A high-purity cathode lithium supplement material, its preparation method and application

Abstract

The present invention discloses a high-purity cathode lithium supplement material, its preparation method and application. A lithium source is sintered at high temperature in a Ni crucible. By mass, in the product, 95.0% < Li₂O < 99.0%, 1.0% < NiO < 3.5%. This product is mixed with a lithium salt and a nickel source and sintered with one-stage temperature control to obtain the high-purity cathode lithium supplement material. A small amount of catalytic NiO is generated during the preparation of Li₂O, which can significantly reduce the decomposition temperature of the lithium source, making the Li₂O particles have a uniform small particle size. When mixing with the nickel source to prepare the lithium supplement Li₂NiO₂, the mixing is more uniform and the purity of the product is high. A small amount of NiO, as one of the subsequent raw material nickel sources, has a larger contact area with Li₂O compared with directly adding a nickel source, improving the nucleation reaction rate, and can significantly reduce the content of impurity NiO and the residual lithium on the surface in the product, further improving the purity and irreversible specific capacity of the lithium supplement Li₂NiO₂.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a high-purity cathode lithium supplementing agent material, a preparation method thereof, and an application thereof. Background Art

[0002] Emerging portable electronic devices and electric vehicles require lithium-ion batteries with high energy density. Nowadays, their energy density needs to be further improved to meet the growing demand for energy storage applications. In the past decade or so, the combination of nickel-rich layered oxide cathodes and graphite anodes has become a prominent battery system. The current nickel-rich ternary cathodes have reached the basic limit of capacity, but the further improvement of the energy density of the full cell is limited by the upper limit of the graphite capacity. Among various alternative anode materials, silicon-based materials have become the most promising choice for the next-generation battery system. Although the anode capacity increases with the introduction of silicon, the overall performance of the current silicon / NCM full cell is still not satisfactory. Due to severe side reactions that produce an unstable solid electrolyte interface SEI, silicon-based anodes usually exhibit significant capacity loss during the initial cycle, resulting in most of the lithium coming out of the cathode being consumed by irreversible reactions, seriously reducing the energy density of the full cell. To solve this problem, cathode lithium supplementation has become a very effective technical solution, which can reduce the initial lithium loss and improve the energy density of lithium-ion batteries by sacrificing a specific lithium supplementing agent material before cycling.

[0003] The positive electrode lithium supplement Li2NiO2 is a commonly used lithium supplement material for current lithium-ion batteries. In the reported preparations of Li2NiO2 that have been made public, the vast majority only focus on the selection of nickel sources, the mixing and sintering processes of nickel and lithium sources, the selection of dopants, the selection of coating agents, etc. There has been very little research on the selection of lithium salts. As one of the main raw materials for preparing Li2NiO2, it plays a crucial role in the purity, residual lithium, and capacity of the product Li2NiO2, and thus affects the improvement effect on the battery system after being mixed with lithium-ion battery positive electrode materials. Chinese invention patent CN113571781B discloses a method for preparing the lithium supplement Li2NiO2. This method involves mixing a composite lithium salt with a nickel source, sintering and crushing to obtain a lithium supplement additive for the positive electrode of a lithium-ion battery. Among them, the lithium source uses a mixed composite lithium salt, and three different lithium salts need to be mixed and then vacuum sintered at high temperature and crushed to obtain a composite lithium salt in a certain proportion. The steps are cumbersome, the cost is high, and the proportion of the prepared mixed lithium salt is not easy to control, which may lead to poor consistency of the finally prepared Li2NiO2. In addition, Chinese invention patent CN109786746A discloses a method for preparing the lithium supplement Li2NiO2. The lithium salt Li2O used in this method is obtained by high-temperature calcination of Li2CO3 in an inert atmosphere. The purity of Li2O > 99.9%. Subsequently, a solid-solid reaction occurs with the nickel source, and it is prone to incomplete reaction, resulting in a relatively high residual lithium in the product and low purity. Summary of the Invention

[0004] The main technical problem to be solved by the present invention is to overcome the problems mentioned in the above background technology, namely, the inappropriate lithium salt used in the preparation of the lithium supplement and the low purity of the lithium supplement, and to provide a high-purity positive electrode lithium supplement material, its preparation method and application. This lithium supplement material has relatively high purity and irreversible specific capacity, and low surface residual lithium. After being mixed with lithium-ion battery positive electrode materials, it can significantly improve the capacity and cycle performance of the battery.

[0005] The present invention provides a method for preparing a high-purity positive electrode lithium supplement material. The chemical general formula of the lithium supplement material is Li2NiO2. The preparation method includes the following steps:

[0006] (1) Lithium source decomposition: At room temperature, place the lithium source in a Ni crucible. In an atmosphere furnace, under a protective atmosphere of nitrogen or argon, heat at a certain heating rate, hold for a certain period of time, and then naturally cool to room temperature. After crushing and pulverizing, a product mainly composed of Li2O is obtained;

[0007] (2) Mixing and sintering: Uniformly mix the product obtained in step (1) with a lithium salt and a nickel source, and perform sintering. In an atmosphere furnace, under a protective atmosphere of nitrogen or argon, heat at a certain heating rate, hold for a certain period of time, and then naturally cool to room temperature. Crush and pulverize;

[0008] (3)Demagnetization: Demagnetize the material pulverized in step (2), and obtain the high-purity cathode lithium supplement material after sieving.

[0009] Further, in step (1), heat up at a heating rate of 1-5 °C / min to 750-950 °C, and keep the temperature for 2-6 h; in step (2), perform sintering by a one-stage temperature-controlled sintering method; heat up at a heating rate of 1-3 °C / min to 600-780 °C, and keep the temperature for 5-15 h.

[0010] Further, in step (1), the lithium source is one or both of lithium hydroxide and lithium hydroxide monohydrate, the initial oxygen content range in the atmosphere furnace is 200-1000 ppm, and in the product composition obtained in step (1), by mass, 95.0% < Li2O < 99.0%, 1.0% < NiO < 3.5%.

[0011] Further, in step (2), the lithium salt is one or both of lithium hydroxide and lithium hydroxide monohydrate; the nickel salt is one or more of nickelous oxide, nickel sesquioxide or nickel hydroxide.

[0012] Further, in step (2), the mass ratio of Li2O in the product of step (1) used to LiOH in the lithium salt used for mixing is (8.8-9.5):1. At the same time, the molar ratio of the total Li in these two lithium salts to the total Ni in the mixture is (2.0-2.3):1, where the total Ni includes a small amount of NiO in step (1) and Ni in the nickel source added in step (2).

[0013] Further, the oxygen content in the atmosphere furnace in step (2) < 10 ppm.

[0014] Further, the mesh number of the sieve used for sieving in step (3) is 350-400 mesh, the average particle size D50 is 8.5-18.0 μm, and the content of magnetic substances after demagnetization < 50 ppb.

[0015] Further, the purity of the lithium supplement material > 95%, the total residual lithium content < 3%, the average particle size D50 is 8.5-18.0 μm, and the specific surface area is 0.22-0.80 m² / g.

[0016] The present invention provides a high-purity cathode lithium supplement material, which is prepared by the above method.

[0017] The present invention provides a lithium-ion battery, in which the above-mentioned cathode lithium supplement material is used in the cathode material, and the first charge specific capacity of the battery > 425 mAh / g, and the irreversible specific capacity is 280-340 mAh / g.

[0018] The present invention also provides an application of a high-purity cathode lithium supplement material in a lithium-ion battery. Beneficial effects

[0019] (1) In the present invention, Li2O is prepared by high-temperature sintering and decomposition of a lithium source in a Ni crucible. In addition to Li2O in the product, a small amount of NiO is also contained. When the lithium source undergoes a high-temperature melting and decomposition reaction, there is a small amount of O2 in the atmosphere furnace, which causes a micro-reaction of the Ni crucible to generate a small amount of transition metal oxide NiO. The catalytic effect of transition metal ions can significantly reduce the decomposition temperature of the lithium source, making the prepared Li2O particles uniform and small in particle size. When mixing with a nickel source to prepare the lithium supplement Li2NiO2 subsequently, the mixing is more uniform, enabling the reactant particles to come into full contact, and thus generating a lithium supplement material Li2NiO2 with higher purity.

[0020] (2) A small amount of NiO contained in the Li2O prepared in the present invention, as one of the raw material nickel sources for subsequent reactions, has a larger contact area with Li2O compared to the directly added nickel source, which is beneficial to the reaction, improves the nucleation reaction rate of preparing the lithium supplement material Li2NiO2, can significantly reduce the content of impurity NiO and surface residual lithium in the product, improve the purity and irreversible specific capacity of the lithium supplement Li2NiO2, and adding the lithium supplement material prepared in the present invention to the cathode active material of a lithium-ion battery can significantly improve the capacity and cycle performance of the battery. Description of the drawings

[0021] Figure 1 is an XRD diagram of the product obtained by high-temperature decomposition of a lithium source in a Ni crucible in Example 1 of the present invention;

[0022] Figure 2 is an XRD diagram of the lithium supplement material prepared in Example 1 of the present invention;

[0023] Figure 3 is an SEM diagram of the product obtained by high-temperature decomposition of a lithium source in a Ni crucible in Example 1 of the present invention;

[0024] Figure 4 is an SEM diagram of the lithium supplement material prepared in Example 1 of the present invention. Specific embodiments

[0025] The present invention will be described in detail below with reference to the embodiments. Example 1

[0026] At room temperature, lithium hydroxide monohydrate was placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 650 ppm. It was heated to 900 °C at a heating rate of 3 °C / min, held for 5 h, and then naturally cooled to room temperature. After crushing and grinding, the mass percentage of the main components of the obtained product was 97.2% for Li2O and 2.5% for NiO.

[0027] The Li2O, LiOH, and NiO prepared above were proportioned according to a molar ratio of Li to Ni of 2.1:1. Among them, Ni included a small amount of NiO contained in Li2O and Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide was 9.0:1. They were uniformly mixed and sintered by a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 8 ppm. It was heated to 660 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature. After crushing, grinding, demagnetizing, and passing through a 400-mesh sieve, the lithium-ion battery cathode lithium supplement agent material Li2NiO2 was obtained. Example 2

[0028] At room temperature, lithium hydroxide monohydrate was placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 520 ppm. It was heated to 800 °C at a heating rate of 3 °C / min, held for 5 h, the furnace pressure was 5 Pa, and then naturally cooled to room temperature. After crushing and grinding, the mass percentage of the main components of the obtained product was 98.5% for Li2O and 1.2% for NiO.

[0029] The Li2O, LiOH, and NiO prepared above were proportioned according to a molar ratio of Li to Ni of 2.1:1. Among them, Ni included a small amount of NiO contained in Li2O and Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide was 9.2:1. They were uniformly mixed and sintered by a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 8 ppm. It was heated to 720 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature. After crushing, grinding, demagnetizing, and passing through a 400-mesh sieve, the lithium-ion battery cathode lithium supplement agent material Li2NiO2 was obtained. [[ID=...]] Example 3

[0030] At room temperature, lithium hydroxide monohydrate was placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 650 ppm. It was heated to 850 °C at a heating rate of 3 °C / min, held for 5 h, and then naturally cooled to room temperature. After crushing and grinding, the mass percentage of the main components of the obtained product was 97.8% for Li2O and 1.9% for NiO.

[0031] The Li2O, LiOH, and NiO prepared above were proportioned according to the molar ratio of Li to Ni of 2.1:1. Among them, Ni included the small amount of NiO in Li2O and the Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide was 9.0:1. They were uniformly mixed and sintered by a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 8 ppm. It was heated to 660 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature. After crushing, grinding, demagnetizing, and passing through a 400-mesh sieve, the lithium-ion battery cathode lithium supplement agent material Li2NiO2 was obtained. Example 4

[0032] At room temperature, lithium hydroxide monohydrate was placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 520 ppm. It was heated to 880 °C at a heating rate of 3 °C / min, held for 5 h, and then naturally cooled to room temperature. After crushing and grinding, the mass percentage of the main components of the obtained product was 98.2% for Li2O and 1.5% for NiO.

[0033] The Li2O, LiOH, and NiO prepared above were proportioned according to the molar ratio of Li to Ni of 2.05:1. Among them, Ni included the small amount of NiO in Li2O and the Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide was 9.4:1. They were uniformly mixed and sintered by a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace was 8 ppm. It was heated to 750 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature. After crushing, grinding, demagnetizing, and passing through a 400-mesh sieve, the lithium-ion battery cathode lithium supplement agent material Li2NiO2 was obtained. Comparative Example 1

[0034] Mix commercially available Li2O with a purity greater than 99% with LiOH and NiO according to a molar ratio of Li to Ni of 2.1:1. Among them, the mass ratio of Li2O to lithium hydroxide is 9.0:1. Mix evenly and sinter using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. Heat up at a heating rate of 2 °C / min to 660 °C, hold for 10 h, naturally cool to room temperature, crush, pulverize, demagnetize, and pass through a 400-mesh sieve to obtain the lithium-ion battery cathode lithium supplement agent material Li2NiO2. Comparative Example 2

[0035] At room temperature, place lithium hydroxide monohydrate in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 650 ppm. Heat up at a heating rate of 3 °C / min to 720 °C, hold for 5 h, naturally cool to room temperature, and the mass percentage content of the main components of the product obtained after crushing and pulverizing is 94.8% Li2O, 2.0% NiO, and 2.9% LiOH.

[0036] Mix the Li2O, LiOH, and NiO prepared above according to a molar ratio of Li to Ni of 2.1:1. Among them, Ni includes a small amount of NiO contained in Li2O and Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide is 9.0:1. Mix evenly and sinter using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. Heat up at a heating rate of 2 °C / min to 660 °C, hold for 10 h, naturally cool to room temperature, crush, pulverize, demagnetize, and pass through a 400-mesh sieve to obtain the lithium-ion battery cathode lithium supplement agent material Li2NiO2. Comparative Example 3

[0037] At room temperature, place lithium hydroxide monohydrate in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 650 ppm. Heat up at a heating rate of 3 °C / min to 980 °C, hold for 5 h, naturally cool to room temperature, and the mass percentage content of the main components of the product obtained after crushing and pulverizing is 94.4% Li2O and 5.5% NiO.

[0038] The prepared Li2O, LiOH, and NiO are proportioned according to a molar ratio of Li to Ni of 2.1:1. Here, Ni includes the small amount of NiO contained in Li2O and the Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide is 9.0:1. They are uniformly mixed and sintered using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. It is heated at a heating rate of 2 °C / min to 660 °C, held for 10 h, naturally cooled to room temperature, crushed, pulverized, demagnetized, and passed through a 400-mesh sieve to obtain the lithium-ion battery cathode lithium supplement agent material Li2NiO2. Comparative Example 4

[0039] At room temperature, monohydrate lithium hydroxide is placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 10 ppm. It is heated at a heating rate of 3 °C / min to 900 °C, held for 5 h, naturally cooled to room temperature, and the mass percentage of the main component of the product obtained after crushing and pulverizing is 99.7% Li2O.

[0040] The prepared Li2O, LiOH, and NiO are proportioned according to a molar ratio of Li to Ni of 2.1:1. Here, Ni refers to the Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide is 9.0:1. They are uniformly mixed and sintered using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. It is heated at a heating rate of 2 °C / min to 660 °C, held for 10 h, naturally cooled to room temperature, crushed, pulverized, demagnetized, and passed through a 400-mesh sieve to obtain the lithium-ion battery cathode lithium supplement agent material Li2NiO2. Comparative Example 5

[0041] At room temperature, monohydrate lithium hydroxide is placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8000 ppm. It is heated at a heating rate of 3 °C / min to 900 °C, held for 5 h, naturally cooled to room temperature, and the mass percentage of the main component of the product obtained after crushing and pulverizing is 94.5% Li2O and 5.2% NiO.

[0042] The prepared Li2O, LiOH, and NiO are proportioned according to the molar ratio of Li to Ni being 2.1:1. Here, Ni includes the small amount of NiO contained in Li2O and the Ni in the added NiO. The mass ratio of Li2O to lithium hydroxide is 9.0:1. They are uniformly mixed and sintered using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. It is heated at a heating rate of 2 °C / min to 660 °C, held for 10 h, naturally cooled to room temperature, crushed, pulverized, demagnetized, and passed through a 400-mesh sieve to obtain the lithium-ion battery cathode lithium supplementing agent material Li2NiO2. Comparative Example 6

[0043] At room temperature, monohydrate lithium hydroxide is placed in a Ni crucible. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 650 ppm. It is heated at a heating rate of 3 °C / min to 900 °C, held for 5 h, and naturally cooled to room temperature. After crushing and pulverizing, the mass percentage content of the main components of the obtained product is 97.2% for Li2O and 2.5% for NiO.

[0044] The prepared Li2O and NiO are proportioned according to the molar ratio of Li to Ni being 2.1:1. Here, Ni includes the small amount of NiO contained in Li2O and the Ni in the added NiO. They are uniformly mixed and sintered using a one-stage temperature-controlled sintering method. In an atmosphere furnace, under a nitrogen protective atmosphere, the initial oxygen content in the furnace is 8 ppm. It is heated at a heating rate of 2 °C / min to 660 °C, held for 10 h, and naturally cooled to room temperature. After crushing, pulverizing, demagnetizing, and passing through a 400-mesh sieve, the lithium-ion battery cathode lithium supplementing agent material Li2NiO2 is obtained.

[0045] Test Example 1

[0046] The lithium supplementing agent material Li2NiO2 of Example 1 is selected as the lithium supplementing agent, and polycrystalline NCM811 is selected as the cathode active material. The addition amount of the lithium supplementing agent is 3 wt% of the cathode active material. The cathode active material and the lithium supplementing agent together are used as the composite cathode active material. According to the mass ratio of composite active cathode material: conductive agent SP: binder PVDF = 97:1.5:1.5, a solution with a solid content of 70% is prepared, stirred evenly to obtain the cathode slurry, coated on an aluminum foil, and assembled into a 604062 type soft-pack battery. After the soft-pack battery is prepared, conventional formation is carried out. The formation voltage is 2.75 - 4.25 V, and the charge-discharge rate is 1C.

[0047] Test Example 2

[0048] The lithium - supplementing agent material Li2NiO2 of Comparative Example 1 was selected as the lithium - supplementing agent, polycrystalline NCM811 was selected as the cathode active material, the addition amount of the lithium - supplementing agent was 3 wt% of the cathode active material, and the cathode active material and the lithium - supplementing agent together served as the composite cathode active material. According to the mass ratio of composite active cathode material: conductive agent SP: binder PVDF = 97:1.5:1.5, a solution with a solid content of 70% was prepared, stirred evenly to obtain the cathode slurry, coated on aluminum foil, and assembled into a 604062 - type soft - package battery.

[0049] After the soft - package battery was prepared, conventional formation was carried out. The formation voltage was 2.75 - 4.25 V, and the charge - discharge rate was 1C. The physical and chemical indexes and electrical performance of the cathode lithium - supplementing agent materials prepared in the examples and comparative examples were evaluated.

[0050] The purity, residual lithium, capacity, and specific surface area of the obtained cathode lithium - supplementing agent materials were evaluated by the following methods.

[0051] (1) Purity

[0052] The powder sample was placed in the sample cell and compacted, then put on the sample holder of the XRD diffractometer, and the instrument door of the XRD diffractometer was closed. The scanning range was set to 15° - 75°, the scanning speed was 15° / min, and the test was started. The test results were quantitatively analyzed using XRD analysis software to calculate the relative mass fraction of the substances contained.

[0053] (2) Residual lithium

[0054] Preparation of the sample solution: Place a 250 mL dry beaker on the analytical balance, weigh 20 g ± 0.0005 g of the lithium - supplementing agent material sample, and record this mass as m. Put a magnetic stir bar into the beaker, accurately measure 100 mL of RO water with a water temperature of 25 ± 2°C using a 100 mL graduated cylinder, slowly add it to the beaker, then seal the beaker mouth with plastic film and place it on a magnetic stirrer, stir at room temperature for 20 minutes, and filter it into a 50 mL volumetric flask within 5 minutes after the stirring ends. Rinse the funnel and volumetric flask 2 - 3 times with the filtrate, and cool to room temperature. Use a clean pipette to suck and release the filtrate to make the concave surface of the filtrate tangent to the scale line of the volumetric flask to obtain the sample solution.

[0055] Residual lithium determination: Inject 50 mL of the sample solution in the volumetric flask into a 250 mL Erlenmeyer flask. Rinse the volumetric flask three times with distilled water and transfer the rinsing solution into the Erlenmeyer flask as well. Add 1 - 2 drops of phenolphthalein indicator to the Erlenmeyer flask. Select a hydrochloric acid standard solution CHCL with an appropriate concentration to titrate the test solution until the red color completely disappears, reaching the end point of the first titration. Record the volume V1 of the hydrochloric acid standard solution consumed in the titration. Then add 4 - 5 drops of methyl red indicator to the Erlenmeyer flask and continue titrating with the hydrochloric acid standard solution until the solution changes from yellow to bright red, which is the end point of the second titration. Record the volume V2 of the hydrochloric acid standard solution consumed in the titration at this time.

[0056] The contents of Li2CO3 and LiOH are expressed in mass percentage and calculated according to the following formula:

[0057]

[0058] Where: V1---the volume of the hydrochloric acid standard solution consumed in the first titration, unit: mL;

[0059] V2---the total volume of the hydrochloric acid standard solution consumed in the two titrations, unit: mL; m---the mass of the sample, unit: g; CHCL---the molar concentration of the hydrochloric acid standard solution, unit: mol / L.

[0060] (3)Capacity

[0061] Assemble the positive electrode lithium supplement agent material into a 2016 - type button cell. The slurry formula is lithium supplement agent: conductive agent SP: binder PVDF = 9:0.5:0.5. After production, under the condition of 23°C, carry out formation at 0.1C charge - discharge and 3 - 4.3V, and the cut - off current is 0.01C.

[0062] (4)Specific surface area

[0063] Use a specific surface area tester with the nitrogen adsorption method in the flowing mode to measure BET.

[0064] Table 1 Comparison data of examples and comparative examples

[0065]

[0066] Table 2 Comparison data of test examples

[0067]

[0068] Evaluation

[0069] As can be seen from Figure 1, the lithium salt components prepared by high - temperature sintering of the lithium source with a Ni crucible in Example 1 are mainly Li2O and a small amount of NiO.

[0070] As can be seen from Table 1, compared with the cathode lithium supplement agent material prepared in Example 1, the purity and irreversible specific capacity of the cathode lithium supplement agent material prepared in Comparative Example 1 are lower, and the residual lithium is higher. This is because the Li2O prepared in Example 1 contains a small amount of NiO. The contact area between this small amount of NiO and Li2O is large, which is conducive to the reaction, improves the nucleation reaction rate of preparing the lithium supplement agent material Li2NiO2, can significantly reduce the content of impurity NiO and surface residual lithium in the product, and improve the purity and irreversible specific capacity of the lithium supplement agent Li2NiO2.

[0071] As can be seen from Table 1, compared with the cathode lithium supplement agent material prepared in Example 1, the purity and irreversible specific capacity of the cathode lithium supplement agent materials prepared in Comparative Examples 2 and 3 are lower, and the residual lithium is higher. This is because in Comparative Example 2, the temperature for high-temperature sintering the lithium source in the Ni crucible is too low, the lithium source reacts incompletely, and there is a small amount of unreacted LiOH, resulting in low purity of the prepared Li2O and low activity during mixing and sintering with the nickel source, which is not conducive to the formation of the lithium supplement agent material. In Comparative Example 3, the temperature for high-temperature sintering the lithium source in the Ni crucible is too high, and the generated Li2O reacts excessively with the Ni crucible, resulting in low purity of Li2O and low activity during subsequent mixing and sintering with the nickel source, which is not conducive to the formation of the lithium supplement agent material. Therefore, the temperature for high-temperature decomposition of the lithium source in the Ni crucible cannot be too low or too high, and it is more appropriate to control it in the range of 780 - 950 °C to obtain Li2O with higher purity.

[0072] As can be seen from Table 1, compared with the cathode lithium supplement agent material prepared in Example 1, the purity and irreversible specific capacity of the cathode lithium supplement agent materials prepared in Comparative Examples 4 and 5 are lower, and the residual lithium is higher. This is because when preparing Li2O in Comparative Example 4, the initial oxygen content in the furnace is too low, and there is basically no O2, resulting in no NiO in the decomposition product. When subsequently mixing evenly with the added nickel source and sintering at high temperature to prepare the lithium supplement agent material Li2NiO2, the nucleation reaction rate is low, which is not conducive to the reaction. When preparing Li2O in Comparative Example 5, the initial oxygen content in the furnace is too high, which promotes the oxidation reaction between the lithium source and the Ni crucible, generating more NiO, resulting in low purity of the prepared Li2O and low activity during subsequent mixing and sintering with the nickel source, which is not conducive to the formation of the lithium supplement agent. Therefore, the initial oxygen content in the furnace for high-temperature decomposition of the lithium source in the Ni crucible cannot be too low or too high, and it is more appropriate to control it in the range of 200 - 1000 ppm to obtain Li2O with higher purity.

[0073] As can be seen from Table 1, compared with the cathode lithium supplement material prepared in Example 1, the purity and irreversible specific capacity of the cathode lithium supplement material prepared in Comparative Example 6 are lower, and the residual lithium is higher. This is because lithium hydroxide was not added during the mixing in Example 6, and during the high-temperature sintering reaction, it was a pure solid-phase to solid-phase reaction, with insufficient contact between the materials and incomplete reaction. While in Example 1, a small amount of lithium hydroxide that can be melted at high temperature was added during the mixing, which is conducive to sufficient contact and reaction between the materials, resulting in a higher purity and lower residual lithium of the prepared lithium supplement material.

[0074] As can be seen from Table 2, when using the cathode lithium supplement material Li2NiO2 prepared in Example 1 of the present invention, compared with the cathode lithium supplement material in Comparative Example 1, after being applied to a soft-pack lithium-ion battery, the first charge specific capacity is significantly increased, while the first discharge specific capacity changes little. There is more available irreversible specific capacity, and the first efficiency loss rate caused by the lithium supplement is more. More lithium can be supplemented to the negative electrode, and the lithium supplement effect is very good. The lithium lost by the cathode material will be significantly reduced, which is beneficial to the subsequent cycle performance.

Claims

1. A preparation method of a high-purity cathode lithium supplement material, the chemical general formula of the lithium supplement material is Li2NiO2, characterized in that, The preparation method comprises the following steps: (1) Lithium source decomposition: At room temperature, place the lithium source in a Ni crucible. In an atmosphere furnace, under a protective atmosphere of nitrogen or argon, heat it at a certain heating rate, hold for a period of time, and then naturally cool to room temperature. After crushing and pulverizing, a product mainly composed of Li2O is obtained; (2) Mixing and sintering: Uniformly mix the product obtained in step (1) with the lithium source and nickel source, and carry out sintering. In an atmosphere furnace, under a protective atmosphere of nitrogen or argon, heat it at a certain heating rate, hold for a period of time, and then naturally cool to room temperature. Crush and pulverize; (3) Demagnetization: Demagnetize the material pulverized in step (2), and obtain the high-purity cathode lithium supplementing agent material after sieving; In step (1), heat it at a heating rate of 1-5 °C / min to 750-950 °C and hold for 2-6 h; in step (2), use a one-stage temperature control sintering method for sintering. Heat it at a heating rate of 1-3 °C / min to 600-780 °C and hold for 5-15 h; In step (1), the lithium source is one or two of lithium hydroxide and lithium hydroxide monohydrate. The initial oxygen content range in the atmosphere furnace is 200-1000 ppm. In the composition of the product obtained in step (1), by mass, 95.0% < Li2O < 99.0%, 1.0% < NiO < 3.5%; In step (2), the mass ratio of Li2O in the product of step (1) used to LiOH in the lithium source for mixing is (8.8-9.5):

1. At the same time, the molar ratio of the total Li of Li2O in the product of step (1) and LiOH in the lithium source for mixing in step (2) to the total Ni in the mixture is (2.0-2.3):1, where the total Ni includes a small amount of NiO in step (1) and Ni in the nickel source added in step (2); In step (2), the oxygen content in the atmosphere furnace < 10 ppm, and the lithium source in step (2) is one or two of lithium hydroxide and lithium hydroxide monohydrate.

2. The preparation method of a high-purity cathode lithium supplement material according to claim 1, characterized in that, The nickel source is one or more of nickel oxide, nickel sesquioxide or nickel hydroxide.

3. The preparation method of a high-purity cathode lithium supplement material as described in claim 1, characterized in that, In step (3), the mesh number of the sieve used for sieving is 350-400 meshes, the average particle size D50 is 8.5-18.0 μm, and the content of magnetic substances after demagnetization < 50 ppb; the purity of the lithium supplementing agent material > 95%, the total residual lithium content < 3%, the average particle size D50 is 8.5-18.0 μm, and the specific surface area is 0.22-0.80 m² / g.

Images