Positive electrode lithium supplement agent and preparation method and application thereof

Abstract

The invention discloses a positive electrode lithium supplement agent and a preparation method and application thereof. The preparation method comprises the following steps: 1) mixing Li5FeO4 with sulfur powder and an oxygen absorbent to obtain a mixture; wherein the addition amount of the sulfur powder is 0.01-0.2% of the mass of the Li5FeO4; the addition amount of the oxygen absorbent is 0.5-3.0% of the mass of the Li5FeO4; the oxygen absorbent is one or more of nickel protoxide, manganese monoxide and vanadium monoxide; and 2) adding a binder into the mixture in the step 1), granulating in an inert atmosphere to obtain spherical precursor particles, and carbonizing and sintering the spherical precursor particles in the inert atmosphere to obtain the positive electrode lithium supplement agent.

Description

Technical Field

[0001] This invention belongs to the field of lithium replenishment technology, specifically relating to a positive electrode lithium replenishment agent, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess characteristics such as high operating voltage, high specific energy, small size, light weight, and long cycle life, making them a focal point of competition in the automotive industry. With the continuous development of lithium-ion batteries in portable electronic devices, electric bicycles, and electric vehicles, the requirements for their energy density and other performance characteristics are becoming increasingly stringent. Lithium loss is the direct cause of battery performance degradation. Lithium replenishment at the positive electrode replenishes the lithium source consumed during battery charging and discharging, thereby improving the battery's energy density and cycle life. Commonly used lithium replenishing agents are lithium-rich oxides. These oxides release lithium ions during battery formation to compensate for the efficiency loss during the first charge and discharge cycle at the negative electrode. Lithium ferrite, as a lithium-rich oxide material, has a theoretical specific capacity of 867 mAh / g, a moderate operating voltage, and the inert substances formed after the first charge and discharge cycle do not participate in subsequent electrochemical processes, making it an ideal positive electrode lithium replenishment additive.

[0003] During the initial charging process, lithium ferrite batteries release a large amount of lithium ions, which in turn releases lattice oxygen atoms. This leads to the oxidation and decomposition of the electrolyte, posing a safety hazard. Currently, to reduce the impact of lattice oxygen on lithium battery performance, sulfur powder is used to coat lithium ferrite. However, excessive sulfur powder coating severely affects lithium replenishment, while insufficient coating results in poor oxygen absorption. Furthermore, the large-scale intercalation and deintercalation of lithium ions during charging and discharging can also cause the collapse of the lithium replenishment agent structure, further impacting battery performance. Summary of the Invention

[0004] To address the above problems, the purpose of this invention is to provide a positive electrode lithium replenishing agent, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a method for preparing a positive electrode lithium supplement, specifically comprising the following steps: 1) Mix Li5FeO4 with sulfur powder and oxygen absorber to obtain a mixture; wherein: the amount of sulfur powder added is 0.01~0.2% of the mass of Li5FeO4; the amount of oxygen absorber added is 0.5~3.0% of the mass of Li5FeO4; the oxygen absorber is one or more of nickel oxide (NiO), manganese monoxide (MnO), and vanadium monoxide (VO); 2) Add a binder to the mixture in step 1) and granulate it under an inert atmosphere to obtain spherical precursor particles; then carbonize and sinter the spherical precursor particles under an inert atmosphere to obtain a positive electrode lithium supplement.

[0006] Preferably, the method for preparing Li5FeO4 in step 1) includes the following steps: After the iron source and lithium source are mixed evenly, they are added to a mixed solvent composed of dichloroethane and water to obtain a mixed solution. The mixed solution is poured into a closed reaction vessel and reacted under pressure and heating to obtain the Li5FeO4 precursor. The Li5FeO4 precursor is sintered under an inert atmosphere to obtain Li5FeO4.

[0007] More preferably, the iron source is one or more of ferric chloride, ferric sulfate, and ferric nitrate; the lithium source is one or more of lithium hydroxide and lithium oxide; the iron source and lithium source are added at a molar ratio of Fe to Li of 1:(5.0~5.2); the volume ratio of dichloroethane to water is (0.8~1.2):(0.4~0.6); and the mass ratio of iron source to mixed solvent is (1~20):150.

[0008] More preferably, the pressurization pressure is 1~2MPa, the heating temperature is 160~200℃, the reaction time is 18~30h, and the D50 of the Li5FeO4 precursor particles in the solution is 0.3~0.8μm, and the Dmax is ≤1.5μm.

[0009] In a further preferred embodiment, after the reaction is complete, solid-liquid separation is performed, and the obtained solid is vacuum dried at 280~320℃ for 9~11h to obtain the Li5FeO4 precursor.

[0010] More preferably, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere; the sintering heating rate is 1-10℃ / min, the sintering temperature is 400-700℃, and the sintering time is 5-20h.

[0011] Preferably, in step 1), the mixing is carried out under an inert atmosphere; the mixing adopts high-speed shear force mixing, and the linear velocity of the shear force mixing is controlled to be 15~35m / s; the mixing temperature is 20~90℃, and the mixing time is 0.25~1h.

[0012] Preferably, in step 2), the binder is one or more of ethylene oxide resin powder, phenolic resin powder, polyimide powder, asphalt powder, polyvinyl alcohol powder, and polytetrafluoroethylene powder, wherein the particle size D50 of the binder is less than 2 μm; the amount of binder added is 0.2~10% of the mass of the mixture.

[0013] Preferably, in step 2), granulation is performed using a high-speed mixing device. The granulation step is as follows: the mixture and binder are added to a high-speed mixing device under an inert atmosphere, and the mixture is first stirred at a low speed of 2-4 m / s for 5-10 minutes, and heated to 70-90°C. After the temperature stabilizes, the linear speed is adjusted to 14-16 m / s for high-speed stirring. After stirring for 25-35 minutes, the mixture is cooled to room temperature while stirring at high speed, and then stirred at high speed for 10-20 minutes to obtain spherical precursor particles.

[0014] More preferably, the particle size of the spherical precursor particles is 3~10μm.

[0015] Preferably, in step 2), the heating rate of carbonization sintering is 1-10℃ / min, the carbonization sintering temperature is 400-1000℃, and the carbonization sintering time is 5-24h.

[0016] Secondly, the present invention provides a positive electrode lithium replenishing agent, which is prepared by the aforementioned preparation method.

[0017] Thirdly, the present invention provides a cathode material, including the aforementioned cathode lithium replenishing agent.

[0018] Fourthly, the present invention provides a lithium-ion battery comprising the aforementioned positive electrode material.

[0019] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: 1) In the method of this invention, sulfur powder and an oxygen absorber are first coated on the surface of lithium ferrite, and then a binder is added for granulation and carbonization sintering. During the carbonization sintering process, sulfur reacts with the residual alkali on the surface of lithium ferrite to generate Li2S and Li2SO3, which can reduce the effect of residual alkali on Li. + The insertion and extraction performance is affected; in addition, Li2S and Li2SO3 will have a synergistic oxygen absorption effect with oxygen absorbers, which can quickly absorb lattice oxygen and convert it into high-valence inorganic substances such as Li2SO4, Ni2O3, MnO2, V2O3, etc. This greatly reduces gas production while ensuring the stability and safety of battery performance.

[0020] 2) The present invention uses a binder to granulate the mixture. Granulation can make the structure of the positive electrode lithium replenishment agent more stable, reduce the structural collapse caused by lithium ion deintercalation, and improve the stability and safety of battery performance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the granulation principle in the method of the present invention.

[0022] Figure 2This is a SEM image of Li5FeO4 prepared in Example 1 of the present invention.

[0023] Figure 3 This is a SEM image of the positive electrode lithium replenishing agent prepared in Example 1 of the present invention. Detailed Implementation

[0024] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] In a first aspect, the present invention provides a method for preparing a positive electrode lithium supplement, specifically comprising the following steps: 1) Mix Li5FeO4 with sulfur powder and oxygen absorber to obtain a mixture; wherein: the amount of sulfur powder added is 0.01~0.2% of the mass of Li5FeO4; the amount of oxygen absorber added is 0.5~3.0% of the mass of Li5FeO4; the oxygen absorber is one or more of nickel oxide (NiO), manganese monoxide (MnO), and vanadium monoxide (VO); 2) Add a binder to the mixture in step 1) and granulate it under an inert atmosphere to obtain spherical precursor particles; then carbonize and sinter the spherical precursor particles under an inert atmosphere to obtain a positive electrode lithium supplement.

[0026] In the preparation method of this invention, sulfur powder and low-valence cation oxide oxygen absorbers are co-coated onto Li5FeO4. During the subsequent carbonization and sintering process, sulfur powder reacts with lithium hydroxide remaining on the surface of Li5FeO4 to produce Li2S and Li2SO3. These sulfides and low-valence oxide oxygen absorbers can absorb lattice oxygen to form high-valence inorganic compounds. These compounds are relatively stable and are deposited on the surface of Li5FeO4, which can effectively isolate water vapor and improve the environmental stability of the Li5FeO4 composite material.

[0027] Research has shown that if only an oxygen absorber is added without sulfur powder, the resulting cathode lithium supplement, when assembled into a battery, will have a lower specific capacity and a higher impedance. This is likely because the oxygen absorber has a certain impact on the cathode. However, adding sulfur powder does not decrease the specific capacity or increase the impedance. This is probably because during the carbonization and sintering process, sulfur reacts with some NiO, MnO, or VO to form Ni2S, MnS, V2S3, etc. These substances not only absorb oxygen but also help reduce impedance and increase the battery's specific capacity.

[0028] In the preparation method of this invention, a secondary particle precursor is formed by granulation under high-speed shear force. A binder binds the components together, and after sintering, the resulting positive electrode lithium replenisher has stronger structural stability. Moreover, the carbon layer after binder sintering has a certain degree of flexibility, which can alleviate the volume change caused by lithium insertion / extraction and prevent particle structure collapse. At the same time, it ensures good contact between primary particles, improves electron transport speed, and guarantees the lithium removal capacity of the lithium replenisher.

[0029] Preferably, the method for preparing Li5FeO4 in step 1) includes the following steps: After the iron source and lithium source are mixed evenly, they are added to a mixed solvent composed of dichloroethane and water to obtain a mixed solution. The mixed solution is poured into a closed reaction vessel and reacted under pressure and heating to obtain the Li5FeO4 precursor. The Li5FeO4 precursor is sintered under an inert atmosphere to obtain Li5FeO4.

[0030] The method for preparing Li5FeO4 in this invention employs a solvothermal reaction, which can reduce lattice defects in Li5FeO4 and improve its stability and lithium replenishment effect. Furthermore, the solvothermal reaction method allows for better control of the particle size distribution of Li5FeO4, making it easier to granulate the mixture of sulfur powder, oxygen absorber, and binder, thus improving the granulation effect.

[0031] More preferably, the iron source is one or more of ferric chloride, ferric sulfate, and ferric nitrate; the lithium source is one or more of lithium hydroxide and lithium oxide; the iron source and lithium source are added according to a Fe to Li molar ratio of 1:(5.0~5.2); the volume ratio of dichloroethane to water is (0.8~1.2):(0.4~0.6), including but not limited to 0.8:0.4, 0.8:0.6, 0.9:0.5, 1.0:0.5, 1.0:0.6, 1.1:0.5, 1.2:0.4, 1.2:0.6, etc.; the mass ratio of iron source to mixed solvent is (1~20):150, including but not limited to 1:150, 2:150, 5:150, 8:150, 10:150, 12:150, 15:150, 18:150, 20:150, etc.

[0032] More preferably, the pressurization pressure is 1~2MPa, including but not limited to 1.0MPa, 1.1MPa, 1.2MPa, 1.3MPa, 1.4MPa, 1.5MPa, 1.6MPa, 1.7MPa, 1.8MPa, 1.9MPa, 2.0MPa, etc.; the heating temperature is 160~200℃, including but not limited to 160℃, 170℃, 180℃, 190℃, 200℃, etc.; the reaction time is 18~30h, including but not limited to 18h, 20h, 22h, 24h, 26h, 28h, 30h, etc.; the D50 of the Li5FeO4 precursor particles in the solution after reaction is 0.3~0.8μm, and the Dmax≤1.5μm.

[0033] In a further preferred embodiment, after the reaction is complete, solid-state separation is performed, and the obtained solid is vacuum dried at 280~320℃ for 9~11h to obtain the Li5FeO4 precursor.

[0034] More preferably, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere; the sintering heating rate is 1 to 10℃ / min, including but not limited to 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, etc.; the sintering temperature is 400 to 700℃, including but not limited to 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc.; the sintering time is 5 to 20h, including but not limited to 5h, 10h, 15h, 20h, etc.

[0035] Preferably, in step 1), the mixing is carried out under an inert atmosphere; the mixing adopts shear mixing, and the linear velocity of the shear mixing is controlled to be 15~35m / s, including but not limited to 15m / s, 20m / s, 25m / s, 30m / s, 35m / s, etc.; the mixing temperature is 20~90℃, including but not limited to 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc.; and the mixing time is 0.25~1h, including but not limited to 0.25h, 0.5h, 0.75h, 1h, etc.

[0036] Preferably, in step 2), the binder is one or more of ethylene oxide resin powder, phenolic resin powder, polyimide powder, asphalt powder, polyvinyl alcohol powder, and polytetrafluoroethylene powder, wherein the particle size D50 of the binder is less than 2 μm; the amount of binder added is 0.2~10% of the mass of the mixture, including but not limited to 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, etc.

[0037] Preferably, in step 2), granulation is performed using a high-speed mixing granulator. The granulation steps are as follows: the mixture and binder are placed in a high-speed mixing granulator under an inert atmosphere, and first, low-speed stirring is performed at an online speed of 2~4m / s for 5~10 minutes, and then heated to 70~90℃. After the temperature stabilizes, the online speed is adjusted to 14~16m / s for high-speed stirring. After stirring for 25~35 minutes, the temperature is lowered to room temperature while stirring at high speed, and stirring is continued at high speed for 10~20 minutes to obtain spherical precursor particles.

[0038] The granulation principle diagram of the high-speed mixing granulator in this invention is shown below. Figure 1 As shown, the high-speed mixing granulator is designed to subject each particle to equal extrusion, impact, and shearing forces through the high-speed rotation of a specially shaped rotor. The shape and arrangement of the rotor enable uniform compounding of particles. By adjusting the rotor speed and running time, particle compounding and precision mixing can be achieved. Furthermore, the cavity employs a jacketed structure, allowing for both heating and water cooling, effectively altering the temperature of the compounded granules during high-speed rotation.

[0039] More preferably, the spherical precursor particles have a particle size of 5~20μm, including but not limited to 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc.

[0040] Preferably, in step 2), the heating rate of carbonization sintering is 1 to 10℃ / min, including but not limited to 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, etc.; the carbonization sintering temperature is 400 to 1000℃, including but not limited to 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc.; and the carbonization sintering time is 5 to 24h, including but not limited to 5h, 10h, 15h, 20h, 24h, etc.

[0041] Secondly, the present invention provides a positive electrode lithium replenishing agent prepared by the aforementioned preparation method.

[0042] Thirdly, the present invention provides a cathode material, including the aforementioned cathode lithium replenishing agent.

[0043] Fourthly, the present invention provides a lithium-ion battery comprising the aforementioned positive electrode material.

[0044] Example 1 The preparation method of the positive electrode lithium supplement in this embodiment includes the following steps: 1) Ferric nitrate and lithium hydroxide were mixed at a Fe to Li molar ratio of 1:5.1 to obtain a mixture. This mixture was then added to a dichloroethane and deionized water mixture at a volume ratio of 1:0.5 (ferric nitrate to the mixed solvent mass ratio was 10:150). The mixture was stirred at 1000 rpm for 10 min to obtain a mixed solution. This solution was then poured into a sealed pressure reaction vessel, pressurized to 1.5 MPa, and heated to 180 °C. The reaction was maintained at this temperature and pressure for 24 h until the precursor particles had a D50 of 0.5 μm and a Dmax ≤ 1.5 μm. After the reaction was complete, the reaction solution was filtered, washed, and the filter residue was vacuum dried at 300 °C for 10 h to obtain the Li5FeO4 precursor. The Li5FeO4 precursor was placed in a sintering furnace and heated to 550 °C at a rate of 5 °C / min under an argon atmosphere. This temperature was maintained for 15 h to obtain Li5FeO4.

[0045] 2) Add sulfur powder, nickel oxide, and Li5FeO4 to a high-speed mixer in a mass ratio of 0.1:2.0:100. Control the mixing temperature at 40℃, turn on the argon atmosphere protection, and mix at a linear speed of 30m / s for 30 minutes to obtain the mixture.

[0046] 3) Add the polyimide powder and the mixture to the high-speed mixer and granulator at a mass ratio of 5:100. Under an inert atmosphere, first stir at a low speed of 3 m / s for 8 minutes, then heat to 80°C. Next, adjust the linear speed to 15 m / s for high-speed stirring and maintain the temperature for 30 minutes. After cooling to room temperature while stirring at high speed, continue stirring at high speed for 15 minutes. (During high-speed stirring, the impeller granulates the material; see the schematic diagram for details.) Figure 1 This process yields spherical precursor particles (with an average particle size of approximately 10 μm). The spherical precursor particles are placed in a sintering furnace and heated to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere. The temperature is then maintained at this level for 15 h to obtain the positive electrode lithium replenishing agent.

[0047] The SEM image of the Li5FeO4 prepared in this embodiment is shown below. Figure 2 As shown: The Li5FeO4 matrix synthesized by the solvothermal reaction method has small primary particles, basically below 1.5 μm, with a relatively high concentration and a morphology of near-spherical.

[0048] The SEM image of the positive electrode lithium replenishment agent prepared in this embodiment is shown below. Figure 3 As shown, the positive electrode lithium supplement is spherical with an average particle size of about 10 μm.

[0049] Comparative Example 1 The process is basically the same as in Example 1, except that in step 2), sulfur powder and nickel oxide are not added, and polyimide powder and Li5FeO4 are granulated directly.

[0050] Comparative Example 2 It is basically the same as Example 1, except that sulfur powder is not added in step 2).

[0051] Comparative Example 3 It is basically the same as Example 1, except that in step 2), nickel oxide is not added.

[0052] Example 2 This is basically the same as Example 1, except that the preparation method of Li5FeO4 in step 1) is different. The specific preparation method is as follows: Lithium hydroxide and ferric oxide were mixed evenly at a molar ratio of Li to Fe of 5.1:1 to obtain a mixture. The mixture was placed in a sintering furnace and heated to 700°C at a heating rate of 6°C / min under an inert atmosphere, and held at this temperature for 15 hours to obtain Li5FeO4.

[0053] Example 3 This is basically the same as Example 1, except that steps 2) and 3) are different. The specific steps are as follows: 2) Sulfur powder, nickel oxide, and Li5FeO4 are mixed in ethanol at a mass ratio of 0.1:2.0:100. The mixture is then heated to 60°C and aged for 30 minutes to obtain a slurry.

[0054] 3) The polyimide resin in the slurry (added at 5% of the total mass of sulfur powder, nickel oxide and Li5FeO4) is milled to obtain a secondary slurry; the secondary slurry is spray-dried and granulated to obtain a granular precursor product; the granular precursor particles are placed in a sintering furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere, and held at this temperature for 15 hours to obtain the positive electrode lithium replenishing agent.

[0055] Example 4 1) Ferric sulfate and lithium hydroxide were mixed at a Fe to Li molar ratio of 1:5.2 to obtain a mixture. This mixture was then added to a mixed solvent of dichloroethane and deionized water at a volume ratio of 0.8:0.6 (the mass ratio of ferric nitrate to the mixed solvent was 1:150). The mixture was stirred at 1000 rpm for 10 min to obtain a mixed solution. This solution was poured into a sealed pressure reaction vessel, pressurized to 1 MPa, and heated to 200°C. The reaction was maintained at this temperature and pressure for 18 h until the precursor particles had a D50 of 0.5 μm and a Dmax ≤ 1.5 μm. After the reaction was complete, the reaction solution was filtered, washed, and the filter residue was vacuum dried at 280°C for 10 h to obtain the Li5FeO4 precursor. The Li5FeO4 precursor was placed in a sintering furnace and heated to 400°C at a rate of 3°C / min under an argon atmosphere. This temperature was maintained for 20 h to obtain Li5FeO4.

[0056] 2) Add sulfur powder, manganese monoxide, and Li5FeO4 to a high-speed mixer in a mass ratio of 0.2:0.5:100. Control the mixing temperature at 30℃, turn on the argon atmosphere protection, set the mixing linear velocity to 8m / s, and mix for 30 minutes to obtain the mixture.

[0057] 3) Add the polyimide powder and the mixture to the high-speed mixer and granulator at a mass ratio of 1:100. Under an inert atmosphere, first stir at a low speed of 3 m / s for 5 minutes, and then heat to 80°C. Next, adjust the linear speed to 15 m / s and stir at a high speed for 30 minutes. After stirring at a constant temperature, cool down to room temperature while stirring at high speed, and continue stirring at high speed for 15 minutes. (During high-speed stirring, the blades granulate the material; see the schematic diagram for the principle.) Figure 1 This process yields spherical precursor particles (with an average particle size of approximately 7 μm). The spherical precursor particles are placed in a sintering furnace and heated to 400 °C at a rate of 5 °C / min under a nitrogen atmosphere. This temperature is then maintained for 24 hours to obtain the positive electrode lithium replenisher.

[0058] Example 5 1) Ferric chloride and lithium hydroxide were mixed at a Fe to Li molar ratio of 1:5.05 to obtain a mixture. The mixture was then added to a mixed solvent of dichloroethane and deionized water at a volume ratio of 1.2:0.4 (the mass ratio of ferric nitrate to the mixed solvent was 20:150). The mixture was stirred at 1000 rpm / min for 10 min to obtain a mixed solution. The mixed solution was then poured into a sealed pressure reaction vessel, pressurized to 2 MPa, heated to 160 °C, and subjected to a heat and pressure holding reaction for 30 h. The reaction proceeded until the precursor particles had a D50 of 0.8 μm and a Dmax ≤ 1.5 μm. After the reaction was complete, the reaction solution was filtered, washed, and the filter residue was vacuum dried at 320 °C for 9 h to obtain the Li5FeO4 precursor. The Li5FeO4 precursor was placed in a sintering furnace and heated to 1000℃ at a rate of 10℃ / min under an argon atmosphere. The temperature was then maintained at this temperature for 5 hours to obtain Li5FeO4.

[0059] 2) Add sulfur powder, vanadium monoxide, and Li5FeO4 to a high-speed mixer in a mass ratio of 0.05:3.0:100. Control the mixing temperature at 50℃, turn on the argon atmosphere protection, set the mixing linear velocity to 50m / s, and mix for 15 minutes to obtain the mixture.

[0060] 3) Add the polyimide powder and the mixture to the high-speed mixer and granulator at a mass ratio of 10:100. Under an inert atmosphere, first stir at a low speed of 3 m / s for 10 minutes, and then heat to 80°C. Next, adjust the linear speed to 15 m / s and stir at a high speed for 30 minutes. After stirring at a constant temperature, cool down to room temperature while stirring at high speed, and continue stirring at high speed for 15 minutes. (During high-speed stirring, the blades granulate the material; see the schematic diagram for the principle.) Figure 1 This process yields spherical precursor particles (with an average particle size of approximately 12 μm). The spherical precursor particles are placed in a sintering furnace and heated to 1000 °C at a rate of 10 °C / min under a nitrogen atmosphere. The temperature is then maintained at this level for 5 hours to obtain the positive electrode lithium replenisher.

[0061] Performance testing: Preparation of the positive electrode sheet: The binder PVDF (polyvinylidene fluoride), the conductive agent CNT (carbon nanotubes), and NMP (N-methyl-2-pyrrolidone) were combined with the positive electrode lithium supplementing agents prepared in Examples 1-5 and Comparative Examples 1-3 to form a positive electrode slurry for coating, thereby preparing the positive electrode sheet. The lithium supplementing material accounted for 91 wt%, the binder for 4 wt%, and the conductive agent for 5 wt%.

[0062] Button cell test: The above positive electrode sheet was cut into small round pieces and assembled into a button cell in a glove box. The glove box environment was: water <0.1ppm, oxygen <1ppm. The counter electrode was a lithium sheet. The electrolyte was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1.0mol / L LiPF6 as the solute. The assembled button cell was tested using the Blue Electric System to measure the specific capacity of the materials.

[0063] Full cell fabrication: The above-mentioned positive electrode sheets are stacked in a Z-shape, alternating between negative electrode-separator-positive electrode-separator-negative electrode, with each cell containing 7 positive electrodes and 8 negative electrodes; each cell is injected with 5.8g of electrolyte; then, the cells undergo chemical decomposition, aging, and capacity testing. The negative electrode is made of graphite material, with the mass ratio of graphite, conductive carbon black, and SBR (styrene-butadiene rubber) being 96:2:2.

[0064] Electrochemical performance testing: Capacity test of positive electrode after lithium replenishment: The positive electrode was assembled into a coin cell and tested using a Xinwei battery cabinet. The initial charge capacity and discharge capacity were measured when the charging voltage was 2.5-4.3V and the charging current was 0.5C.

[0065] Gas generation test of lithium-ion battery cells: In-situ differential electrochemical mass spectrometry was performed on the lithium-ion battery cells assembled with the positive electrode lithium-ion additives of Examples 1-5 and Comparative Examples 1-3. The gas generation during the first charging cycle (formation stage) was measured, with a voltage window of 2.0V to 4.3V and a charging current of 0.05C. After the battery was charged to 4.3V at a constant voltage and stored at 70°C for 48 hours, its gas generation was measured. Table 1 As can be seen from the data in Table 1, the battery assembled in Example 1 has a higher specific capacity and lower gas production during formation and storage. In Comparative Example 1, no sulfur or nickel oxide was added to the lithium replenishment agent, and the assembled battery exhibited relatively high gas production during both formation and storage. In Comparative Example 2, nickel oxide was added to the lithium replenishment agent, but no sulfur was added. The specific capacity of the assembled battery decreased, possibly because nickel oxide affects the performance of the cathode material. Although the gas production during formation and storage decreased compared to Comparative Example 1, it still exhibited relatively high gas production. In Comparative Example 3, sulfur was added to the lithium replenishment agent, but no nickel oxide was added. Although the gas production during formation and storage decreased compared to Comparative Example 1, it still exhibited relatively high gas production. The comparison between Example 1 and Comparative Examples 1-3 suggests that sulfur and nickel oxide may have a synergistic effect, effectively reducing gas production in the cathode material.

[0066] Compared to Example 1, Example 2 mainly uses a solid-state method to synthesize Li5FeO4. The assembled battery exhibits a slight decrease in specific capacity and a certain increase in gas production during formation and storage. This may be because the Li5FeO4 prepared by the solvothermal method in Example 1 has better stability or better binding with sulfur and nickel oxide, thereby further improving the electrochemical performance of the lithium supplement. Compared to Example 1, Example 3 mainly uses spray drying granulation. The assembled battery exhibits a slight decrease in specific capacity and a certain increase in gas production during formation and storage. This may be due to the sublimation of sulfur during spray drying, which significantly reduces the sulfur content in the dried material, leading to a certain decrease in performance. In Examples 4 and 5, process parameters were adjusted. The performance of the assembled batteries fluctuated to some extent, but overall, they exhibited good comprehensive electrochemical performance.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode lithium supplement, characterized in that, Includes the following steps: 1) Mix Li5FeO4 with sulfur powder and oxygen absorber to obtain a mixture; wherein: the amount of sulfur powder added is 0.01~0.2% of the mass of Li5FeO4; the amount of oxygen absorber added is 0.5~3.0% of the mass of Li5FeO4; the oxygen absorber is one or more of nickel oxide, manganese monoxide, and vanadium monoxide; 2) Add a binder to the mixture in step 1) and granulate it under an inert atmosphere to obtain spherical precursor particles; then carbonize and sinter the spherical precursor particles under an inert atmosphere to obtain a positive electrode lithium supplement.

2. The method for preparing the positive electrode lithium supplement according to claim 1, characterized in that, The preparation method of Li5FeO4 in step 1) includes the following steps: After the iron source and lithium source are mixed evenly, they are added to a mixed solvent composed of dichloroethane and water to obtain a mixed solution. The mixed solution is poured into a closed reaction vessel and reacted under pressure and heating to obtain the Li5FeO4 precursor. The Li5FeO4 precursor is sintered under an inert atmosphere to obtain Li5FeO4.

3. The method for preparing the positive electrode lithium supplement agent according to claim 2, characterized in that, The iron source is one or more of ferric chloride, ferric sulfate, and ferric nitrate. and / or The lithium source is one or more of lithium hydroxide and lithium oxide; and / or The iron source and lithium source are added at a molar ratio of Fe to Li of 1:(5.0~5.2); and / or The volume ratio of dichloroethane to water is (0.8~1.2):(0.4~0.6); the mass ratio of iron source to mixed solvent is (1~20):

150.

4. The method for preparing the positive electrode lithium replenishing agent according to claim 2, characterized in that, The pressurization pressure is 1~2MPa, the heating temperature is 160~200℃, the reaction time is 18~30h, and the D50 of the Li5FeO4 precursor particles in the solution is 0.3~0.8μm, and the Dmax is ≤1.5μm. And / or: The inert atmosphere is an argon atmosphere or a nitrogen atmosphere; And / or: The sintering heating rate is 1-10℃ / min, the sintering temperature is 400-700℃, and the sintering time is 5-20h.

5. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, In step 1), mixing is carried out under an inert atmosphere; shear mixing is used, and the linear velocity of shear mixing is controlled at 15~35m / s; the mixing temperature is 20~90℃, and the mixing time is 0.25~1h.

6. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, In step 2), the binder is one or more of ethylene oxide resin powder, phenolic resin powder, polyimide powder, asphalt powder, polyvinyl alcohol powder, and polytetrafluoroethylene powder, wherein the particle size D50 of the binder is less than 2μm; the amount of binder added is 0.2~10% of the mass of the mixture.

7. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, In step 2), granulation is performed using a high-speed mixing device. The granulation process is as follows: the mixture and binder are added to the high-speed mixing device under an inert atmosphere. The mixture is first stirred at a low speed of 2-4 m / s for 5-10 minutes, and then heated to 70-90°C. After the temperature stabilizes, the linear speed is adjusted to 14-16 m / s for high-speed stirring. After stirring for 25-35 minutes, the mixture is cooled to room temperature while stirring at high speed, and then stirred at high speed for 10-20 minutes to obtain spherical precursor particles. The particle size of the spherical precursor particles is 3-10 μm.

8. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, In step 2), the heating rate of carbonization sintering is 1-10℃ / min, the carbonization sintering temperature is 400-1000℃, and the carbonization sintering time is 5-24h.

9. A positive electrode lithium replenishing agent, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 8.

10. A positive electrode material, characterized in that, Includes the positive electrode lithium replenishing agent as described in claim 9.

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