A preparation method of lithium nitride

Abstract

This invention relates to a method for preparing lithium nitride. By ball milling the initial lithium nitride material in a mixed atmosphere of nitrogen and argon in a specific ratio, the mass ratio of α-Li3N to β-Li3N in lithium nitride can be controlled within the range of (95-60):(5-40), thereby reducing the reactivity of lithium nitride itself and improving its stability in air. At the same time, when lithium nitride is added as a positive electrode lithium replenishment additive in the positive electrode material of lithium-ion batteries, lithium nitride exhibits the characteristics of low decomposition potential and high decomposition rate during the first charge cycle. Only a very small amount of lithium nitride is needed to compensate for the active lithium consumed during the formation of the SEI film. Lithium nitride has high compatibility and lithium replenishment performance in the positive electrode material of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a method for preparing lithium nitride. Background Technology

[0002] During the first charge and discharge cycle of a lithium-ion battery, the electrolyte decomposes, forming a solid electrolyte interphase (SEI) film on the negative electrode surface. This process consumes active lithium ions in the battery, converting them into lithium carbonate, lithium fluoride, and alkyl lithium components within the SEI, resulting in low coulombic efficiency and capacity reduction in the first cycle. To address these issues, researchers have proposed lithium replenishment technologies for lithium-ion batteries. Currently, lithium replenishment technologies for lithium-ion batteries are mainly divided into two processes: negative electrode replenishment and positive electrode replenishment. Due to safety and cost considerations, positive electrode replenishment has received widespread attention compared to negative electrode replenishment, leading to the application of positive electrode replenishment additives. Lithium nitride is a promising positive electrode replenishment agent. However, lithium nitride itself has high reactivity, poor stability in air, and its decomposition potential and decomposition rate require further improvement. Summary of the Invention

[0003] In view of the problems existing in the background art, the present invention provides a method for preparing lithium nitride. The lithium nitride prepared by this method has high stability in air, low decomposition potential, and high decomposition rate.

[0004] Specifically, the method for preparing lithium nitride provided by the present invention includes the following steps:

[0005] Lithium metal is nitrided to obtain the initial lithium nitride material;

[0006] The initial lithium nitride material was ball-milled in a mixed atmosphere of nitrogen and argon to obtain a lithium nitride product, wherein the flow rate ratio of nitrogen to argon was (5-40):(95-60).

[0007] This invention ball-mills the initial lithium nitride material in a mixed atmosphere of nitrogen and argon in a specific ratio. This allows the mass ratio of α-Li3N to β-Li3N in lithium nitride to be controlled within the range of (95-60):(5-40), thereby reducing the reactivity of lithium nitride itself, improving its stability in air, lowering the decomposition potential of lithium nitride, increasing the decomposition rate, and thus improving its compatibility and lithium replenishment performance in lithium-ion battery cathode materials.

[0008] In addition, the lithium nitride obtained by the preparation method of the present invention has high purity (over 98%), small particle size (D50 particle size can be 1-10 μm) and uniform particle size distribution.

[0009] In particular, by adjusting the preparation parameters, the present invention can preferably control the mass ratio of α-Li3N to β-Li3N in lithium nitride at (90-70):(10-30), which is more conducive to improving the stability of lithium nitride in air, while reducing the decomposition potential of lithium nitride and increasing the decomposition rate.

[0010] In some embodiments, the flow rate ratio of nitrogen to argon can be (5-40):(95-60), for example, 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, or 40:60. Optimizing the flow rate ratio of nitrogen to argon helps to further control the mass ratio of α-Li3N and β-Li3N in lithium nitride within a preferred range, thereby further reducing the reactivity of lithium nitride itself, improving its stability in air, and simultaneously lowering the decomposition potential of lithium nitride, thus increasing the decomposition rate.

[0011] In some specific embodiments, the flow rate ratio of nitrogen to argon can be (10-30):(90-70).

[0012] In some embodiments, the ball milling speed can be 100-1000 rpm. The ball milling speed directly affects the mechanical force collision; if the speed is too high, α-Li3N is prone to phase transition, forming β-Li3N. By controlling the ball milling speed within the above range, it is beneficial to control the mass ratio of α-Li3N to β-Li3N in lithium nitride within a suitable range, thus maintaining the characteristics of low decomposition potential and high capacity while reducing the high reactivity of lithium nitride.

[0013] In some specific embodiments, the rotational speed of the ball mill can be 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm.

[0014] In some preferred embodiments, the ball milling speed can be 450-800 rpm, for example, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, and 800 rpm. Optimizing the ball milling speed helps to further reduce the reactivity of lithium nitride, improve its stability in air, and simultaneously lower the decomposition potential of lithium nitride, thereby increasing the decomposition rate.

[0015] In some embodiments, the ball milling time can be 0.5-25 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, or 25 h, preferably 1-12 h. Optimizing the ball milling time within the above range is beneficial for the preparation of lithium nitride with small and uniform particle size distribution, and also beneficial for preparing α-Li3N and β-Li3N products with the target mass ratio. If the ball milling time is too short, sufficient ball milling cannot be achieved, which is detrimental to the phase transformation of α-Li3N and β-Li3N in lithium nitride; if the ball milling time is too long, the temperature inside the ball mill is too high, the proportion of the β phase in the target product is too high, and the reactivity is too low.

[0016] In this invention, the ball milling time is the effective operating time of the ball mill, excluding the downtime during intermittent operation.

[0017] In some embodiments, the ball-to-material ratio can be (1-50):1, for example, 1:1, 5:1, 10:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1, preferably (15-25):1. In this invention, the ball-to-material ratio refers to the ratio of the weight of the grinding balls to the weight of the initial lithium nitride material. By controlling the ball-to-material ratio within the above range, it is beneficial to form lithium nitride with small particle size and uniform distribution.

[0018] In some embodiments, the diameter of the grinding balls used in the ball milling process can be 0.1–20 mm, for example, one or more combinations of 0.3 mm, 0.5 mm, 1 mm, 3 mm, 5 mm, 8 mm, 10 mm, 15 mm, and 20 mm. By controlling the diameter of the grinding balls within the above range, it is beneficial to improve ball milling efficiency, reduce ball milling time, and improve the particle size uniformity of lithium nitride products.

[0019] In some embodiments, the preparation of the initial lithium nitride material includes: nitriding the metallic lithium at 0-60°C in a nitrogen-containing atmosphere for 1-72 hours, pulverizing it, and then calcining it in a nitrogen-containing atmosphere.

[0020] This invention employs a method of low-temperature nitriding, followed by pulverization and calcination to prepare the initial lithium nitride material. This method avoids introducing other impurities, improves the purity of the initial lithium nitride material, and consequently improves the purity of the final lithium nitride product. High-purity lithium nitride is beneficial for reducing the decomposition potential and increasing the decomposition capacity. Compared to methods that directly calcine metallic lithium to prepare lithium nitride, this invention avoids the problem of metallic lithium readily reacting with reactors, crucibles, and other equipment under high-temperature conditions, thereby introducing impurities.

[0021] In some specific embodiments, the nitriding temperature may be, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C. Controlling the nitriding temperature within these ranges facilitates thorough nitriding. If the temperature is too low, the nitriding rate of metallic lithium is slow; if the temperature is too high, metallic lithium readily reacts with other metallic elements or non-metallic materials in the lithium metal, reducing the purity of lithium nitride.

[0022] Nitriding methods can be selected from natural nitriding or nitriding after surface treatment of lithium metal. Surface treatment of lithium metal before nitriding is preferred, as it can accelerate the nitriding rate and improve the nitriding yield of lithium metal. "Natural nitriding" refers to directly placing lithium metal in a nitrogen-containing atmosphere at 20-30°C for nitriding without heating.

[0023] In some specific embodiments, the nitriding time may be, for example, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, 55 h, 60 h, 65 h, 70 h, or 72 h. The nitriding time is related to the nitriding temperature; the higher the nitriding temperature, the shorter the corresponding nitriding time.

[0024] In some specific embodiments, the nitrogen-containing atmosphere includes a mixture of nitrogen and argon or nitrogen gas, preferably nitrogen gas.

[0025] In some specific embodiments, the lithium metal may be one or more of lithium powder, lithium strip, lithium sheet, lithium ingot, lithium rope, and lithium alloy.

[0026] In some specific embodiments, the pulverization is carried out in an inert atmosphere. The inert atmosphere may be nitrogen, argon, or a mixture thereof. The pulverization may be performed by grinding, crushing, ball milling, sand milling, etc.

[0027] In some specific embodiments, the calcination temperature can be 100-900℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, or 900℃. The ratio of α-Li3N to β-Li3N in lithium nitride is related to the calcination temperature; the higher the temperature, the higher the proportion of α-Li3N; the lower the temperature, the lower the proportion of α-Li3N. The calcination time can be 1-25 hours, for example, 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, or 25 hours. The calcination time is related to the calcination temperature; the higher the calcination temperature, the shorter the corresponding calcination time.

[0028] By controlling the calcination temperature and calcination time within the above range, it is beneficial to control the ratio of α-Li3N and β-Li3N in lithium nitride within a suitable range, thereby further reducing the reactivity of lithium nitride itself, improving its stability in air, and simultaneously reducing the decomposition potential of lithium nitride and increasing the decomposition rate.

[0029] Preferably, the calcination temperature can be 100-150℃ and the time can be 20-25h.

[0030] The lithium nitride prepared by the method of this invention can be used as a positive electrode lithium supplement additive in lithium-ion batteries. Specifically, during the positive electrode slurry preparation process, the lithium nitride is mixed uniformly with positive electrode active material, conductive agent, binder and solvent, and then coated, rolled and dried to prepare the positive electrode sheet.

[0031] The mass fraction of lithium nitride in the positive electrode active material layer is 0.1% to 5%.

[0032] The positive electrode active material includes, but is not limited to, at least one of NCM, NCA, LiFePO4, LiCoO2 and LiMnO2, wherein NCM is a nickel-cobalt-manganese ternary positive electrode material and NCA is a nickel-cobalt-aluminum ternary positive electrode material.

[0033] The conductive agent includes, but is not limited to, one or more of carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene.

[0034] The adhesive includes, but is not limited to, one or more of polyvinylidene fluoride, polyvinyl alcohol, polyvinylidene fluoride resin, and polytetrafluoroethylene.

[0035] The solvents include, but are not limited to, one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and tetrahydrofuran.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention provides a method for preparing lithium nitride. By ball milling the initial lithium nitride material in a mixed atmosphere of nitrogen and argon in a specific ratio, the mass ratio of α-Li3N to β-Li3N in lithium nitride can be controlled within the range of (95-60):(5-40), thereby reducing the reactivity of lithium nitride and improving its stability in air. At the same time, when lithium nitride is added as a positive electrode lithium replenishment additive in the positive electrode material of lithium-ion batteries, lithium nitride exhibits the characteristics of low decomposition potential and high decomposition rate during the first charge cycle. Only a very small amount of lithium nitride is needed to compensate for the active lithium consumed during the formation of the SEI film. Lithium nitride has high compatibility and lithium replenishment performance in the positive electrode material of lithium-ion batteries.

[0038] In addition, the lithium nitride obtained by the preparation method of the present invention has high purity, small particle size and uniform particle size distribution. Attached Figure Description

[0039] Figure 1 This is the X-ray diffraction (XRD) pattern of lithium nitride prepared in Example 1.

[0040] Figure 2 This is a scanning electron microscope (SEM) image of the lithium nitride prepared in Example 1. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. In the embodiments, unless otherwise specified, the raw materials used are commercially available, and the methods used in the following embodiments are conventional methods in the art unless otherwise specified.

[0042] Preparation of lithium nitride

[0043] Example 1

[0044] Inside a nitrogen glove box, 50g of lithium sheet was weighed. The surface coating of the lithium sheet was broken by external force. Nitrification was carried out at 25℃ for 20 hours, and the lithium sheet turned blackish-red, indicating the initial reaction that produced lithium nitride material, which was relatively hard. The lithium nitride material was ground in a mortar for 30 minutes and then transferred to a nitrogen tube furnace for calcination at 100℃ for 25 hours to obtain red lithium nitride, which was the initial lithium nitride material. 3mm milling beads were selected, with a ball-to-material ratio of 20:1. The milling atmosphere was selected as nitrogen:argon flow rate ratio of 15:85, and the milling speed was 700 rpm. The milling process was repeated 6 times: 10 minutes of operation followed by a 5-minute rest period (i.e., the total milling time was 1 hour). The product was collected and sieved through a 400-mesh sieve. The undersize material was used as a lithium-ion battery positive electrode additive.

[0045] Figure 1 The XRD pattern of the lithium nitride product prepared in this embodiment is shown. After refinement of the XRD characterization results, it can be analyzed that the lithium nitride material obtained in Example 1 has a purity of 99.2%, mainly composed of α-Li3N and β-Li3N, with no lithium hydroxide, lithium carbonate, or lithium oxide impurities present. The ratio of α-Li3N to β-Li3N is 84:16.

[0046] Figure 2 The scanning electron microscope (SEM) image of the lithium nitride product prepared in this embodiment is shown, exhibiting a uniform particle size distribution. Particle size analysis was performed using a laser particle size analyzer, and the D0 of the lithium nitride product was determined to be... 50 The particle size is 2.51 μm.

[0047] Examples 2-7

[0048] Lithium nitride was prepared according to the method described in Example 1, except that the nitrogen:argon flow rate ratio selected for the ball milling atmosphere was different from that in Example 1, as shown in Table 1 below.

[0049] Table 1

[0050]

[0051] Examples 8-14

[0052] Lithium nitride was prepared according to the method described in Example 1, except that the ball milling speed was different from that in Example 1, as shown in Table 2 below.

[0053] Table 2

[0054]

[0055] Examples 15-19

[0056] Lithium nitride was prepared according to the method described in Example 1, except that the ball milling time was different from that in Example 1, as shown in Table 3 below.

[0057] Table 3

[0058]

[0059] Examples 20-25

[0060] Lithium nitride was prepared according to the method described in Example 1, except that the ball-to-material ratio was different from that in Example 1, as shown in Table 4 below.

[0061] Table 4

[0062]

[0063] Example 26

[0064] Lithium nitride was prepared according to the method described in Example 1, except that the preparation method of the initial lithium nitride material differed from that in Example 1. Specifically, 50g of lithium sheet was weighed and placed in a nitrogen tube furnace, calcined at 200°C for 20 hours to obtain red lithium nitride, which was the initial lithium nitride material. The D50 particle size of the lithium nitride product was determined to be 2.65μm, and the purity was 85%. XRD data analysis detected the formation of lithium oxide and lithium hydroxide. The mass ratio of α-Li3N to β-Li3N in the lithium nitride product was determined to be 69:31.

[0065] Examples 27-29

[0066] Lithium nitride was prepared according to the method described in Example 1, except that the nitriding temperature and nitriding time of the lithium sheet were different from those in Example 1 after the coating was destroyed, as shown in Table 5.

[0067] Table 5

[0068]

[0069] Examples 30-32

[0070] Lithium nitride was prepared according to the method described in Example 1, except that the calcination temperature and time were different from those in Example 1, as shown in Table 6.

[0071] Table 6

[0072]

[0073] Comparative Examples 1-4

[0074] Lithium nitride was prepared according to the method described in Example 1, except that the ball milling atmosphere was different from that in Example 1, as shown in Table 7 below.

[0075] Table 7

[0076]

[0077]

[0078] The lithium nitride prepared in the examples and comparative examples were used to prepare lithium iron phosphate half-cells containing lithium nitride with cathode materials, wherein the amount of lithium nitride material was 2% of the total mass of the cathode active material, and the relevant electrochemical performance was tested.

[0079] Preparation of lithium iron phosphate half-cells containing lithium nitride

[0080] 1.96g of lithium iron phosphate was dispersed in an appropriate amount of N,N-dimethylformamide (DMF). After stirring and mixing thoroughly, 0.04g of lithium nitride, 0.0526g of polyvinylidene fluoride (PVDF) binder (added as a PVDF-DMF gel), and 0.0526g of conductive agent SP were added. Homogenization continued until the slurry had good fluidity, yielding the positive electrode slurry. Aluminum foil was used as the positive electrode current collector. Lithium foil was used as the negative electrode. After coating, drying, and assembly, a half-cell was formed.

[0081] Preparation of pure lithium iron phosphate half-cells (without lithium nitride)

[0082] 2g of lithium iron phosphate was dispersed in an appropriate amount of DMF and stirred until homogeneous. Then, 0.0526g of PVDF binder (added as a slurry formed by PVDF and DMF) and 0.0526g of SP conductive agent were added, and homogenization continued until the slurry had good fluidity, yielding the positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and lithium foil was used as the negative electrode. The slurry was then coated, dried, and assembled into a half-cell.

[0083] Half-cell performance test

[0084] 1. First-round lithium nitride delithiation count test

[0085] The charge / discharge tests of the two types of half-cells were conducted on the Blue Battery testing system. The charge / discharge voltage was 2.0-4.5V, and the charge / discharge rate was 0.05C. The specific capacity of the first charge / discharge cycle was tested, and the number of lithium nitride delithiations in the first cycle was calculated according to the following formula:

[0086] First-cycle lithium nitride delithiation count = (First-cycle charging specific capacity of lithium iron phosphate half-cell containing lithium nitride - First-cycle charging specific capacity of lithium iron phosphate half-cell) * 3 / (Lithium nitride addition amount * Theoretical capacity of lithium nitride)

[0087] The theoretical capacity of lithium nitride is 2309 mAh / g.

[0088] The test results are shown in Table 8 below.

[0089] 2. Lithium nitride decomposition potential test

[0090] Half-cell charge-discharge tests were conducted on the Blue Battery testing system. The charge-discharge voltage ranged from 2.0 to 4.5V, and the charge-discharge rate was 0.05C. The first charging plateau and the capacity change of the lithium iron phosphate half-cell after adding lithium nitride were observed, and the lithium nitride decomposition potential was obtained. The test results are shown in Table 8 below.

[0091] 3. Air stability test

[0092] Inside a fume hood, 1g of lithium nitride was weighed from each of the different samples and exposed to air. The mass change of lithium nitride was recorded every 15 minutes for 2 hours. Samples with a mass change <0.015g / 15min were rated as excellent; those with a mass change ≤0.015g / 15min <0.025g / 15min were rated as good; those with a mass change ≤0.025g / 15min <0.035g / 15min were rated as fair; and those with a mass change >0.035g / 15min were rated as poor. The test results are shown in Table 8 below.

[0093] Table 8

[0094]

[0095] Comparative examples and comparative cases show that the present invention can control the mass ratio of α-Li3N to β-Li3N in lithium nitride within the range of (95-60):(5-40), particularly within the range of (90-70):(10-30), thereby reducing the reactivity of lithium nitride and improving its stability in air. Simultaneously, it lowers the decomposition potential of lithium nitride (≤4.1V) and increases the decomposition rate, achieving a first-cycle lithium nitride delithiation count of over 2.2. Only a very small amount (≤3%) of lithium nitride is needed to compensate for the active lithium consumed in SEI film formation. The decomposition release products are active lithium and nitrogen gas, which can be released outside the battery during the formation stage, significantly improving the stability and safety performance of the lithium-ion battery system.

[0096] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing lithium nitride, characterized in that, Includes the following steps: Lithium metal was nitrided in a nitrogen atmosphere at 0-60℃ for 1-72 hours, pulverized, and then calcined in a nitrogen atmosphere to nitrid the lithium metal, thus obtaining the initial lithium nitride material. The initial lithium nitride material was ball-milled in a mixed atmosphere of nitrogen and argon to obtain a lithium nitride product, wherein the flow rate ratio of nitrogen to argon was (5-40):(95-60). The ball mill rotates at a speed of 100-1000 rpm; The ball milling time is 0.5-25 hours; The ball-to-material ratio is (1-50):

1.

2. The preparation method according to claim 1, characterized in that, The flow rate ratio of nitrogen to argon is (10-30):(90-70).

3. The preparation method according to claim 1, characterized in that, The ball mill rotates at a speed of 450-800 rpm.

4. The preparation method according to claim 1 or 2, characterized in that, The ball milling time is 1-12 hours.

5. The preparation method according to claim 1 or 2, characterized in that, The ball-to-material ratio is (15-25):

1.

6. The preparation method according to claim 1, characterized in that, The calcination temperature is 100-900℃ and the time is 1-25h.

7. The preparation method according to claim 6, characterized in that, The calcination temperature is 100-150℃ and the time is 20-25h.

8. The preparation method according to claim 1, characterized in that, The nitrogen-containing atmosphere includes a mixture of nitrogen and argon or nitrogen gas alone.

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