Battery negative electrode material, preparation method thereof, negative electrode plate, lithium ion battery and electric equipment

Abstract

The invention relates to the field of lithium ion batteries, and discloses a battery negative electrode material and a preparation method thereof, a negative electrode plate, a lithium ion battery and electric equipment. The battery negative electrode material comprises a negative electrode active substance, a conductive agent, polyvinylidene fluoride and a cationic polyelectrolyte-polyion liquid compound with the mass percent not more than 2%, the cationic polyelectrolyte-polyion liquid compound is a compound formed by complexing polythiophene and Na < + > PSS <->. According to the invention, a compound formed by complexing polythiophene and Na < + > PSS <-> is used as a novel binder to be matched with conventional polyvinylidene fluoride, so that the problems of large viscosity change, particle aggregation and non-uniform surface density of the lithium titanate battery negative electrode slurry can be improved, and the peeling strength of a lithium titanate battery negative electrode plate is remarkably improved; and the resistivity of the negative pole piece of the lithium titanate battery is obviously reduced, and meanwhile, the high-rate charge and discharge efficiency of the lithium titanate battery is also improved.

Description

TECHNICAL FIELD

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

[0002] The lithium titanate material has a spinel structure, and as a kind of lithium battery negative active material, it will not deform during charging and discharging, so the lithium titanate battery has the advantages of large rate charging and discharging performance, ultra-long cycle life, extremely high safety, stable charging platform, wide use temperature range, etc. However, the theoretical capacity of the lithium titanate material is low, about 175 mAh / g, which is only about half of the theoretical capacity of the traditional negative electrode material graphite (372 mAh / g). At present, the capacity of the lithium titanate battery can be improved from the aspects of the lithium titanate material itself, conductive agent, binder, etc. By reducing the particle size of the lithium titanate particles, the compaction density can be improved, but in the preparation of the slurry, the negative electrode sheet is still made by using the traditional PVDF oily binder, which not only causes large changes in the viscosity of the slurry, poor particle dispersion, poor coating consistency, but also causes low peeling strength of the electrode sheet, poor flexibility, easy powdering and peeling, etc. At the same time, PVDF is insulating to ions and electrons, which limits the conduction efficiency of lithium ions and electrons, and thus increases the internal resistance of the electrode sheet, affecting the rate performance and cycle performance of the battery. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a battery negative electrode material and a preparation method thereof, so that the peeling strength of the negative electrode sheet formed by the negative electrode material is significantly improved, and the resistivity is significantly reduced.

[0004] Another purpose of the present application is to provide a battery negative electrode slurry and a preparation method thereof, so that the high rate (10C) charging and discharging efficiency of the lithium ion battery formed by the negative electrode material is obviously improved.

[0005] Another purpose of the present application is to provide a negative electrode sheet, a lithium ion battery and an electric device prepared based on the above-mentioned negative electrode material.

[0006] In order to solve the above technical problems / achieve the above purposes or at least partially solve the above technical problems / achieve the above purposes, as a first aspect of the present application, a battery negative electrode material is provided, which comprises a negative active material, a conductive agent, polyvinylidene fluoride and a conjugated polyelectrolyte-polyionic liquid complex (CPE-PIL complex) with a mass percentage of not more than 2%; the conjugated polyelectrolyte-polyionic liquid complex is a complex formed by complexation of polythiophene and Na + PSS - .

[0007] Optionally, the mass percentage of the conjugated polyelectrolyte-polyionic liquid complex is 0.5-2%.

[0008] Optionally, the polythiophene includes poly[3-(5-trimethylammoniumpentyl)thiophene bromide].

[0009] Optionally, the negative electrode active material includes lithium titanate, and the conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene.

[0010] As a second aspect of the present application, a method for preparing the battery negative electrode material as described in the present application is provided, comprising:

[0011] Polyvinylidene fluoride and a conjugated polyelectrolyte-polyionic liquid complex are added to an organic solvent and stirred evenly to form a mixed glue solution. A conductive agent is then added and stirred evenly to form a conductive slurry. Finally, a negative electrode active material is added and dispersed evenly to obtain a negative electrode slurry. The negative electrode material is obtained after drying and removing the organic solvent.

[0012] As a third aspect of the present application, a negative electrode plate is provided, comprising a current collector and the negative electrode material described in the present application coated on the surface of the current collector.

[0013] As a fourth aspect of the present application, a lithium-ion battery is provided, comprising a positive electrode plate, the negative electrode plate described in the present application, a separator and an electrolyte.

[0014] As a fifth aspect of the present application, an electrical device is provided, comprising the lithium-ion battery described in the present application, wherein the lithium-ion battery provides electrical energy for the electrical device.

[0015] As a sixth aspect of the present application, a conjugated polyelectrolyte-polyionic liquid complex is provided for use in preparing a negative electrode material for a battery; the conjugated polyelectrolyte-polyionic liquid complex is polythiophene and Na + PSS - Complex formed by complexation.

[0016] Optionally, the battery comprises a lithium titanate battery.

[0017] This application uses polythiophene and Na + PSS - The complex formed by complexation is used as a new binder in combination with conventional polyvinylidene fluoride, which can improve the problems of large viscosity variation, particle agglomeration, and uneven surface density of the negative electrode slurry of lithium titanate batteries, significantly improve the peel strength of the negative electrode sheets of lithium titanate batteries, and significantly reduce the resistivity of the negative electrode sheets of lithium titanate batteries. At the same time, it also improves the high-rate charge and discharge efficiency of lithium titanate batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The normal temperature 4C / 4C cycle retention rate comparison curves of various embodiments and comparative examples are shown. DETAILED DESCRIPTION

[0019] The application discloses a battery negative electrode material and a preparation method thereof, a negative electrode sheet, a lithium ion battery and an electric equipment. Those skilled in the art can refer to the content herein and appropriately improve process parameters to realize. It should be particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are regarded as included in the application. The products, processes and applications described in the application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the preparation method described herein without departing from the content, spirit and scope of the application to realize and apply the technology of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0020] It should be noted that in this text, if relationship terms such as "first" and "second", "step 1" and "step 2", and "(1)" and "(2)" and the like appear, they are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element. Meanwhile, the embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0021] In a first aspect of the application, a battery negative electrode material is provided, comprising a negative electrode active material, a conductive agent, polyvinylidene fluoride and a conjugated polyelectrolyte-polyionic liquid complex (CPE-PIL complex) with a mass percentage of not more than 2%; the conjugated polyelectrolyte-polyionic liquid complex is a complex formed by complexing polythiophene and Na + PSS - complex.

[0022] The polythiophene can be poly[3-(5-trimethylammonium pentyl) thiophene bromide], and the side chain modification group makes it carry a negative charge, and the Na - of PSS+ Form ionic bonds, stabilize the complex structure, and improve the mechanical strength and structural stability of the adhesive. Moreover, these functional groups and PSS - The sulfonic acid groups and water molecules form hydrogen bonds, which enhances the interfacial adhesion between the binder and the electrode material (such as active material, current collector). In addition, the thiophene ring conjugated system of the polythiophene molecular chain interacts with each other to form a conductive path, giving the binder electronic conductivity, which is beneficial to the charge transfer of the battery electrode. The battery prepared using the negative electrode material of the present application has a negative electrode sheet with higher peel strength, stronger stability and lower impedance, which can avoid the large change in slurry viscosity, poor particle dispersion, uneven surface density, poor flexibility of the negative electrode sheet, easy powder loss and falling off during the manufacturing process, and improve the high-rate charge and discharge performance of the battery.

[0023] In certain embodiments of the present application, the mass percentage of the polyvinylidene fluoride is 1-2.5%, such as 1.0%, 1.5%, 2.0%, 2.5% or any value between the two. The mass percentage of the cationic polyelectrolyte-polyionic liquid complex is 0.5-2%, such as 0.5%, 1.0%, 1.5%, 2.0% or any value between the two. Although the CPE-PIL complex has good ion and electron conductivity, excessive addition during the preparation of lithium titanate negative electrode slurry will affect the electrical properties, processability and cost of lithium titanate batteries; more than 2% will hinder the Li + Diffusion in the solid phase causes capacity loss, and the insulating polyelectrolyte (PSS) contained in the CPE-PIL composite reduces contact between the conductive agent and the active material, increasing interfacial impedance. Furthermore, the polyelectrolyte chains in the CPE-PIL composite readily absorb water, and excessive amounts react with the alkaline groups on the lithium titanate surface to form a gel, resulting in poor slurry fluidity.

[0024] In certain embodiments of the present application, the negative electrode active material includes lithium titanate, which has the following properties:

[0025] 1μm≤particle size≤18μm, 3.0m 2 / g≤Specific surface area≤26.0m 2 / g, 0.8g / cm 3 ≤Tap density≤1.8g / cm 3 .

[0026] In some embodiments of the present application, the conductive agent can be a conventional material in the art, for example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, and graphene, wherein the conductive carbon black includes but is not limited to SP, Ketjen black, and acetylene black. In some other embodiments of the present application, the mass percentage of the conductive agent is 1-5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5.0%, or any value between any two of them. In some other embodiments of the present application, the conductive agent includes 1.2% of conductive carbon black SP and 1.8% of carbon nanotubes.

[0027] In a second aspect of the present application, a preparation method of the battery negative electrode material as described in the present application is provided, comprising:

[0028] The polyvinylidene fluoride and the conjugated polyelectrolyte-polyion liquid composite are added to an organic solvent, stirred to form a mixed glue solution, then the conductive agent is added and stirred to form a conductive slurry, and finally the negative electrode active material is added and dispersed to obtain a negative electrode slurry. After drying to remove the organic solvent, the negative electrode material is obtained.

[0029] In some embodiments of the present application, the organic solvent includes but is not limited to N-methyl pyrrolidone (NMP), and the solid content of the mixed glue solution is 6%; in some other embodiments of the present application, the viscosity of the negative electrode slurry is adjusted to 8000 mPa·s-10000 mPa·s using an organic solvent.

[0030] In a third aspect of the present application, a negative electrode tab is provided, comprising a current collector and the negative electrode material as described in the present application coated on the surface of the current collector.

[0031] In some embodiments of the present application, the current collector includes a metal foil, for example, an aluminum foil, a copper foil, or the like; and the negative electrode material is composed of high-compaction lithium titanate, SP, CNT, PVDF, and CPE-PIL, which is coated on the metal foil after being prepared into a slurry by NMP, rolled, and tabbed to obtain the negative electrode tab.

[0032] In a fourth aspect of the present application, a lithium ion battery is provided, comprising a positive electrode tab, the negative electrode tab as described in the present application, and a separator and an electrolyte, and the battery type includes but is not limited to a soft pack battery, a button cell, a square cell, a cylindrical cell, a full cell, a half cell, and the like.

[0033] In some embodiments of the present application, the positive electrode tab comprises a current collector and a positive electrode material coated on the surface of the current collector, which is composed of active material (such as one or both of lithium manganate and lithium cobaltate), conductive agent and binder, and the ratio can be selected as 90:5:5. In the positive electrode tab, the conductive agent and the binder can both be conventional materials in the art, for example, the conductive agent can be selected from conductive carbon black SP, ketchen black, carbon nanotube, graphene and the like, and the binder can be selected from PVDF, SBR, CMC and the like.

[0034] In a fifth aspect of the present application, a power-using device is provided, which comprises the lithium ion battery described in the present application, and the lithium ion battery provides power for the power-using device. The power-using device can be various devices or equipment driven by the lithium ion battery, including but not limited to electric vehicles, electric cars, balance cars, flat cars, aircraft, lighting equipment, household appliances, smart terminals and other equipment or devices that need to be driven by electric energy.

[0035] As a sixth aspect of the present application, the soft package battery composed of the negative electrode material of the present application has a maximum peel strength of the negative electrode tab of 101.8 N / m and a minimum resistivity of 17.8 Ω·cm, while the soft package battery composed of the negative electrode material using only PVDF has a peel strength of the negative electrode tab of only 23.2 N / m and a resistivity as high as 76.6 Ω·cm. In addition, the soft package battery composed of the negative electrode material of the present application also shows extremely excellent electrochemical performance in 10C charging and discharging efficiency. Based on this, the present application provides the use of the conjugated polyelectrolyte-polyionic liquid complex in the preparation of a battery negative electrode material; the conjugated polyelectrolyte-polyionic liquid complex is a complex formed by the complexation of polythiophene and Na + PSS - complex. In some embodiments of the present application, the conjugated polyelectrolyte-polyionic liquid complex is used in the preparation of a lithium titanate battery negative electrode material.

[0036] In the various groups of comparative experiments provided in the present application, unless otherwise specified, the experimental conditions, materials and the like remain the same except for the differences indicated by each group in order to have comparability. The experimental materials and reagents used in the examples can be obtained from commercial channels unless otherwise specified.

[0037] The following further describes a battery negative electrode material and a preparation method thereof, a negative electrode tab, a lithium ion battery and a power-using device provided in the present application.

[0038] Example 1:

[0039] A binder PVDF is added to the NMP solution, and a glue solution is obtained after rapid stirring;

[0040] CPE-PIL complex was added into the glue solution, and after high-speed stirring, a mixed glue solution with a solid content of 6% was obtained; the CPE-PIL complex was poly[3-(5-trimethylammonium pentyl) thiophene bromide] and Na + PSS - complex formed by complexation, wherein the poly[3-(5-trimethylammonium pentyl) thiophene bromide] was purchased from Guangzhou Yuanda New Materials Co., Ltd.;

[0041] The conductive agent SP and the CNT slurry were added into the mixed glue solution, and after long-time high-speed stirring, a conductive slurry was obtained;

[0042] High-pressure lithium titanate was added into the conductive slurry, and after high-speed stirring, a uniformly dispersed negative electrode slurry was obtained;

[0043] The viscosity was adjusted by adding a certain proportion of NMP solution, and a qualified lithium titanate negative electrode slurry with a viscosity of 80000 mPa·s-10000 mPa·s and a fineness of 12 μm was obtained.

[0044] The prepared lithium titanate negative electrode slurry was subjected to coating, rolling, sheet making, baking, lamination, drying, liquid injection, formation, and containerization processes to obtain a soft package battery.

[0045] Comparative Example 1:

[0046] The binder PVDF was added into the NMP solution, and after rapid stirring, a glue solution was obtained;

[0047] The conductive agent SP and the CNT slurry were added into the glue solution, and after long-time high-speed stirring, a conductive slurry was obtained;

[0048] High-pressure lithium titanate was added into the conductive slurry, and after high-speed stirring, a uniformly dispersed negative electrode slurry was obtained;

[0049] The viscosity was adjusted by adding a certain proportion of NMP solution, and a qualified lithium titanate negative electrode slurry with a viscosity of 8000 mPa·s-10000 mPa·s and a fineness of 12 μm was obtained.

[0050] The prepared lithium titanate negative electrode slurry was subjected to coating, rolling, sheet making, baking, lamination, drying, liquid injection, formation, and containerization processes to obtain a soft package battery.

[0051] Comparative Example 2:

[0052] The binder PVDF was added into the NMP solution, and after rapid stirring, a glue solution was obtained;

[0053] CPE-PIL complex was added to the glue solution, and after high-speed stirring, a mixed glue solution with a solid content of 6% was obtained; the CPE-PIL complex was a complex formed by complexing carboxylated polyfluorene (PFBT-COOH) and polyethyleneimine (B-PEI);

[0054] The conductive agent SP and CNT slurry were added to the mixed glue solution, and after long-time high-speed stirring, a conductive slurry was obtained;

[0055] High-density lithium titanate was added to the conductive slurry, and after high-speed stirring, a uniformly dispersed negative electrode slurry was obtained;

[0056] The viscosity was adjusted by adding a certain proportion of NMP solution, and a qualified lithium titanate negative electrode slurry with a viscosity of 8000-10000 mPa·s and a fineness of 12 μm was obtained.

[0057] The prepared lithium titanate negative electrode slurry was subjected to coating, rolling, sheet making, baking, lamination, drying, liquid injection, formation, and capacity distribution processes to obtain a soft package battery.

[0058] Comparative Example 3:

[0059] CPE-PIL complex was added to the NMP solution, and after high-speed stirring, a glue solution with a solid content of 6% was obtained; the CPE-PIL complex was a complex formed by complexing poly[3-(5-trimethylammonium pentyl) thiophene] and Na + PSS - to form a complex;

[0060] The conductive agent SP and CNT slurry were added to the glue solution, and after long-time high-speed stirring, a conductive slurry was obtained;

[0061] High-density lithium titanate was added to the conductive slurry, and after high-speed stirring, a uniformly dispersed negative electrode slurry was obtained;

[0062] The viscosity was adjusted by adding a certain proportion of NMP solution, and a qualified lithium titanate negative electrode slurry with a viscosity of 8000-10000 mPa·s and a fineness of 12 μm was obtained.

[0063] The prepared lithium titanate negative electrode slurry was subjected to coating, rolling, sheet making, baking, lamination, drying, liquid injection, formation, and capacity distribution processes to obtain a soft package battery.

[0064] Experimental Example:

[0065] The soft package batteries assembled with the negative electrode materials of the application scheme and the materials of Comparative Examples 1-3 were tested, with focus on the electrode strip peeling strength, resistivity, normal temperature rate charge / discharge efficiency, and normal temperature cycle retention rate (4C charge / 4C discharge):

[0066] The specific material formulations of the comparative examples and the examples are shown in Table 1 below.

[0067] Table 1

[0068]

[0069]

[0070] The relevant experimental results are shown in Tables 2 and 3 below, and Figure 1 ;

[0071] Table 2

[0072]

[0073] According to the results in Table 2, it can be seen directly that the peel strength of the electrode sheet gradually increases with the CPC content from 0.5% to 2%, and reaches a maximum of about 100 N / m, when PVDF and poly[3-(5-trimethylammonium pentyl) thiophene] are used in combination with the CPC formed by complexation of Na + PSS - . Comparative Example 1 is an example in which the electrode sheet is prepared using only PVDF, Comparative Example 2 is an example in which the electrode sheet is prepared using PVDF and PFBT-COOH in combination with the CPC formed by complexation of B-PEI, and Comparative Example 3 is an example in which the electrode sheet is prepared using only poly[3-(5-trimethylammonium pentyl) thiophene] in combination with the CPC formed by complexation of Na + PSS - . The peel strength of the electrode sheet in each of these comparative examples is significantly lower than that in each of the examples.

[0074] In addition, in terms of the effect of reducing the resistivity, each of the examples also exhibits the same trend as the peel strength.

[0075] Table 3

[0076]

[0077] According to the results in Table 3, there is no difference in the charge and discharge efficiency of each of the examples and the comparative examples under the condition of 1C / 1C, but as the rate gradually increases, the decrease in the charge and discharge efficiency of each of the comparative examples increases, while the decrease in the charge and discharge efficiency of each of the examples is smaller. Under the condition of 10C / 10C, the charge and discharge efficiency of each of the examples remains at 90%, while the highest charge and discharge efficiency in the comparative examples is 88% in Comparative Example 1.

[0078] According to the results in Table 3, there is no difference in the charge and discharge efficiency of each of the examples and the comparative examples under the condition of 1C / 1C, but as the rate gradually increases, the decrease in the charge and discharge efficiency of each of the comparative examples increases, while the decrease in the charge and discharge efficiency of each of the examples is smaller. Under the condition of 10C / 10C, the charge and discharge efficiency of each of the examples remains at 90%, while the highest charge and discharge efficiency in the comparative examples is 88% in Comparative Example 1. Figure 1The results can also be compared visually to show the cycle performance difference between each pair of examples and examples, and it can be seen from the figure that after 1500 cycles at 4C / 4C room temperature, the capacity retention rate from high to low is in turn example 4, example 3, example 2, example 1, comparative example 1, comparative example 3 and comparative example 2, the capacity retention rate of the examples is all above 80%, while the capacity retention rate of the comparative examples is all below 80%.

[0079] In summary, the example of comparative example 1 shows that the effect of using PVDF alone is not as good as the battery performance of using PVDF and CPC in combination, the example of comparative example 2 shows that a specific CPC and PVDF need to be used in combination to achieve the expected battery performance; the example of comparative example 3 shows that the amount of CPC should not be too high, and CPC should not be used alone, otherwise the battery performance will be poor.

[0080] The above is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A battery negative electrode material, characterized in that: The invention comprises a negative electrode active material, a conductive agent, polyvinylidene fluoride and a conjugated polyelectrolyte-polyionic liquid complex with a mass percentage not exceeding 2%; the conjugated polyelectrolyte-polyionic liquid complex is polythiophene and Na + PSS - Complex formed by complexation.

2. The battery negative electrode material according to claim 1, characterized in that The mass percentage of the conjugated polyelectrolyte-polyionic liquid complex is 0.5-2%.

3. The battery negative electrode material according to claim 1, characterized in that The polythiophene includes poly[3-(5-trimethylammoniumpentyl)thiophene bromide].

4. The battery negative electrode material according to claim 1, characterized in that The negative electrode active material includes lithium titanate, and the conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene.

5. A method for preparing a negative electrode material for a battery as claimed in claim 1, characterized in that: include: Polyvinylidene fluoride and a conjugated polyelectrolyte-polyionic liquid complex are added to an organic solvent and stirred evenly to form a mixed glue solution. A conductive agent is then added and stirred evenly to form a conductive slurry. Finally, a negative electrode active material is added and dispersed evenly to obtain a negative electrode slurry. The negative electrode material is obtained after drying and removing the organic solvent.

6. A negative electrode plate, characterized in that: The invention comprises a current collector and the negative electrode material according to any one of claims 1 to 3 coated on the surface of the current collector.

7. A lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet as claimed in claim 6, a separator and an electrolyte.

8. An electrical device, characterized in that: The lithium-ion battery according to claim 7 is included, and the lithium-ion battery provides electrical energy for the electrical device.

9. Application of conjugated polyelectrolyte-polyionic liquid complex in the preparation of battery negative electrode materials; the conjugated polyelectrolyte-polyionic liquid complex is polythiophene and Na + PSS - Complex formed by complexation.

10. The use according to claim 9, characterized in that The battery comprises a lithium titanate battery.

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