A high-entropy alloy modified high-nickel cobalt-free positive electrode material and a preparation method thereof

Abstract

The application relates to a high-entropy alloy modified high-nickel cobalt-free positive electrode material and a preparation method thereof, and belongs to the field of chemical energy storage batteries. First, nickel ions, manganese ions and three kinds of transition metal ions are doped into a precursor through a coprecipitation method, and then lithium salt and a fourth transition metal salt are mixed with the precursor to be sintered, so that the high-entropy alloy modified high-nickel cobalt-free positive electrode material is obtained, and the chemical formula is LiNi x Mn y TM (1‑x‑y) / 4 TM (1‑x‑y) / 4 TM (1‑x‑y) / 4 TM (1‑x‑y) / 4O2, 0.8

Description

Technical Field

[0001] The present invention relates to a high-entropy alloy modified high-nickel cobalt-free cathode material and a preparation method thereof, belonging to the field of chemical energy storage batteries. Background Art

[0002] Cathode materials are a key part limiting the energy density of lithium-ion batteries. Among them, high-nickel layered cathodes have become the most promising cathode materials for next-generation lithium-ion batteries due to their high energy density, high rate performance, and good safety. However, high-nickel cathode materials still have many problems at present, including irreversible phase transition, particle microcracks caused by stress release during cycling, and erosion of the material surface by electrolyte decomposition, especially slow kinetics caused by cation mixing under high cut-off voltages. Among them, low-cobalt or cobalt-free high-nickel cathode materials have attracted more and more attention due to their lower cost. However, low-cobalt or cobalt-free high-nickel cathode materials will aggravate cation mixing, thereby seriously affecting their kinetic process and further deteriorating the electrochemical performance. In order to solve and improve these problems and meet people's performance requirements for power batteries, many scientific researchers have carried out a number of improvement methods, such as coating, modification, and precursor process design, to improve the rate performance, cycle life and safety of cathode materials. Summary of the Invention

[0003] The purpose of the present invention is to provide a high-entropy alloy modified high-nickel cobalt-free cathode material and a preparation method thereof. Through two processes of coprecipitation to prepare a hydroxide precursor and sintering, modification of the high-entropy alloy is carried out, so as to realize doping of the high-entropy alloy in the surface layer and bulk phase of the cathode material. This modification method effectively improves the rate performance and cycle life of the high-nickel cobalt-free cathode.

[0004] In order to achieve the above objective, the technical scheme of the present invention is as follows:

[0005] A high-entropy alloy modified high-nickel cobalt-free cathode material, the chemical formula of the high-nickel cobalt-free cathode material is LiNi x Mn y TM (1-x-y) / 4 TM (1-x-y) / 4 TM (1-x-y) / 4 TM (1-x-y) / 4 O2, where 0.8<x<1, 0<y<0.2, 0<x+y<1, and each TM is one of transition metal elements.

[0006] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material described, nickel ions, manganese ions and three types of transition metal ions are first doped into the precursor by a coprecipitation method, and then a lithium salt and a fourth transition metal salt are mixed with the precursor and sintered together to obtain the high-entropy alloy modified high-nickel cobalt-free cathode material.

[0007] The preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material specifically includes the following steps:

[0008] Step (1): Using water as a solution and a mixed alkaline solution of ammonia and sodium hydroxide as a complexing agent and precipitant, a mixed metal salt solution prepared with five metal salts is added dropwise to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material precursor by co-precipitation.

[0009] Step (2): After mixing the precursor, lithium salt and metal salt in a mortar, calcining is carried out under oxygen. First, pre-calcination is carried out at a lower temperature, and then the temperature is increased for calcination. After the sintering process is completed, a high-entropy alloy modified high-nickel cobalt-free cathode material is obtained.

[0010] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, in step (1), the five mixed metal salt solutions are nickel sulfate hexahydrate and manganese sulfate monohydrate, plus a mixed aqueous solution of three of the following: ferric sulfate hydrate, cobalt sulfate heptahydrate, lanthanum nitrate hydrate, titanium oxysulfate, zirconium oxychloride, magnesium sulfate, vanadium oxysulfate, anhydrous calcium chloride, and ammonium molybdate. The total concentration of metal ions in the mixed metal salt solutions is 1-3 mol / L.

[0011] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, in step (2), the molar ratio of precursor: lithium salt: fourth transition metal salt is 1:1.02~1.08:0.005~0.015, and the fourth transition metal salt is one of lanthanum nitrate hydrate, titanium oxysulfate, zirconium oxychloride, magnesium sulfate and anhydrous calcium chloride.

[0012] The preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, wherein the molar ratio of nickel, manganese and the other four transition metal salts is x:y:(1-xy) / 4:(1-xy) / 4:(1-xy) / 4:(1-xy) / 4, 0.8 <x<1,0<y<0.2,0<x+y<1。

[0013] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, in step (2), the pre-calcination temperature is 400-500℃ and the pre-calcination time is 4-6 hours.

[0014] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, in step (2), the calcination temperature is 750-830℃ and the sintering time is 10-20 hours.

[0015] In the preparation method of the high-entropy alloy modified high-nickel cobalt-free cathode material, in step (1), the mixed alkaline solution is composed of 1-4 mol / L sodium hydroxide solution and 1.5-5 mol / L ammonia solution, and the pH value is adjusted and stabilized to 10-12 by the mixed alkaline solution.

[0016] The design concept of this invention is: focusing on low cost, high abundance and applicability, this invention selects a variety of different metal ion combinations to replace cobalt in the ternary cathode, so as to improve the high rate and long cycle performance of the high-nickel cobalt-free cathode.

[0017] The advantages and beneficial effects of this invention are as follows:

[0018] 1. This invention achieves the doping of high-nickel cobalt-free cathode materials with four metals by modifying them with high-entropy alloys during the precursor preparation process and then calcining them, thereby significantly improving the rate performance and cycle stability of the materials.

[0019] 2. The high-entropy alloy modified high-nickel cobalt-free cathode material of this invention has outstanding high-rate performance. At a charge-discharge rate of 20C, the discharge capacity is 135.9mAh / g, which is 3 times that of the nickel-cobalt-manganese ternary cathode material with the same molar ratio.

[0020] 3. The doping method of the present invention is simple to operate, does not change the existing process flow, significantly improves the electrochemical performance of cobalt-free cathode materials, is easy to implement in industrial technology, and can be applied on a large scale. Attached Figure Description

[0021] Figure 1 The figures show the X-ray diffraction (XRD) patterns of the final cathode materials prepared in Examples 1-4. In the figures, the horizontal axis 2θ represents the diffraction angle (°), and the vertical axis Intensity represents the relative intensity (au).

[0022] Figure 2 The images shown are scanning electron microscope (SEM) images of the final product cathode materials prepared in Examples 1-4.

[0023] Figure 3 The image shows the energy dispersive spectroscopy (EDS) pattern of the final product prepared in Example 1.

[0024] Figure 4 The image shows the energy dispersive spectroscopy (EDS) pattern of the final product prepared in Example 2.

[0025] Figure 5 The graphs show the electrochemical performance of the batteries assembled in Examples 1-4 at different charge-discharge rates from 2.7 to 4.4 V. In the graphs, the horizontal axis represents the cycle number, and the vertical axis represents the specific capacity (mAh·g). -1 ).

[0026] Figure 6The graphs show the electrochemical performance of the batteries assembled in Examples 1-4 at 2.7-4.4V with a 1C charge-discharge rate. In the graphs, the horizontal axis represents the cycle number, and the vertical axis represents the specific capacity (mAh·g). -1 ). Detailed Implementation

[0027] In its specific implementation, this invention proposes a high-entropy alloy-modified high-nickel cobalt-free cathode material and its preparation method. The obtained material is formed by mixing and grinding a high-entropy alloy-modified nickel-manganese hydroxide precursor prepared by co-precipitation method, LiOH·H2O, and metal salt to form a mixed solid powder, calcining it under oxygen, and cooling it to obtain the high-entropy alloy-modified high-nickel cobalt-free cathode material. The specific steps are as follows:

[0028] Step (1) Deionized water is added to the reactor as the base solution. Under a protective atmosphere, a mixed metal salt solution and a mixed alkali solution are added dropwise to the reactor. The dropping rate of the mixed alkali is controlled to stabilize the pH value within a certain range, and a co-precipitation reaction is carried out to synthesize the precursor. After the feed is completed, stirring is continued, and the precipitate is aged to obtain a precipitate. The precipitate is filtered, washed, and vacuum dried to obtain a modified high-nickel cobalt-free cathode material precursor.

[0029] Step (2) The modified precursor, lithium salt, and a metal salt are added to a mortar in a certain ratio and mixed and ground evenly. Under an oxygen atmosphere, the precursor is subjected to two stages of pre-calcination and calcination to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material.

[0030] To better understand the present invention, it will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Furthermore, the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, and the endpoint values ​​of various ranges and individual point values, can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] Assembly and testing of CR2032 button batteries: The positive electrode material (the final product prepared in the comparative example and the example), Ketjen black: polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 90:5.5:4.5 to prepare a slurry, which was then coated onto aluminum foil. After drying, the aluminum foil loaded with active material was cut into small round pieces with a diameter of 12 mm using a cutting machine and used as the positive electrode. Lithium metal sheet was used as the negative electrode, polypropylene (PP) was used as the separator, and a 1M carbonate solution with a molar concentration was used as the electrolyte (where the solvent is ethylene carbonate: diethyl carbonate: methyl ethyl carbonate in a volume ratio of 3:2:5, and the solute is LiPF6). All batteries were assembled in an argon atmosphere glove box.

[0032] The assembled CR2032 button cell was tested using a CT2001A LAND battery tester. The 1C current density was defined as 180 mAh / g, the charge / discharge range was 2.7–4.4 V, and the test temperature was 25 °C.

[0033] Example 1

[0034] In this embodiment, deionized water was added to the reactor, and the pH was adjusted to 11 by adding 3 mol / L ammonia and 4 mol / L sodium hydroxide. Under a protective atmosphere (e.g., argon), a mixed metal salt solution of 2 mol / L nickel sulfate hexahydrate, manganese sulfate monohydrate, titanium oxysulfate, zirconium oxychloride, and anhydrous magnesium sulfate (prepared with a molar ratio of Ni:Mn:Ti:Zr:Mg = 0.83:0.13:0.01:0.01:0.01) was added dropwise to the reactor. The pH was stabilized at 11 by adjusting the dropping rate of the mixed alkaline solution, and a co-precipitation reaction was carried out. After the feeding was completed, stirring was continued for 2 hours, and the mixture was aged for 1 hour to obtain a precipitate. The precipitate was filtered, washed, and vacuum dried to obtain the cathode material precursor. The precursor was mixed with LiOH·H2O and calcium chloride and ground until homogeneous. The molar ratio of the precursor to LiOH·H2O and calcium chloride was 1:1.06:0.01. The material was calcined in a tube furnace under an oxygen atmosphere. First, it was pre-calcined at 450℃ for 5 hours, and then calcined at 780℃ for 17 hours. The heating rate during the pre-calcination and calcination stages was 5 min / ℃. Finally, it was cooled to 200℃ at a cooling rate of 5 min / ℃ to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material (marked NMCTZM).

[0035] A battery assembled using the cathode material obtained in this embodiment exhibits the following characteristics: at a 1C charge-discharge rate, the initial 1C discharge capacity is 186.9 mAh / g, and after 100 1C cycles, the capacity is 177.6 mAh / g, with a capacity retention rate of 95.1%. At a high 20C rate, it contributes a specific capacity of 135.9 mAh / g.

[0036] Example 2

[0037] In this embodiment, deionized water was added to the reactor, and the pH was adjusted to 11 by adding 3 mol / L ammonia and 4 mol / L sodium hydroxide. Under a protective atmosphere (e.g., argon), a mixed metal salt solution of 2 mol / L nickel sulfate hexahydrate, manganese sulfate monohydrate, ammonium molybdate, ferric sulfate hydrate, and vanadium oxysulfate (prepared with a molar ratio of Ni:Mn:Mo:Fe:V = 0.83:0.13:0.01:0.01:0.01) was added dropwise to the reactor. The pH was stabilized at 11 by adjusting the dropping rate of the mixed alkaline solution to carry out a co-precipitation reaction. After the feeding was completed, stirring was continued for 2 hours, and the mixture was aged for 1 hour to obtain a precipitate. The precipitate was filtered, washed, and vacuum dried to obtain the cathode material precursor. The precursor was ground and mixed evenly with LiOH·H2O and lanthanum nitrate hydrate, with a molar ratio of precursor to LiOH·H2O and lanthanum nitrate hydrate of 1:1.06:0.01. The high-entropy alloy modified high-nickel cobalt-free cathode material (labeled NMLMFV) was first pre-calcined at 450℃ for 5 hours in an oxygen atmosphere in a tube furnace, and then calcined at 780℃ for 17 hours. The heating rate during the pre-calcination and calcination stages was 5 min / ℃. Finally, the temperature was lowered to 200℃ at a cooling rate of 5 min / ℃ to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material.

[0038] A battery assembled using the cathode material obtained in this embodiment exhibits the following characteristics: at a 1C charge-discharge rate, the initial 1C discharge capacity is 182.6 mAh / g, and after 100 1C cycles, the capacity is 176.1 mAh / g, with a capacity retention rate of 96.4%. At a high 20C rate, it contributes a specific capacity of 89.1 mAh / g.

[0039] Example 3

[0040] In this embodiment, deionized water was added to the reactor, and the pH was adjusted to 11 by adding 3 mol / L ammonia and 4 mol / L sodium hydroxide. Under a protective atmosphere (e.g., argon), a mixed metal salt solution of 2 mol / L nickel sulfate hexahydrate, manganese sulfate monohydrate, and cobalt sulfate heptahydrate (prepared with a molar ratio of Ni:Mn:Co = 0.83:0.13:0.04) was added dropwise to the reactor. The pH was stabilized at 11 by adjusting the dropping rate of the mixed alkaline solution to carry out a co-precipitation reaction. After the feeding was completed, stirring was continued for 2 hours, and the mixture was aged for 1 hour to obtain a precipitate. The precipitate was filtered, washed, and vacuum dried to obtain the cathode material precursor. The precursor was ground and mixed evenly with LiOH·H2O, with a molar ratio of precursor to LiOH·H2O of 1:1.05. The material was calcined in a tube furnace under an oxygen atmosphere. First, it was pre-calcined at 450°C for 5 hours, and then calcined at 780°C for 17 hours. The heating rate during the pre-calcination and calcination stages was 5 min / °C. Finally, it was cooled to 200°C at a cooling rate of 5 min / °C to obtain a high-entropy alloy modified high-nickel cathode material (labeled NMC).

[0041] A battery assembled using the cathode material obtained in this embodiment showed the following results: at a 1C charge-discharge rate, the initial 1C discharge capacity was 193.15 mAh / g, and after 100 1C cycles, the capacity was 119.01 mAh / g, with a capacity retention rate of 61.6%. At a high 20C rate, it contributed a specific capacity of 56.2 mAh / g.

[0042] Example 4

[0043] In this embodiment, deionized water was added to the reactor, and the pH was adjusted to 11 by adding 3 mol / L ammonia and 4 mol / L sodium hydroxide. Under a protective atmosphere (e.g., argon), a mixed metal salt solution of 2 mol / L nickel sulfate hexahydrate and manganese sulfate monohydrate (prepared at a molar ratio of Ni:Mn = 0.83:0.17) was added dropwise to the reactor. The pH was stabilized at 11 by adjusting the dropping rate of the mixed alkaline solution to carry out a co-precipitation reaction. After the feeding was completed, stirring was continued for 2 hours, and the mixture was aged for 1 hour to obtain a precipitate. The precipitate was filtered, washed, and vacuum dried to obtain the cathode material precursor. The precursor was ground and mixed evenly with LiOH·H2O at a molar ratio of 1:1.05. The material was calcined in a tube furnace under an oxygen atmosphere. First, it was pre-calcined at 450℃ for 5 hours, and then calcined at 780℃ for 17 hours. The heating rate during the pre-calcination and calcination stages was 5 min / ℃. Finally, it was cooled to 200℃ at a cooling rate of 5 min / ℃ to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material (marked as NM).

[0044] A battery assembled using the cathode material obtained in this embodiment showed the following results: at a 1C charge-discharge rate, the initial 1C discharge capacity was 152.1 mAh / g, and after 100 1C cycles, the capacity was 129.5 mAh / g, with a capacity retention rate of 85.1%. At a high rate of 20C, it contributed a specific capacity of 1.2 mAh / g.

[0045] like Figure 1 As shown, the X-ray diffraction (XRD) patterns of the final product cathode materials prepared in Examples 1-4 are obtained from... Figure 1 It can be seen that the modification of high-entropy alloys did not change the crystal structure of the materials; all the modified materials still retained their original crystal structure. Space group.

[0046] like Figure 2 As shown, the scanning electron microscope (SEM) images of the final product cathode materials prepared in Examples 1-4 are obtained from... Figure 2 It can be seen that the primary particles of the cathode material modified by the high-entropy alloy change from rod-shaped to block-shaped. This indicates the growth along the a-axis and b-axis.

[0047] like Figure 3 As shown, the energy dispersive spectroscopy (EDS) pattern of the final product prepared in Example 1 is obtained by... Figure 3 It can be seen that the selected metal elements were successfully doped.

[0048] like Figure 4 As shown, the energy dispersive spectroscopy (EDS) pattern of the final product prepared in Example 2 is obtained from... Figure 4 It can be seen that the selected metal elements were successfully doped.

[0049] like Figure 5 As shown, the electrochemical performance of the batteries assembled in Examples 1-4 at different charge-discharge rates of 2.7-4.4V is illustrated by [the graph showing the electrochemical performance of the batteries]. Figure 5 It can be seen that the rate performance of the final products prepared in Examples 1 and 2 is significantly improved, indicating that high-entropy modification plays an important role in improving the rate performance of cobalt-free cathodes.

[0050] like Figure 6 As shown, the electrochemical performance of the batteries assembled in Examples 1-4 at 2.7-4.4V at a 1C rate charge-discharge cycle is illustrated in the graph. Figure 6 It can be seen that the cycling performance of the final products prepared in Examples 1 and 2 is significantly improved, indicating that high-entropy modification plays an important role in improving the long-cycle performance of cobalt-free cathodes.

[0051] The results show that the high-entropy alloy-modified high-nickel cobalt-free cathode material of this invention has a more stable structure and an increased lithium-ion migration rate. The obtained material exhibits excellent high-rate performance and cycle stability. Batteries assembled using the cathode material obtained in this invention show the following performance indicators: at a 1C charge-discharge rate, the initial 1C discharge capacity can reach over 186 mAh / g; after 100 cycles at 1C, the capacity can reach over 177 mAh / g, with a capacity retention rate of over 90%. At a high rate of 20C, it can contribute a specific capacity of over 135 mAh / g. The process of this invention is simple, does not change the original industrial synthesis route, and is easily industrialized.

Claims

1. A method for preparing a high-nickel, cobalt-free cathode material modified with a high-entropy alloy, characterized in that, The high-nickel, cobalt-free cathode material has the chemical formula LiNi. 0.83 Mn 0.13 Mg 0.01 Ca 0.01 Ti 0.01 Zr 0.01 O2; First, nickel ions, manganese ions, and three transition metal ions are doped into the precursor via co-precipitation. Then, lithium salt and a fourth transition metal salt are mixed and sintered together. This process of preparing the hydroxide precursor via co-precipitation and sintering modifies the high-entropy alloy, achieving doping of the high-entropy alloy in both the surface and bulk phases of the cathode material. This yields a high-nickel, cobalt-free cathode material modified with the high-entropy alloy. The modified high-nickel, cobalt-free cathode material retains its high-entropy alloy properties. Space group; The method specifically includes the following steps: Step (1): Using water as a solution and a mixed alkaline solution of ammonia and sodium hydroxide as a complexing agent and precipitant, a mixed metal salt solution prepared by nickel salt, manganese salt, magnesium salt, titanium salt and zirconium salt is added dropwise to obtain a high-entropy alloy modified high-nickel cobalt-free cathode material precursor by co-precipitation. Step (2): After mixing the precursor, lithium salt and calcium salt in a mortar, calcining is carried out under oxygen. First, pre-calcination is carried out at a lower temperature, and then the temperature is increased for calcination. After the sintering process is completed, a high-entropy alloy modified high-nickel cobalt-free cathode material is obtained. The molar ratio of nickel salt, manganese salt, magnesium salt, calcium salt, titanium salt and zirconium salt is 0.83:0.13:0.01:0.01:0.01:0.

01.

2. The method for preparing the high-nickel, cobalt-free cathode material modified with high-entropy alloy as described in claim 1, characterized in that, In step (1), the nickel salt, manganese salt, magnesium salt, titanium salt and zirconium salt are nickel sulfate hexahydrate, manganese sulfate monohydrate, magnesium sulfate, titanium oxysulfate and zirconium oxychloride, respectively, and the total concentration of metal ions in the mixed metal salt solution is 1 to 3 mol / L.

3. The method for preparing high-nickel, cobalt-free cathode material modified with high-entropy alloy as described in claim 2, characterized in that, In step (2), the lithium salt is LiOH·H2O, the calcium salt is calcium chloride, and the molar ratio of the precursor to LiOH·H2O and calcium chloride is 1:1.06:0.

01.

4. The method for preparing the high-nickel, cobalt-free cathode material modified with high-entropy alloy as described in claim 1, characterized in that, In step (2), the preheating temperature is 400-500℃ and the preheating time is 4-6 hours.

5. The method for preparing the high-nickel, cobalt-free cathode material modified with high-entropy alloy as described in claim 1, characterized in that, In step (2), the calcination temperature is 750-830℃ and the sintering time is 10-20 hours.

6. The method for preparing the high-nickel, cobalt-free cathode material modified with high-entropy alloy as described in claim 1, characterized in that, In step (1), the mixed alkaline solution consists of 1-4 mol / L sodium hydroxide solution and 1.5-5 mol / L ammonia solution, and the pH value is adjusted and stabilized to 10-12 by the mixed alkaline solution.

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