Method for separating negative electrode material and current collector of lithium ion battery

Abstract

The invention discloses a method for separating a negative electrode material and a current collector of a lithium ion battery, and relates to the technical field of lithium ion battery recovery, and the method comprises the following steps: crushing a battery negative electrode sheet to obtain a crushed material; adding the crushed material and water into a stirrer, and fully stirring for 30 minutes to obtain a mixed material solution; enabling the mixed material solution to automatically flow to a screen belt for vibrating screening and washing to obtain an oversize material current collector and an undersize material negative electrode material suspension; filtering the screen underflow to obtain a filter cake negative electrode material and filtrate water, and enabling the filtrate water to flow back to the step S2 for cyclic utilization; the steps are continuously carried out; through continuous processes of crushing, mixing, stirring, screening, washing and filtering, a complete negative electrode material and current collector recovery process is formed, and the method has the advantages of simple process, low material recovery cost, environmental protection, no pollution, low product impurity content and the like, and is beneficial to industrial application of the technology.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery recycling, and in particular to a method for separating a negative electrode material and a current collector of a lithium ion battery. Background Art

[0002] Commonly used negative electrode sheets of lithium batteries mainly include current collectors (copper foil), negative electrode materials (graphite) and binders. The negative electrode materials are coated on the surface of the current collector by the binder. Since graphite has a wide source in the traditional sense and has low added value in recycling, negative electrode recycling in actual applications mainly focuses on the recovery of metal copper in the current collector in negative electrode materials, resulting in reduced or wasted graphite activity. At present, negative electrode recycling is mainly divided into three methods: wet method, pyrolysis and mechanical separation. Wet recycling uses acid and alkali treatment to leach negative electrode metal materials with a high recovery rate, but the acid and alkali treatment process is difficult, has high safety risks, and requires large investment in environmental protection facilities. The pyrolysis recovery process is simple and uses high-temperature incineration or pyrolysis to remove graphite and binders from negative electrode sheets and separate metal copper, but there are problems such as high energy consumption and low recovery rate; mechanical separation uses physical crushing and sorting to separate graphite and metal copper, but it is affected by the binder and cannot be completely separated. The metal and graphite are mixed with each other, the product purity is affected, and the equipment requirements are high.

[0003] In response to these problems, the patent document with publication number CN114530641 A in the prior art discloses a method for recycling the negative electrodes of waste lithium-ion batteries, which separates the positive electrode material and the current collector by water immersion and then removes the impurity ions in the negative electrode material by organic acid immersion and carbon dioxide; the patent document with publication number CN 111792642A discloses a method and equipment for stripping the negative electrode sheets of retired batteries and deep impurity removal of graphite, which separates the current collector and graphite by water washing in a kettle with a filter basket, thereby realizing intermittent operation of the separation process.

[0004] The above patents have certain characteristics in their respective recovery technologies. However, the operation effect of continuous material input and output is still not achieved during the separation process, and the influence of metal impurities in the design of separation equipment still needs to be improved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for separating a negative electrode material and a current collector of a lithium ion battery to solve the following technical problems:

[0006] How to achieve better separation between the current collector and negative electrode material in the battery negative electrode sheet?

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for separating a negative electrode material and a current collector of a lithium-ion battery is carried out according to the following steps:

[0009] S1: crushing the negative electrode sheet of the battery to obtain crushed materials;

[0010] S2: Add the crushed material and water into a stirrer and stir thoroughly for 30 minutes to obtain a mixed solution;

[0011] S3: Allow the mixed solution to flow onto the screen belt for vibration screening and washing to obtain a screen-surface current collector and a screen-surface negative electrode material suspension;

[0012] S4: filtering the sieve material to obtain filter cake negative electrode material and filtrate water, and the filtrate water is refluxed to step S2 for recycling;

[0013] The steps S1-S4 are performed continuously.

[0014] In a further embodiment of the present invention: in step S1, the battery negative electrode sheet includes a negative electrode material and a current collector connected by an aqueous binder, wherein the material of the battery negative electrode sheet includes any one of graphite, tin-based, silicon-based, oxides, transition metal nitrides, silicon-carbon or any combination of multiple thereof.

[0015] In a further embodiment of the present invention: in step S1, the length and width of the crushed material are both 0.1-2 cm.

[0016] In a further embodiment of the present invention: in step S2, the mass ratio of the crushed material to water is 1:(0.5-10), preferably 1:(0.5-4), and more preferably 1:(0.5-1).

[0017] In a further embodiment of the present invention: in step S2, washing resin particles are also added to the agitator, wherein the washing resin particles include porous resin particles and detergent in a mass ratio of 3:(1-1.5); preferably 3:1.2.

[0018] In a further embodiment of the present invention, the washing resin particles are added in an amount of 15% of the crushed material.

[0019] In a further embodiment of the present invention: the preparation method of the washing resin particles is: the porous resin particles are ultrasonically mixed with a detergent, and then transferred to a heating box for drying, and then vibrated and granulated to obtain the washing resin particles;

[0020] Preferably, the drying temperature is 80°C and the drying time is 2h;

[0021] Preferably, the particles are vibrated and classified by a vibrating screen.

[0022] In a further embodiment of the present invention, the porous resin particles are polymer adsorption resins, preferably D101 macroporous adsorption resins.

[0023] In a further embodiment of the present invention, the detergent is a surfactant, including but not limited to one or more of sodium alkylbenzene sulfonate, polyoxyethylene ether, and quaternary ammonium salt.

[0024] In the washing resin particles, the detergent is loaded through the mesopores of the porous resin particles. When the porous resin particles come into contact with water, the detergent therein dissolves in the water. The formed detergent solution can dissolve the binder between the negative electrode material and the current collector in the crushed material, thereby accelerating the separation of the current collector from the negative electrode material. When the binder is dissolved by the detergent, under the action of stirring, the binder is absorbed by the mesopores of the porous resin particles vacated by the dissolution of the detergent, which is beneficial to the desorption and separation of the binder from the current collector, thereby obtaining a current collector with no adhesive residue on its adhesive surface.

[0025] Beneficial effects of the present invention:

[0026] (1) The present invention forms a complete negative electrode material and current collector recovery process through a continuous process of crushing, mixing, stirring, screening, washing and filtering. The process is simple, the material recovery cost is low, and the environment is environmentally friendly and pollution-free. By adjusting the ratio of crushed material to water and the stirring time, the impurity content of the product is minimized, which is conducive to the industrial application of technology.

[0027] (2) The washing resin particles added in the method of the present invention are loaded with detergent through the mesopores of the porous resin particles. When the porous resin particles come into contact with water, the detergent therein dissolves in the water. The formed detergent solution can dissolve the binder between the negative electrode material and the current collector in the crushed material, thereby accelerating the separation of the current collector from the negative electrode material. When the binder is dissolved by the detergent, under the action of stirring, the binder is absorbed by the mesopores of the porous resin particles vacated by the dissolution of the detergent, which is beneficial to the desorption and separation of the binder from the current collector, so that the adhesive surface of the obtained current collector is free of adhesive residue, which can reduce the impurity content when the current collector is recovered and improve the separation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] Figure 1 It is a flow chart of the method for separating the negative electrode material and the current collector of a lithium ion battery of the present invention;

[0030] Figure 2 Schematic diagram of the structure of a stirring separator in a device for separating negative electrode materials and current collectors of lithium-ion batteries in an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the structure of a cleaning screen in a device for separating negative electrode materials and current collectors of lithium-ion batteries in an embodiment of the present invention.

[0032] In the figure: 1. stirring separator; 101. separator housing; 102. separator inlet; 103. separator outlet; 104. jet tube; 105. stirring mechanism 1; 106. stirring mechanism 2; 107. brush; 108. spoiler; 109. anti-short flow baffle; 2. cleaning screener; 201. screener housing; 202. screener inlet; 203. collector outlet; 204. suspension outlet; 205. screen; 206. vibration mechanism; 207. flushing nozzle. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0034] See also Figure 1 The present invention discloses a method for separating a negative electrode material and a current collector of a lithium ion battery, which is carried out according to the following steps:

[0035] S1: crush the negative electrode sheet of the battery to obtain crushed materials with a length and width of 0.1-2 cm;

[0036] The battery negative electrode sheet includes a negative electrode material and a current collector connected by an aqueous binder, wherein the negative electrode material of the battery negative electrode sheet includes any one or any combination of graphite, tin-based, silicon-based, oxide, transition metal nitride, silicon-carbon.

[0037] S2: Add the crushed material and water into a stirrer and stir thoroughly for 30 minutes to obtain a mixed solution;

[0038] The mass ratio of crushed material to water is 1:(0.5-10);

[0039] Furthermore, washing resin particles can be added to the agitator in an amount of 15% of the crushed material; the washing resin particles include porous resin particles (polymer adsorption resin, such as D101 macroporous adsorption resin) and detergent (surfactant, including but not limited to one or more of sodium alkylbenzene sulfonate, polyoxyethylene ether, and quaternary ammonium salt) in a mass ratio of 3: (1-1.5), and the preparation method is: the porous resin particles and the detergent are ultrasonically mixed and then transferred to a heating box for drying (dried at 80°C for 2h), and then a vibrating screen is used for vibration and particle classification to obtain the washing resin particles.

[0040] S3: Allow the mixed solution to flow onto the screen belt for vibration screening and washing to obtain a screen-surface current collector and a screen-surface negative electrode material suspension;

[0041] S4: filtering the sieve material to obtain filter cake negative electrode material and filtrate water, and the filtrate water is refluxed to step S2 for recycling;

[0042] The crushing, mixing, stirring, screening, washing and filtering in steps S1-S4 are performed continuously in sequence.

[0043] See also Figure 2-3 The present invention also discloses a device for separating the negative electrode material and the current collector of the above-mentioned lithium-ion battery, including a stirring separator 1 and a cleaning screen 2, both of which will be introduced in detail below.

[0044] Figure 2 The stirring separator 1 comprises a separator shell 101 , a separator inlet 102 is arranged at the top of the left end, and a separator outlet 103 is arranged at the top of the right end, and the height of the separator outlet 103 is lower than the height of the separator inlet 102 to ensure that the solution can flow out from the separator outlet 103 by itself.

[0045] A stirring mechanism 1 105 and a stirring mechanism 2 106 with exactly the same structure are arranged side by side inside the separator shell 101. The specific structures of the two are not limited as long as the stirring requirements are met. For example, the stirring mechanism 105 and the stirring mechanism 2 106 are both a combination structure including a stirring shaft, a motor for driving the stirring shaft to rotate, and a stirring paddle installed on the stirring shaft, and a brush 107 is provided on the stirring paddles of both to enhance the stirring and washing effects; an anti-short flow baffle 109 is provided between the stirring mechanism 1 105 and the stirring mechanism 2 106, and the anti-short flow baffle 109 is used to limit the flow path of the solution, increase the residence time, and prevent the solution from flowing directly from the upper part of the tank body to the separator outlet 103.

[0046] A jet tube 104 is installed at the bottom of the separator shell 101, and the input end of the jet tube 104 is connected to a water inlet pump, and a plurality of jet nozzles are installed on the jet tube 104. The jet tube 104, the water inlet pump and the jet nozzle constitute a jet mechanism. The water inlet pump pumps water into the jet tube 104, and the water is sprayed into the separator shell 101 through the jet nozzle to achieve water inlet; at the same time, a spoiler 108 is also installed on the inner wall of the separator shell 101 to prevent the solution from rotating in the same direction to form vortexes and laminar flow, and can promote the mutual friction and collision of solids in the separator shell 101 and the contact with the stirring paddle, thereby enhancing the stirring and separation effect.

[0047] The method of using the stirring separator 1 is as follows: the crushed material of the battery negative electrode sheet is put into the separator shell 101 from the separator inlet 102, and then a certain proportion of water is injected into the separator shell 101 through the jet mechanism, and then the stirring mechanism 1 105 and the stirring mechanism 2 106 are turned on, and the stirring paddles of the two are made to rotate in opposite directions. The brush 107 on the stirring paddle stirs and separates the crushed material, thereby separating the current collector and the negative electrode material of the crushed material. After the stirring is completed, the mixed solution of the current collector, the negative electrode material and the water flows out from the separator outlet 103 and then cleans the sifter 2.

[0048] Figure 3 The cleaning screen 2 comprises a screen housing 201, a screen inlet 202 is arranged at the top of the right end of the screen housing 201, a collector outlet 203 and a suspension outlet 204 are arranged at the bottom of the left end, a linear screen 205 is arranged in the cleaning screen 2, a vibration mechanism 206 is arranged at the bottom of the cleaning screen 2, and the screen 205 and the vibration mechanism 206 together constitute a linear vibrating screen; one end of the screen 205 is connected to the screen inlet 202, and the other end is connected to the collector outlet 203, so as to divide the interior of the cleaning screen housing 201 into two parts, the upper and lower parts; the mesh diameter of the screen 205 is 50 mesh, and the inclination angle is greater than 2°, so that the collector can slide smoothly to the collector outlet 203.

[0049] A plurality of flushing nozzles 207 are arranged on the inner top wall of the screen housing 201, and the flushing nozzles 207 are connected to a water pump to achieve water intake; the flushing nozzles 207 are installed in the form of a gantry on the top of the rear section of the linear vibrating screen to flush the collector during the vibrating screen process.

[0050] The method for using the cleaning screen 2 is as follows: the mixed solution enters the screen housing 201 through the screen inlet 202 and falls on the screen 205. The screen 205 vibrates under the action of the vibration mechanism 206, and the flushing nozzle 207 flushes the rear half of the screen 205, thereby leaving the collector on the screen 205, and the negative electrode material and water in the mixed solution fall from the mesh of the screen 205. Finally, the screened material collector is discharged from the collector outlet 203, and the suspension of the negative electrode material and water is discharged from the suspension outlet 204; wherein, the suspension is filtered after being discharged to obtain the filter cake negative electrode material and the filtrate water, and the filtrate water can be returned to step S2 for recycling, which is more energy-saving and environmentally friendly.

[0051] Next, the above-mentioned equipment is used to implement the method for separating the negative electrode material and the current collector of a lithium-ion battery of the present invention, as follows.

[0052] Example 1

[0053] A hammer crusher is used to crush 5 kg of negative electrode sheets (the negative electrode material is graphite) into fragments of about 0.5 CM-1 CM in size, and the fragments are added into the stirring separator 1. 2.5 kg of water (the mass ratio of the crushed material to water is 1:0.5) is injected through the jet mechanism. After the stirring mechanism 1 105 and the stirring mechanism 2 106 are turned on and stirred for 30 minutes, the mixed solution is allowed to flow into the cleaning screen 2 by gravity, and is separated by vibration by a linear vibrating screen machine. At the same time, it is rinsed by a flushing nozzle 207 to separate the current collector and the negative electrode material in the mixture. The material on the screen is the current collector, which is discharged from the current collector outlet 203, and the material under the screen is a suspension of the negative electrode material and water, which is discharged from the suspension outlet 204.

[0054] Example 2

[0055] Compared with Example 1, the only difference is that the water injected by the jet mechanism is increased from 2.5 kg to 5 kg (the mass ratio of crushed material to water is 1:1), and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0056] Example 3

[0057] Compared with Example 1, the only difference is that the water injected by the jet mechanism is increased from 2.5 kg to 10 kg (the mass ratio of crushed material to water is 1:2), and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0058] Example 4

[0059] Compared with Example 1, the only difference is that the water injected by the jet mechanism is increased from 2.5 kg to 15 kg (the mass ratio of crushed material to water is 1:3), and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0060] Example 5

[0061] Compared with Example 1, the only difference is that the water injected by the jet mechanism is increased from 2.5 kg to 5 kg (the mass ratio of crushed material to water is 1:1), and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0062] The oversize current collectors obtained in Examples 1-5 were dried in a nitrogen atmosphere respectively, and then weighed to calculate the weight ratio of the oversize current collector relative to the crushed material, and the calculation results are listed in Table 1, which is shown below:

[0063] Table 1

[0064] Corresponding embodiment Example 1 Example 2 Example 3 Example 4 Example 5 Mass ratio of crushed material to water 1:0.5 1:1 1:2 1:3 1:4 Weight percentage of oversize (100%) 34.04 34.20 36.07 39.8 45.30

[0065] By analyzing the data in Table 1, it can be seen that the weight proportion of the oversize in Examples 1-2 is lower, which can explain that the greater the proportion of water added, the greater the impact on the mutual friction and stirring effect of the fragments in the stirring tank, resulting in some negative electrode materials being unable to be peeled off from the current collector. Therefore, the weight proportion of the oversize in Examples 3-5 is higher; however, too low an amount of water added will also cause the fragments to be unable to suspend and flow in the solution. Therefore, from the perspective of recovery effect, the optimal addition ratio of crushed material to water should be 1:(0.5-1).

[0066] Example 6

[0067] Compared with Example 2, the only difference is that the stirring time is shortened from 30 min to 15 min, and other conditions are exactly the same, and finally an oversize fluid collector and an undersize suspension are obtained.

[0068] Example 7

[0069] Compared with Example 2, the only difference is that the stirring time is increased from 30 min to 45 min, and other conditions are exactly the same, and finally an oversize fluid collector and an undersize suspension are obtained.

[0070] Example 8

[0071] Compared with Example 2, the only difference is that the stirring time is increased from 30 min to 15 min, and other conditions are exactly the same, and finally an oversize fluid collector and an undersize suspension are obtained.

[0072] The oversize fluid collectors obtained in Example 2 and Examples 6-8 were dried in a nitrogen atmosphere, and then the weight ratio of the oversize fluid collectors to the crushed material was weighed and calculated, and the calculation results were listed in Table 2, which is shown below:

[0073] Table 2

[0074] Corresponding embodiment Example 6 Example 2 Example 7 Example 8 Stirring time (min) 15 30 45 60 Weight percentage of oversize (100%) 36.88 34.20 34.14 34.08

[0075] By analyzing the data in Table 2, it can be seen that as the stirring time increases, the weight percentage of the sieve material gradually decreases, indicating that the more thoroughly the negative electrode material is stripped, after the stirring time exceeds 30 minutes, the weight percentage of the sieve material basically remains constant. At this time, the negative electrode material is basically completely stripped from the current collector. Therefore, the optimal stirring time for the crushed material and water should be 30 minutes.

[0076] Example 9

[0077] Compared with Example 2, the only difference is that 0.75 g of washing resin particles are added when the crushed material is added to the stirring separator 1, and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0078] The preparation steps of the washing resin particles are as follows: ultrasonically mix D101 macroporous adsorption resin (>50 mesh) and sodium alkylbenzene sulfonate in a mass ratio of 3:1, transfer to a heating box and dry at 80°C for 2h, and then use a vibrating screen to vibrate and classify the particles to obtain the washing resin particles.

[0079] Example 10

[0080] Compared with Example 9, the only difference is that the mass ratio of D101 macroporous adsorption resin to sodium alkylbenzene sulfonate in the washing resin particles is 3:1.2, and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0081] Embodiment 11

[0082] Compared with Example 9, the only difference is that the mass ratio of D101 macroporous adsorption resin to sodium alkylbenzene sulfonate in the washing resin particles is 3:1.5, and other conditions are exactly the same, and finally an oversize collector and an undersize suspension are obtained.

[0083] The oversize fluid collectors obtained in Example 2 and Examples 9-11 were dried in a nitrogen atmosphere, and then the weight ratio of the oversize fluid collectors to the crushed material was weighed and calculated, and the calculation results were listed in Table 3, which is shown below:

[0084] Table 3

[0085]

[0086] By analyzing the data in Table 3, it can be seen that the weight proportion of the oversize in Examples 9-11 is less than that in Example 2, which indicates that the addition of washing resin particles is beneficial to removing the adhesive on the current collector, thereby reducing the weight proportion of the oversize; among Examples 9-11, the weight proportion of the oversize in Example 10 is the lowest, which indicates that the optimal mass ratio of D101 macroporous adsorption resin and sodium alkylbenzene sulfonate in the washing resin particles should be 3:1.2.

[0087] In the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction and a specific direction structure and operation, and therefore, cannot be understood as a limitation on the present invention. In addition, "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0088] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0089] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for separating a negative electrode material and a current collector of a lithium ion battery, characterized in that: Follow these steps: S1: crushing the negative electrode sheet of the battery to obtain crushed materials; S2: Add the crushed material and water into a stirrer and stir thoroughly for 30 minutes to obtain a mixed solution; S3: Allow the mixed solution to flow onto the screen belt for vibration screening and washing to obtain a screen-surface current collector and a screen-surface negative electrode material suspension; S4: filtering the sieve material to obtain filter cake negative electrode material and filtrate water, and the filtrate water is refluxed to step S2 for recycling; The steps S1-S4 are performed continuously.

2. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 1, characterized in that: In step S1, the battery negative electrode sheet includes a negative electrode material and a current collector connected by an aqueous binder, wherein the material of the battery negative electrode sheet includes any one of graphite, tin-based, silicon-based, oxide, transition metal nitride, silicon-carbon or any combination of multiple thereof.

3. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 1, characterized in that: In step S1, the length and width of the crushed material are both 0.1-2 cm.

4. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 1, characterized in that: In step S2, the mass ratio of the crushed material to water is 1:(0.5-10).

5. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 1, characterized in that: In step S2, washing resin particles are also added to the agitator, wherein the washing resin particles include porous resin particles and a detergent in a mass ratio of 3:(1-1.5).

6. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 5, characterized in that: The washing resin particles were added in an amount of 15% of the crushed material.

7. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 5, characterized in that: The preparation method of the washing resin particles is as follows: the porous resin particles are ultrasonically mixed with a detergent, and then transferred to a heating box for drying, and then vibrated and granulated to obtain the washing resin particles.

8. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 5, characterized in that: The porous resin particles are polymer adsorption resins.

9. The method for separating the negative electrode material and the current collector of a lithium ion battery according to claim 5, characterized in that: The detergent is a surfactant.

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