Double-coated lithium supplementing material, preparation method thereof, positive electrode sheet and battery

Abstract

The application belongs to the technical field of batteries, and provides a double-layer coated lithium supplementing material, a preparation method thereof, a positive electrode sheet and a battery, the double-layer coated lithium supplementing material comprising a core, a silicon nitride coating layer and a carbon coating layer; the silicon nitride coating layer is located on the surface of the core, and the carbon coating layer is located on the surface of the side of the silicon nitride coating layer away from the core; the core comprises lithium-rich lithium iron oxide and / or lithium-rich lithium nickelate. The lithium supplementing material in the application is coated with a silicon nitride layer first and then a carbon layer, thereby avoiding the reaction between carbon and the core substance, and at the same time, the carbon coating layer is used to enhance the electronic conductivity of the lithium supplementing material, inhibit the reaction between the lithium supplementing material and environmental moisture, and improve the processing performance of the positive electrode slurry, thereby solving the problems of poor conductivity and low environmental stability of the lithium supplementing material and poor stability of the positive electrode slurry after the addition of the lithium supplementing material.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a double-layer coated lithium replenishment material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium-ion batteries are currently the fastest-growing new energy storage technology. To meet the lifespan of energy storage systems of more than 20 years, the cycle life of lithium-ion cells is usually required to be more than 10,000 cycles, while the cycle life of conventional lithium iron phosphate cells is less than 8,000 cycles. Therefore, existing technologies use pre-lithiation technology to improve the cycle life of cells. Specifically, this involves storing a portion of lithium at the negative electrode to compensate for the lithium consumption caused by the repair of the SEI (solid electrolyte interface) during cycling.

[0003] Currently, commonly used lithium replenishment materials include lithium iron ferrite (such as Li5FeO4) and lithium nickel ferrite (such as Li2NiO2), which have high irreversible capacity characteristics. After the initial charge and lithium removal, a certain amount of lithium can be stored at the negative electrode. Adding only 2-3% can improve the cycle life of the cell by more than 20%, demonstrating a very significant lithium replenishment effect. However, in practical applications, lithium iron ferrite and lithium nickel ferrite have poor conductivity, requiring a very small current, such as 0.01C, to remove lithium ions during charging, which also prolongs the formation time, greatly affecting production capacity and cost. In addition, the surface of lithium replenishment materials has a lot of residual alkali, which easily reacts with water in the air, causing changes in its surface structure. It usually requires an ambient dew point below -30°C and is prone to PVDF (polyvinylidene fluoride) denaturation, causing slurry gelation. It needs to be coated as soon as possible, otherwise there is a risk of clogging the slurry channels.

[0004] To improve the conductivity of lithium iron phosphate and lithium nickel phosphate supplementary materials, carbon or oxides are typically coated onto the surface of the materials. Carbon coatings offer good conductivity and lithium-ion conductivity, and also provide moisture barrier properties, improving slurry stability. A conventional method for carbon coating involves mixing organic carbon sources such as glucose with the supplementary material followed by high-temperature pyrolysis. However, carbon readily reacts with the supplementary material at high temperatures, causing structural changes that can affect the material's electrical properties. Furthermore, if the heat treatment temperature is not high enough, the conductivity of the supplementary material is low, the carbon coating is incomplete, and the surface is not adequately protected, leading to easy gelation of the slurry. While oxide coatings can protect the material surface, they generally employ solid-phase mixing methods, resulting in incomplete coatings and difficulty in controlling the coating thickness.

[0005] Based on the above research, there is a need to provide a lithium replenishment material with good conductivity, high stability, and the ability to improve the stability of electrode slurry. Summary of the Invention

[0006] The purpose of this invention is to provide a double-layer coated lithium replenishment material and its preparation method, a positive electrode sheet, and a battery. The lithium replenishment material is prepared by first coating a silicon nitride layer and then coating a carbon layer, which avoids the reaction between carbon and the core material. At the same time, the carbon coating layer enhances the electronic conductivity of the lithium replenishment material, inhibits its reaction with environmental moisture, and improves the processing performance of the positive electrode slurry. This solves the problems of poor conductivity, low environmental stability, and poor stability of the positive electrode slurry after adding the lithium replenishment material.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a double-layer coated lithium replenishment material, the double-layer coated lithium replenishment material comprising a core, a silicon nitride coating layer and a carbon coating layer.

[0009] The silicon nitride coating is located on the surface of the core, and the carbon coating is located on the surface of the silicon nitride coating away from the core.

[0010] The core comprises lithium iron ferrite rich in lithium and / or lithium nickel ferrite rich in lithium.

[0011] In some embodiments, the thickness of the silicon nitride coating layer is 0.5 nm to 5 nm.

[0012] In some embodiments, the thickness of the carbon coating layer is 1 nm to 10 nm.

[0013] In some embodiments, the kernel's particle size D50 is 1 μm-10 μm.

[0014] In a second aspect, the present invention provides a method for preparing a double-layer coated lithium-replenishing material as described in the first aspect, the method comprising the following steps:

[0015] A silicon nitride cladding layer is prepared on the surface of the core.

[0016] A carbon coating layer is then prepared on the surface of the silicon nitride coating layer to obtain the double-coated lithium supplement material.

[0017] In some embodiments, a silicon nitride coating layer is prepared using the PECVD method.

[0018] In some embodiments, the deposition temperature for preparing the silicon nitride coating is 150°C-400°C.

[0019] In some embodiments, the deposition atmosphere for preparing the silicon nitride coating includes a silicon source gas, a nitrogen source gas, and an inert gas.

[0020] In some embodiments, the deposition power for preparing the silicon nitride coating is 300-1500W, the deposition pressure is 50-300Pa, and the deposition time is 0.1-1h.

[0021] In some embodiments, the carbon coating layer is prepared using the PECVD method.

[0022] In some embodiments, the deposition temperature for preparing the carbon coating is 150°C-400°C.

[0023] In some embodiments, the deposition atmosphere for preparing the carbon coating layer includes a carbon source gas and an inert gas.

[0024] In some embodiments, the deposition power for preparing the carbon coating is 300-1500W, the deposition pressure is 50-300Pa, and the deposition time is 0.5-5h.

[0025] In some embodiments, after the silicon nitride coating layer is prepared, the gas used to prepare the silicon nitride coating layer is stopped, the vacuum is evacuated to below 1 Pa, and then carbon source gas and inert gas are introduced to prepare the carbon coating layer.

[0026] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a double-layer coated lithium replenishing material as described in the first aspect, or comprising a double-layer coated lithium replenishing material prepared by the preparation method described in the second aspect.

[0027] Fourthly, the present invention provides a battery comprising a positive electrode as described in the third aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The lithium replenishment material of this invention, through double-layer coating, not only improves conductivity but also prevents the carbon coating layer from reacting with the core, thereby improving its capacity utilization in the battery. Under the same charging rate conditions, such as at 0.1C, the charging capacity can be increased by up to 55%. At the same time, it also improves the stability of the positive electrode slurry. For example, the positive electrode slurry containing the uncoated lithium replenishment material has basically no fluidity after standing for 24 hours in a 5% humidity environment, while the positive electrode slurry containing the double-coated lithium replenishment material of this invention can still have good fluidity after standing for 24 hours in a 5%-10% humidity environment.

[0030] In addition, the vapor phase coating method of the double-layer coated lithium replenishment material described in this invention has a good coating effect, and the PECVD used is a mature production equipment in the semiconductor industry, which has strong controllability and is easy to achieve large-scale batch preparation. Attached Figure Description

[0031] Figure 1This is a schematic diagram of the structure of the double-layer coated lithium replenishment material described in this invention.

[0032] Figure 2 This is a flowchart of the preferred preparation method described in this invention.

[0033] Figure 3 This is a TEM image of the double-layer coated lithium replenishment material described in Embodiment 1 of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0035] In a first aspect, the present invention provides a double-layer coated lithium replenishment material, the double-layer coated lithium replenishment material comprising a core, a silicon nitride coating layer and a carbon coating layer;

[0036] The silicon nitride coating is located on the surface of the core, and the carbon coating is located on the surface of the silicon nitride coating away from the core;

[0037] The core comprises lithium iron ferrite rich in lithium and / or lithium nickel ferrite rich in lithium.

[0038] A schematic diagram of the structure of the double-layer coated lithium replenishment material of the present invention is shown below. Figure 1 As shown, it includes a core 1, a silicon nitride coating layer 2 on the surface of the core 1, and a carbon coating layer 3 on the side of the silicon nitride coating layer 2 away from the core 1.

[0039] This invention employs lithium iron phosphate and / or lithium nickel phosphate as the core, with a double-layer coating on its surface. The coating directly covering the core surface is a silicon nitride coating, and the coating on the surface of the silicon nitride coating is a carbon coating. This isolates the carbon coating from the core, preventing reaction between the carbon and the core material. Simultaneously, the outermost carbon coating enhances the electronic conductivity of the lithium replenishment material, inhibits the reaction between the core and moisture in the environment, and improves the processing performance of the lithium replenishment material after being added to the positive electrode slurry. Furthermore, the silicon nitride coating not only prevents the carbon coating from directly contacting the core and reacting, thus not affecting the function of the lithium replenishment material and the carbon coating, but also further inhibits the reaction between external moisture and the lithium replenishment material, improving the stability of the lithium replenishment material.

[0040] For example, the general chemical formula of the lithium iron ferrite rich in this invention is Li. a Fe bO4, wherein 4.4 ≤ a ≤ 5.6, for example, it can be 4.4, 4.6, 4.8, 5.0, 5.2, 5.4 or 5.6, and 0.8 ≤ b ≤ 1.2, for example, it can be 0.8, 0.9, 1.0, 1.1 or 1.2; the general chemical formula of the lithium-rich nickel oxide is Li. c Ni d O2, where 1.8≤c≤2.2, for example, can be 1.8, 1.9, 2.0, 2.1 or 2.2, and 0.8≤d≤1.2, for example, can be 0.8, 0.9, 1.0, 1.1 or 1.2, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0041] For example, the general chemical formula of silicon nitride in this invention is Si. x N y , where x>0, y>0, such as Si3N4.

[0042] In one specific embodiment, the thickness of the silicon nitride coating layer is 0.5nm-5nm, for example, it can be 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm or 5nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] The core of the present invention is covered with an ultra-thin silicon nitride coating layer. If the silicon nitride coating layer is too thick, it will lead to a decrease in the rate performance of the material. If the silicon nitride coating layer is too thin, it cannot form a continuous and complete coating layer and cannot play a role in protecting the core material. Therefore, in order to ensure that the double-coated lithium supplement material can play its optimal role, the thickness of the silicon nitride coating layer is preferably 0.5nm-5nm.

[0044] In one specific embodiment, the thickness of the carbon coating layer is 1nm-10nm, for example, it can be 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] The thickness of the carbon coating layer described in this invention affects the conductivity, stability, and lithium ion extraction performance of the lithium replenishment material. This invention preferably uses a carbon coating layer within a specific range to further improve the performance of the double-coated lithium replenishment material.

[0046] In one specific embodiment, the particle size D50 of the core is 1μm-10μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] The particle size D50 of the core described in this invention is within a specific range, which is beneficial for lithium ion extraction and coating layer preparation, thereby further improving the performance of the double-coated lithium replenishment material.

[0048] In a second aspect, the present invention provides a method for preparing a double-layer coated lithium-replenishing material as described in the first aspect, the method comprising the following steps:

[0049] A silicon nitride coating layer is prepared on the surface of the core.

[0050] A carbon coating layer is then prepared on the surface of the silicon nitride coating layer to obtain the double-coated lithium supplement material.

[0051] In one specific embodiment, a silicon nitride coating layer is prepared using PECVD (plasma-enhanced chemical vapor deposition).

[0052] This invention uses PECVD to prepare silicon nitride and carbon coating layers, which can improve the uniformity and density of the coating layers, and the thickness of the coating layers is easy to control. Furthermore, the continuous preparation of silicon nitride and carbon coating layers can be achieved by changing the deposition gas.

[0053] In one specific embodiment, the deposition temperature for preparing the silicon nitride coating is 150℃-400℃, for example, it can be 150℃, 200℃, 250℃, 300℃, 350℃ or 400℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0054] The present invention prepares the silicon nitride coating at a lower temperature, which can better avoid the reaction between the coating material and the core lithium replenishment material and ensure the performance of the core lithium replenishment material. However, if the deposition temperature is too low, it will affect the reaction formation of silicon nitride.

[0055] In one specific embodiment, the deposition atmosphere for preparing the silicon nitride coating includes a silicon source gas, a nitrogen source gas, and an inert gas.

[0056] For example, the silicon source gas includes SiH4, the nitrogen source gas includes ammonia, and the inert gas includes argon, although nitrogen may also be used as the inert gas. The deposition atmosphere for preparing the silicon nitride coating may include 5-15 vol% of silicon source gas (e.g., 5 vol%, 8 vol%, 10 vol%, 12 vol%, or 15 vol%), 5-15 vol% of nitrogen source gas (e.g., 5 vol%, 8 vol%, 10 vol%, 12 vol%, or 15 vol%), and 70-90 vol% of inert gas (e.g., 70 vol%, 75 vol%, 80 vol%, 85 vol%, or 90 vol%).

[0057] In one specific embodiment, the deposition power for preparing the silicon nitride coating is 300-1500W, for example, 300W, 500W, 700W, 900W, 1100W, 1300W or 1500W; the deposition pressure is 50-300Pa, for example, 50Pa, 100Pa, 150Pa, 200Pa, 250Pa or 300Pa; and the deposition time is 0.1-1h, for example, 0.1h, 0.3h, 0.5h, 0.7h, 0.9h or 1h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] In one specific embodiment, the carbon coating layer is prepared using PECVD (plasma-enhanced chemical vapor deposition).

[0059] In one specific embodiment, the deposition temperature for preparing the carbon coating layer is 150℃-400℃, for example, it can be 150℃, 200℃, 250℃, 300℃, 350℃ or 400℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0060] Similarly, the present invention also prepares the carbon coating layer at a lower temperature to further avoid the reaction between the coating material and the core lithium replenishment material.

[0061] In one specific embodiment, the deposition atmosphere for preparing the carbon coating layer includes a carbon source gas and an inert gas.

[0062] Exemplarily, the carbon source gas includes any one or a combination of at least two of methane, ethane, acetylene, ethylene, or propylene, and the inert gas includes argon, which may also be replaced by nitrogen; exemplarily, the deposition atmosphere for preparing the carbon coating may include 5-15 vol% of the carbon source gas (e.g., 5 vol%, 8 vol%, 10 vol%, 12 vol%, or 15 vol%) and 85-95 vol% of the inert gas (e.g., 85 vol%, 88 vol%, 90 vol%, 92 vol%, 94 vol%, or 95 vol%).

[0063] In one specific embodiment, the deposition power for preparing the carbon coating layer is 300-1500W, for example, 300W, 500W, 700W, 900W, 1100W, 1300W or 1500W; the deposition pressure is 50-300Pa, for example, 50Pa, 100Pa, 150Pa, 200Pa, 250Pa or 300Pa; and the deposition time is 0.5-5h, for example, 0.5h, 1h, 1.5h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] In one specific embodiment, after the silicon nitride coating layer is prepared, the gas for preparing the silicon nitride coating layer is stopped, and the vacuum is evacuated to below 1 Pa, for example, 1 Pa, 0.5 Pa, 0.3 Pa or 0.1 Pa. Then, carbon source gas and inert gas are introduced to prepare the carbon coating layer.

[0065] The silicon nitride coating and carbon coating described in this invention are both prepared by PECVD. The continuous preparation of the silicon nitride coating and carbon coating can be achieved by changing the gas introduced, thereby shortening the preparation process and saving steps.

[0066] As a preferred technical solution of the preparation method described in this invention, the flowchart is as follows: Figure 2 As shown, it includes the following steps:

[0067] S1: Provides the kernel.

[0068] S2: Using the PECVD method, silicon source gas, nitrogen source gas and inert gas are introduced to coat silicon nitride on the core surface to obtain a core@silicon nitride coating layer.

[0069] S3: Using the PECVD method, carbon source gas and inert gas are introduced to continue coating carbon on the surface of the core@silicon nitride coating layer, resulting in a core@silicon nitride coating layer@carbon coating layer, which is the double-coated lithium supplement material.

[0070] As a further preferred technical solution of the preparation method of the present invention, the method includes the following steps:

[0071] S1: Place the core in the crucible, and then place the crucible on the substrate in the PECVD equipment cavity.

[0072] S2: Evacuate the PECVD equipment to below 1 Pa and heat the substrate to 150℃-400℃.

[0073] S3: Introduce silicon source, nitrogen source and inert gas, ignite plasma, maintain power in the range of 300-1500W, maintain reaction pressure in the range of 50-300Pa, and after reaction for 0.1-1h, obtain silicon nitride coating layer.

[0074] S4: Stop the gas supply and evacuate to below 1 Pa.

[0075] S5: Introduce carbon source gas, maintain reaction pressure at 50-300 Pa, ignite plasma, maintain power in the range of 300-1500 W, and react for 0.5-5 hours.

[0076] S6: Stop the gas supply, evacuate, turn off the plasma, stop heating, and when the substrate temperature drops below 100°C, introduce nitrogen gas to bring the cavity to atmospheric pressure. Remove the powder material from the crucible to obtain the double-layer coated lithium replenishment material.

[0077] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a double-layer coated lithium replenishing material as described in the first aspect, or comprising a double-layer coated lithium replenishing material prepared by the preparation method described in the second aspect.

[0078] The double-layer coated lithium replenishing material of the present invention is directly added to the positive electrode slurry for use. The amount added is 2wt%-3wt% of the total mass of the positive electrode slurry excluding the solvent. That is, the content of the double-layer coated lithium replenishing material in the active layer of the positive electrode sheet is 2wt%-3wt%.

[0079] Fourthly, the present invention provides a battery (such as a lithium-ion battery) comprising a positive electrode as described in the third aspect.

[0080] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0081] Example 1

[0082] This embodiment provides a double-layer coated lithium replenishment material, which includes a core with a particle size D50 of 5 μm, a silicon nitride coating layer with a thickness of 2 nm, and a carbon coating layer with a thickness of 5 nm. The core is Li5FeO4, the silicon nitride coating layer is located on the surface of the core, and the carbon coating layer is located on the surface of the silicon nitride coating layer away from the core.

[0083] The preparation method of the double-layer coated lithium replenishment material includes the following steps:

[0084] (1) Place 100g of the core in a clean crucible, and then place the crucible on the substrate in the PECVD equipment cavity.

[0085] (2) Adjust the substrate height to place the sample in the plasma reaction area, evacuate the reaction chamber to 1 Pa, and heat the substrate to 250°C.

[0086] (3) Introduce a mixed gas including 5 vol% SiH4, 5 vol% NH3 and 90 vol% argon, ignite the plasma, maintain the radio frequency power in the range of 1000W, maintain the reaction pressure in the range of 100Pa, and after reacting for 10 minutes, obtain the silicon nitride coating layer.

[0087] (4) Stop the gas supply and evacuate to 1 Pa.

[0088] (5) Introduce a mixed gas consisting of 5 vol% acetylene and 95 vol% argon, maintain the reaction pressure at 100 Pa, ignite the plasma, maintain the radio frequency power within the range of 500 W, and react for 0.5 hours.

[0089] (6) Stop the gas supply, turn off the plasma, stop heating, and when the substrate temperature drops to 80°C, introduce nitrogen gas to bring the cavity to normal pressure. Take out the powder material from the crucible to obtain the double-layer coated lithium replenishment material.

[0090] The TEM image of the double-layer coated lithium replenishment material described in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that there are silicon nitride coating and carbon coating on the core surface.

[0091] Example 2

[0092] This embodiment provides a double-layer coated lithium replenishment material, which includes a core with a particle size D50 of 10 μm, a silicon nitride coating layer with a thickness of 1.5 nm, and a carbon coating layer with a thickness of 1 nm. The core is Li2NiO2, the silicon nitride coating layer is located on the surface of the core, and the carbon coating layer is located on the surface of the silicon nitride coating layer away from the core.

[0093] The preparation method of the double-layer coated lithium replenishment material includes the following steps:

[0094] (1) Place 100g of the core in a clean crucible, and then place the crucible on the substrate in the PECVD equipment cavity.

[0095] (2) Adjust the substrate height to place the sample in the plasma reaction area, evacuate the reaction chamber to 0.5 Pa, and heat the substrate to 400 °C.

[0096] (3) A mixed gas consisting of 5 vol% SiH4, 5 vol% NH3 and 90 vol% argon is introduced, the plasma is ignited, the radio frequency power is maintained in the range of 300W, the reaction pressure is maintained in the range of 300Pa, and after the reaction is carried out for 0.1h, a silicon nitride coating layer is obtained.

[0097] (4) Stop the gas supply and evacuate to 1 Pa.

[0098] (5) Introduce a mixed gas consisting of 5 vol% methane and 95 vol% argon, maintain the reaction pressure at 50 Pa, ignite the plasma, maintain the radio frequency power within the range of 300 W, and react for 1 hour.

[0099] (6) Stop the gas supply, turn off the plasma, stop heating, and when the substrate temperature drops to 100°C, introduce nitrogen gas to bring the cavity to normal pressure. Take out the powder material from the crucible to obtain the double-layer coated lithium replenishment material.

[0100] Example 3

[0101] This embodiment provides a double-layer coated lithium replenishment material, which includes a core with a particle size D50 of 1 μm, a silicon nitride coating layer with a thickness of 5 nm, and a carbon coating layer with a thickness of 10 nm. The core is Li5FeO4, the silicon nitride coating layer is located on the surface of the core, and the carbon coating layer is located on the surface of the silicon nitride coating layer away from the core.

[0102] The preparation method of the double-layer coated lithium replenishment material includes the following steps:

[0103] (1) Place 100g of the core in a clean crucible, and then place the crucible on the substrate in the PECVD equipment cavity.

[0104] (2) Adjust the substrate height to place the sample in the plasma reaction area, evacuate the reaction chamber to less than 1 Pa, and heat the substrate to 150°C.

[0105] (3) A mixed gas consisting of 15 vol% SiH4, 15 vol% NH3 and 70 vol% argon is introduced, the plasma is ignited, the radio frequency power is maintained in the range of 1500W, the reaction pressure is maintained in the range of 50Pa, and after 1 hour of reaction, a silicon nitride coating layer is obtained.

[0106] (4) Stop the gas supply and evacuate to below 1 Pa.

[0107] (5) Introduce a mixed gas consisting of 15 vol% acetylene and 85 vol% argon, maintain the reaction pressure at 300 Pa, ignite the plasma, maintain the radio frequency power within the range of 1500 W, and react for 5 hours.

[0108] (6) Stop the gas supply, turn off the plasma, stop heating, and when the substrate temperature drops to 50°C, introduce nitrogen gas to bring the cavity to normal pressure. Take out the powder material from the crucible to obtain the double-layer coated lithium replenishment material.

[0109] Example 4

[0110] This embodiment provides a double-layer coated lithium replenishment material, which is the same as that in Embodiment 1 except that the thickness of the silicon nitride coating layer is 0.5 nm.

[0111] Example 5

[0112] This embodiment provides a double-layer coated lithium replenishment material, which is the same as that in Embodiment 1 except that the thickness of the silicon nitride coating layer is 0.1 nm.

[0113] Example 6

[0114] This embodiment provides a double-layer coated lithium replenishment material, which is the same as that in Embodiment 1 except that the thickness of the silicon nitride coating layer is 7 nm.

[0115] Example 7

[0116] This embodiment provides a double-layer coated lithium replenishment material. Except for step (2) of its preparation method, in which the substrate is heated to 100°C to change the adaptability of the obtained double-layer coated lithium replenishment material, the rest is the same as in Example 1.

[0117] Example 8

[0118] This embodiment provides a double-layer coated lithium replenishment material. Except for step (2) of its preparation method, in which the substrate is heated to 450°C to change the adaptability of the obtained double-layer coated lithium replenishment material, the rest is the same as in Example 1.

[0119] Comparative Example 1

[0120] This comparative example provides a lithium replenishing material, wherein the lithium replenishing material is Li5FeO4 with a particle size D50 of 5 μm.

[0121] Comparative Example 2

[0122] This comparative example provides a lithium replenishment material, which is the same as that in Example 1 except that it does not include a silicon nitride coating layer.

[0123] The preparation method of the lithium replenishment material described in this comparative example is the same as that in Example 1, except that steps (3) and (4) for preparing the silicon nitride coating layer are not performed.

[0124] The positive electrode slurry was formed by thoroughly mixing 2 wt% of the lithium supplement material obtained from the above examples and comparative examples, 94 wt% of lithium iron phosphate, 2 wt% of carbon black, and 2 wt% of PVDF with solvent NMP. The static viscosity of the positive electrode slurry was measured at 0 h, 2 h, 4 h, 8 h, and 24 h under a 5% humidity environment. The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] The above-mentioned positive electrode slurry (freshly prepared) was then used to make a positive electrode sheet, which was then combined with a graphite negative electrode, a PE separator, and a lithium hexafluorophosphate electrolyte to prepare a 2Ah battery cell. The cell was charged to 4.1V at a current of 0.1C. The initial charge capacity and the charge capacity of the lithium iron phosphate battery (Example 2 shows the charge capacity of lithium nickel oxide) are shown in Table 2.

[0128] Table 2

[0129]

[0130] As can be seen from Tables 1 and 2:

[0131] As shown in Examples 1-3 and Comparative Example 1, the present invention, through the double-layer coating of silicon nitride and carbon, can improve the stability of the positive electrode slurry and possess a higher charging capacity. As shown in Examples 1-3 and Comparative Example 2, the present invention, through the silicon nitride coating layer, can prevent the core material from reacting with the carbon coating layer, thereby preventing the lithium replenishment material from underperforming. As shown in Examples 1 and Examples 4-6, the present invention preferably uses a thinner silicon nitride coating layer to avoid affecting the performance of the lithium replenishment material, but the thickness of the silicon nitride coating layer should not be too thin to ensure that it performs optimally. As shown in Examples 1 and Examples 7-8, the present invention preferably prepares the silicon nitride coating layer and the carbon coating layer at a specific temperature to ensure the smooth deposition of the coating layer and prevent the core material from reacting with the coating material, thereby further improving the stability and electrochemical performance of the lithium replenishment material.

[0132] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A double-layer coated lithium replenishment material, characterized in that, The double-layered lithium replenishment material includes a core, a silicon nitride coating layer, and a carbon coating layer; The silicon nitride coating is located on the surface of the core, and the carbon coating is located on the surface of the silicon nitride coating away from the core; The core comprises lithium iron ferrite rich in lithium and / or lithium nickel ferrite rich in lithium. The thickness of the silicon nitride coating layer is 0.5nm-5nm; the silicon nitride coating layer separates the carbon coating layer from the core to prevent carbon from reacting with the core material.

2. The double-layer coated lithium replenishment material according to claim 1, characterized in that, The thickness of the carbon coating layer is 1 nm to 10 nm; And / or, the particle size D50 of the kernel is 1μm-10μm.

3. A method for preparing a double-layer coated lithium-supplementing material as described in claim 1, characterized in that, The preparation method includes the following steps: A silicon nitride coating layer is prepared on the surface of the core; A carbon coating layer is then prepared on the surface of the silicon nitride coating layer to obtain the double-coated lithium supplement material.

4. The preparation method according to claim 3, characterized in that, Silicon nitride coating was prepared using PECVD. And / or, the deposition temperature for preparing the silicon nitride coating is 150℃-400℃; And / or, the deposition atmosphere for preparing the silicon nitride coating includes a silicon source gas, a nitrogen source gas, and an inert gas.

5. The preparation method according to claim 4, characterized in that, The deposition power for preparing the silicon nitride coating is 300-1500W, the deposition pressure is 50-300Pa, and the deposition time is 0.1-1h.

6. The preparation method according to claim 3, characterized in that, Carbon coatings were prepared using PECVD. And / or, the deposition temperature for preparing the carbon coating is 150℃-400℃; And / or, the deposition atmosphere for preparing the carbon coating includes a carbon source gas and an inert gas; And / or, the deposition power for preparing the carbon coating is 300-1500W, the deposition pressure is 50-300Pa, and the deposition time is 0.5-5h.

7. The preparation method according to claim 3, characterized in that, After the silicon nitride coating layer is prepared, the gas used to prepare the silicon nitride coating layer is stopped. After the vacuum is reduced to below 1 Pa, carbon source gas and inert gas are introduced to prepare the carbon coating layer.

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes the double-layer coated lithium replenishing material as described in claim 1 or 2, or the double-layer coated lithium replenishing material prepared by the preparation method described in any one of claims 3-7.

9. A battery, characterized in that, The battery includes the positive electrode as described in claim 8.

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