Ta-Ti double-gradient doped lithium ion battery high-nickel positive electrode material, battery and preparation method

Abstract

The invention discloses a Ta-Ti double-gradient doped lithium ion battery high-nickel positive electrode material, a battery and a preparation method, according to the positive electrode material, through a surface-bulk phase partition functional design, Ta < 5 + > is subjected to gradient enrichment on the surface of the material to form a Li-Ta-O protective layer so as to inhibit electrolyte erosion, Ti < 4 + > is uniformly doped in a bulk phase and forms a strong Ti-O bond with an oxygen framework, and the high-nickel positive electrode material can be used for preparing a lithium ion battery. And the lattice structure is synergistically stabilized, Li / Ni mixed arrangement is reduced, the lattice constant is expanded, and a lithium ion diffusion channel is optimized. The positive electrode material has the advantages of high specific capacity, long cycle life and excellent rate capability, and solves the technical bottlenecks of fast cycle attenuation and remarkable capacity loss caused by structural instability and single element doping of the traditional high-nickel material.

Description

Technical Field

[0001] The present invention relates to battery technology, and particularly to a high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, a battery, and a preparation method thereof. Background Art

[0002] With the rapid popularization of high-energy-density lithium-ion batteries in the fields of electric vehicles and energy storage, high-nickel cathode materials (LiMn 0.1 Ni 0.8 Co 0.1 O2) have become the focus of the industry due to their low cost and high specific capacity. However, in the prior art, the intrinsic instability of the layered structure of high-nickel materials (Ni≥80%) (such as severe H2-H3 phase transformation and lattice oxygen escape), high cation mixing degree (Ni 2+ and Li + have similar radii resulting in Li layer occupancy), and insufficient cycle life (capacity decay ≥25% after 200 cycles) and other problems seriously hinder their large-scale application. One of the key technologies to optimize the performance of high-nickel materials is the coordinated regulation of multi-scale structural defect repair and interface stability. Aiming at the bottlenecks of traditional single-element doping (such as Al, Mg, Ta, etc.) including single modification dimension (only suppressing phase transformation or reducing mixing) and insufficient doping element synergy (such as excessive doping blocking lithium channels), a breakthrough solution is urgently needed.

[0003] It should be noted that the information disclosed in the above background art section is only used for understanding the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] The main purpose of the present invention is to overcome the defects existing in the above background art, and to provide a high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, a battery, and a preparation method thereof.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, the cathode material being LiMn 0.1 Ta 0.0 1Ti 0.01 Ni 0.78 Co 0.1 O2, wherein Ta 5+ gradually enriches on the surface of the material to form a Li-Ta-O protective layer, and Ti 4+ is uniformly doped in the bulk phase and forms strong Ti-O bonds with the oxygen framework.

[0006] A preparation method of a high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, comprising the following steps: S1. Mix Li2CO3 and the high-nickel ternary precursor material evenly according to the stoichiometric ratio. S2. Add Ta2O5 and TiO2 to the mixture in step S1, and control the molar ratio of Li:Mn:Ta:Ti:Ni:Co to be 1:0.1:0.01:0.01:0.78:0.1, and mix evenly. S3. Under an oxygen atmosphere, pre-calcine the mixed materials first, and then increase the temperature for calcination to obtain the Ta-Ti dual-gradient doped high-nickel cathode material LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2.

[0007] Further, in step S1, the high-nickel ternary precursor material is Mn 0.1 Ni 0.8 Co 0.1 (OH)2.

[0008] Further, in step S3, the pre-calcination temperature is 450°C to 550°C, and the calcination time is 3 hours to 5 hours; the temperature increase for calcination is 750°C to 800°C, and the calcination time is 10 hours to 12 hours.

[0009] A lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte using the positive electrode material.

[0010] Further, the lithium-ion battery includes a metallic lithium negative electrode and an electrolyte containing LiPF6, and the electrolyte is prepared by mixing EMC, DEC, and FEC in a volume ratio of (0.8 - 1.2):(0.8 - 1.2):(0.8 - 1.2).

[0011] The present invention has the following beneficial effects: The present invention provides a method for modifying a Ta-Ti dual-gradient doped high-nickel cathode material. According to the surface-bulk partition functionalization design, site-selective doping is performed on the LiMn 0.1 Ni 0.8 Co 0.1 O2 material. Using the gradient sintering method, the surface passivation effect of Ta 5+ (forming a Li-Ta-O protective layer to inhibit electrolyte erosion) and the bulk lattice anchoring effect of Ti 4+ (stabilizing the oxygen framework through strong Ti-O bonds and inhibiting Ni 2+ migration) are utilized to achieve the synergistic improvement of high specific capacity (≥226 mAh / g@0.2C) and ultra-long cycle stability (cycle capacity retention rate ≥811% after 250 cycles), overcoming the core defects of fast cycle attenuation of high-nickel materials and functional conflicts of doped elements in the prior art.

[0012] Other beneficial effects in the embodiments of the present invention will be further described below. Brief Description of the Drawings

[0013] Figure 1 It is a technical route diagram for the material synthesis of the present invention.

[0014] Figure 2 It is an XRD pattern of the sample in the embodiment of the present invention.

[0015] Figure 3 It is a refined XRD pattern of the sample in the embodiment of the present invention.

[0016] Figure 4 It is a scanning electron microscope image of NCM.

[0017] Figure 5 It is a scanning electron microscope image of TaTi-NCM in the embodiment of the present invention.

[0018] Figure 6 It is an EDS spectrum of TaTi-NCM in the embodiment of the present invention.

[0019] Figure 7 It is a TEM image of TaTi-NCM in the embodiment of the present invention.

[0020] Figure 8 It is a charge-discharge graph of the sample in the embodiment of the present invention.

[0021] Figure 9 It is a long cycle life graph of the sample in the embodiment of the present invention.

[0022] Figure 10 It is a rate graph of the sample in the embodiment of the present invention.

[0023] Figure 11 It is an impedance graph of the sample in the embodiment of the present invention.

[0024] Figure 12 It is a lithium ion diffusion coefficient graph of the sample in the embodiment of the present invention. Detailed Embodiments

[0025] The following provides a detailed description of the embodiments of the present invention. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0026] The embodiment of the present invention provides a high-nickel cathode material for a lithium-ion battery with Ta-Ti double-gradient doping. The cathode material is LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2, through surface-bulk partition functionalization design, where Ta5+ Form a Li-Ta-O protective layer by gradient enrichment on the material surface, Ti 4+ Be uniformly doped in the bulk phase and form strong Ti-O bonds with the oxygen framework, thereby synergistically inhibiting electrolyte erosion, stabilizing the lattice structure and reducing Li / Ni mixing.

[0027] The embodiment of the present invention also provides a preparation method of a high-nickel cathode material for a lithium-ion battery with Ta-Ti double-gradient doping, including the following steps: Step S1: Mix Li2CO3 and the high-nickel ternary precursor material evenly according to the stoichiometric ratio; Step S2: Add Ta2O5 and TiO2 to the mixture in step S1, and control the molar ratio of Li:Mn:Ta:Ti:Ni:Co to be 1:0.1:0.01:0.01:0.78:0.1, and mix evenly; Step S3: Under an oxygen atmosphere, pre-calcine the mixed materials first, and then raise the temperature for calcination to obtain the high-nickel cathode material LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2.

[0028] In some embodiments, in step S1, the high-nickel ternary precursor material is Mn 0.1 Ni 0.8 Co 0.1 (OH)2.

[0029] In some embodiments, in step S3, under an oxygen atmosphere, pre-calcine the mixed materials at 450°C to 550°C for 3 hours to 5 hours first, and then raise the temperature to 750°C to 800°C for calcination for 10 hours to 12 hours to obtain the high-nickel cathode material with Ta-Ti double-gradient doping.

[0030] The embodiment of the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode and an electrolyte using the positive electrode material.

[0031] In some embodiments, the lithium-ion battery includes a metallic lithium negative electrode and an electrolyte containing LiPF6, and the electrolyte is prepared by mixing EMC, DEC and FEC according to a volume ratio of (0.8 - 1.2):(0.8 - 1.2):(0.8 - 1.2).

[0032] The present invention designs through surface-bulk phase partition functionalization, and uses Ta 5+ Gradient enrichment on the material surface to form a Li-Ta-O protective layer to inhibit electrolyte erosion, while Ti 4+Uniformly doped into the bulk phase, the lattice oxygen framework is stabilized by strong Ti-O bonds and Li / Ni mixing is reduced. Utilizing the synergistic effect of Ta-Ti double gradient doping, high specific capacity, long cycle life and excellent rate performance of the high-nickel cathode material LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2 are achieved. At the same time, by expanding the layer spacing to optimize the lithium ion diffusion channel, the technical bottlenecks of fast cycle attenuation and significant capacity loss caused by the structural instability and single function of doping elements in traditional high-nickel materials are solved.

[0033] The specific embodiments of the present invention and experimental verification are further described below.

[0034] Using the high-temperature solid-state calcination method, three cathode materials with different doping strategies were designed and synthesized, specifically as follows: Sample 1 (control group): Using Li2CO3 and Mn 0.1 Ni 0.8 Co 0.1 (OH)2 as raw materials, mixed and calcined in appropriate proportions to synthesize the reference material LiMn 0.1 Ni 0.8 Co 0.1 O2 (abbreviated as NCM).

[0035] Sample 2 (Ta single doping group): On the basis of Sample 1, Ta2O5 was introduced as the tantalum source, and mixed and calcined according to the ratio of Li:Mn:Ni:Co:Ta = 1:0.1:0.78:0.1:0.02 to obtain the doped material LiMn 0.1 Ta 0.02 Ni 0.78 Co 0.1 O2 (abbreviated as Ta-NCM).

[0036] Sample 3 (Ta-Ti double doping group): Further introducing TiO2 as the titanium source on the basis of Sample 2, and mixed and calcined according to the ratio of Li:Mn:Ta:Ti:Ni:Co = 1:0.1:0.01:0.01:0.78:0.1 to obtain the final material LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2 (abbreviated as TaTi-NCM).

[0037] All three samples were prepared by a two-step temperature-raising calcination method: First, the uniformly mixed raw materials were pre-calcined in an oxygen atmosphere at 500 °C for 4 hours, and then high-temperature calcined at 780 °C for 11 hours to obtain the target product. The material synthesis process route is asFigure 1 As shown below: The crystal structure of the samples was characterized by X-ray diffraction (XRD). The test was carried out using a Bruker D8 Advance diffractometer, with a Cu Kα ray (λ = 0.15406 nm) as the radiation source, and the working conditions were a tube voltage of 45 kV and a tube current of 40 mA. The test was carried out at a scanning rate of 10° / min in the 2θ range of 10° - 90°. The XRD patterns of the three samples are as Figure 2 shown. The results show that all samples exhibit the layered structure characteristics of the R-3m space group, and no formation of heterogeneous phases was found.

[0038] Detailed crystal structure information was obtained by refinement using GSAS II software, as Figure 3 shown. The relevant refinement results are summarized in Table 1. The XRD refinement results show that after Ta / Ti double doping, the degree of mixing of Li + / Ni 2+ decreased from 4.4% in the original material to 2.4%, significantly suppressing the Li / Ni mixing phenomenon. In addition, the increase in the c-axis lattice constant indicates an expansion of the layer spacing, which is beneficial to optimizing the lithium-ion diffusion channels and thus improving the electrochemical performance of the material.

[0039] Table 1. Summary of XRD refinement data

[0040] The morphologies of NCM and TaTi-NCM were characterized by a field emission scanning electron microscope (HITACHI S-4800, SU 8010) and equipped with an energy dispersive spectrometer (EDS, IXRF SYSTEM, 550i). The relevant results are as Figure 4 and Figure 5 shown. The scanning electron micrographs show that the synthesized TaTi-NCM material has a spherical particle structure with a uniform distribution. As Figure 6 shown, the EDS element distribution maps further show that the elements of Mn, Ni, Co, Ta, Ti, and O are evenly distributed in the TaTi-NCM particles, indicating that the doping elements were successfully introduced and achieved good dispersion.

[0041] Transmission electron microscope (TEM) images were obtained by FEI Tecnai T12 and FEI Tecnai G2 F30 instruments, and the samples were prepared by a focused ion beam system (FIB, Scios, FEI). As Figure 7As shown, a distinct Li-Ta-O protective layer is formed on the surface of TaTi-NCM. Combining the results of various characterizations such as XRD, SEM, and TEM, it can be concluded that this technology is based on the theory of repairing lattice defects in high-nickel materials and adopts a dual-path design strategy, including: (1) Ta 5+ Gradient enrichment on the material surface to form a Li-Ta-O protective layer, effectively inhibiting the erosion of the electrolyte on the cathode material; (2) Ta 5+ Uniform doping with Ti4 + in the bulk phase, enhancing the crystal structure stability by means of strong Ta-O and Ti-O bonds, thereby improving the structural integrity and electrochemical performance of the material.

[0042] To prepare the electrode slurry, the cathode active material, acetylene black, and polyvinylidene fluoride (PVDF, Solef 5130) were mixed at a mass ratio of 8:1:1 in an N-methylpyrrolidone (NMP) solvent and stirred evenly. The prepared slurry was uniformly coated on an aluminum foil current collector, and the mass loading of the active material was 2 - 3 mg·cm -2 . The coated electrode was dried in a vacuum oven at 120 °C for 12 hours, and then punched into circular electrode sheets with a diameter of 12 mm and transferred to a glove box filled with argon.

[0043] The battery was assembled using a CR2032 coin cell structure, with the prepared cathode as the positive electrode sheet, metallic lithium as the negative electrode, and Celgard PP2400 membrane as the separator. 60 μL of electrolyte was injected into each battery, and the electrolyte used was 1 M LiPF6 dissolved in a solvent mixture prepared from ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) at a volume ratio of 1:1:1.

[0044] The electrochemical performance test of the coin cell was carried out on a multi-channel battery test system, and the voltage range was 2.8 - 4.3 V (versus Li + / Li). As Figure 8 shown, the initial discharge specific capacity of the TaTi-NCM material reached 226 mAh / g at a current density of 0.2 C, significantly higher than that of the undoped NCM material (194 mAh / g), indicating that the dual-doping strategy effectively improved the reversible capacity and lithium-ion storage ability of the material. As Figure 9 shown, after three activation cycles at a current density of C / 5, the battery was subjected to a long-term cycling test at 1 C. The results showed that the TaTi-NCM material still maintained a capacity retention rate of 81% after 250 cycles, significantly better than 71% of the undoped sample NCM, indicating that the dual-doping strategy has significant advantages in improving structural stability and cycle life. In addition, as Figure 10As shown, the TaTi-NCM sample exhibits excellent rate performance under different C-rate conditions, further verifying its good electrochemical kinetics and lithium-ion diffusion ability.

[0045] Electrochemical impedance spectroscopy (EIS) tests were carried out on a multi-channel electrochemical workstation, and the test frequency range was from 100 kHz to 10 mHz. As Figure 11 shown, compared with the undoped NCM material, the impedance of the TaTi-NCM sample is significantly reduced, indicating that the dual-doping strategy effectively reduces the interfacial resistance and improves the migration ability of lithium ions in the electrode material, thus contributing to the improvement of the electrochemistry reaction kinetics performance of the material.

[0046] The lithium-ion diffusion coefficient (D) was measured by the galvanostatic intermittent titration technique (GITT). The test was carried out at a current density of 0.1C, and the voltage range was 2.8–4.3V. During the test, the battery was charged at a constant current for 20 minutes, and then left standing for 3 hours to achieve a quasi-equilibrium state. As Figure 12 shown, compared with the undoped NCM material, the TaTi-NCM sample exhibits a higher lithium-ion diffusion coefficient, indicating that the dual-doping strategy effectively optimizes the crystal structure of the material, broadens the lithium-ion migration channels and reduces the diffusion resistance, thus contributing to the improvement of the rate performance and kinetic reaction activity of the material.

[0047] In summary, by constructing a Ta-Ti dual-gradient doping system, a specific capacity of up to 226 mAh / g (0.2C) and a capacity retention rate of ≥81% after 250 cycles were achieved, and the performance is significantly better than that of the existing high-nickel single-doping system. Through the synergistic enhancement mechanism of "surface passivation + bulk strengthening", the present invention effectively breaks through the technical bottleneck of the single modification dimension of the traditional doping strategy, establishes a new paradigm for material design with significant competitiveness, and has important technical value and application prospects.

[0048] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, they can also make several substitutions or modifications to these described embodiments, and these substitution or modification methods should all be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. Without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of protection of the patent application.

Claims

1. A high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, characterized in that, The positive electrode material is LiMn 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2, in which Ta 5+ is gradient-enriched on the material surface to form a Li-Ta-O protective layer, and Ti 4+ is uniformly doped in the bulk phase and forms strong Ti-O bonds with the oxygen framework.

2. A preparation method of a high-nickel cathode material for lithium-ion batteries with Ta-Ti double-gradient doping, characterized in that, It includes the following steps: S1. Mix Li2CO3 and the high-nickel ternary precursor material evenly according to the stoichiometric ratio; S2. Add Ta2O5 and TiO2 to the mixture in step S1, and control the molar ratio of Li:Mn:Ta:Ti:Ni:Co to be 1:0.1:0.01:0.01:0.78:0.1, and mix evenly; S3. Under an oxygen atmosphere, pre-calcine the mixed materials first and then increase the temperature for calcination to obtain the high-nickel cathode material LiMn with Ta-Ti double-gradient doping 0.1 Ta 0.01 Ti 0.01 Ni 0.78 Co 0.1 O2.

3. The preparation method according to claim 2, wherein, The high-nickel ternary precursor material is Mn 0.1 Ni 0.8 Co 0.1 (OH)2.

4. The preparation method according to claim 2 or 3, characterized in that, In step S3, the pre-calcination temperature is 450°C to 550°C, and the calcination time is 3 hours to 5 hours; the heating and calcination temperature is 750°C to 800°C, and the calcination time is 10 hours to 12 hours.

5. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode and an electrolyte using the positive electrode material as described in claim 1.

6. The lithium ion battery according to claim 5, wherein It includes a metallic lithium negative electrode and an electrolyte containing LiPF6, and the electrolyte is prepared by mixing EMC, DEC and FEC according to a volume ratio of (0.8 - 1.2):(0.8 - 1.2):(0.8 - 1.2).

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