Silicate modified ternary positive electrode material and preparation and application thereof

Abstract

The invention discloses a silicate modified ternary positive electrode material and preparation and application thereof, and belongs to the technical field of ternary lithium battery positive electrode materials, the preparation method comprises the following steps: dissolving sodium metasilicate in a sodium hydroxide solution, adding NixCoyMn (1-x-y) (OH) 2 (0.5 < = x < = 0.6, 0.1 < y < 0.4) into the sodium metasilicate solution, uniformly mixing, drying, and sintering to obtain a modified precursor; and mixing the modified precursor with a lithium source, controlling the molar ratio of Li to Me to be (1.03-1.05): 1, calcining, cooling, and grinding. SiO4 < 4-> is introduced into tetrahedral vacancies between the transition metal layer and the Li layer of the positive electrode material, so that the NCM is endowed with a stable bulk phase structure and an interface structure, and the electrochemical performance of the NCM with medium Ni content is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of ternary lithium battery cathode material technology, specifically to a silicate-modified ternary cathode material and its preparation and application. Background Technology

[0002] Lithium-ion batteries (LIBs) are a crucial component of electric vehicles and energy storage systems. In recent years, much research has focused on improving LIB performance. Traditional LIB cathode materials, such as LiCoO2 (LCO), suffer from drawbacks such as high cost, high toxicity, and low capacity, and numerous research efforts are underway to overcome these shortcomings. Among these, LiNiO2 (LNO), possessing the same structure as LCO, exhibits advantages such as high specific capacity, high stability, and good electrochemical reversibility, making it an increasingly attractive cathode material. However, non-stoichiometric reactivity, irreversible phase transition, and byproduct gases generated during charging / discharging limit the practical application prospects of LNO.

[0003] Modified LNO, including LiNi x Co y Mn z O2 (NCM ternary cathode, where x+y+z=1) and Ni-rich layered NCM (x+y+z=1, x≥0.6) (nrNCM) are environmentally friendly cathode materials with high energy density and have been studied to overcome the aforementioned limitations of LNO. The energy density of NCM ternary cathode materials can be increased by utilizing more Li ions at higher cutoff voltages or by increasing the Ni content in the material. However, nrNCM with a Ni content greater than 80% typically exhibits reduced capacity retention and thermal stability because anisotropic volume changes in the secondary particles during the H2-H3 phase transition during charge and discharge lead to microcrack formation. These microcracks create electrolyte permeation channels, resulting in unstable and reactive Ni. 4+ It reacts with the electrolyte to form a NiO layer, which accelerates the degradation of primary particles and capacity decay in the positive electrode.

[0004] NCM522 and NCM622 with moderate Ni content are considered promising cathode materials due to their ease of synthesis, enhanced energy density, and high cutoff voltage. However, NCMs with moderate Ni content exhibit poor electrochemical stability because, at higher operating voltages, residual Li decomposes and oxygen is released from the lattice due to structural degradation. Furthermore, inherent impurities in NCM (such as LiOH and Li₂CO₃) promote gas evolution via Li₂CO₃ decomposition at high voltages. Considering that the residual Li and Ni content is a key factor in gas evolution, surface modification of NCM using various doping materials is necessary to improve the electrochemical performance of the cathode, necessitating the preparation of ternary cathode materials with high electrochemical stability. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this invention provides a new silicate-modified NCM ternary cathode material and its preparation method for NCM with medium Ni content, aiming to improve the interfacial stability between the cathode material and the electrolyte, so as to enhance the electrochemical performance of LIB cathode.

[0006] In a first aspect, the present invention provides a method for preparing a silicate-modified ternary cathode material, comprising the following steps: S1. Dissolve sodium metasilicate in sodium hydroxide solution, maintain the pH of the solution at 10.5-12.0, and make the concentration of sodium metasilicate 0.02-0.05 mol / L; S2. Add nickel-cobalt-manganese hydroxide to the solution obtained in step S1 to make the solid-liquid ratio 1g:(15-30)mL, mix well, dry and sinter to obtain the modified precursor; the nickel-cobalt-manganese hydroxide is Ni x Co y Mn (1-x-y) (OH)2, where 0.5≤x≤0.6, 0.1<y<0.4; S3. The modified precursor is mixed with a lithium source, and the molar ratio of Li:Me (representing the total number of moles of Ni, Co, and Mn) is controlled to be (1.03-1.05):1. After calcination, cooling and grinding are performed to obtain the silicate-modified ternary cathode material.

[0007] In the above preparation method, sodium metasilicate is selected from anhydrous sodium metasilicate (Na2SiO3), sodium metasilicate pentahydrate (Na2SiO3·5H2O), and sodium metasilicate nonahydrate (Na2SiO3·9H2O). Sodium metasilicate undergoes a hydrolysis reaction in aqueous solution. This invention maintains the pH of the solution to allow the monomeric silicate ions (SiO4) to undergo a hydrolysis reaction. 4- It exists stably in the environment, avoiding condensation into polysilicic acid or colloids.

[0008] Further, in step S2, the product is dried at 80-120°C.

[0009] Further, in step S2, the sintering conditions are: sintering at 420-480℃ for 8-12 hours. This invention achieves SiO4… 4- Embedded within the structure, avoiding its mere presence on the surface.

[0010] Furthermore, the lithium source is lithium hydroxide.

[0011] Further, in step S3, the calcination conditions are as follows: heating to 880-920°C in an atmosphere furnace at a heating rate of 5-10°C / min, and maintaining at this temperature for 14-18 hours, wherein the atmosphere inside the atmosphere furnace is a flowing air atmosphere.

[0012] Secondly, this invention provides a silicate-modified ternary cathode material, which is obtained by the preparation method provided by this invention. Compared to unmodified NCM, this invention uses SiO4. 4- Doping with NCM alters surface chemistry, restricts particle growth in one direction, and reduces Li ion diffusion distance to promote Li ion mobility and improve the rate capability of the NCM cathode; furthermore, SiO4... 4- The doping on the surface of NCM particles also introduces a Li4SiO4 layer with high ionic conductivity, preventing direct contact between the electrode and the electrolyte, reducing side reactions of residual Li and Ni in the NCM particles, and decreasing the synthesis of residual alkaline substances on the material surface, thus reducing interfacial impedance and improving rate performance. This special dual-modification structural design endows NCM with a stable bulk and interfacial structure, significantly improving its electrochemical performance.

[0013] Thirdly, based on the silicate-modified ternary cathode material provided by this invention, at least the following products also fall within the scope of protection of this invention: A positive electrode sheet containing the silicate-modified ternary positive electrode material described in this invention; A secondary battery comprising the aforementioned positive electrode plate; An electrical device comprising the aforementioned secondary battery.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention introduces SiO4 into the tetrahedral vacancies between the transition metal layer and the Li layer of the cathode material. 4- This effectively improves the electrochemical performance of NCMs with moderate Ni content. Specifically, on the one hand, by adding an appropriate amount of SiO4... 4-In its presence, primary grain growth is suppressed, and lithium-ion diffusion channels are shortened. On the other hand, a Li4SiO4 protective layer forms on the surface, reducing residual alkali (such as Li2CO3) and suppressing side reactions between the cathode and electrolyte, thus enhancing rate performance and capacity retention. Furthermore, the synthesis process of the silicate-modified ternary cathode material in this invention is simple. Therefore, the present invention has good commercialization potential and economic benefits. Attached Figure Description

[0015] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0016] Figure 1 This is a flowchart illustrating the preparation process of the silicate-modified ternary cathode material in this invention. Figure 2 This is a SEM image of the silicate-modified ternary cathode material in this invention; Figure 3 This is a diagram showing the SEM-EDS elemental analysis results of the silicate-modified ternary cathode material in this invention; Figure 4 The graph shows the electrochemical performance test results of the silicate-modified ternary cathode material in this invention. The left graph shows the change in discharge capacity with the number of cycles (0.2C), and the right graph shows the discharge capacity test results at different rates. Detailed Implementation

[0017] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art; the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the invention.

[0019] Medium-Ni content NCM is considered a promising cathode material due to its ease of synthesis, enhanced energy density, and high cutoff voltage; however, it often exhibits poor electrochemical stability. To address this issue, this invention provides a silicate-modified ternary cathode material, its preparation, and its application. This is achieved by introducing SiO4 into the tetrahedral vacancies between the transition metal layer and the Li layer of the cathode material. 4- This endows NCM with a stable bulk and interfacial structure, thereby significantly improving its electrochemical performance.

[0020] Please refer to Figure 1 This invention provides a method for preparing silicate-modified ternary cathode materials, comprising the following steps: (1) Preparation of modified solution: Dissolve sodium hydroxide in water and make the pH 10.5-12.0, dissolve sodium metasilicate in sodium hydroxide solution and keep the pH of the solution between 10.5-12.0, and the concentration of Na2SiO3 is 0.02-0.05mol / L; (2) Precursor modification: Ni cobalt manganese hydroxide (Ni x Co y Mn (1-x-y) (OH)2, 0.5≤x≤0.6, 0.1<y<0.4) was added to the above modified solution, mixed well, dried and sintered to obtain the modified precursor; (3) Preparation of cathode material: The modified precursor is mixed with lithium hydroxide, and the molar ratio of Li:Me (total molar number of Ni, Co, Mn) is controlled to be (1.03-1.05):1; the mixture is calcined in an atmosphere furnace, and after calcination, heating is stopped, the mixture is cooled, and ground to obtain cathode material.

[0021] Furthermore, in some embodiments, the drying temperature in step (2) is 80-120°C, and the sintering conditions are: sintering at 420-480°C for 8-12 hours.

[0022] Further, in some embodiments, the calcination conditions in step (3) are: heating to 880-920°C in an atmosphere furnace at a heating rate of 5-10°C / min, and maintaining at this temperature for 14-18 hours, wherein the atmosphere inside the atmosphere furnace is a flowing air atmosphere.

[0023] Compared to cathode materials obtained by directly calcining a mixture of precursor and lithium hydroxide, the electrical performance of the silicate-modified ternary cathode material prepared by the method of this invention is significantly improved.

[0024] This invention also provides a positive electrode sheet and a secondary battery containing the positive electrode sheet, wherein the material of the positive electrode sheet includes the above-mentioned silicate-modified ternary positive electrode material, conductive agent, binder, aluminum foil, etc.

[0025] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0026] Example 1 This example demonstrates the preparation of a silicate-modified ternary cathode material, the preparation process of which is as follows: (1) Preparation of modified solution.

[0027] Sodium hydroxide was dissolved in water to make the pH 11. Anhydrous sodium metasilicate was dissolved in the sodium hydroxide solution and the pH of the solution was maintained between 10.5 and 12.0. The concentration of Na2SiO3 was 0.03 mol / L.

[0028] (2) Precursor modification, Nickel-cobalt-manganese hydroxide (Ni 0.55 Co 0.20 Mn 0.25 (OH)2) was added to the above modified solution to make the solid-liquid ratio 1:15 (g:mL), stirred evenly at room temperature, and then dried at 80℃. After drying, it was placed in a muffle furnace and sintered at 450℃ for 10h to obtain the modified precursor.

[0029] (3) Preparation of cathode material.

[0030] The modified precursor was thoroughly mixed with lithium hydroxide, and the molar ratio of Li:Me (total molar number of Ni, Co, Mn) was controlled to be 1.05:1. The mixture was placed in an atmosphere furnace and heated to 900°C at a heating rate of 10°C / min. Then, it was kept at this temperature for 18 hours. The entire calcination process was carried out in a flowing compressed air atmosphere. After calcination was completed, heating was stopped and the mixture was cooled. After grinding, the final cathode material was obtained.

[0031] Example 2 This example prepares a silicate-modified ternary cathode material. Unlike Example 1, the nickel-cobalt-manganese hydroxide used in this example is specifically Ni... 0.55 Co 0.25 Mn 0.20 (OH)2.

[0032] Example 3 This example prepares a silicate-modified ternary cathode material. Unlike Example 1, in this example, the solid-liquid ratio in the nickel-cobalt-manganese hydroxide modified solution is 1:30 (g:mL).

[0033] Comparative Example 1 This example demonstrates the preparation of a ternary cathode material, and the preparation process is as follows: Precursor (Ni) 0.55 Co 0.20 Mn 0.25Lithium hydroxide (LiOH)₂ is thoroughly mixed with lithium hydroxide, and the molar ratio of Li to Me (total molar amounts of Ni, Co, and Mn) is controlled at 1.05:1. The mixture is placed in an atmosphere furnace and heated to 900°C at a heating rate of 5-10°C / min, and then held at this temperature for 18 hours. The entire calcination process is carried out in a flowing compressed air atmosphere. After calcination is completed, heating is stopped and the mixture is cooled. After grinding, the cathode material is obtained.

[0034] Example 4 This example provides a positive electrode and a secondary battery.

[0035] The preparation method of the positive electrode sheet is as follows: First, 90% of the positive electrode material, 7% of acetylene black (conductive agent) and 3% of polyvinylidene fluoride (PVDF) (binder) are thoroughly mixed and stirred for 4 hours. The resulting slurry is uniformly coated on aluminum foil and dried in a vacuum oven at 120°C for 12 hours. Then, the dried aluminum foil is perforated into a disc with a diameter of 12 mm.

[0036] The above-mentioned positive electrode, lithium metal sheet (negative electrode) and electrolyte are assembled into a coin cell in an argon-filled glove box. The electrolyte is obtained by dissolving 1 mol / L lithium hexafluorophosphate (LiPF6) in a mixture of ethyl carbonate (EC) and dimethyl carbonate (DMC) (EC∶DMC = 1∶1 volume ratio).

[0037] Test and Result Analysis: 1. Surface morphology and elemental analysis.

[0038] The surface morphology of the cathode materials obtained in Comparative Example 1 and Example 1 was observed by scanning electron microscopy, and the results are as follows: Figure 2 As shown, the upper figure shows the cathode material prepared in Example 1, and the lower figure shows the cathode material prepared in Example 2. From... Figure 2 It can be seen that the primary grains in Example 1 are significantly smaller than those in the control example.

[0039] Furthermore, the cathode material obtained in Example 1 was analyzed by SEM-EDS, and the results are shown in (see...). Figure 3 The surface layer is mainly composed of Si and O elements.

[0040] 2. Electrochemical detection.

[0041] First, the positive electrode materials prepared in Example 1 and Comparative Example 1 were used to prepare corresponding positive electrode sheets and coin cells according to the method in Example 4. Then, the cycle performance and rate performance of the coin cells were tested on a battery testing system using a constant current method at various current densities within the range of 2.5-4.35V. All electrochemical measurements were performed at room temperature. The results are shown in Table 1 and... Figure 2 As shown.

[0042] Table 1. Electrical performance of coin cells obtained with different cathode materials (0.2C)

[0043] exist Figure 2 In the left graph, the horizontal axis represents the number of charge-discharge cycles, and the vertical axis represents the discharge capacity. It can be seen that the capacity of Example 1 decreases at a significantly slower rate with increasing cycle count compared to the control example. Similarly, the horizontal and vertical axes of the right graph are the same, and the five stages in the curve represent different charge-discharge rates (speeds).

[0044] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing a silicate-modified ternary cathode material, characterized in that, Includes the following steps: S1. Dissolve sodium metasilicate in sodium hydroxide solution, maintain the pH of the solution at 10.5-12.0, and make the concentration of sodium metasilicate 0.02-0.05 mol / L; S2. Add nickel-cobalt-manganese hydroxide to the solution obtained in step S1 to make the solid-liquid ratio 1g:(15-30)mL, mix well, dry and sinter to obtain the modified precursor; the nickel-cobalt-manganese hydroxide is Ni x Co y Mn (1-x-y) (OH)2, where 0.5≤x≤0.6, 0.1<y<0.4; S3. The modified precursor is mixed with a lithium source, and the molar ratio of Li:Me is controlled to be (1.03-1.05):

1. After calcination, cooling and grinding are performed to obtain the silicate-modified ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The sodium metasilicate is selected from anhydrous sodium metasilicate, sodium metasilicate pentahydrate, and sodium metasilicate nonahydrate.

3. The preparation method according to claim 1, characterized in that, In step S2, the product is dried at 80-120°C.

4. The preparation method according to claim 1, characterized in that, In step S2, the sintering conditions are: sintering at 420-480℃ for 8-12 hours.

5. The preparation method according to claim 1, characterized in that, The lithium source is lithium hydroxide.

6. The preparation method according to claim 1, characterized in that, In step S3, the calcination conditions are as follows: heating to 880-920°C in an atmosphere furnace at a heating rate of 5-10°C / min, and maintaining at this temperature for 14-18 hours, wherein the atmosphere inside the atmosphere furnace is a flowing air atmosphere.

7. The silicate-modified ternary cathode material prepared by the preparation method according to any one of claims 1-6.

8. A positive electrode sheet, characterized in that, It includes the silicate-modified ternary cathode material as described in claim 7.

9. A secondary battery, characterized in that, It contains the positive electrode sheet as described in claim 8.

10. An electrical device, characterized in that, It contains the secondary battery as described in claim 9.

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