Negative electrode slurry and preparation method thereof, negative electrode pole piece, alkali metal ion battery and slurry homogenizing device

Abstract

The invention provides negative electrode slurry and a preparation method thereof, a negative electrode pole piece, a lithium ion battery and a slurry homogenizing device, and belongs to the technical field of alkali metal ion batteries. The negative electrode slurry contains a negative electrode active material, a negative electrode binder, a negative electrode conductive agent and a negative electrode solvent, the negative electrode binder contains 0-1% by mass of carboxymethyl cellulose and 0-1% by mass of butadiene styrene rubber, and the total mass of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent is 100%. The negative electrode slurry contains nano bubbles, and the Dv50 of the nano bubbles is less than or equal to 1000nm. Compared with the negative electrode paste in the prior art, the negative electrode paste disclosed by the invention does not contain CMC or contains a relatively low proportion of CMC, and the electrochemical performance of the battery cell and the volume expansion in the circulation or storage process are improved while a good dispersion effect on negative electrode particles is achieved.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal ion battery technology, specifically relating to a negative electrode slurry and its preparation method, a negative electrode sheet and an alkali metal ion battery, and a homogenizing device. Background Technology

[0002] Current alkali metal ion battery negative electrode slurries primarily use graphite, hard carbon, and other materials as negative electrode active materials, conductive carbon black (SP) and other materials as negative electrode conductive agents, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as negative electrode binders, and water as a negative electrode solvent. The Dv50 of CMC in current alkali metal ion battery negative electrode slurries is generally 5μm to 50μm. Taking the total mass of the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent as 100%, the mass fraction of CMC is generally greater than 0 and less than or equal to 2%. CMC is a polyanionic water-soluble polymer. CMC carries a negative charge on its surface. When CMC adsorbs onto the surface of negative electrode particles such as the negative electrode active material and the negative electrode conductive agent, it causes the surface of the negative electrode particles to carry a negative charge. The repulsion between like charges achieves the effect of dispersing the negative electrode particles. The zeta potential of this negative electrode slurry is generally -35mV to -55mV, and its intensity is generally 0.15 to 0.25. Under these conditions, the dispersion uniformity of the negative electrode particles is good. It should be noted that the zeta potential of this negative electrode slurry refers to the sliding plane potential of the liquid-phase dispersed particles (i.e., the negative electrode particles adsorbed with CMC) in the negative electrode slurry.

[0003] Taking the preparation method of alkali metal ion battery negative electrode slurry using CMC and SBR as negative electrode binders as an example, the preparation method includes the following steps: S1. Adding negative electrode solvent into a homogenizing device; S2. Adding CMC into the homogenizing device and mixing it with the negative electrode solvent to obtain a colloid; S3. Adding negative electrode active material and negative electrode conductive agent into a homogenizing tank and mixing them to obtain a mixed dry material; S4. Adding the colloid to the homogenizing tank step by step and mixing it with the mixed dry material until the slurry viscosity reaches the expected viscosity, then stopping the addition of colloid; S5. Adding SBR into the homogenizing tank and dispersing it evenly to obtain the negative electrode slurry.

[0004] Without CMC, the negative electrode particles will agglomerate, leading to uneven capacity distribution on the negative electrode surface and potentially causing lithium plating. Furthermore, the increased local expansion during charging and discharging can cause particle breakage and electrolyte drying, resulting in capacity loss and affecting cell safety. While adding CMC can disperse the negative electrode particles and alleviate agglomeration, it also negatively impacts the cell's electrochemical performance and volume expansion during cycling or storage. Additionally, adding CMC increases production costs. Therefore, the key challenge is to reduce the proportion of CMC in the negative electrode slurry, or even eliminate it completely, to achieve good particle dispersion while simultaneously improving the cell's electrochemical performance and reducing volume expansion during cycling or storage. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a negative electrode slurry and its preparation method, a negative electrode sheet and a lithium-ion battery, and a homogenizing device. Compared to existing negative electrode slurries, the negative electrode slurry of this invention can be CMC-free or contain a low proportion of CMC, achieving good dispersion of negative electrode particles while improving the electrochemical performance of the battery cell and reducing volume expansion during cycling or storage.

[0006] In a first aspect, embodiments of the present invention provide a negative electrode slurry containing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a negative electrode solvent. The negative electrode binder contains carboxymethyl cellulose and styrene-butadiene rubber. The carboxymethyl cellulose has a mass fraction of 0-1%, based on the total mass of the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent being 100%. The negative electrode slurry contains nanobubbles, and the Dv50 of the nanobubbles is less than or equal to 1000 nm.

[0007] The advantages and technical effects of the negative electrode slurry in this invention are as follows:

[0008] (1) The surface of the nanobubbles carries a negative charge. When the nanobubbles are adsorbed on the surface of the negative electrode particles, the surface of the negative electrode particles will carry a negative charge. The negative electrode particles can be dispersed by the mutual repulsion of like charges. This effect is consistent with the effect of CMC.

[0009] (2) In the prior art, the Dv50 of CMC in the negative electrode slurry is 5μm to 50μm, while the Dv50 of nanobubbles in the negative electrode slurry of the present invention is less than or equal to 1000nm, which has a smaller scale than CMC. Therefore, compared with CMC, nanobubbles have a larger specific surface area, which can make the Zeta potential of the negative electrode slurry smaller and the dispersion effect of negative electrode particles better.

[0010] (3) Compared with the negative electrode slurry in the prior art, the negative electrode slurry of the present invention partially or completely replaces CMC by introducing nanobubbles with Dv50 less than or equal to 1000nm, which can reduce the Zeta potential of the negative electrode slurry and achieve a good dispersion effect on the negative electrode particles.

[0011] (4) Nanobubbles with Dv50 less than or equal to 1000 nm have good stability and can exist stably in the negative electrode slurry for a long time.

[0012] (5) Subsequently, the negative electrode slurry of the present invention is applied to the negative electrode current collector and the negative electrode sheet semi-finished product is dried. The nano bubbles escape, but since the negative electrode particles in the negative electrode system are uniformly dispersed in the liquid state, the gap between the negative electrode particles in the negative electrode active layer obtained after drying remains unchanged. That is to say, the dispersion state between the negative electrode particles is still maintained, and the negative electrode particles will not agglomerate again during the drying process. Therefore, the present invention adds nano bubbles to the negative electrode system to partially or completely replace CMC, which can make the negative electrode particles in the negative electrode active layer uniformly dispersed.

[0013] (6) In the prior art, the mass fraction of CMC in the negative electrode slurry is greater than 0 and less than or equal to 2% when the total mass of the negative electrode active material, negative electrode binder and negative electrode conductive agent is 100%. However, in the negative electrode slurry of the present invention, the mass fraction of CMC is 0 to 1% when the total mass of the negative electrode active material, negative electrode binder and negative electrode conductive agent is 100%. Since the proportion of CMC in the negative electrode slurry is reduced or there is no CMC at all, the electrochemical performance of the cell and the expansion during cycling or storage can be improved.

[0014] (7) The negative electrode slurry of the present invention can reduce the CMC ratio or even make the CMC ratio 0 by introducing nano bubbles with Dv50 less than or equal to 1000nm, thereby optimizing production costs.

[0015] In some embodiments, the Dv50 of the nanobubbles is less than or equal to 500 nm.

[0016] In some embodiments, the zeta potential of the negative electrode slurry is less than or equal to -40mV.

[0017] In some embodiments, the zeta potential of the negative electrode slurry is -80mV to -40mV.

[0018] In some embodiments, the intensity of the zeta potential of the negative electrode slurry is 0.25 to 0.3.

[0019] Secondly, embodiments of the present invention provide a method for preparing a negative electrode slurry, comprising the following steps:

[0020] S1. A homogenizing device is provided, the homogenizing device comprising a first homogenizing tank and an ejector disposed on the first homogenizing tank, wherein the outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank; a negative electrode solvent and a gas source are added into the first homogenizing tank through the ejector, wherein the flow rate of the negative electrode solvent is greater than 0.5 m / s, thereby obtaining a negative electrode solvent containing nanobubbles;

[0021] S2. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the carboxymethyl cellulose is added to the first homogenizing tank and mixed with the negative electrode solvent containing nanobubbles to obtain a mixture;

[0022] When the mass fraction of carboxymethyl cellulose is 0, S2 is not performed;

[0023] S3. The negative electrode active material and the negative electrode conductive agent are added to the second homogenizing tank and mixed to obtain a mixed dry material;

[0024] S4. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the mixture is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product.

[0025] When the mass fraction of the carboxymethyl cellulose is 0, the negative electrode solvent containing nanobubbles is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product.

[0026] S5. The styrene-butadiene rubber is added to the second homogenizing tank and mixed with the negative electrode slurry semi-finished product to obtain the negative electrode slurry.

[0027] The advantages and technical effects of the preparation method of this invention are as follows:

[0028] (1) The preparation method of the present invention uses the homogenizing device provided in the fifth aspect of the present invention to complete step S1. The homogenizing device is provided with an ejector on the first homogenizing tank. The outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank. Therefore, during the process of adding the negative electrode solvent into the first homogenizing tank, the ejector is used to form a liquid medium rich in nanobubbles, thereby achieving the purpose of introducing nanobubbles into the negative electrode slurry.

[0029] (2) In step S1, the flow rate of the negative electrode solvent is greater than or equal to 0.5 m / s, so that the Dv50 of the generated nanobubbles is less than or equal to 1000 nm.

[0030] (3) The preparation method of this invention adds nanobubbles with Dv50 less than or equal to 1000 nm to the negative electrode system to partially or completely replace CMC, which can achieve a good negative electrode particle dispersion effect, improve the electrochemical performance of the battery cell and the expansion during cycling or storage. In addition, reducing the CMC ratio to 0 can also optimize production costs.

[0031] Thirdly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one side of the current collector, wherein the negative electrode active layer is prepared from the negative electrode slurry described in the first aspect.

[0032] The advantages and technical effects of the negative electrode sheet in this embodiment of the invention are as follows:

[0033] Since the negative electrode active layer of the negative electrode sheet is prepared by using the negative electrode slurry described in the first aspect in the embodiments of the present invention, the negative electrode particles of the negative electrode sheet of the embodiments of the present invention have better dispersion uniformity compared with the negative electrode sheets in the prior art. In addition, the negative electrode sheet of the embodiments of the present invention has better electrochemical performance, and the volume expansion of the negative electrode sheet during cycling and storage is also smaller. Furthermore, the production cost of the negative electrode sheet of the embodiments of the present invention is lower.

[0034] Fourthly, embodiments of the present invention provide a lithium-ion battery, including the negative electrode sheet described in the third aspect.

[0035] The advantages and technical effects of the lithium-ion battery of this invention are as follows:

[0036] Since the embodiments of the present invention use the negative electrode sheet described in the third aspect to assemble lithium-ion batteries, the negative electrode particles of the lithium-ion batteries of the embodiments of the present invention have better dispersion uniformity compared with lithium-ion batteries in the prior art. In addition, the lithium-ion batteries of the embodiments of the present invention have better electrochemical performance and smaller volume expansion during cycling and storage. Furthermore, the production cost of the lithium-ion batteries of the embodiments of the present invention is lower.

[0037] Fifthly, embodiments of the present invention provide a homogenizing device, including a first homogenizing tank and an ejector disposed on the first homogenizing tank, wherein the outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank.

[0038] The advantages and technical effects of the homogenizing device of this invention are as follows:

[0039] In the homogenizing apparatus of this invention, a jet injector is provided on the first homogenizing tank. The outlet of the diffuser tube of the jet injector is connected to the inner cavity of the first homogenizing tank. When the negative electrode solvent is added to the first homogenizing tank through the jet injector, the gas source is simultaneously drawn into the jet injector by utilizing the Venturi effect of the jet injector, thereby generating nanobubbles and mixing the nanobubbles into the negative electrode solvent. The Dv50 of the nanobubbles can be adjusted by adjusting the flow rate of the negative electrode solvent. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the homogenizing device according to an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the jet ejector of the homogenizing device according to an embodiment of the present invention;

[0042] Explanation of reference numerals in the attached figures:

[0043] 1-First homogenizing tank; 11-Inner cavity; 2-Ejector; 21-Nozzle; 22-Suction pipe; 23-Gas chamber; 24-Mixing pipe; 25-Diffuser pipe. Detailed Implementation

[0044] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0045] In a first aspect, embodiments of the present invention provide a negative electrode slurry, wherein the total mass of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent is 100%, the mass fraction of the carboxymethyl cellulose is 0-1%, and the negative electrode slurry contains nanobubbles, wherein the Dv50 of the nanobubbles is less than or equal to 1000 nm.

[0046] Nanobubbles are bubbles with a particle size of nanometers, representing a special gaseous state existing at the gas-liquid interface. In the negative electrode slurry of this invention, the nanobubbles have a Dv50 of less than or equal to 1000 nm, where Dv50 is the particle size corresponding to a 50% volume percentage of nanobubbles. The Dv50 of CMC used in the prior art is generally 5 μm to 50 μm, while the nanobubbles in the negative electrode slurry of this invention have a Dv50 of less than or equal to 1000 nm, exhibiting a smaller particle size than CMC. Therefore, compared to CMC, nanobubbles with a Dv50 of less than or equal to 1000 nm have a larger specific surface area, resulting in a lower zeta potential in the negative electrode slurry and better dispersion of the negative electrode particles. Therefore, by adding nanobubbles with a Dv50 of less than or equal to 1000 nm to the negative electrode system to partially or completely replace CMC, this invention can achieve good dispersion of negative electrode particles, while also improving cell cycling or storage expansion, and reducing the proportion of CMC can optimize production costs.

[0047] Furthermore, nanobubbles with a Dv50 of less than or equal to 1000 nm exhibit high stability, maintaining a relatively constant particle size for several days or even more than ten days after their formation. The time between preparing the negative electrode slurry and coating it onto the current collector to form the negative electrode active layer is relatively short, allowing the Dv50 of the nanobubbles in the negative electrode slurry to remain within the range of less than or equal to 1000 nm during this period.

[0048] Subsequently, after the negative electrode slurry of this embodiment is coated onto the current collector and the negative electrode sheet is dried, nanobubbles escape. However, since the negative electrode particles in the liquid negative electrode system are uniformly dispersed, the gaps between the negative electrode particles in the dried negative electrode active layer remain unchanged. In other words, the dispersion state between the negative electrode particles is maintained, and the negative electrode particles will not agglomerate again during the drying process. Therefore, this embodiment of the invention, by adding nanobubbles with a Dv50 of less than or equal to 1000 nm to the negative electrode system to partially or completely replace CMC, can achieve a good negative electrode particle dispersion effect, while also improving cell cycling or storage expansion, and reducing the CMC ratio can optimize production costs.

[0049] In the preparation method of this invention, the Dv50 of the nanobubbles is less than or equal to 1000 nm, such as 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc. When the Dv50 of the nanobubbles is greater than 1000 nm, on the one hand, it will lead to an increase in the Zeta potential of the negative electrode slurry, which is not conducive to achieving a good negative electrode particle dispersion effect; on the other hand, it will lead to poor stability of the nanobubbles, which will have a greater time limit on the subsequent slurry coating process. If the negative electrode slurry cannot be coated quickly, the dispersion uniformity between the negative electrode particles in the negative electrode slurry will become worse.

[0050] Preferably, the Dv50 of the nanobubbles is less than or equal to 500 nm, such as 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc. More preferably, the Dv50 of the nanobubbles is 100 nm to 300 nm. Even more preferably, the Dv50 of the nanobubbles is 120 nm to 180 nm. When the Dv50 of the nanobubbles is too high, it is not conducive to improving the dispersion uniformity between the negative electrode particles; on the other hand, it is also not conducive to improving the stability of the nanobubbles. When the Dv50 of the nanobubbles is too low, it is also not conducive to improving the stability of the nanobubbles.

[0051] In some embodiments, the Zeta potential of the negative electrode slurry is less than or equal to -40mV, such as -40mV, -45mV, -50mV, -55mV, -60mV, -65mV, -70mV, -75mV, -80mV, etc. Preferably, the Zeta potential of the negative electrode slurry is between -80mV and -40mV. When the Zeta potential of the negative electrode slurry is too high, it is not conducive to improving the dispersion uniformity between negative electrode particles. When the Zeta potential of the negative electrode slurry is too low, it indicates that the Dv50 of the nanobubbles in the negative electrode slurry is too small, the nanobubbles are not stable enough, which is not conducive to maintaining the Zeta potential of the negative electrode slurry at a low level, and is not conducive to subsequent coating processes; or it indicates that there is too much CMC in the negative electrode slurry.

[0052] In some embodiments, the Zeta potential intensity of the negative electrode slurry is greater than or equal to 0.2, such as 0.2, 0.22, 0.25, 0.28, 0.3, etc. The number of nanobubbles in the negative electrode slurry cannot be directly measured, but the number of nanobubbles in the negative electrode slurry is correlated with the intensity of the Zeta potential. It can be considered that when the Zeta potential intensity of the negative electrode slurry is greater than or equal to 0.2, sufficient nanobubbles can be guaranteed in the negative electrode slurry, facilitating the full utilization of its good dispersion effect on the negative electrode particles.

[0053] Preferably, the intensity of the Zeta potential of the negative electrode slurry is 0.25–0.3. When the intensity of the Zeta potential of the negative electrode slurry is too low, it indicates that the number of nanobubbles in the slurry is insufficient, which is detrimental to improving the dispersion effect of the negative electrode particles and makes it difficult to reduce particle agglomeration. When the intensity of the Zeta potential of the negative electrode slurry is too high, it indicates that the number of nanobubbles in the slurry is excessive, and it will not significantly enhance the dispersion effect of the negative electrode particles, thus hindering cost reduction and efficiency improvement.

[0054] Secondly, embodiments of the present invention provide a method for preparing a negative electrode slurry, comprising the following steps:

[0055] S1. A homogenizing device is provided, the homogenizing device comprising a first homogenizing tank and an ejector disposed on the first homogenizing tank, wherein the outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank; a negative electrode solvent and a gas source are added into the first homogenizing tank through the ejector, wherein the flow rate of the negative electrode solvent is greater than or equal to 0.5 m / s, thereby obtaining a negative electrode solvent containing nanobubbles;

[0056] S2. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the carboxymethyl cellulose is added to the first homogenizing tank and mixed with the negative electrode solvent containing nanobubbles to obtain a mixture;

[0057] When the mass fraction of carboxymethyl cellulose is 0, S2 is not performed;

[0058] S3. The negative electrode active material and the negative electrode conductive agent are added to the second homogenizing tank and mixed to obtain a mixed dry material;

[0059] S4. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the mixture is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product.

[0060] When the mass fraction of the carboxymethyl cellulose is 0, the negative electrode solvent containing nanobubbles is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product.

[0061] S5. The styrene-butadiene rubber is added to the second homogenizing tank and mixed with the negative electrode slurry semi-finished product to obtain the negative electrode slurry.

[0062] The preparation method of this invention uses the homogenizing device provided in the fifth aspect of this invention to complete step S1. The homogenizing device is provided with an ejector on the first homogenizing tank. The outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank. Therefore, during the process of adding the negative electrode solvent into the first homogenizing tank, the ejector is used to form a liquid medium rich in nanobubbles, thereby achieving the purpose of introducing nanobubbles into the negative electrode slurry.

[0063] The preparation method of this invention controls the flow rate of the negative electrode solvent to be greater than or equal to 0.5 m / s, which can add nanobubbles with Dv50 less than or equal to 1000 nm to the negative electrode system to partially or completely replace CMC. This can achieve a good negative electrode particle dispersion effect, improve cell cycling or storage process expansion, and reduce the proportion of CMC to optimize production costs.

[0064] It should be noted that there is no specific order between steps S1 and S2 and step S3. For example, step S3 can be performed at the same time as steps S1 and S2, or steps S1 and S2 can be performed first and then step S3, or step S3 can be performed first and then steps S1 and S2.

[0065] In the preparation method of this invention, the flow rate of the negative electrode solvent in step S1 is greater than or equal to 0.5 m / s, for example, 0.5 m / s, 0.8 m / s, 1 m / s, 1.2 m / s, 1.4 m / s, 1.6 m / s, 1.8 m / s, 2 m / s, etc. When the flow rate of the negative electrode solvent is less than 0.5 m / s, it is difficult to generate nanobubbles with a Dv50 of less than or equal to 1000 nm. The higher the flow rate of the negative electrode solvent, the smaller the Dv50 of the generated nanobubbles.

[0066] The preparation method of this invention does not particularly limit the type of gas source; it can be any gas source, such as at least one of air, oxygen, nitrogen, rare gases, and reducing gases. Because the components in the negative electrode slurry have high chemical stability and are difficult to oxidize or reduce, any gas source can be used to manufacture nanobubbles without negatively impacting the negative electrode slurry.

[0067] Thirdly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one side of the current collector, wherein the negative electrode active layer is prepared from the negative electrode slurry described in the first aspect.

[0068] Since the negative electrode active layer of the negative electrode sheet is prepared by using the negative electrode slurry described in the first aspect in the embodiments of the present invention, the negative electrode particles in the negative electrode sheet of the embodiments of the present invention have better dispersion uniformity compared with the negative electrode sheets in the prior art. In addition, the negative electrode sheet of the embodiments of the present invention has better electrochemical performance, and the volume expansion of the negative electrode sheet during cycling and storage is also smaller. Furthermore, the production cost of the negative electrode sheet of the embodiments of the present invention is lower.

[0069] Fourthly, embodiments of the present invention provide a lithium-ion battery, including the negative electrode sheet described in the third aspect.

[0070] Since the embodiments of the present invention use the negative electrode sheet described in the third aspect to assemble lithium-ion batteries, the negative electrode particles of the lithium-ion batteries of the embodiments of the present invention have better dispersion uniformity compared with lithium-ion batteries in the prior art. In addition, the lithium-ion batteries of the embodiments of the present invention have better electrochemical performance and smaller volume expansion during cycling and storage. Furthermore, the production cost of the lithium-ion batteries of the embodiments of the present invention is lower.

[0071] Fifthly, embodiments of the present invention provide a homogenizing apparatus, such as... Figure 1 and Figure 2 As shown, the homogenizing device includes a first homogenizing tank 1 and an ejector 2 disposed on the first homogenizing tank 1. The outlet of the diffuser tube 25 of the ejector 2 is connected to the inner cavity 11 of the first homogenizing tank 1.

[0072] The homogenizing apparatus of this embodiment of the invention does not have any particular limitations on the specific structure of the first homogenizing tank. Figure 1 The first homogenizing tank shown is only a schematic diagram.

[0073] The ejector 2 generally includes a nozzle 21, an air intake pipe 22, and an air chamber 23 connected to the nozzle 21 and the air intake pipe 22. The outlet of the air chamber 23 is connected to the inlet of the mixing pipe 24, and the outlet of the mixing pipe 24 is connected to the inlet of the diffuser 25. In the homogenizing device of this embodiment, an ejector 2 is provided on the first homogenizing tank 1. The outlet of the diffuser 25 of the ejector 2 is connected to the inner cavity of the first homogenizing tank 1. When it is necessary to add negative electrode solvent and introduce nanobubbles into the first homogenizing tank 1, the negative electrode solvent is introduced from the nozzle 21 of the ejector 2, while the air intake pipe 12 of the ejector 2 is connected to the air source. When the negative electrode solvent enters the first homogenizing tank 1 through the ejector 2, a Venturi effect is generated, and the air source is simultaneously drawn into the ejector 2, thereby generating nanobubbles and mixing the nanobubbles into the negative electrode solvent. The Dv50 of the nanobubbles can be adjusted by adjusting the flow rate of the negative electrode solvent.

[0074] In some embodiments, such as Figure 1 and Figure 2As shown, the diffuser tube 25 of the jet injector 2 penetrates the side wall 12 of the first homogenizing tank 1, and the outlet of the diffuser tube 25 of the jet injector is connected to the inner cavity 11 of the first homogenizing tank 1.

[0075] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0076] The structure of the homogenizing device used in step S1 of the following embodiments is as follows: Figure 1 and Figure 2 As shown, the homogenizing device includes a first homogenizing tank 1 and an ejector 2 disposed on the first homogenizing tank 1. The first homogenizing tank can be any homogenizing tank in the prior art. The ejector 2 can include a nozzle 21, an air intake pipe 22, and an air chamber 23 connected to the nozzle 21 and the air intake pipe 22. The outlet of the air chamber 23 is connected to the inlet of the mixing pipe 24, and the outlet of the mixing pipe 24 is connected to the inlet of the diffuser 25. The diffuser 25 of the ejector 2 passes through the side wall 12 of the first homogenizing tank 1, and the outlet of the diffuser 25 of the ejector 2 is connected to the inner cavity 11 of the first homogenizing tank 1.

[0077] Example 1

[0078] A negative electrode slurry is composed of a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a negative electrode solvent. The negative electrode active material is graphite, the negative electrode conductive agent is conductive carbon black (SP), the negative electrode binder is carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the negative electrode solvent is deionized water. Based on the total mass of the negative electrode active material, negative electrode binder, and negative electrode conductive agent being 100%, the negative electrode slurry contains 97% graphite, 1% SP, 1% CMC, and 1% SBR. The solid content of the negative electrode slurry is 50%. The negative electrode slurry also disperses nanobubbles with a Dv50 of 1000 nm. The zeta potential of the negative electrode slurry is -35 mV, and the intensity of the zeta potential is 0.2.

[0079] A method for preparing a negative electrode slurry, the specific steps of which are as follows:

[0080] S1. Deionized water is introduced into the nozzle 21 of the ejector 2, and the air intake pipe 22 of the ejector 2 is connected to the air. Deionized water and air are added into the first homogenizing tank through the ejector. The flow rate of deionized water is 0.5 m / s, and a negative electrode solvent containing nanobubbles is obtained.

[0081] S2. Add CMC into the first homogenizing tank through the feed port at the top of the first homogenizing tank, and stir at a linear speed of 100 r / min for 60 min to mix CMC with the negative electrode solvent containing nano bubbles evenly to obtain a mixture for later use.

[0082] S3. Add graphite and SP to the second homogenizing tank and stir at a linear speed of 100 r / min for 60 min to obtain a mixed dry material.

[0083] S4. Add a portion of the mixture to the second homogenizing tank and stir at a linear speed of 180 r / min for 60 min. Test the viscosity of the slurry. Then add the mixture in multiple steps and stir at a linear speed of 100 r / min for 30 min. Test the viscosity of the slurry after each addition of the mixture until the viscosity of the slurry reaches the expected viscosity of 3500 mps ± 1000. Stop adding the adhesive solution to obtain the negative electrode slurry semi-finished product.

[0084] S5. Add the SBR to the second homogenizing tank and stir at a linear speed of 100 r / min for 60 min to obtain the negative electrode slurry. The magnitude and intensity of the zeta potential of the negative electrode slurry are tested using a zeta potential analyzer.

[0085] Application Example 1

[0086] A negative electrode sheet is prepared as follows: the negative electrode slurry of Example 1 is slit-coated onto both sides of the negative electrode current collector to obtain a negative electrode sheet semi-finished product, and then the negative electrode sheet semi-finished product is dried at 80°C for 3 hours to obtain the negative electrode sheet.

[0087] A lithium-ion battery, the preparation method of which is as follows:

[0088] (1) Using lithium nickel cobalt manganese oxide as the positive electrode active material, carbon nanotubes as the positive electrode conductive agent, polytetrafluoroethylene (PTFE) as the positive electrode binder, and N-methylpyrrolidone (NMP) as the positive electrode solvent, the above raw materials are mixed evenly to prepare a positive electrode slurry. Based on the total mass of the positive electrode active material, positive electrode binder and positive electrode conductive agent as 100%, the mass fraction of lithium nickel cobalt manganese oxide is 97.5%, the mass fraction of carbon nanotubes is 0.5%, the mass fraction of PTFE is 2%, and the solid content of the positive electrode slurry is 70%.

[0089] (2) The positive electrode slurry is coated onto both sides of the positive electrode current collector to obtain a positive electrode semi-finished product. Then the positive electrode semi-finished product is dried at 80°C for 3 hours to obtain a positive electrode sheet.

[0090] (3) The positive electrode, negative electrode and separator are wound together to make a cell. The cell is put into a cylindrical shell, electrolyte is injected, and the shell is sealed with a cover plate to obtain a lithium-ion battery.

[0091] Example 2

[0092] The difference between the negative electrode slurry of this embodiment and the negative electrode slurry of Example 1 is that the Dv50 of the nanobubbles in this negative electrode slurry is 800 nm, the Zeta potential of this negative electrode slurry is -40 mV, and the intensity of the Zeta potential of this negative electrode slurry is 0.2.

[0093] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1, except that the flow rate of deionized water in step S1 of the preparation method of the negative electrode slurry in this embodiment is 1 m / s.

[0094] Application Example 2

[0095] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet and lithium-ion battery of this application embodiment are prepared using the negative electrode slurry of embodiment 2.

[0096] Example 3

[0097] The negative electrode slurry in this embodiment is the same as that in Example 1, except that the Dv50 of the nanobubbles in this negative electrode slurry is 400 nm, the Zeta potential of this negative electrode slurry is -45 mV, and the intensity of the Zeta potential of this negative electrode slurry is 0.25.

[0098] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1, except that the flow rate of deionized water in step S1 of the preparation method of the negative electrode slurry in this embodiment is 1.5 m / s.

[0099] Application Example 3

[0100] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet and lithium-ion battery of this application embodiment are prepared using the negative electrode slurry of embodiment 3.

[0101] Example 4

[0102] The negative electrode slurry in this embodiment is the same as that in Example 1, except that the Dv50 of the nanobubbles in the negative electrode slurry in this embodiment is 300 nm, the Zeta potential of the negative electrode slurry is -50 mV, and the intensity of the Zeta potential of the negative electrode slurry is 0.25.

[0103] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1, except that the flow rate of deionized water in step S1 of the preparation method of the negative electrode slurry in this embodiment is 2 m / s.

[0104] Application Example 4

[0105] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet is prepared using the negative electrode slurry of embodiment 4.

[0106] Example 5

[0107] The negative electrode slurry in this embodiment is the same as that in Example 1, except that the Dv50 of the nanobubbles in this embodiment is 150 nm, the Zeta potential of this negative electrode slurry is -55 mV, and the intensity of the Zeta potential of this negative electrode slurry is 0.3.

[0108] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1, except that the flow rate of deionized water in step S1 of the preparation method of the negative electrode slurry in this embodiment is 2.5 m / s.

[0109] Application Example 5

[0110] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet is prepared using the negative electrode slurry of embodiment 5.

[0111] Example 6

[0112] The negative electrode slurry in this embodiment is the same as that in Example 1, except that the mass fraction of CMC in the negative electrode slurry of this embodiment is 0, the Dv50 of the nanobubbles is 150nm, the zeta potential of the negative electrode slurry is -52mV, and the intensity of the zeta potential of the negative electrode slurry is 0.3.

[0113] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1, except that the flow rate of deionized water in step S1 of the preparation method of the negative electrode slurry in this embodiment is 2.5 m / s.

[0114] Application Example 6

[0115] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet is prepared using the negative electrode slurry of embodiment 6.

[0116] The preparation method of the negative electrode slurry in this embodiment is the same as that in Example 1. The difference is that step S2 is omitted. In step S4, a portion of the negative electrode solvent containing nanobubbles is added to the second homogenizing tank and stirred at a linear speed of 180 r / min for 60 min. The viscosity of the slurry is tested. Then, the negative electrode solvent containing nanobubbles is added in multiple steps and stirred at a linear speed of 100 r / min for 30 min. The viscosity of the slurry is tested after each addition of the mixture until the viscosity of the slurry reaches the expected viscosity of 3500 mps ± 1000. Then, the addition of the adhesive is stopped, and the negative electrode slurry semi-finished product is obtained.

[0117] Comparative Example 1

[0118] The negative electrode slurry of this comparative example is the same as that of Example 1, except that the negative electrode slurry of this comparative example does not contain nanobubbles, the zeta potential of this negative electrode slurry is -35mV, and the intensity of the zeta potential of this negative electrode slurry is 0.15.

[0119] The preparation method of the negative electrode slurry in this comparative example is the same as that in Example 1. The difference is that in step S1 of the preparation method of the negative electrode slurry in this comparative example, instead of adding deionized water to the first homogenizing tank through the jet injector 2 set on the first homogenizing tank, deionized water is added into the first homogenizing tank through the feed port at the top of the first homogenizing tank. The flow rate of the deionized water is 0.5 m / s, and the resulting negative electrode solvent does not contain nanobubbles.

[0120] Application Comparative Example 1

[0121] The negative electrode sheet and lithium-ion battery of this application embodiment are the same as those of application embodiment 1, except that the negative electrode sheet is prepared using the negative electrode slurry of comparative example 1.

[0122] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0123] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode slurry comprising a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a negative electrode solvent, wherein the negative electrode binder comprises carboxymethyl cellulose and styrene-butadiene rubber, characterized in that, With the total mass of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent being 100%, the mass fraction of the carboxymethyl cellulose is 0-1%, and the negative electrode slurry contains nanobubbles with a Dv50 of less than or equal to 1000 nm.

2. The negative electrode slurry according to claim 1, characterized in that, The Dv50 of the nanobubbles is less than or equal to 500 nm.

3. The negative electrode slurry according to claim 1, characterized in that, The zeta potential of the negative electrode slurry is less than or equal to -40mV.

4. The negative electrode slurry according to claim 3, characterized in that, The zeta potential of the negative electrode slurry is -80mV to -40mV.

5. The negative electrode slurry according to claim 1, characterized in that, The intensity of the zeta potential of the negative electrode slurry is greater than or equal to 0.

2.

6. The negative electrode slurry according to claim 5, characterized in that, The intensity of the zeta potential of the negative electrode slurry is 0.25 to 0.

3.

7. The method for preparing the negative electrode slurry according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. A homogenizing device is provided, the homogenizing device comprising a first homogenizing tank and an ejector disposed on the first homogenizing tank, wherein the outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank; a negative electrode solvent and a gas source are added into the first homogenizing tank through the ejector, wherein the flow rate of the negative electrode solvent is greater than or equal to 0.5 m / s, thereby obtaining a negative electrode solvent containing nanobubbles; S2. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the carboxymethyl cellulose is added to the first homogenizing tank and mixed with the negative electrode solvent containing nanobubbles to obtain a mixture; When the mass fraction of carboxymethyl cellulose is 0, S2 is not performed; S3. The negative electrode active material and the negative electrode conductive agent are added to the second homogenizing tank and mixed to obtain a mixed dry material; S4. When the mass fraction of the carboxymethyl cellulose is greater than 0 and less than or equal to 1%, the mixture is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product. When the mass fraction of the carboxymethyl cellulose is 0, the negative electrode solvent containing nanobubbles is added stepwise to the second homogenizing tank and mixed with the mixed dry material until the viscosity of the slurry reaches the expected viscosity. Then the addition of the adhesive is stopped to obtain the negative electrode slurry semi-finished product. S5. The styrene-butadiene rubber is added to the second homogenizing tank and mixed with the negative electrode slurry semi-finished product to obtain the negative electrode slurry.

8. A negative electrode sheet, said negative electrode sheet comprising a current collector and a negative electrode active layer disposed on at least one side of said current collector, characterized in that, The negative electrode active layer is prepared from the negative electrode slurry according to any one of claims 1 to 6.

9. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 7.

10. A homogenizing device, characterized in that, It includes a first homogenizing tank and an ejector disposed on the first homogenizing tank, wherein the outlet of the diffuser tube of the ejector is connected to the inner cavity of the first homogenizing tank.

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