Modification method for simply and remarkably improving crystal structure and cycling stability of ultra-high nickel cobalt-free positive electrode material

Abstract

The invention discloses a modification method for simply and remarkably improving the crystal structure and cycle stability of an ultrahigh-nickel cobalt-free positive electrode material, which is characterized in that Nb / Ti elements are doped into the LiNi0. 9Mn0. 1O2 crystal structure through a one-step high-temperature solid-phase sintering process, the microstructure of the material is optimized, and a stable crystal frame is constructed. According to the technology, the primary particle structure is adjusted, the particle strength is improved, transition metal dissolution and electrolyte decomposition are inhibited, particle breakage and structure distortion in the circulation process are reduced, and the electrode reaction reversibility is enhanced. The modified positive electrode has high specific capacity, excellent cycle stability and rate capability, and the capacity retention rate of the total battery assembled by taking graphite as the negative electrode can reach 98% after 500 cycles. The structure and the cycling stability of the material are remarkably improved through an Nb / Ti double-doping strategy, and the preparation method is simple in process, low in cost and easy for large-scale production and has outstanding commercial application potential.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and particularly to a modification method that simply and significantly improves the crystal structure and cycle stability of a high-nickel cobalt-free cathode material. Background Art

[0002] Developing high-nickel cobalt-free layered cathode materials is a key path to improving the energy density of lithium-ion batteries, reducing costs, and achieving sustainable development. With the surging demand for high-energy-density batteries in electric vehicles and energy storage systems, traditional cobalt-containing ternary materials (such as NCM, NCA) are severely restricted from large-scale commercial applications due to the scarcity of cobalt resources, high prices, and geopolitical risks in the supply chain. High-nickel design (nickel content ≥ 90%) can not only significantly reduce the material cost by reducing the cobalt usage or even completely removing cobalt, but also alleviate the environmental burden and ethical challenges brought by cobalt mining, which conforms to the development concept of green and low-carbon.

[0003] From a performance perspective, the high-nickel structure can greatly improve the specific capacity of the cathode material (≥ 220 mAh g -1 ) by increasing the nickel ratio, thereby increasing the energy density of a single battery cell to over 300 Wh kg -1 or more to meet the long-range requirements. However, when the nickel content is increased to over 90%, the material faces problems such as increased cation mixing, irreversible H2-H3 phase transformation, and lattice oxygen precipitation, resulting in the expansion of particle microcracks, the dissolution of transition metals, and the deterioration of interfacial side reactions during the cycling process, leading to capacity decay, decreased rate and cycle performance, and poor safety performance, which greatly limits its wide promotion in practical applications. Therefore, in the field of high-nickel layered oxide cathode materials, how to maintain excellent electrochemical performance while significantly reducing or completely removing cobalt is undoubtedly a huge challenge.

[0004] To address these challenges, researchers have explored various methods, including element doping, surface modification, core-shell structure design, etc. Among these strategies, element doping is widely regarded as one of the most effective methods to improve its structural stability. Commonly used doping elements include Mg, Al, Ti, Mo, W, etc., and the introduction of these elements has significantly improved the overall structure and performance of the material. However, a single doping method often fails to solve multiple problems simultaneously.

[0005] By co-doping Nb and Ti elements, the structural and performance defects of high-nickel cobalt-free layered oxides can be improved simultaneously. This synergistic effect not only enhances the structural stability of the material itself but also significantly improves its cycle and rate performance. Summary of the Invention

[0006] The object of the present invention is: in view of the above problems, the present invention provides a modification method that is simple and can significantly improve the crystal structure and cycle stability of a high-nickel cobalt-free cathode material.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] Design a modification method that is simple and can significantly improve the crystal structure and cycle stability of a high-nickel cobalt-free cathode material, including the following steps:

[0009] (1) Raw material ratio: Weigh appropriate amounts of high-nickel cobalt-free precursor, lithium source, niobium source, and titanium source;

[0010] (2) Mechanical mixing: Grind the powder obtained in step (1) evenly;

[0011] (3) Gradient calcination: Perform gradient calcination on the evenly powdered material obtained in step (2) to obtain high-nickel cobalt-free cathode material particles with Nb / Ti double doping and significantly improved crystal structure and cycle stability.

[0012] According to the above scheme, in step (1), the high-nickel cobalt-free precursor, lithium source, niobium source, and titanium source are weighed according to a molar ratio of 1 - 2x:1.01 - 1.10:x:x (where 0.0025 ≤ x ≤ 0.02).

[0013] According to the above scheme, in step (1), the high-nickel cobalt-free precursor is Ni 0.9 Mn 0.1 (OH) 2 .

[0014] According to the above scheme, in step (1), the lithium source is one or more of lithium hydroxide, lithium carbonate, and lithium nitrate. The niobium source can be at least one of niobium pentoxide, niobium oxalate, and niobium pentachloride, and the titanium source is titanium dioxide or tetrabutyl titanate.

[0015] According to the above scheme, in step (3), the calcination atmosphere is oxygen, the pre-calcination temperature is 300 - 600 °C, the heating rate is 1 - 10 °C / min, the calcination time is 4 - 6 h, and then the final calcination temperature is 730 - 780 °C, the heating rate is 1 - 10 °C / min, and the calcination time is 10 - 18 h.

[0016] The beneficial effect of the present invention is: By adopting a simple one-step high-temperature solid-state sintering process, Nb / Ti is successfully doped into the high-nickel cobalt-free cathode material LiNi 0.9 Mn 0.1 O 2, its overall structure has been optimized. This strategy adjusts the microscopic morphology of primary particles, improves particle strength, constructs a stable crystal framework, slows down the decomposition of the organic electrolyte on the cathode surface, inhibits the dissolution of transition metals, reduces the fragmentation and even pulverization of particles during cycling, alleviates structural distortion, and improves the reversibility of the electrode reaction. The one-step solid-phase method avoids complex processes and is suitable for large-scale production. Description of the Drawings

[0017] Figure 1 It is a scanning electron microscope image of the blank sample of the ultra-high nickel cobalt-free cathode material prepared in the steps of Example 1 of the present invention.

[0018] Figure 2 It is a scanning electron microscope image of the ultra-high nickel cobalt-free cathode material with a double doping amount of Nb / Ti of 0.5 mol% each prepared in the steps of Example 2 of the present invention.

[0019] Figure 3 It is a scanning electron microscope image of the ultra-high nickel cobalt-free cathode material with a double doping amount of Nb / Ti of 1 mol% each prepared in the steps of Example 3 of the present invention.

[0020] Figure 4 It is a scanning electron microscope image of the ultra-high nickel cobalt-free cathode material with a double doping amount of Nb / Ti of 1.5 mol% each prepared in the steps of Example 3 of the present invention.

[0021] Figure 5 It is a comparison chart of the discharge specific capacity of the ultra-high nickel cobalt-free cathode material prepared in the steps of Example 1, Example 2, Example 3, and Example 4 of the present invention after 200 cycles at an ambient temperature of 25 °C, a cut-off voltage of 2.7 - 4.3 V, and a 1C rate.

[0022] Figure 6 It is a comparison chart of the discharge specific capacity of the ultra-high nickel cobalt-free cathode material prepared in the steps of Example 1, Example 2, Example 3, and Example 4 of the present invention at different rates at an ambient temperature of 25 °C and a cut-off voltage of 2.7 - 4.3 V.

[0023] Figure 7 It is a graph of the discharge capacity and charge-discharge efficiency of the all-cell assembled with the ultra-high nickel cobalt-free cathode material obtained in the steps of Example 2 of the present invention and a graphite anode after 500 cycles at an ambient temperature of 25 °C, a cut-off voltage of 2.7 - 4.3 V, and a 1C rate.

[0024] Figure 8 It is a SEM image of the ultra-high nickel cobalt-free cathode material obtained in the steps of Example 1 of the present invention after 200 cycles at an ambient temperature of 25 °C, a cut-off voltage of 2.7 - 4.3 V, and a 1C rate.

[0025] Figure 9 It is the SEM image of the ultra-high nickel cobalt-free cathode material obtained in the steps of Embodiment 2 of the present invention after 200 cycles at an ambient temperature of 25°C, a cut-off voltage of 2.7 - 4.3V, and a 1C rate. Detailed implementation manners

[0026] The following examples are used to illustrate the detailed implementation manners of the present invention. However, the following examples are only used to illustrate the present invention in detail and do not limit the scope of the present invention in any way. In the following examples, the equipment components involved are conventional equipment components unless otherwise specified; the industrial raw materials involved are commercially available conventional industrial raw materials unless otherwise specified. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Additionally, the endpoints and any values within the ranges disclosed herein are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, combinations can be made between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values to obtain one or more new numerical ranges, which should be considered specifically disclosed herein.

[0027] The following Comparative Example 1 is an example of an ultra-high nickel cobalt-free cathode material prepared by a traditional calcination method; Examples 2, 3, and 4 are examples of the present invention. The ultra-high nickel cobalt-free cathode materials prepared in Example 1 and Examples 2, 3, and 4 of the present invention are characterized and analyzed. The analysis methods include:

[0028] 1. Scanning electron microscope (SEM) test: Scanning electron microscope, instrument model: SU5000;

[0029] 2. Assembly and test of CR2032 button cells: The ultra-high nickel cobalt-free cathode material (the final product prepared in Example 1, Example 2, and Example 3), conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) are made into a slurry in a mass ratio of 8:1:1 and coated on aluminum foil. The dried aluminum foil loaded with the slurry is cut into small round pieces with a diameter of about 12 mm using a cutting machine and used as the positive electrode. A lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and a 1M carbonate solution is used as the electrolyte (wherein, the solvent is a mixed solution of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, and the solute is LiPF 6 ). A CR2032 button cell is assembled in an argon atmosphere glove box.

[0030] Example 1 (unmodified)

[0031] Precursor Ni 0.9 Mn 0.1 (OH) 2, the lithium source LiOH·H 2 O was weighed according to a molar ratio of 1:1.05. It was placed in a mortar and ground for 60 min until evenly mixed, and the obtained uniform powder was calcined in a tube furnace under an oxygen atmosphere. First, it was heated to 500 °C at a heating rate of 5 °C / min and pre-sintered for 5 h; then it was heated to 750 °C at a heating rate of 5 °C / min, and the calcination time was 15 h; then it was naturally cooled to room temperature. The cooled material was crushed to obtain a high-nickel cobalt-free cathode material LiNi 0.9 Mn 0.1 O 2 , denoted as NM90.

[0032] This Example 1 was used as a control group, and the SEM image of the blank sample of the prepared cathode material (LiNi 0.9 Mn 0.1 O 2 ) is as shown in Figure 1 . It can be seen that the LiNi 0.9 Mn 0.1 O 2 cathode material particles are secondary spheres composed of primary particles and have a regular shape.

[0033] Example 2 (the molar percentages of Nb and Ti are each 0.5%)

[0034] According to the precursor Ni 0.9 Mn 0.1 (OH) 2 , the lithium source LiOH·H 2 O, the niobium source Nb 2 O 5 , the titanium source TiO 2 were weighed according to a molar ratio of 1:1.05:0.005:0.005, and the rest was the same as in Example 1, to obtain an Nb / Ti double-doped high-nickel cobalt-free cathode material, denoted as NM90-NT0.5.

[0035] The SEM image of the cathode material prepared in Example 2 is as shown in Figure 2 . Compared with Example 1, the overall shape remains unchanged, but the primary particles become slightly smaller.

[0036] Example 3 (the molar percentages of Nb and Ti are each 1%)

[0037] According to the precursor Ni 0.9 Mn 0.1 (OH) 2 , the lithium source LiOH·H 2 O, the niobium source Nb 2 O 5 , the titanium source TiO 2Weigh according to a molar ratio of 0.98:1.05:0.01:0.01, and the rest is the same as in Example 1 to obtain an ultra-high nickel cobalt-free cathode material doped with Nb / Ti, denoted as NM90-NT1.

[0038] The SEM image of the cathode material prepared in Example 3 is as Figure 3 shown. Compared with Example 2, the primary particles become smaller.

[0039] Example 4 (molar percentages of Nb and Ti are each 1.5%)

[0040] Weigh according to the precursor Ni 0.9 Mn 0.1 (OH) 2 , lithium source LiOH·H 2 O, niobium source Nb 2 O 5 , titanium source TiO 2 Weigh according to a molar ratio of 0.97:1.05:0.015:0.015, and the rest is the same as in Example 1 to obtain an ultra-high nickel cobalt-free cathode material doped with Nb / Ti, denoted as NM90-NT1.5.

[0041] The SEM image of the synthesized cathode material in Example 4 is as Figure 4 shown. It can be seen that the secondary particles are still spherical. Compared with Example 3, the primary particles become smaller more significantly.

[0042] The comparison of the electrochemical properties of the ultra-high nickel cobalt-free cathode material before and after modification in the present invention is as follows:

[0043] The materials obtained in Example 1, Example 2, Example 3 and Example 4 are all subjected to a cycle test at an ambient temperature of 25 °C, a cut-off voltage of 2.7 - 4.3 V, and a rate of 1C (1C = 210 mA h g -1 ). The cycle test results are as Figure 5 shown. The initial discharge specific capacities of Example 1, Example 2, Example 3 and Example 4 are 198.65 mA h g -1 , 196.37 mA h g -1 , 197.67 mA h g -1 , 193.73 mA h g -1 respectively. After 200 cycles, the discharge specific capacities are 144.13 mA h g -1 , 179.34 mA h g -1 , 172.41 mA h g -1 , 164.58 mA h g -1, the capacity retention rates are 72.55%, 91.33%, 87.22%, and 84.95% respectively. By comparison, although the initial discharge specific capacity of Example 2, Example 3, and Example 4 is slightly lower than that of Example 1, the cyclic capacity retention rates after 200 cycles are significantly higher than that of Example 1. All materials were tested for rate performance at an ambient temperature of 25 °C, a cut-off voltage of 2.7 - 4.3 V, and different rates. The test results are as Figure 6 shown. As the rate increases, the gap in discharge specific capacity between Example 1 and Example 2, Example 3, and Example 4 at the same rate gradually becomes larger.

[0044] The positive electrode material obtained in Example 2 was assembled with a graphite negative electrode into a full cell and cycled 500 times at 1C within a voltage window of 2.7 - 4.3 V. The results are as Figure 7 shown, with a capacity retention rate as high as 98% and a Coulomb efficiency > 99.5%. In addition, the batteries after 200 cycles of Example 1 and Example 2 were disassembled and SEM images were taken. The results are as Figure 8 and Figure 9 . Obvious cracks were found on the surface of the secondary particles of NM90, while the surface of the secondary particles of NM90 - NT0.5 was smooth and the structure was intact, which is beneficial for stable long-term cycling. Combining the above test results, it is confirmed that this invention, through a simple Nb / Ti dual-element co-doping and gradient calcination process, significantly improves the crystal structure and cycling stability of the ultra-high nickel cobalt-free positive electrode material while maintaining a high specific capacity, providing an effective solution for the development of high-energy density power batteries.

[0045] The above has described the present invention in detail in conjunction with the embodiments. However, those skilled in the art can understand that without departing from the purpose of the present invention, various specific parameters in the above embodiments can be changed to form multiple specific embodiments, which are all within the common variation range of the present invention and will not be elaborated herein one by one.

Claims

1. A simple and significant modification method for improving the crystal structure and cycle stability of ultra-high nickel cobalt-free cathode materials, characterized in that: One-step high temperature solid phase sintering process: (1) Raw material ratio: weigh appropriate amounts of ultra-high nickel cobalt-free precursor, lithium source, niobium source, and titanium source; (2) Mechanical mixing: Grind the powder obtained in step (1) uniformly; (3) Gradient calcination: The uniform powder obtained in step (2) is subjected to gradient calcination to obtain ultra-high nickel cobalt-free positive electrode material particles with Nb / Ti dual doping and significantly improved crystal structure and cycle stability.

2. A modification method for simply and significantly improving the crystal structure and cycle stability of ultra-high nickel cobalt-free positive electrode materials according to claim 1, characterized in that: In step (1), the ratio of the ultra-high nickel cobalt-free precursor, lithium source, niobium source and titanium source is 1-2x: The molar ratio of 1.01-1.10: x: x (where 0.0025≤x≤0.02) is weighed.

3. A modification method for simply and significantly improving the crystal structure and cycle stability of ultra-high nickel cobalt-free positive electrode materials according to claim 1, characterized in that: The ultra-high nickel-free cobalt precursor in step (1) is Ni 0.9 Mn 0.1 (OH)2.

4. A modification method for simply and significantly improving the crystal structure and cycle stability of ultra-high nickel cobalt-free positive electrode materials according to claim 1, characterized in that: In step (1), the lithium source is one or more of lithium hydroxide, lithium carbonate, and lithium nitrate; the niobium source can be at least one of niobium pentoxide, niobium oxalate, and niobium pentachloride; and the titanium source is titanium dioxide or tetrabutyl titanate.

5. A modification method for simply and significantly improving the crystal structure and cycle stability of ultra-high nickel cobalt-free positive electrode materials according to claim 1, characterized in that: In step (3), the calcination atmosphere is oxygen, the pre-calcination temperature is 300-600°C, the heating rate is 1-10°C / min, the calcination time is 4-6 h, and then the final calcination temperature is 730-780°C, the heating rate is 1-10°C / min, and the calcination time is 10-18 h.

6. A simple and significant modification method for improving the crystal structure and cycle stability of ultra-high nickel cobalt-free cathode materials, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

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