A lithium-ion battery lithium supplement based on gasification decomposition and its application

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses a lithium replenisher for lithium-ion batteries based on gasification decomposition and its application. The lithium replenisher is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate, and lithium nitride. The lithium replenisher in the present invention can achieve a lithium replenishment process through the combined action of an electric field and thermal energy. The lithium replenisher is dispersed and added to the positive electrode slurry to complete lithium replenishment during the early formation process. The decomposed "by-products" are removed from the battery system in the form of gas, thus avoiding the impact of newly generated substances on the battery system from the design source, retaining the advantage of the high stability of the compound lithium replenisher; and can achieve the same lithium replenishment efficiency as metallic lithium, ensuring that the lithium-ion battery has high electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery lithium supplement based on gasification decomposition and applications thereof. Background Art

[0002] Lithium-ion batteries are important media for the conversion and storage of electrical energy. They have the advantages of high energy density, long cycle life, and good rate performance. They are widely used in portable electronic products, large-scale energy storage, and various power sources. However, the solid electrolyte interface film (SEI) and other "side reactions" formed during the charging and discharging process will cause the initial capacity loss and subsequent capacity decay of the battery, which will directly lead to a decrease in the coulombic efficiency of the first cycle, a shortened battery life, and a loss of energy density. In order to compensate for the lithium loss caused by various factors (forming irreversible "dead lithium"), industry insiders have studied a variety of lithium replenishment methods, which can be divided into two categories according to the type of lithium source: metallic lithium source and compound lithium source.

[0003] The most direct and effective way to replenish lithium is to use a metal lithium source. Metal lithium sources include lithium sheets and lithium powder. This method of replenishing lithium can theoretically achieve 100% "efficiency" (the percentage of active lithium in the mass of the lithium replenisher), but it is very difficult to achieve in terms of technology, mainly because the activity of the metal element is too high. During the manufacturing process of the battery, it is easy to catch fire, explode, and become inactivated. Metal lithium will become inactivated by reacting with oxygen, nitrogen, and moisture in the air. Compound lithium sources replenish lithium by providing a large amount of irreversible Li + , to compensate for the loss of active lithium in the cycle. The Chinese invention patent with publication number CN109301242A discloses a method of using Li5FeO4 as a compound lithium source to release Li during charging. + , forming inactive (or very low activity) substances, thereby playing a role in lithium replenishment. However, compared with metallic lithium sources, this lithium replenishment method has a very low "efficiency" and will eventually form "excess" substances with no electrochemical activity in the battery system.

[0004] In addition, it should be noted that many lithium-containing compounds themselves have no lithium replenishing effect, such as lithium carbonate, lithium oxide, lithium sulfate, lithium phosphate, lithium hydroxide, lithium peroxide, etc. When these compounds are added to the battery system, they only form inactive "dead lithium". Summary of the Invention

[0005] In order to solve the technical problem of low lithium replenishment efficiency of compound lithium sources, the present invention provides a lithium replenisher for lithium-ion batteries based on gasification decomposition and its application. The lithium replenisher does not leave "excess matter" with no electrochemical activity, can achieve the same lithium replenishment efficiency as metallic lithium, has high stability, and is very easy to implement in the process.

[0006] The specific technical solutions of the present invention are:

[0007] In a first aspect, the present invention provides a lithium supplement for lithium-ion batteries based on gasification decomposition, wherein the lithium supplement is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate and lithium nitride.

[0008] The lithium replenisher in the present invention is a compound lithium replenisher with high stability. It decomposes under the action of electrical and thermal energy during the replenishment process. All elements except lithium are present as gases or low-boiling-point liquids after decomposition, which can be removed by heating and negative pressure. This not only leaves no electrochemically inactive "excess" but also improves the efficiency of lithium replenishment using the compound lithium source (active lithium accounts for 100% of the mass percentage of lithium in the lithium replenisher). This lithium replenisher can achieve the same lithium replenishment efficiency as metallic lithium, while avoiding the possibility of fire, explosion, and deactivation, and is very easy to implement.

[0009] For lithium formate, lithium acetate, lithium propionate, lithium butyrate, and lithium isobutyrate, decompose as follows:

[0010]

[0011] When two or more are mixed and added, in addition to the above decomposition methods, they will also decompose in the following ways:

[0012]

[0013] In the above formula, R, R1, and R2 are selected from H, CH3, C2H5, CH2CH2CH3, and CH(CH3)2.

[0014] For lithium nitride and lithium oxalate, the decomposition is as follows:

[0015]

[0016] Preferably, the lithium supplement agent is anionic or partially decomposed with negative charge during the lithium supplement process.

[0017] Preferably, the decomposition products contain gas or low-boiling-point liquid.

[0018] Preferably, the gas or low-boiling-point liquid is at least one of carbon dioxide, hydrogen, nitrogen, methane, ethane, propane, butane, pentane, hexane, 2,3-dimethylbutane, 2-methylpropane, 2-methylbutane, and 2-methylpentane.

[0019] Preferably, the lithium supplement agent is pretreated before the lithium supplement process, and the pretreatment comprises the following steps:

[0020] (1) The biochar is crushed and ball-milled, dispersed in water, ammonium molybdate is added and mixed, and then an ethanol solution containing cobalt hydroxide is added and ultrasonically dispersed, followed by centrifugation and removal of the supernatant, and drying to obtain a reactant; the mass volume ratio of the biochar, ammonium molybdate, water, and the ethanol solution containing cobalt hydroxide is 1 g: 0.3-0.5 g: 200 mL: 100-150 mL;

[0021] (2) calcining the reactants in a mixed gas atmosphere with a volume ratio of argon to hydrogen of 7 to 8:1 in stages, first calcining at 200 to 250° C. for 30 to 50 minutes and then calcining at 500 to 600° C. for 1 to 2 hours to obtain a mesoporous molybdenum dioxide composite material;

[0022] (3) Dispersing the mesoporous molybdenum dioxide composite material in water or ethanol, and then adding a lithium supplement agent, wherein the mass ratio of the mesoporous molybdenum dioxide composite material to the lithium supplement agent is 0.1:1-1.5; then sand milling in a sand mill for 2-3 hours, and then spray drying to obtain a pretreated lithium supplement agent.

[0023] The present invention loads the lithium supplement agent on the mesoporous molybdenum dioxide composite material to improve its conductivity, electrochemical activity and ion mobility. In addition, when the lithium supplement agent is mixed with the electrode material, it is difficult to be evenly dispersed in the electrode slurry and is prone to flocculation or agglomeration. Molybdenum dioxide has high conductivity and high chemical stability, especially its efficient charge transfer properties, which helps the lithium supplement agent decompose Li + The effective lithium replenishment effect after treatment improves the efficiency of lithium replenishment. The in-situ generation of a molybdenum dioxide skeleton on biochar can provide a stable and dense conductive network for the lithium replenisher. In addition, biochar has a rich pore structure, a large specific surface area and contains a large number of oxygen-containing active groups on the surface, which can be firmly combined with the molybdenum dioxide precursor to improve structural stability. The calcination of biochar will also pyrolyze to generate CO gas. Together with the hydrogen atmosphere, it promotes the reduction of cobalt oxide after the thermal decomposition of cobalt hydroxide to metallic cobalt, which can act as an active site to modify the molybdenum dioxide material, change the electronic structure and improve the conductivity. Then, the lithium replenisher is evenly distributed on the mesoporous molybdenum dioxide composite material through sand milling dispersion. The particles are evenly distributed and have a large specific surface area. While being able to form a uniform dispersion, it has high conductivity. The gas or low-boiling point liquid generated by the decomposition of the lithium replenisher can also escape better, thereby having a better lithium replenishment effect.

[0024] The purpose of the staged calcination in step (2) is to partially thermally decompose the cobalt hydroxide into cobalt oxide first, which will first form a solid solution with the generated molybdenum dioxide to improve the bonding, and then further reduce to form a metallic cobalt-modified molybdenum dioxide structure. The calcination temperature and time will affect the structural defects and the electronic structure of the active sites of the metal phase, thereby affecting the conductivity and lithium replenishment effect.

[0025] Preferably, in step (1), the ethanol solution containing cobalt hydroxide is obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution is 0.1 g:5-6 mL.

[0026] During the pretreatment of the lithium supplement, the ratio of each raw material needs to be controlled, which is conducive to the formation of a stable and dense conductive network and a high ion migration efficiency.

[0027] Preferably, in step (3), the concentration of the mesoporous molybdenum dioxide composite material dispersed in water or ethanol is 3 to 5 mg / mL.

[0028] In a second aspect, the present invention further provides the use of the above-mentioned lithium supplement agent in a lithium-ion battery. The lithium supplement agent is added during the preparation of the positive electrode slurry and is coated on a current collector to obtain a positive electrode.

[0029] The preferred method for using lithium replenishers in lithium-ion batteries is to disperse the replenisher into the cathode slurry to complete the replenishment during the early formation process. However, adding the replenisher into the electrolyte does not provide ideal solubility, which reduces the replenishment effect.

[0030] Preferably, the positive electrode slurry comprises a positive electrode material, a conductive agent, a binder and a solvent; and the added amount of the lithium supplement agent is 0.4 to 0.8% of the weight of the positive electrode material.

[0031] Preferably, the lithium supplement agent decomposes in the lithium-ion battery; the decomposition occurs during the formation process or during a heat treatment process after the formation process; the temperature of the heat treatment process is 30 to 100° C. and the time is 1 to 5 hours; after the decomposition, the gas or low-boiling-point liquid generated during the decomposition is removed by negative pressure.

[0032] The formation process and heat treatment process are designed to enable the lithium supplement agent to effectively decompose and discharge the gas or low-boiling point liquid produced after decomposition, thereby improving the lithium supplement effect and ensuring that the lithium-ion battery has higher electrochemical performance.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The lithium supplement agent can achieve the lithium supplement process through the combined action of electric field and thermal energy, retaining the advantage of high stability of the compound lithium supplement agent;

[0035] (2) The lithium supplement agent can achieve the same lithium supplement efficiency as metallic lithium, and the mass percentage of active lithium in the lithium supplement agent is 100%;

[0036] (3) The "by-products" after the decomposition of the lithium supplement are removed from the battery system in the form of gas, avoiding the impact of newly generated substances on the battery system from the design source;

[0037] (4) The lithium replenisher is dispersed and added into the positive electrode slurry to complete the lithium replenishment in the early formation process, improve the lithium replenishment effect, and ensure that the lithium-ion battery has higher electrochemical performance. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the embodiments.

[0039] Overall embodiment

[0040] 1. Lithium supplements

[0041] The lithium supplement is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate, and lithium nitride. During the lithium supplement process, the lithium supplement produces anions or decomposes into negatively charged parts. The decomposition products contain gases or low-boiling-point liquids, including at least one of carbon dioxide, hydrogen, nitrogen, methane, ethane, propane, butane, pentane, hexane, 2,3-dimethylbutane, 2-methylpropane, 2-methylbutane, and 2-methylpentane.

[0042] The lithium supplement agent can be pre-treated before the lithium supplement process to improve the lithium supplement effect. The pre-treatment includes the following steps:

[0043] (1) The biomass char is crushed and ball-milled, dispersed in water, ammonium molybdate is added and mixed, and then an ethanol solution containing cobalt hydroxide is added and ultrasonically dispersed, followed by centrifugation and removal of the supernatant, and drying to obtain a reactant; the mass volume ratio of the biomass char, ammonium molybdate, water, and the ethanol solution containing cobalt hydroxide is 1g:0.3-0.5g:200mL:100-150mL; the ethanol solution containing cobalt hydroxide is obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to the ethanol solution is 0.1g:5-6mL;

[0044] (2) calcining the reactants in a mixed gas atmosphere with a volume ratio of argon to hydrogen of 7 to 8:1 in stages, first calcining at 200 to 250° C. for 30 to 50 minutes and then calcining at 500 to 600° C. for 1 to 2 hours to obtain a mesoporous molybdenum dioxide composite material;

[0045] (3) The mesoporous molybdenum dioxide composite material is dispersed in water or ethanol to obtain a mixed solution with a concentration of 3 to 5 mg / mL, and then a lithium supplement agent is added, wherein the mass ratio of the mesoporous molybdenum dioxide composite material to the lithium supplement agent is 0.1:1 to 1.5; then, the mixture is ground in a sand mill for 2 to 3 hours, and then spray-dried to obtain a pretreated lithium supplement agent.

[0046] 2. Lithium-ion battery positive electrode: The positive electrode slurry includes positive electrode material, lithium supplement agent, conductive agent, binder and solvent. The amount of lithium supplement agent added is 0.4-0.8% of the weight of the positive electrode material. The positive electrode slurry is coated on the current collector to obtain the positive electrode.

[0047] Negative electrode: standard graphite electrode.

[0048] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, negative pressure formation is employed. After formation, the battery is heated at a rate of 1°C per minute to 30-100°C while maintaining a negative pressure of 0.05 MPa. The temperature is then programmed to remove gases or low-boiling-point liquids generated during decomposition using negative pressure. Formation is completed after the battery cools naturally, and the sealing pins are welded.

[0049] Example 1

[0050] Lithium-ion batteries using lithium acetate as a lithium supplement:

[0051] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP with a mass ratio of 95:3:2 were mixed evenly, and then lithium acetate that was ball-milled and passed through a 200-mesh sieve was added to obtain a positive electrode slurry. The amount of lithium acetate added was 0.6% of the weight of the ternary positive electrode material NCM811, and the amount of solvent NMP added was 60% of the weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0052] Negative electrode: standard graphite electrode.

[0053] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the temperature is raised to 90°C at a rate of 1°C per minute while maintaining the negative pressure at 0.05 MPa. The temperature is then maintained for 1.5 hours. After the formation is completed, the temperature is allowed to cool naturally, and the sealing pins are welded.

[0054] Example 2

[0055] Lithium-ion batteries using lithium formate as a lithium supplement:

[0056] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP with a mass ratio of 95:3:2 were mixed evenly, and then lithium formate that was ball-milled and passed through a 200-mesh sieve was added to obtain a positive electrode slurry. The amount of lithium formate added was 0.4% by weight of the ternary positive electrode material NCM811, and the amount of solvent NMP added was 60% by weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0057] Negative electrode: standard graphite electrode.

[0058] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the battery is heated at a programmed rate of 1°C per minute to 75°C while maintaining a negative pressure of 0.05 MPa. The temperature is then maintained at this temperature for 3 hours. After the battery is cooled naturally, the formation is completed and the sealing pins are welded.

[0059] Example 3

[0060] Lithium-ion batteries using lithium oxalate as a lithium supplement:

[0061] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP in a mass ratio of 95:3:2 were mixed evenly, and then lithium oxalate that was ball-milled and passed through a 200-mesh sieve was added to obtain a positive electrode slurry. The amount of lithium oxalate added was 0.4% of the weight of the ternary positive electrode material NCM811, and the amount of solvent NMP added was 60% of the weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0062] Negative electrode: standard graphite electrode.

[0063] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the battery is heated to 95°C at a rate of 1°C per minute while maintaining the negative pressure at 0.05 MPa. The temperature is then programmed to maintain the temperature for 2 hours. After the battery cools naturally, the formation is completed and the sealing pins are welded.

[0064] Example 4

[0065] The difference from Example 2 is that the lithium supplement agent is pretreated before the lithium supplement process.

[0066] The pretreatment of lithium formate includes the following steps:

[0067] (1) 1 g of biochar was crushed and ball-milled and then dispersed in 200 mL of water, 0.4 g of ammonium molybdate was added and mixed, and then 130 mL of an ethanol solution containing cobalt hydroxide was added and ultrasonically dispersed, wherein the ethanol solution containing cobalt hydroxide was obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution was 0.1 g:5 mL, and then centrifuged and the supernatant was removed, and the reactant was dried to obtain a reactant;

[0068] (2) calcining the reactants in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 in stages, first calcining at 200°C for 40 minutes and then calcining at 550°C for 1 hour to obtain a mesoporous molybdenum dioxide composite material;

[0069] (3) 0.3 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 3 mg / mL, and 1.2 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2.5 h, and then spray-dried to obtain pretreated lithium formate.

[0070] Lithium-ion batteries using pretreated lithium formate as a lithium supplement:

[0071] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP in a mass ratio of 95:3:2 were mixed evenly, and then ground and pretreated lithium formate was added to obtain a positive electrode slurry. The amount of pretreated lithium formate added was 0.4% of the weight of the ternary positive electrode material NCM811, and the amount of solvent NMP added was 60% of the weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0072] Negative electrode: standard graphite electrode.

[0073] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the battery is heated at a programmed rate of 1°C per minute to 75°C while maintaining a negative pressure of 0.05 MPa. The temperature is then maintained at this temperature for 3 hours. After the battery is cooled naturally, the formation is completed and the sealing pins are welded.

[0074] Example 5

[0075] The difference from Example 2 is that the lithium supplement agent is pretreated before the lithium supplement process.

[0076] The pretreatment of lithium formate includes the following steps:

[0077] (1) 1 g of biochar was crushed and ball-milled and then dispersed in 200 mL of water, 0.4 g of ammonium molybdate was added and mixed, and then 150 mL of an ethanol solution containing cobalt hydroxide was added and ultrasonically dispersed, wherein the ethanol solution containing cobalt hydroxide was obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution was 0.1 g:6 mL, and then centrifuged and the supernatant was removed, and the reactant was dried to obtain a reactant;

[0078] (2) calcining the reactants in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 in stages, first calcining at 200°C for 30 minutes and then calcining at 600°C for 1 hour to obtain a mesoporous molybdenum dioxide composite material;

[0079] (3) 0.4 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 4 mg / mL, and 1 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2 h, and then spray-dried to obtain pretreated lithium formate.

[0080] Lithium-ion batteries using pretreated lithium formate as a lithium supplement:

[0081] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP in a mass ratio of 95:3:2 were mixed evenly, and then ground and pretreated lithium formate was added to obtain a positive electrode slurry. The amount of pretreated lithium formate added was 0.4% of the weight of the ternary positive electrode material NCM811, and the amount of solvent NMP added was 60% of the weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0082] Negative electrode: standard graphite electrode.

[0083] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the battery is heated at a programmed rate of 1°C per minute to 75°C while maintaining a negative pressure of 0.05 MPa. The temperature is then maintained at this temperature for 3 hours. After the battery is cooled naturally, the formation is completed and the sealing pins are welded.

[0084] Comparative Example 1

[0085] The difference from Example 2 is that no lithium supplement agent is added.

[0086] Lithium-ion battery:

[0087] Positive electrode: The ternary positive electrode material NCM811, conductive carbon black SP, binder PVDF and solvent NMP in a mass ratio of 95:3:2 were mixed evenly to obtain a positive electrode slurry. The amount of solvent NMP added was 60% of the weight of the positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a positive electrode.

[0088] Negative electrode: standard graphite electrode.

[0089] The positive and negative electrodes are rolled, assembled, and then injected into a square aluminum-cased lithium-ion battery. During the lithium-ion battery formation process, a negative pressure of 0.05 MPa is used. After formation, the battery is heated at a programmed rate of 1°C per minute to 75°C while maintaining a negative pressure of 0.05 MPa. The temperature is then maintained at this temperature for 3 hours. After the battery is cooled naturally, the formation is completed and the sealing pins are welded.

[0090] Comparative Example 2

[0091] The difference from Example 4 is that no biochar is added during the pretreatment of lithium formate.

[0092] The pretreatment of lithium formate includes the following steps:

[0093] (1) adding 0.4 g of ammonium molybdate to 200 mL of water, and then adding 130 mL of an ethanol solution containing cobalt hydroxide, followed by ultrasonic dispersion, wherein the ethanol solution containing cobalt hydroxide is obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to the ethanol solution is 0.1 g:5 mL, then centrifuging and removing the supernatant, and drying to obtain a reactant;

[0094] (2) calcining the reactants in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 in stages, first calcining at 200°C for 40 minutes and then calcining at 550°C for 1 hour to obtain a mesoporous molybdenum dioxide composite material;

[0095] (3) 0.3 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 3 mg / mL, and 1.2 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2.5 h, and then spray-dried to obtain pretreated lithium formate.

[0096] Comparative Example 3

[0097] The difference from Example 4 is that no cobalt hydroxide is added during the pretreatment of lithium formate.

[0098] The pretreatment of lithium formate includes the following steps:

[0099] (1) 1 g of biochar was crushed and ball-milled, then dispersed in 200 mL of water, 0.4 g of ammonium molybdate was added and mixed, then centrifuged and the supernatant was removed, and the reactant was obtained after drying;

[0100] (2) calcining the reactants in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 in stages, first calcining at 200°C for 40 minutes and then calcining at 550°C for 1 hour to obtain a mesoporous molybdenum dioxide composite material;

[0101] (3) 0.3 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 3 mg / mL, and 1.2 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2.5 h, and then spray-dried to obtain pretreated lithium formate.

[0102] Comparative Example 4

[0103] The difference from Example 4 is that during the pretreatment of lithium formate, too much biochar was added.

[0104] The pretreatment of lithium formate includes the following steps:

[0105] (1) 2 g of biochar was crushed and ball-milled and then dispersed in 200 mL of water, 0.4 g of ammonium molybdate was added and mixed, and then 130 mL of an ethanol solution containing cobalt hydroxide was added and ultrasonically dispersed, wherein the ethanol solution containing cobalt hydroxide was obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution was 0.1 g:5 mL, and then centrifuged and the supernatant was removed, and the reactant was dried to obtain a reactant;

[0106] (2) calcining the reactants in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 in stages, first calcining at 200°C for 40 minutes and then calcining at 550°C for 1 hour to obtain a mesoporous molybdenum dioxide composite material;

[0107] (3) 0.3 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 3 mg / mL, and 1.2 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2.5 h, and then spray-dried to obtain pretreated lithium formate.

[0108] Comparative Example 5

[0109] The difference from Example 4 is that during the pretreatment of lithium formate, one-step calcination is adopted.

[0110] The pretreatment of lithium formate includes the following steps:

[0111] (1) 1 g of biochar was crushed and ball-milled and then dispersed in 200 mL of water, 0.4 g of ammonium molybdate was added and mixed, and then 130 mL of an ethanol solution containing cobalt hydroxide was added and ultrasonically dispersed, wherein the ethanol solution containing cobalt hydroxide was obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution was 0.1 g:5 mL, and then centrifuged and the supernatant was removed, and the reactant was dried to obtain a reactant;

[0112] (2) calcining the reactants at 550° C. for 2 h in a mixed gas atmosphere of argon and hydrogen with a volume ratio of 8:1 to obtain a mesoporous molybdenum dioxide composite material;

[0113] (3) 0.3 g of the mesoporous molybdenum dioxide composite material was dispersed in water to obtain a mixed solution with a concentration of 3 mg / mL, and 1.2 g of lithium formate was added. The mixture was sand-milled in a sand mill for 2.5 h, and then spray-dried to obtain pretreated lithium formate.

[0114] Table 1

[0115]

[0116] In Table 1, the charge and discharge voltage of the battery is 2.5 to 3.6V.

[0117] As shown in Table 1, it can be seen from Examples 1-5 and Comparative Example 1 that the lithium replenishing agent of the present invention has a high lithium replenishing efficiency, and the lithium replenishing agent after pretreatment can further improve the conductivity, and the lithium ion battery prepared has high capacity and high first charge and discharge efficiency, and still has high capacity after 100 cycles, which shows that the lithium replenishing agent can more effectively reduce the capacity loss problem of the battery during the first charge and discharge process. It can be seen from Comparative Examples 2-4 that biochar can serve as a carbon skeleton while generating a small amount of reducing gas to promote the reduction of cobalt oxide to cobalt, and cobalt atoms doped with molybdenum dioxide materials can further improve conductivity and ion migration efficiency. However, the reducing gas atmosphere formed by adding too much biochar will be unfavorable for the formation of molybdenum dioxide, and the electrochemical performance will be reduced. It can be seen from Comparative Example 5 that a good molybdenum dioxide composite structure cannot be formed by one-step calcination, and the lithium replenishing efficiency will also decrease.

[0118] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0119] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A pretreatment method for a lithium supplement, characterized in that: include: (1) The biochar was crushed and ball-milled, dispersed in water, and ammonium molybdate was added and mixed. Then, an ethanol solution containing cobalt hydroxide was added and ultrasonicated. The ratio of biochar, ammonium molybdate, water, and ethanol solution containing cobalt hydroxide was 1 g: 0.3-0.5 g: 200 mL: 100-150 mL. The mixture was centrifuged, the supernatant was removed, and the mixture was dried to obtain the reactant. (2) calcining the reactants in a mixed gas atmosphere with a volume ratio of argon to hydrogen of 7 to 8:1 in stages, first calcining at 200 to 250°C for 30 to 50 minutes and then calcining at 500 to 600°C for 1 to 2 hours to obtain a mesoporous molybdenum dioxide composite material; (3) Dispersing the mesoporous molybdenum dioxide composite material in water or ethanol, adding a lithium supplement, wherein the mass ratio of the mesoporous molybdenum dioxide composite material to the lithium supplement is 0.1:1~1.5, the lithium supplement is a lithium ion battery lithium supplement based on gasification decomposition, and the lithium supplement is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate and lithium nitride; sand milling in a sand mill for 2~3 hours, and spray drying.

2. The pretreatment method of lithium supplement agent according to claim 1, characterized in that: The lithium supplement agent decomposes into anions or negatively charged parts during the lithium supplement process.

3. The pretreatment method of lithium supplement according to claim 2, characterized in that: The decomposition products of the decomposition contain gas.

4. The pretreatment method of lithium supplement according to claim 3, characterized in that: The decomposition product is at least one of carbon dioxide, hydrogen, nitrogen, methane, ethane, propane, butane, pentane, hexane, 2,3-dimethylbutane, 2-methylpropane, 2-methylbutane, and 2-methylpentane.

5. The pretreatment method of lithium supplement according to claim 1, characterized in that: In step (1), the ethanol solution containing cobalt hydroxide is obtained by dispersing cobalt hydroxide in an ethanol solution, and the mass volume ratio of cobalt hydroxide to ethanol solution is 0.1 g:5-6 mL.

6. The pretreatment method of lithium supplement according to claim 1, characterized in that: In step (3), the concentration of the mesoporous molybdenum dioxide composite material dispersed in water or ethanol is 3-5 mg / mL; the mass ratio of the mesoporous molybdenum dioxide composite material to the lithium supplement agent is 0.1:1-1.

5.

7. Use of the pretreated lithium supplement obtained by the method according to any one of claims 1 to 6 in a lithium ion battery, characterized in that: The pre-treated lithium supplement agent is added during the preparation of the positive electrode slurry and is coated on the current collector to obtain the positive electrode.

8. The use according to claim 7, characterized in that The positive electrode slurry includes a positive electrode material, a conductive agent, a binder and a solvent; the added amount of the pretreated lithium supplement agent is 0.4-0.8% of the weight of the positive electrode material.

9. The use according to claim 7, characterized in that The pretreated lithium supplement agent decomposes in the lithium-ion battery; the decomposition occurs during the formation process or during a heat treatment process after the formation process; the temperature of the heat treatment process is 30-100° C. and the time is 1-5 hours; after the decomposition, the gas or low-boiling-point liquid generated during the decomposition is removed by negative pressure.

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