Electrode interface modified material, electrode and lithium ion battery

Abstract

The invention discloses an electrode interface modified material, an electrode and a lithium ion battery, and belongs to the technical field of lithium batteries. The electrode interface modification material comprises an organic material and an inorganic material, wherein the organic material is a conductive polymer; the inorganic material is a lithium salt. The inorganic lithium salt is added into the conductive polymer to form the composite material, so that the electrode interface modification has good toughness and strength, the Li < + > transmission problem of the lithium ion battery under high rate can be improved, and the high rate performance of the battery is enhanced; the stress change caused by the electrode volume change in the charging and discharging process can be effectively released, and the structure is kept stable; direct contact between an electrode and electrolyte can be avoided, side reaction of an interface is reduced, the electrode is protected as an artificial interface layer, and the cycle life and the cycle stability of the lithium ion battery are prolonged; the modified interface layer can also permeate into electrode pores to enhance contact between active substance particles.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and more particularly, to an electrode interface modification material, an electrode, and a lithium-ion battery. Background Art

[0002] The high energy density and relatively excellent cycle life of secondary lithium-ion batteries have led to an increasing range of applications in modern life. In particular, the development of power batteries and consumer electronics products has put forward higher requirements for their cycle safety and cycle life.

[0003] During long-term charge and discharge processes, cation mixing and transition metal dissolution occur in ternary cathode materials such as NCMxyz and NCAxyz, as well as lithium manganese iron phosphate (LMFP) cathode materials developed on the basis of lithium iron phosphate, resulting in structural degradation, which greatly accelerates the life attenuation of lithium-ion batteries. At the same time, direct contact between the positive and negative electrodes and the electrolyte is also likely to cause various side reactions. In particular, the formation of the solid electrolyte interphase (SEI) at the negative electrode / electrolyte interface has a very important impact on the cycle stability of the battery.

[0004] Surface coating of electrode active materials is a common and effective method. For cathode materials, it can stabilize the crystal structure and inhibit cation dissolution. For anode materials, it can alleviate the cracking and thickening of the interface layer caused by volume expansion during charge and discharge, and reduce the hindrance to lithium-ion migration, thereby improving the cycle life of the battery. For the purpose of improving electrochemical performance, the coating material often needs to have excellent ionic and electronic conductivity and chemical stability. Poly(3,4-ethylenedioxythiophene) and its derivatives, as an excellent conductive polymer, not only meet this requirement but also have a certain viscosity to adhere to the active material and prevent the active material from falling off the current collector during the cycle. Their excellent performance as coating materials has been revealed in previous research. However, the coating process will increase the material synthesis steps, require significant modification of existing production equipment and process flows, and it is impossible to achieve effective and uniform coating during large-scale production. In addition, the organic shell layer does not participate in the reaction during charge and discharge, so the behavior of coating each particle will greatly increase the proportion of non-active substances in the electrode structure, thereby reducing the energy density of the battery cell. Summary of the Invention

[0005] The main objective of this application is to provide an electrode interface modification material, an electrode, and a lithium-ion battery to solve the problems of easy occurrence of side reactions, unstable interface layer structure, and poor battery cycle stability in the prior art.

[0006] To achieve the above object, according to one aspect of the present application, there is provided an electrode interface modification material, which includes an organic material and an inorganic material; wherein, the organic material is a conductive polymer; and the inorganic material is a lithium salt.

[0007] Further, the weight ratio of the inorganic material to the organic material is (0.5 - 20):(80 - 99.5); preferably (2 - 15):(85 - 98); more preferably (5 - 10):(90 - 95).

[0008] Further, the median particle size D50 of the lithium salt is 30 - 200 nm; preferably 50 - 100 nm.

[0009] Further, the conductive polymer is selected from at least one of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), polyaniline, and polypyrrole.

[0010] Further, the lithium salt is selected from lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate; preferably γ-LiAlO2.

[0011] Further, the chemical formula of the fluorinated derivative of lithium metaaluminate is LiAlO 2-x F x , where 0 < x < 0.5; more preferably x = 0.05 - 0.2.

[0012] According to the second aspect of the present application, there is provided an electrode, which includes an electrode body and an interface modification layer. The electrode body includes a current collector and active layers attached to two opposite surfaces of the current collector; the interface modification layer is attached to the surface of the active layer away from the current collector; wherein, the material of the interface modification layer is the above-mentioned electrode interface modification material.

[0013] Further, the thickness of the interface modification layer is 0.2 - 40 μm; 0.5 - 30 μm; more preferably 10 - 20 μm.

[0014] Further, the interface modification layer is attached to two opposite surfaces of the active layer away from the current collector.

[0015] Further, the active material of the active layer includes a positive electrode active material and a negative electrode active material; the positive electrode active material is selected from at least one of NCMxyz, NCAxyz, and LMFP.

[0016] Further, NCMxyz is selected from at least one of NCM811, NCM111, and NCM523.

[0017] Further, NCAxyz is selected from at least one of NCA111, NCA811, NCA622, NCA721, and NCA532.

[0018] Furthermore, the negative electrode active material is graphite.

[0019] According to the third aspect of the present application, a method for preparing the above electrode is provided:

[0020] Step S1: Mix a conductive polymer, a lithium salt, and a solvent to obtain a suspension;

[0021] Step S2: Coat the suspension on the surface of the electrode body, and form an interfacial modification layer after curing to obtain the electrode.

[0022] Furthermore, the viscosity of the suspension is 200 - 10000 mPa·S; preferably 200 - 5000 mPa·S.

[0023] Furthermore, the solvent is a solvent that can dissolve the conductive polymer.

[0024] Furthermore, the solvent is selected from at least one of water, ethanol, N - methylpyrrolidone, and dimethylformamide.

[0025] Furthermore, the coating method includes transfer coating or extrusion coating.

[0026] Furthermore, the lithium salt is selected from lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate; preferably γ - LiAlO₂.

[0027] Furthermore, the preparation method of the fluorinated derivative of lithium metaaluminate includes: heating and reacting lithium metaaluminate with a fluorinating agent to obtain the fluorinated derivative of lithium metaaluminate.

[0028] Furthermore, the fluorinating agent is selected from at least one of ammonium fluoride, ammonium bifluoride, HF, CFx, and NF₃.

[0029] Furthermore, when the fluorinating agent is solid, the weight ratio of lithium metaaluminate to the fluorinating agent is (80 - 95):(5 - 20); the process of the heating reaction includes: keeping warm at 100°C - 200°C for 2 - 4 h.

[0030] Furthermore, when the fluorinating agent is gas, lithium metaaluminate and the fluorinating agent are heated and reacted in a tube furnace; the process of the heating reaction includes: keeping warm at 150°C - 250°C for 1 - 2 h; the flow rate of the fluorinating agent is 50 - 200 mL / min.

[0031] According to the fourth aspect of the present application, a lithium - ion battery is provided, and the electrode of the lithium - ion battery is the above electrode.

[0032] Applying the technical solution of the present application, an electrode interface modification material, an electrode, and a lithium-ion battery are provided; by adding an inorganic lithium salt to a conductive polymer to form a composite material, the electrode interface modification has good toughness and strength, which can improve the Li + transport problem at high rates of the lithium-ion battery, enhancing the high-rate performance of the battery; it can effectively release the stress change caused by the volume change of the electrode during charge and discharge, maintaining the structural stability; it can avoid the direct contact between the electrode and the electrolyte, reducing the interfacial side reactions, protecting the electrode as an artificial interface layer, and prolonging the cycle life and cycle stability of the lithium-ion battery; this modified interface layer can also penetrate into the pores of the electrode, enhancing the contact between the active material particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings forming a part of this application are used to provide a further understanding of the application. The schematic embodiments and descriptions thereof of the application are used to explain the application and do not constitute an improper limitation of the application. In the drawings:

[0034] Figure 1 It shows a schematic diagram of the charge and discharge volume change of the negative electrode with a modified layer on the surface in Embodiment 1 and Embodiment 2 of the present application;

[0035] Figure 2 It shows a schematic diagram of the charge and discharge volume change of the negative electrode without a modified layer on the surface in Comparative Example 2 of the present application;

[0036] Figure 3 It shows a scanning electron microscope of the cross-section of the surface of the positive electrode with a modified layer in Embodiment 3 of the present application Figure 1 ;

[0037] Figure 4 It shows a scanning electron microscope of the cross-section of the surface of the positive electrode with a modified layer in Embodiment 3 of the present application Figure 2 ;

[0038] Figure 5 It shows a scanning electron microscope image of the cross-section of the surface of the positive electrode without a modified layer in Comparative Example 2 of the present application;

[0039] Figure 6 It shows the charge and discharge curves of the battery cells of Embodiment 3 and Comparative Example 2 (control) of the present application.

[0040] Reference Signs:

[0041] 1. Current collector; 2. Active layer; 3. Interface modification layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and embodiments.

[0043] As mentioned in the background art, using poly(3,4-ethylenedioxythiophene) and its derivatives as the electrode interface layer material will reduce the energy density of the battery cell, unable to ensure the structural stability of the electrode, and is not conducive to the cycle life of the battery.

[0044] According to one aspect of the present application, an electrode interface modification material is provided, which includes an organic material and an inorganic material; wherein, the organic material is a conductive polymer; the inorganic material is a lithium salt.

[0045] The electrode interface modification material provided by the present application adds an inorganic lithium salt to the conductive polymer, making the electrode interface modification have higher strength while having good toughness. The addition of the lithium salt can improve the Li + transmission rate of the lithium-ion battery at high rates, enhancing the high-rate performance of the battery; the higher strength of this material can ensure the stability of the electrode structure during charge and discharge; as an artificial interface layer, it protects the electrode and reduces interfacial side reactions, prolonging the cycle life and cycle stability of the lithium-ion battery. When the capacity retention rate is 80%, the cycle life is increased by 15% - 75%.

[0046] In some embodiments, the weight ratio of the inorganic material to the organic material is (0.5 - 20):(80 - 99.5); that is, the weight percentage of the inorganic material in the composite modification material is 0.5% - 20%, and the weight percentage of the organic material is 80% - 99.5%; further, the weight percentage of the inorganic material is 2% - 15%, and the weight percentage of the organic material is 85% - 98%; for example, the content of the lithium salt is any value among 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or the range value between any two of them; the content of the conductive polymer is any value among 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99.5% or the range value between any two of them; further, the weight ratio of the inorganic material to the organic material is (2 - 15):(85 - 98), that is, the inorganic material accounts for 2% - 15%, and the organic material accounts for 85% - 98%; and further (5 - 10):(90 - 95); that is, the inorganic material accounts for 5% - 10%, and the organic material accounts for 90% - 95%. Using the above ratios can form an effective ion path on the electrode surface, reduce the ion interface impedance, and improve the battery energy density.

[0047] In some embodiments, the lithium salt is lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate. The above lithium salt provides lithium ions for the electrode interface layer, Li +Li can partially occupy the interior of the material + position and has good lithium ion conductivity, improving the Li + transport rate of the lithium ion battery at high rates and enhancing the high rate performance of the battery.

[0048] In some embodiments, the median particle sizes D50 of lithium metaaluminate and fluorinated derivatives of lithium metaaluminate are 30-200 nm respectively; for example, the median particle size D50 of the lithium salt is any value among 30, 50, 80, 100, 120, 150, 180, 200 nm or a range value between any two of them; each is preferably 50-100 nm. Controlling the D50 particle size of the lithium salt within the above range results in good film-forming properties at the electrode interface, moderate film-forming density, which can provide a suitable channel for lithium ion transport, has good electrical conductivity, and also has reasonable strength to cope with stress release during charge and discharge, which is beneficial to the high rate cycling performance of the battery cell.

[0049] In some embodiments, the conductive polymer is selected from at least one of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), polyaniline, and polypyrrole. The above conductive polymer first has excellent electrical conductivity. As a material for the electrode interface layer, it can reduce the internal resistance of the battery and improve the electrochemical performance; it has good chemical stability, can prevent direct contact with the electrode interface or electrolyte, and reduce side reactions during battery charge and discharge; it has good flexibility and ductility, can adapt to the volume change of the electrode during charge and discharge, and improve electrode stability; it has good adhesion, can firmly bind to the electrode interface, and prevent the active material from falling off during cycling; more importantly, the conductive polymer and the inorganic lithium salt have good miscibility, can provide a path for lithium ion transport, and the porous structure of the inorganic material provides a fast transport channel for lithium ions, ensuring the efficient charge and discharge of the lithium ion battery. Compared with the traditional method of directly coating the electrode interface with a conductive polymer, the proportion of inactive substances is reduced, thereby improving the energy density of the battery cell.

[0050] In some embodiments, the chemical formula of the fluorinated derivative of lithium metaaluminate is LiAlO 2-x F x , where 0 < x < 0.5, and further x = 0.05 - 0.2; here x represents the fluorine content. While maintaining the original electrochemical advantages, the introduced F -It can enhance the thermal stability of the structure. By controlling the fluorine content within the above range, the thermal stability of the electrode and the safety performance of the electrode interface can be further enhanced. Meanwhile, the side reactions with the electrolyte can be reduced, and the chemical stability of the interface can be enhanced. Further, lithium metaaluminate is preferably γ-LiAlO2. Lithium metaaluminate in the γ crystal form has better conductivity. Adding it as an electrode interface material in the conductive polymer can further improve its conductivity, which is more beneficial to the high-rate cycling performance of the battery. The organic PEDOT:PSS and the inorganic fluorinated lithium metaaluminate LiAlO 2-x F x (0 < x < 0.5) mixture makes the composite interface layer have good toughness and strength, can effectively release the stress change caused by the volume change of the electrode during charge and discharge, and maintain the structural stability.

[0051] In some embodiments, the weight ratio of fluorinated lithium metaaluminate to poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is (5-10):(90-95); that is, the weight percentage of fluorinated lithium metaaluminate in the composite modified material is 5% - 10%, and the weight percentage of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is 90% - 95%. Further, the thickness of the interface modification layer is 20 - 30 μm. With the above compounding ratio of the inorganic material and the organic material and the thickness of the interface modification layer within the above specific range, the prepared electrode can significantly improve the cycling performance of the battery cell. For example, under the test conditions of 45°C 1C / 1C, the number of cycles when the capacity retention rate is 80% is at least more than 800 cycles.

[0052] In some embodiments, the weight ratio of fluorinated lithium metaaluminate to poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is (4-6):(94-96); preferably, the weight percentage of fluorinated lithium metaaluminate in the composite modified material is 5%, and the weight percentage of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is 95%. Further, the thickness of the interface modification layer is 28 - 32 μm, preferably 30 μm. With the above compounding ratio of the inorganic material and the organic material and the thickness of the interface modification layer within the above specific range, the prepared electrode can significantly improve the cycling performance of the battery cell. For example, under the test conditions of 45°C 1C / 1C, the number of cycles when the capacity retention rate is 80% is at least more than 1000 cycles.

[0053] In some embodiments, the weight ratio of lithium fluoroaluminate to poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is (8 - 12):(88 - 90); preferably, the weight percentage of lithium fluoroaluminate in the composite modified material is 10%, and the weight percentage of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is 90%; further, the thickness of the interface modification layer is 18 - 22 μm, preferably 20 μm. When the inorganic material and the organic material adopt the above compounding ratio and the thickness of the interface modification layer within the above specific range, the prepared electrode can significantly improve the cycle performance of the battery cell. For example, under the test conditions of 45°C, 1C / 1C, the number of cycles when the capacity retention rate is 80% is at least more than 1100 cycles.

[0054] In some embodiments, the weight ratio of lithium fluoroaluminate to poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is (4 - 6):(94 - 96); preferably, the weight percentage of lithium fluoroaluminate in the composite modified material is 5%, and the weight percentage of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is 95%; further, the thickness of the interface modification layer is 18 - 22 μm, preferably 20 μm. When the inorganic material and the organic material adopt the above compounding ratio and the thickness of the interface modification layer within the above specific range, the prepared electrode can significantly improve the cycle performance of the battery cell. For example, under the test conditions of 45°C, 1C / 1C, the number of cycles when the capacity retention rate is 80% is at least more than 1200 cycles.

[0055] According to the second aspect of the present application, an electrode is provided. The electrode includes an electrode body and an interface modification layer. The electrode body includes a current collector 1 and active layers 2 attached to two opposite surfaces of the current collector; the interface modification layer 3 is attached to the surface of the active layer away from the current collector; wherein, the material of the interface modification layer is the above-mentioned electrode interface modification material. By attaching an additional interface modification layer on the surface of the electrode body, it can protect the electrode interface from direct contact with the electrolyte to reduce side reactions, endow the electrode with good toughness and higher strength, improve the Li + transport rate of the lithium-ion battery at high rates, enhance the high-rate performance of the battery, and ensure the stability of the electrode structure during charge and discharge.

[0056] In some embodiments, the thickness of the interface modification layer is 0.2 - 40 μm; preferably 0.5 - 30 μm; more preferably 10 - 20 μm. Controlling the above thickness range can provide good protection for the electrode interface, reduce the electron transfer resistance, and is beneficial to conductivity and the high-rate cycle performance of the battery cell.

[0057] In some embodiments, the active layer includes a positive electrode active layer and a negative electrode active layer, and the above-mentioned modified interfacial material can be used on the surface of the positive electrode active layer or on the surface of the negative electrode active layer; for example, the positive electrode active material is selected from at least one of NCMxyz, NCAxyz, and LMFP; wherein, NCMxyz can be selected from at least one of NCM811, NCM111, and NCM523; NCAxyz can be selected from at least one of NCA111, NCA811, NCA622, NCA721, and NCA532; the negative electrode active material is graphite.

[0058] According to the third aspect of the present application, a method for preparing the above electrode is provided, including:

[0059] Step S1: Mix a conductive polymer, a lithium salt, and a solvent to obtain a suspension;

[0060] Step S2: Coat the suspension on the surface of the electrode body, and form an interfacial modification layer after curing to obtain the electrode.

[0061] In some embodiments, the solvent is a solvent that can dissolve the conductive polymer, such as at least one of water, ethanol, N-methylpyrrolidone, and dimethylformamide; preferably, it is as safe, low-toxic, and volatile as possible during use. The coating method includes transfer coating or extrusion coating; the viscosity of the suspension is 200-10000 mPa·S; for example, the viscosity of the suspension is any value among 200, 500, 800, 1000, 1200, 1500, 1800, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9500, 10000 mPa·S or a range value between any two of them; preferably 200-5000 mPa·S. If the viscosity of the modified material is too small, the film-forming property is poor, and it cannot protect the electrode interface well. If the lithium salt content is small, the strength of the modified material will become low, which is not conducive to the release of charge-discharge stress, the transmission of lithium ions, and the stability of the cell structure and high-rate cycling performance; if the viscosity is too large, the lithium salt is unevenly distributed, easy to form clusters, not easy to form a film, and the toughness is poor, which is not conducive to the release of charge-discharge stress, and will also affect the stability of the cell structure and high-rate cycling performance; only when the viscosity is controlled within the above range can the lithium ion transmission, electronic conductivity, and stress relief ability be improved.

[0062] The inorganic material lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate of the present application can be selected from the prior art or prepared by oneself. Especially for fluorinated derivatives of lithium metaaluminate, the fluorine content can be flexibly adjusted during the self-preparation process.

[0063] In some embodiments, the lithium salt is selected from lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate; preferably γ-LiAlO2; wherein, the preparation method of the fluorinated derivative of lithium metaaluminate includes: heating and reacting lithium metaaluminate with a fluorinating agent to obtain the fluorinated derivative of lithium metaaluminate. The fluorinated derivative of lithium metaaluminate prepared by this method has good performance and is suitable for compounding with a conductive polymer and then being applied to an electrode interface modification material. The fluorinating agent is selected from at least one of ammonium fluoride, ammonium bifluoride, HF, CFx, and NF3. When the fluorinating agent is a solid, such as ammonium fluoride and ammonium bifluoride, the weight ratio of lithium metaaluminate to the fluorinating agent is (80-95):(5-20); the process of the heating reaction includes: maintaining the temperature at 100°C to 200°C for 2 to 4 hours. When the fluorinating agent is a gas, such as HF and NF3, lithium metaaluminate and the fluorinating agent are heated and reacted in a tube furnace; the process of the heating reaction includes: maintaining the temperature at 150°C to 250°C for 1 to 2 hours; the flow rate of the introduced fluorinating agent is 50 to 200 mL / min. It is controlled by controlling the gas flow rate and the fluorination time.

[0064] Under the above reaction conditions, the fluorine content introduced with the above ratio is appropriate, and it can improve the heat resistance of the electrode structure and the safety performance of the battery cell when used in the electrode interface modification material.

[0065] In some embodiments, the preparation method of lithium metaaluminate includes:

[0066] Step S1-1: Mix lithium nitrate, aluminum nitrate, and citric acid in water to form a mixed solution, and stir it into a gel;

[0067] Step S1-2: Keep the gel at a temperature of 900°C to 1100°C for 2 to 5 hours to obtain lithium metaaluminate.

[0068] In some embodiments, in step S1-1, the molar ratio of lithium nitrate, aluminum nitrate, and citric acid is 1:1:(7-9); lithium nitrate, aluminum nitrate, and citric acid are dissolved in deionized water at a temperature of 70°C to 90°C to form a mixed solution; preferably 70°C to 75°C; in step S1-2, the gel is kept at a temperature of 950°C to 1000°C for 2 to 4 hours. Using the above reaction ratio and reaction conditions, lithium metaaluminate with good performance can be obtained, which is suitable for compounding with a conductive polymer to form an electrode interface modification material.

[0069] According to the third aspect of the present application, a lithium-ion battery is provided, and the electrode of the lithium-ion battery is the above electrode. The electrode modified with the above interface modification material can be a positive electrode or a negative electrode, or both the positive electrode and the negative electrode are modified, and the obtained lithium-ion battery has good structural stability, thermal stability, and high-rate cycle performance.

[0070] The present application will be further described in detail below in conjunction with specific embodiments, which should not be construed as limiting the scope claimed by the present application.

[0071] The raw materials used in the embodiments of the present application are all existing technologies and are commercially available; for example, the chemical abbreviation of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is PEDOT:PSS, purchased from Aladdin.

[0072] Example 1

[0073] Lithium fluoroaluminate: 0.5M lithium nitrate LiNO3 and 0.5M aluminum nitrate nonahydrate Al(NO3)3·9H2O were mixed and dissolved in deionized water at 70°C to obtain solution A. 4M citric acid was dissolved in deionized water to obtain solution B. Solution B was slowly added to solution A, and continuous stirring was carried out until the water evaporated to form a gel. The gel was collected and transferred to a quartz boat, heated to 1000°C in a muffle furnace, and kept warm for 4h. The calcined lithium aluminate powder was collected. The lithium aluminate powder and ammonium bifluoride were fully mixed and ground according to a weight ratio of 90:10. Subsequently, the reaction was carried out at 150°C in a muffle furnace for 2h, and the reaction product lithium fluoroaluminate LiAlO 1.93 F 0.07 was collected and ground to a median particle size D50 of 50nm.

[0074] Modified material: Weigh the PEDOT:PSS solid powder and the above-mentioned LiAlO 1.93 F 0.07 powder, and the weight ratio of the two is 95:5, that is, the weight percentage of lithium fluoroaluminate in the modified material is 5%; the compounded modified material is denoted as PEDOT:PSS@LiAlO 1.93 F 0.07 .

[0075] Suspension: When in use, PEDOT:PSS@LiAlO 1.93 F 0.07 can be dissolved in water to form a PEDOT:PSS@LiAlO 1.93 F 0.07 suspension. Alternatively, PEDOT:PSS can be dissolved in water to form a PEDOT:PSS solution before compounding, and then the above-mentioned lithium fluoroaluminate LiAlO 1.93 F 0.07 is added to the PEDOT:PSS solution, and finally water is added to adjust the viscosity, and ultrasonic dispersion is carried out for 30min to form a uniform suspension, and the viscosity of the suspension is adjusted to 500mPa·S;

[0076] Electrode modified interface layer: The suspension is sprayed on two surfaces of the negative graphite layer and dried at 60 °C, and an organic-inorganic composite interface modification layer with a thickness of about 20 μm is formed on the two opposite surfaces of the graphite layer; the volume change of the negative electrode during charge and discharge is as Figure 1 shown.

[0077] Example 2

[0078] 0.5 M lithium nitrate LiNO3 and 0.5 M aluminum nitrate nonahydrate Al(NO3)3·9H2O are mixed and dissolved in deionized water at 70 °C to obtain solution A. 4 M citric acid is dissolved in deionized water to obtain solution B. Solution B is slowly added to solution A and continuously stirred until the water evaporates to form a gel. The gel is collected and transferred to a quartz boat, heated to 1000 °C in a muffle furnace, and kept warm for 4 h. The calcined lithium metaaluminate powder is collected. The lithium metaaluminate powder and ammonium bifluoride are fully mixed and ground according to a weight ratio of 80:20, and then reacted at 150 °C in a muffle furnace for 2 h. The reaction product lithium fluoroaluminate LiAlO 1.75 F 0.25 is collected and ground to a particle size D50 of 80 nm.

[0079] Modified material: Weigh PEDOT:PSS solid powder and the above-mentioned LiAlO 1.75 F 0.25 powder, and the weight ratio of the two is 95:5, that is, the weight percentage of lithium fluoroaluminate in the modified material is 5%; the compounded modified material is denoted as PEDOT:PSS@LiAlO 1.75 F 0.25 .

[0080] Suspension: When in use, PEDOT:PSS@LiAlO 1.75 F 0.25 can be dissolved in water to form a PEDOT:PSS@LiAlO 1.75 F 0.25 suspension, or PEDOT:PSS can be dissolved in water to form a PEDOT:PSS solution before compounding, and then the above-mentioned lithium fluoroaluminate LiAlO 1.75 F 0.25 is added to the PEDOT:PSS solution, and finally water is added to adjust the viscosity, and ultrasonic dispersion is carried out for 30 min to form a uniform suspension, and the viscosity of the suspension is controlled to be 1000 mPa·S;

[0081] Electrode modified interface layer: The suspension is sprayed on the surface of the graphite negative electrode and dried at 60 °C to form an organic-inorganic composite interface modification layer with a thickness of about 20 μm; the volume change of the negative electrode during charge and discharge is as Figure 1 shown.

[0082] Example 3

[0083] 0.5M lithium nitrate LiNO3 and 0.5M aluminum nitrate nonahydrate Al(NO3)3·9H2O were mixed and dissolved in 70°C deionized water to obtain solution A. 4M citric acid was dissolved in deionized water to obtain solution B. Solution B was slowly added to solution A and stirred continuously until the water evaporated to form a gel. The gel was collected and transferred to a quartz boat, heated to 1000°C in a muffle furnace and kept warm for 4 hours. The calcined lithium aluminate powder was collected. The lithium aluminate powder and ammonium bifluoride were fully mixed and ground according to a weight ratio of 80:20, and then reacted at 150°C in a muffle furnace for 2 hours. The reaction product, lithium fluoroaluminate LiAlO 1.75 F 0.25 , and ground to a particle size D50 of 100 nm.

[0084] Modified materials: weigh PEDOT:PSS solid powder and the above-mentioned LiAlO 1.75 F 0.25 The weight ratio of the two is 95:5, that is, the weight of lithium fluoroaluminate in the modified material accounts for 5%; the composite modified material is recorded as PEDOT:PSS@LiAlO 1.75 F 0.25 .

[0085] Suspension: PEDOT:PSS@LiAlO can be dissolved in ethanol when in use. 1.75 F 0.25 Formation of PEDOT:PSS@LiAlO 1.75 F 0.25 Suspension, or PEDOT:PSS can be dissolved in ethanol to form a PEDOT:PSS solution before compounding, and then the above-mentioned lithium fluoride aluminate LiAlO 1.75 F 0.25 Add to PEDOT:PSS solution, add ethanol to adjust viscosity, and disperse by ultrasonic for 30 min to form a uniform suspension. The viscosity of the suspension is adjusted to 2000 mPa·S.

[0086] Electrode modified interface layer: The suspension was sprayed on the surface of the NCM811 positive electrode and dried at 60°C to form an organic-inorganic composite interface modified layer with a thickness of about 20 μm. The cross-sectional microstructure is shown in Figure 3 , Figure 4 shown.

[0087] Example 4

[0088] 0.5M lithium nitrate LiNO3 and 0.5M aluminum nitrate nonahydrate Al(NO3)3·9H2O were mixed and dissolved in 70°C deionized water to obtain solution A. 4M citric acid was dissolved in deionized water to obtain solution B. Solution B was slowly added to solution A and stirred continuously until the water evaporated to form a gel. The gel was collected and transferred to a quartz boat, heated to 1000°C in a muffle furnace and kept warm for 4 hours. The calcined lithium aluminate powder was collected. The lithium aluminate powder and ammonium bifluoride were fully mixed and ground in a mass ratio of 80:20, and then reacted at 150°C in a muffle furnace for 2 hours. The reaction product, lithium fluoroaluminate LiAlO 1.75 F 0.25 , and ground to a particle size D50 of 150 nm.

[0089] Modified materials: weigh PEDOT:PSS solid powder and the above-mentioned LiAlO 1.75 F 0.25 The weight ratio of the two is 95:5, that is, the weight of lithium fluoroaluminate in the modified material accounts for 5%; the composite modified material is recorded as PEDOT:PSS@LiAlO 1.75 F 0.25 .

[0090] Suspension: PEDOT:PSS@LiAlO can be dissolved in ethanol when in use. 1.75 F 0.25 Formation of PEDOT:PSS@LiAlO 1.75 F 0.25 Suspension, or PEDOT:PSS can be dissolved in ethanol to form a PEDOT:PSS solution before compounding, and then the above-mentioned lithium fluoride aluminate LiAlO 1.75 F 0.25 Add it to the PEDOT:PSS solution, and finally add ethanol to adjust the viscosity. Ultrasonic dispersion is performed for 30 minutes to form a uniform suspension. The viscosity of the suspension is adjusted to 3000 mPa·S.

[0091] Electrode modified interface layer: The suspension was sprayed on the surface of the NCM811 positive electrode and dried at 60°C to form an organic-inorganic composite interface modified layer with a thickness of about 30 μm.

[0092] Example 5

[0093] 0.5M lithium nitrate LiNO3 and 0.5M aluminum nitrate nonahydrate Al(NO3)3·9H2O were mixed and dissolved in 70℃ deionized water to obtain solution A. 4M citric acid was dissolved in deionized water to obtain solution B. Solution B was slowly added to solution A and stirred continuously until the water evaporated to form a gel. The gel was collected and transferred to a quartz boat, heated to 1000℃ in a muffle furnace and kept warm for 4h. The calcined lithium aluminate powder was collected. The lithium aluminate and ammonium bifluoride were fully mixed and ground in a mass ratio of 80:20, and then reacted at 150℃ in a muffle furnace for 2h. The reaction product, lithium fluoroaluminate LiAlO 1.75 F 0.25 , and ground to a particle size D50 of 200 nm.

[0094] Modified materials: weigh PEDOT:PSS solid powder and the above-mentioned LiAlO 1.75 F 0.25 The weight ratio of the two is 90:10, that is, the weight of lithium fluoroaluminate in the modified material accounts for 10%; the composite modified material is recorded as PEDOT:PSS@LiAlO 1.75 F 0.25 .

[0095] Suspension: PEDOT:PSS@LiAlO can be dissolved in ethanol when in use. 1.75 F 0.25 Formation of PEDOT:PSS@LiAlO 1.75 F 0.25 Suspension, or PEDOT:PSS can be dissolved in ethanol to form a PEDOT:PSS solution before compounding, and then the above-mentioned lithium fluoride aluminate LiAlO 1.75 F 0.25 Add to PEDOT:PSS solution, add ethanol to adjust viscosity, and disperse by ultrasonic for 30 min to form a uniform suspension. The viscosity of the suspension is adjusted to 4000 mPa·S.

[0096] Electrode modified interface layer: The suspension was sprayed on the surface of the NCM811 positive electrode and dried at 60°C to form an organic-inorganic composite interface modified layer with a thickness of about 20 μm.

[0097] Example 6

[0098] The difference between Example 6 and Example 3 is that the conductive polymer is replaced by polypyrrole, CAS No. 30604-81-0.

[0099] Example 7

[0100] The difference between Example 7 and Example 3 is that the content of lithium fluoroaluminate in the composite modified material is 0.5 wt %.

[0101] Example 8

[0102] The difference between Example 8 and Example 3 is that the content of lithium fluoroaluminate in the compound modified material is 2 wt%.

[0103] Example 9

[0104] The difference between Example 9 and Example 3 is that the content of lithium fluoroaluminate in the compound modified material is 10 wt%.

[0105] Example 10

[0106] The difference between Example 10 and Example 3 is that the content of lithium fluoroaluminate in the compound modified material is 15 wt%.

[0107] Example 11

[0108] The difference between Example 11 and Example 3 is that the content of lithium fluoroaluminate in the compound modified material is 20 wt%.

[0109] Example 12

[0110] The difference between Example 12 and Example 3 is that the median particle size D50 of lithium fluoroaluminate is 50 nm respectively.

[0111] Example 13

[0112] The difference between Example 13 and Example 3 is that the median particle size D50 of lithium fluoroaluminate is 150 nm respectively.

[0113] Example 14

[0114] The difference between Example 14 and Example 3 is that the median particle size D50 of lithium fluoroaluminate is 200 nm respectively.

[0115] Example 15

[0116] The difference between Example 15 and Example 3 is that the fluorinating agent is ammonium fluoride.

[0117] Example 16

[0118] The difference between Example 16 and Example 3 is that the weight ratio of lithium aluminate to ammonium bifluoride is 95:5.

[0119] Comparative Example 1

[0120] The difference between Comparative Example 1 and Example 3 is that the modified material is PEDOT:PSS, without lithium salt; a suspension is prepared for spraying during use.

[0121] Comparative Example 2

[0122] The difference between Comparative Example 2 and Example 3 is that there is no interfacial modification layer on the surfaces of both the positive electrode and the negative electrode; the volume change of this electrode during charge and discharge is as Figure 2 shown and Figure 5 shown.

[0123] Test Example

[0124] The electrode sheets prepared in Examples 1 to 16 and Comparative Examples 1 to 2 were assembled into lithium-ion batteries for testing:

[0125] 1) Electrode preparation and battery assembly: The prepared electrodes were cut into electrode sheets with fixed dimensions. The size of the negative electrode was 96 mm × 126 mm, and the size of the positive electrode was 93 mm × 123 mm. In a Z-shaped stacking method, the graphite negative electrode, the separator, and the NCM811 positive electrode were assembled in sequence and then subjected to steps such as tab welding, casing, baking, electrolyte injection (the electrolyte of lithium hexafluorophosphate from Shinzo), formation, and grading to prepare a 10 Ah soft-pack battery cell.

[0126] 2) Battery testing: The assembled soft-pack battery cells were tested in a temperature-controlled environment (room temperature 25 °C, high temperature 45 °C). A Neware device was used for charge and discharge testing. The charge and discharge voltage window was set to 3.0 - 4.5 V. During the charging process, a constant current and constant voltage method was adopted. It was charged at a 1C rate to 4.3 V, and then continued to be charged at a constant voltage until the current density was less than 0.05C. During the discharging process, a constant current method was adopted, and the current density was set to 1C. Then it was left standing for 10 min. This was taken as a complete charge and discharge cycle. The cycle performance of the lithium-ion batteries obtained in different examples and comparative examples was recorded, as shown in Table 1; the charge and discharge curves of the battery cells of Example 3 and Comparative Example 2 are as Figure 6 shown.

[0127] Table 1

[0128] modified electrode 45°C 1C cycle capacity retention rate % number of cycles Example 1 80％ 883 Example 2 80％ 909 Example 3 80％ 1257 Example 4 80％ 1052 Example 5 80％ 1131 Example 6 80％ 984 Example 7 80％ 894 Example 8 80％ 923 Example 9 80％ 1120 Example 10 80％ 1023 Example 11 80％ 876 Example 12 80％ 925 Example 13 80％ 1120 Example 14 80％ 899 Example 15 80％ 1194 Example 16 80％ 1025 Comparative Example 1 80％ 830 Comparative Example 2 80％ 800

[0129] The results in Table 1 show that the battery cells assembled with the electrodes having an interfacial modification layer prepared in Examples 1 to 16 of the present application have good cycle performance. When the capacity retention rate is 80%, the number of cycle times reaches 883 - 1257, and the number of cycle times in Examples 3 to 5 reaches 1052 - 1257; compared with the 800 cycle times of Examples 3 to 5 and Comparative Example 2, the cycle performance is significantly improved; it shows that by attaching an organic-inorganic composite interfacial modification layer on the surface of the positive electrode in the present application, the cycle performance of the battery cell can be significantly improved.

[0130] Although a PEDOT:PSS protective layer was coated on the surface of the positive electrode in Comparative Example 1, the cycle performance was only 830 times, which was significantly lower than the cycle performance of the battery cell prepared in Example 3 of the present application; it shows that adding a lithium salt material to the conductive polymer can significantly improve the electrochemical performance of the battery cell.

[0131] Compared with the negative electrodes of Examples 1-2 and Comparative Example 2, the cycling performance is also significantly improved; it shows that attaching a modified layer on the surface of the negative electrode can significantly enhance the electrochemical performance of the battery cell.

[0132] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of this application described here can be implemented in an order other than those described here, for example.

[0133] The above are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. An electrode interface modification material, characterized in that, The electrode interface modification material includes an organic material and an inorganic material; Among them, the organic material is a conductive polymer; the inorganic material is a lithium salt.

2. The electrode interface modification material according to claim 1, wherein The weight ratio of the inorganic material to the organic material is (0.5 - 20):(80 - 99.5); preferably (2 - 15):(85 - 98); more preferably (5 - 10):(90 - 95).

3. The electrode interface modification material according to claim 1 or 2, characterized in that The median particle size D50 of the lithium salt is 30 - 200 nm; preferably 50 - 100 nm.

4. The electrode interface modification material according to any one of claims 1 to 3, characterized in that The conductive polymer is selected from at least one of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), polyaniline, and polypyrrole; And / or, the lithium salt is selected from lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate; preferably γ-LiAlO2; Preferably, the chemical formula of the lithium fluoroaluminate derivative is LiAlO 2-x F x , where 0 < x < 0.5; more preferably, x = 0.05 - 0.

2.

5. An electrode, characterized in that, The electrode includes an electrode body and an interface modification layer. The electrode body includes a current collector and active layers attached to two opposite surfaces of the current collector; the interface modification layer is attached to the surface of the active layer away from the current collector; wherein, the material of the interface modification layer is the electrode interface modification material according to any one of claims 1 to 4.

6. The electrode according to claim 5, wherein The thickness of the interface modification layer is 0.2 - 40 μm; preferably 0.5 - 30 μm; more preferably 10 - 20 μm; And / or, the interface modification layer is attached to two opposite surfaces of the active layer away from the current collector; And / or, the active material of the active layer includes a positive electrode active material and a negative electrode active material; the positive electrode active material is selected from at least one of NCMxyz, NCAxyz, and LMFP; Preferably, the NCMxyz is selected from at least one of NCM811, NCM111, and NCM523; Preferably, the NCAxyz is selected from at least one of NCA111, NCA811, NCA622, NCA721, and NCA532; Preferably, the negative electrode active material is graphite.

7. A method for preparing the electrode according to claim 5 or 6, characterized in that, The preparation method includes the following steps: Step S1: Mix the conductive polymer, lithium salt, and solvent to obtain a suspension; Step S2: Coat the suspension on the surface of the electrode body, and after curing, form the interface modification layer, thus obtaining the electrode.

8. The preparation method of the electrode according to claim 7, wherein, The viscosity of the suspension is 200 - 10000 mPa·S; preferably 200 - 5000 mPa·S; And / or, the solvent is a solvent that dissolves the conductive polymer; preferably, the solvent is selected from at least one of water, ethanol, N-methylpyrrolidone, and dimethylformamide; And / or, the coating method includes transfer coating or extrusion coating.

9. The method for preparing the electrode according to claim 7 or 8, characterized in that, The lithium salt is selected from lithium metaaluminate and / or fluorinated derivatives of lithium metaaluminate; preferably γ-LiAlO2; Preferably, the preparation method of the fluorinated derivative of lithium metaaluminate includes: heating and reacting lithium metaaluminate with a fluorinating agent to obtain the fluorinated derivative of lithium metaaluminate; Preferably, the fluorinating agent is selected from at least one of ammonium fluoride, ammonium bifluoride, HF, CFx, and NF3; Preferably, when the fluorinating agent is a solid, the weight ratio of lithium metaaluminate to the fluorinating agent is (80 - 95): (5 - 20); The process of the heating reaction includes: heat preservation for 2 - 4 h under the condition of 100°C - 200°C; Preferably, when the fluorination reagent is a gas, the lithium metaaluminate and the fluorination reagent carry out the heating reaction in a tubular furnace; The process of the heating reaction includes: heat preservation for 1 - 2 h under the condition of 150°C - 250°C; The flow rate of the fluorination reagent is 50 - 200 mL / min.

10. A lithium-ion battery, characterized in that, The electrode of the lithium ion battery is the electrode described in claim 5 or 6 or the electrode prepared by the preparation method of the electrode described in any one of claims 7 to 9.

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