Lithium-ion battery electrode sheet and preparation method thereof

Abstract

The present invention relates to a lithium-ion battery electrode sheet and a preparation method thereof, comprising the following steps: (1) adding an aromatic diamine, an aromatic dianhydride, and a conductive agent to a solvent, and subjecting the mixture to a polymerization reaction to obtain a reaction solution; wherein the ratio of the aromatic diamine, the aromatic dianhydride, and the conductive agent is (2-4) mmol: (2-4) mmol: (40-60) mg; (2) evaporating and concentrating the reaction solution to obtain a precursor slurry; and (3) coating the precursor slurry on a current collector, and sintering the resulting lithium-ion battery electrode sheet. The present invention completes the mixing of a binder, a conductive agent, and an active material during the synthesis of the precursor material, greatly simplifying the preparation process compared to traditional processes, not requiring a high-precision mixer or excessive solvent for slurrying, and effectively shortening the preparation time. Furthermore, the resulting battery electrode sheet has excellent electrochemical properties, good cycle performance, and good stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery electrode sheet and a preparation method thereof. Background Art

[0002] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. The performance of lithium-ion batteries depends largely on the choice of their electrode materials. As for negative electrode materials, although there has been extensive research on traditional inorganic materials and some important scientific research results have been achieved, they still have many shortcomings. First, inorganic materials are scarce and non-renewable. Second, during the battery charging and discharging process, inorganic materials are prone to exothermic reactions with the electrolyte, causing thermal runaway. Organic materials, as new lithium-ion battery negative electrode materials, have great research value due to their abundant resources, environmental friendliness, sustainable regeneration, and high theoretical specific capacity.

[0003] The manufacture of electrode sheets is an important process in the preparation of lithium-ion batteries, which is mainly divided into two important steps: one is the preparation of slurry, and the other is the coating of slurry on the positive and negative current collectors. During the slurry manufacturing process, the active material, conductive agent, adhesive, etc. are mixed and dispersed evenly with the solvent through a mixer or disperser to form a freely flowing electrode slurry; battery slurry coating is the next process after the preparation of the slurry is completed. The main purpose of this process is to evenly coat the slurry with good stability, good viscosity and good fluidity on the positive and negative current collectors, and then remove the solvent in the slurry by drying. Pole sheet manufacturing is a key process in the preparation of lithium-ion batteries. At present, the entire manufacturing process of battery pole sheets is lengthy and cumbersome, with complex processes, a large number of equipment, and very high investment costs. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies and provide a lithium ion battery electrode sheet and a preparation method thereof, simplify the process, and improve the cycle performance of the battery made using the electrode sheet.

[0005] In order to achieve the above technical purpose, the technical solution of the preparation method of the present invention is:

[0006] The following steps are involved:

[0007] (1) adding an aromatic diamine, an aromatic dianhydride, and a conductive agent to a solvent, and subjecting the mixture to a polymerization reaction to obtain a reaction solution; wherein the ratio of the aromatic diamine, the aromatic dianhydride, and the conductive agent is (2-4) mmol: (2-4) mmol: (40-60) mg;

[0008] (2) evaporating and concentrating the reaction solution to obtain a precursor slurry;

[0009] (3) The precursor slurry is coated on the current collector and sintered to obtain a lithium-ion battery electrode sheet.

[0010] Furthermore, in step (1), the aromatic diamine includes terephthalamide; the aromatic dianhydride includes 1,2,4,5-pyromellitic dianhydride; and the conductive agent includes superconductive carbon black.

[0011] Furthermore, in step (1), the solvent is N-methylpyrrolidone; and the ratio of the aromatic diamine to N-methylpyrrolidone is (2-4) mmol: (20-40) mL.

[0012] Furthermore, in step (1), the polymerization reaction is carried out at 160-200° C. for 6-10 hours.

[0013] Furthermore, in step (2), the reaction solution is evaporated and concentrated in a vacuum oven to a viscosity of 3000 to 5000 mPa / s.

[0014] Furthermore, the temperature during evaporation and concentration is 130-150° C., and the time is 60-80 minutes.

[0015] Furthermore, in step (3), the current collector is copper foil.

[0016] Furthermore, in step (3), the sintering is carried out in an inert gas atmosphere at 280-320° C. for 7-9 hours.

[0017] Furthermore, the heating rate during sintering is 2-5°C / min.

[0018] The lithium-ion battery electrode sheet is prepared by the above preparation method.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] First, the present invention uses aromatic diamine and aromatic dianhydride as monomers for preliminary polymerization, and obtains a precursor slurry through evaporation and concentration. The mixing of binder, conductive agent and active material is completed when the precursor material is synthesized, and there is no need to add conductive agent again for mixing in the subsequent slurry preparation; second, the precursor slurry of the present invention is then coated and sintered to form polyimide. In the preparation process of the negative electrode of the lithium-ion battery, the polyimide can be used as both a binder and an active material, and there is no need to mix the binder again subsequently; third, the evaporation of the solvent on the electrode sheet after coating is completed simultaneously during the sintering process; through the cooperation of the above aspects, the present invention greatly simplifies the preparation process compared with the traditional process, does not require a high-precision mixer, does not require too much solvent for slurrying, and effectively shortens the preparation time; at the same time, the obtained battery electrode has excellent electrochemical properties, good cycle performance and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The infrared spectra of the prepared electrode materials PMTA and PMTAC (a mixture of PMTA and conductive carbon black);

[0022] Figure 2 The polyimide material PMTAC lithium ion battery negative electrode prepared by the present invention is 100mAhg -1 Cycle performance diagram;

[0023] Figure 3 The prepared polyimide material PMTAC lithium ion battery negative electrode is 1000mAhg -1 Cycle performance diagram;

[0024] Figure 4 This is a SEM image of the PMTA electrode sheet prepared in Example 2;

[0025] Figure 5 : is a SEM image of the PMTAC electrode sheet prepared in Example 1;

[0026] Figure 6 Impedance diagram of the polyimide material PMTAC lithium ion battery prepared in Example 3 before and after cycling;

[0027] Figure 7 The electrode sheet assembled battery prepared in Example 1 is 100 mAhg -1 Cycle performance diagram;

[0028] Figure 8 The electrode sheet assembled battery prepared in Example 2 is 100 mAhg -1 Cycle performance diagram. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] The method for preparing a lithium-ion battery electrode of the present invention comprises the following steps:

[0031] (1) Mixing: Mix the raw material powders according to the process ratio, add an appropriate amount of conductive agent, and mix them evenly to obtain a mixed raw material;

[0032] The raw material powder includes the following components in parts by weight: the usage ratio of aromatic diamine, aromatic dianhydride and conductive agent is (2-4) mmol: (2-4) mmol: (40-60) mg, preferably 3 mmol: 3 mmol: (40-60) mg, specifically, the conductive agent can be 40 mg, 50 mg and 60 mg, etc.; preferably, the raw materials include PMDA (1,2,4,5-pyromellitic dianhydride) and TA (terephthalamide), and the conductive agent includes superconductive carbon black (Carbon ECP).

[0033] (2) Preparing a precursor; adding an appropriate amount of solvent to the mixed raw materials to obtain a reaction solution, and placing it in an oil bath for high-temperature polymerization;

[0034] The solvent is an organic solvent, preferably, the solvent includes N-methylpyrrolidone (NMP), the amount ratio of the aromatic diamine and N-methylpyrrolidone is (2-4) mmol: (20-40) mL; the heating temperature is 160-200° C., and the heating and stirring time is 6-10 h.

[0035] (3) evaporation; taking a portion of the solution obtained by the reaction and placing it in a vacuum oven to evaporate most of the solvent therein to obtain a slurry;

[0036] The obtained solution is a uniform mixture of polyamic acid (polyimide precursor) and conductive agent solution. The volume of the taken-out part of the solution is 2.5 ml, which is placed in a vacuum drying oven at an evaporation temperature of 130-150° C. and a vacuum evaporation time of 60-80 min, specifically 60 min, 70 min or 80 min, etc.

[0037] (4) Coating: The slurry is evenly coated on the positive and negative electrode current collectors; the current collector can be made of copper foil; the coating thickness can be adjusted according to the situation, preferably 10 to 100 μm, more specifically, such as 50 μm, 60 μm or 70 μm.

[0038] (5) Sintering: The organic material-based lithium-ion battery electrode sheet is synthesized at high temperature in an inert gas atmosphere. The inert gas is nitrogen, the sintering temperature is 280-320°C, and the synthesis time is 7-9 hours. The organic material is a polyimide material PMTAC containing conductive carbon black.

[0039] The polyimide of the present invention can serve as both a binder and an active material during the preparation of lithium-ion battery negative electrodes. The binder, conductive agent, and active material are mixed during the synthesis of the precursor material. The polyimide precursor is selected from PMDA, TA, and superconductive carbon black. The viscosity of the slurry is controlled by controlling the drying time. The method of the present invention improves the cumbersome process of traditional electrode sheet preparation and significantly shortens the time required for electrode sheet preparation. The prepared electrode sheet has excellent cycle performance and stability. Specific advantages of the present invention are as follows:

[0040] 1. In the present invention, the conductive agent is added and mixed evenly when the precursor material is synthesized. In the subsequent slurry preparation, there is no need to add the conductive agent again for mixing, which greatly shortens the preparation time.

[0041] 2. The present invention utilizes the characteristic that polyimide itself can be used as a binder to bond the conductive agent and the active material (polyimide). There is no need to mix the binder again later, so the preparation process is further simplified.

[0042] 3. The present invention can control the viscosity of the solvent (3000-5000 mPa / s) by controlling the evaporation time, making the preparation of the slurry simpler.

[0043] 4. The present invention combines the evaporation of the solvent on the electrode after coating and the sintering of the material into one step, further reducing the preparation time of the electrode.

[0044] 5. The present invention improves the surface roughness and electrochemical performance by increasing the specific surface area of high-temperature calcination.

[0045] 6. The battery electrode manufacturing method of the present invention greatly simplifies the process flow, does not require a high-precision mixer, and does not require too much solvent for slurry preparation. It is not only beneficial to environmental protection and energy saving, but also solves the problems of slurry precipitation and agglomeration.

[0046] 7. The battery electrode prepared by the present invention has excellent electrochemical performance. Compared with the electrode prepared by the traditional preparation method, the cycle performance is more stable and the capacity is also improved.

[0047] The present invention is further described in detail below through specific examples.

[0048] Example 1

[0049] (1) Weigh 3 mmol each of PMDA (1,2,4,5-pyromellitic dianhydride) and TA (terephthalamide) and 50 mg of superconductive carbon black (Carbon ECP) as a conductive agent;

[0050] (2) 3 mmol of dried PMDA, 3 mmol of TA, and 50 mg of conductive carbon black were added to a flask, and then added to 30 mL of N-methylpyrrolidone and mixed uniformly to obtain a reaction solution;

[0051] (3) transferring the reaction solution obtained in step (2) to an oil bath for high-temperature polymerization reaction for 10 hours at a reaction temperature of 180°C;

[0052] (4) Measure 2.5 mL of the mixed solution obtained after the reaction in step (3), transfer it to a 5 mL small beaker, and then place it in a vacuum drying oven and dry it for 70 min at a drying temperature of 140° C. to obtain a precursor slurry;

[0053] (5) evenly applying the precursor slurry obtained in step (4) on a copper foil to obtain an organic precursor material electrode sheet;

[0054] (6) The electrode sheet obtained in step (5) was sintered at 300° C. for 8 hours in a nitrogen atmosphere with a heating rate of 5° C. / min in a tubular furnace to obtain a PMTAC-based lithium-ion battery electrode sheet.

[0055] Example 2

[0056] (1) Weigh 3 mmol each of PMDA (1,2,4,5-pyromellitic dianhydride) and TA (terephthalamide);

[0057] (2) Add 3 mmol of oven-dried PMDA and 3 mmol of TA to a flask and add 30 mL of N-methylpyrrolidone to mix well.

[0058] (3) The reaction solution obtained in step (2) was transferred to an oil bath and reacted at a high temperature of 180° C. for 10 hours;

[0059] (4) Measure 2.5 mL of the mixed solution obtained after the reaction in step (3), transfer it to a 5 mL small beaker, and then place it in a vacuum drying oven and dry it for 70 min at a drying temperature of 140° C. to obtain a precursor slurry;

[0060] (5) evenly applying the precursor slurry obtained in step (4) on a copper foil to obtain an organic precursor material electrode sheet;

[0061] (6) The electrode sheet obtained in step (5) was sintered at 300° C. for 8 hours in a nitrogen atmosphere with a heating rate of 5° C. / min in a tube furnace to obtain a PMTA-based electrode sheet.

[0062] Example 3

[0063] (1) Weigh 3 mmol each of PMDA (1,2,4,5-pyromellitic dianhydride) and TA (terephthalamide) and 50 mg of superconductive carbon black (Carbon ECP) as a conductive agent;

[0064] (2) Add 3 mmol of PMDA and 3 mmol of TA, and 50 mg of conductive carbon black to a flask, and add 30 mL of N-methylpyrrolidone to mix well;

[0065] (3) The reaction solution obtained in step (2) was transferred to an oil bath and reacted at a high temperature of 180° C. for 10 hours;

[0066] (4) Measure 2.5 mL of the mixed solution obtained after the reaction in step (3), transfer it to a 5 mL small beaker, and then place it in a vacuum drying oven and dry it for 60 min at a drying temperature of 140° C. to obtain a precursor slurry;

[0067] (5) evenly applying the precursor slurry obtained in step (4) on a copper foil to obtain an organic precursor material electrode sheet;

[0068] (6) The electrode sheet obtained in step (5) was sintered at 300°C for 8 hours in a nitrogen atmosphere with a heating rate of 5°C / min in a tube furnace.

[0069] Example 4

[0070] (1) Weigh 3 mmol each of PMDA (1,2,4,5-pyromellitic dianhydride) and TA (terephthalamide) and 50 mg of superconductive carbon black (Carbon ECP) as a conductive agent;

[0071] (2) Add 3 mmol of dried PMDA, 3 mmol of TA, and 50 mg of conductive carbon black into a flask and add 30 mL of N-methylpyrrolidone to mix well.

[0072] (3) The reaction solution obtained in step (2) was transferred to an oil bath and reacted at a high temperature of 180° C. for 10 hours;

[0073] (4) Measure 2.5 mL of the mixed solution obtained after the reaction in step (3), transfer it to a 5 mL small beaker, and then place it in a vacuum drying oven and dry it for 70 min at a drying temperature of 140° C. to obtain a precursor slurry;

[0074] (5) evenly applying the precursor slurry obtained in step (4) on a copper foil to obtain an organic precursor material electrode sheet;

[0075] (6) The electrode sheet obtained in step (5) was sintered at 300°C for 8 hours in a nitrogen atmosphere with a heating rate of 2°C / min in a tube furnace.

[0076] from Figure 1 It can be seen that the amide functional groups of polyimide exist stably before and after the addition of conductive carbon black, and the present invention prepares the polyimide material.

[0077] Figure 2 It can be seen that when the polyimide electrode sheet (PMTAC) prepared by the present invention is used as the negative electrode material of a lithium-ion battery, the test is carried out at a current density of 0.1A / g, and the initial discharge capacity is 1870mAh / g. After 100 cycles, the charging capacity can still be maintained at more than 95%, showing excellent cycle performance. This shows that the material prepared by this new preparation process of the present invention has good electrochemical properties, indicating that the role of the electrode sheet prepared by this method in the negative electrode of lithium-ion batteries has been reflected.

[0078] from Figure 3 It can be seen that at a higher current density, such as 1A / g, the initial charging capacity is 775mAh / g. After 323 cycles, the charging capacity reaches a maximum of 1077mAh / g, and the coulombic efficiency is 99.6%. After 500 cycles, it can still maintain a capacity of 821mAh / g. The electrochemical performance of the battery is still excellent.

[0079] Figure 4 This indicates that the PMTA material prepared using the new preparation process of the present invention forms a uniform crystal image.

[0080] Figure 5 It shows that after adding conductive carbon black, it can be evenly mixed in the PMTA material.

[0081] Figure 6 This shows that the impedance values of the lithium-ion battery prepared by the new method of the present invention before and after cycling are also excellent.

[0082] Example 5

[0083] The amount of the conductive agent was changed to 40 mg and 60 mg, and the other conditions were the same as in Example 1. The prepared electrode sheets were tested, and the results are shown in Table 1 below.

[0084] Table 1 Effects of different conductive agent dosages

[0085]

[0086] As can be seen from Table 1, when the amount of conductive agent is too much at 60 mg, the capacity remains basically unchanged, but too much conductive agent will lead to a decrease in the energy density of the battery. When the amount of conductive agent is too little at 40 mg, the capacity is significantly reduced and the cycle stability of the battery is also slightly worse. Therefore, relative to 3 mmol of PMDA, the preferred amount of conductive agent in the present invention is 50 mg.

[0087] Comparative Example 1

[0088] The electrode sheet was prepared by a conventional process, mainly by synthesizing polyimide from two monomers with the same preparation parameters as in Example 1, and then adding a binder and a conductive agent to prepare the electrode sheet. Specifically, PTFE was used as the binder.

[0089] The electrochemical properties of the obtained electrode sheets are as follows Figure 7 As shown, the discharge capacity of the first cycle is 1520 mAh / g, the charge capacity of the first week is only 832 mAh / g, and the capacity after 50 cycles is 587 mAh / g, which is much lower than the 1030 mAh / g of Example 1.

[0090] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention utilizes the good adhesion of polyimide and can be used as a binder. After the precursor solution is prepared, the solution is evaporated at high temperature to the concentration required for the slurry, and then directly coated. Compared with the traditional method, there is no need to add binders and organic solvents later, which not only saves time, but also is more environmentally friendly without adding toxic organic solvents. When the polyimide is finally sintered, the electrode sheet is thinner than the powder sample and has a larger specific surface area. The sintered material has a rough surface, which greatly improves the electrochemical performance. In summary, compared with the traditional method, it not only saves the time of preparing the electrode sheet and reduces pollution, but also the prepared electrode sheet has better chemical properties.

[0091] Comparative Example 2

[0092] The monomers were replaced with pyromellitic anhydride and melamine, and the performance test of the obtained electrode was as follows: Figure 8 As shown, the discharge capacity of the first cycle is 794 mAh / g, and the capacity after 50 cycles is 715 mAh / g, which is much lower than the 1030 mAh / g of Example 1. Therefore, the polyimide monomers of the present invention are preferably pyromellitic anhydride and terephthalamide.

[0093] The method of the present invention uses a one-pot synthesis technology to uniformly mix pyromellitic anhydride, terephthalamide and conductive carbon black in an oil bath to form a mixture of polyamic acid and conductive carbon black. A vacuum drying oven is then used to remove the solvent and control the slurry to the required viscosity. The main feature is that the preparation, drying and coating of active materials are integrated together, which greatly reduces the time from material preparation to electrode sheet preparation. The electrode sheet is then sintered at high temperature to form the required polyimide, and its characteristic as a strong binder is utilized to establish a stable and firm connection between the electrode material particles and the electrode material and the current collector. The negative electrode material prepared by the present invention has excellent cycle stability and conductivity. The electrode sheet preparation process is simple, low cost, and excellent comprehensive performance, and has broad prospects in the preparation of lithium-ion battery electrode sheets.

[0094] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a lithium-ion battery electrode sheet, characterized in that: The following steps are involved: (1) adding aromatic diamine, aromatic dianhydride and conductive agent to a solvent and performing polymerization reaction to obtain a reaction solution; The ratio of aromatic diamine, aromatic dianhydride and conductive agent is (2-4) mmol: (2-4) mmol: (40-60) mg; (2) Evaporating and concentrating the reaction liquid to obtain a precursor slurry; (3) Coating the precursor slurry on the current collector and sintering to obtain the negative electrode sheet of the lithium-ion battery; In step (1), the aromatic diamine includes terephthalamide; the aromatic dianhydride includes 1,2,4,5-pyromellitic dianhydride; and the conductive agent includes superconductive carbon black; In step (3), sintering is carried out in an inert gas atmosphere at 280-320°C for 7-9 hours.

2. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: In step (1), the solvent is N-methylpyrrolidone; the amount ratio of the aromatic diamine to N-methylpyrrolidone is (2-4) mmol: (20-40) mL.

3. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: In step (1), the polymerization reaction is carried out at 160-200° C. for 6-10 hours.

4. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: In step (2), the reaction solution is evaporated and concentrated in a vacuum oven to a viscosity of 3000 to 5000 mPa / s.

5. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: The temperature during evaporation and concentration is 130-150°C and the time is 60-80 minutes.

6. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: In step (3), the current collector is copper foil.

7. The method for preparing a lithium-ion battery electrode sheet according to claim 1, wherein: The heating rate during sintering is 2 to 5 °C / min.

8. A lithium-ion battery electrode sheet prepared according to the preparation method according to any one of claims 1 to 7.

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