Separation method and detection method for impurity metal particles in cathode powder

Abstract

A separation method for impurity metal particles in a cathode powder. The separation method comprises: providing a first separation liquid and a second separation liquid, wherein the density of the second separation liquid is greater than that of the first separation liquid, and the density of the second separation liquid is less than that of impurity metal particles in the cathode powder; mixing the cathode powder with some of the first separation liquid to form a suspension; adding the second separation liquid to a container, and adding the other part of the first separation liquid to the container to create layering; and adding the suspension into the container having the layered solution, such that the impurity metal particles sink to the bottom of the second separation liquid, thereby achieving separation. Further provided is a detection method for impurity metal particles in a cathode powder.

Description

Separation and detection methods of impure metal particles in cathode powder Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for separating and detecting impure metal particles in cathode powder. Background Art

[0002] Research has found that the cathode powder used in secondary batteries may contain impure metal particles, which may originate from the cathode active material itself or from equipment such as transportation pipelines. These impure metal particles, once incorporated into the cathode slurry and then applied to and wound into the battery cell, can chemically deposit and pierce the separator during use, causing the cathode and cathode to overlap and leading to poor self-discharge.

[0003] Therefore, in order to understand the types and contents of impurity metal particles and thus effectively control them, how to effectively separate the impurity metal particles in cathode powder has become an urgent concern and a problem that needs to be solved.

[0004] Summary of the Invention

[0005] In view of the problems existing in the background technology, the first aspect of the present application provides a method for separating impurity metal particles in cathode powder, which can effectively separate impurity metal particles in cathode powder.

[0006] The method for separating impurity metal particles in cathode powder provided in the first aspect of the present application comprises the following steps:

[0007] Providing a first separation liquid and a second separation liquid, wherein the density of the second separation liquid is greater than the density of the first separation liquid and the density of the second separation liquid is less than the density of the impurity metal particles in the cathode powder;

[0008] Mixing the cathode powder with a portion of the first separation liquid to form a suspension;

[0009] adding the second separation liquid to the container, and adding another portion of the first separation liquid to the container to form layers; and

[0010] The suspension is added to the container with the separated solution, and the impurity metal particles are allowed to sink to the bottom of the second separation liquid, thereby achieving separation.

[0011] This application adopts a physical method to effectively separate the impurity metal particles in the cathode powder. The method is simple to operate, saves time and labor, and lays the foundation for detecting the type and content of impurity metal particles.

[0012] In some embodiments, according to the first aspect, a first example of the first aspect is proposed, the density of the first separation liquid is recorded as ρ1, the density of the second separation liquid is recorded as ρ2, the difference between ρ2 and ρ1 is recorded as Δρ, and Δρ is greater than 0.1.

[0013] By optimizing the density difference between the first separation liquid and the second separation liquid, the detection rate can be further improved.

[0014] In some embodiments, according to the first aspect, a second example of the first aspect is proposed, and Δρ is 0.1-0.83.

[0015] By optimizing the density difference between the first separation liquid and the second separation liquid, the detection rate can be further improved.

[0016] In some embodiments, according to the first aspect, a third example of the first aspect is provided, where the first separation liquid includes: a mixture of ethanol and water, a mixture of ethanol and benzene, ethanol, or benzene.

[0017] In some embodiments, the second separation liquid includes one or more of water, dichloromethane, chloroform, carbon tetrachloride, and perchloroethylene.

[0018] By optimizing the types of the first separation liquid and the second separation liquid, the detection rate can be further improved.

[0019] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, wherein the first separation liquid includes a mixture of ethanol and water, and the volume percentage of ethanol is 48%-90%.

[0020] By optimizing the volume concentration of the ethanol aqueous solution, the density of the ethanol aqueous solution can be optimized, and then the density difference between the first separation liquid and the second separation liquid can be optimized, which is beneficial to further improve the detection rate.

[0021] In some embodiments, according to the first aspect, a fifth example of the first aspect is provided, wherein the cathode powder includes a cathode active material, and the cathode active material includes lithium iron phosphate.

[0022] The separation method of the present application is more suitable for separating cathode powder containing lithium iron phosphate, and has a better separation effect.

[0023] In some embodiments, according to the first aspect, a sixth example of the first aspect is provided, wherein another portion of the first separation liquid is slowly added to form layers.

[0024] In some embodiments, the suspension is added slowly to maintain a layered state.

[0025] In some embodiments, the container is kept stationary at all times to maintain the stratified state.

[0026] By maintaining the stratified state, it is beneficial to achieve effective separation of impurity metal particles from the cathode powder.

[0027] In some embodiments, according to the first aspect, a seventh example of the first aspect is proposed, and the separation method of the present application further includes: collecting the impurity metal particles after the impurity metal particles sink to the bottom of the second separation liquid.

[0028] In some embodiments, according to the first aspect, an eighth example of the first aspect is provided, which controls the time from the formation of the stratification to the end of the collection to maintain the stratification state.

[0029] By controlling the operation time to maintain the stratified state, it is beneficial to achieve effective separation of impurity metal particles from the cathode powder.

[0030] In some embodiments, according to the first aspect, a ninth example of the first aspect is provided, wherein the container comprises a cylindrical container. A first liquid outlet is provided on a sidewall of the cylindrical container, and a second liquid outlet is provided on a bottom of the cylindrical container. A second separation liquid is added to the container such that the liquid level of the second separation liquid is higher than the first liquid outlet. Collecting the impurity metal particles comprises: opening the first liquid outlet to discharge the liquid until the liquid above the first liquid outlet is completely discharged, and then opening the second liquid outlet to discharge the liquid after completion.

[0031] By making the liquid level of the second separation liquid higher than the first liquid outlet and collecting the impurity metal particles after discharging the liquid in a certain order, it is beneficial to separate the impurity metal particles from the cathode powder, and avoid the cathode powder in the upper layer from entering the lower layer before collecting the impurity metal particles, that is, avoid the cathode powder in the first separation liquid from entering the second separation liquid, causing the impurity metal particles to be re-mixed with the cathode powder.

[0032] A second aspect of the present application provides a method for detecting impurity metal particles in cathode powder, which can accurately detect the type and content of the impurity metal particles.

[0033] The method for detecting impurity metal particles in cathode powder provided in the second aspect of the present application comprises the following steps:

[0034] According to the method of the first aspect of the present application, impurity metal particles are separated from the cathode powder, and the cathode powder is weighed before being mixed with a portion of the first separation liquid;

[0035] The type and / or weight of the separated impurity metal particles are detected, the content of the impurity metal particles in the cathode powder is calculated, and the element type of the impurity metal particles is detected.

[0036] The detection method of the present application has the advantages of high efficiency and high detection rate, and can provide certain data support for the level of impure metal particles in the incoming material.

[0037] In some embodiments, according to the second aspect, a first example of the second aspect is provided, where after weighing the cathode powder and before mixing the cathode powder with a portion of the first separation liquid, the method further includes: screening the cathode powder to remove small particles in the cathode powder.

[0038] In some embodiments, the sieve used is 1200-2000 mesh.

[0039] The particle size of the impurity metal particles in the cathode powder is usually larger than the particle size of the main component cathode active material particles. In order to improve the efficiency of separation and detection, a sieve can be used after weighing to screen out the small particles in the cathode powder to prevent the suspension from being added to the first separation liquid in the container at one time. At the same time, in order to prevent the impurity metal particles from being screened out, the mesh size of the sieve needs to be optimized. This application uses a sieve with a mesh size of 1200-2000, which can not only screen out the small particles in the cathode powder, but also prevent the impurity metal particles from being screened out.

[0040] In some embodiments, according to the second aspect, a second example of the second aspect is proposed, and the method for detecting the type and / or weight of the separated impurity metal particles includes: one or more of: particle detector detection method, Phenomenon scanning electron microscope detection method, spectrophotometry, titration method, atomic emission spectrometry, X-ray fluorescence spectroscopy, inductively coupled plasma spectroscopy, and spark direct reading spectroscopy.

[0041] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0043] FIG1 is a schematic diagram of a container used in an embodiment of the present application.

[0044] Description of reference numerals:

[0045] 10 is an alcohol layer, 20 is a water layer, 30 is an impurity metal particle layer, 100 is a first liquid outlet, and 200 is a second liquid outlet. DETAILED DESCRIPTION

[0046] The exemplary embodiments of the present disclosure will be described in more detail below. However, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions.

[0048] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0049] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and “multiple” in “one or more” means more than two (including two).

[0050] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists, A and B exist at the same time, and B exists.

[0051] The above summary of the invention of this application is not intended to describe every disclosed embodiment or every implementation in this application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0052] Research has found that the cathode powder used in secondary batteries may contain impure metal particles, which may originate from the cathode active material itself or from equipment such as transportation pipelines. These impure metal particles enter the cathode slurry and, after being coated and wound into the battery cell, can chemically deposit and pierce the separator during use, causing the cathode and anode to overlap and leading to poor self-discharge. Therefore, in order to understand the type and content of impure metal particles and effectively control them, how to effectively separate the impure metal particles from the cathode powder has become a pressing concern and a problem that needs to be solved.

[0053] In order to solve the above problems, the present application designs a method for separating impurity metal particles in cathode powder, which uses a first separation liquid and a second separation liquid with different densities to form layers, so that the impurity metal particles sink to the bottom of the second separation liquid and the cathode powder is intercepted in the first separation liquid, thereby achieving effective separation of impurity metal particles. This physical method is simple to operate, saves time and effort, and lays the foundation for detecting the type and content of impurity metal particles.

[0054] In a first aspect, according to some embodiments of the present application, the present application provides a method for separating impurity metal particles in a cathode powder, comprising the following steps:

[0055] Providing a first separation liquid and a second separation liquid, wherein the density of the second separation liquid is greater than the density of the first separation liquid, and the density of the second separation liquid is less than the density of the impurity metal particles in the cathode powder;

[0056] Mixing the cathode powder with a portion of the first separation liquid to form a suspension;

[0057] adding the second separation liquid to the container, and adding another portion of the first separation liquid to the container to form layers; and

[0058] The suspension is added to the container with the separated solution, and the impurity metal particles are allowed to sink to the bottom of the second separation liquid, thereby achieving separation.

[0059] Since the density of the first separation liquid is lower than that of the second separation liquid, the first separation liquid and the second separation liquid exist in the container in a layered state, with the first separation liquid located in the upper layer and the second separation liquid located in the lower layer.

[0060] Impure metal particles in the cathode powder may originate from the cathode active material itself or from equipment such as transport pipelines or mixing tanks. Impure metal particles typically include one or more of Cu, Zn, Al, Fe, Cr, Ti, Ni, and Mg. Because impure metal particles are generally dense, they quickly sink to the bottom of the second separation liquid, effectively separating them from the cathode powder.

[0061] In some embodiments, the density of the first separation liquid is recorded as ρ1, the density of the second separation liquid is recorded as ρ2, the difference between ρ2 and ρ1 is recorded as Δρ, and Δρ is greater than 0.1.

[0062] Optimizing the density difference between the first and second separating liquids facilitates the formation of stratified layers within the container. A larger density difference facilitates stratification, which in turn facilitates better separation of impurity metal particles and improves detection rates. If the density difference is too small, stratification is unlikely to occur between the first and second separating liquids, resulting in inability to achieve separation.

[0063] In some embodiments, Δρ is 0.1-0.83 g / cm 3 For example, Δρ can be 0.1 g / cm 3 , 0.11g / cm 3 , 0.12g / cm 3 , 0.13g / cm 3 , 0.14g / cm 3 , 0.15g / cm 3 , 0.16g / cm 3 , 0.17g / cm 3 , 0.18g / cm 3 , 0.19g / cm 3 , 0.2g / cm 3 , 0.25g / cm 3 , 0.3g / cm 3 , 0.35g / cm 3 , 0.4g / cm 3 , 0.45g / cm 3 , 0.5g / cm 3 , 0.55g / cm 3 , 0.6g / cm 3 , 0.65g / cm 3 , 0.7g / cm 3 , 0.75g / cm 3 , 0.8g / cm 3 or 0.83g / cm 3 .

[0064] By optimizing the density difference between the first separation liquid and the second separation liquid, the detection rate can be further improved.

[0065] In some specific embodiments, the density of the first separation liquid may be 0.79-0.9 g / cm 3 , for example, 0.79 g / cm 3 , 0.8g / cm 3 , 0.81g / cm 3 , 0.82g / cm 3, 0.83g / cm 3 、0.84g / cm 3 , 0.85g / cm 3 , 0.86g / cm 3 , 0.87g / cm 3 、0.88g / cm 3 , 0.89g / cm 3 or 0.9g / cm 3 .

[0066] In some specific embodiments, the density of the second separation liquid may be 1-2 g / cm 3 , for example, 1 g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 or 2g / cm 3 .

[0067] In some embodiments, the first separation liquid comprises ethanol, benzene, a mixture of ethanol and benzene, or a mixture of ethanol and water. And / or, the second separation liquid comprises one or more of water, dichloromethane, chloroform, carbon tetrachloride, and perchloroethylene.

[0068] By optimizing the types of the first separation liquid and the second separation liquid, the detection rate can be further improved.

[0069] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, wherein the first separation liquid includes a mixture of ethanol and water, wherein the volume percentage of ethanol is 48%-90%.

[0070] By optimizing the volume concentration of the ethanol aqueous solution, the density of the ethanol aqueous solution can be optimized, and then the density difference between the first separation liquid and the second separation liquid can be optimized, which is beneficial to further improve the detection rate.

[0071] In some embodiments, the volume percentage of ethanol in the mixture of ethanol and water may be, for example, 48%, 49%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0072] In some specific embodiments, the first separation liquid includes a mixture of ethanol and water, and the second separation liquid includes water.

[0073] In some embodiments, the cathode powder includes a cathode active material, and the cathode active material includes lithium iron phosphate.

[0074] The separation method of the present application is more suitable for separating cathode powder containing lithium iron phosphate, and has a better separation effect.

[0075] In some embodiments, another portion of the first separation liquid is slowly added to form layers; and / or the suspension is slowly added to maintain the layers; and / or the container is kept stationary to maintain the layers.

[0076] By forming and maintaining a stratified state, it is beneficial to effectively separate the impurity metal particles from the cathode powder. In particular, when the first separating liquid and the second separating liquid are miscible or partially miscible, it is necessary to slowly add the remaining first separating liquid, and / or slowly add the suspension, and / or keep the container still.

[0077] In some specific embodiments, another portion of the first separation liquid is slowly added to form layers; and the suspension liquid is slowly added to maintain the layers; and the container is kept stationary to maintain the layers.

[0078] By slowly adding the first separation liquid and the suspension liquid and keeping the container still, mixing of the first separation liquid and the second separation liquid can be reduced, which is conducive to forming and maintaining a stratified state.

[0079] In some embodiments, the addition can be performed slowly along the vessel wall or a guide rod.

[0080] In some embodiments, the separation method of the present application further includes: collecting the impurity metal particles after the impurity metal particles sink to the bottom of the second separation liquid.

[0081] In some embodiments, the time from formation of the stratification to completion of collection is controlled to maintain the stratified state.

[0082] Maintaining a stratified state by controlling the operation time facilitates the effective separation of impurity metal particles from the cathode powder. In particular, when the first and second separating liquids are miscible or partially miscible, the operation time should be minimized to ensure that separation is complete during the stratification period. This prevents the first and second separating liquids from dissolving into each other, making separation impossible.

[0083] In some specific embodiments, the time from forming the layers to the end of collection is controlled to be within 300 s. For example, the time from forming the layers to the end of collection can be controlled to be 300 s, 290 s, 280 s, 270 s, 260 s, 250 s, 240 s, 230 s, 220 s, 210 s, 200 s, 190 s, 180 s, 170 s, 160 s, 150 s, 140 s, 130 s, 120 s, 110 s, 100 s, 90 s, 80 s, 70 s, or 60 s.

[0084] In some embodiments, the container comprises a cylindrical container. A first liquid outlet is provided on the sidewall of the cylindrical container and a second liquid outlet is provided on the bottom. A second separation liquid is added to the container such that the liquid level of the second separation liquid is higher than the first liquid outlet. Collecting the impurity metal particles comprises: opening the first liquid outlet to discharge the liquid until the liquid above the first liquid outlet is completely discharged, and then opening the second liquid outlet to discharge the liquid.

[0085] By making the liquid level of the second separation liquid higher than the first liquid outlet and collecting the impurity metal particles after discharging the liquid in a certain order, it is beneficial to separate the impurity metal particles from the cathode powder, and avoid the cathode powder in the upper layer from entering the lower layer before collecting the impurity metal particles, that is, avoid the cathode powder in the first separation liquid from entering the second separation liquid, causing the impurity metal particles to be re-mixed with the cathode powder.

[0086] In some embodiments, the container comprises a chromatography column, as shown in Figure 1. The chromatography column has a first liquid outlet 100 on its sidewall and a second liquid outlet 200 at its bottom.

[0087] In some embodiments, in the step of forming a suspension, the mass volume ratio of the cathode powder and the first separation liquid can be controlled so that powder aggregation will not occur at the bottom when the suspension is stirred, and the suspension can be poured into the first separation liquid in the container at one time, thereby improving the separation effect.

[0088] In some embodiments, in the step of forming layers, after adding another portion of the first separating liquid to the container, the height of the upper first separating liquid layer is about 10-50 mm, for example, 10 mm, 20 mm, 30 mm, 40 mm or 50 mm.

[0089] A second aspect of the present application provides a method for detecting impure metal particles in cathode powder, which can accurately detect the type and content of the impurity metal particles.

[0090] The method for detecting impurity metal particles in cathode powder provided in the second aspect of the present application comprises the following steps:

[0091] According to the method of the first aspect of the present application, impurity metal particles are separated from the cathode powder, wherein the cathode powder is weighed before being mixed with a portion of the first separation liquid; and

[0092] The type and / or weight of the separated impurity metal particles are detected, the content of the impurity metal particles in the cathode powder is calculated, and the element type of the impurity metal particles is detected.

[0093] The detection method of the present application has the advantages of high efficiency and high detection rate, and can provide certain data support for the level of impurity metal particles in the incoming materials. The existing technology usually adopts chemical methods such as inductively coupled plasma atomic emission spectrometry to detect impurity metal particles in cathode powder. The single sampling amount of the chemical method is small, and multiple sampling and multiple detection are required to avoid sampling accidental errors. Therefore, the efficiency is low and a large amount of manpower and material resources are consumed during detection. In addition, the single sampling amount of the chemical method is small, which will result in a small number of impurity metal particles and a low detection rate. In addition, chemical methods such as ion complexation cannot detect metal particles such as Cu with a particle size of less than 20μm, so the detection rate is low. Compared with the existing technology, the single sampling amount of the present application is large, which can avoid sampling accidental errors, and has the advantages of high efficiency, high detection rate, and saving manpower and material resources.

[0094] In some embodiments, after weighing the cathode powder and before mixing the cathode powder with a portion of the first separation liquid, the detection method further comprises: sieving the cathode powder to remove small particles in the cathode powder. The sieving uses a sieve with a mesh size of 1200-2200.

[0095] The particle size range of the main component cathode active material particles in the cathode powder is usually 0.1-1μm, and the particle size range of the impurity metal particles is usually 5-100μm. The particle size of the impurity metal particles is generally larger than the particle size of the main component cathode active material particles. In order to improve the efficiency of separation and detection, a sieve can be used after weighing to screen out the small particles in the cathode powder. At the same time, in order to prevent the impurity metal particles from being screened out, the mesh number of the sieve needs to be optimized. This application uses a sieve with a mesh number of 1200-2000, which can not only screen out the small particles in the cathode powder, but also prevent the impurity metal particles from being screened out.

[0096] In some specific embodiments, the mesh size of the sieve can be 1200 mesh, 1300 mesh, 1400 mesh, 1500 mesh, 1600 mesh, 1700 mesh, 1800 mesh, 1900 mesh, 2000 mesh, 2100 mesh, or 2200 mesh.

[0097] In some specific embodiments, the cathode powder on the screen can be rinsed with water to remove small particles from the cathode powder. Ultrapure water is preferably used for rinsing to avoid the introduction of metal particles. After rinsing, the cathode powder on the screen can be rinsed onto filter paper in a suction filter for filtration. The filtered filter cake and filter paper are then placed in a container, and a portion of the first separating liquid is added for ultrasonic separation. After removing the filter paper, a suspension is obtained.

[0098] In some embodiments, the detection method includes one or more of: particle detector detection, Phenom scanning electron microscopy, spectrophotometry, titration, atomic emission spectrometry, X-ray fluorescence spectrometry, inductively coupled plasma spectrometry, and spark direct reading spectrometry. Of course, in addition to these detection methods, other detection methods commonly used in the art may also be used to detect the type and content of impurity metal particles.

[0099] The following examples further describe the present disclosure. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all reagents used in the examples are commercially available or synthesized according to conventional methods, and all instruments used in the examples are commercially available.

[0100] The lithium iron phosphate cathode powder used in the examples and comparative examples is from the same batch. For the same batch of cathode powder, a higher content of impurity metal particles is measured, which means a higher detection rate of the detection method.

[0101] Example 1

[0102] (1) Separation of impurity metal particles in cathode powder

[0103] 1kg of lithium iron phosphate cathode powder is placed in a 2000 mesh sieve, ultrapure water is added to the sieve to rinse the cathode powder, and the small particles in the cathode powder are removed. Repeat the addition of ultrapure water to the sieve to rinse the cathode powder until the small particles in the cathode powder are completely sieved out. Afterwards, the cathode powder on the sieve is rinsed onto the filter paper of the suction filter for suction filtration, and the filtered filter paper and the filter cake are placed in a beaker, and 150ml of 75% alcohol by volume (density ρ1 is 0.85g / ml, i.e., the first separation liquid) is poured in for ultrasonic vibration separation, and then the filter paper is removed to obtain a suspension. 300ml of water (density ρ2 is 1g / ml, i.e., the second separation liquid) is poured into a chromatography column with a volume of 500ml, so that the water surface is higher than the first liquid outlet 100, and a water layer 20 is obtained, as shown in Figure 1. During the entire experimental process, the chromatography column remains stationary. Next, 10 ml of 75% alcohol by volume is slowly poured along the glass rod, allowing the alcohol and water to form separate layers, with the alcohol layer reaching a height of approximately 10-20 mm. Immediately thereafter, the entire suspension is slowly added to the alcohol in the chromatography column along the glass rod, forming an alcohol layer 10. After standing, the impure metal particles in the cathode powder settle to the bottom of the water layer 20, forming an impure metal particle layer 30. Other cathode powder particles are intercepted by the alcohol layer above, resulting in a black upper alcohol layer and a transparent lower water layer.

[0104] (2) Collecting impurity metal particles

[0105] Open the first liquid outlet 100 and slowly drain the liquid until all the liquid above the first liquid outlet 100 is drained. Then, open the second liquid outlet 200 and drain the liquid. Collect the impure metal particles flowing out of the second liquid outlet 200 into a beaker. Filter the impure metal particles onto filter paper, place the filter paper in a clean glass dish, add glue to secure the impure metal particles, and then dry. The time from stratification to the end of collection is controlled to 200 seconds, and the stratification state is maintained throughout this period.

[0106] (3) Detect the content and type of impurity metal particles

[0107] The weight of the impurity metal particles collected in step 2 was measured using a Phenom scanning electron microscope (SEM), recorded as m (kg). The content of the impurity metal particles in the cathode powder, ω, was calculated as (m ÷ 1) × 100%. The elemental composition of the impurity metal particles was also determined using a SEM. The results are shown in Table 1 below.

[0108] Table 1

[0109] Example 2: Verification of the accuracy of the detection method through spike recovery experiments

[0110] The method described in Example 1 was followed, except that 10 g of metallic Fe particles with a particle size of 50-100 μm were added to 1 kg of the lithium iron phosphate cathode powder before the powder was placed through a 2000-mesh sieve. The test results are shown in Table 2 below.

[0111] Table 2

[0112] It can be seen from the spiked recovery experiment of Example 2 that the detection method of Example 1 can accurately detect the impurity metal particles in the cathode powder with an accuracy of up to 95%.

[0113] Examples 3-6

[0114] The method described in Example 1 was followed, except that the parameters listed in Table 3 below were different. The test results are shown in Table 3 below.

[0115] Table 3

[0116] Examples 7-10

[0117] The method described in Example 1 was followed, except that the parameters listed in Table 4 below were different. The test results are shown in Table 4 below.

[0118] Table 4

[0119] Examples 11-13

[0120] The method described in Example 1 was followed, except that the time from formation of the layers to the end of collection was controlled as shown in Table 5. The test results are shown in Table 5.

[0121] Table 5

[0122] Example 14

[0123] The method described in Example 1 was followed, except that after the impure metal particles settled to the bottom of the water layer, the second liquid outlet was opened directly to quickly drain the liquid, and the impure metal particles were collected in a beaker. The test results are shown in Table 6 below.

[0124] Table 6

[0125] Examples 15-16

[0126] The method described in Example 1 was followed, except that the mesh sizes of the sieves used were different, as shown in Table 7. The test results are shown in Table 7.

[0127] Table 7

[0128] Comparative Example 1

[0129] The method described in Example 1 was followed, except that the filter paper after suction filtration and the filter cake were placed in a beaker, 150 ml of water (the second separating liquid) was poured into the beaker for ultrasonic separation, and the filter paper was removed to obtain a suspension. After the suspension was slowly added to the alcohol in the chromatography column along a glass rod, the stratification state in the chromatography column was destroyed, the upper layer of alcohol and the lower layer of water became mutually soluble, and the impurity metal particles in the cathode powder could not be separated.

[0130] It can be seen from the above embodiments and comparative examples that the present application can effectively separate the impurity metal particles in the cathode powder, and can detect the content and type of impurity metal particles with high efficiency and high detection rate, and can provide certain data support for the level of impurity metal particles in the incoming material.

[0131] The foregoing description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed herein are intended to be encompassed within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for separating impure metal particles from cathode powder, wherein: The method comprises: Providing a first separation liquid and a second separation liquid, wherein the density of the second separation liquid is greater than the density of the first separation liquid, and the density of the second separation liquid is less than the density of the impurity metal particles in the cathode powder; Mixing cathode powder with a portion of the first separation liquid to form a suspension; adding the second separation liquid into a container, and adding another portion of the first separation liquid into the container to form layers; and The suspension is added to the container with the stratified solution, so that the impurity metal particles sink to the bottom of the second separation liquid, thereby achieving separation.

2. The method according to claim 1, wherein: The density of the first separation liquid is denoted as ρ1, the density of the second separation liquid is denoted as ρ2, the difference between ρ2 and ρ1 is denoted as Δρ, and Δρ is greater than 0.

1.

3. The method according to claim 2, wherein: Dr is 0.1-0.83g / cm 3 。 4. The method according to any one of claims 1 to 3, wherein: The first separation liquid includes: a mixture of ethanol and water, a mixture of ethanol and benzene, ethanol, or benzene.

5. The method according to any one of claims 1 to 4, wherein: The second separation liquid includes one or more of water, dichloromethane, chloroform, carbon tetrachloride, and perchloroethylene.

6. The method according to claim 4, wherein: The first separation liquid comprises a mixture of ethanol and water, and the volume percentage of ethanol is 48%-90%.

7. The method according to any one of claims 1 to 6, wherein: The cathode powder includes a cathode active material; the cathode active material includes lithium iron phosphate.

8. The method according to any one of claims 1 to 7, wherein: The other portion of the first separated liquid is slowly added to form layers.

9. The method according to any one of claims 1 to 8, wherein: The suspension was added slowly to maintain the layered state.

10. The method according to any one of claims 1 to 9, wherein: The container is kept still at all times to maintain the stratified state.

11. The method according to any one of claims 1 to 10, wherein: The method further comprises: After the impurity metal particles sink to the bottom of the second separation liquid, the impurity metal particles are collected.

12. The method according to claim 11, wherein: The time from the formation of the stratification to the end of the collection is controlled to maintain the stratification state.

13. The method according to claim 11, wherein: The container comprises a columnar container, a first liquid outlet is provided on the side wall of the columnar container, and a second liquid outlet is provided at the bottom of the columnar container; adding the second separation liquid into the container so that the liquid level of the second separation liquid is higher than the first liquid outlet; Collecting the impurity metal particles includes: opening the first liquid outlet to discharge liquid until the liquid above the first liquid outlet is completely discharged, and then opening the second liquid outlet to discharge liquid after completion.

14. A method for detecting impure metal particles in cathode powder, wherein: The method comprises: The method according to any one of claims 1 to 13, separating impure metal particles in the cathode powder, and weighing the cathode powder before mixing the cathode powder with a portion of the first separation liquid; The type and / or weight of the separated impurity metal particles are detected, the content of the impurity metal particles in the cathode powder is calculated, and the element type of the impurity metal particles is detected.

15. The method according to claim 14, wherein: After weighing the cathode powder and before mixing the cathode powder with a portion of the first separation liquid, the method further comprises: The cathode powder is sieved to remove small particles in the cathode powder.

16. The method according to claim 15, wherein: The mesh number of the sieve used in the screening is 1200-2200 mesh.

17. The method according to any one of claims 14 to 16, wherein: The method for detecting the type and / or weight of the separated impurity metal particles includes: one or more of a particle detector detection method, a Phenomenon scanning electron microscope detection method, a spectrophotometer, a titration method, an atomic emission spectrometry method, an X-ray fluorescence spectrometry method, an inductively coupled plasma spectrometry method, and a spark direct reading spectrometry method.

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