysis.

[0009] If the main elements in the point analysis data are Ni and O, it means that the lithium supplement is LNO (Li2NiO2); if the main elements in the point analysis data are Fe and O, it means that the lithium supplement is LFO (Li5FeO4).

[0010] The present invention also includes a method for testing the content of a positive electrode lithium supplement, comprising the following steps:

[0011] 1) confirming the type of the positive electrode lithium supplement and the type of the positive electrode active material by the method described above;

[0012] 2) drawing a standard curve; the abscissa of the standard curve is the content of the lithium supplement agent, and the ordinate is the area percentage of the lithium supplement agent obtained by mapping test using a scanning electron microscope-energy spectrometer;

[0013] 3) Mapping the sample to be tested by scanning electron microscope-energy spectrometer, and obtain the distribution picture of characteristic elements of lithium supplement particles by analyzing the mapping data;

[0014] 4) processing the image obtained in step 3) and performing statistical processing to obtain the area percentage of all particles of the lithium supplement particle;

[0015] 5) Substituting the area percentage obtained in step 4) into the standard curve obtained in step 2) to obtain the content of the lithium supplement.

[0016] In the test method for the content of the positive electrode lithium supplement agent, step 2) can be at any position, not limited to the above position, such as step 2) can be before step 1) or after step 4). That is, the standard curve can be prepared before measuring the area percentage of the lithium supplement agent particles of the sample to be tested, or it can be prepared after measuring the area percentage of the lithium supplement agent particles of the sample to be tested.

[0017] The method for confirming the type of positive electrode active material in step 1) comprises the following steps: performing point analysis on particles other than lithium supplement particles by scanning electron microscope-energy spectrometer, and determining the type of positive electrode active material in the sample to be tested by analyzing the element content data of the point analysis.

[0018] If the main elements are Fe, P, and O, the positive electrode active material of the sample to be tested is lithium iron phosphate LFP; if the main elements are Ni, Co, Mn, and O, the positive electrode active material of the sample to be tested is nickel-cobalt-manganese ternary material; if the main elements are Co and O, the positive electrode active material of the sample to be tested is lithium cobalt oxide.

[0019] The method for determining the characteristic elements in step 3) is:

[0020] When LNO lithium supplement is added to lithium iron phosphate system, the characteristic element is Ni element, and when LFO lithium supplement is added to lithium iron phosphate system, the characteristic element of lithium supplement is P element;

[0021] When LFO is added to the nickel-cobalt-manganese ternary system and the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Fe;

[0022] When LNO is added to the nickel-cobalt-manganese ternary system, the characteristic elements that characterize the lithium supplement are Co and Mn elements;

[0023] When LNO is added to the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Ni.

[0024] The specific steps of step 2) are: preparing positive electrode sheets with different gradient lithium supplement content; using steps 3)-step 4) to test to obtain the area percentage corresponding to the different gradient lithium supplement content, using the known lithium supplement content as the horizontal coordinate and the obtained different lithium supplement area percentage as the vertical coordinate to draw a standard curve, and obtain the relationship between the lithium supplement content and the area ratio Y=aX+b.

[0025] In step 2), the morphology of the sample to be tested is observed using a scanning electron microscope-energy dispersive spectrometer and the sample to be tested is polished before the Mapping test.

[0026] The polishing depth is 3 μm-10 μm; preferably, an ion beam polisher is used to thin and polish the sample to be tested; preferably, argon ions are used for thinning and polishing, the ion beam energy is 5 keV, and the plane polishing time is 1.5 hours.

[0027] The specific steps of step 4) are: converting the image into a binary image by using Image J image processing software, adjusting the threshold so that all target particles are selected, and then obtaining the area percentage of all selected particles by statistics; preferably, the threshold is 0-255.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The technical solution of the present application can determine the type of positive electrode lithium replenisher. In addition, by establishing a standard curve, the content of the lithium replenisher in the positive electrode sheet can be obtained, which can ultimately provide corresponding data support for the reverse analysis of the electrode sheet formula in the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a test result diagram of the lithium supplement agent of Example 1;

[0031] Figure 2 This is a picture processing diagram of the lithium supplement agent of Example 1;

[0032] Figure 3 is a standard curve diagram of the lithium supplement agent of Example 1;

[0033] Figure 4 This is a test result diagram of the lithium supplement agent of Example 2;

[0034] Figure 5 This is a picture processing diagram of the lithium supplement agent of Example 2;

[0035] Figure 6 is a standard curve diagram of the lithium supplement agent of Example 2;

[0036] Figure 7 This is a test result diagram of the lithium supplement agent of Example 3;

[0037] Figure 8 This is a picture processing diagram of the lithium supplement agent of Example 3;

[0038] Fig. 9 This is a standard curve diagram of the lithium supplement of Example 3. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0040] Example 1

[0041] 1. A method for determining the type of a positive electrode lithium supplement agent comprises the following steps: using a scanning electron microscope-energy spectrometer to perform morphological observation and mapping test on a sample to be tested, finding the location of lithium supplement agent particles through characteristic elements of the lithium supplement agent, performing point analysis on the particles of the lithium supplement agent through a scanning electron microscope-energy spectrometer, and determining the type of lithium supplement agent in the sample to be tested by analyzing the element content data of the point analysis.

[0042] If the main elements in the point analysis data are Ni and O, it means that the lithium supplement is LNO; if the main elements in the point analysis data are Fe and O, it means that the lithium supplement is LFO.

[0043] like Figure 1 As shown, the element content data of the point analysis of the sample to be tested is analyzed, and its main elements are Fe and O, indicating that the lithium supplement is LFO, wherein Figure 1 The yellow area in middle c is the LFO particles;

[0044] 2. A method for testing the content of a positive electrode lithium supplement, comprising the following steps:

[0045] 1) Using the above method to confirm the type of positive electrode lithium supplement and the type of positive electrode active material;

[0046] The method for confirming the type of positive electrode active material includes the following steps: performing point analysis on particles other than lithium supplement particles by scanning electron microscope-energy spectrometer, and determining the type of positive electrode active material in the sample to be tested by analyzing the element content data of the point analysis.

[0047] Specifically, if the main elements are Fe, P, and O, the positive electrode active material of the sample to be tested is LFP; if the main elements are Ni, Co, Mn, and O, the positive electrode active material of the sample to be tested is a nickel-cobalt-manganese ternary material; if the main elements are Co and O, the positive electrode active material of the sample to be tested is lithium cobalt oxide.

[0048] The particles other than the lithium supplement particles of the sample to be tested were analyzed, and the main elements were Fe, P, and O, indicating that the positive electrode of the electrode sample was a lithium iron phosphate LFP system;

[0049] 2) drawing a standard curve; the abscissa of the standard curve is the content of the lithium supplement agent, and the ordinate is the area percentage of the lithium supplement agent obtained by a scanning electron microscope-energy spectrometer mapping test; specifically comprising the following steps:

[0050] 2.1) Prepare LFP system positive electrode sheets with different gradient lithium supplement LFO content, where different gradients refer to the amount of lithium supplement added when designing the positive electrode sheet formula, and the amount of LFO lithium supplement added (by weight) is 0.5%, 1.5%, 2.5%, and 3% respectively;

[0051] 2.2) Polish the prepared LFP positive electrode sheet: Cut the positive electrode sheet to a size of about 1cm×1cm, and stick it on the flat polishing sample stage of the ion beam polisher. The equipment model is Gatan 697.C. Use argon ions to thin and polish the sample. The ion beam energy is 5keV, the flat polishing time is 1.5h, and the polishing depth is 3μm-10μm. Under this condition, the pollutants on the surface of the electrode can be removed cleanly, the polishing time will not be too long, and the test efficiency is relatively high. Subsequent testing needs to be carried out immediately after polishing, because the lithium supplement is sensitive to environmental conditions, such as moisture. If it cannot be tested immediately, the polished sample needs to be encapsulated in aluminum plastic.

[0052] The mapping test of positive electrode sheets with different gradient contents was carried out by scanning electron microscope-energy spectrometer at x500 times. By analyzing the mapping data, the distribution picture of characteristic element P of lithium supplement particles was obtained ( Figure 2 (shown in a);

[0053] When LNO lithium supplement is added to lithium iron phosphate system, the characteristic element is Ni element, and when LFO lithium supplement is added to lithium iron phosphate system, the characteristic element of lithium supplement is P element;

[0054] When LFO is added to the nickel-cobalt-manganese ternary system and the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Fe;

[0055] When LNO is added to the nickel-cobalt-manganese ternary system, the characteristic elements that characterize the lithium supplement are Co and Mn elements;

[0056] When LNO is added to the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Ni.

[0057] Therefore, in this embodiment, P is selected as the characteristic element for testing.

[0058] 2.3) The image obtained in step 1.2) is processed and the area percentage of all particles of the lithium supplement particle is obtained by statistical processing; first, the image is converted into a binary image (adjust the image type to 8-bit, i.e., changed to a grayscale image), such as Figure 2 As shown in b, by adjusting the threshold, when the threshold is 17, all target particles are selected, and then statistical processing is performed to obtain the area percentage X of all selected lithium supplement particles;

[0059] 2.4) A standard curve is drawn with the known lithium supplement content as the horizontal axis and the obtained percentage of the area of ​​different lithium supplements as the vertical axis to obtain the relationship between the lithium supplement content and the area ratio Y=aX+b, Figure 3 As shown in FIG. 1 , Y=0.7569X+0.0009.

[0060] 3) A scanning electron microscope-energy spectrometer is used to perform a mapping test on the sample to be tested, and a picture of the characteristic element distribution of the lithium supplement agent particles is obtained by analyzing the mapping data; the above test shows that the lithium supplement agent is LFO and the positive electrode active material is a lithium iron phosphate system, so the characteristic element is P element.

[0061] 4) The image obtained in step 3) is processed in the same manner as in step 2.3, and the area percentage of all particles of the lithium supplementing agent particles is obtained by statistical processing as X=2.25%;

[0062] 5) Substitute the area percentage obtained in step 4) into the standard curve obtained in step 2) to obtain the content of the lithium supplement agent. The content of the lithium supplement agent in the sample to be tested is obtained by calculation as Y=0.7569*2.25%+0.0009=1.79%.

[0063] Evaluation of the accuracy of lithium supplement content determination results:

[0064] The sample with known lithium supplement agent content was used as the sample to be tested, and the lithium supplement agent content was measured by the lithium supplement agent content determination method in the positive electrode sheet established in this patent. The test results are shown in Table 1 below.

[0065] Table 1

[0066] Known content Test content Relative error 1.50％ 1.56％ 4.00％ 2.50％ 2.38％ -4.80％ 3.00％ 2.86％ -4.67％

[0067] From the above test data, it can be seen that the absolute value of the relative error is within 5% (it is generally believed that when the absolute value of the relative error is ≤5%, the data is relatively accurate), so using this method to test the content of lithium supplement is relatively accurate.

[0068] Example 2

[0069] 1. A method for determining the type of a positive electrode lithium supplement agent comprises the following steps: using a scanning electron microscope-energy spectrometer to perform morphological observation and mapping test on a sample to be tested, finding the location of lithium supplement agent particles through characteristic elements of the lithium supplement agent, performing point analysis on the particles of the lithium supplement agent through a scanning electron microscope-energy spectrometer, and determining the type of lithium supplement agent in the sample to be tested by analyzing the element content data of the point analysis.

[0070] If the main elements in the point analysis data are Ni and O, it means that the lithium supplement is LNO; if the main elements in the point analysis data are Fe and O, it means that the lithium supplement is LFO.

[0071] like Figure 4 As shown, the element content data of the point analysis of the sample to be tested is analyzed, and its main elements are Ni and O, indicating that the lithium supplement is LNO, Figure 5 The black area in middle a is LNO particles;

[0072] 2. A method for testing the content of a positive electrode lithium supplement, comprising the following steps:

[0073] 1) Using the above method to confirm the type of positive electrode lithium supplement and the type of positive electrode active material;

[0074] The method for confirming the type of positive electrode active material includes the following steps: performing point analysis on particles other than lithium supplement particles by scanning electron microscope-energy spectrometer, and determining the type of positive electrode active material in the sample to be tested by analyzing the element content data of the point analysis.

[0075] Specifically, if the main elements are Fe, P, and O, the positive electrode active material of the sample to be tested is LFP; if the main elements are Ni, Co, Mn, and O, the positive electrode active material of the sample to be tested is a nickel-cobalt-manganese ternary material; if the main elements are Co and O, the positive electrode active material of the sample to be tested is lithium cobalt oxide.

[0076] The particles other than the lithium supplement particles of the sample to be tested were analyzed, and the main elements were Fe, P, and O, indicating that the positive electrode of the electrode sample was a lithium iron phosphate LFP system;

[0077] 2) drawing a standard curve; the abscissa of the standard curve is the content of the lithium supplement agent, and the ordinate is the area percentage of the lithium supplement agent obtained by a scanning electron microscope-energy spectrometer mapping test; specifically comprising the following steps:

[0078] 2.1) Prepare LFP system positive electrode sheets with different gradient lithium supplement LFO content, where different gradients refer to the amount of lithium supplement added when designing the positive electrode sheet formula, and the amount of LFO lithium supplement added (by weight) is 0.5%, 1.5%, 2.5%, and 3% respectively;

[0079] 2.2) Polish the prepared LFP positive electrode sheet: Cut the positive electrode sheet to a size of about 1cm×1cm, and stick it on the flat polishing sample stage of the ion beam polisher. The equipment model is Gatan 697.C. Use argon ions to thin and polish the sample. The ion beam energy is 5keV, the flat polishing time is 1.5h, and the polishing depth is 3μm-10μm. Under this condition, the pollutants on the surface of the electrode can be removed cleanly, the polishing time will not be too long, and the test efficiency is relatively high. Subsequent testing needs to be carried out immediately after polishing, because the lithium supplement is sensitive to environmental conditions, such as moisture. If it cannot be tested immediately, the polished sample needs to be encapsulated in aluminum plastic.

[0080] The mapping test of positive electrode sheets with different gradient contents was carried out by scanning electron microscope-energy spectrometer at x500 times. By analyzing the mapping data, the distribution picture of Ni, a characteristic element of lithium supplement particles, was obtained ( Figure 5 (shown in a);

[0081] When LNO lithium supplement is added to lithium iron phosphate system, the characteristic element is Ni element, and when LFO lithium supplement is added to lithium iron phosphate system, the characteristic element of lithium supplement is P element;

[0082] When LFO is added to the nickel-cobalt-manganese ternary system and the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Fe;

[0083] When LNO is added to the nickel-cobalt-manganese ternary system, the characteristic elements that characterize the lithium supplement are Co and Mn elements;

[0084] When LNO is added to the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Ni.

[0085] Therefore, in this embodiment, Ni is selected as the characteristic element for testing.

[0086] 2.3) The image obtained in step 2.2) is processed and the area percentage of all particles of the lithium supplement particle is obtained by statistical processing; first, the image is converted into a binary image (adjust the image type to 8-bit, i.e., changed to a grayscale image), such as Figure 5 As shown in b, by adjusting the threshold, when the threshold is 21, all target particles are selected, and then the area percentage X of all selected lithium supplement particles is obtained through statistical processing;

[0087] 2.4) A standard curve is drawn with the known lithium supplement content as the horizontal axis and the obtained percentage of the area of ​​different lithium supplements as the vertical axis to obtain the relationship between the lithium supplement content and the area ratio Y=aX+b, Figure 6 As shown in , Y=0.9177X+0.001.

[0088] 3) A scanning electron microscope-energy spectrometer was used to perform mapping test on the sample to be tested, and the mapping data was analyzed to obtain a picture of the distribution of characteristic elements of the lithium supplement agent particles; the above test showed that the lithium supplement agent was LNO and the positive electrode active material was a lithium iron phosphate system, so the characteristic element was Ni.

[0089] 4) The image obtained in step 3) is processed in the same manner as in step 2.3, and the area percentage of all particles of the lithium supplementing agent particles is obtained by statistical processing as X=2.77%;

[0090] 5) Substitute the area percentage obtained in step 4) into the standard curve obtained in step 2) to obtain the content of the lithium supplement agent. The content of the lithium supplement agent in the sample to be tested is obtained by calculation as Y=0.9177*2.77%+0.001=2.64%.

[0091] Evaluation of the accuracy of lithium supplement content determination results:

[0092] The sample with known lithium supplement agent content was used as the sample to be tested, and the lithium supplement agent content was measured by the method for measuring the lithium supplement agent content in the positive electrode sheet established in this patent. The test results are shown in Table 2 below.

[0093] Table 2

[0094] Known content Test content Relative error 1.50％ 1.44％ -4.33％ 2.50％ 2.61％ 4.40％ 3.00％ 2.89％ -3.67％

[0095] From the above test data, it can be seen that the absolute value of the relative error is within 5% (it is generally believed that when the absolute value of the relative error is ≤5%, the data is relatively accurate), so using this method to test the content of lithium supplement is relatively accurate.

[0096] Example 3

[0097] 1. A method for determining the type of a positive electrode lithium supplement agent comprises the following steps: using a scanning electron microscope-energy spectrometer to perform morphological observation and mapping test on a sample to be tested, finding the location of lithium supplement agent particles through characteristic elements of the lithium supplement agent, performing point analysis on the particles of the lithium supplement agent through a scanning electron microscope-energy spectrometer, and determining the type of lithium supplement agent in the sample to be tested by analyzing the element content data of the point analysis.

[0098] If the main elements in the point analysis data are Ni and O, it means that the lithium supplement is LNO; if the main elements in the point analysis data are Fe and O, it means that the lithium supplement is LFO.

[0099] like Figure 7 As shown, the element content data of the point analysis of the sample to be tested is analyzed, and its main elements are Fe and O, indicating that the lithium supplement is LFO, Figure 8 The black area in middle a is the LFO particles;

[0100] 2. A method for testing the content of a positive electrode lithium supplement, comprising the following steps:

[0101] 1) Using the above method to confirm the type of positive electrode lithium supplement and the type of positive electrode active material;

[0102] The method for confirming the type of positive electrode active material includes the following steps: performing point analysis on particles other than lithium supplement particles by scanning electron microscope-energy spectrometer, and determining the type of positive electrode active material in the sample to be tested by analyzing the element content data of the point analysis.

[0103] Specifically, if the main elements are Fe, P, and O, the positive electrode active material of the sample to be tested is LFP; if the main elements are Ni, Co, Mn, and O, the positive electrode active material of the sample to be tested is a nickel-cobalt-manganese ternary material; if the main elements are Co and O, the positive electrode active material of the sample to be tested is lithium cobalt oxide.

[0104] The particles other than the lithium supplement particles of the sample to be tested were analyzed, and the main elements were Ni, Co, Mn, and O, indicating that the positive electrode of the electrode sample was a ternary system of nickel, cobalt, and manganese;

[0105] 2) drawing a standard curve; the abscissa of the standard curve is the content of the lithium supplement agent, and the ordinate is the area percentage of the lithium supplement agent obtained by a scanning electron microscope-energy spectrometer mapping test; specifically comprising the following steps:

[0106] 2.1) preparing nickel-cobalt-manganese ternary system positive electrode sheets with different gradient lithium supplement LFO contents, where different gradients refer to the amount of lithium supplement added when designing the positive electrode sheet formula, and the amount of LFO lithium supplement added (by weight) is 0.5%, 1.5%, 2.5%, and 3% respectively;

[0107] 2.2) Polish the prepared nickel-cobalt-manganese ternary system positive electrode sheet: Cut the positive electrode sheet to a size of about 1cm×1cm, and stick it on the flat polishing sample stage of the ion beam polisher. The equipment model is Gatan697.C. Use argon ions to thin and polish the sample. The ion beam energy is 5keV, the flat polishing time is 1.5h, and the polishing depth is 3μm-10μm. Under this condition, the pollutants on the surface of the electrode can be removed cleanly, the polishing time will not be too long, and the test efficiency is relatively high. Subsequent testing needs to be carried out immediately after polishing, because the lithium supplement is sensitive to environmental conditions, such as moisture. If it cannot be tested immediately, the polished sample needs to be packaged in aluminum plastic.

[0108] The mapping test of positive electrode sheets with different gradient contents was carried out by scanning electron microscope-energy spectrometer at x500 times. By analyzing the mapping data, the distribution picture of Fe, a characteristic element of lithium supplement particles, was obtained ( Figure 8 (shown in a);

[0109] When LNO lithium supplement is added to lithium iron phosphate system, the characteristic element is Ni element, and when LFO lithium supplement is added to lithium iron phosphate system, the characteristic element of lithium supplement is P element;

[0110] When LFO is added to the nickel-cobalt-manganese ternary system and the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Fe;

[0111] When LNO is added to the nickel-cobalt-manganese ternary system, the characteristic elements that characterize the lithium supplement are Co and Mn elements;

[0112] When LNO is added to the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Ni.

[0113] Therefore, Fe is selected as the characteristic element for testing in this embodiment.

[0114] 2.3) The image obtained in step 2.2) is processed and the area percentage of all particles of the lithium supplement particle is obtained by statistical processing; first, the image is converted into a binary image (adjust the image type to 8-bit, i.e., changed to a grayscale image), such as Figure 8 As shown in b, by adjusting the threshold, when the threshold is 14, all target particles are selected, and then the area percentage X of all selected lithium supplement particles is obtained through statistical processing;

[0115] 2.4) A standard curve is drawn with the known lithium supplement content as the horizontal axis and the obtained percentage of the area of ​​different lithium supplements as the vertical axis to obtain the relationship between the lithium supplement content and the area ratio Y=aX+b, Figure 6 As shown in , Y=0.9669X+0.0004.

[0116] 3) A scanning electron microscope-energy spectrometer is used to perform mapping test on the sample to be tested, and a picture of the characteristic element distribution of the lithium supplement agent particles is obtained by analyzing the mapping data; the above test shows that the lithium supplement agent is LFO, and the positive electrode active material is a nickel-cobalt-manganese ternary system, so the characteristic element is Fe.

[0117] 4) The image obtained in step 3) is processed in the same manner as in step 2.3), and the area percentage of all particles of the lithium supplementing agent particles is obtained by statistical processing as X=1.70%;

[0118] 5) Substitute the area percentage obtained in step 4) into the standard curve obtained in step 2) to obtain the content of the lithium supplement agent. The content of the lithium supplement agent in the sample to be tested is calculated to be Y=0.9669*2.45%+0.0004=1.68%.

[0119] Evaluation of the accuracy of lithium supplement content determination results:

[0120] The sample with known lithium supplement agent content was used as the sample to be tested, and the lithium supplement agent content was measured by the method for measuring the lithium supplement agent content in the positive electrode sheet established in this patent. The test results are shown in Table 3 below.

[0121] Table 3

[0122] Known content Test content Relative error 1.50％ 1.44％ -4.00％ 2.50％ 2.59％ 3.60％ 3.00％ 2.87％ -4.33％

[0123] From the above test data, it can be seen that the absolute value of the relative error is within 5% (it is generally believed that when the absolute value of the relative error is ≤5%, the data is relatively accurate), so using this method to test the content of lithium supplement is relatively accurate.

[0124] In summary, the technical solution of the present application can determine the types of positive electrode lithium replenishers and positive electrode active materials. In addition, by establishing a standard curve, the content of lithium replenishers in the positive electrode sheet can be obtained, which can ultimately provide corresponding data support for the reverse analysis of the electrode sheet formula in lithium-ion batteries.

[0125] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining the type of positive electrode lithium supplement, characterized in that: The steps include: Use scanning electron microscope-energy spectrometer to observe the morphology and conduct mapping test on the sample to be tested, and find out the location of lithium supplement particles through the characteristic elements of lithium supplement; The particles of the lithium supplement agent are point analyzed by a scanning electron microscope-energy spectrometer, and the type of the lithium supplement agent in the sample to be tested is determined by analyzing the element content data of the point analysis.

2. The method for determining the type of positive electrode lithium supplement according to claim 1, characterized in that: If the main elements in the point analysis data are Ni and O, it means that the lithium supplement is LNO; if the main elements in the point analysis data are Fe and O, it means that the lithium supplement is LFO.

3. A method for testing the content of a positive electrode lithium supplement, characterized in that: The steps include: 1) using the method of claim 1 or 2 to confirm the type of positive electrode lithium supplement and the type of positive electrode active material; 2) drawing a standard curve; the abscissa of the standard curve is the content of the lithium supplement agent, and the ordinate is the area percentage of the lithium supplement agent obtained by mapping test using a scanning electron microscope-energy spectrometer; 3) Perform mapping test on the sample to be tested by scanning electron microscope-energy spectrometer, and obtain the distribution picture of characteristic elements of lithium supplement particles by analyzing the mapping data; 4) processing the image obtained in step 3) and performing statistical processing to obtain the area percentage of all particles of the lithium supplement particle; 5) Substituting the area percentage obtained in step 4) into the standard curve obtained in step 2) to obtain the content of the lithium supplement.

4. The method for testing the content of positive electrode lithium supplement according to claim 3, characterized in that: The method for confirming the type of positive electrode active material in step 1) comprises the following steps: performing point analysis on particles other than lithium supplement particles by scanning electron microscope-energy spectrometer, and determining the type of positive electrode active material in the sample to be tested by analyzing the element content data of the point analysis.

5. The method for testing the content of positive electrode lithium supplement according to claim 4, characterized in that: If the main elements are Fe, P, and O, the positive electrode active material of the sample to be tested is lithium iron phosphate LFP; if the main elements are Ni, Co, Mn, and O, the positive electrode active material of the sample to be tested is nickel-cobalt-manganese ternary material; if the main elements are Co and O, the positive electrode active material of the sample to be tested is lithium cobalt oxide.

6. The method for testing the content of positive electrode lithium supplement according to claim 3, characterized in that: The method for determining the characteristic elements in step 3) is: When LNO lithium supplement is added to lithium iron phosphate system, the characteristic element is Ni, and when LFO lithium supplement is added to lithium iron phosphate system, the characteristic element of the lithium supplement is P. When LFO is added to the nickel-cobalt-manganese ternary system and the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Fe; When LNO is added to the nickel-cobalt-manganese ternary system, the characteristic elements that characterize the lithium supplement are Co and Mn elements; When LNO is added to the lithium cobalt oxide system, the characteristic element characterizing the lithium supplement is Ni.

7. The method for testing the content of positive electrode lithium supplement according to claim 3, characterized in that: The specific steps of step 2) are: preparing positive electrode sheets with different gradient lithium supplement content; using steps 3)-step 4) to test to obtain the area percentage corresponding to the different gradient lithium supplement content, using the known lithium supplement content as the horizontal coordinate and the obtained different lithium supplement area percentage as the vertical coordinate to draw a standard curve, and obtain the relationship between the lithium supplement content and the area ratio Y=aX+b.

8. The method for determining the content of the positive electrode lithium supplement according to claim 3, characterized in that: In step 2), the morphology of the sample to be tested is observed using a scanning electron microscope-energy dispersive spectrometer and the sample to be tested is polished before the mapping test.

9. The method for determining the content of the positive electrode lithium supplement according to claim 8, characterized in that: The polishing depth is 3 μm-10 μm; preferably, an ion beam polisher is used to thin and polish the sample to be tested; preferably, argon ions are used for thinning and polishing, the ion beam energy is 5 keV, and the plane polishing time is 1.5 hours.

10. The method for testing the content of positive electrode lithium supplement according to claim 3, characterized in that: The specific steps of step 4) are: converting the image into a binary image by using Image J image processing software, adjusting the threshold so that all target particles are selected, and then obtaining the area percentage of all selected particles by statistics; preferably, the threshold is 0-255.

Images