Negative electrode slurry and preparation method, battery negative electrode sheet, secondary battery, and electric device

Abstract

The embodiment of the application discloses a negative electrode slurry and a preparation method thereof, a battery negative electrode sheet, a secondary battery and an electric device, which comprise the following components by weight: 100 parts of a negative electrode active material; 0.1-6 parts of a conductive agent; 0.1-7 parts of a binder; 95-120 parts of deionized water; and 0.1-2 parts of a second solvent; the second solvent is insoluble in water, and the second solvent can be mixed with water to form a suspension. The negative electrode slurry provided by the embodiment of the application has the characteristics of high viscosity at a low shear speed and low viscosity at a high shear speed, has high solid content and good stability, and when used as a negative electrode coating material, can improve the profile of the edge of the coating material, significantly reduce the width of the thinning area of the material, and improve the volume specific capacity of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a negative electrode slurry and a preparation method thereof, a battery negative electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, due to the continuous improvement of performance indicators of secondary batteries and the reduction of degree of electricity cost, the proportion of lithium ion secondary batteries in the energy storage field is continuously increasing. At present, for graphite negative electrodes, a negative electrode slurry of a water-based binder system is usually used. However, the existing slurry of the water-based binder system has the defect of low viscosity, which leads to a large and thin width of the thinning area after coating the coating material, affects the active material load per unit area of the coated electrode sheet, and thus reduces the volume specific capacity of the battery cell. Therefore, it is necessary to develop an electrode slurry to improve the width of the thinning area after coating the coating material, and further improve the volume specific capacity of the battery cell. SUMMARY

[0003] In view of this, the present application provides a negative electrode slurry and a preparation method thereof, a battery negative electrode sheet, a secondary battery and an electric device. The negative electrode slurry has the characteristics of high viscosity at low shear speed and low viscosity at high shear speed, high solid content and good stability. When used as a negative electrode coating material, it can improve the profile of the edge of the coating material, significantly reduce the width of the thinning area of the coating material, and improve the volume specific capacity of the battery cell.

[0004] In a first aspect, the present application provides a negative electrode slurry, which comprises the following components by weight:

[0005] Negative electrode active material: 100 parts;

[0006] Conductive agent: 0.1-6 parts;

[0007] Binder: 0.1-7 parts;

[0008] Water: 95-120 parts;

[0009] Second solvent: 0.1-2 parts;

[0010] The second solvent is insoluble in water, and the second solvent can be mixed with water to form a suspension.

[0011] In the present application, the second solvent includes an organic alcohol solvent that is insoluble in water.

[0012] In the present application, the organic alcohol solvent includes at least one of a fatty alcohol, an aromatic alcohol and a polymer polyol.

[0013] In the present application, the fatty alcohol includes a C5-C 18 fatty alcohol.

[0014] In the embodiment of the present application, the weight ratio of the negative active material, water and the second solvent is 100:(95-105):(0.5-2).

[0015] In the embodiment of the present application, the viscosity of the negative slurry at 25℃±2℃, 0.1s -1 -10s -1 is 1.4Pa·s-300Pa·s.

[0016] In the embodiment of the present application, the solid content of the negative slurry is 47%-53%.

[0017] In the embodiment of the present application, the negative slurry further comprises 0.2-8 parts by weight of a dispersant.

[0018] In the embodiment of the present application, the negative active material comprises one or more of graphite material, hard carbon material, soft carbon material, silicon-based material and tin-based material; the conductive agent comprises one or more of carbon black, carbon fiber, conductive graphite and carbon nanotube; the binder comprises one or more of styrene-butadiene rubber emulsion, nitrile rubber, butadiene rubber, styrene-acrylic emulsion, polyacrylic acid, polyacrylate, polyacrylonitrile, polyvinyl alcohol and polyacrylamide; and the dispersant comprises one or more of sodium carboxymethyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, sodium polyacrylate, sodium polymethacrylate, lithium polyacrylate and lithium polymethacrylate.

[0019] The negative slurry provided by the first aspect of the embodiment of the present application, on the one hand, by adding the second solvent immiscible with water in the slurry of the water-based binder system, the slurry forms a capillary suspension slurry, which can significantly change the rheological properties of the fluid, so that the slurry is gelatinous, and the viscosity is higher at a low shear rate compared with the slurry of the water-based binder system without adding the second solvent, and the capillary suspension slurry has good stability and is not prone to delamination and sedimentation; on the other hand, by reducing the proportion of water, the solid content of the slurry is improved, which can further enhance the viscosity, reduce the drying time, save energy and reduce emissions, and improve the production capacity. When the negative slurry provided by the embodiment of the present application is used in the coating process, a thick edge can be formed after the slurry contacts the current collector, which can significantly reduce the width of the thinning area of the coating and improve the volume specific capacity of the battery.

[0020] In the second aspect, the embodiment of the present application provides a preparation method of the negative slurry of the first aspect of the embodiment of the present application, which comprises the following steps:

[0021] Mixing the negative active material, the conductive agent and water to obtain a first slurry;

[0022] Mixing the second solvent, the binder and the first slurry to obtain the negative slurry.

[0023] In the embodiment of the present application, the mixing of the negative active material, the conductive agent and water also includes adding a dispersant to obtain the first slurry.

[0024] The preparation method of the negative slurry provided by the second aspect of the embodiment of the present application has a simple preparation process; the uniformity of the slurry is improved through the multi-step stirring mode, the slurry is well dispersed, and the consistency and stability of the prepared negative slurry are high.

[0025] In a third aspect, the embodiment of the present application provides a battery negative plate, which comprises a negative current collector and an active material layer arranged on the negative current collector, and the active material layer is prepared by using the negative slurry according to the first aspect of the embodiment of the present application.

[0026] The battery negative plate provided by the third aspect of the embodiment of the present application has high viscosity of the negative slurry, small width of the coating thinning area, high active material load per unit area of the negative plate, and high energy density and power density of the prepared battery.

[0027] In a fourth aspect, the embodiment of the present application provides a secondary battery, which comprises a positive electrode, a negative electrode, and a separator and an electrolyte between the positive electrode and the negative electrode, and the negative electrode comprises the battery negative plate according to the third aspect of the embodiment of the present application.

[0028] The secondary battery provided by the fourth aspect of the embodiment of the present application has high active material load per unit area of the battery negative plate, and thus has high volume specific capacity of the battery cell, and can be applied to a power consumption device with high energy density requirement.

[0029] In a fifth aspect, the embodiment of the present application further provides a power consumption device, which comprises the secondary battery according to the fourth aspect of the embodiment of the present application.

[0030] The power consumption device provided by the fifth aspect of the embodiment of the present application adopts the secondary battery provided by the fourth aspect as a power supply, the secondary battery has high specific capacity, can stably provide high energy density of electric energy for the power consumption device, and improves the use performance of the power consumption device. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the background art, the drawings needed to be used in the embodiments of the present application or the background art will be described below.

[0032] Figure 1 is a preparation flowchart of the negative slurry in an embodiment of the present application;

[0033] Figure 2 is a preparation flowchart of the negative slurry in a specific embodiment of the present application;

[0034] Figure 3 3. This is a comparison of the morphologies of the thinned areas of the negative electrode slurries coated on the negative electrode current collectors in Example 1, Example 2, and Comparative Example 1 of the present invention;

[0035] Figure 4 3 is a comparison diagram of the appearance of the negative electrode slurries in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention;

[0036] Figure 5 3 is a comparison chart of the viscosity curves of the negative electrode slurries in Example 2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0038] In recent years, with the rapid development of lithium-ion battery technology, its application has been rapidly expanded, from the earliest 3C products to gradually shifting to the power battery and energy storage markets. The manufacturing process of lithium battery cells includes pulping, coating, rolling, slitting, assembly, welding, packaging, liquid injection and formation. Among them, the coating process has a large impact on the entire production process of lithium-ion batteries. The quality of its dressing determines the smooth progress of subsequent processes and is a core link that affects battery performance and endurance. The quality control of the coating dressing includes the width of the dressing, the relative position of the dressing and the electrode, the consistency of the dressing thickness (surface density), the width and morphology of the dressing thinning area, etc. Currently, for graphite negative electrodes, negative electrode slurries with aqueous binder systems are generally used. However, the existing aqueous binder system slurries have the problem of low viscosity, which results in the width of the thinning area after the coating dressing being too large and thin, and the active material loading per unit area of ​​the coated electrode, thereby reducing the volumetric capacity of the battery cell. Therefore, it is necessary to develop an electrode slurry to improve the morphology of the thinned area after coating and increase the volumetric capacity of the battery cell.

[0039] Based on this, an embodiment of the present invention provides a negative electrode slurry, comprising the following components in parts by weight:

[0040] Negative electrode active material: 100 parts;

[0041] Conductive agent: 0.1-6 parts;

[0042] Adhesive: 0.1-7 parts;

[0043] Water: 95-120 parts;

[0044] Second solvent: 0.1-2 parts;

[0045] The second solvent is insoluble in water and can be mixed with water to form a suspension.

[0046] The negative electrode slurry provided by the embodiment of the present application adds a small amount of water-immiscible second solvent to the slurry of the existing water-based binder system, so that the slurry forms a capillary suspension slurry. The capillary suspension slurry can significantly change the rheological properties of the fluid, so that the slurry is gel-like. Compared with the slurry of the water-based binder system without adding the second solvent, the viscosity of the slurry is higher at low shear rate, and the capillary suspension slurry has good stability and is not prone to delamination and sedimentation. Specifically, at low shear rate, the capillary force between water, the second solvent and the solid particles in the slurry can cause the particles in the slurry to flocculate, thereby changing the flow properties of the slurry. Moreover, as the volume fraction of the second solvent increases, the yield stress and viscosity of the slurry can increase by several orders of magnitude. When the high-viscosity slurry contacts the current collector, a thick edge can be formed, which can significantly reduce the width of the slurry thinning area and improve the volume specific capacity of the battery. At high shear rate, the high shear force can destroy the capillary force between water, the second solvent and the solid particles in the slurry, so that the viscosity of the slurry is reduced, thereby facilitating the coating of the negative electrode slurry at high shear rate. Therefore, the negative electrode slurry provided by the embodiment of the present application has the characteristics of high viscosity at low shear rate and low viscosity at high shear rate. The slurry can be coated on the current collector at low shear rate to form a thick edge, thereby reducing the width of the slurry thinning area, and the normal coating of the slurry at high shear rate can be ensured.

[0047] The negative electrode slurry provided by the embodiment of the present application reduces the proportion of water added, thereby increasing the solid content of the slurry, further enhancing the viscosity of the slurry, reducing the drying time of the slurry, saving energy, reducing emissions and improving productivity. In some embodiments, the weight of water can be 95 parts, 98 parts, 100 parts, 102 parts, 105 parts, 108 parts, 110 parts, 115 parts, 117 parts or 120 parts.

[0048] In the embodiment of the present application, the second solvent includes a water-insoluble organic alcohol solvent.

[0049] In the embodiment of the present application, the organic alcohol solvent can be at least one of a fatty alcohol, an aromatic alcohol and a polymer polyol. Specifically, the aromatic alcohol can be phenethyl alcohol or phenylpropyl alcohol, and the polymer polyol can be a polyester polyol or a polyurea polyol.

[0050] In the embodiment of the present application, the fatty alcohol includes a C5-C 18 fatty alcohol, i.e., the number of carbon atoms in the fatty alcohol is 5-18. The fatty alcohol can be volatilized in the subsequent drying process, leaving a microporous structure, increasing the specific surface area and porosity of the electrode, thereby increasing the contact area between the electrode and the electrolyte and the diffusion rate of lithium ions. In addition, the fatty alcohol can also reduce the amount of binder and increase the content of conductive agent, thereby further improving the conductivity and capacity of the electrode. In some embodiments, the number of carbon atoms in the fatty alcohol can be 5, 6, 7, 8, 9, 10, 11, 12, 15 or 18. In some embodiments, the C5-C18 The fatty alcohol may be n-pentanol, isopentanol, n-hexanol, isohexanol, n-heptanol, isoheptanol, n-octanol, isooctyl alcohol, n-nonanol, isononyl alcohol, n-decanol or isodecanol. 18 The fatty alcohol has a specific density of 0.75-0.90 and is insoluble in water. Adding it to the slurry of the aqueous binder system can improve the contour morphology of the edge of the coated dressing, further reduce the width of the thinning area of ​​the dressing, and increase the volume capacity of the battery cell.

[0051] In an embodiment of the present invention, the weight portion of the second solvent is 0.1 parts to 2 parts. In some embodiments, the weight portion of the second solvent can be 0.1 parts, 0.2 parts, 0.4 parts, 0.5 parts, 0.7 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts. Adding the second solvent in the above amount produces a capillary suspension slurry having high viscosity at low shear rates and low viscosity at high shear rates. This allows the slurry to be coated on the current collector at low shear rates to form a thick edge to reduce the width of the thinning zone of the dressing, while also ensuring normal coating of the slurry at high shear rates.

[0052] In an embodiment of the present invention, the weight ratio of the negative electrode active material, water and the second solvent is 100: (95-105): (0.5-2). The amount of the second solvent added is a key factor affecting the flowability of the slurry, and the degree of its influence on the flowability of the slurry is related to the solid content of the slurry. The solid content of the slurry refers to the proportion of solid substances such as active materials, conductive agents, binders, etc. in the overall mass of the slurry among the various components of the slurry. Specifically, for a negative electrode slurry with a certain solid content, the more the second solvent is added, the greater the viscosity of the slurry, but too much addition will make the slurry too viscous and prone to agglomeration and unable to be coated, so it is necessary to control the amount of the second solvent at a certain solid content. Because the solid content of the slurry mainly depends on the addition ratio of the negative electrode active material and water, the effect of the second solvent on the flowability of the slurry is directly related to the addition ratio of the negative electrode active material and water. Controlling the weight ratio of the negative electrode active material, water, and the second solvent to 100:(95-105):(0.5-2) can more effectively increase the viscosity of the negative electrode slurry and control the viscosity of the slurry within an appropriate range, thereby ensuring both the dynamic performance and adhesion of the slurry.

[0053] In an embodiment of the present invention, the solids content of the negative electrode slurry is 47%-53%. In some embodiments, the solids content of the negative electrode slurry can be 47%, 48%, 49%, 50%, 51%, 52%, or 53%. There is a positive correlation between the solids content and viscosity of the negative electrode slurry. Within a certain range, as the solids content increases, the viscosity of the negative electrode slurry also increases. Controlling the solids content of the negative electrode slurry within the above range is beneficial for forming a thick skived area after coating and also facilitates drying of the slurry.

[0054] In some embodiments, the viscosity of the negative electrode slurry at 25℃±2℃, 0.1s -1 -10s -1 may be in the range of 1.4Pa·s-300Pa·s. In some embodiments, the viscosity of the negative electrode slurry at 25℃±2℃, 0.1s -1 -10s -1 may be in the range of 13Pa·s-250Pa·s. The viscosity is measured by a rheometer, and the specific test method is as follows: 1) turn on the power of the rheometer, select the appropriate rotor, select the rotation mode, and adjust the equipment parameters (environmental temperature: 25℃, rotation speed: 10-30 revolutions / minute), 2) put 100-150mL slurry into the cylinder of the rheometer, lower the rotor height so that the rotor is at the middle height position of the slurry, and start testing after standing for 10s. After the test is completed, the data is read. At low shear rate, the viscosity of the negative electrode slurry provided by the present application is higher than one time or more than the viscosity of the conventional slurry, which can better reduce the flowability of the slurry along the coating width direction to form a thick thinning area and reduce the width of the slurry thinning area.

[0055] In some embodiments, the negative electrode slurry further comprises 0.2 parts by weight-8 parts by weight of a dispersant. In some embodiments, the parts by weight of the dispersant can be 0.2 parts, 0.5 parts, 1 part, 1.6 parts, 2 parts, 2.5 parts, 2.8 parts, 3 parts, 3.5 parts, 4 parts, 5 parts, 6 parts, 7 parts or 8 parts. The dispersant can make the solid particles in the negative electrode slurry more uniformly dispersed, prevent the particles from agglomerating and caking due to the increase in viscosity, and thus maintain the homogeneous structure of the slurry and improve the stability of the battery.

[0056] In some embodiments, the dispersant can be one or more of sodium carboxymethyl cellulose (CMC), carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, sodium polyacrylate, sodium polymethacrylate, lithium polyacrylate and lithium polymethacrylate. In some embodiments, the dispersant can be sodium carboxymethyl cellulose powder or sodium carboxymethyl cellulose hydrosol, and the solid content of the sodium carboxymethyl cellulose hydrosol can be 2%-5%. Sodium carboxymethyl cellulose plays a key role in the dispersion of negative electrode active materials and the prevention of particle settling, and can improve the consistency and stability of the negative electrode slurry. Sodium carboxymethyl cellulose also has good compatibility and can be used in combination with styrene-butadiene rubber emulsion to more fully exert the bonding effect and improve the overall performance of the battery slurry.

[0057] In some embodiments, the negative electrode active material can be one or more of graphite material, hard carbon material, soft carbon material, silicon-based material and tin-based material. In some embodiments, the particle size D50 of the negative electrode active material is 6μm-20μm, the specific surface area is 1m 2 / g-4m2 The particle size testing equipment is a laser particle size analyzer, and the detailed testing method refers to GB / T 21524-2008. The negative electrode active material provided in the embodiments of the present application has the characteristics of high theoretical specific capacity, high stability, good electrical conductivity and rich resources, and can be used to prepare a lithium battery negative electrode slurry, thereby better improving the cycle life and rate performance of the battery.

[0058] In the embodiments of the present application, the weight fraction of the conductive agent is 0.1-6 parts. In some embodiments, the weight fraction of the conductive agent can be 0.1, 0.5, 0.8, 1, 1.3, 1.6, 2, 2.5, 3, 4, 5 or 6 parts. The conductive agent can be one or more of carbon black, vapor grown carbon fiber (VGCF), conductive graphite and carbon nanotube. The conductive agent provided in the embodiments of the present application has excellent electrical conductivity, chemical stability, corrosion resistance and oxidation resistance, can be adapted to various active materials, can increase the electrical conductivity of the slurry, and effectively improve the energy density, rate performance and cycle life of the battery.

[0059] In the embodiments of the present application, the weight fraction of the binder is 0.1-7 parts. In some embodiments, the weight fraction of the binder can be 0.1, 0.5, 0.8, 1, 1.3, 1.6, 2, 2.5, 3.06, 3.5, 4, 5, 6 or 7 parts. The binder can be various binder materials suitable for negative electrode slurry, for example, can be one or more of styrene butadiene rubber emulsion (SBR), nitrile rubber, butadiene rubber, styrene-acrylic emulsion, polyacrylic acid, polyacrylate, polyacrylonitrile, polyvinyl alcohol and polyacrylamide. In some embodiments, the solid content of the styrene butadiene rubber emulsion is 49%-51%. The binder is an important component of the secondary battery, and the performance of the binder directly affects the performance of the battery. The above binder has strong bonding strength and good mechanical stability, can well bond the electrode active material, the conductive agent and the current collector, plays a role of adhesion and thickening, and makes the prepared battery more stable and has more excellent performance.

[0060] The negative electrode slurry provided in the embodiments of the present application significantly improves the flow performance of the slurry by adding a second solvent immiscible with water in the water-based system slurry, has the characteristics of high viscosity at low shear rate and low viscosity at high shear rate, can form thick edges on the current collector at low shear rate to reduce the width of the thin area of the coating, and can ensure normal coating of the slurry at high shear rate. When applied to a secondary battery, the specific capacity of the battery cell can be improved, and the electrochemical performance of the battery can be improved.

[0061] The embodiments of the present application also provide a preparation method of the negative electrode slurry, as shown in Figure 1 the formula.

[0062] S101, mixing the negative active material, the conductive agent and water to obtain a first slurry;

[0063] S102, mixing the second solvent and the binder with the first slurry to obtain the negative electrode slurry;

[0064] or adding the binder into the first slurry to perform first mixing and stirring, and then adding the second solvent to perform second mixing and stirring to obtain the negative electrode slurry.

[0065] In step S101, the process of mixing and stirring the negative active material, the conductive agent and water also includes adding a dispersant to obtain the first slurry. The water can be deionized water with high purity by removing ions and impurities to reduce the influence of impurities in the negative electrode slurry on the performance of the battery. The preparation of the first slurry can first mix and stir the conductive agent, the dispersant and water, the stirring speed is 30 rpm-60 rpm, and the stirring time is 20 min-30 min, and then add the negative active material to mix and stir, the stirring speed is 60 rpm-70 rpm, and the stirring time is 40 min-60 min.

[0066] In step S102, the second solvent can be added to the first slurry to perform first mixing and stirring, and then the binder is added to perform second mixing and stirring to obtain the negative electrode slurry; or the binder is added to the first slurry to perform first mixing and stirring, and then the second solvent is added to perform second mixing and stirring to obtain the negative electrode slurry. The speed of the first mixing and stirring can be 50 rpm-60 rpm, and the stirring time can be 30 min-50 min; the speed of the second mixing and stirring can be 50 rpm-60 rpm, and the stirring time can be 20 min-40 min. After mixing and stirring the second solvent into the first slurry, deionized water can be further added to adjust the viscosity of the slurry.

[0067] In the embodiment of the application, the prepared negative electrode slurry can be transferred to a coating storage tank for a coating process. If the coating process is not performed immediately, the negative electrode slurry can be stored in a stirring tank with low-speed stirring to maintain the stability of the negative electrode slurry.

[0068] In one specific embodiment of the application, the preparation process of the negative electrode slurry is as follows Figure 2As shown, the specific steps are: according to the formula of the slurry, the capacity of the stirring tank and the coating yield level, the weight of each component in the formula is determined. At a temperature of 25℃±2℃, first, sodium carboxymethyl cellulose (CMC), a conductive agent and deionized water are put into the stirring tank and stirred for 30min, the stirring speed of the slurry is 30rpm-60rpm, then the negative electrode active material is added and stirred for 60min, the stirring speed of the slurry is 60rpm-70rpm, to obtain the first slurry. After the stirring of the negative electrode active material is completed, the second solvent and deionized water are added to the first slurry and continue to stir for 30min, the stirring speed of the slurry is 50rpm-60rpm, finally, the butyl rubber emulsion is added and continue to stir for 30min, the stirring speed of the slurry is 30rpm-40rpm, and finally the above-mentioned negative electrode slurry of the embodiment of the present application is prepared.

[0069] The preparation method of the negative electrode slurry provided by the embodiment of the present application has a simple preparation process; and the uniformity of the slurry is improved by the multi-step stirring mode, the good dispersion of the slurry is realized, and the consistency and stability of the prepared negative electrode slurry are higher.

[0070] The embodiment of the present application also provides a battery negative electrode sheet, which comprises a negative electrode current collector and an active material layer arranged on the negative electrode current collector, and the active material layer is prepared by using the negative electrode slurry in any of the above-mentioned embodiments.

[0071] The battery negative electrode sheet provided by the embodiment of the present application has high viscosity of the negative electrode slurry, small width of the coating thinning area, and high active material loading per unit area of the negative electrode sheet, so that the energy density and the power density of the prepared battery are higher.

[0072] The embodiment of the present application also provides a secondary battery, which comprises a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, and the negative electrode comprises the battery negative electrode sheet in any of the above-mentioned embodiments.

[0073] The secondary battery provided by the embodiment of the present application has high active material loading per unit area of the battery negative electrode sheet, so that the volume specific capacity of the prepared battery is higher, and the secondary battery can be applied to a power consumption equipment with high energy density demand.

[0074] Correspondingly, the embodiment of the present application also provides a power consumption equipment, which comprises the secondary battery in any of the above-mentioned embodiments. Specifically, the power consumption equipment can be an electric vehicle, an electric motorcycle, an electric bicycle, a mobile phone, a computer, a camera, an electronic book player or a wearable device.

[0075] The power consumption equipment provided by the embodiment of the present application adopts the secondary battery as a power supply, the secondary battery has higher specific capacity, can stably provide high energy density electric energy for the power consumption equipment, and improves the use performance of the power consumption equipment.

[0076] The following further describes the embodiments of the present application in multiple examples.

[0077] Example 1

[0078] (1) Preparation of negative electrode slurry

[0079] The raw materials for preparing the negative electrode slurry were weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene styrene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersant) 1.6 parts; n-heptanol (second solvent) 0.5 parts; deionized water 95 parts.

[0080] First, the sodium carboxymethyl cellulose, carbon black and deionized water were put into a stirring tank and stirred for 30 min at a stirring speed of 30 rpm-60 rpm, then the graphite powder was added and stirred for 60 min at a stirring speed of 60 rpm-70 rpm, to obtain a first slurry. After the stirring of the graphite powder was completed, the n-heptanol and deionized water were added to the first slurry and stirred for 30 min at a stirring speed of 50 rpm-60 rpm, and finally the butadiene styrene rubber emulsion was added and stirred for 30 min at a stirring speed of 30 rpm-40 rpm, to obtain the negative electrode slurry of Example 1.

[0081] (2) Coating

[0082] According to the design requirements of the battery cell, the negative electrode slurry of Example 1 was coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 1.

[0083] Example 2

[0084] (1) Preparation of negative electrode slurry

[0085] The raw materials for preparing the negative electrode slurry were weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene styrene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersant) 1.6 parts; n-heptanol (second solvent) 1 part; deionized water 95 parts.

[0086] The above raw materials were mixed and stirred to obtain the negative electrode slurry of Example 2, and the stirring process was the same as that of Example 1.

[0087] (2) Coating

[0088] According to the design requirements of the battery cell, the negative electrode slurry of Example 2 was coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 2.

[0089] Example 3

[0090] (1) Preparation of negative electrode slurry

[0091] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene styrene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersing agent) 1.6 parts; n-heptanol (second solvent) 2 parts; deionized water 95 parts.

[0092] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 3, and the stirring process is the same as that of Example 1.

[0093] Example 4

[0094] (1) Preparation of negative electrode slurry

[0095] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene styrene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersing agent) 1.6 parts; n-heptanol (second solvent) 0.1 parts; deionized water 95 parts.

[0096] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 4, and the stirring process is the same as that of Example 1.

[0097] (2) Coating

[0098] According to the design requirements of the battery cell, the negative electrode slurry of Example 4 is coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 4.

[0099] Example 5

[0100] (1) Preparation of negative electrode slurry

[0101] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene styrene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersing agent) 1.6 parts; n-heptanol (second solvent) 1 part; deionized water 120 parts.

[0102] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 5, and the stirring process is the same as that of Example 1.

[0103] (2) Coating

[0104] According to the design requirements of the battery cell, the negative electrode slurry of Example 5 is coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 5.

[0105] Example 6

[0106] (1) Preparation of negative electrode slurry

[0107] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersing agent) 1.6 parts; n-heptanol (second solvent) 1 part; deionized water 110 parts.

[0108] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 6, and the stirring process is the same as that of Example 1.

[0109] (2) Coating

[0110] According to the design requirements of the battery cell, the negative electrode slurry of Example 6 is coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 6.

[0111] Example 7

[0112] (1) Preparation of negative electrode slurry

[0113] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; n-heptanol (second solvent) 0.5 parts; deionized water 95 parts.

[0114] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 7, and the stirring process is the same as that of Example 1.

[0115] (2) Coating

[0116] According to the design requirements of the battery cell, the negative electrode slurry of Example 7 is coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 7.

[0117] Example 8

[0118] (1) Preparation of negative electrode slurry

[0119] The raw materials for preparing the negative electrode slurry are weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 0.2 parts; carbon black (conductive agent) 5.6 parts; n-pentanol (second solvent) 1.5 parts; deionized water 108 parts.

[0120] The above raw materials are mixed and stirred to prepare the negative electrode slurry of Example 8, and the stirring process is the same as that of Example 1.

[0121] (2) Coating

[0122] According to the design requirements of the battery cell, the negative electrode slurry of Example 8 is coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 8.

[0123] Example 9

[0124] (1) Preparation of negative electrode slurry

[0125] The raw materials for preparing the negative electrode slurry were weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 6.8 parts; carbon black (conductive agent) 0.5 parts; n-decanol (second solvent) 0.2 parts; deionized water 100 parts.

[0126] The above raw materials were mixed and stirred to prepare the negative electrode slurry of Example 9, and the stirring process was the same as that of Example 1.

[0127] (2) Coating

[0128] According to the design requirements of the battery cell, the negative electrode slurry of Example 9 was coated on the foil of the electrode sheet to obtain the coated electrode sheet of Example 9.

[0129] Comparative Example 1

[0130] (1) Preparation of negative electrode slurry

[0131] The raw materials for preparing the negative electrode slurry were weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersant) 1.6 parts; deionized water 95 parts.

[0132] The above raw materials were mixed and stirred to prepare the negative electrode slurry of Comparative Example 1, and the stirring process was the same as that of Example 1.

[0133] (2) Coating

[0134] The negative electrode slurry of Comparative Example 1 was coated on the foil of the electrode sheet to obtain the coated electrode sheet of Comparative Example 1, and the coating process was the same as that of Example 1.

[0135] Comparative Example 2

[0136] (1) Preparation of negative electrode slurry

[0137] The raw materials for preparing the negative electrode slurry were weighed according to the following weight parts: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersant) 1.6 parts; n-heptanol (second solvent) 1 part; deionized water 130 parts.

[0138] The above raw materials were mixed and stirred to prepare the negative electrode slurry of Comparative Example 2, and the stirring process was the same as that of Example 1.

[0139] (2) Coating

[0140] The negative electrode slurry of Comparative Example 2 was coated on the foil of the electrode sheet to obtain the coated electrode sheet of Comparative Example 2, and the coating process was the same as that of Example 1.

[0141] Comparative Example 3

[0142] (1) Preparation of negative electrode slurry

[0143] The raw materials for preparing the negative electrode slurry were weighed according to the following parts by weight: graphite powder (negative electrode active material) 100 parts; butadiene rubber emulsion (binder) 3.06 parts; carbon black (conductive agent) 1 part; sodium carboxymethyl cellulose (dispersant) 1.6 parts; n-propanol 1 part; deionized water 95 parts.

[0144] The above raw materials were mixed and stirred to obtain the negative electrode slurry of Comparative Example 3, and the stirring process was the same as that of Example 1.

[0145] (2) Coating

[0146] The negative electrode slurry of Comparative Example 3 was coated on the electrode foil to obtain the coated electrode of Comparative Example 3, and the coating process was the same as that of Example 1.

[0147] Performance test

[0148] (1) Thinning zone width test

[0149] After the coated electrodes prepared in Examples 1-9 and Comparative Examples 1-3 were dried, the thinning zone width and profile were observed using a microscope. The measurement method of the thinning zone width was as follows: the electrode was clamped with two 0.5 mm steel plates, the cross section of the electrode was directly opposite the microscope lens, the height of the electrode was 1-2 mm higher than that of the steel plate, then a VHX-7000n high precision microscope was used to take a picture, and the width of the thinning zone was measured by image processing, and the average value was taken by measuring three times. The thinning zone width measurement results are shown in Table 1 and Figure 3 From Figure 3 it can be seen that the thinning zone width of the coated electrodes of Examples 1 and 2 is significantly smaller than that of Comparative Example 1, indicating that the second solvent insoluble in water added in the negative electrode slurry of the present application can effectively reduce the thinning zone width of the coated electrode.

[0150] (2) Adhesion test

[0151] The viscosity and flowability of the negative electrode slurries of Examples 1-3 and Comparative Example 1 were tested by the dropping method. 2 mL of the negative electrode slurry was taken with a rubber bulb dropper, then the slurry was squeezed out at a distance of 5 cm from the horizontal table, the slurry morphology was observed and photographed, and the results are shown in Figure 4 From Figure 4 it can be seen that the content of n-heptanol in the negative electrode slurries of Examples 1-3 is gradually increasing, and the slurry becomes more and more thick with the increase of the content of n-heptanol.

[0152] Then, a rheometer was used to test the viscosity of the negative electrode slurries of Examples 1-9 and Comparative Examples 1-3. The specific test method is as follows: 1) Turn on the power of the rheometer, select a suitable rotor, select the rotation mode, and debug the equipment parameters (ambient temperature: 25°C, speed: 10-30 rpm), 2) Add 100-150mL of negative electrode slurry to the measuring cylinder of the rheometer, lower the rotor height so that the rotor is at the middle height position of the slurry, and start the test after standing for 10s. After the test is completed, read the data. The negative electrode slurries of Examples 1-9 and Comparative Example 1 have a viscosity of 8s. -1 The viscosity under shear rate is shown in Table 1. The viscosity curves of the negative electrode slurries of Example 2 and Comparative Example 1 are shown in Table 1. Figure 5 As shown. Figure 5 It can be seen that in 0.1s -1 Under shear rate, the viscosity of the negative electrode slurry of Example 2 is 250Pa·s, and the viscosity of the slurry of Comparative Example 1 is 18Pa·s. Compared with Comparative Example 1, the viscosity of the slurry of Example 2 is increased by about 13 times by adding 1% of the mass of the negative electrode active material n-heptanol. -1 At the shear rate, the viscosity of Example 2 and Comparative Example 1 is not much different. This shows that the embodiment of the present invention can significantly improve the viscosity of the slurry at low shear rates by adding a small amount of a water-insoluble second solvent to the aqueous slurry, but has little effect on the viscosity of the slurry at high shear rates.

[0153] Table 1 Measurement results of the width of the thinned area of ​​the coated electrode and the viscosity of the negative electrode slurry

[0154]

[0155] As shown in Table 1, the viscosity of the negative electrode slurries of Examples 1-9 was higher than that of Comparative Examples 1-3, and the width of the skived area of ​​the coated electrode sheets of Examples 1-9 was smaller than that of Comparative Examples 1-3. This indicates that the addition of a water-insoluble second solvent to the negative electrode slurry in the present invention effectively increases the viscosity, thereby reducing the width of the skived area of ​​the coated electrode sheet. As shown in Examples 1-4, within the range specified in the present invention, the higher the content of the second solvent in the negative electrode slurry, the greater the viscosity of the negative electrode slurry and the smaller the width of the skived area of ​​the coated electrode sheet. As shown in Examples 2, 5, and 6, the viscosity of the negative electrode slurry prepared with a weight ratio of 100:(95-110):1 of negative electrode active material, water, and the second solvent was higher, and the width of the skived area was better reduced. As shown in Example 2 and Comparative Example 2, the amount of water in the negative electrode slurry exceeding the range specified in the present invention results in excessively low viscosity, resulting in excessively wide skived areas of the coated electrode sheet.

[0156] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent of the present application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A negative electrode slurry, characterized in that: The composition comprises the following components in parts by weight: Negative electrode active material: 100 parts; Conductive agent: 0.1-6 parts; Adhesive: 0.1-7 parts; Water: 95-120 parts; Second solvent: 0.1-2 parts; The second solvent is insoluble in water and can be mixed with water to form a suspension.

2. The negative electrode slurry according to claim 1, wherein The second solvent includes an organic alcohol solvent that is insoluble in water.

3. The negative electrode slurry according to claim 2, wherein The organic alcohol solvent includes at least one of aliphatic alcohol, aromatic alcohol, and polymer polyol.

4. The negative electrode slurry according to claim 3, wherein The fatty alcohols include C5-C 18 of fatty alcohols.

5. The negative electrode slurry according to claim 1, wherein The weight ratio of the negative electrode active material, water and the second solvent is 100:(95-105):(0.5-2).

6. The negative electrode slurry according to claim 1, wherein The negative electrode slurry is heated at 25°C ± 2°C and 0.1s -1 -10s -1 The viscosity range at the shear rate is 1.4Pa·s-300Pa·s.

7. The negative electrode slurry according to claim 1, wherein The solid content of the negative electrode slurry is 47%-53%.

8. The negative electrode slurry according to claim 1, wherein The negative electrode slurry further includes 0.2 parts by weight to 8 parts by weight of a dispersant.

9. The negative electrode slurry according to claim 8, wherein The negative electrode active material includes one or more of graphite materials, hard carbon materials, soft carbon materials, silicon-based materials and tin-based materials; the conductive agent includes one or more of carbon black, carbon fiber, conductive graphite and carbon nanotubes; the binder includes one or more of styrene-butadiene rubber latex, nitrile rubber, butadiene rubber, styrene-acrylic latex, polyacrylic acid, polyacrylate, polyacrylonitrile, polyvinyl alcohol and polyacrylamide; the dispersant includes one or more of sodium carboxymethyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, sodium polyacrylate, sodium polymethacrylate, lithium polyacrylate and lithium polymethacrylate.

10. A method for preparing a negative electrode slurry according to any one of claims 1 to 9, characterized in that: The following steps are involved: Mixing the negative electrode active material, the conductive agent and water to obtain a first slurry; The negative electrode slurry is obtained by mixing a second solvent, a binder and the first slurry.

11. The method for preparing the negative electrode slurry according to claim 10, wherein: The process of mixing the negative electrode active material, the conductive agent and water further includes adding a dispersant to obtain the first slurry.

12. A battery negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and an active material layer arranged on the negative electrode current collector, wherein the active material layer is prepared by using the negative electrode slurry according to any one of claims 1 to 9.

13. A secondary battery, characterized in that: The battery comprises a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the negative electrode comprises the battery negative electrode sheet as claimed in claim 12.

14. An electrical device, characterized in that: The secondary battery according to claim 13 is included.

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