Negative electrode composition, negative electrode slurry, preparation method of negative electrode slurry, negative electrode plate, battery and preparation method of battery

Abstract

The invention relates to the field of batteries, in particular to a negative electrode composition, negative electrode slurry, a preparation method of the negative electrode slurry, a negative electrode plate, a battery and a preparation method of the battery. The negative electrode composition comprises a negative electrode active material, a conductive agent, carboxylic ester and a binder, wherein the conductive agent comprises a single-walled carbon nanotube, and the negative electrode active material comprises a carbon material and a silicon material; the mass of the carboxylic ester is 0.1%-3% of the mass of the carbon material. The negative electrode composition provided by the invention can effectively reduce the internal resistance of the battery, improve the energy density and long-term electrical property of the battery, and also can effectively inhibit the volume expansion of the negative electrode active material in the charge-discharge process.

Description

TECHNICAL FIELD

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

[0002] With the increasing demand for high energy density batteries, the traditional method is to add different amounts of silicon to graphite to improve the energy density of the battery, but this method cannot effectively solve the problems of poor cycle stability, high internal resistance, long-term use of the negative electrode material, and volume expansion of silicon. SUMMARY

[0003] Therefore, the present application is devoted to providing a negative electrode composition, a negative electrode slurry and a preparation method thereof, a negative electrode sheet, a battery and a preparation method thereof. The negative electrode composition can effectively reduce the internal resistance of the battery when used to prepare the battery, improve the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion of the negative electrode active material during the charging and discharging process.

[0004] To solve the above technical problems, the present application is implemented as follows: The first aspect of the present application provides a negative electrode composition, comprising a negative electrode active material, a conductive agent, a carboxylate and a binder; wherein the conductive agent comprises single-walled carbon nanotubes, the negative electrode active material comprises a carbon material and a silicon material; and the mass of the carboxylate is 0.1%-3% of the mass of the carbon material.

[0005] In some embodiments, the carboxylate in the negative electrode composition is attached to the carbon material.

[0006] In some embodiments, the carboxylate comprises C1-C18 alkyl carboxylate and / or C8-C18 aryl carboxylate.

[0007] In some embodiments, the carbon material comprises one or more of natural graphite, primary particle artificial graphite, secondary particle artificial graphite, needle coke graphite, petroleum coke graphite and coated graphite composite material.

[0008] In some embodiments, the silicon material comprises one or more of silicon monoxide, silicon carbon, pre-magnesia silicon and pre-lithium silicon.

[0009] In some embodiments, the conductive agent further comprises a conductive agent A, which is different from the single-walled carbon nanotubes.

[0010] In some embodiments, the binder comprises one or more of cellulose salt binder, polyacrylic binder, polyacrylonitrile binder and butadiene-styrene rubber binder.

[0011] In some embodiments, the mass of the silicon material is 0.1%-15% of the mass of the carbon material.

[0012] In some embodiments, the mass of the single-walled carbon nanotubes is = the mass of the silicon material a, a is 0.6%-3%.

[0013] In some embodiments, the mass of the single-walled carbon nanotubes is 0.02%-0.2% of the mass of the carbon material.

[0014] In some embodiments, the mass of the conductive agent is 0.5%-1.5% of the mass of the carbon material.

[0015] In some embodiments, the mass of the binder is 2%-4% of the mass of the carbon material.

[0016] In some embodiments, the C1-C18 alkyl carboxylate has the chemical formula R 11 COOR 12 , wherein R 11 is a C1-C3 alkyl group, and R 12 is a C1-C18 alkyl group.

[0017] In some embodiments, the C8-C18 aryl carboxylate includes C8-C18 benzoate and / or C8-C18 o-methylbenzoate. In some embodiments, the carboxylate includes C1-C18 alkyl carboxylate and C8-C18 aryl carboxylate in a mass ratio of (0.5-3):1.

[0018] In some embodiments, the conductive agent A includes conductive carbon black and / or graphene.

[0019] In some embodiments, the mass of the silicon material is 1%-10% of the mass of the carbon material.

[0020] The second aspect of the present application provides a negative electrode slurry including water and the negative electrode composition of the first aspect of the present application.

[0021] The third aspect of the present application provides a method for preparing a negative electrode slurry, including the following steps: mixing water and a negative electrode composition; wherein the negative electrode composition is the negative electrode composition of the first aspect of the present application.

[0022] In some embodiments, the method for preparing the negative electrode slurry includes the following steps: S1, the conductive agent, the binder and part of the water are first mixed, and then the silicon material is added for second mixing to obtain a conductive glue solution; S2, the carboxylate is third mixed with the carbon material, and then added into the conductive glue solution for fourth mixing, and then the remaining water is added to adjust the viscosity of the system to obtain a negative electrode slurry.

[0023] The fourth aspect of the present application provides a negative electrode tab, comprising: a negative electrode current collector and a negative electrode active layer. The negative electrode active layer is arranged on at least one surface of the negative electrode current collector. The negative electrode active layer comprises the negative electrode composition of the first aspect of the present application, or the negative electrode active layer comprises a layer formed after drying the negative electrode slurry of the second aspect of the present application, or the negative electrode active layer comprises a layer formed after drying the negative electrode slurry prepared by the preparation method of the negative electrode slurry of the third aspect of the present application.

[0024] The fifth aspect of the present application provides a preparation method of a battery, comprising the following steps: The positive electrode tab, the negative electrode tab and the separator are wound or laminated into an electrode core, which is then put into a shell, electrolyte is injected, and then packaging, standing, formation, and capacity grading are performed to obtain a battery. The negative electrode tab comprises the negative electrode tab of the fourth aspect of the present application.

[0025] In some embodiments, the electrolyte comprises an organic solvent and a lithium salt, and the organic solvent comprises a carbonate solvent.

[0026] In some embodiments, the formation conditions include: constant current charging at 0.01C-0.33C to 0.1V-4.3V at 40℃-50℃, and then constant current charging at 0.33C to 4.0-4.15V.

[0027] In some embodiments, the capacity grading conditions include: constant current and constant voltage charging at 0.1C-0.15C to 4.2V-4.3V at 40℃-50℃, and the cutoff current is 0.05C.

[0028] The sixth aspect of the present application provides a battery prepared by the preparation method of the battery of the fifth aspect of the present application.

[0029] Through the above technical solution, the present application has the following beneficial technical effects: The carboxylate in the negative electrode composition of the present application is not dissolved in water during the negative electrode homogenization process, and when using the negative electrode sheet containing the negative electrode composition of the present application to prepare a battery, the carboxylate is dissolved in the solvent during the formation process, increasing the porosity of the electrode sheet, reducing the ion transmission impedance, and reserving space for the expansion of the negative electrode active material, which is directly manifested as a decrease in negative electrode rebound; at the same time, the single-walled carbon nanotubes can be better attached to the carbon material under the action of the binder, which can increase the conductivity of the negative electrode side, to a certain extent, reduce the characteristics of the expansion of the negative electrode active material, and thus better increase the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion problem of the negative electrode active material during the charging and discharging process.

[0030] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and together with the following specific embodiments, serve to explain the present application, but do not constitute a limitation on the present application.

[0032] Figure 1 Nyquist comparison chart of the batteries in Examples 1-8 and the battery in Comparative Example 1 is shown.

[0033] Figure 2 A comparison chart of the cycle gas production test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 is shown.

[0034] Figure 3 A comparison chart of the cycle performance test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 at 25 DEG C is shown.

[0035] Figure 4 A comparison chart of the cycle performance test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 at 45 DEG C is shown. DETAILED DESCRIPTION

[0036] The present application discloses a negative electrode composition, a negative electrode slurry and a preparation method thereof, a negative electrode sheet, a battery and a preparation method thereof, and those skilled in the art can refer to the content herein and appropriately improve the process parameters to realize. It is particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by the preferred embodiments, and the relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0037] In the description of the present application, the list of items connected by the term "at least one of" or other similar terms implies any combination of the listed items. For example, if A, B, and C are listed, the phrase "at least one of A, B, and C" means A alone; B alone; C alone; A and B together; A and C together; B and C together; or A, B, and C together. The items A can include a single element or multiple elements. The items B can include a single element or multiple elements. The items C can include a single element or multiple elements.

[0038] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within the range of values are included in the range. The endpoints of the ranges and any values are included in the range even if the endpoints or values are not expressly mentioned. The ranges include values that are approximately the recited values even minor variations are intended to be within the scope of the ranges. For values that are not numerical, the scope of the ranges include values that are approximately the recited values even minor variations are intended to be within the scope of the ranges.

[0039] If not specifically explained, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0040] If not specifically explained, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0041] If not specifically explained, the "includes" and "contains" mentioned in the present application represent open type, and can also be closed type. For example, the "includes" and "contains" can represent that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0042] [Negative electrode composition] The first aspect of the present application provides a negative electrode composition, comprising a negative electrode active material, a conductive agent, a carboxylate and a binder; wherein the conductive agent comprises single-walled carbon nanotubes, the negative electrode active material comprises a carbon material and a silicon material; the mass of the carboxylate is 0.1%-3% (for example, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 3%, or a range composed of any two of the above values) of the mass of the carbon material.

[0043] The negative electrode composition in the application can reduce the internal resistance of the battery, improve the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion of the negative electrode active material during the charging and discharging process. The reason is that during the preparation of the battery, the carboxylic acid ester is dissolved in the solvent during the formation process, increasing the porosity of the pole piece, reducing the ion transmission impedance, and reserving space for the expansion of the negative electrode active material; and cooperating with the conductive material to increase the conductive capacity of the negative electrode side, which can reduce the expansion of the negative electrode active material to a certain extent, while improving the cycle performance.

[0044] Generally, the traditional way to improve the porosity of the negative electrode pole piece is to add a pore-forming agent to the negative electrode slurry, then coat the negative electrode slurry on the current collector, and then dry. The pore-forming agent can achieve the effect of pore-forming, and after the negative electrode pole piece is dried, certain voids are formed, but the voids inside the entire negative electrode pole piece are relatively uneven, which also affects the yield of the negative electrode pole piece. In the present application, the pores formed by the dissolution of the carboxylic acid ester in the electrolyte during the formation process are more uniform and do not affect the yield of the pole piece.

[0045] carboxylate The various components in the negative electrode composition of the present application can be independently stored, or at least two components can be mixed and stored.

[0046] According to the present application, in some embodiments, the carboxylic acid ester is attached to the carbon material.

[0047] In order to attach the carboxylic acid ester to the carbon material, the carboxylic acid ester is mixed with the carbon material in the present application, and the two can be mixed and stored, or mixed and used at the time of use.

[0048] In the present application, by controlling the attachment of the carboxylic acid ester to the carbon material, the carboxylic acid ester is fixed in the pore structure of the carbon material by physical adsorption, which can better increase the stability and reactivity of the material, thereby better increasing the porosity of the pole piece and reducing the ion transmission impedance.

[0049] According to the present application, the carboxylic acid ester is an organic compound formed by esterification reaction of carboxylic acid and alcohol (or phenol), and in some embodiments, the carboxylic acid ester includes C1-C18 alkyl carboxylic acid ester and / or C8-C18 aryl carboxylic acid ester.

[0050] The above-mentioned carboxylic acid ester in the present application can be attached to the surface of the carbon material by a specific chemical reaction or physical adsorption method, which is used to improve the hydrophilicity, dispersibility or other properties of the material. Thus, the negative electrode composition can better improve the electrochemical performance of the battery.

[0051] According to the present application, in some embodiments, the chemical formula of the C1-C18 alkyl carboxylic acid ester is R 11 COOR 12 , wherein R11 is C1-C3 alkyl, R 12 is C1-C18 alkyl. That is, the C1-C18 alkyl carboxylate can be formate (HCOOR 12 ), acetate (CH3COOR 12 ), propionate (CH2CH2COOR 12 ). The aforementioned alkyl group can be a branched alkyl group or a linear alkyl group, and is preferably a linear alkyl group. Examples of the C1-C18 alkyl group include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, undecyl, dodecyl, and the like. Specifically, the C1-C18 alkyl carboxylate can be methyl formate, methyl acetate, methyl propionate, and the like.

[0052] According to the present application, in some embodiments, the C8-C18 aryl carboxylate includes C8-C18 benzoate and / or C8-C18 o-methylbenzoate, wherein it is understood that the chemical formula of the benzoate is C6H5COOR 21 , R 21 is a C1-C11 alkyl group, and the chemical formula of the o-methylbenzoate is C7H7COOR 22 , R 22 is a C1-C10 alkyl group. The aforementioned alkyl group can be a branched alkyl group or a linear alkyl group, and is preferably a linear alkyl group. Specifically, the C8-C18 aryl carboxylate is methyl benzoate and / or ethyl benzoate.

[0053] According to the present application, "the carboxylate includes C1-C18 alkyl carboxylate and / or C8-C18 aryl carboxylate" means that, in some embodiments, the carboxylate includes at least C1-C18 alkyl carboxylate; in some embodiments, the carboxylate includes at least C8-C18 aryl carboxylate; in some embodiments, the carboxylate includes C1-C18 alkyl carboxylate and C8-C18 aryl carboxylate. When the carboxylate includes C1-C18 alkyl carboxylate and C8-C18 aryl carboxylate, the ratio of the two is not particularly limited, as long as the purpose of the present application can be achieved, and in some embodiments, the carboxylate includes C1-C18 alkyl carboxylate and C8-C18 aryl carboxylate in a mass ratio of (0.5-3):1 (for example, 0.5:1, 0.8:1, 1:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1).

[0054] As an example, the carboxylate is methyl benzoate.

[0055] As an example, the carboxylate is ethyl benzoate.

[0056] As an example, the carboxylate is methyl propionate.

[0057] As an example, the carboxylate is methyl benzoate and methyl propionate in a mass ratio of 1:1.

[0058] negative active material According to the present application, the specific selection of the carbon material is not particularly limited as long as the purpose of the present application can be achieved, and in some embodiments, the carbon material can include but is not limited to one or more of natural graphite, primary particle artificial graphite, secondary particle artificial graphite, needle coke graphite, petroleum coke graphite, and coated graphite composite material. In the present application, the secondary particle artificial graphite is used as an exemplary illustration of the advantages of the present application, but it does not represent a limitation of the present application. Among them, the secondary particle artificial graphite refers to a primary graphite material formed by reprocessing natural graphite or primary artificial graphite particles, such as after balling treatment, mechanical grinding and chemical modification of the material, and the present application does not have a special limitation on its specific selection, which can be any one of the secondary particle artificial graphite adapted to the current market product classification.

[0059] According to the present application, the addition of silicon material can improve the energy density of the battery. Compared with carbon material, the volume change of silicon material during charging and discharging is more serious, which can cause the battery to have poor cycle stability, high internal resistance, and decreased electrical performance after long-term use. The existing method cannot effectively solve the problem caused by the volume expansion of silicon, and in the present application, by adding carboxylate and cooperating with the addition of conductive agent, especially single-walled carbon nanotubes and other components in the system, the negative electrode composition can reduce the ion transmission impedance when used in the battery, and at the same time, it can reserve space for silicon expansion. Therefore, the negative electrode composition in the present application can not only improve the energy density of the battery, but also reduce the ion transmission impedance, inhibit the expansion of the negative electrode active material (which can be intuitively manifested as a decrease in negative electrode rebound), and further improve the long-term electrical performance of the battery. As long as the purpose of the present application can be achieved, the specific type of silicon material is not particularly limited, and in some embodiments, the silicon material can include but is not limited to one or more of silicon monoxide, silicon carbon, pre-magnesium silicon, and pre-lithium silicon. In the present application, silicon monoxide is used as an exemplary illustration of the advantages of the present application, but it does not represent a limitation of the present application.

[0060] According to the present application, in some embodiments, the mass of the silicon material is 0.1%-15% of the mass of the carbon material, for example, 0.1%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 15%, or a range formed by any two of the above values; preferably, in some embodiments, the mass of the silicon material is 1%-10% of the mass of the carbon material.

[0061] In the present application, the amount of silicon material is controlled within the above range, which can better reduce the ion transmission impedance and improve the energy density and long-term electrical performance of the battery containing the negative electrode sheet of the present application.

[0062] conductive agent According to the present application, in some embodiments, the mass of the single-walled carbon nanotubes is 0.02%-0.2% of the mass of the carbon material, for example, 0.02%, 0.03%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or a range formed by any two of the above values. a, a is 0.6%-3%, for example, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range formed by any two of the above values, preferably 0.8%-2%.

[0063] In the present application, by controlling the content of the single-walled carbon nanotubes and the silicon material in the negative electrode composition to satisfy the above relationship, the ion transmission impedance can be better reduced, and the energy density and long-term electrical properties of the battery containing the negative electrode sheet of the present application can be improved.

[0064] According to the present application, in some embodiments, the mass of the single-walled carbon nanotubes is 0.02%-0.2% of the mass of the carbon material, for example, 0.02%, 0.03%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or a range formed by any two of the above values.

[0065] In the present application, by controlling the amount of single-walled carbon nanotubes within the above range, the ion transmission impedance can be better reduced, and the energy density and long-term electrical properties of the battery containing the negative electrode sheet of the present application can be improved.

[0066] According to the present application, in some embodiments, the conductive agent further includes a conductive agent A, which is different from the single-walled carbon nanotubes.

[0067] In the present application, the conductive agent A, which is different from the single-walled carbon nanotubes, cooperates with the single-walled carbon nanotubes to better increase the conductivity of the negative electrode sheet, further reduce the expansion of the negative electrode sheet, and improve the cycle performance.

[0068] According to the present application, the specific type of conductive agent A is not particularly limited as long as it is different from the single-walled carbon nanotubes, and in some embodiments, the conductive agent A includes conductive carbon black and / or graphene, and preferably includes conductive carbon black.

[0069] According to the present application, the content of the conductive agent can be selected within a relatively wide range as long as the purpose of the present application is achieved, and in some embodiments, the mass of the conductive agent is 0.5%-1.5% of the mass of the carbon material, for example, 0.5%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.5%, or a range formed by any two of the above values.

[0070] binder The binder is an auxiliary material capable of ensuring the structural integrity of the negative electrode sheet, and the type of the binder can be any binder in the art, and the amount of the binder can be the amount in the art. In some embodiments, the binder includes one or more of a cellulose salt binder, a polyacrylic binder, a polyacrylonitrile binder, and a styrene-butadiene rubber binder. In some embodiments, the amount of the binder is 2% to 4% of the mass of the carbon material, for example, 2%, 2.5%, 3%, 3.5%, or 4%, without limitation.

[0071] [The negative electrode slurry] The second aspect of the present application provides a negative electrode slurry including water and a negative electrode composition, wherein the negative electrode composition is the negative electrode composition provided in the first aspect of the present application.

[0072] In the present application, when a battery is prepared by using the negative electrode slurry in the present application, the porosity of the negative electrode sheet can be effectively improved, and the pore uniformity is good, which can reduce the internal resistance of the battery, improve the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion of the negative electrode active material during the charging and discharging process.

[0073] In the present application, the viscosity and solid content of the negative electrode slurry can be adjusted by the amount of water added, and the viscosity and solid content of the negative electrode slurry can be the conventional viscosity and solid content in the art, which is beneficial to control the coating weight and film thickness of the negative electrode sheet. For example, the viscosity of the negative electrode slurry is 2000 mPa·s to 4000 mPa·s, and for example, the solid content of the negative electrode slurry is 40% to 50%.

[0074] [Preparation of the negative electrode slurry] The third aspect of the present application provides a preparation method of a negative electrode slurry, including the following steps: mixing water and a negative electrode composition; wherein the negative electrode composition is the negative electrode composition provided in the first aspect of the present application.

[0075] In the present application, when the negative electrode slurry prepared is used in a battery, the porosity of the negative electrode sheet can be effectively improved, and the pore uniformity is good, which can reduce the internal resistance of the battery, improve the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion of the negative electrode active material during the charging and discharging process.

[0076] According to the present application, the amount of water and the negative electrode composition is such that the solid content and viscosity of the negative electrode slurry finally prepared are within the range capable of controlling the coating weight and film thickness of the negative electrode sheet, for example, the amount of water is such that the viscosity of the negative electrode slurry prepared is 2000 mPa·s to 4000 mPa·s, and the solid content is 40% to 50%.

[0077] According to the present application, in some embodiments, the preparation method of the negative electrode slurry comprises the following steps: S1, the conductive agent, the binder and part of the water are first mixed, and then the silicon material is added for second mixing to obtain a conductive glue solution; S2, the carboxylic acid ester and the carbon material are third mixed, and then added into the conductive glue solution for fourth mixing, and then the remaining water is added to adjust the viscosity of the system to obtain the negative electrode slurry.

[0078] In the present application, by mixing the carboxylic acid ester and the carbon material, then adding into the conductive glue solution for mixing, and finally using water to adjust the viscosity of the system, the carboxylic acid ester can be better attached to the carbon material, and then when the prepared negative electrode slurry is used in the battery, the solvent dissolved in the electrolyte during the formation process can better increase the porosity of the pole piece, reduce the ion transmission impedance, and at the same time reserve space for the expansion of the negative electrode active material, which intuitively reduces the negative electrode rebound. Further increase the long-term electrical performance of the battery.

[0079] According to the present application, in step S1, the amount of part of the water is not particularly limited, and a conductive glue solution with a certain concentration can be prepared, and the amount of part of the water is 1%-10% of the mass of the binder.

[0080] According to the present application, the specific conditions of the first mixing and the second mixing in step S1, and the third mixing and the fourth mixing in step S2 are not particularly limited, as long as each of them makes the corresponding components uniformly mixed, and this will not be described one by one.

[0081] According to the present application, when the carboxylic acid ester and the carbon material are third mixed and then added into the conductive glue solution, in order to make the mixing more uniform, the material after mixing the carboxylic acid ester and the carbon material can be divided into multiple batches and added into the conductive glue solution for fourth mixing, for example, the carboxylic acid ester and the carbon material are third mixed and then divided into 3 batches according to the mass, and then added into the conductive glue solution for fourth mixing.

[0082] [Negative electrode pole piece] The fourth aspect of the present application provides a negative electrode pole piece, which comprises a negative electrode current collector and a negative electrode active layer; the negative electrode active layer is arranged on at least one surface of the negative electrode current collector; The negative electrode active layer comprises the negative electrode composition provided by the first aspect of the present application, or the negative electrode active layer comprises the layer formed after drying the negative electrode slurry provided by the second aspect of the present application, or the negative electrode active layer comprises the layer formed after drying the negative electrode slurry prepared by the preparation method of the negative electrode slurry provided by the third aspect of the present application.

[0083] The negative pole piece in the application can effectively improve the porosity of the negative pole piece, and the pore uniformity is good, which can reduce the internal resistance of the battery, improve the energy density and long-term electrical performance of the battery, and effectively inhibit the volume expansion of the negative active material during the charging and discharging process.

[0084] The negative pole current collector in the application can adopt any kind known in the art, for example, can be a light foil (i.e. a material without additional surface treatment, which can be a copper foil), or a coated current collector, i.e. the surface of the light foil is coated with a conductive carbon coating, a metal nano coating, etc.

[0085] According to the application, the negative active layer can be arranged on both surfaces of the negative pole current collector, or on one surface of the negative pole current collector, and is preferably arranged on both surfaces of the negative pole current collector.

[0086] According to the application, the compaction density of the negative active layer can be in the range commonly used in the art, as long as the negative active material particles can be in close contact and the content of the negative active material in a unit volume can be increased, for example, the compaction density of the negative active layer can be 1.3 cm 3 / mg-1.7 cm 3 / mg.

[0087] According to the application, the preparation method of the negative pole piece can be carried out according to the conventional method in the art, and in some embodiments, the preparation method of the negative pole piece comprises: coating the above-mentioned negative pole slurry on at least one surface of the negative pole current collector, and then drying, rolling, and drying to obtain the negative pole piece; wherein the areal density of the coating is generally 5.5 mg / cm 2 -11 mg / cm 2 The purpose of rolling is to roll the negative active layer to a certain compaction density; drying is to dry the moisture; and drying can be carried out in a vacuum environment at 80-100°C for 4-6h.

[0088] [Preparation of the battery] The fifth aspect of the application provides a preparation method of a battery, comprising the following steps: The positive pole piece, the negative pole piece, and the separator are wound or laminated into an electric core, which is then put into a shell, electrolyte is injected, and then packaging, standing, formation, and capacity distribution are carried out to obtain the battery.

[0089] negative electrode sheet According to the application, the negative pole piece comprises the negative pole piece provided in the fourth aspect of the application.

[0090] In the battery in the present application, the carboxylate in the negative electrode sheet is dissolved in the solvent in the electrolyte during the activation and formation process in the preparation process, thereby increasing the porosity of the sheet, reducing the ion transmission impedance, reserving space for the expansion of the negative electrode sheet, and ultimately improving the long-term electrical performance of the battery.

[0091] positive electrode sheet According to the present application, the positive electrode sheet can be a conventional positive electrode sheet in the art, including a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.

[0092] In the positive electrode sheet, the positive electrode current collector can be a metal foil or a composite current collector, and as an example, the positive electrode current collector is an aluminum foil.

[0093] In the positive electrode sheet, the positive electrode active material can be NCM9, NCM811, NCM523, NCM622, LFP, and the selected material can be primary particles, secondary particles, secondary sintering, tertiary sintering, etc. The present application is not limited to these materials, and other conventional and well-known materials that can be used as secondary battery positive electrode active materials can also be used.

[0094] According to the present application, the positive electrode active layer usually further includes a binder and a conductive agent, etc. The binder and the conductive agent can be conventional types in the art, and as an example, the binder can include but is not limited to polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); and as an example, the conductive agent can include but is not limited to at least one of conductive carbon black, carbon nanotubes, graphene, and nanocarbon fibers.

[0095] According to the present application, the positive electrode sheet is usually coated by a positive electrode slurry, and is formed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material and optional conductive agent and binder, etc. in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP).

[0096] electrolyte The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. As long as the purpose of the present application can be achieved, the electrolyte can be any electrolyte in the art, and in some embodiments, the electrolyte includes an organic solvent and a lithium salt. In addition, additives can also be used in the electrolyte as needed.

[0097] The organic solvent in the present application can be any organic solvent known in the prior art that can be used as an electrolyte, and the specific selection thereof is not particularly limited. In some embodiments, the organic solvent includes, but is not limited to, carbonate solvents, which can specifically include at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). The lithium salt in the present application as an electrolyte, and the specific type thereof is not particularly limited, and can be any electrolyte known in the prior art, which can specifically be lithium hexafluorophosphate (LiPF6), lithium bis-trifluoromethylsulfonylimide (LiTFSI), etc. The additive in the present application can be any additive known in the prior art that can be used as an electrolyte additive. For example, some film-forming additives (which can specifically be vinylene carbonate), can also be silicon-based materials (such as nano-silicon particles, silicon monoxide (SiO), silicon-carbon composite (Si / C), etc.) in a silicon-doped electrolyte formulation, and can contain other functional additives (such as antioxidants, flame retardants, overcharge protection agents, etc.).

[0098] The concentration of the above-mentioned lithium salt in the electrolyte can be a conventional concentration in the art, for example, the concentration of the lithium salt in the electrolyte is 5wt%-15wt%.

[0099] separator The separator is arranged between the positive electrode sheet and the negative electrode sheet, and can play a role of isolation. The specific type of the separator can be a conventional type in the art as long as the purpose of the present application can be achieved, and is not particularly limited, and thus will not be described herein.

[0100] preparation conditions In the process of preparing the battery, the packaging, the standing, the formation, and the capacity grading are each a conventional operation method in the art. In some embodiments, the standing conditions include standing at 30-40℃ for 3h-10h. The above-mentioned formation is the first charging of the battery after standing, which generally uses a small current to charge and activate. In some embodiments, the formation conditions include charging at a rate of 0.01C-0.33C to 0.1V-4.3V, and then charging at a rate of 0.33C to 4.0-4.15V at 40℃-50℃. The above-mentioned capacity grading is one or more complete charging and discharging cycles of the battery after formation, which generally is constant current charging and discharging. In some embodiments, the capacity grading conditions include constant current constant voltage charging at a rate of 0.1C-0.15C to 4.2V-4.3V at 40℃-50℃, and the cutoff current is 0.05C.

[0101] According to the present application, the type of the shell can be selected as needed, for example, the shell can be a hard shell or a soft pack.

[0102] [Battery] The sixth aspect of the present application provides a battery prepared by the preparation method of the battery provided by the fifth aspect of the present application.

[0103] The battery in the present application has excellent long-term cycle electrical performance.

[0104] The present application is further described in detail by the following examples. The raw materials used in the examples can be obtained by commercial channels.

[0105] Example 1 Preparation of negative electrode slurry: The single-walled carbon nanotubes, conductive carbon black, polyacrylic acid binder and water were mixed uniformly, and then silicon monoxide was added and mixed uniformly to obtain a conductive sizing material, and the mass of the polyacrylic acid binder was 6% of the mass of the water; The secondary particle artificial graphite and methyl benzoate were mixed uniformly to obtain a mixture, the mixture was evenly divided into 3 batches according to the mass, and the conductive sizing material was added and mixed uniformly, and then the mixture was scraped, and then water was added to adjust the viscosity of the slurry, so as to obtain a negative electrode slurry with a solid content of 43wt% and a viscosity of 2280mPa·S; The mass of the single-walled carbon nanotubes was 0.03% of the mass of the secondary particle artificial graphite; The mass of the conductive carbon black was 0.9% of the mass of the secondary particle artificial graphite; The mass of the polyacrylic acid binder was 2.5% of the mass of the secondary particle artificial graphite; The mass of the silicon monoxide was 5% of the mass of the secondary particle artificial graphite; The mass of the methyl benzoate was 0.25% of the mass of the secondary particle artificial graphite.

[0106] Preparation of negative electrode sheet: The above negative electrode slurry was uniformly coated on both sides of a 12μm copper foil, and the coating surface density was 8mg / cm 2 After coating, the water was dried in an oven and reserved, and then rolling was performed to achieve a compaction density of 1.55cm 3 / mg, and finally the negative electrode sheet was obtained by placing it in a vacuum environment at 85℃ for 4h.

[0107] Preparation of positive electrode sheet: A slurry was prepared by mixing NCM811 positive electrode active material, PVDF binder, conductive carbon black and carbon nanotubes in NMP solvent in a mass ratio of 92:4:1:2, and then coated on both surfaces of an aluminum foil, dried and rolled to form a positive electrode sheet.

[0108] Electrolyte: The electrolyte was: 85wt% solvent (EC+DMC+EMC, volume ratio 1:1:1), 10wt% lithium salt LiPF6 and 5wt% additive (vinylene carbonate).

[0109] Preparation of the battery: The positive electrode sheet, the separator (celegard 2400), and the negative electrode sheet were prepared into a stack core by a Z-shaped stacking machine, and then were placed into a shell, injected with electrolyte, and packaged. After that, the battery was placed at 35°C for 5h, and then was placed at 45°C, and was charged at a rate of 0.05C to 3.2V, and then was charged at a rate of 0.33C to 4.0V, and then was charged at a rate of 0.1C to 4.2V, and the cutoff current was 0.05C. Finally, the battery was placed for 12h, and the battery was obtained.

[0110] Example 2 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The mass of the single-walled carbon nanotubes was 0.001% of the mass of the secondary particle artificial graphite; The mass of the conductive carbon black was 0.92% of the mass of the secondary particle artificial graphite.

[0111] The rest was the same as Example 1, and finally the negative electrode sheet and the corresponding battery were prepared.

[0112] Example 3 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The methyl benzoate was replaced by ethyl benzoate, and the mass of the ethyl benzoate was 0.5% of the mass of the secondary particle artificial graphite; The mass of the single-walled carbon nanotubes was 0.05% of the mass of the secondary particle artificial graphite; The mass of the conductive carbon black was 1% of the mass of the secondary particle artificial graphite. The mass of the polyacrylic acid binder was 4% of the mass of the secondary particle artificial graphite. The mass of the silicon monoxide was 6% of the mass of the secondary particle artificial graphite.

[0113] The rest was the same as Example 1, and finally the negative electrode sheet and the corresponding battery were prepared.

[0114] Example 4 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The mass of the single-walled carbon nanotubes was 0.05% of the mass of the secondary particle artificial graphite; The mass of the methyl benzoate was 0.5% of the mass of the secondary particle artificial graphite.

[0115] The rest was the same as Example 1, and finally the negative electrode sheet and the corresponding battery were prepared.

[0116] Example 5 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The mass of the single-walled carbon nanotubes is 0.1% of the mass of the secondary-particle artificial graphite; The mass of the methyl benzoate is 0.5% of the mass of the secondary-particle artificial graphite.

[0117] The rest is the same as in Example 1, and finally the negative electrode sheet and the corresponding battery are prepared.

[0118] Example 6 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The mass of the methyl benzoate is 3% of the mass of the secondary-particle artificial graphite.

[0119] The rest is the same as in Example 1, and finally the negative electrode sheet and the corresponding battery are prepared.

[0120] Example 7 According to the method of Example 1, except that in the preparation of the negative electrode slurry: The methyl benzoate is replaced by methyl propionate, and the mass of the methyl propionate is 0.5% of the mass of the secondary-particle artificial graphite.

[0121] The rest is the same as in Example 1, and finally the negative electrode sheet and the corresponding battery are prepared.

[0122] Example 8 According to the method of Example 1, except that: The secondary-particle artificial graphite, methyl benzoate and methyl propionate are mixed uniformly to obtain a mixture, the mixture is evenly divided into 3 batches according to the mass, and then added into the conductive glue for mixing and scraping, and then water is added to adjust the viscosity of the slurry, so as to obtain a negative electrode slurry with a solid content of 43wt% and a viscosity of 2280mPa·S; wherein the mass of the methyl propionate is 0.25% of the mass of the secondary-particle artificial graphite; The rest is the same as in Example 1, and finally the negative electrode sheet and the corresponding battery are prepared.

[0123] Comparative Example 1 According to the method of Example 1, except that: No methyl benzoate is added, and the mass of the single-walled carbon nanotubes is 0.03% of the mass of the secondary-particle artificial graphite; finally, it is placed in a vacuum environment at 80°C for 4h and then taken out; The rest is the same as in Example 1, and finally the negative electrode sheet and the corresponding battery are prepared.

[0124] Performance test 1. EIS test: Electrochemical impedance test was performed on the battery at 50% SOC and 25℃: a single-channel Zennar electrochemical workstation from the Physical and Chemical Center was used; the symmetric battery was equipped with an acrylic clamp plate and two dovetail clamps to ensure interface contact and equal pressure conditions; the frequency range was 1 Hz-10 KHZ; the alternating current was 10 uA-100 uA, and the obtained data was plotted into a Nyquist graph using ZView software.

[0125] 2. Cycle gas production test: The volume of the battery before and after the volume change was calculated, i.e., the volume change of the battery, by using the drainage method to measure the volume of the battery at full charge after a certain number of charge and discharge cycles, which was the gas production of the battery (gas production, mL / Ah).

[0126] 3. Full charge rebound (fixed point thickness measurement): The thickness of the same electrode at the same position in the full charge state was measured using a digital micrometer, which was used as the calculation of the full charge rebound rate.

[0127] 4. Cycle performance test: Cycle performance: the battery was placed in a 25℃ and 45℃ constant temperature box, respectively, and was subjected to 1C / 1C charge and discharge, and the cycle number when the capacity retention rate decreased to 80%.

[0128] The Nyquist comparison of the batteries in Examples 1-8 and the battery in Comparative Example 1 is shown in FIG. Figure 1

[0129] The cycle gas production test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 are shown in FIG. Figure 2 The vertical coordinate unit is "mL / Ah".

[0130] The cycle performance test results of the batteries in Examples 1-3 and the battery in Comparative Example 1 at 25℃ are shown in FIG. Figure 3

[0131] The cycle performance test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 at 45℃ are shown in FIG. Figure 4 carboxylate negative active material conductive agent binder negative electrode sheet positive electrode sheet electrolyte separator preparation conditions

[0132] The test results of the batteries in Examples 1-8 and the battery in Comparative Example 1 are shown in Table 1.

[0133] Table 1 From the above test results, it can be seen that the negative electrode composition in the present application has a low full charge rebound rate when used in a battery, and the cycle number is greatly increased.

[0134] The above description is only a preferred embodiment of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.​​​

Claims

1. A negative electrode composition, characterized in that, Includes negative electrode active materials, conductive agents, carboxylic acid esters, and binders; The conductive agent includes single-walled carbon nanotubes, and the negative electrode active material includes carbon materials and silicon materials. The mass of the carboxylic acid ester is 0.1%-3% of the mass of the carbon material.

2. The negative electrode composition according to claim 1, characterized in that, In the negative electrode composition, the carboxylic acid ester is attached to the carbon material; And / or, the carboxylic esters include C1-C18 alkyl carboxylic esters and / or C8-C18 aryl carboxylic esters; And / or, the carbon material includes one or more of natural graphite, primary particulate artificial graphite, secondary particulate artificial graphite, needle coke graphite, petroleum coke graphite, and coated graphite composite materials. And / or, the silicon material includes one or more of silicon suboxide, silicon carbide, pre-magnesium silicon, and pre-lithiated silicon; And / or, the conductive agent further includes conductive agent A, which is different from single-walled carbon nanotubes; And / or, the adhesive includes one or more of cellulose salt adhesives, polyacrylic acid adhesives, polyacrylonitrile adhesives, and styrene-butadiene rubber adhesives; And / or, the mass of the silicon material is 0.1%-15% of the mass of the carbon material; And / or, the mass of the single-walled carbon nanotubes equals the mass of the silicon material. a, a is 0.6%-3%; And / or, the mass of the single-walled carbon nanotube is 0.02%-0.2% of the mass of the carbon material; And / or, the mass of the conductive agent is 0.5%-1.5% of the mass of the carbon material; And / or, the mass of the binder is 2%-4% of the mass of the carbon material.

3. The negative electrode composition according to claim 2, characterized in that, The general chemical formula of the C1-C18 alkyl carboxylic acid ester is R. 11 COOR 12 , where R 11 It is a C1-C3 alkyl group, R 12 It is a C1-C18 alkyl group; And / or, the C8-C18 aryl carboxylic acid esters include C8-C18 benzoate esters and / or C8-C18 o-methylbenzoate esters; And / or, the carboxylic ester comprises a C1-C18 alkyl carboxylic ester and a C8-C18 aryl carboxylic ester in a mass ratio of (0.5-3):1; And / or, the conductive agent A comprises conductive carbon black and / or graphene; And / or, the mass of the silicon material is 1%-10% of the mass of the carbon material.

4. A negative electrode slurry, characterized in that, Includes water and the negative electrode composition according to any one of claims 1-3.

5. A method for preparing a negative electrode slurry, characterized in that, Includes the following steps: Water and a negative electrode composition are mixed; wherein the negative electrode composition is the negative electrode composition according to any one of claims 1-3.

6. The method for preparing the negative electrode slurry according to claim 5, characterized in that, The preparation method of the negative electrode slurry includes the following steps: S1. The conductive agent, binder and some water are mixed in the first mixture, and then silicon material is added for the second mixture to obtain the conductive adhesive liquid; S2. After the carboxylic acid ester and carbon material are mixed for the third time, they are added to the conductive adhesive for the fourth mixing. Then, the remaining water is added to adjust the viscosity of the system to obtain the negative electrode slurry.

7. A negative electrode sheet, characterized in that, include: Negative electrode current collector and negative electrode active layer; The negative electrode active layer is disposed on at least one surface of the negative electrode current collector; The negative electrode active layer comprises the negative electrode composition according to any one of claims 1-3, or the negative electrode active layer comprises a layer formed after drying the negative electrode slurry according to claim 4, or the negative electrode active layer comprises a layer formed after drying the negative electrode slurry prepared by the method of preparing the negative electrode slurry according to claim 5 or 6.

8. A method for preparing a battery, characterized in that, Includes the following steps: The positive electrode, negative electrode and separator are wound or stacked together to form a cell, which is then placed in a casing and injected with electrolyte. After that, it is packaged, left to stand, formed and tested for capacity to obtain a battery. The negative electrode sheet includes the negative electrode sheet described in claim 7.

9. The method for preparing a battery according to claim 8, characterized in that, The electrolyte includes an organic solvent and a lithium salt, and the organic solvent includes carbonate solvents. And / or, the formation conditions include: charging to 0.1V-4.3V at a constant current rate of 0.01C-0.33C at 40℃-50℃, and then charging to 4.0-4.15V at a constant current rate of 0.33C. And / or, the conditions for the capacity division include: charging 4.2V-4.3V at a constant current and constant voltage at a rate of 0.1C-0.15C at 40℃-50℃, with a cutoff current of 0.05C.

10. A battery prepared by the method of preparation of the battery according to claim 8 or 9.

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