Lithium ion battery and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a lithium ion battery and a preparation method thereof, which are at least beneficial to improving the performance of the lithium ion battery. The preparation method comprises the following steps: preparing the negative plate, and weighing the negative active material, the SPEEK-Li and the conductive agent; adding the negative electrode active material, the conductive agent and the SPEEK-Li into a stirrer for blending, wherein the stirring time is 20-40 minutes; adding deionized water, kneading and stirring, wherein the stirring time is 120-130 minutes; adding an aqueous solution of PAA-Li, and stirring for 110-120 minutes; performing defoaming stirring, wherein the stirring time is 20-30 minutes; coating the stirred mixed slurry on a negative current collector through a coating machine oven, and drying to obtain a negative plate; and providing a positive plate and a diaphragm, carrying out winding treatment or lamination treatment on the positive plate, the diaphragm and the negative plate, putting into a shell, and injecting an electrolyte into the shell to obtain the lithium ion battery.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to a lithium-ion battery and a preparation method thereof. Background Art

[0002] Compared with traditional nickel-metal hydride batteries and lead-acid batteries, lithium-ion secondary batteries have the advantages of light weight, low environmental pollution, high working voltage, high energy density, and long cycle life, and are widely used in fields such as consumer electronics products, electric vehicles, and energy storage.

[0003] Common binders for lithium-ion batteries mainly include polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyolefins (such as polypropylene, polyethylene, etc.), polyvinylidene fluoride (PVDF), modified styrene-butadiene rubber, fluorinated rubber, polyurethane, etc. As an important component of the lithium-ion battery electrode, the main function of the binder is to ensure a certain bonding strength between active material particles and between active particles and the current collector during the use of the battery, and at the same time is conducive to the formation of the SEI film (Solid Electrolyte Interface membrane).

[0004] However, the commonly used binders for lithium-ion batteries currently have problems of relatively high swelling rate and relatively large resistivity, resulting in reduced efficiency of lithium-ion batteries. Summary of the Invention

[0005] Embodiments of this application provide a lithium-ion battery and a preparation method thereof, which at least helps to improve the performance of the lithium-ion battery.

[0006] According to some embodiments of the present application, on the one hand, an embodiment of the present application provides a method for preparing a lithium-ion battery, including: preparing a negative electrode sheet, and the preparation steps include: weighing 85 to 99 parts of negative electrode active material, 0.35 to 8.1 parts of SPEEK-Li, and 0.5 to 6 parts of conductive agent; adding the negative electrode active material, conductive agent and SPEEK-Li into a blender for blending, and the blending time is 20 to 40 minutes; adding 78 to 82 parts of deionized water for kneading and stirring, and the stirring time is 120 to 130 minutes; adding an aqueous solution of 0.9 to 8.65 parts of PAA-Li, the total mass fraction of SPEEK-Li and PAA-Li is 0.5 to 9 parts, the mass fraction ratio of SPEEK-Li to PAA-Li is (7 to 9):(3 to 1), and the concentration of the aqueous solution of PAA-Li is 0.128 mol / L to 0.64 mol / L, and the stirring time is 110 to 120 minutes; performing defoaming stirring, and the stirring time is 20 to 30 minutes; coating the stirred mixed slurry on a negative electrode current collector through a coating machine oven and drying to obtain a negative electrode sheet; providing a positive electrode sheet and a separator, winding or laminating the positive electrode sheet, separator and negative electrode sheet and then putting them into a housing, and injecting electrolyte into the housing to obtain a lithium-ion battery.

[0007] In some embodiments, before performing defoaming stirring, it further includes: viscosity-adjusting stirring, adjusting the viscosity of the mixed slurry to 3500 mPa·s to 9500 mPa·s, and the solid content is 55% to 60%, and the stirring time is 30 to 40 minutes, wherein the stirring rate of defoaming stirring is less than the stirring rate of viscosity-adjusting stirring.

[0008] In some embodiments, the coating machine oven includes 5 sections, and the temperatures are 90°C to 100°C, 100°C to 105°C, 100°C to 105°C, 105°C to 110°C, 105°C to 110°C in sequence.

[0009] In some embodiments, the preparation steps of SPEEK-Li include: adding PEEK into concentrated sulfuric acid, the mass ratio of PEEK to concentrated sulfuric acid is 1:(10 to 20), the concentration of concentrated sulfuric acid is 96% to 98%, stirring at 60°C to 100°C for 20 to 30 hours, quenching the obtained mixed solution with cold water, filtering to obtain a white solid, dissolving the white solid in deionized water, neutralizing with an aqueous solution of 0.5M to 1M LiOH, and drying to obtain SPEEK-Li.

[0010] In some embodiments, before dissolving the white solid in deionized water and neutralizing it with an aqueous solution of 0.5M to 1M LiOH, it includes: performing dialysis purification on the white solid, with a molecular cut-off value of 1000 Da, and obtaining a purified white solid after rotary evaporation.

[0011] In some embodiments, the preparation steps of the aqueous solution of PAA-Li include: dissolving polyacrylic acid in deionized water to obtain an aqueous solution of polyacrylic acid, adding an aqueous solution of LiOH to the aqueous solution of polyacrylic acid for reaction to obtain an aqueous solution of PAA-Li, wherein the molar ratio of polyacrylic acid to LiOH is 1:(0.3-1), the concentration of the aqueous solution of acrylic acid is 0.14 mol / L - 0.69 mol / L, and the concentration of the aqueous solution of LiOH is 1.22 mol / L - 2.44 mol / L.

[0012] According to some embodiments of the present application, on the other hand, the present application also provides a lithium-ion battery, including: a housing, and a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte disposed in the housing in a stacked manner. The negative electrode sheet includes: a negative electrode current collector and a negative electrode material layer covering the surface of the negative electrode current collector. The mass fractions of each substance in the negative electrode material layer are as follows: 85-99 parts of negative electrode active material, 0.5-9 parts of binder, and 0.5-6 parts of conductive agent, wherein the binder is composed of PAA-Li and SPEEK-Li, and the mass fraction ratio of SPEEK-Li to PAA-Li is (7-9):(3-1).

[0013] In some embodiments, the thickness of the negative electrode material layer is 140 μm - 150 μm.

[0014] In some embodiments, the average molecular weight of SPEEK-Li is greater than 1000.

[0015] In some embodiments, the average molecular weight of PAA-Li is 50000 - 80000.

[0016] The technical solutions provided by the embodiments of the present application have at least the following advantages:

[0017] In the lithium-ion battery and its preparation method provided by the embodiments of the present application, the negative electrode material layer of the lithium-ion battery includes a negative electrode active material, a conductive agent, and a binder. The binder is composed of SPEEK-Li and PAA-Li. As a binder, SPEEK-Li has lower electrolyte swelling and higher mechanical stability. A large number of sulfonic acid group side chains are linked to the main chain of SPEEK-Li. The sulfonic acid group has good hydrophilicity and high-temperature resistance. On the one hand, it can absorb a large amount of electrolyte, greatly improving the liquid absorption rate of the negative electrode sheet. On the other hand, it improves the heat resistance of the negative electrode sheet, ensuring the safety performance of the battery; PAA-Li can supplement additional lithium sources to improve the initial Coulomb efficiency and alleviate the loss of initial active lithium. In addition, both SPEEK-Li and PAA-Li are pre-lithiated, which can increase the ionic conductivity. With the peristaltic movement of the binder molecular chain, the migration of lithium ions is greatly promoted. In the preparation method of the lithium-ion battery provided by the embodiments of the present application, the prepared negative electrode sheet can take into account the requirements of the lithium-ion battery for rate performance and long cycle life compared with the conventional negative electrode sheet, improving the cycle life and rate performance of the lithium-ion battery. SPEEK-Li and PAA-Li as binders improve the adhesion ability between the negative electrode sheet and the current collector and reduce the swelling rate of the negative electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a proportional limitation; in order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is a flowchart corresponding to the preparation steps of the negative electrode sheet provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] As can be seen from the background art, the commonly used binders in current lithium-ion batteries have problems of relatively high swelling rate and large resistivity, resulting in reduced efficiency of lithium-ion batteries.

[0021] The embodiments of the present application provide a lithium-ion battery and its preparation method, which are at least beneficial to improving the performance of the lithium-ion battery.

[0022] References to "embodiments" in this application mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0023] The embodiments of the present application will be described in detail below in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are provided to help readers better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0024] Figure 1 It is a flowchart corresponding to the preparation steps of the negative electrode sheet provided in the embodiments of the present application.

[0025] According to some embodiments of the present application, on the one hand, a method for preparing a lithium-ion battery is provided, including:

[0026] Preparing a negative electrode sheet, and the preparation steps are as follows: S11 to S16:

[0027] S11: Weigh 85 to 99 parts of negative electrode active material, 0.35 to 8.1 parts of SPEEK-Li, and 0.5 to 6 parts of conductive agent.

[0028] The negative electrode active material can be selected from graphite, silicon, silicon-based composites, etc. Graphite has the advantages of low cost, good cycle stability, high electrical conductivity, and large specific capacity; silicon has a higher specific capacity and specific energy density than graphite, but there are problems with its cycle stability and mechanical strength; silicon-based composites are composite materials composed of a mixture of silicon and other materials, which can overcome the disadvantages of silicon and at the same time exert the advantages of silicon. Common silicon-based composites include silicon nanoparticles, nanoporous silicon materials, carbon-coated silicon, and nitrogen-coated silicon, etc. In addition to the above materials, the negative electrode active material can also be selected from materials such as lithium titanate and lithium aluminum alloy.

[0029] SPEEK-Li is lithiated sulfonated polyether ether ketone.

[0030] In some embodiments, the preparation steps of SPEEK-Li include: adding polyetheretherketone (PEEK) into concentrated sulfuric acid, where the mass ratio of PEEK to concentrated sulfuric acid is 1:(10 - 20), the concentration of concentrated sulfuric acid is 96% - 98%, stirring at 60°C - 100°C for 20 - 30 hours, quenching the obtained mixture with cold water, filtering to obtain a white solid, dissolving the white solid in deionized water, neutralizing with an aqueous solution of 0.5M - 1M LiOH, and drying to obtain SPEEK-Li.

[0031] In some embodiments, before dissolving the white solid in deionized water and neutralizing with an aqueous solution of 0.5M - 1M LiOH, it includes: performing dialysis purification on the white solid with a molecular cut-off value of 1000Da, and obtaining the purified white solid after rotary evaporation.

[0032] The conductive agent can be selected from one or more of carbon black, conductive graphite, carbon nanotubes, graphene, acetylene black AB, Ketjen black KB, and vapor grown carbon fiber (VGCF).

[0033] S12: Add the negative electrode active material, conductive agent, and SPEEK-Li into a blender for blending, and the blending time is 20 - 40 minutes.

[0034] S13: Add 78 - 82 parts of deionized water for kneading and stirring, and the stirring time is 120 - 130 minutes.

[0035] S14: Add 0.9 - 8.65 parts of an aqueous solution of PAA-Li, the total mass fraction of SPEEK-Li and PAA-Li is 0.5 - 9 parts, the mass fraction ratio of SPEEK-Li to PAA-Li is (7 - 9):(3 - 1), and the concentration of the aqueous solution of PAA-Li is 0.128mol / L - 0.64mol / L, and the stirring time is 110 - 120 minutes.

[0036] PAA-Li is lithiated polyacrylic acid.

[0037] In some embodiments, the preparation steps of the aqueous solution of PAA-Li include: dissolving polyacrylic acid in deionized water to obtain an aqueous solution of polyacrylic acid, adding an aqueous solution of LiOH to the aqueous solution of polyacrylic acid for reaction to obtain an aqueous solution of PAA-Li, where the molar ratio of polyacrylic acid to LiOH is 1:(0.3 - 1), the concentration of the aqueous solution of acrylic acid is 0.14mol / L - 0.69mol / L, and the concentration of the aqueous solution of LiOH is 1.22mol / L - 2.44mol / L.

[0038] S15: Conduct defoaming agitation for 20 to 30 minutes. The rate of defoaming agitation can be a revolution speed of 20 ± 1 rpm.

[0039] In some embodiments, before conducting defoaming agitation, it further includes: viscosity-adjusting agitation to adjust the viscosity of the mixed slurry to 3500 mPa·s to 9500 mPa·s, with a solid content of 55% to 60%, and the agitation time is 30 to 40 minutes. Among them, the agitation rate of defoaming agitation is less than that of viscosity-adjusting agitation. The rate of viscosity-adjusting agitation is a revolution speed of 25 ± 1 rpm.

[0040] The mixed slurry is a solid-liquid mixed fluid. To meet the requirements of subsequent coating processes, a suitable viscosity range of the mixed slurry is beneficial for the mixed slurry to have good fluidity, leveling property, and rheological property. Fluidity can be observed by stirring the mixed slurry and letting it flow down naturally. If it flows continuously without interruption, it indicates good fluidity; the leveling property affects the flatness and uniformity of coating; rheological property refers to the deformation characteristics of the mixed slurry during flow, and its quality affects the quality of the electrode sheet.

[0041] S16: Coat the stirred mixed slurry onto the negative current collector through the coating machine oven and dry it to obtain a negative electrode sheet.

[0042] The material of the negative current collector can be selected from copper foil.

[0043] In some embodiments, the coating machine oven includes 5 sections, and the temperatures are 90°C to 100°C, 100°C to 105°C, 100°C to 105°C, 105°C to 110°C, and 105°C to 110°C in sequence.

[0044] Provide a positive electrode sheet and a separator, wind or stack the positive electrode sheet, separator, and negative electrode sheet, then place them in a housing, and inject electrolyte into the housing to obtain a lithium-ion battery.

[0045] The positive electrode sheet includes a positive current collector and a positive electrode material layer covering the surface of the positive current collector.

[0046] The material of the positive current collector can be selected from aluminum foil.

[0047] The positive electrode material layer includes positive electrode active material, conductive agent, binder, etc.

[0048] The material of the positive electrode active material can be selected from layered structure materials, spinel structure materials, polyanion-type materials, etc. Layered structure materials include lithium cobalt oxide (LiCoO 2 ) and lithium nickel cobalt manganese oxide (NCM); spinel structure materials include lithium manganese oxide (LiMn 2 O 4 );polyanion-type materials include lithium iron phosphate (LiFePO 4)。

[0049] The conductive agent can be selected from one or more of carbon black, conductive graphite, carbon nanotubes, graphene, acetylene black AB, Ketjen black KB, and vapor grown carbon fiber.

[0050] The binder can be selected from polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyolefins (such as polypropylene, polyethylene, etc.), polyvinylidene fluoride (PVDF), modified styrene-butadiene rubber, fluorinated rubber, polyurethane, etc.

[0051] The separator can be selected from polypropylene (PP) microporous separator, polyethylene (PE) microporous separator, PE / PP composite microporous separator, copolymer diaphragm of propylene and ethylene, or polyethylene homopolymer diaphragm, etc.

[0052] The winding process is a process of winding the positive electrode sheet, separator, and negative electrode sheet stacked in sequence into a core roll in a certain order, mainly used for the production of square and cylindrical lithium batteries.

[0053] The stacking process is an assembly method of constructing an electric core by layer-by-layer stacking of components such as positive electrode sheets, separators, and negative electrode sheets. The process of the stacking process can generally be divided into a stacking type and a folding type. Compared with the winding process, the process requirements for the stacking winding have higher tension control. The stacking process is mainly used for the manufacture of large square batteries, ultra-thin batteries, and special-shaped batteries.

[0054] The electrolyte contains a solvent, a solute, and an additive. The solvent can be selected from ethylene carbonate (EC), polycarbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), sulfite, or carboxylate, etc.; the solute can be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, or lithium bis(oxalato)borate, etc.; the additive can be selected from a film-forming additive, an overcharge protection additive, a high and low temperature additive, or a flame retardant additive, etc.

[0055] Correspondingly, another embodiment of the present application also provides a lithium ion battery, which can be manufactured by using the preparation method of the lithium ion battery provided in the above embodiment. For the same or corresponding parts as the previous embodiment, reference can be made to the corresponding description of the previous embodiment, and details will not be described in detail below.

[0056] The lithium ion battery provided by the embodiment of the present application includes: a housing, and a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte that are stacked and arranged in the housing. The negative electrode sheet includes: a negative electrode current collector and a negative electrode material layer covering the surface of the negative electrode current collector. The mass fractions of each substance in the negative electrode material layer are as follows: 85-99 parts of negative electrode active material, 0.5-9 parts of binder, and 0.5-6 parts of conductive agent. Among them, the binder is composed of PAA-Li and SPEEK-Li, and the mass fraction ratio of SPEEK-Li to PAA-Li is (7-9):(3-1).

[0057] In some embodiments, the thickness of the negative electrode material layer is 140 μm to 150 μm, and specifically may be 140 μm, 143 μm, 146, 148 μm or 150 μm.

[0058] In some embodiments, the average molecular weight of SPEEK-Li is greater than 1000, and specifically may be 1000, 1300, 1500 or 2000.

[0059] In some embodiments, the average molecular weight of PAA-Li is 50,000 to 80,000, and specifically may be 50,000, 56,000, 60,000, 67,000, 70,000, 78,500 or 80,000.

[0060] In the lithium-ion battery and its preparation method provided by the embodiments of the present application, the negative electrode material layer of the lithium-ion battery includes a negative electrode active material, a conductive agent and a binder. The binder is composed of SPEEK-Li and PAA-Li. SPEEK-Li as a binder has lower electrolyte swelling and higher mechanical stability. A large number of sulfonic acid group side chains are linked to the main chain of SPEEK-Li. The sulfonic acid group has good hydrophilicity and high temperature resistance. On the one hand, it can absorb a large amount of electrolyte, greatly improving the liquid absorption rate of the negative electrode sheet. On the other hand, it improves the heat resistance of the negative electrode sheet, ensuring the safety performance of the battery; PAA-Li can supplement additional lithium sources to improve the first Coulomb efficiency and alleviate the loss of initial active lithium. In addition, both SPEEK-Li and PAA-Li are pre-lithiated, which can increase the ionic conductivity. With the peristaltic movement of the binder molecular chain, the migration of lithium ions is greatly promoted. Through the preparation method of the lithium-ion battery provided by the embodiments of the present application, the prepared negative electrode sheet can meet the requirements of the lithium-ion battery for rate performance and long cycle at the same time, improving the cycle life and rate performance of the lithium-ion battery. SPEEK-Li and PAA-Li as binders improve the adhesion ability between the negative electrode sheet and the current collector, reducing the expansion rate of the negative electrode sheet.

[0061] The sulfonic acid group (-SO 3 H) of SPEEK-Li forms -SO 3Li has high ionic conductivity, SPEEK-Li has good mechanical strength and chemical stability, and is suitable as the matrix of electrolyte or electrode materials. Polyacrylic acid lithium (PAA-Li) of PAA-Li has abundant lithium carboxylate groups (-COOLi), which can provide a large number of lithium ions. PAA-Li has excellent flexibility and interfacial compatibility, and can form good contact with electrode materials. SPEEK-Li provides high ionic conductivity and mechanical support, while PAA-Li provides more lithium ion sources and interfacial compatibility. The combination of the two can form a complementary effect. The synergistic effect of SPEEK-Li and PAA-Li can form a dual lithium ion transport channel (lithium sulfonate and lithium carboxylate), significantly improving the ionic conductivity of the electrolyte. Through molecular dynamics simulation or experimental data, it is proved that the combination of the two can improve the lithium ion transference number (t + ) and conductivity. The high mechanical strength of SPEEK-Li can inhibit the growth of lithium dendrites and improve the safety of the battery; the flexibility and interfacial compatibility of PAA-Li can form a stable interfacial layer with electrode materials, reducing the interfacial impedance. The combination of SPEEK-Li and PAA-Li can form an interfacial layer of "rigidity and flexibility combined", which can not only inhibit lithium dendrites but also reduce the interfacial impedance, thereby improving the cycle stability of the battery. The chemical stability of SPEEK-Li can broaden the electrochemical window of the electrolyte and is applicable to high-voltage cathode materials; the high lithium ion concentration of PAA-Li can improve the rate performance of the battery. After the combination of the two, the electrolyte has both a wide electrochemical window and high ionic conductivity, which can significantly improve the energy density and power density of the battery.

[0062] The following are specific embodiments of this application:

[0063] Example 1

[0064] Preparation of SPEEK-Li: Add PEEK to concentrated sulfuric acid according to the mass ratio of PEEK to concentrated sulfuric acid of 1:15. The concentration of concentrated sulfuric acid is 98%. Stir at 80 °C for 20 hours. Quench the obtained mixture with cold water, filter to obtain a white solid, purify the white solid by dialysis, and obtain the purified white solid after rotary evaporation. The molecular cut-off value of dialysis purification is 1000 Da. Dissolve the purified white solid in deionized water, neutralize it with an aqueous solution of 0.5 M LiOH, and dry it to obtain SPEEK-Li.

[0065] Preparation of PAA-Li: Polyacrylic acid was dissolved in deionized water to obtain an aqueous solution of polyacrylic acid. An aqueous solution of LiOH was added to the aqueous solution of polyacrylic acid for reaction to obtain an aqueous solution of PAA-Li. Among them, the molar ratio of polyacrylic acid to LiOH was 1:0.6, the concentration of the aqueous solution of acrylic acid was 0.45 mol / L, the concentration of the aqueous solution of LiOH was 1.7 mol / L, and the molecular weight of PAA-Li was 50,000.

[0066] Preparation of the negative electrode sheet: Weigh 90 parts of graphite, 4 parts of the above-mentioned SPEEK-Li, and 3 parts of conductive carbon black SP; add graphite, SPEEK-Li, and SP to a blender for stirring, and the stirring time is 30 minutes; add 80 parts of deionized water for kneading and stirring, and the stirring time is 120 minutes; add 2 parts of the aqueous solution of PAA-Li, and the concentration of the aqueous solution of PAA-Li is 0.45 mol / L, and the stirring time is 120 minutes; carry out viscosity-adjusting stirring to adjust the viscosity of the mixed slurry to 6500 mPa·s to 9500 mPa·s, and the solid content is 58%, the stirring time is 40 minutes, and the stirring rate is 25 rpm; carry out defoaming stirring, the stirring rate is 20 rpm, and the stirring time is 30 minutes; coat the stirred mixed slurry on the copper foil through a coater oven and dry it to obtain the negative electrode sheet. The coater oven includes 5 sections, and the temperatures are 90°C, 100°C, 100°C, 105°C, and 105°C in sequence.

[0067] Preparation of the lithium-ion battery: The positive electrode sheet, the separator, and the negative electrode sheet prepared above were wound and then placed in a housing, and the electrolyte was injected into the housing to obtain a lithium-ion battery.

[0068] The differences between Example 2, Example 3, and Comparative Example 5 and Example 1 are that the mass ratio of SPEEK-Li to PAA-Li is different; the differences between Comparative Examples 1 to 4 and Comparative Examples 6 to 8 and Example 1 are that the types of adhesives used are different. For specific references, see Table 1.

[0069] Table 1 Types of adhesives and their ratios corresponding to different examples and comparative examples

[0070] Experimental Example Parts by mass of the adhesive Type of adhesive Mass ratio Example 1 6 SPEEK-Li and PAA-Li 8:2 Example 2 6 SPEEK-Li and PAA-Li 7:3 Example 3 6 SPEEK-Li and PAA-Li 9:1 Comparative Example 1 6 SPEEK-Li - Comparative Example 2 6 PAA-Li - Comparative Example 3 6 CMC - Comparative Example 4 6 SBR - Comparative Example 5 6 SPEEK-Li and PAA-Li 5:5 Comparative Example 6 6 SPEEK-Li and CMC 8:2 Comparative Example 7 6 SPEEK-Li and SBR 8:2 Comparative Example 8 6 CMC and PAA-Li 8:2 Comparative Example 9 6 SBR and PAA-Li 8:2

[0071] The difference between Example 4 and Example 1 is that the molecular cut-off value for dialysis purification of SPEEK-Li is different; the difference between Comparative Example 10 and Example 1 is that SPEEK-Li was not dialyzed and purified; the difference between Comparative Example 11 and Example 1 is that the average molecular weight of PAA-Li is different. For specific references, see Table 2.

[0072] Table 2 Molecular cut-off values corresponding to different examples and comparative examples

[0073] Experimental Example Molecular cut-off value Average molecular weight of SPEEK-Li Average molecular weight of PAA-Li Example 1 1000 1500 50000 Example 4 3000 3500 50000 Comparative Example 10 - 800 50000 Comparative Example 11 1000 1500 5000

[0074] Table 4 shows the test results of the swelling rate, liquid absorption rate, adhesion strength, mechanical strength, and resistivity of the negative electrode sheets corresponding to different examples and comparative examples; Table 5 shows the test results of the initial Coulomb efficiency, rate performance, cycle performance, and reversible specific capacity of the lithium-ion batteries corresponding to different examples and corresponding ratios.

[0075] Table 4 Swelling rate, liquid absorption rate, adhesion strength, mechanical strength, and resistivity corresponding to different examples and comparative examples

[0076]

[0077] Table 5 Initial Coulomb efficiency, rate performance, cycle performance, and reversible specific capacity of the lithium-ion batteries corresponding to different examples and corresponding ratios

[0078]

[0079] Referring to Examples 1 to 3 and Comparative Examples 1 to 9 in Table 3, it is found that when SPEEK-Li and PAA-Li are used synergistically as binders for the negative electrode sheet and the mass ratio of SPEEK-Li and PAA-Li is within a suitable range, the synergistic use of SPEEK-Li and PAA-Li as binders is beneficial to reducing the swelling rate of the negative electrode sheet, increasing the liquid absorption rate of the negative electrode sheet, and at the same time maintaining good mechanical stability and adhesion strength of the negative electrode sheet.

[0080] Referring to Examples 1 to 3 and Comparative Examples 1 to 4 in Table 4, it is found that compared with using conventional CMC binder and SBR binder for the negative electrode sheet in the lithium-ion battery, when SPEEK-Li and PAA-Li are used synergistically as binders and the mass ratio of SPEEK-Li and PAA-Li is within a suitable range, the reversible specific capacity and cycle stability of the lithium-ion battery can be improved, and the negatively charged nanochannels of SPEEK-Li and PAA-Li as binders can improve the initial Coulomb efficiency and rate performance of the lithium-ion battery.

[0081] Referring to Examples 1, 4, Comparative Example 10, and Comparative Example 11 in Table 3, it is found that the average molecular weight of SPEEK-Li and the average molecular weight of PAA-Li in the negative electrode sheet both need to be within an appropriate range to maintain good adhesion strength and mechanical strength of the negative electrode sheet.

[0082] Referring to Examples 1, 4, Comparative Example 10, and Comparative Example 11 in Table 4, it is found that the average molecular weight of SPEEK-Li and the average molecular weight of PAA-Li in the negative electrode sheet both need to be within an appropriate range, which is beneficial to maintaining the initial Coulomb efficiency, rate performance, cycle performance, and reversible specific capacity of the lithium-ion battery.

[0083] Those of ordinary skill in the art can understand that the above-described embodiments are specific examples for implementing the present application. In actual applications, various changes can be made to them in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A method for preparing a lithium ion battery, characterized in that: include: Prepare the negative electrode sheet, the preparation steps include: Weigh 85-99 parts of negative electrode active material, 0.35-8.1 parts of SPEEK-Li and 0.5-6 parts of conductive agent; Add the negative electrode active material, the conductive agent and the SPEEK-Li into a mixer and mix them for 20 to 40 minutes; Add 78-82 parts of deionized water and knead and stir for 120-130 minutes; 0.9 to 8.65 parts of an aqueous solution of PAA-Li are added, the total mass fraction of the SPEEK-Li and the PAA-Li is 0.5 to 9 parts, the mass fraction ratio of the SPEEK-Li to the PAA-Li is (7 to 9):(3 to 1), and the concentration of the aqueous solution of PAA-Li is 0.128 mol / L to 0.64 mol / L, and the stirring time is 110 to 120 minutes; Defoaming and stirring are performed for 20 to 30 minutes; Applying the stirred mixed slurry on the negative electrode current collector through a coating machine oven and drying it to obtain the negative electrode sheet; A positive electrode sheet and a separator are provided, and the positive electrode sheet, the separator and the negative electrode sheet are wound or stacked and then placed in a shell, and an electrolyte is injected into the shell to obtain the lithium-ion battery.

2. The method for preparing a lithium ion battery according to claim 1, characterized in that: Before the defoaming stirring, it also includes: viscosity adjustment stirring, adjusting the viscosity of the mixed slurry to 3500mPa·s~9500mPa·s, and the solid content to 55%~60%, and the stirring time is 30~40 minutes, wherein the stirring rate of the defoaming stirring is lower than the stirring rate of the viscosity adjustment stirring.

3. The method for preparing a lithium ion battery according to claim 1, characterized in that: The coating machine oven comprises 5 sections, and the temperatures are 90°C to 100°C, 100°C to 105°C, 100°C to 105°C, 105°C to 110°C, and 105°C to 110°C in sequence.

4. The method for preparing a lithium ion battery according to claim 1, characterized in that: The preparation steps of SPEEK-Li include: PEEK is added to concentrated sulfuric acid, the mass ratio of PEEK to the concentrated sulfuric acid is 1: (10-20), the concentration of the concentrated sulfuric acid is 96%-98%, and the mixture is stirred at 60°C-100°C for 20-30 hours. The obtained mixed solution is quenched with cold water, filtered to obtain a white solid, and the white solid is dissolved in deionized water, neutralized with a 0.5M-1M LiOH aqueous solution, and dried to obtain the SPEEK-Li.

5. The method for preparing a lithium ion battery according to claim 4, characterized in that: Before the white solid is dissolved in deionized water and neutralized with a 0.5M to 1M LiOH aqueous solution, the method includes: dialysis purification of the white solid with a molecular cutoff value of 1000Da, and rotary evaporation to obtain the purified white solid.

6. The method for preparing a lithium ion battery according to claim 1, characterized in that: The steps of preparing the PAA-Li aqueous solution include: Polyacrylic acid is dissolved in deionized water to obtain an aqueous solution of polyacrylic acid, and an aqueous solution of LiOH is added to the aqueous solution of polyacrylic acid for reaction to obtain an aqueous solution of PAA-Li, wherein the molar ratio of the polyacrylic acid to LiOH is 1:(0.3-1), the concentration of the aqueous solution of acrylic acid is 0.14 mol / L-0.69 mol / L, and the concentration of the aqueous solution of LiOH is 1.22 mol / L-2.44 mol / L.

7. A lithium ion battery, characterized in that: include: A shell, and a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte that are stacked and located in the shell, wherein the negative electrode sheet comprises: A negative electrode current collector and a negative electrode material layer covering the surface of the negative electrode current collector, wherein the mass fractions of each substance in the negative electrode material layer are as follows: 85 to 99 parts of negative electrode active material, 0.5 to 9 parts of adhesive and 0.5 to 6 parts of conductive agent, wherein the adhesive is composed of PAA-Li and SPEEK-Li, and the mass fraction ratio of the SPEEK-Li to the PAA-Li is (7 to 9):(3 to 1).

8. The lithium-ion battery according to claim 7, characterized in that: The thickness of the negative electrode material layer is 140 μm to 150 μm.

9. The lithium-ion battery according to claim 7, characterized in that: The average molecular weight of the SPEEK-Li is greater than 1000.

10. The lithium ion battery according to claim 7, characterized in that: The average molecular weight of the PAA-Li is 50,000 to 80,000.

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