Lithium supplementing method based on supercritical carbon dioxide, modified conductive agent, and pole piece

Abstract

The application relates to a lithium supplementing method based on supercritical carbon dioxide, a modified conductive agent and a pole piece. The conductive agent and a catalyst are added into a lithium salt mixed solution, carbon dioxide is introduced, and a first mixture is obtained; the lithium salt mixed solution comprises a first lithium salt and a second lithium salt, and the decomposition temperature of the first lithium salt is lower than that of the second lithium salt; the first mixture is subjected to temperature and pressure increasing treatment, so that the carbon dioxide reaches a supercritical state, and after stirring, the pressure is reduced to normal pressure, so as to obtain a second mixture; the second mixture is subjected to first temperature increasing treatment under a reducing atmosphere, so that the first lithium salt is decomposed into a lithium-containing intermediate product; second temperature increasing treatment is conducted, so that the second lithium salt is melted and reduced into metallic lithium; third temperature increasing treatment is conducted, so that the lithium-containing intermediate product is decomposed and reduced into metallic lithium, and a lithiumized conductive agent is obtained. The application has high adaptability, does not need to design lithium supplementing agents for the positive and negative electrodes respectively, and can be directly applied to the positive or negative electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium supplementing method based on supercritical carbon dioxide, a modified conductive agent and a pole piece. BACKGROUND

[0002] During the first charge-discharge process of a lithium ion battery, the formation of a solid electrolyte interface (SEI) film or the occurrence of an irreversible side reaction will cause a large loss of active lithium, resulting in a decrease in capacity and a decrease in energy density of the battery cell. To solve this problem, there are two solutions in the industry: one is to select a battery cell main material with high initial efficiency and design a suitable battery cell system under the premise of meeting the performance index requirements of the battery cell; the other is to supplement lithium to the battery cell to make up for the loss of active lithium during the first charge-discharge process.

[0003] In the industry, lithium supplementing for lithium ion batteries is divided into positive electrode side lithium supplementing and negative electrode side lithium supplementing.

[0004] Positive electrode lithium supplementing usually involves adding lithium supplementing additives (such as Li3NiO2, etc.) to the positive electrode slurry. During the first charge of the battery, these compounds release lithium ions to supplement the active lithium consumed by the SEI film in the negative electrode material.

[0005] Negative electrode lithium supplementing involves introducing an additional lithium source into the negative electrode active material to compensate for the active lithium consumed during the first charge-discharge process. Common negative electrode lithium supplementing methods include lithium foil supplementing, lithium powder supplementing, chemical supplementing and self-discharge mechanism lithiation, etc.

[0006] The above-mentioned positive electrode lithium supplementing method cannot be applied to negative electrode lithium supplementing, and similarly, the above-mentioned negative electrode lithium supplementing method cannot be applied to positive electrode lithium supplementing. Positive and negative electrode lithium supplementing need to be designed with lithium supplementing agents and supporting lithium supplementing methods, which have poor adaptability, SUMMARY

[0007] The present application provides a lithium supplementing method based on supercritical carbon dioxide, a modified conductive agent and a pole piece. The present application has high adaptability and does not need to design lithium supplementing agents for positive and negative electrodes. The modified conductive agent for lithium supplementing can be directly applied to positive or negative electrodes.

[0008] In a first aspect, a lithium supplementing method based on supercritical carbon dioxide is provided, which includes:

[0009] The conductive agent and the catalyst are added to a lithium salt mixed solution, and carbon dioxide is introduced to obtain a first mixture; the lithium salt mixed solution includes a first lithium salt and a second lithium salt, and the decomposition temperature of the first lithium salt is lower than that of the second lithium salt;

[0010] The first mixture is subjected to temperature and pressure increasing treatment to make the carbon dioxide reach a supercritical state, and then the pressure is reduced to atmospheric pressure after stirring to obtain a second mixture;

[0011] performing a first temperature rising process on the second mixture under a reducing atmosphere to decompose the first lithium salt into a lithium-containing intermediate product and a byproduct gas;

[0012] performing a second temperature rising process to melt and reduce the second lithium salt into metallic lithium and a byproduct gas;

[0013] performing a third temperature rising process to decompose and reduce the lithium-containing intermediate product into metallic lithium and a byproduct gas to obtain a lithiated conductive agent.

[0014] In some embodiments, the first lithium salt is lithium oxalate, the second lithium salt is lithium acetate, and the lithium-containing intermediate product is lithium carbonate.

[0015] In some embodiments, the first temperature rising process comprises: rising temperature to 250-280°C at a temperature rising rate of 1-5°C / min and maintaining for 1-2h;

[0016] the second temperature rising process comprises: rising temperature to 340-360°C at a temperature rising rate of 1-5°C / min and maintaining for 0.5-1h;

[0017] the third temperature rising process comprises: rising temperature to 400-450°C at a temperature rising rate of 1-5°C / min and maintaining for 0.5-1h.

[0018] In some embodiments, before rising temperature to 250-280°C, the first temperature rising process further comprises: first washing away residual moisture in the second mixture, then drying at 80-100°C, then rising temperature to 140-200°C at a temperature rising rate of 1-5°C / min and maintaining for 0.5-1h, and finally vacuumizing to remove crystal water in lithium acetate.

[0019] In some embodiments, after the first temperature rising process, the second temperature rising process and / or the third temperature rising process, the lithium supplementing method further comprises: vacuumizing and back-filling protective gas to remove the byproduct gas.

[0020] In some embodiments, after the third temperature rising process, the lithium supplementing method further comprises: first lowering temperature to a preset temperature at a first temperature lowering rate, and then lowering temperature to room temperature with the furnace;

[0021] and / or, the third temperature rising process comprises: vacuumizing to reduce partial pressure of the byproduct gas.

[0022] In some embodiments, the catalyst comprises one or more of cobalt oxide Co3O4, ferric oxide Fe2O3 and molybdenum oxide / cobalt MoO2 / Co composite catalyst.

[0023] In some embodiments, the catalyst is added in an amount of 0.5-1.5 wt% of the total mass of the lithium salt.

[0024] In some embodiments, the reducing atmosphere comprises a reducing gas and an inert carrier gas, the reducing gas comprises hydrogen, and the reducing gas accounts for 3-8% of the reducing atmosphere.

[0025] In some embodiments, the conductive agent comprises one or more of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCF), conductive carbon black, and acetylene black.

[0026] In some embodiments, the ratio of the total mass of the conductive agent and the lithium salt is (0.58-1.21):1.

[0027] In some embodiments, the mass ratio of the first lithium salt and the second lithium salt is 1:(1-3).

[0028] In some embodiments, the lithium ion concentration in the lithium salt mixed solution is 0.4-0.8 mol / L.

[0029] In some embodiments, the solvent in the lithium salt mixed solution is an aqueous solution of methanol, ethanol, propanol, or acetone, and the volume ratio of methanol, ethanol, propanol, or acetone to water is 1:(1-1.3).

[0030] In some embodiments, the method of adding the conductive agent and the catalyst to the lithium salt mixed solution and introducing carbon dioxide to obtain the first mixture comprises: adding the conductive agent to a reaction kettle, and then adding the catalyst and the lithium salt mixed solution to the reaction kettle to obtain a reaction system, the volume of the reaction system accounting for 5-10% of the volume of the reaction kettle, pre-cooling the reaction kettle to 5-10°C, and introducing carbon dioxide to a pressure of 5-7 MPa to make the carbon dioxide in a liquid state.

[0031] In some embodiments, the temperature and pressure increasing process comprises: increasing the temperature to 30-50°C and increasing the pressure to 10-15 MPa.

[0032] In some embodiments, the depressurization rate when depressurizing to normal pressure is not greater than 1 MPa / min.

[0033] In a second aspect, a modified conductive agent is provided, which is prepared by the supercritical carbon dioxide-based lithium supplementing method as described in any of the above.

[0034] In a third aspect, a pole piece is provided, which comprises the modified conductive agent as described above.

[0035] In some embodiments, it further comprises a binder, a solid-state electrolyte, and an active material, wherein the mass ratio of the modified conductive agent, the binder, the solid-state electrolyte, and the active material is 1-5:3-5:0-40:50-96.

[0036] In some embodiments, the binder comprises one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyisobutylene (PIB), and styrene-ethylene-butylene-styrene block copolymer (SEBS).

[0037] And / or, the solid-state electrolyte comprises one or more of a sulfide electrolyte, an oxide electrolyte, a halide electrolyte, and a polymer electrolyte.

[0038] And / or, the active material is a positive electrode active material or a negative electrode active material, the positive electrode active material comprises one or more of a ternary positive electrode, lithium cobaltate, lithium iron phosphate, lithium manganate, lithium iron manganese phosphate, and a lithium-rich manganese-based material; and the negative electrode active material comprises one or more of a graphite-based negative electrode and a silicon-based negative electrode.

[0039] In some embodiments, the electrode sheet is a positive electrode sheet or a negative electrode sheet.

[0040] In a fourth aspect, a battery is provided, comprising the electrode sheet according to any one of the above.

[0041] The technical solutions provided by the present application have the following beneficial effects:

[0042] The present application uses supercritical carbon dioxide as a solvent. When stirring, the low viscosity, high diffusivity, and no solvent residue characteristics of supercritical CO2 are used to achieve uniform dispersion of lithium salt inside the conductive agent. Meanwhile, the gradient pressure reduction process induces directional crystallization of lithium salt, reducing surface agglomeration.

[0043] The present application uses first and second lithium salts with different decomposition temperatures as lithium supplement sources. In a step-by-step heating heat treatment process, the decomposition process is carried out in stages, and the melting filling synergistic effect is combined to achieve uniform deposition of lithium supplement components. Then, under the action of a reducing atmosphere and a catalyst, lithium salt generates metallic lithium and byproduct gas, avoiding the generation of inert substances, and chemically adsorbing to defect sites such as carboxyl and hydroxyl groups on the surface of the conductive agent to form lithium-carbon compounds, achieving the lithium supplement function of the modified conductive agent.

[0044] The present application uses a step-by-step heat treatment process to achieve stage-by-stage decomposition, avoid local overheating, and improve the structural integrity of the conductive agent.

[0045] Compared with the current positive and negative electrodes, the present application has high adaptability and does not need to design lithium supplement agents for positive and negative electrodes. The lithium supplement modified conductive agent can be directly applied to positive or negative electrodes. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on these drawings.

[0047] Figure 1 The 0.1C charge-discharge schematic diagram provided by the present application. DETAILED DESCRIPTION

[0048] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0049] The present application provides a lithium supplement method based on supercritical carbon dioxide, which comprises the following steps:

[0050] S1: adding a conductive agent and a catalyst into a lithium salt mixed solution, and introducing carbon dioxide to obtain a first mixture; the lithium salt mixed solution comprises a first lithium salt and a second lithium salt, and the decomposition temperature of the first lithium salt is lower than that of the second lithium salt.

[0051] In step S1, the lithium salt mixed solution is prepared first, and then the conductive agent is added after stirring to form a homogeneous system.

[0052] The first lithium salt can be lithium oxalate, and the second lithium salt can be lithium acetate.

[0053] S2: performing temperature and pressure increasing treatment on the first mixture to make the carbon dioxide reach a supercritical state, and then stirring and reducing the pressure to normal pressure to obtain a second mixture.

[0054] In step S2, the carbon dioxide is made to reach a supercritical state, and the lithium salt mixed solution is dispersed in the supercritical carbon dioxide. The lithium salt is dispersed more uniformly by virtue of the strong dispersing property of the supercritical carbon dioxide. In the present application, the supercritical carbon dioxide is used as a solvent. When stirring, the low viscosity, high diffusivity and no solvent residue characteristics of the supercritical CO2 are used to realize the uniform dispersion of the lithium salt in the conductive agent. At the same time, the gradient pressure reduction process induces the directional crystallization of the lithium salt, and reduces the surface agglomeration.

[0055] S3: performing first temperature increasing treatment on the second mixture under a reducing atmosphere to decompose the first lithium salt into a lithium-containing intermediate product and a byproduct gas.

[0056] In the present application, when lithium oxalate is used as the first lithium salt, the lithium-containing intermediate product obtained by decomposition is lithium carbonate. It can be understood that, in the first temperature rising treatment, the reducing atmosphere does not directly participate in the reaction, and the main role is to establish a reducing atmosphere, protect the functional groups such as carboxyl and hydroxyl on the surface of the conductive agent, and reserve active sites for subsequent reactions. Lithium oxalate decomposes under the action of the catalyst at the corresponding decomposition temperature, thereby generating the lithium-containing intermediate product.

[0057] S4: After the first temperature rising treatment, a second temperature rising treatment is performed under a reducing atmosphere, so that the second lithium salt is decomposed into metallic lithium and byproduct gas.

[0058] In step S4, the molten second lithium salt can fill the pores generated by decomposition, promote the uniformity of internal lithium supplement modification of the conductive agent, and avoid local aggregation.

[0059] In step S4, the reducing atmosphere participates in the reduction reaction, and Li + is reduced to metallic Li.

[0060] S5: After the second temperature rising treatment, a third temperature rising treatment is performed under a reducing atmosphere, so that the lithium-containing intermediate product is decomposed and reduced into metallic lithium and byproduct gas, thereby obtaining the lithiated conductive agent.

[0061] In step S5, the reducing atmosphere does not directly participate in the reaction, and the main role is to establish a reducing atmosphere, protect the functional groups such as carboxyl and hydroxyl on the surface of the conductive agent, and reserve active sites for subsequent reactions. The lithium-containing intermediate product decomposes under the action of the catalyst at the corresponding decomposition temperature, thereby generating metallic lithium.

[0062] The present application generates metallic lithium and byproduct gas by steps S3-S5, avoids the generation of inert substances, and the byproduct gas can be subsequently discharged.

[0063] The present application uses the first lithium salt and the second lithium salt with different decomposition temperatures as the lithium supplement source, and makes the decomposition process proceed step by step in the stepwise heating heat treatment process, and simultaneously combines the synergistic effect of melting filling, to realize the uniform deposition of the lithium supplement component. Then, under the action of the reducing atmosphere and the catalyst, the lithium salt generates metallic lithium and byproduct gas, avoids the generation of inert substances, chemically adsorbs the defect sites such as carboxyl and hydroxyl on the surface of the conductive agent, forms a lithium-carbon compound, and realizes the lithium supplement function of the modified conductive agent.

[0064] The present application uses the stepwise heat treatment process to realize the decomposition in stages, avoids local overheating, and improves the structural integrity of the conductive agent.

[0065] Compared with the current positive and negative, the lithium supplement agent and the matching lithium supplement method need to be designed respectively, the adaptability of the application is high, and the lithium supplement modified conductive agent can be directly applied to the positive electrode or the negative electrode without designing the lithium supplement agent for the positive electrode and the negative electrode respectively.

[0066] In order to realize the step-by-step process of lithium salt decomposition, and at the same time, realize the uniform deposition of lithium supplement components by combining the synergistic effect of melting filling, taking lithium oxalate and lithium acetate as an example, the first temperature rising treatment includes: heating to 250-280 DEG C at a heating rate of 1-5 DEG C / min, and keeping for 1-2h;

[0067] The second temperature rising treatment includes: heating to 340-360 DEG C at a heating rate of 1-5 DEG C / min, and keeping for 0.5-1h;

[0068] The third temperature rising treatment includes: heating to 400-450 DEG C at a heating rate of 1-5 DEG C / min, and keeping for 0.5-1h.

[0069] The heating rate of 1-5 DEG C / min can ensure that the material is heated uniformly and the decomposition reaction in each stage is stable; correspondingly, the holding temperature and holding time in each stage are determined, so that the best decomposition process in each stage under the catalyst and reducing gas atmosphere, and ensure that each decomposition reaction is complete.

[0070] In order to avoid the influence of by-product gas, further, negative pressure exhaust can be used, specifically, after the first temperature rising treatment, the second temperature rising treatment and the third temperature rising treatment are finished, the lithium supplement method further includes: after the holding is finished, vacuumizing and backfilling protective gas to exhaust by-product gas. For example, as an example, after the holding is finished, vacuumizing to 10 -4 ~10 -2 Pa, and backfilling protective gas such as argon to exhaust by-product gas, after three cycles, reducing atmosphere is introduced again to normal pressure.

[0071] Further, before heating to 250-280 DEG C, the first temperature rising treatment further includes: first washing away the residual moisture in the second mixture, then drying treatment at 80-100 DEG C, then heating to 140-200 DEG C at a heating rate of 1-5 DEG C / min, keeping for 0.5-1h, and finally vacuumizing to remove the crystal water in lithium acetate.

[0072] The purpose of removing residual moisture and crystal water is to prevent the reaction between produced metal lithium and water in the subsequent decomposition process.

[0073] Further, after the third temperature rising treatment, the lithium supplement method further comprises: first cooling to a preset temperature at a first cooling rate, and then cooling to room temperature with the furnace. For example, as an example, cooling to 150℃ at a cooling rate of 1-5℃ / min, and then cooling to room temperature with the furnace. In the two-stage cooling process, the uniform cooling in the early stage can avoid the damage to the material caused by rapid temperature change.

[0074] Further, the third temperature rising treatment further comprises: vacuumizing to reduce the partial pressure of the byproduct gas and promote the decomposition process.

[0075] The catalyst comprises one or more of cobalt oxide Co3O4, ferric oxide Fe2O3, and molybdenum oxide / cobalt MoO2 / Co composite catalyst. The catalyst is added in an amount of 0.5-1.5wt% of the total mass of the lithium salt.

[0076] In the above steps S3-S5, the reducing atmosphere comprises a reducing gas and an inert carrier gas, the reducing gas comprises hydrogen, and the proportion of the reducing gas in the reducing atmosphere is 3-8%. If the proportion is too low, it will not work, and if the proportion is too high, there will be too many side reactions.

[0077] The intermediate product of the decomposition of lithium oxalate and lithium acetate is lithium carbonate, which can be reduced by hydrogen to obtain metallic lithium and byproduct gas, including carbon dioxide and water vapor.

[0078] The conductive agent comprises one or more of carbon nanotubes CNTs, vapor-deposited carbon fibers VGCF, conductive carbon black, and acetylene black. The proportion of the conductive agent to the total mass of the lithium salt is (0.58-1.21):1.

[0079] In the above step S1, in the lithium salt mixed solution, the mass ratio of the first lithium salt to the second lithium salt is 1:(1-3).

[0080] In the lithium salt mixed solution, the solvent is an aqueous solution of methanol, ethanol, propanol, or acetone, and the volume ratio of methanol, ethanol, propanol, or acetone to water is 1:(1-1.3). Two kinds of solvents are used because the solubility of the two kinds of lithium salts in methanol, ethanol, propanol, or acetone is not good, and the solubility of pure water in supercritical carbon dioxide is not good.

[0081] Taking lithium oxalate and lithium acetate as an example, lithium acetate and lithium oxalate are dissolved in an ethanol / water mixed solvent at a mass ratio of 1:3, the volume ratio of ethanol to water is 1:(1-1.3), and the lithium ion concentration is controlled at 0.4-0.8mol / L. Ultrasonic assistance (20-40kHz) and mechanical stirring (200-500rpm) are turned on for 30-60 minutes to ensure that the lithium salt is completely dissolved and a homogeneous system is formed.

[0082] In the step S1, the conductive agent and the catalyst are added into the lithium salt mixed solution, and carbon dioxide is introduced to obtain the first mixture, including: adding the conductive agent into a reaction kettle, and then adding the catalyst and the lithium salt mixed solution into the reaction kettle to obtain a reaction system, the volume of the reaction system is 5-10% of the volume of the reaction kettle, the reaction kettle is pre-cooled to 5-110 DEG C, and carbon dioxide is introduced to 5-7 MPa to make the carbon dioxide in liquid state.

[0083] In the step S2, the temperature and pressure increasing treatment includes: increasing the temperature to 30-50 DEG C, and increasing the pressure to 10-15 MPa to make the carbon dioxide in supercritical state between liquid and gas.

[0084] In the step S2, the pressure decreasing rate is not more than 1 MPa / min when the pressure is decreased to normal pressure, which can make the lithium salt uniformly dispersed.

[0085] The application further provides a modified conductive agent prepared by the above-mentioned lithium supplementing method based on supercritical carbon dioxide.

[0086] The application further provides a pole piece comprising the modified conductive agent.

[0087] The pole piece further comprises a binder, a solid electrolyte and an active material, wherein the mass ratio of the modified conductive agent, the binder, the solid electrolyte and the active material is 1-5: 3-5: 0-40: 50-96.

[0088] The binder comprises one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyisobutylene (PIB) and styrene-ethylene-butylene-styrene block copolymer (SEBS).

[0089] The solid electrolyte comprises one or more of sulfide electrolyte, oxide electrolyte, halide electrolyte and polymer electrolyte.

[0090] The active material is a positive electrode active material or a negative electrode active material, the positive electrode active material comprises one or more of ternary positive electrode, lithium cobaltate, lithium iron phosphate, lithium manganate, lithium iron manganese phosphate and lithium-rich manganese-based material, and the negative electrode active material comprises one or more of graphite-based negative electrode and silicon-based negative electrode.

[0091] The pole piece is a positive electrode pole piece or a negative electrode pole piece.

[0092] The application further provides a battery comprising the pole piece.

[0093] At least one of the positive electrode pole piece and the negative electrode pole piece of the battery contains the modified conductive agent.

[0094] The present application is described in detail below by some examples.

[0095] Example 1

[0096] Step 1: Dissolve 0.7 g of lithium acetate and 0.3 g of lithium oxalate in an ethanol / water mixed solvent (volume ratio 1:1), control the lithium ion concentration at 0.5 mol / L, then add 0.01 g of Co3O4 catalyst.

[0097] Step 2: Turn on ultrasonic assistance (30 kHz) and mechanical stirring (400 rpm) for 40 minutes to ensure that the lithium salt is completely dissolved and a homogeneous system is formed.

[0098] Step 3: Place 0.85 g of carbon nanotubes CNTs to be modified by lithium supplementation in the reaction kettle, and at the same time, place the homogeneous solution in Step 2 into the reaction kettle, while controlling the volume to be 8% of the reaction kettle, then pre-cool the reaction kettle to 10℃, and introduce CO2 to a pressure of 7 MPa, at this time the carbon dioxide is in a liquid state, obtaining a first mixture.

[0099] Step 4: Increase the temperature of the reaction kettle to 40℃, and pressurize to 12 MPa to make the system reach a supercritical state, and mechanically stir (3000 rpm) for 40 minutes.

[0100] Step 5: Slowly reduce the pressure to atmospheric pressure at a rate of 0.5 MPa / min to allow the lithium salt to be directionally deposited, obtaining a modified precursor material (i.e., a second mixture).

[0101] Step 6: The second mixture obtained in Step 5 is washed and filtered with ethanol to remove residual water, and is subjected to drying treatment at 100℃, and then is placed in a high-temperature reaction kettle equipped with H2 / Ar gas circuit and vacuum system, first heated to about 160℃ at a rate of 2℃ / min under the protection of inert gas such as argon, and kept for 1 hour, and then vacuum exhausts the waste gas.

[0102] Then heated to 265℃ at a rate of 2℃ / min, and kept for 1 hour (H2 / Ar mixed gas, H2 ratio 5%, flow rate 50 mL / min), under the action of the catalyst, the lithium oxalate decomposes at this temperature to generate loose porous Li2CO3 and CO gas, vacuum exhausts to 10 -3 Pa and backfills with a protective gas such as inert gas Ar to remove the byproduct gas; after three cycles of gas circulation, H2 / Ar mixed gas is introduced again, and the pressure is kept at atmospheric pressure.

[0103] Step 7: Increase to 350℃ at a rate of 5℃ / min, and keep for 0.5 h to make the lithium acetate melt and decompose into metallic lithium and byproduct gas, and then vacuum exhaust to 10 -3Pa, and backfilling the protective gas, and then vacuumizing, and then the cycle of vacuumizing and gas inflating is repeated for 3 times to make sure that the byproduct gas is completely removed, and then the temperature is decreased to 150°C at a rate of 5°C / min, and then the temperature is decreased to room temperature to obtain the lithiated carbon nanotubes.

[0104] In this process, the lithium oxalate is completely decomposed, and the lithium acetate is melted (melting point ≥ 286°C) in the heating process, and fills the loose lithium carbonate pores generated in step 6 and the surface voids of the conductive agent, avoids local aggregation, and further promotes the uniformity of lithium supplement, and in the process of heat preservation, the Li + The liquid lithium is generated at the reduction site. After the heat preservation is completed, the tail gas treatment is performed, and the treatment mode is the same as that in step 6.

[0105] After the tail gas treatment is completed, the inert protective gas is introduced until the pressure is ≥ 0.5 MPa, so as to promote the uniform distribution of the liquid lithium and the chemical adsorption of the surface of the conductive agent, form a lithium-carbon composite structure, and realize the prelithiation of the conductive agent.

[0106] Step 8: increase to 400°C at a rate of 5°C / min, and then vacuumize to 10 -3 Pa, and heat preservation for 1 h, and then vacuumize to reduce the partial pressure of the gas such as CO / CO2 generated after the reaction of lithium carbonate (Li2CO3), promote the decomposition process of lithium carbonate (Li2CO3) to occur, and the Li2O generated by the decomposition subsequently generates the metal lithium by the carbothermal reduction reaction on the surface of the conductive agent, so as to realize the prelithiation of the conductive agent. Then vacuumize to 10 -3 Pa, and backfill the protective gas, and then vacuumize-gas inflate cycle is repeated for 3 times to make sure that the byproduct gas is completely removed, and then decrease to 150°C at a rate of 5°C / min, and then decrease to room temperature to obtain the lithiated carbon nanotubes.

[0107] Step 9: according to the mass ratio of lithiated carbon nanotubes: PTFE: oxide solid electrolyte: silicon-carbon negative electrode = 3:3:14:80, the pole piece is prepared, and the battery is assembled.

[0108] Example 2

[0109] The difference between this example and example 1 is that in step 1, the lithium acetate is 0.5 g, and the lithium oxalate is 0.5 g, in step 3, the carbon nanotubes are replaced by conductive graphite, and the weight is 0.70 g, and the rest is the same as example 1.

[0110] Example 3

[0111] The difference between this example and example 1 is that in step 3, the carbon nanotubes are replaced by conductive graphite, and in step 5, the pressure is decreased to atmospheric pressure at a rate of 1 MPa / min, and the rest is the same as example 1.

[0112] Example 4

[0113] The difference between this embodiment and embodiment 1 is that carbon nanotubes are replaced by VGCF in step 3, and the holding time is shortened to 0.3 h in step 8, and the rest is the same as embodiment 1.

[0114] Example 5

[0115] The difference between this embodiment and embodiment 1 is that 1.21 g of carbon nanotubes to be modified by lithium supplement is added in step 3, and the rest is the same as embodiment 1.

[0116] Example 6

[0117] The difference between this embodiment and embodiment 1 is that the decomposition temperature of lithium oxalate is adjusted from 265°C to 250°C in step 6.

[0118] Example 7

[0119] The difference between this embodiment and embodiment 1 is that the decomposition temperature of lithium oxalate is adjusted from 265°C to 280°C in step 6.

[0120] Example 8

[0121] The difference between this embodiment and embodiment 1 is that the catalyst is replaced by iron trioxide Fe2O3 in step 1, and the content is adjusted to 0.5 wt%, and the rest is the same as embodiment 1.

[0122] Example 9

[0123] The difference between this embodiment and embodiment 1 is that the catalyst is replaced by molybdenum oxide / cobalt MoO2 / Co composite catalyst in step 1, and the content is adjusted to 1.5 wt%, and the rest is the same as embodiment 1.

[0124] Example 10

[0125] The difference between this embodiment and embodiment 1 is that the lithium ion concentration is adjusted to 0.2 mol / L by adjusting the solvent content in step 1, and the rest is the same as embodiment 1.

[0126] Example 11

[0127] The difference between this embodiment and embodiment 1 is that the pressure reduction process is reduced to atmospheric pressure at a rate of 5 MPa / min in step 5, and the rest is the same as embodiment 1.

[0128] Example 12

[0129] The difference between this embodiment and embodiment 1 is that CO2 is not passed in step 3, i.e. without supercritical CO2, and the rest is the same as embodiment 1.

[0130] Example 13

[0131] The embodiment differs from example 1 in that the amount of lithium acetate is replaced by the amount of lithium oxalate, ensuring the consistency of lithium ion concentration, and the rest is the same as example 1.

[0132] Example 14

[0133] The embodiment differs from example 1 in that in step 9, the same kind of non-pre-lithiated conductive agent is used during electrode preparation, and the rest is the same as example 1.

[0134] Example 15

[0135] The embodiment differs from example 1 in that in step 1, no catalyst is added, and the rest is the same as example 1.

[0136] Example 16

[0137] The embodiment differs from example 1 in that the amount of lithium oxalate is replaced by the amount of lithium acetate, ensuring the consistency of lithium ion concentration, and the rest is the same as example 1.

[0138] The mold cell batteries of each embodiment are assembled, in which the counter electrode uses lithium-indium alloy. According to the gram capacity of the main material used and the gram capacity of the main material of the electrode sheet, the theoretical battery capacity is calculated, and the initial efficiency of the battery is obtained by charging and discharging at a current of 0.1C,

[0139] The battery is tested for cell initial efficiency, and the test results are shown in Tables 1 and Figure 1

[0140] Table 1

[0141]

[0142] From the test data in Table 1, the initial coulombic efficiency of examples 1-11 is higher than that of example 12, indicating that using supercritical carbon dioxide as a solvent and using lithium sources with different decomposition temperatures for three times of temperature rising treatment can improve the initial coulombic efficiency.

[0143] Comparing example 1 and example 10, it can be seen that the lithium salt concentration in step 1 is reduced, the pre-lithiation degree of the conductive agent is reduced, and the initial efficiency is relatively reduced.

[0144] Comparing example 1 and example 11, it can be seen that the depressurization rate is too fast, the lithium salt is deposited unevenly, which affects the subsequent lithiation process, and the initial efficiency is relatively reduced.

[0145] Comparing example 1 and example 12, it can be seen that no CO2 is introduced, i.e. there is no dispersion effect of supercritical carbon dioxide, the uniformity of lithium salt distribution is reduced, the pre-lithiation of the conductive agent is affected, and the final cell initial efficiency is reduced.

[0146] ​As can be seen from Comparative Example 1 and Example 13, Example 16, it is difficult to achieve uniformity of the lithiumation modification of the conductive agent, thereby affecting the initial efficiency of the battery cell. For example, in Example 13, there is no lithium acetate component, i.e., no melting filling stage and direct reduction distribution prelithiation process of molten lithium ions, which affects the prelithiation uniformity and degree of prelithiation of the conductive agent, resulting in a decrease in the initial efficiency of the final battery cell.

[0147] As can be seen from Comparative Example 1 and Example 14, the prelithiated conductive agent can effectively improve the initial efficiency of the battery cell.

[0148] As can be seen from Comparative Example 1 and Example 15, without adding a catalyst, the decomposition reaction of lithium oxalate and lithium acetate is difficult to proceed, the conductive agent is not prelithiated, and the lithium salt and other impurities present affect the final initial efficiency of the battery cell.

[0149] In the description of the present application, it should be noted that the terms "upper", "lower", and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. Unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or a connection between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0150] It should be noted that in the present application, relational terms such as "first" and "second" and the like are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element.

[0151] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above.

Claims

1. A supercritical carbon dioxide-based lithium supplementing method characterized by, It comprises: adding a conductive agent and a catalyst into a lithium salt mixed solution, and introducing carbon dioxide to obtain a first mixture; The lithium salt mixed solution comprises a first lithium salt and a second lithium salt, the decomposition temperature of the first lithium salt is lower than that of the second lithium salt, and the lithium ion concentration in the lithium salt mixed solution is 0.4-0.8 mol / L; The first mixture is subjected to temperature and pressure increasing treatment to make the carbon dioxide reach a supercritical state, and then stirred and reduced to atmospheric pressure to obtain a second mixture, and the pressure reduction rate when reduced to atmospheric pressure is not greater than 1 MPa / min; The second mixture is subjected to first temperature increasing treatment in a reducing atmosphere to make the first lithium salt decompose into a lithium-containing intermediate and a byproduct gas; Second temperature increasing treatment is performed to make the second lithium salt melt and reduce to metallic lithium and a byproduct gas; Third temperature increasing treatment is performed to make the lithium-containing intermediate decompose and reduce to metallic lithium and a byproduct gas to obtain a lithiated conductive agent.

2. The supercritical carbon dioxide-based lithium supplementation method of claim 1, wherein: The first lithium salt is lithium oxalate, the second lithium salt is lithium acetate, and the lithium-containing intermediate is lithium carbonate.

3. The supercritical carbon dioxide-based lithium supplementing method according to claim 2, characterized in that: The first temperature increasing treatment comprises: increasing the temperature to 250-280℃ at a temperature increasing rate of 1-5℃ / min, and maintaining the temperature for 1-2 h; The second temperature increasing treatment comprises: increasing the temperature to 340-360℃ at a temperature increasing rate of 1-5℃ / min, and maintaining the temperature for 0.5-1 h; The third temperature increasing treatment comprises: increasing the temperature to 400-450℃ at a temperature increasing rate of 1-5℃ / min, and maintaining the temperature for 0.5-1 h.

4. The supercritical carbon dioxide-based lithium supplementing method according to claim 3, characterized in that: Before increasing the temperature to 250-280℃, the first temperature increasing treatment further comprises: first washing away the residual moisture in the second mixture, then drying treatment at 80-100℃, then increasing the temperature to 140-200℃ at a temperature increasing rate of 1-5℃ / min, maintaining the temperature for 0.5-1 h, and finally vacuumizing to remove the crystal water in lithium acetate.

5. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, characterized in that: After the first temperature increasing treatment, the second temperature increasing treatment and / or the third temperature increasing treatment are completed, the lithium supplementing method further comprises: vacuumizing and back-filling a protective gas to remove the byproduct gas.

6. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, characterized in that: After the third temperature increasing treatment, the lithium supplementing method further comprises: first decreasing the temperature to a preset temperature at a first temperature decreasing rate, and then decreasing the temperature to room temperature along with the furnace; And / or, the third temperature increasing treatment comprises: vacuumizing to reduce the partial pressure of the byproduct gas.

7. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, characterized in that: The catalyst comprises one or more of cobalt oxide Co3O4, diiron trioxide Fe2O3 and molybdenum oxide / cobalt MoO2 / Co composite catalyst.

8. The supercritical carbon dioxide-based lithium supplementing method according to claim 7, characterized by: The catalyst is added in an amount of 0.5-1.5 wt% of the total mass of the lithium salt.

9. The supercritical carbon dioxide-based lithium supplementation method of claim 1, wherein: The reducing atmosphere comprises a reducing gas and an inert carrier gas, the reducing gas comprises hydrogen, and the proportion of the reducing gas in the reducing atmosphere is 3-8%.

10. The supercritical carbon dioxide-based lithium supplementation method of claim 1, wherein: The conductive agent comprises one or more of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCF), conductive carbon black, and acetylene black.

11. The supercritical carbon dioxide-based lithium supplementation method of claim 1, wherein: The mass ratio of the conductive agent to the total mass of the lithium salt is (0.58-1.21):

1.

12. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, wherein: The mass ratio of the first lithium salt to the second lithium salt is 1:(1-3).

13. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, wherein: In the lithium salt mixed solution, the solvent is a water solution of methanol, ethanol, propanol, or acetone, and the volume ratio of methanol, ethanol, propanol, or acetone to water is 1:(1-1.3).

14. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, wherein: The conductive agent and the catalyst are added to the lithium salt mixed solution, and carbon dioxide is introduced to obtain a first mixture, comprising: adding the conductive agent to a reaction kettle, and then adding the catalyst and the lithium salt mixed solution to the reaction kettle to obtain a reaction system, the volume of the reaction system is 5-10% of the volume of the reaction kettle, the reaction kettle is pre-cooled to 5-10℃, and carbon dioxide is introduced to a pressure of 5-7 MPa to make the carbon dioxide in a liquid state.

15. The supercritical carbon dioxide-based lithium supplementing method according to claim 1, wherein: The temperature and pressure increasing treatment comprises: increasing the temperature to 30-50℃ and increasing the pressure to 10-15 MPa.

16. A modified conductive agent, characterized by: The modified conductive agent is prepared by the supercritical carbon dioxide-based lithium supplementing method according to any one of claims 1-15.

17. A pole piece characterized by, The modified conductive agent comprises the modified conductive agent according to claim 16.

18. The pole piece of claim 17, wherein The modified conductive agent further comprises a binder, a solid-state electrolyte, and an active material, and the mass ratio of the modified conductive agent, the binder, the solid-state electrolyte, and the active material is 1-5:3-5:0-40:50-96.

19. The pole piece according to claim 18, wherein: The binder comprises one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyisobutylene (PIB), and styrene-ethylene-butylene-styrene block copolymer (SEBS); And / or, the solid-state electrolyte comprises one or more of sulfide electrolyte, oxide electrolyte, halide electrolyte, and polymer electrolyte; And / or, the active material is a positive electrode active material or a negative electrode active material, the positive electrode active material comprises one or more of ternary positive electrode, lithium cobaltate, lithium iron phosphate, lithium manganate, lithium manganese iron phosphate, and lithium-rich manganese-based material, and the negative electrode active material comprises one or more of graphite-based negative electrode and silicon-based negative electrode.

20. The pole piece of claim 17, wherein The pole piece is a positive electrode pole piece or a negative electrode pole piece.

21. A battery, characterized by The pole piece comprises the pole piece according to any one of claims 17-20.

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