A composite lithium supplement agent, its preparation method and application

Abstract

This application belongs to the field of lithium-ion battery technology, specifically relating to a composite lithium replenishing agent, its preparation method, and its application. The composite lithium replenishing agent includes a lithium replenishing agent; a vanadium source layer coated on the surface of the lithium replenishing agent; and a graphene and cellulose composite layer coated on the surface of the vanadium source layer. The beneficial effects of this application include: the composite lithium replenishing agent has reduced residual alkali content, low gas production, and high conductivity, which can improve the charge-discharge performance and cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a composite lithium replenishing agent, its preparation method, and its application. Background Technology

[0002] In current commercial lithium-ion battery manufacturing processes, after cell assembly, casing, baking, and electrolyte filling, an irreversible reaction occurs between lithium ions and the electrolyte at the solid-liquid interface during the first charge-discharge cycle. This reaction forms a solid electrolyte interphase (SEI) film, resulting in irreversible lithium ion consumption. During subsequent cell cycles, various aging processes cause further irreversible lithium ion consumption, leading to performance degradation and reduced lifespan. Existing technologies compensate for this irreversible lithium ion consumption by adding a lithium replenishing agent to the positive electrode. This agent releases lithium ions during the first charge-discharge cycle or continues to release them in subsequent cycles, thereby improving the cell's cycle life.

[0003] However, existing lithium replenishing agents have high residual alkali content, are sensitive to air, and have problems such as difficult processing and storage in battery cell applications. In addition, some lithium replenishing agents lose their activity after one discharge, leaving residues in the battery cell electrodes and affecting performance. Summary of the Invention

[0004] This application provides a composite lithium replenishing agent, its preparation method, and its application, aiming to solve the problems of lithium replenishing agents being sensitive to air, difficult to process, and difficult to store, thereby improving their performance and increasing the cycle life of lithium-ion batteries.

[0005] The first aspect of this application provides a composite lithium replenishing agent, comprising a lithium replenishing agent; a vanadium source layer coated on the surface of the lithium replenishing agent; and a graphene and cellulose composite layer coated on the surface of the vanadium source layer.

[0006] The composite lithium replenishing agent described in this application, after being double-coated, largely isolates the reaction between external air moisture and CO2 and the lithium replenishing agent core, thereby improving the lithium replenishing agent's tolerance to the storage environment and enhancing the feasibility of its effective application in battery cell manufacturing.

[0007] Furthermore, the reduced residual alkali content on the surface of the double-coated lithium supplement reduces its reactivity with the electrolyte and decreases gas production. The metal compounds and vanadium oxides or vanadates in the lithium supplement possess a favorable spatial structure, forming channels for rapid ion or electron diffusion. After being mixed and coated in an ethanol solution, the cellulose composite powder not only fills the gaps between the metal compounds, forming a dense protective layer, but also generates conductive polymers after low-temperature sintering. This enhances the overall conductivity of the lithium supplement, reduces polarization, improves battery charge-discharge performance, and simultaneously reduces particle agglomeration during homogenization, improving material dispersibility.

[0008] According to some embodiments of the composite lithium replenishing agent described in this application, the lithium replenishing agent includes a lithium source and a metal compound.

[0009] According to some embodiments of the composite lithium supplement agent described in this application, the lithium source includes one or more of LiOH, Li2CO3, Li2O, Li2O2, LiNO3, and Li2SO4.

[0010] According to some embodiments of the composite lithium supplement agent described in this application, the metal compound includes one or more of Fe2O3, Fe3O4, FeCl3, Fe(OH)3, NiO, NiSO4, and Ni(OH)2.

[0011] According to some embodiments of the composite lithium supplement agent described in this application, the molar ratio of the lithium source to the metal compound is (2-7):1.

[0012] According to some embodiments of the composite lithium replenishing agent described in this application, the particle size D50 of the lithium replenishing agent is 8-13 μm.

[0013] According to some embodiments of the composite lithium supplement agent described in this application, the vanadium source layer includes vanadium oxalate, ammonium metavanadate, vanadium pentoxide, and V6O. 13 One or more of VO2(B) and V2O3.

[0014] According to some embodiments of the composite lithium replenishing agent described in this application, the mass ratio of the lithium replenishing agent to the vanadium source layer is 100:(1-8), preferably 100:(3-5).

[0015] According to some embodiments of the composite lithium supplement described in this application, the cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl cellulose, and ethylcellulose.

[0016] According to some embodiments of the composite lithium supplement described in this application, the cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, and ethyl cellulose.

[0017] According to some embodiments of the composite lithium supplement agent described in this application, the mass ratio of graphene to cellulose is 1:(0.6-1.6), preferably 1:(0.8-1.3).

[0018] According to some embodiments of the composite lithium replenishing agent described in this application, the total mass ratio of the lithium replenishing agent and the vanadium source layer to the mass ratio of the composite layer is 100:(1-8).

[0019] According to some embodiments of the composite lithium replenishing agent described in this application, the particle size D50 of the composite lithium replenishing agent is 8-13 μm.

[0020] A second aspect of this application provides a method for preparing the composite lithium supplement agent described in the first aspect of this application, comprising the following steps:

[0021] (1) The lithium replenishing agent and vanadium source are mixed and sintered for the first time to obtain a lithium replenishing agent intermediate coated with a vanadium source layer;

[0022] (2) The lithium supplement intermediate, graphene, cellulose and organic solvent are mixed to obtain a mixture;

[0023] (3) The mixture is filtered, the resulting solid is dried and then sintered a second time to obtain the composite lithium supplement.

[0024] The preparation method described in this application first coats the vanadium source to form a non-inert coating layer, which can provide ion channels for the lithium supplement and improve ion conductivity. Then, the pre-mixed graphene and cellulose materials are coated a second time, which can fill the defects formed by the first coating, provide secondary protection, and form a dense electronic conductive network to improve the conductivity of the powder.

[0025] According to some embodiments of the composite lithium replenishing agent preparation method described in this application, in step (1), the preparation method of the lithium replenishing agent includes the following steps: mixing a lithium source and a metal compound and ball milling them, sintering the ball milling product in a vacuum environment to obtain the lithium replenishing agent.

[0026] According to some embodiments of the composite lithium supplement preparation method described in this application, the ball milling speed is 600-1200 r / min, and the ball milling time is 2-5 h.

[0027] According to some embodiments of the composite lithium supplement preparation method described in this application, the temperature of the sintering ball milling product is 700-1000℃, and the time for sintering the ball milling product is 2-6h.

[0028] According to some embodiments of the composite lithium supplement preparation method described in this application, the heating rate of the sintered ball mill product is 5-15℃ / min.

[0029] According to some embodiments of the composite lithium supplement preparation method described in this application, the first sintering is carried out in an inert atmosphere, preferably, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0030] According to some embodiments of the composite lithium supplement preparation method described in this application, the temperature of the first sintering is 200-500℃, and the time of the first sintering is 2-6h.

[0031] According to some embodiments of the composite lithium supplement preparation method described in this application, the heating rate of the first sintering is 5-15℃ / min.

[0032] According to some embodiments of the composite lithium replenishing agent preparation method described in this application, the particle size D50 of the lithium replenishing agent intermediate is 8-13 μm.

[0033] According to some embodiments of the composite lithium supplement preparation method described in this application, in step (2), the graphene, the cellulose and the organic solvent are first mixed, and the first mixed product is filtered and dried to obtain cellulose composite powder; then the cellulose composite powder, the lithium supplement intermediate and the organic solvent are mixed a second time.

[0034] According to some embodiments of the composite lithium supplement preparation method described in this application, the first mixing speed is 1000-1600 r / min, and the first mixing time is 2-5 h.

[0035] According to some embodiments of the composite lithium supplement preparation method described in this application, in the first mixing step, the solid-liquid ratio of the graphene and the cellulose to the organic solvent is (0.1-0.2) mg: 1 ml.

[0036] According to some embodiments of the composite lithium supplement preparation method described in this application, the organic solvent includes ethanol and / or N-methylpyrrolidone.

[0037] According to some embodiments of the composite lithium supplement preparation method described in this application, the particle size D50 of the cellulose composite powder is ≤30 μm.

[0038] According to some embodiments of the composite lithium supplement preparation method described in this application, in the second mixing step, the solid-liquid ratio of the lithium supplement intermediate and the cellulose composite powder to the organic solvent is (1-10) mg: 1 ml.

[0039] According to some embodiments of the composite lithium supplement preparation method described in this application, the second mixing speed is 1000-1600 r / min, and the second mixing time is 0.5-2 h.

[0040] According to some embodiments of the composite lithium supplement preparation method described in this application, in step (3), the second sintering is carried out under an inert atmosphere, preferably, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0041] According to some embodiments of the composite lithium supplement preparation method described in this application, in step (3), the temperature of the second sintering is 200-400℃, and the time of the second sintering is 1-3h.

[0042] According to some embodiments of the composite lithium supplement preparation method described in this application, in step (3), the heating rate of the second sintering is 2-10℃ / min.

[0043] A third aspect of this application provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the composite lithium replenishing agent described in the first aspect of this application or the composite lithium replenishing agent obtained by the preparation method described in the second aspect of this application.

[0044] According to some embodiments of the lithium-ion battery described in this application, the mass percentage of the composite lithium replenishing agent in the positive electrode material of the lithium-ion battery is 0.1%-10%. Detailed Implementation

[0045] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0047] This application provides a composite lithium replenishing agent, including a lithium replenishing agent;

[0048] A vanadium source layer coated on the surface of the lithium replenishing agent;

[0049] A graphene and cellulose composite layer coated on the surface of the vanadium source layer.

[0050] The composite lithium replenishing agent described in this application, after being double-coated, largely isolates the reaction between external air moisture and CO2 and the lithium replenishing agent core, thereby improving the lithium replenishing agent's tolerance to the storage environment and enhancing the feasibility of its effective application in battery cell manufacturing.

[0051] Furthermore, the reduced residual alkali content on the surface of the double-coated lithium supplement reduces its reactivity with the electrolyte and decreases gas production. The metal compounds and vanadium oxides or vanadates in the lithium supplement possess a favorable spatial structure, forming channels for rapid ion or electron diffusion. After being mixed and coated in an ethanol solution, the cellulose composite powder not only fills the gaps between the metal compounds, forming a dense protective layer, but also generates conductive polymers after low-temperature sintering. This enhances the overall conductivity of the lithium supplement, reduces polarization, improves battery charge-discharge performance, and simultaneously reduces particle agglomeration during homogenization, improving material dispersibility.

[0052] In some embodiments of this application, the lithium replenishing agent includes a lithium source and a metal compound.

[0053] In some embodiments of this application, the lithium source includes one or more of LiOH, Li2CO3, Li2O, Li2O2, LiNO3, and Li2SO4.

[0054] In some embodiments of this application, the metal compound includes one or more of Fe2O3, Fe3O4, FeCl3, Fe(OH)3, NiO, NiSO4, and Ni(OH)2.

[0055] In some embodiments of this application, the molar ratio of the lithium source to the metal compound is (2-7):1, for example 2:1, 3:1, 4:1, 5:1, 7:1, etc.

[0056] In some embodiments of this application, the particle size D50 of the lithium replenishing agent is 8-13 μm, such as 8 μm, 9 μm, 9.5 μm, 10.2 μm, 10.8 μm, 11.3 μm, 11.8 μm, 12.6 μm, 13 μm, etc.

[0057] In some embodiments of this application, the vanadium source layer includes vanadium oxalate, ammonium metavanadate, vanadium pentoxide, and V6O. 13 One or more of VO2(B) and V2O3.

[0058] Vanadium salts or vanadium oxides can coat the surface of lithium supplements, inhibiting further reaction between the supplements and moisture in the air, and their interlayer structure can greatly promote the reaction of lithium. + The free diffusion of the molecules enhances their ionic conductivity.

[0059] In some embodiments of this application, the mass ratio of the lithium replenishing agent to the vanadium source layer is 100:(1-8), for example 100:1, 100:2.5, 100:3, 100:3.6, 100:4.3, 100:4.8, 100:5.2, 100:6.3, 100:7.1, 100:8, etc.

[0060] In some embodiments of this application, the mass ratio of the lithium replenishing agent to the vanadium source layer is 100:(3-5).

[0061] In some embodiments of this application, the cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl cellulose, and ethylcellulose.

[0062] In some embodiments of this application, the cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, and ethyl cellulose.

[0063] The celluloses described in this application are all cellulose ether derivatives, which are stable, widely available, easy to use, and readily soluble in organic solvents. Hydroxypropyl cellulose, hydroxypropyl methylcellulose, and ethyl cellulose are further preferred.

[0064] In some embodiments of this application, the mass ratio of graphene to cellulose is 1:(0.6-1.6), for example 1:0.6, 1:0.8, 1:1.2, 1:1.4, 1:1.6, etc.

[0065] In some embodiments of this application, the mass ratio of graphene to cellulose is 1:(0.8-1.3).

[0066] In some embodiments of this application, the total mass ratio of the lithium replenishing agent and the vanadium source layer to the mass ratio of the composite layer is 100:(1-8), for example 100:1, 100:2, 100:2.6, 100:3.2, 100:4.6, 100:5.3, 100:6, etc.

[0067] In some embodiments of this application, the particle size D50 of the composite lithium supplement is 8-13 μm, such as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc.

[0068] This application also provides a method for preparing the composite lithium supplement agent described in the first aspect of this application, comprising the following steps:

[0069] (1) The lithium replenishing agent and vanadium source are mixed and sintered for the first time to obtain a lithium replenishing agent intermediate coated with a vanadium source layer;

[0070] (2) The lithium supplement intermediate, graphene, cellulose and organic solvent are mixed to obtain a mixture;

[0071] (3) The mixture is filtered, the resulting solid is dried and then sintered a second time to obtain the composite lithium supplement.

[0072] The preparation method described in this application first coats the vanadium source to form a non-inert coating layer, which can provide ion channels for the lithium supplement and improve ion conductivity. Then, the pre-mixed graphene and cellulose materials are coated a second time, which can fill the defects formed by the first coating, provide secondary protection, and form a dense electronic conductive network to improve the conductivity of the powder.

[0073] In some embodiments of this application, step (1) of the preparation method of the lithium replenishing agent includes the following steps: mixing a lithium source and a metal compound and ball milling them, sintering the ball milling product in a vacuum environment to obtain the lithium replenishing agent.

[0074] In some embodiments of this application, the rotational speed of the ball mill is 600-1200 r / min, such as 600 r / min, 680 r / min, 720 r / min, 780 r / min, 830 r / min, 890 r / min, 930 r / min, 1100 r / min, 1200 r / min, etc., and the ball milling time is 2-5 hours, such as 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0075] In some embodiments of this application, the temperature of the sintered ball milling product is 700-1000℃, such as 700℃, 780℃, 830℃, 880℃, 960℃, 1000℃, etc., and the time for sintering the ball milling product is 2-6h, such as 2h, 3h, 4h, 6h, etc.

[0076] In some embodiments of this application, the heating rate of the sintered ball mill product is 5-15℃ / min, such as 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, etc.

[0077] In some embodiments of this application, the first sintering is performed in an inert atmosphere.

[0078] In some embodiments of this application, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0079] In some embodiments of this application, the temperature of the first sintering is 200-500℃, such as 200℃, 260℃, 300℃, 320℃, 370℃, 400℃, 430℃, 480℃, 500℃, etc., and the time of the first sintering is 2-6h, such as 2h, 4h, 6h, etc.

[0080] In some embodiments of this application, the heating rate of the first sintering is 5-15℃ / min, such as 5℃ / min, 8℃ / min, 12℃ / min, 13℃ / min, 15℃ / min, etc.

[0081] In some embodiments of this application, the particle size D50 of the lithium replenishing agent intermediate is 8-13 μm, such as 8 μm, 9 μm, 12 μm, 13 μm, etc.

[0082] In some embodiments of this application, in step (2), the graphene, the cellulose and the organic solvent are first mixed, and the first mixed product is filtered and dried to obtain cellulose composite powder; then the cellulose composite powder, the lithium supplement intermediate and the organic solvent are mixed a second time.

[0083] Premixing graphene and cellulose separately allows them to bond tightly. The interaction between the nonpolar surface of graphene and the hydrophobic molecular chains of cellulose promotes graphene exfoliation and cellulose nanostructuring, fostering a highly dense structure between the two materials. This results in an ultra-high specific surface area, forming a continuous conductive network that provides pathways for rapid ion diffusion and charge transport.

[0084] In some embodiments of this application, the first mixing speed is 1000-1600 r / min, such as 1000 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1600 r / min, etc., and the first mixing time is 2-5 h, such as 2 h, 3 h, 5 h, etc.

[0085] In some embodiments of this application, the solid-liquid ratio of the graphene and the cellulose to the organic solvent is (0.1-0.2) mg: 1 ml.

[0086] In some embodiments of this application, the particle size D50 of the cellulose composite powder is ≤30um, such as 30um, 26um, 23um, 20um, 18um, 15um, etc.

[0087] In some embodiments of this application, the organic solvent includes ethanol and / or N-methylpyrrolidone.

[0088] In some embodiments of this application, in the second mixing step, the solid-liquid ratio of the lithium supplement intermediate and the cellulose composite powder to the organic solvent is (1-10) mg: 1 ml.

[0089] In some embodiments of this application, the second mixing speed is 1000-1600 r / min, such as 1000 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1600 r / min, etc., preferably 1100-1400 r / min, and the second mixing time is 0.5-2 h, such as 0.5 h, 0.8 h, 1.2 h, 1.5 h, 2 h, etc.

[0090] High-speed shearing further enabled the exfoliation of graphene, the nano-sizing of cellulose, and the in-situ composite hybridization of the two, and made them uniformly dispersed on the surface of the lithium supplement.

[0091] In some embodiments of this application, in step (3), the second sintering is carried out under an inert atmosphere, preferably including a nitrogen atmosphere and / or an argon atmosphere.

[0092] In some embodiments of this application, in step (3), the temperature of the second sintering is 200-400℃, such as 200℃, 260℃, 280℃, 320℃, 360℃, 400℃, etc., and the time of the second sintering is 1-3h, such as 1h, 2h, 3h, etc.

[0093] In some embodiments of this application, in step (3), the heating rate of the second sintering is 2-10℃ / min, for example 2℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, etc.

[0094] This application also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the composite lithium replenishing agent described in the first aspect of this application or the composite lithium replenishing agent obtained by the preparation method described in the second aspect of this application.

[0095] In the process of preparing lithium-ion batteries using composite lithium supplementation agents, the slurry dispersion effect is good during homogenization, and the viscosity and solid content meet the coating requirements. This can improve the process window, resulting in low electrode resistance, low internal resistance, small polarization, and long cycle life of the prepared lithium-ion batteries.

[0096] In some embodiments of this application, the mass percentage of the composite lithium replenishing agent in the positive electrode material of the lithium-ion battery is 0.1%-10%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.7%, 3.6%, 4.3%, 5.7%, 6.8%, 7.4%, 8.2%, 9.1%, 10%, etc.

[0097] The technical solution of this application will be further described below with reference to specific embodiments.

[0098] Example 1

[0099] A method for preparing a composite lithium supplement includes the following steps:

[0100] (1) LiOH and NiO were mixed evenly in a molar ratio of 4:1 and ball-milled at a speed of 800 r / min for 3 h. The ball-milled product was then sintered at high temperature in a vacuum environment at a heating rate of 8 °C / min. When the sintering temperature reached 900 °C, it was held for 4 h to obtain lithium supplement powder with a particle size D50 of 12.1 μm.

[0101] (2) The lithium supplement powder and V6O 13 The powders were mixed uniformly at a mass ratio of 100:3 and sintered at a low temperature under a nitrogen inert atmosphere. The sintering temperature was increased at a rate of 8°C, and the sintering temperature was maintained at 400°C for 4 hours to obtain coated V6O particles with a particle size D50 of 12.1 μm. 13 Lithium supplementation intermediate.

[0102] (3) Graphene and ethyl cellulose were mixed at a mass ratio of 1:0.9. Then, the mixture of graphene and ethyl cellulose and ethanol solution were mixed evenly in a shear mixer at a solid-liquid ratio of 0.14 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 3 h. After the shearing was completed, the mixture was centrifuged, filtered and dried to obtain cellulose composite powder with a particle size D50 of 22 μm.

[0103] (4) The lithium supplement intermediate and cellulose composite powder were mixed at a mass ratio of 100:3. Then, the mixture of lithium supplement intermediate and cellulose composite powder was sheared and mixed with ethanol solution at a solid-liquid ratio of 6 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 1 h. After centrifugation, filtration and drying, it was sintered at low temperature in a nitrogen inert atmosphere. The sintering temperature rise rate was 5℃ / min. When the sintering temperature reached 300℃, it was held for 2 h to obtain a composite lithium supplement with a particle size D50 of 12.3 μm.

[0104] Example 2

[0105] The only difference between the composite lithium replenishing agent described in Example 2 and that in Example 1 is that the mass ratio of the lithium replenishing agent to the vanadium source layer is different during the preparation process of the composite lithium replenishing agent described in Example 2 compared to Example 1.

[0106] The specific operating steps include:

[0107] A method for preparing a composite lithium supplement includes the following steps:

[0108] (1) LiOH and NiO were mixed evenly in a molar ratio of 4:1 and ball-milled at a speed of 800 r / min for 3 h. The ball-milled product was then sintered at high temperature in a vacuum environment at a heating rate of 8 °C / min. When the sintering temperature reached 900 °C, it was held for 4 h to obtain lithium supplement powder with a particle size D50 of 12.1 μm.

[0109] (2) The lithium supplement powder and V6O 13 The powders were mixed uniformly at a mass ratio of 100:5 and sintered at a low temperature under a nitrogen inert atmosphere. The sintering temperature rise rate was 8°C, and the sintering temperature was maintained at 400°C for 4 hours to obtain coated V6O with a particle size D50 of 12.1 μm. 13 Lithium supplementation intermediate.

[0110] (3) Graphene and ethyl cellulose were mixed at a mass ratio of 1:0.9. Then, the mixture of graphene and ethyl cellulose and ethanol solution were mixed evenly in a shear mixer at a solid-liquid ratio of 0.14 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 3 h. After the shearing was completed, the mixture was centrifuged, filtered and dried to obtain cellulose composite powder with a particle size D50 of 22 μm.

[0111] (4) The lithium supplement intermediate and cellulose composite powder were mixed at a mass ratio of 100:3. Then, the mixture of lithium supplement intermediate and cellulose composite powder was sheared and mixed with ethanol solution at a solid-liquid ratio of 6 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 1 h. After centrifugation, filtration and drying, it was sintered at low temperature in a nitrogen inert atmosphere. The sintering temperature rise rate was 5℃ / min. When the sintering temperature reached 300℃, it was held for 2 h to obtain a composite lithium supplement with a particle size D50 of 12.3 μm.

[0112] Example 3

[0113] The only difference between the composite lithium replenishing agent described in Example 3 and that in Example 1 is that, during the preparation of the composite lithium replenishing agent in Example 3, the mass ratio of the lithium replenishing agent to the vanadium source layer is 100:7.

[0114] Example 4

[0115] The only difference between the composite lithium supplement in Example 4 and Example 1 is that methyl cellulose is used instead of ethyl cellulose in the preparation process of the composite lithium supplement in Example 4.

[0116] Example 5

[0117] The only difference between the composite lithium supplement in Example 5 and Example 1 is that carboxymethyl cellulose is used instead of ethyl cellulose in the preparation process of the composite lithium supplement in Example 5.

[0118] Example 6

[0119] The only difference between the composite lithium supplement in Example 6 and Example 1 is that hydroxyethyl cellulose is used instead of ethyl cellulose in the preparation process of the composite lithium supplement in Example 6.

[0120] Example 7

[0121] The only difference between the composite lithium supplement in Example 7 and Example 1 is that hydroxypropyl cellulose is used instead of ethyl cellulose in the preparation process of the composite lithium supplement in Example 7.

[0122] Example 8

[0123] The only difference between the composite lithium supplement in Example 8 and Example 1 is that hydroxypropyl methylcellulose is used instead of ethyl cellulose in the preparation process of the composite lithium supplement in Example 8.

[0124] Example 9

[0125] The only difference between the composite lithium supplement in Example 9 and Example 1 is that the mass ratio of graphene to cellulose in the preparation process of the composite lithium supplement in Example 9 is 1:0.6.

[0126] Example 10

[0127] The only difference between the composite lithium supplement in Example 10 and Example 1 is that the mass ratio of graphene to cellulose in the preparation process of the composite lithium supplement in Example 10 is 1:1.2.

[0128] Example 11

[0129] The only difference between the composite lithium supplement in Example 11 and Example 1 is that the mass ratio of graphene to cellulose in the preparation process of the composite lithium supplement in Example 11 is 1:1.5.

[0130] Example 12

[0131] The only difference between the composite lithium supplement agent described in Example 12 and that in Example 1 is that the rotational speed of the mixing and shearing of the lithium supplement agent intermediate and the cellulose composite powder during the preparation of the composite lithium supplement agent in Example 12 is 800 r / min.

[0132] Example 13

[0133] The only difference between the composite lithium supplement agent described in Example 13 and that in Example 1 is that the rotational speed during the mixing and shearing of the lithium supplement agent intermediate and the cellulose composite powder in the preparation process of the composite lithium supplement agent in Example 13 is 1100 r / min.

[0134] Example 14

[0135] The only difference between the composite lithium supplement agent described in Example 14 and that in Example 1 is that the rotational speed during the mixing and shearing of the lithium supplement agent intermediate and the cellulose composite powder in the preparation process of the composite lithium supplement agent in Example 14 is 1700 r / min.

[0136] Comparative Example 1

[0137] The only difference between the composite lithium supplement in Comparative Example 1 and Example 1 is that TiO2 is used instead of vanadium source in the preparation process of the composite lithium supplement in Comparative Example 1.

[0138] Comparative Example 2

[0139] The only difference between the composite lithium supplement in Comparative Example 2 and Example 1 is that Cr2O3 is used instead of vanadium source in the preparation process of the composite lithium supplement in Comparative Example 2.

[0140] Comparative Example 3

[0141] The only difference between the composite lithium replenishing agent described in Comparative Example 3 and Example 1 is that only the vanadium source layer is coated during the preparation process of the composite lithium replenishing agent described in Comparative Example 3.

[0142] The specific operating steps include:

[0143] A method for preparing a composite lithium supplement includes the following steps:

[0144] (1) LiOH and NiO were mixed evenly in a molar ratio of 4:1 and ball-milled at a speed of 800 r / min for 3 h. The ball-milled product was then sintered at high temperature in a vacuum environment at a heating rate of 8 °C / min. When the sintering temperature reached 900 °C, it was held for 4 h to obtain lithium supplement powder with a particle size D50 of 12.1 μm.

[0145] (2) The lithium supplement powder and V6O 13 The powders were mixed uniformly at a mass ratio of 100:3 and sintered at a low temperature under a nitrogen inert atmosphere. The sintering temperature was increased at a rate of 8°C, and the sintering temperature was maintained at 400°C for 4 hours to obtain coated V6O particles with a particle size D50 of 12.1 μm. 13 A composite lithium supplement.

[0146] Comparative Example 4

[0147] The only difference between the composite lithium supplement described in Comparative Example 4 and Example 1 is that the composite lithium supplement described in Comparative Example 4 is prepared by coating the lithium supplement with a mixture of graphene and cellulose.

[0148] The specific operating steps include:

[0149] A method for preparing a composite lithium supplement includes the following steps:

[0150] (1) LiOH and NiO were mixed evenly in a molar ratio of 4:1 and ball-milled at a speed of 800 r / min for 3 h. The ball-milled product was then sintered at high temperature in a vacuum environment at a heating rate of 8 °C / min. When the sintering temperature reached 900 °C, it was held for 4 h to obtain lithium supplement powder with a particle size D50 of 12.1 μm.

[0151] (2) Graphene and ethyl cellulose were mixed at a mass ratio of 1:0.9. Then, the mixture of graphene and ethyl cellulose and ethanol solution were mixed evenly in a shear mixer at a solid-liquid ratio of 0.14 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 3 h. After the shearing was completed, the mixture was centrifuged, filtered and dried to obtain cellulose composite powder with a particle size D50 of 22 μm.

[0152] (3) The lithium supplement powder and cellulose composite powder were mixed at a mass ratio of 100:3. Then, the mixture of lithium supplement powder and cellulose composite powder was sheared and mixed evenly with ethanol solution at a solid-liquid ratio of 6 mg / ml. The mixing shearing speed was 1400 r / min and the shearing time was 1 h. After centrifugation, filtration and drying, it was sintered at low temperature in a nitrogen inert atmosphere. The sintering heating rate was 5℃ / min. When the sintering temperature reached 300℃, it was held for 2 h to obtain the composite lithium supplement.

[0153] Comparative Example 5

[0154] The only difference between the composite lithium replenisher described in Comparative Example 5 and Example 1 is that the composite lithium replenisher described in Comparative Example 5 is first coated with a mixture of graphene and cellulose, and then coated with a vanadium source.

[0155] The specific operating steps include:

[0156] A method for preparing a composite lithium supplement includes the following steps:

[0157] (1) LiOH and NiO were mixed evenly in a molar ratio of 4:1 and ball-milled at a speed of 800 r / min for 3 h. The ball-milled product was then sintered at high temperature in a vacuum environment at a heating rate of 8 °C / min. When the sintering temperature reached 900 °C, it was held for 4 h to obtain lithium supplement powder with a particle size D50 of 12.1 μm.

[0158] (2) Graphene and ethyl cellulose were mixed at a mass ratio of 1:0.9. Then, the mixture of graphene and ethyl cellulose and ethanol solution were mixed evenly in a shear mixer at a solid-liquid ratio of 0.14 mg / ml. The mixing and shearing speed was 1400 r / min and the shearing time was 3 h. After the shearing was completed, the mixture was centrifuged, filtered and dried to obtain cellulose composite powder with a particle size D50 of 22 μm.

[0159] (3) The lithium supplement powder and cellulose composite powder were mixed at a mass ratio of 100:3. Then, the mixture of lithium supplement powder and cellulose composite powder was sheared and mixed evenly with ethanol solution at a solid-liquid ratio of 6 mg / ml. The mixing shearing speed was 1400 r / min and the shearing time was 1 h. After centrifugation, filtration and drying, it was sintered at low temperature in a nitrogen inert atmosphere. The sintering heating rate was 5℃ / min. When the sintering temperature reached 300℃, it was held for 2 h to obtain the lithium supplement intermediate.

[0160] (4) The lithium supplement intermediate and V6O 13 The powders were mixed evenly at a mass ratio of 100:3 and sintered at a low temperature in a nitrogen inert atmosphere. The sintering temperature was increased at a rate of 8°C, and the sintering temperature was maintained at 400°C for 4 hours to obtain the composite lithium supplement.

[0161] Performance study of the composite lithium supplementer described in Examples 1-14 and Comparative Examples 1-5 of this application

[0162] The composite lithium supplementer described in Examples 1-14 and Comparative Examples 1-5 of this application, accounting for 2.5% of the total mass of the positive electrode sheet, was added to the positive electrode active material. The mixture was uniformly mixed using conventional processes, and the positive electrode sheet was prepared by coating, rolling and die cutting. The positive electrode sheet was then assembled with the negative electrode sheet and separator through a stacking or winding process to obtain a soft-pack battery. Processing performance data and electrochemical performance data were obtained.

[0163] The positive electrode slurry formulation was prepared according to the mass ratio of lithium iron phosphate: lithium supplementer (composite lithium supplementer described in Examples 1-14 and Comparative Examples 1-5): conductive carbon black: polyvinylidene fluoride (PVDF) of 93.8:3.2:1:2. The negative electrode slurry formulation was prepared according to the mass ratio of graphite: conductive carbon black: carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) of 95.8:1.2:1.2:1.8. The electrolyte was a mixture of 1 mol / L LiPF6 and ethyl cellulose (EC): epoxy molding compound (EMC): dimethyl carbonate (DMC) (volume ratio of 4:3:3).

[0164] The battery's first-week charge / discharge current ratio was 0.05C / 0.1C, and the first-week voltage range was 2.5-4.2V. The cycle current ratio was 0.2C / 0.2C, and the voltage range was 2.5-3.65V. The battery's designed capacity was 3.6Ah. The surface free lithium content, positive electrode homogenization process data, first-week charge capacity, and capacity retention rate after 800 cycles were tested after the lithium replenishment agent was left to stand for 24 hours. The data are shown in Table 1 below.

[0165] Table 1

[0166]

[0167] As can be seen from Table 1, based on different mass ratios of lithium replenishing agent and vanadium source, the vanadium source ratios used in Examples 1 and 2 are superior, with low free lithium content on the surface of the lithium replenishing agent, qualified homogenization processing test data, and good lithium battery performance. The vanadium source ratio in Example 3 is relatively high, the coating layer is slightly thicker, which is not conducive to ion transport, the polarization internal resistance is relatively large, and the cycle performance is slightly better. The preferred mass ratio of lithium replenishing agent to vanadium source is 100:(3-5).

[0168] Based on the mixing of graphene with different celluloses, the cellulose types selected in Examples 4, 5, and 6 were unsuitable, resulting in poor mixing of the prepared cellulose composite powder, which was not conducive to uniform coating of the lithium supplement, leading to mediocre processing effects and poor battery performance. In contrast, the lithium supplement and lithium battery performance prepared using the cellulose types selected in Examples 1, 7, and 8 were better. Ethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose are preferred celluloses.

[0169] Based on the different mass ratios of graphene and cellulose, the graphene and cellulose mixtures used in Examples 1 and 9 are of better quality, resulting in better performance of the lithium supplement and lithium battery. The mass ratio of the mixture in Example 9 is too small, and the mass ratio of the mixture in Example 11 is too large, which is not conducive to improving the performance of the lithium supplement and the performance of the prepared lithium battery. Therefore, the preferred mass ratio of graphene and cellulose is 1:(0.8-1.3).

[0170] Based on different second mixing shear rates, the mixing rates used in Examples 1 and 13 are better, the cellulose complex is uniformly coated on the surface of the lithium replenishing agent, and the performance of the lithium replenishing agent and lithium battery is better. The mixing rate in Example 12 is too small and the mixing rate in Example 14 is too large, which is not conducive to improving the performance of the lithium replenishing agent. Therefore, the second mixing rate is preferably 1000-1600 r / min.

[0171] Compared with different metal compound coatings, Comparative Examples 1 and 2, which were coated with metal element compounds of the same period, showed poor improvement in lithium replenishment effect, which was not conducive to the performance of the prepared lithium battery.

[0172] Comparative Examples 3 (vanadium source coating), 4 (cellulose composite powder coating), and 5 (cellulose composite powder coating followed by vanadium source coating) all showed poor improvement in the processing performance and electrochemical performance of the lithium supplement, which was detrimental to the performance of the prepared lithium battery.

[0173] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A composite lithium supplement, characterized in that, The lithium supplement includes a lithium source and a metal compound; the lithium source includes one or more of LiOH, Li2CO3, Li2O, Li2O2, LiNO3 and Li2SO4, and the metal compound includes one or more of Fe2O3, Fe3O4, FeCl3, Fe(OH)3, NiO, NiSO4 and Ni(OH)2. A vanadium source layer is coated on the surface of the lithium replenishing agent; the vanadium source layer includes vanadium oxalate, ammonium metavanadate, vanadium pentoxide, and V6O. 13 One or more of VO2(B) and V2O3; A graphene and cellulose composite layer coated on the surface of the vanadium source layer; The mass ratio of the lithium supplement to the vanadium source is 100:(3-5), and the mass ratio of the graphene to the cellulose is 1:(0.8-1.3). The preparation method of the composite lithium supplement includes the following steps: (1) The lithium replenishing agent and vanadium source are mixed and sintered for the first time to obtain a lithium replenishing agent intermediate coated with a vanadium source layer; (2) The lithium supplement intermediate, graphene, cellulose and organic solvent are mixed to obtain a mixture; (3) The mixture is filtered, the resulting solid is dried and then sintered for a second time to obtain the composite lithium supplement.

2. The composite lithium supplement agent according to claim 1, characterized in that, The molar ratio of the lithium source to the metal compound is (2-7):1; The lithium replenishing agent has a particle size D50 of 8-13 μm.

3. The composite lithium supplement agent according to claim 1, characterized in that, The cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and ethylcellulose; And / or, the total mass ratio of the lithium supplement and the vanadium source to the mass ratio of the composite layer is 100:(1-8). And / or, the particle size D50 of the composite lithium supplement is 8-13 μm.

4. The composite lithium supplement agent according to claim 1, characterized in that, The cellulose includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, and ethyl cellulose.

5. The composite lithium supplement agent according to claim 1, characterized in that, In step (1), the preparation method of the lithium supplement includes the following steps: mixing a lithium source and a metal compound and ball milling them, sintering the ball milling product in a vacuum environment to obtain the lithium supplement.

6. The composite lithium supplement agent according to claim 5, characterized in that, The ball mill rotates at a speed of 600-1200 r / min, and the ball milling time is 2-5 h. And / or, the temperature of the sintered ball milling product is 700-1000℃, and the time for sintering the ball milling product is 2-6h; And / or, the heating rate of the sintered ball mill product is 5-15℃ / min.

7. The composite lithium supplement agent according to claim 1, characterized in that, The first sintering is carried out in an inert atmosphere, which includes a nitrogen atmosphere and / or an argon atmosphere; And / or, the temperature of the first sintering is 200-500℃, and the time of the first sintering is 2-6h; And / or, the heating rate of the first sintering is 5-15℃ / min; And / or, the particle size D50 of the lithium supplement intermediate is 8-13 μm.

8. The composite lithium supplement agent according to claim 1, characterized in that, In step (2), the graphene, the cellulose and the organic solvent are first mixed, and the first mixed product is filtered and dried to obtain cellulose composite powder; then the cellulose composite powder, the lithium supplement intermediate and the organic solvent are mixed a second time.

9. The composite lithium supplement agent according to claim 8, characterized in that, The first mixing speed is 1000-1600 r / min, and the first mixing time is 2-5 h; And / or, in the first mixing step, the solid-liquid ratio of the graphene and the cellulose to the organic solvent is (0.1-0.2) mg: 1 ml; And / or, the organic solvent includes ethanol and / or N-methylpyrrolidone; And / or, the particle size D50 of the cellulose composite powder is ≤30 μm.

10. The composite lithium supplement agent according to claim 8, characterized in that, In the second mixing step, the solid-liquid ratio of the lithium supplement intermediate and the cellulose composite powder to the organic solvent is (1-10) mg: 1 ml; And / or, the second mixing rate is 1000-1600 r / min, and the second mixing time is 0.5-2 h; And / or, in step (3), the second sintering is carried out under an inert atmosphere, which includes a nitrogen atmosphere and / or an argon atmosphere; And / or, in step (3), the temperature of the second sintering is 200-400℃, and the time of the second sintering is 1-3h; And / or, in step (3), the heating rate of the second sintering is 2-10℃ / min.

11. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery comprises the composite lithium replenishing agent as described in any one of claims 1-10; The mass percentage of the composite lithium replenishing agent in the positive electrode material of the lithium-ion battery is 0.1%-10%.

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