Doping-coating synergistic lithium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a lithium ion battery cathode material with a doping-coating synergistic effect and a preparation method thereof. The lithium ion battery cathode material is a MoB-doped NCM811 material obtained by directly introducing MoB into a high nickel cathode material NCM811 by a solid phase sintering method; the MoB-doped NCM811 material comprises: a Mo-doped layered NCM811 material, and a LiTM x B y O z The coating layer is coated on the surface of the Mo-doped layered NCM811 material; wherein x, y, and z satisfy 1+x+y=z / 2, and TM represents a transition metal element. The present invention uses MoB to achieve "one-time modification and double optimization". On the one hand, Mo is doped into the layered NCM811 material to reduce the internal lithium-nickel ion mixing phenomenon of the material. On the other hand, the B element forms LiTM on the surface of the NCM811 material. x B y O z The coating layer reduces the rock salt phase on the surface of the traditional NCM811 material, enhances the structural stability of the positive electrode material, and achieves a joint improvement in high specific capacity and long cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery positive electrode material with synergistic doping and coating and a preparation method thereof. Background Art

[0002] As one of the most widely used energy storage systems, lithium-ion batteries have shown great development potential in the fields of electric vehicles, consumer electronics and renewable energy storage. x Co y Mn z O2) has become a particularly popular cathode material in lithium-ion batteries due to its high energy density, good cycle stability, and relatively low cost. With the rapid expansion of the electric vehicle market and the increasing demand for longer driving range, the research and development of NCM811 materials has received widespread attention. However, the widespread application of NCM811 materials still faces several challenges. First, while the high nickel content improves energy density, it also places higher demands on the material's stability and safety. Second, the intermixing of transition metal (TM) ions and lithium ions in NCM811 can cause a series of problems, including electrode capacity fading, reduced structural stability, and decreased electrical conductivity. This intermixing can make it difficult for lithium ions to insert and deinsert, resulting in a reduction in reversible capacity, which in turn affects the battery's energy density and cycle retention. Summary of the Invention

[0003] In view of this, the present invention proposes a lithium-ion battery positive electrode material with a doping-coating synergistic effect and a preparation method thereof. By introducing molybdenum boride (MoB) into the high-nickel positive electrode material NCM811, the MoB doping-coating synergistic effect is achieved in the modification of the high-nickel positive electrode material of the lithium-ion battery, so as to solve the problems of mixed arrangement, capacity reduction and cycle attenuation existing in the above-mentioned prior art.

[0004] According to one aspect of the present invention, a doping-coating synergistic lithium-ion battery cathode material is proposed, wherein the lithium-ion battery cathode material is a MoB-doped NCM811 material obtained by directly introducing MoB into a high-nickel cathode material NCM811 by a solid-phase sintering method; the MoB-doped NCM811 material comprises: a Mo-doped layered NCM811 material, and a LiTM x B y O z The coating layer is coated on the surface of the Mo-doped layered NCM811 material; wherein x, y, and z satisfy 1+x+y=z / 2, and TM represents a transition metal element.

[0005] Furthermore, the transition metal element is Mo.

[0006] Furthermore, the Mo-doped layered NCM811 material has a uniformly distributed spherical particle structure inside. The spherical particle structure is a secondary grain composed of primary grains, and the particle size is 3-5 microns.

[0007] According to another aspect of the present invention, a method for preparing the aforementioned lithium-ion battery positive electrode material is also proposed, comprising: mixing MoB and high-nickel positive electrode material NCM811 in a predetermined proportion, and then performing solid-phase sintering using a two-step temperature-raising calcination method to obtain the MoB-doped NCM811 material.

[0008] Furthermore, the high nickel cathode material NCM811 is a mixture of LiOH·H2O and Ni i Co j Mn k (OH)2 is used as raw material, mixed and calcined according to a preset ratio, and the chemical formula is LiNi i Co j Mn k O2; where i+j+k=1.

[0009] Furthermore, the amount of MoB used is 0.2 wt% to 0.4 wt% of the high nickel positive electrode material NCM811, preferably 0.3 wt%.

[0010] Furthermore, the solid phase sintering includes: first calcining the mixture of the MoB and the high nickel positive electrode material NCM811 in a first temperature range, and then heating it to a second temperature range for calcination.

[0011] Furthermore, the first temperature range is 400-600° C., and the second temperature range is 750-900° C.; the calcination time in the first temperature range is 3-6 hours, and the calcination time in the second temperature range is 9-12 hours.

[0012] Furthermore, the calcination process in the first temperature range includes: calcination at 500° C. for 4 hours; and the calcination process in the second temperature range includes: calcination at 780° C. for 11 hours.

[0013] Furthermore, the solid phase sintering is performed in an oxygen atmosphere.

[0014] The beneficial effects of the technical solution of the present invention are reflected in the following aspects: the lithium-ion battery positive electrode material with synergistic doping and coating proposed in the above technical solution of the present invention is a modified MoB-doped NCM811 material obtained by directly introducing MoB into the traditional high-nickel positive electrode material NCM811 through a solid-phase sintering method. The doping modification of MoB reduces the lithium-nickel ion mixing phenomenon inside the traditional NCM811 material under the action of Mo doping; at the same time, the B element forms LiTM on the surface of the NCM811 material. x By O z The coating reduces the rock salt phase structure on the surface of the traditional NCM811 material, enhancing the structural stability of the cathode material and achieving both high specific capacity (≥200 mAh / g@1C) and long-cycle stability (capacity retention ≥81% after 200 cycles). In other words, by introducing MoB in a single step, this invention avoids the introduction of anionic impurities, achieving a "single modification, dual optimization" effect. This also addresses the key issue of capacity reduction and cycle attenuation caused by the dual modification of doping and coating in high-nickel cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of MoB-doped NCM811 material (denoted as NCM-MoB) obtained by directly introducing MoB into high-nickel positive electrode material NCM811 through a solid-phase sintering method in an embodiment of the present invention.

[0016] Figure 2 1 and 2 are XRD patterns of the existing NCM811 material and the NCM-MoB material of the embodiment of the present invention.

[0017] Figure 3 These are scanning electron microscope images of the existing NCM811 material and the NCM-MoB material of the embodiment of the present invention before cycling.

[0018] Figure 4 It is the scanning electron microscope spectrum of the existing NCM811 material and the NCM-MoB material of the embodiment of the present invention after cycling.

[0019] Figure 5 1 is a transmission electron microscope image of the NCM-MoB material according to an embodiment of the present invention.

[0020] Figure 6 1 is a cycle life diagram of the NCM-MoB material according to an embodiment of the present invention.

[0021] Figure 7 It is a magnification diagram of the NCM-MoB material of an embodiment of the present invention.

[0022] Figure 8 1 is a long cycle life graph of the NCM-MoB material according to an embodiment of the present invention.

[0023] Figure 9 Graph showing the lithium ion diffusion coefficient of the NCM-MoB material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings, specific implementation methods, and examples, which are provided for the purpose of illustration only and are not intended to be limiting.

[0025] The present invention adopts a high-temperature solid-phase calcination method to design and synthesize a lithium-ion battery positive electrode material with a doping-coating synergistic effect, as follows:

[0026] Sample 1 (control group): LiOH·H2O and Ni i Co j Mn k (OH)2 is used as raw material, mixed in appropriate proportions and calcined to synthesize the benchmark material NCM811, the chemical formula of which is LiNi i Co j Mn k In some specific embodiments, LiOH·H2O raw material and Ni i Co j Mn k The ratio of (OH)2 raw materials is 1.03:1. In some embodiments, i≈0.8, j≈k≈0.1, and i+j+k=1. For example, i can take a value between 0.7 and 0.9, j can take a value between 0.05 and 0.15, and k can take a value between 0.05 and 0.15.

[0027] Sample 2 (introduction of MoB): Based on the NCM811 material of sample 1, molybdenum boron (MoB) was introduced and mixed and calcined, wherein the amount of MoB accounted for 0.3wt% of the amount of NCM811 material, to obtain MoB-doped NCM811 material.

[0028] Specifically, in this embodiment of the present invention, the process of preparing sample 2 includes:

[0029] 1) LiOH·H2O and Ni i Co j Mn k (OH)2 is used as raw material, mixed and calcined in proportion to obtain the benchmark material NCM811, the chemical formula of which is LiNi i Co j Mn k O2; i≈0.8, j≈k≈0.1, i+j+k=1.

[0030] 2) Based on the NCM811 material, MoB is introduced for mixed calcination. Specifically, a two-step high-temperature solid-phase sintering method is adopted, including: mixing MoB and NCM811 materials, and then calcining them at 500°C for 4 hours, and then heating to 780°C for 11 hours to obtain the lithium-ion battery positive electrode material of the present invention - MoB-doped NCM811 material.

[0031] It should be noted that in the above-mentioned high-temperature solid-phase sintering process, the temperatures of the two-stage calcination are not limited to 500°C and 780°C, and the calcination time is not limited to 4 hours and 11 hours. They can fluctuate around these values. For example, the first stage can be kept in the temperature range of 400-600°C, the calcination time can be 3-6 hours, and it can be carried out in an oxygen atmosphere; the second stage can be kept in the temperature range of 750-900°C, the calcination time can be 9-12 hours, and it can be carried out in an oxygen atmosphere.

[0032] like Figure 1 The structure diagram of the MoB-doped NCM811 material (abbreviated as NCM-MoB) prepared by the above process in the embodiment of the present invention is shown in FIG. Figure 1 The structure of the obtained NCM-MoB material mainly includes a layered Mo-doped NCM811 material 11 and a LiTM coated on the surface of the Mo-doped NCM811 material. x B y O z The coating layer 10, wherein TM represents a transition metal element (such as Mo), can enhance the structural stability. In the embodiment of the present invention, LiTM x B y O z The chemical formula of the coating is LiMo x B y O z , where x, y, z satisfy 1+x+y=z / 2. The surface of NCM811 material has a rock salt phase structure before modification. After modification with MoB, the LiTM x B y O z The coating layer, on the one hand, reduces the rock salt phase structure, optimizes the performance, and enhances the stability of the material structure. At the same time, it can reduce the contact between the electrode and the electrolyte to reduce the occurrence of side reactions.

[0033] The NCM-MoB material of the embodiment of the present invention reduces the mixing phenomenon of lithium and nickel ions by Mo doping. Figure 2 The following are XRD patterns of the existing NCM811 material (sample 1) and the NCM-MoB material (sample 2) according to the embodiment of the present invention. Figure 2 The results show that after the introduction of MoB in the embodiment of the present invention, no other impurities are introduced, the lattice structure does not change, and only Mo ions replace Li ions, which is beneficial to the embedding and de-embedding process of lithium ions in the positive electrode material and optimizes the energy density and cycle retention rate of the battery.

[0034] The present invention also uses a scanning electron microscope (SEM) to observe the morphology of the sample. Figure 3(a), (b), (c), and (d) are scanning electron microscope images of the existing NCM811 material (sample 1) before cycling, and (e), (f), (g), and (h) are scanning electron microscope images of the NCM-MoB material (sample 2) according to an embodiment of the present invention before cycling. Figure 3 It can be seen that the NCM-MoB material has a uniformly distributed spherical particle structure. After the introduction of MoB, the size of the grains is significantly reduced, and the specific surface area is larger. The increase in the specific surface area of ​​the grains can improve the reaction activity, lithium ion conductivity, improve the cycle stability, enhance the conductivity and increase the specific capacity.

[0035] like Figure 4 (a) and (b) are scanning electron microscope images of the existing NCM811 material (sample 1) after cycling, and (c) and (d) are scanning electron microscope images of the NCM-MoB material (sample 2) according to an embodiment of the present invention after cycling. Figure 4 It can be seen that the existing NCM811 material samples showed large cracks in the grains after cycling; while the samples after the introduction of MoB in the present invention showed significantly fewer cracks in the grains after cycling. This shows that MoB doping effectively improves the stability of the NCM811 material, laying the foundation for improving the cycle retention rate of the battery.

[0036] The transmission electron microscope image of the NCM-MoB material of the embodiment of the present invention is as follows Figure 5 As shown, there is a coating layer on the surface of NCM-MoB material——LiTM x B y O z layer( Figure 5 The light gray area on the right side of the graph shows the crystals, and the rock salt phase within the grains differs from that in the original NCM811 material. By introducing MoB, a "one-step modification, two-step optimization" experimental strategy was implemented, which resulted in phase changes within the grains and the formation of a protective layer on the surface. This reduced electrolyte erosion on the cathode material, ultimately significantly improving the grain stability.

[0037] Another embodiment of the present invention further provides the use of the aforementioned NCM-MoB material in a lithium-ion battery, where the NCM-MoB material is used as a positive electrode material for the lithium-ion battery.

[0038] During the preparation of the electrode slurry, the positive electrode active material, acetylene black and PVDF binder were added to the N-methylpyrrolidone solvent system in a mass ratio of 8:1:1 and uniformly dispersed by magnetic stirring. The resulting slurry was loaded on the surface of the aluminum foil substrate by doctor blade coating, and the surface density of the active material was controlled to be 2-3 mg / cm 2 The coated electrode was vacuum dried at 120°C for 12 hours to remove the residual solvent, and then punched out into a 12 mm diameter disc electrode using a mold and placed in a vacuum drying oven for later use.

[0039] The battery assembly process utilizes a CR2032 coin cell system with lithium metal foil as the counter electrode and Celgard PP2400 polypropylene microporous membrane as the separator. The electrolyte system consists of 1 mol / L LiPF₆ dissolved in an equal volume mixture of EMC, DEC, and FEC. Each cell is precisely injected with 70 μL of electrolyte. All assembly operations are performed in an inert atmosphere glove box to ensure that the water and oxygen content of the battery system is controlled below the ppm level.

[0040] The electrochemical characterization of CR2032 button cells was performed using constant current charge and discharge mode, with the test voltage window set to 2.8-4.3 V. The electrochemical analysis data are shown in Figure 2. Figure 6 The results show that the initial discharge capacity of the Mo-doped NCM-MoB cathode material exceeds 200 mAh g at a 1C rate. -1 , which is significantly improved compared with the original NCM811 material, which confirms the enhancement effect of transition metal doping on the lithium storage capacity of layered oxide materials. In terms of cycle stability evaluation, such as Figure 7 As shown in the figure, the capacity retention rate of the NCM-MoB electrode after 200 cycles is above 81%, while the capacity retention rate of the control group NCM811 battery is lower. This difference indicates that the LiTM x B y O z The coating has significant advantages in improving structural stability and cycle life.

[0041] like Figure 8 The electrochemical long cycle diagram of the NCM-MoB material of the present invention is shown. x B y O z The coating stabilizes the NCM material at the microscopic level, helping to mitigate adverse changes during the lithiation and delithiation processes of lithium ions, thereby enhancing the mechanical stability of the electrode material. The NCM-MoB battery retained approximately 60% of its capacity after 1,000 charge-discharge cycles, demonstrating its excellent cycling stability. Conventional NCM811 materials typically experience significant capacity decay at such high cycle counts, but the introduction of MoB into the NCM material significantly slows this process.

[0042] The lithium ion diffusion coefficient was measured by the constant current intermittent titration technique (GITT) in the voltage range of 2.8–4.3 V. During the test, the battery was first charged at a constant current and then left to stand for a period of time to achieve a quasi-equilibrium state. Figure 9As shown, the horizontal axis represents the potential and the vertical axis D represents the lithium ion diffusion coefficient. It can be seen that compared with the unmodified NCM811 material, the modified NCM-MoB material battery of the present invention exhibits a higher lithium ion diffusion coefficient, indicating that the Mo doping strategy effectively optimizes the crystal structure of the material, broadens the lithium ion migration channel and reduces the diffusion resistance, thereby accelerating the migration rate of lithium ions in the electrode material, thereby significantly improving the charge and discharge rate and battery power performance. This improvement can reduce internal resistance, enhance battery efficiency, and improve cycle stability and life.

[0043] In summary, the introduction of a trace amount of MoB into NCM811 material can achieve the effect of "one modification, double optimization", avoiding the introduction of other anionic impurities. The introduction of MoB helps to improve the overall conductivity of the electrode, thereby improving the diffusion efficiency of lithium ions and improving the rate performance of the battery. Secondly, the introduction of MoB can form LiTM on the surface of the electrode grains. x B y O z The layer enhances the structural stability of the electrode material and reduces the structural reorganization and volume change during the charge and discharge process, thereby improving the cycle life and durability of the battery. By introducing MoB, the initial discharge capacity of the positive electrode material at a 1C rate exceeds 200mAh g -1 , the capacity retention rate is above 81% after 200 cycles.

[0044] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art will recognize that several equivalent substitutions or obvious variations can be made without departing from the scope of the present invention, and that any equivalent performance or application should be considered to fall within the scope of protection of the present invention.

Claims

1. A lithium-ion battery cathode material with synergistic doping and coating, characterized in that: The lithium-ion battery positive electrode material is a MoB-doped NCM811 material obtained by directly introducing MoB into the high-nickel positive electrode material NCM811 by a solid phase sintering method, wherein the amount of MoB is 0.2wt%~0.4wt% of the high-nickel positive electrode material NCM811; the MoB-doped NCM811 material includes: Mo-doped layered NCM811 material, and LiTM x B y O z A coating layer is coated on the surface of the Mo-doped layered NCM811 material; wherein x, y, and z satisfy 1+x+y=z / 2, TM represents a transition metal element; and the transition metal element is Mo.

2. The lithium-ion battery cathode material according to claim 1, wherein The Mo-doped layered NCM811 material has a uniformly distributed spherical particle structure inside. The spherical particle structure is a secondary grain composed of primary grains, and the particle size is 3-5 microns.

3. The method for preparing a positive electrode material for a lithium ion battery according to any one of claims 1 to 2, wherein: include: MoB and high-nickel positive electrode material NCM811 are mixed in a predetermined ratio, and then solid-phase sintering is performed using a two-step temperature-raising calcination method to obtain the MoB-doped NCM811 material.

4. The method for preparing a positive electrode material for a lithium ion battery according to claim 3, wherein: The high nickel cathode material NCM811 is a composite of LiOH·H2O and Ni i Co j Mn k (OH)2 is used as raw material, mixed and calcined according to a preset ratio, and the chemical formula is LiNi i Co j Mn k O2; where i+j+k=1.

5. The method for preparing a positive electrode material for a lithium ion battery according to claim 3 or 4, wherein: The amount of MoB used is 0.3 wt % of the high nickel positive electrode material NCM811.

6. The method for preparing a positive electrode material for a lithium ion battery according to claim 3, wherein: The solid phase sintering includes: first calcining the mixture of the MoB and the high nickel positive electrode material NCM811 in a first temperature range, and then heating it to a second temperature range for calcination.

7. The method for preparing a positive electrode material for a lithium ion battery according to claim 6, wherein: The first temperature range is 400-600° C., and the second temperature range is 750-900° C.; the calcination time in the first temperature range is 3-6 hours, and the calcination time in the second temperature range is 9-12 hours.

8. The method for preparing a positive electrode material for a lithium-ion battery according to claim 7, wherein: The calcination process in the first temperature range includes: calcination at 500° C. for 4 hours; the calcination process in the second temperature range includes: calcination at 780° C. for 11 hours.

9. The method for preparing a positive electrode material for a lithium ion battery according to claim 3 or 6, wherein: The solid phase sintering is performed in an oxygen atmosphere.

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