Preparation method of ultrahigh nickel cobalt-free single crystal positive electrode material with long cycle stability under high voltage and large current driven by high entropy

Abstract

The invention discloses an Mg / Nb / Al co-doped and coated single crystal LiNi0. 9Mn0. 1O2 positive electrode material, and the cycling stability is obviously enhanced. The formed high-entropy layer enables lattice oxygen to be highly reversible, precipitation and release of oxygen are effectively inhibited, formation of oxygen vacancies is slowed down, and transition metal ions are anchored. In the lithium removal / intercalation process, reversibility of H2-H3 phase change is improved, crystal face slippage is relieved, accumulation and release of anisotropic lattice strain are relieved, and Li < + > dynamic diffusion is promoted. Meanwhile, an Al2O3 / LiAlO2 interface formed on the surface induces formation of thin and stable CEI, HF attack and dissolution of metal ions are improved, and the material has rapid charging and discharging capacity and high-voltage stability. Therefore, the high-entropy single-crystal positive electrode material plays a crucial role in effectively improving the rate capability and the cycling stability of the ultrahigh-nickel cobalt-free negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and particularly to a preparation method of a high-entropy-driven ultra-high nickel cobalt-free single crystal cathode material with long cycle stability under high voltage and large current. Background Art

[0002] Lithium-ion batteries (LiBs), as efficient energy storage systems, play an irreplaceable role in promoting the clean energy transition and achieving the carbon neutrality goal. However, in order to meet the requirements of electric vehicles and large-scale energy storage systems for higher energy density, lower cost, and higher sustainability, traditional cathode materials must undergo a profound innovation. Currently, layered cathode materials based on nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA) systems are still the mainstream choice, but the dependence on cobalt brings serious economic and environmental problems. In addition, in order to further improve the energy density, the high-nickel cathode (nickel content > 80%) has become an important trend.

[0003] Developing cobalt-free, high-nickel cathode materials with high capacity and stability has become the research frontier in this field. Nano-scale single crystal high-nickel layered materials have attracted much attention due to their structural stability and ion transport performance during cycling.

[0004] As the lithium-ion battery cathode material develops towards high nickel and cobalt-free, its cycle stability decreases significantly. The main reasons include that cobalt plays a role in stabilizing the lattice structure in traditional cathode materials. After removing cobalt, the material is prone to polarization under high-rate charge and discharge conditions, resulting in uneven distribution of lithium ions during insertion and extraction, and then causing local stress concentration. This stress accumulation will lead to microcracks, pulverization, and oxygen evolution of the material, thus significantly reducing the cycle life, especially obvious at high rates. Since the cathode material is directly exposed to the electrolyte environment, HF generated by the reaction of H2O in the electrolyte with LiPF6 will erode the cathode interface, resulting in the dissolution of transition metals. These dissolved metal ions are reduced after migrating to the anode, forming metal deposits and damaging the solid electrolyte interface film (SEI). During repeated charge and discharge processes, this process continuously consumes lithium ions and electrolyte molecules, exacerbating capacity decay and affecting the long-term stability of the battery.

[0005] In the high-entropy single crystal cathode material, Ni can improve the reversible capacity and charge compensation, Mn plays a supporting role in the structure, Mg improves the structural stability during the insertion and extraction of lithium ions, and Nb replacing transition metal (TM) ions helps to form TM-O-Nb, inhibiting the oxidation of lattice oxygen and enhancing the stability of lattice oxygen (because the Nb-O bond is much stronger than the TM-O bond), and Nb 5+It does not participate in the oxidation process, resulting in a decrease in the oxygen vacancy concentration in the material, thereby reducing the in-plane migration of TM, improving the reversibility of lattice plane sliding. Al forms LiAlO₂ and γ-Al₂O₃ films on the surface, constructing a stable lithium-ion channel, while blocking the erosion of the electrolyte and the damage to the structure caused by HF and other side reactions. In addition, this high-entropy layer can effectively inhibit the disorder of Li / Ni cations, enhance the reversibility of the H₂-H₃ phase change in the material, and reduce the stress and strain during lithium-ion deintercalation and insertion. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a high-entropy-driven ultra-high nickel cobalt-free single crystal cathode material with long-cycle stability under high voltage and large current in view of the above problems. This synthesis method simplifies the complex steps required for the traditional preparation of high-nickel ternary single crystal materials, providing a low-cost and high-efficiency solution for actual industrial production.

[0007] The technical solution adopted by the present invention is as follows: A preparation method of a high-entropy-driven ultra-high nickel cobalt-free single crystal cathode material with long-cycle stability under high voltage and large current, characterized by comprising the following steps:

[0008] S1. Weigh an appropriate amount of ultra-high nickel cobalt-free precursor and lithium source according to a molar ratio of 1:1.01 - 1:1.08, and add KCl and LiCl as cosolvents. Grind them repeatedly for 30 - 60 min until evenly mixed to obtain a first mixture;

[0009] Place the first mixture in a tube furnace and use a gradient calcination technique under an oxygen atmosphere to obtain a blank sample of the ultra-high nickel cobalt-free cathode material;

[0010] The temperature control conditions for the gradient calcination are: heat up at a heating rate of 1 - 10 °C / min to 400 - 600 °C, hold for 3 - 6 h, and then heat up at a heating rate of 1 - 10 °C / min to 800 - 820 °C, hold for 10 - 18 h;

[0011] S2. A preparation method of a high-entropy-driven ultra-high nickel cobalt-free single crystal cathode material with long-cycle stability under high voltage and large current follows the steps of S1, and synchronously adds Mg(NO₃)₂ and C 10 H₅NbO 20 ·xH₂O to obtain a single crystal cathode material;

[0012] Put the single crystal cathode material and C₉H 21 AlO₃ into a glass bottle, add anhydrous ethanol, seal and stir for 10 h, transfer it to an oil bath at 60 - 80 °C to evaporate to dryness, and then anneal it in a tube furnace at 500 - 600 °C in an oxygen atmosphere for 300 min to obtain a high-entropy single crystal cathode material;

[0013] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: We synthesized Mg / Al / Nb co-doped and coated nickel-rich single crystal LiNi 0.9 Mn 0.1 O2, which, as a cathode material, has good electrochemical performance and structural stability at high voltages and high SOC. The test results show that Mg / Al / Nb, as an external dopant, can enter the surface layer of the structure and form a high-entropy region, while a uniform Al2O3 and LiAlO2 coating layer is formed on the outer layer. The high-entropy layer can inhibit the precipitation and migration of oxygen, enhance the stability of lattice oxygen, make the lattice oxygen highly reversible, and thus slow down the formation of oxygen vacancies. At the same time, the high-entropy region can promote the reversibility of the H2-H3 phase transition of the material, and weaken the stress / strain during deintercalation / lithiation. The formed pillar effect stabilizes the reversible reaction sites of lattice oxygen while releasing stress, effectively alleviating the in-plane migration and lattice plane sliding during phase transition. The above results show that the precisely prepared near-surface high-entropy nickel-rich single crystal is highly effective in reducing the synthesis cost and solving the problem of single-crystal chemo-mechanical degradation, and the satisfactory electrochemical performance is also a solution to accelerate its commercial application. Brief Description of the Drawings

[0014] Figure 1 is a scanning electron microscope (SEM) image of the final product prepared in Example 1 of the present invention;

[0015] Figure 2 is a scanning electron microscope (SEM) image of the final product prepared in Example 2 of the present invention;

[0016] Figure 3 is a comparison chart of the discharge specific capacity of the final products prepared in Example 1 and Example 2 of the present invention at 25 °C, a cut-off voltage of 2.7 - 4.3 V, and a 5 C rate for 400 cycles;

[0017] Figure 4 is a comparison chart of the discharge specific capacity of the final products prepared in Example 1 and Example 2 of the present invention at 25 °C, a cut-off voltage of 2.7 - 4.3 V, and different rates;

[0018] Figure 5 is a schematic diagram of the long-cycle capacity of the full cell of Example 2 of the present invention. Detailed Embodiments

[0019] The present invention will be described in detail below with reference to the accompanying drawings. In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. 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. In addition, the endpoints and any values disclosed in this document are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0020] The following are the methods for material characterization and analysis used in Example 1 and Example 2:

[0021] Scanning electron microscope (SEM) test: Scanning electron microscope, instrument model: SU5000.

[0022] Assembly and test of CR2025 button battery: The positive electrode material (the final products prepared in Example 1 and Example 2), conductive carbon black (super p), and polyvinylidene fluoride (PVDF) are made into a slurry according to 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 as the positive electrode. A lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and a 1 M carbonate solution is used as the electrolyte (wherein the solvent is a mixed solution of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a volume ratio of 1:1:1, and the solute is LiPF6). A CR2025 button battery is assembled in a glove box under an argon atmosphere.

[0023] Example 1

[0024] The molar ratio of the precursor Ni 0.9 Mn 0.1 O2 and LiOH·H2O is 1:1.05, and then (KCl, LiCl) with a mass ratio of 1:0.3 to the mixture is weighed and put into a ball mill for ball milling. The ball-milled mixed powder is put into a tubular furnace, heated to 500 °C and calcined for 300 min, then heated to 820 °C and calcined for 900 min, and then naturally cooled. During this period, oxygen is continuously introduced to obtain a single-crystal positive electrode material.

[0025] As Figure 1 shown, the particles are uneven and there is agglomeration. The particles that are not fully grown will become pseudo-capacity in the performance test, resulting in structural fragmentation and crystal plane rotation.

[0026] Example 2

[0027] The precursor Ni 0.9 Mn 0.1 O2 and Mg(NO3)2, C 10 H5NbO 20 ·xH2O are placed in a beaker according to a molar ratio of 1:0.005:0.0025. After adding absolute ethanol and ultrasonically treating for 30 min, it is heated in a water bath at 65 °C until evaporated to dryness. The dried mixture and LiOH·H2O are weighed at a molar ratio of 1:1.05, and (KCl, LiCl) with a mass ratio of 1:0.3 to the mixture is weighed and put into a ball mill for ball milling. The ball-milled mixed powder is placed in a tube furnace, heated to 500 °C and calcined for 300 min, then heated to 820 °C and calcined for 900 min, and then naturally cooled. During this period, oxygen is continuously introduced to obtain a single-crystal cathode material. It and C9H 21 AlO3 are placed in a glass bottle according to a molar ratio of 1:0.01, absolute ethanol is added, sealed and stirred for 10 h, transferred to an oil bath at 70 °C and evaporated to dryness, and then annealed in a tube furnace at 500 °C for 300 min in an oxygen atmosphere to obtain a high-entropy single-crystal cathode material.

[0028] As Figure 2 shown, the high-entropy material particles grow uniformly without agglomeration, that is, the surface is not easily reactive with water and oxygen, the structure is stable, and obvious structural changes are not likely to occur during testing.

[0029] As Figure 3 shown, there are obvious differences in stability between Example 1 and Example 2 under high current and high number of cycles. The stability of Example 2 is significantly higher than that of Example 1, indicating that the high-entropy single-crystal cathode material makes an outstanding contribution to the cycle stability of the battery.

[0030] As Figure 4 shown, there is a large gap in rate performance between Example 1 and Example 2. At high rates, Example 2 has a higher capacity performance, and at low rates, it has better capacity stability, indicating that its structure has high reversibility and can better stably cycle.

[0031] As Figure 5 shown, the performance of Example 2 in the full battery is shown. It has good cycle stability and can still have a capacity retention rate of 93% after cycling 800 times at high SOC.

[0032] The above has described the present invention in detail in combination with the embodiments. However, those skilled in the art can understand that without departing from the gist 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 change range of the present invention and will not be elaborated here one by one.

Claims

1. A method for preparing an ultra-high nickel cobalt-free single crystal positive electrode material with long cycle stability under high voltage and high current driven by high entropy, characterized in that: It is composed of a variety of metal cations, which increases the entropy value of the material system and improves the lattice stability; reduces the tendency of phase separation, reduces the structural collapse during charging and discharging, and improves the cycle stability; the single crystal structure reduces the interface between particles, reduces the problem of particle breakage caused by volume expansion during charging and discharging; avoids the resistance generated by the interface between particles in polycrystalline materials, and improves the electron transmission capacity; single crystal particles reduce the structural degradation caused by interface side reactions during the cycle and improve the cycle life.

2. The method according to claim 1, characterized in that The following steps are involved: S1. Weigh an appropriate amount of an ultra-high nickel cobalt-free precursor and a lithium source according to a molar ratio of 1:1.01-1:1.08, add KCl and LiCl as co-solvents, and grind repeatedly for 30-60 min until the mixture is uniformly mixed to obtain a first mixture, place the first mixture in a tube furnace, and use a gradient calcination technology under an oxygen atmosphere to obtain an ultra-high nickel cobalt-free cathode material blank sample; The temperature control conditions of the gradient calcination are: heating to 400-600°C at a heating rate of 1-10°C / min, keeping warm for 3-6 hours, then heating to 800-820°C at a heating rate of 1-10°C / min, keeping warm for 10-18 hours; S2. According to the steps of S1, weigh an appropriate amount of high-nickel cobalt-free precursor Ni 0.9 After Mn0.1(OH)2, Mg(NO3)2 and C were added simultaneously 10 H5B 20 xH2O to obtain a single crystal positive electrode material; the single crystal positive electrode material and C9H 21 AlO3 is put into a glass bottle and anhydrous ethanol is added, which is sealed and stirred for 10 hours, then transferred to an oil bath pot and evaporated at 60-80°C, and then annealed at 500-600°C for 300 minutes in an oxygen atmosphere in a tubular furnace to obtain a high entropy single crystal positive electrode material.

3. The method according to claim 2, characterized in that The high entropy composition of the single crystal high entropy positive electrode material can be Ni, Mn, Mg, Nb, Al and the like.

4. The method according to claim 2, characterized in that The ratio of the precursor to the lithium source is between 1:1.01-1:1.08, and the lithium source can be lithium hydroxide, lithium nitrate, or lithium carbonate.

5. The method according to claim 2, characterized in that The high entropy cathode material adopts a gradient calcination process.

6. The method according to claim 2, characterized in that According to the material requirements, adjust the dosage ratio of the co-solvents KCl and LiCl.

7. The method according to claim 2, characterized in that The ultra-high nickel precursor is Ni 0.9 Mn 0.1 (OH)2.

8. The method according to claim 2, characterized in that The certain oxygen atmosphere flow rate is 1-10 L / min.

9. The method according to claim 2, characterized in that During the preparation process, the high temperature range is between 800-820℃.

10. The method according to claim 2, characterized in that The annealing temperature range is 500-600°C.

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