A surface high-entropy and internal middle-entropy step-doped high-nickel layered oxide positive electrode material and a preparation method thereof

Abstract

The application belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material and a preparation method thereof. The preparation method of the surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material is characterized in that more than five elements are doped on the surface of the material to form a surface high-entropy reconstruction layer, and four elements are doped in the material to form a medium-entropy doped structure. The high-entropy reconstruction layer on the surface can form a superlattice structure on the surface by the synergistic effect of multiple elements and reduce the valence of nickel on the surface to realize the stability of the interface structure and reduce the occurrence of side reactions with electrolyte. This method can significantly improve the cycle stability of the high-nickel layered oxide positive electrode material, and is a method with simple process, low cost, convenient operation and excellent performance, and has industrialized production application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a surface high-entropy and internal medium-entropy gradient doped high-nickel layered oxide positive electrode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used due to their high energy density, long cycle life, low self-discharge and no memory effect. With the rapid development of electric vehicles and portable electronic devices, the existing energy density of lithium ion batteries has been unable to meet the demand for long endurance. Since the positive electrode material of the lithium ion battery is the main factor limiting the improvement of the energy density of the battery and the realization of long endurance, the use of high energy density positive electrode materials has become the preferred way to improve lithium ion batteries.

[0003] In recent years, high-nickel layered oxide positive electrode materials have rapidly become the preferred raw material for high-energy-density batteries due to their high reversible specific capacity. However, high-nickel layered oxide positive electrode materials still face many challenges in application: for example, during charging, the unstable Ni 4+ ions on the surface of the positive electrode can easily cause side reactions; for example, electrolyte decomposition, metal ion dissolution and lattice oxygen release; for example, during the cycle process, lattice expansion and contraction cause microcracks to occur, which in turn exponentially increases the interface area between the positive electrode and the electrolyte, causing the interface side reaction to penetrate into the material particle interior; for example, during the charging and discharging process, Ni 2+ in the transition metal layer can migrate to the lithium layer, occupy lithium vacancies to form cationic disordering, causing a large number of lithium ions to be inactivated, and the change in structure can cause adverse irreversible phase changes and lattice oxygen release.

[0004] For the problems existing in high-nickel layered oxide positive electrode materials, the common method in the prior art is to use surface coating and bulk doping in coordination to modify the layered oxide. Among them, surface modification (surface coating) can form a chemically inert protective layer, inhibit the decomposition of the electrolyte, slow down the surface structure degradation, and effectively improve the stability of the electrode-electrolyte interface. Bulk doping can improve the electronic structure of the transition metal outside, enhance the bond energy of the transition metal ion and oxygen, and increase the electronic conductivity of the material, inhibit lithium-nickel disordering, and relieve the crystal expansion and lattice oxygen release during the charging and discharging process. For this, there are some reports in the prior art, for example, a metal oxide coated modified doped ternary positive electrode material and a preparation method thereof are disclosed in Chinese Patent No. CN105118967A, which modifies the surface of the high-nickel layered oxide of the lithium ion battery by surface coating and bulk doping, so that it has higher electronic conductivity and cycle stability, but this patent cannot solve the problem of microcracks caused by the difference in volume expansion between the coating layer and the bulk of the high-nickel layered oxide electrode.

[0005] Based on the problems existing in the prior art, the present application adopts various metal sources as dopants to perform bulk doping and surface reconstruction on high-nickel layered oxide positive electrode materials (such as NCM) of lithium ion batteries, and adjusts the types of dopants, process parameters and specific implementation procedures to realize the improvement of the energy density and the cycle stability and other electrochemical performances of the positive electrode materials. SUMMARY

[0006] The present application aims at the deficiencies of the prior art, and provides a surface high-entropy internal medium-entropy gradient-doped high-nickel layered oxide positive electrode material and a preparation method thereof. The surface of the material is doped with more than five elements to form a surface high-entropy reconstruction layer, and the internal medium of the material is doped with four elements to form a medium-entropy doped structure. The surface high-entropy reconstruction layer can form a superlattice structure on the surface by utilizing the synergistic effect of multiple elements and reduce the valence of nickel on the surface to realize the stability of the interface structure and reduce the occurrence of side reactions with electrolyte. In addition, the gradient structure of the surface high-entropy reconstruction layer and the internal medium-entropy doped structure can relieve the lattice mismatch in the volume expansion and contraction process and reduce the generation of microcracks. This method can significantly improve the cycle stability of the high-nickel layered oxide positive electrode material, and is a method with simple process, low cost, convenient operation and excellent performance, which has the prospect of industrial production and application.

[0007] In order to achieve the above technical purpose, the present application adopts the following technical scheme:

[0008] A preparation method of a surface high-entropy internal medium-entropy gradient-doped high-nickel layered oxide positive electrode material, comprising the following steps:

[0009] 1) uniformly mixing a high-nickel layered oxide precursor, a metal doping precursor I and a lithium source according to a certain proportion, and then placing them in an atmosphere furnace to perform primary sintering under a modified atmosphere to obtain a doped high-nickel layered oxide positive electrode material;

[0010] 2) uniformly mixing the high-nickel layered oxide positive electrode material in step 1) and a metal doping precursor II according to a certain proportion, and then placing them in an atmosphere furnace to perform secondary sintering under a modified atmosphere to obtain a surface high-entropy internal medium-entropy gradient-doped high-nickel layered oxide positive electrode material.

[0011] Further, the chemical formula of the high-nickel layered oxide precursor in step 1) is Ni 1-x-y-z Co x Mn y Al z (OH)2, x>0, y>0, z>0, 0.6≤(1-x-y-z)<1.

[0012] Further preferably, in step 1), the chemical formula of the high-nickel layered oxide precursor is Ni 0.96 Co0.015 Mn 0.015 Al 0.01 (OH)2.

[0013] Further, the metal-doped precursor one in step 1) is one or more of metal oxides, metal nitrates, metal sulfates, metal acetates, metal carbonates, and metal organic salts; preferably, the metal in step 1) is one or more of sodium, magnesium, potassium, calcium, scandium, titanium, vanadium, chromium, iron, copper, zinc, gallium, germanium, yttrium, zirconium, niobium, molybdenum, tantalum, tungsten, lanthanum, neodymium, cerium, and europium.

[0014] Further, the lithium source in step 1) is any one of lithium carbonate and lithium hydroxide.

[0015] Further preferably, the molar ratio of the high-nickel layered oxide precursor to the metal-doped precursor one and the lithium source in step 1) is 1:(0.00005-0.1):(1-1.2). Further, the one-step sintering in step 1) includes a first-stage sintering and a second-stage sintering.

[0016] Further preferably, the temperature of the first-stage sintering is 200-670°C, the time of the first-stage sintering is 1-9h, the temperature of the second-stage sintering is 600-900°C, and the time of the second-stage sintering is 6-24h.

[0017] Further, the metal-doped precursor two in step 2) is one or more of metal oxides, metal nitrates, metal sulfates, metal acetates, metal carbonates, and metal organic salts; preferably, the metal element in step 2) is one or more of sodium, magnesium, potassium, calcium, scandium, titanium, vanadium, chromium, iron, copper, zinc, gallium, germanium, yttrium, zirconium, niobium, molybdenum, tantalum, tungsten, lanthanum, neodymium, cerium, and europium, and is different from the metal element selected in the metal-doped precursor one in step 1).

[0018] Further preferably, the molar ratio of the high-nickel layered oxide precursor to the metal-doped precursor two in step 2) is 1:(0.00005-0.1).

[0019] Further, the temperature of the second-step sintering in step 2) is 300-900°C, and the sintering time is 0.5-15h.

[0020] Further, the modification atmosphere in step 1) and step 2) is an oxygen atmosphere, a nitrogen atmosphere, an ammonia atmosphere, a sulfur dioxide atmosphere, a hydrogen sulfide atmosphere, or a combination atmosphere of any two of the five atmospheres, or a combination atmosphere of any three of the five atmospheres, or a combination atmosphere of any four of the five atmospheres, or a combination atmosphere of the five atmospheres.

[0021] Further preferably, when the modified atmosphere is a mixture of two gases, the ratio in the mixture is oxygen: other gas = (6-10):(1-4), and the other gas is nitrogen, ammonia, sulfur dioxide or hydrogen sulfide.

[0022] Further, the surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material is prepared by the surface modification method, has good electric capacity and charge-discharge performance, and can be used to prepare a lithium ion battery.

[0023] Further, based on the overall inventive concept, the application further provides application of the surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material in preparation of a lithium ion battery.

[0024] Further, the application further provides a method for preparing a lithium ion battery by using the surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material, and specifically includes the following steps:

[0025] a. A certain amount of surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material, conductive agent and binder are placed in a container to obtain a mixed powder;

[0026] b. A solvent is added to the mixed powder in step a, and ultrasonic dispersion is performed at a power of 80-100 W for 8-12 min, and then a polytetrafluoroethylene magnetic sub is put into the container to stir at a rotating speed of 300-400 r / min for 8-12 h, so that the high-nickel layered oxide positive electrode material and the conductive agent are uniformly dispersed to obtain a mixed slurry;

[0027] c. The mixed slurry in step b is coated on an aluminum foil (current collector), dried at a temperature of 60-80℃ for 8-12 h, and then made into a button electrode sheet with a diameter of 12 mm; then the prepared electrode sheet is used as a working electrode, a metal lithium sheet is used as a counter electrode, a separator is mounted, a high-nickel 4.3V electrolyte is used as an electrolyte, and a button cell is assembled, and the battery model is a CR2032 type button cell.

[0028] Specifically, the conductive agent in step a is carbon black (Super-P), and the binder is PVDF.

[0029] Specifically, the solvent is selected from one of deionized water, ethanol and NMP.

[0030] Specifically, the mass of the solvent is 1-1.5 times the mass of the mixed powder.

[0031] Specifically, in the mixed slurry obtained in step b, the weight ratio of the surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material, the conductive agent and the binder is (16-18):1:(1-2).

[0032] Specifically, the diaphragm type is a polypropylene diaphragm, and main components of an electrolyte used by the battery are: lithium salt (lithium hexafluorophosphate); preferably, the electrolyte is 1M LiPF6 in EC: EMC = 3:7 Vol%, and 2wt% vinylene carbonate VC additive is added.

[0033] Specifically, in step c, the loading amount of the mixed slurry on the prepared electrode sheet is 1-5 mg / cm 2 .

[0034] Further, based on a total inventive concept, the application also provides a lithium ion battery prepared by using the surface high-entropy internal entropy gradient doped high-nickel layered oxide positive electrode material.

[0035] Compared with the prior art, the application has the following advantages:

[0036] 1. The preparation method of the application performs surface reconstruction on the surface of the layered oxide through high-entropy doping, constructs an ultra-stable superlattice structure at the weakest interface, reduces the occurrence of side reactions, and avoids the decrease of discharge specific capacity caused by excessive doping.

[0037] 2. The application performs medium-entropy doping in the bulk phase, effectively enhances the bond energy of transition metals and oxygen through multi-element synergy, reduces lithium-nickel mixing, slows down the adverse phase change, and inhibits lattice oxygen release.

[0038] 3. The application improves and relieves the surface structure and internal lattice mismatch in the volume expansion and contraction process through the gradient structure of surface high-entropy and internal medium-entropy, and reduces the generation of micro-cracks in the cycle process. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The scanning electron microscope image of the high-nickel layered oxide positive electrode material prepared in Example 1;

[0040] Figure 2 The scanning electron microscope image of the high-nickel layered oxide positive electrode material prepared in Example 2;

[0041] Figure 3 The scanning electron microscope image of the high-nickel layered oxide positive electrode material prepared in Example 3;

[0042] Figure 4 The cycle performance graph of Comparative Example 1, Comparative Example 2, Example 1, Example 2 and Example 3;

[0043] Figure 5 The rate performance graph of Comparative Example 1, Comparative Example 2, Example 1, Example 2 and Example 3. DETAILED DESCRIPTION

[0044] The application will be further described in conjunction with the accompanying drawings. The embodiments are implemented on the premise of the technical solutions of the application, and detailed implementation modes and processes are given, but the protection scope of the application is not limited to the following embodiments.

[0045] The experimental methods not specified in the following examples are generally carried out according to conventional conditions, and the raw materials and reagents used, if not specifically stated, are all conventional commercially available products.

[0046] The precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2 used in the comparative examples and the embodiments is provided by Henan Xinxiang Tianli Energy Co., Ltd., and its preparation method is a conventional method in the prior art, which is not the point of the application and will not be described in detail.

[0047] Comparative Example 1

[0048] In Comparative Example 1, the precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2 and LiOH·H2O are uniformly mixed in a molar ratio of 1:1.03, and then two-stage sintering is carried out under a pure oxygen atmosphere, the temperature of the first-stage sintering is 400℃, the sintering time is 4h, the temperature of the second-stage sintering is 720℃, and the sintering time is 10h, to obtain a LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0049] Comparative Example 2

[0050] Comparative Example 2 provides a preparation method of a medium-entropy doped high-nickel layered oxide positive electrode material, and the specific steps are as follows:

[0051] 1) The precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2, TiO2 and LiOH·H2O are uniformly mixed in a molar ratio of 1:0.003:1.03, and then two-stage sintering is carried out under an oxygen atmosphere, the temperature of the first-stage sintering is 400℃, the sintering time is 4h, the temperature of the second-stage sintering is 720℃, and the sintering time is 10h, to obtain a titanium-doped LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0052] 2) The high-nickel layered oxide positive electrode material in step 1) and TiO2 are uniformly mixed in a molar ratio of 1:0.006, sintered in an oxygen atmosphere, the sintering temperature is 500℃, and the sintering time is 4h, to obtain a LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0053] Example 1

[0054] Example 1 provides a preparation method of a surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material, and the specific steps are as follows:

[0055] 1) The precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2, TiO2 and LiOH·H2O are uniformly mixed in a molar ratio of 1:0.003:1.03, and then two-stage sintering is performed in an oxygen atmosphere, the temperature of the first stage sintering is 400℃, the sintering time is 4h, the temperature of the second stage sintering is 720℃, and the sintering time is 10h, to obtain a titanium-doped LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0056] 2) The high-nickel layered oxide positive electrode material in step 1), TiO2 and MoO3 are uniformly mixed in a molar ratio of 1:0.004:0.002, sintered in an oxygen atmosphere, the sintering temperature is 500℃, and the sintering time is 4h, to obtain a surface high-entropy internal medium-entropy doped LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material. The SEM image of the surface high-entropy internal medium-entropy doped high-nickel layered oxide positive electrode material prepared in Example 1 is shown in Figure 1 From Figure 1 it can be seen that the spherical particles are complete, and the material surface is uniformly coated with nanoparticles.

[0057] Example 2

[0058] Example 2 provides a preparation method of a surface high-entropy internal medium-entropy gradient doped high-nickel layered oxide positive electrode material, and the difference between Example 2 and Example 1 is in step 2);

[0059] Specifically, step 2) involves uniformly mixing the high-nickel layered oxide cathode material, TiO2, and WO3 from step 1) in a molar ratio of 1:0.004:0.002, and sintering it in an oxygen atmosphere at a temperature of 500°C for 4 hours to obtain LiNi with high entropy doping on the surface and medium entropy doping inside. 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide cathode material. SEM image of the high-entropy surface and medium-entropy internal doped high-nickel layered oxide cathode material prepared in Example 2 is shown below. Figure 2 As shown, from Figure 2 As can be seen, the spherical particles are intact, and the material surface is uniformly coated with nanoparticles.

[0060] Example 3

[0061] Example 3 provides a method for preparing a high-nickel layered oxide cathode material with high surface entropy and medium internal entropy stepwise doping. The difference between Example 3 and Example 1 is step 2).

[0062] Specifically, step 2) involves uniformly mixing the layered oxide cathode, TiO2, and Nb2O5 from step 1) in a molar ratio of 1:0.004:0.002, and sintering them in an oxygen atmosphere at a temperature of 500℃ for 4 hours to obtain LiNi with high entropy doping on the surface and medium entropy doping inside. 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide cathode material. SEM image of the high-entropy surface and medium-entropy internal doped high-nickel layered oxide cathode material prepared in Example 3 is shown below. Figure 3 As shown, from Figure 3 As can be seen, the spherical particles are intact, and the material surface is uniformly coated with nanoparticles.

[0063] Example 4

[0064] Example 4 provides a method for preparing a high-nickel layered oxide cathode material with high surface entropy and medium interior entropy, which is doped in a stepped manner. The specific steps are as follows:

[0065] 1) The precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)₂, TiO₂, and LiOH·H₂O were uniformly mixed in a molar ratio of 1:0.003:1.03, and then subjected to two-stage sintering in a mixed gas atmosphere with an oxygen to nitrogen molar ratio of 8:2. The first-stage sintering temperature was 400℃ and the sintering time was 4 h, and the second-stage sintering temperature was 720℃ and the sintering time was 10 h, yielding titanium-doped LiNi.0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material;

[0066] 2) The high-nickel layered oxide positive electrode material, TiO2 and MoO3 in step 1) are uniformly mixed in a molar ratio of 1:0.004:0.002, and sintering is performed in a mixed gas atmosphere of oxygen and nitrogen in a molar ratio of 8:2, the sintering temperature is 500°C, and the sintering time is 4h, to obtain a LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0067] Example 5

[0068] Example 5 provides a preparation method of a surface high-entropy and internal medium-entropy gradient-doped high-nickel layered oxide positive electrode material, and the specific steps are as follows:

[0069] 1) The precursor Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2, ZrO2 and LiOH·H2O are uniformly mixed in a molar ratio of 1:0.005:1.03, and then two-stage sintering is performed in an oxygen atmosphere, the temperature of the first stage sintering is 400°C, the sintering time is 4h, the temperature of the second stage sintering is 720°C, and the sintering time is 10h, to obtain a zirconium-doped LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material;

[0070] 2) The high-nickel layered oxide positive electrode material, ZrO2 and MoO3 in step 1) are uniformly mixed in a molar ratio of 1:0.002:0.001, and sintering is performed in an oxygen atmosphere, the sintering temperature is 500°C, and the sintering time is 4h, to obtain a LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxide positive electrode material.

[0071] Application test

[0072] The products prepared in Examples 1-3 and Comparative Examples 1-2 are used to prepare lithium ion batteries, and the specific preparation method is as follows:

[0073] a. The active material (product prepared in Example 1, 2, 3 or Comparative Example 1, 2) was mixed with carbon black (Super-P, conductive agent, Shenzhen Kejing Wisdom Technology Co., Ltd., CAS 1333-86-4), binder PVDF (polyvinylidene fluoride) according to a mass ratio of 90:5:5 to obtain a mixed powder;

[0074] b. Then the mixed powder in step a was added into a solvent (N-methyl pyrrolidone, NMP) in a mixing container and mixed uniformly, the mass of the solvent was 1.5 times the mass of the mixed powder, then ultrasonic dispersion was carried out for 8 min under a power of 100 W, then a polytetrafluoroethylene magnetic stirrer was put into the mixing container and stirred at a rotation speed of 400 r / min for 10 h to make the active material and carbon black (Super-P) uniformly dispersed, to obtain a mixed slurry;

[0075] c. The mixed slurry in step b was coated on an aluminum foil, and dried at a temperature of 80°C for 12 h to prepare an electrode sheet with a loading of 5 mg / cm 2 of active material; then in an argon-protected glove box, the prepared electrode sheet was used as a working electrode, a lithium metal sheet was used as a counter electrode, a high-nickel 4.6V electrolyte (1M LiPF6, EC: EMC = 3:7 Vol%, with 2wt% vinylene carbonate VC additive) was used as an electrolyte, a polypropylene separator was used, a CR2032 type button cell was assembled as a battery model, and a constant current charge-discharge test was carried out.

[0076] The cycle performance of the products prepared in Comparative Examples 1-3 and Comparative Examples 1-2 was compared, and the cycle performance test was carried out by assembling a CR2032 button cell for constant current charge-discharge between 3-4.3V, and the results are shown in Table 1 and Figure 4 Figure 4 The corresponding coulombic efficiency after 100 cycles at 0.5C rate is shown in Table 1. Figure 4

[0077] Table 1 shows the initial specific capacity and capacity retention rate at 100 cycles of Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3 at a cycle of 0.5C.

[0078] Sample Initial discharge specific capacity (mAh / g) 100 cycle capacity retention Comparative Example 1 203.9 mAh / g 59.2％ Comparative Example 2 205.1 mAh / g 80.5％ Example 1 206.7 mAh / g 89.8％ Example 2 205.9 mAh / g 87.3％ Example 3 204.2 mAh / g 86.2％

[0079] From Table 1 and Figure 4 , it can be seen that the initial discharge specific capacity of Comparative Example 1 is 203.9 mAh / g, and the capacity retention rate after 100 cycles is 59.2%. The initial discharge specific capacity of Comparative Example 2 does not change significantly compared with Comparative Example 1, but the capacity retention rate after 100 cycles is improved to 80.5%.

[0080] ​​The initial discharge specific capacity of Examples 1-3 is almost the same compared with Comparative Examples 1 and 2. The 100 cycle capacity retention of Examples 1-3 is higher than that of Comparative Examples 1 and 2 after 100 cycles. The above results show that the high-entropy middle-entropy gradient doping method of the present application can improve the cycle stability of LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxides.

[0081] The rate performance of the products prepared in Comparative Examples 1-3 and Comparative Examples 1-2 is compared. The rate performance test is realized by assembling CR2032 button cells and performing constant current charge and discharge at different rates between 3 and 4.3 V. The results are shown in the following table. Figure 5

[0082] The discharge specific capacity of Examples 1-3 is improved at different rates compared with Comparative Examples 1 and 2. Especially at 5C high rate, the discharge specific capacity of Examples 1-3 is much higher than that of Comparative Examples 1 and 2. The above results show that the high-entropy middle-entropy gradient doping method of the present application can improve the rate performance of LiNi 0.96 Co 0.015 Mn 0.015 Al 0.01 O2 high-nickel layered oxides.

[0083] In summary, the preparation method of the surface high-entropy internal middle-entropy gradient doping high-nickel layered oxide positive electrode material of the present application improves the cycle stability of high-nickel layered oxides and has good application value, and is suitable for process application.

[0084] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.​

Claims

1. A high-entropy surface, medium-entropy internally doped high-nickel layered oxide cathode material, characterized in that, It is prepared through the following steps: 1) The high-nickel layered oxide precursor, metal-doped precursor and lithium source are uniformly mixed in a certain proportion, and then placed in an atmosphere furnace for sintering under a modified atmosphere to obtain the doped high-nickel layered oxide cathode material. 2) The high-nickel layered oxide cathode material from step 1) is uniformly mixed with the metal-doped precursor II in a certain proportion, and then placed in an atmosphere furnace for secondary sintering under a modified atmosphere to obtain a high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material. In step 1), the chemical formula of the high-nickel layered oxide precursor is Ni 0.96 Co 0.015 Mn 0.015 Al 0.01 (OH)2; The metal-doped precursor mentioned in step 1) is either TiO2 or ZrO2; The lithium source mentioned in step 1) is LiOH∙H2O; In step 1), the molar ratio of the high-nickel layered oxide precursor to the metal-doped precursor and the lithium source is 1:0.003:1.03 or 1:0.005:1.

03. Step 1) The first sintering includes a first-stage sintering and a second-stage sintering; the temperature of the first-stage sintering is 400℃; the time of the first-stage sintering is 4h; the temperature of the second-stage sintering is 720℃; the time of the second-stage sintering is 10h. Step 2) The metal-doped precursor is any one of the following combinations: TiO2 and MoO3, TiO2 and WO3, TiO2 and Nb2O5, or ZrO2 and MoO3. When the metal-doped precursor in step 2) is a combination of TiO2 and MoO3, the molar ratio of the high-nickel layered oxide cathode material, TiO2, and MoO3 is 1:0.004:0.

002. When the metal-doped precursor in step 2) is a combination of TiO2 and WO3, the molar ratio of the high-nickel layered oxide cathode material, TiO2, and WO3 is 1:0.004:0.

002. When the metal-doped precursor in step 2) is a combination of TiO2 and Nb2O5, the molar ratio of the high-nickel layered oxide cathode material, TiO2, and Nb2O5 is 1:0.004:0.

002. When the metal-doped precursor in step 2) is a combination of ZrO2 and MoO3, the molar ratio of the high-nickel layered oxide cathode material, ZrO2, and MoO3 is 1:0.002:0.

001. The secondary sintering temperature in step 2) is 500℃, and the sintering time is 4h.

2. The high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material as described in claim 1, characterized in that, In step 1), the modified atmosphere in step 2) is an oxygen atmosphere, or a combination of oxygen and nitrogen atmosphere.

3. The high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material as described in claim 2, characterized in that, When the modified atmosphere is a combination of oxygen and nitrogen, the molar ratio of oxygen to nitrogen is (6~10):(1~4).

4. The application of the high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material according to any one of claims 1 to 3 in the preparation of lithium-ion batteries, characterized in that, The high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material is used to make CR2032 coin-type lithium-ion batteries, which have good charge-discharge performance, rate performance and cycle stability. a. A certain amount of high-entropy surface and medium-entropy internally doped high-nickel layered oxide cathode material, conductive agent and binder are placed in a container to obtain a mixed powder; b. Add solvent to the mixed powder from step a, and ultrasonically disperse it for 80-100 W for 8-12 min. Then, place a polytetrafluoroethylene magnet in a container and stir at 300-400 r / min for 8-12 h to ensure that the high-nickel layered oxide cathode material and conductive agent are evenly dispersed to obtain a mixed slurry. c. Coat the mixed slurry from step b onto aluminum foil and dry it at 60~80℃ for 8~12 h, then make it into a button electrode sheet with a diameter of 12 mm; then use the prepared electrode sheet as the working electrode, the lithium metal sheet as the counter electrode, install a separator, use high nickel 4.3V electrolyte, assemble a button cell, and the battery model is a CR2032 type button cell.

5. The application as described in claim 4, characterized in that, In step a, the conductive agent is carbon black Super-P; the binder is PVDF; the solvent in step b is selected from deionized water, ethanol and NMP; the mass of the solvent is 1 to 1.5 times the mass of the mixed powder.

6. The application as described in claim 4, characterized in that, In the mixed slurry obtained in step b, the weight ratio of the high-entropy surface and medium-entropy interior doped high-nickel layered oxide cathode material, conductive agent, and binder is (16-18):1:(1-2).

7. The application as described in claim 4, characterized in that, The separator is a polypropylene separator, and the electrolyte used in the battery is 1M LiPF6 in EC:EMC = 3:7 Vol%, with 2 wt% vinylene carbonate VC additive.

8. The application as described in claim 4, characterized in that, In step c, the loading of the mixed slurry on the prepared electrode sheet is 1~5 mg / cm². 2 .

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