Aluminum-fluorine-doped positive electrode material and preparation method thereof, positive electrode plate and battery

Abstract

The invention discloses an aluminum-fluorine-doped positive electrode material and a preparation method thereof, a positive electrode plate and a battery, the molecular formula of the aluminum-fluorine-doped positive electrode material is LiAl < x > Ni < 0.8-x > Co < 0.1 > Mn < 0.1 > O < 2-y > Fy, x is more than or equal to 0.01 and less than or equal to 0.05, and y is more than or equal to 0.025 and less than or equal to 0.075. According to the positive electrode material provided by the invention, part of Ni sites in LiNi0. 8Co0. 1Mn0. 1O2 are replaced by Al < 3 + > through an aluminum-fluorine co-doping strategy so as to inhibit cation mixing and stabilize a layered structure, and meanwhile, lattice oxygen is partially replaced by F <-> so as to enhance M-O (M = Ni / Co / Mn) bond energy, so that collaborative optimization of bulk phase structure stability and interface oxygen stability is realized from an atomic scale; therefore, the core problems of short cycle life, fast capacity fading, insufficient rate capability and the like of the NCM811 material are solved.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to an aluminum-fluorine doped cathode material, a preparation method thereof, a cathode electrode sheet, and a battery. Background Art

[0002] The high-nickel ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) has become a key material for the next generation of high-energy density lithium-ion batteries due to its high specific capacity and high working voltage. However, its commercial application still faces severe challenges: (1) Poor structural stability leads to capacity attenuation and low capacity retention rate; (2) Severe interfacial side reactions deteriorate the cycling performance; (3) The intrinsic electronic conductivity of NCM811 is relatively low, and the Li + diffusion rate is slow, resulting in increased polarization during high-rate charge and discharge, and a significant decrease in the actual available capacity. For example, the capacity retention rate is less than 60% at a 5C rate. Summary of the Invention

[0003] In view of this, this application provides an aluminum-fluorine doped cathode material, a preparation method thereof, a cathode electrode sheet, and a battery that can solve the above technical problems.

[0004] In the first aspect of this application, an aluminum-fluorine doped cathode material is provided, and the molecular formula of the aluminum-fluorine doped cathode material is LiAl x Ni 0.8-x Co 0.1 Mn 0.1 O 2-y F y , where 0.01 ≤ x ≤ 0.05 and 0.025 ≤ y ≤ 0.075.

[0005] In some embodiments, the molecular formula of the aluminum-fluorine doped cathode material is LiAl 0.03 Ni 0.77 Co 0.1 Mn 0. 1O 1.95 F 0.05 .

[0006] In some embodiments, the average particle size of the cathode material is 180 μm to 250 μm.

[0007] In the second aspect of this application, a preparation method of the aluminum-fluorine doped cathode material is provided, including the following steps: Mix LiNi 0.8 Co 0.1 Mn 0.1 O2, a lithium source, an aluminum source, and a fluorine source according to the stoichiometric ratio of the aluminum-fluorine doped cathode material to obtain a mixture; Calcine the mixture.

[0008] In some embodiments, the aluminum source includes at least one of aluminum oxide or aluminum hydroxide, and / or the fluorine source includes at least one of ammonium fluoride or lithium fluoride.

[0009] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium oxide, lithium fluoride or lithium carbonate.

[0010] In some embodiments, the calcination temperature is 750 °C to 850 °C.

[0011] In some embodiments, the calcination specifically includes: heating the mixture to the calcination temperature at a rate of 2 °C / min to 5 °C / min, and holding for 5 h to 8 h.

[0012] The third aspect of the present application provides a positive electrode plate, and the positive electrode plate includes the aluminum- and fluorine-doped positive electrode material described above.

[0013] The fourth aspect of the present application provides a battery, and the battery includes the positive electrode plate.

[0014] In the aluminum- and fluorine-doped positive electrode material provided by the present application, Al 3+ substitutes for part of the Ni sites in LiNi 0.8 Co 0.1 Mn 0.1 O2 to inhibit cation mixing and stabilize the layered structure. At the same time, by F - partially substituting lattice oxygen to enhance the M-O (M = Ni / Co / Mn) bond energy, the synergistic optimization of the bulk structure stability and the interfacial oxygen stability is realized at the atomic scale, thereby solving the core problems such as the short cycle life and low capacity retention rate of the NCM811 material. Description of the Drawings

[0015] Figure 1 XRD patterns of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0016] Figure 2 SEM images of the materials obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0017] Figure 3 TEM images of Example 1 and Comparative Example 1 and EDS spectrum of Example 1.

[0018] Figure 4 Charge-discharge curves of Example 1 and Comparative Example 1.

[0019] Figure 5The rate curves of Examples 1 to 3 and Comparative Examples 1 and 2.

[0020] Figure 6 The rate curves of Examples 1 to 3 and Comparative Examples 1 to 3 at a voltage of 2.8 V to 4.3 V and a current density of 1C.

[0021] Figure 7 The impedance spectrogram (EIS diagram) of Examples 1 to 3 and Comparative Examples 1 to 3.

[0022] Figure 8 Scanning electron microscope images of the positive electrode materials in Example 1 and Comparative Example 1 after 300 cycles at a current density of 1C.

[0023] The following specific embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. Specific Embodiments

[0024] The embodiments of the present application will be described in detail below. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and should not be construed as a limitation of the present application. The reagents and materials described in the following embodiments can all be obtained through commercial channels.

[0025] Many specific details are set forth in the following description in order to fully understand the embodiments of the present application. The described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the embodiments of the present application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments of the present application belong. The terms used in the specification of the present application herein are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application.

[0027] The present application provides a positive electrode material doped with aluminum and fluorine. The molecular formula of the positive electrode material doped with aluminum and fluorine is LiAl x Ni 0.8-x Co 0.1 Mn 0.1 O 2-y F y, wherein, 0.01 ≤ x ≤ 0.05, 0.025 ≤ y ≤ 0.075. For example, x can be 0.01, 0.02, 0.03, 0.04, 0.05 or any value within the range formed by any two of the above values, and y can be 0.025, 0.030, 0.035, 0.040, 0.045, 0.050, 0.055, 0.060, 0.065, 0.070, 0.075 or any value within the range formed by any two of the above values.

[0028] The cathode material provided by this application uses Al 3+ to replace part of the Ni sites in LiNi 0.8 Co 0.1 Mn 0.1 O2 to inhibit cation mixing and stabilize the layered structure. At the same time, through F - partially replacing lattice oxygen to enhance the M-O (M = Ni / Co / Mn) bond energy, the synergistic optimization of bulk structure stability and interface oxygen stability is realized at the atomic scale, thereby solving the core problems such as short cycle life, fast capacity decay and insufficient rate performance of NCM811 materials.

[0029] Preferably, the molecular formula of the aluminum-fluorine doped cathode material is LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O 1.95 F 0.05 , that is, preferably x = 0.030 and y = 0.050. By optimizing the doping ratios of Al 3+ and F - , the element distribution can be made more uniform and the production of impurity phases can be avoided, thereby further improving the cycle life, fast capacity decay and rate performance of the material.

[0030] Specifically, the average particle size of the aluminum-fluorine doped cathode material is 180 μm to 250 μm. For example, it can be 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm or any value within the range formed by any two of the above values. In this application, the "particle size" refers to the secondary particle size of the aluminum-fluorine doped cathode material. The average particle size is measured by a scanning electron microscope.

[0031] This application also provides a preparation method of the above aluminum-fluorine doped cathode material, including the following steps: Mix LiNi 0.8 Co 0.1 Mn 0.1 O2, a lithium source, an aluminum source and a fluorine source according to the stoichiometric ratio of the aluminum-fluorine doped cathode material to obtain a mixture; The mixture is calcined.

[0032] Specifically, LiNi 0.8 Co 0.1 Mn 0.1 O2 is NCM811. LiNi 0.8 Co 0.1 Mn 0.1 O2 can be directly selected from commercial products, or it can be made at home.

[0033] Specifically, the aluminum source includes at least one of aluminum oxide or aluminum hydroxide. For example, in some embodiments, aluminum oxide is selected as the aluminum source; in some embodiments, aluminum hydroxide is selected as the aluminum source; in other embodiments, aluminum oxide and aluminum hydroxide are selected as the aluminum source.

[0034] Specifically, the fluorine source includes at least one of ammonium fluoride or lithium fluoride. For example, in some embodiments, ammonium fluoride is selected as the fluorine source; in some embodiments, lithium fluoride is selected as the fluorine source; in other embodiments, ammonium fluoride and lithium fluoride are selected as the fluorine source.

[0035] Specifically, the lithium source includes at least one of lithium hydroxide, lithium oxide, lithium fluoride or lithium carbonate. For example, in some embodiments, lithium oxide is selected as the lithium source; in some embodiments, lithium fluoride is selected as the lithium source; in other embodiments, lithium hydroxide and lithium fluoride are selected as the lithium source.

[0036] Specifically, the calcination temperature is 750°C to 850°C. For example, the calcination temperature can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, or any value within the range formed by any two of the above values. Controlling the calcination temperature within the above range is beneficial to Al 3+ and F - Doped with LiNi 0.8 Co 0.1 Mn 0.1 O2 structure and replace Ni atoms and O atoms. If the calcination temperature is too high or too low, Al 3+ and F - Cannot be doped into LiNi 0.8 Co 0.1 Mn 0.1 In the O2 structure, LiNi 0.8 Co 0.1 Mn 0.1 The probability of forming a coating outside O2 increases.

[0037] Specifically, the calcination step includes: heating the mixture to the calcination temperature at a rate of 2°C / min to 5°C / min and holding for 5 h to 8 h. For example, the heating rate can be 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any value within the range formed by any two of the above values.

[0038] Specifically, after the calcination step is completed, annealing is further included, and the annealing rate can be 5°C / min to 8°C / min. For example, the annealing rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, or any value within the range formed by any two of the above values. This application does not impose special restrictions on annealing and the annealing rate. In some other embodiments, cooling can also be achieved by natural cooling after the calcination step is completed.

[0039] This application also provides a positive electrode plate, which includes the above-mentioned aluminum-fluorine-doped positive electrode material. For example, a positive electrode plate includes a current collector and a positive electrode active coating provided on the surface of the current collector, and the positive electrode active coating contains the above-mentioned aluminum-fluorine-doped positive electrode material.

[0040] This application also provides a battery, which includes the above-mentioned positive electrode plate. For example, the battery can be a lithium battery.

[0041] The following will describe this application in detail with reference to embodiments. In the embodiments and comparative examples of this application, LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, aluminum oxide, and ammonium fluoride are all from the same commercially available product.

[0042] Example 1 Preparation of NCM-Al 0.03 F 0.05 : Mix LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, aluminum oxide, and ammonium fluoride evenly at a molar ratio of 1:1:0.03:0.05 to obtain a mixture. Calcinate the mixture in a tube furnace, heat it to the calcination temperature of 800°C at a rate of 5°C / min, and then hold for 5 h. Finally, anneal it to room temperature at a rate of 5°C / min to obtain LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O 1.95 F 0.05 .

[0043] Example 2 Preparation of NCM-Al 0.03 F 0.025 : Mix LiNi0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, aluminum oxide, and ammonium fluoride are uniformly mixed at a molar ratio of 1:1:0.03:0.025 to obtain a mixture. The mixture is calcined in a tubular furnace, heated to a calcination temperature of 800 °C at a rate of 5 °C / min, and then held for 5 h. Finally, it is annealed to room temperature at a rate of 5 °C / min to obtain LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O 1.975 F 0.025 。

[0044] Example 3 Preparation of NCM-Al 0.03 F 0.075 : LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, aluminum oxide, and ammonium fluoride are uniformly mixed at a molar ratio of 1:1:0.03:0.075 to obtain a mixture. The mixture is calcined in a tubular furnace, heated to a calcination temperature of 800 °C at a rate of 5 °C / min, and then held for 5 h. Finally, it is annealed to room temperature at a rate of 5 °C / min to obtain LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O 1.925 F 0.075 。

[0045] Comparative Example 1 Commercially available LiNi 0.8 Co 0.1 Mn 0.1 O2, without any treatment.

[0046] Comparative Example 2 Preparation of NCM-Al 0.03 : LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, and aluminum oxide are uniformly mixed at a molar ratio of 1:1:0.03 to obtain a mixture. The mixture is calcined in a tubular furnace, heated to a calcination temperature of 800 °C at a rate of 5 °C / min, and then held for 5 h. Finally, it is annealed to room temperature at a rate of 5 °C / min to obtain LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O2.

[0047] Comparative Example 3 Preparation of NCM-F0.05 : Mix LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium hydroxide, and ammonium fluoride evenly at a molar ratio of 1:1:0.05 to obtain a mixture. Calcinate the mixture in a tube furnace, heating it to the calcination temperature of 800 °C at a rate of 5 °C / min, and then holding for 5 h. Finally, anneal it to room temperature at a rate of 5 °C / min to obtain LiNi 0.8 Co 0.1 Mn 0.1 O 1.95 F 0.05 .

[0048] Place the materials obtained in Example 1 and Comparative Examples 1 to 3 in an X-ray diffractometer for X-ray diffraction testing, and process the test results to obtain the Figure 1 shown XRD pattern. Among them, the model of the X-ray diffractometer is SmartLab, and the manufacturer is Shanghai Lijing Scientific Instruments Co., Ltd. The test conditions are 5° / min, and the test range is 10° to 90°. Use Rietveld software to process the test results. Figure 1 In (a) is the XRD pattern of Comparative Example 1, Figure 1 In (b) is the XRD pattern of Example 1, Figure 1 In (c) is the XRD pattern of Comparative Example 2, Figure 1 In (d) is the XRD pattern of Comparative Example 3. It can be seen from Figure 1 that the diffraction peaks of the materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are similar, all showing an α-NaFeO2 structure and belonging to the R-3m space group. It can be seen from the data processing results that Figure 1 the Rwp (R-weighted pattern factor) of (a) to (d) is less than 5%, proving the high accuracy of the processing of the X-ray diffraction test results. The XRD patterns of Examples 2 and 3 in this application are similar to that of Example 1, so they will not be elaborated here.

[0049] Characterize the morphologies of the materials obtained in Example 1 and Comparative Examples 1 to 3 using a scanning electron microscope (model SU8010, Hitachi, Japan) to obtain the Figure 2 shown SEM images. Figure 2 In (a) is the SEM image of Comparative Example 1, Figure 2 In (e) is the enlarged view of (a); Figure 2 In (b) is the SEM image of Example 1, Figure 2 In (f) is the enlarged view of (b); Figure 2 In (c) is the SEM image of Comparative Example 2, Figure 2 In (g) is the enlarged view of (c);Figure 2 In (d) is the SEM image of Comparative Example 3, Figure 2 and (h) in it is the enlarged view of (d). As can be seen from Figure 2 Examples 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, the materials are all secondary particles formed by the aggregation of primary particles, and the secondary particles are spherical. The particle size of the primary particles is roughly between 200 nm and 500 nm, and the particle size of the secondary particles is roughly between 180 μm and 250 μm.

[0050] The internal structure, elemental content, and elemental distribution of the material obtained in Example 1 were observed and measured using a transmission electron microscope (model Tecnai G2 F30, FEI Company, USA) and an energy spectrometer, and Figure 3 . Figure 3 Among them, (a) is the TEM image of Comparative Example 1, (b) is the TEM image of Example 1, and (c) is the EDS image of Example 1. Comparing Figure 3 the (a) and (b) of Figure 3 it can be seen that the undoped NCM811 as a whole presents a layered structure, and the edge of the particles is a rock salt phase structure. The structure of the material doped with Al and F (i.e., Example 1) does not change. Further elemental distribution analysis was carried out on Example 1. As can be seen from

[0051] <Electrochemical Performance Analysis> Adopting the packaging method of coin cells, the materials of Examples 1-3 and Comparative Examples 1-3 were used as the positive electrode active materials respectively, the conductive agent was acetylene black, the binder was polyvinylidene fluoride, and the current collector was aluminum foil. The positive electrode slurry was prepared by mixing the positive electrode active material, conductive agent, and binder at a mass ratio of 8:1:1, and the positive electrode slurry was coated on one side surface of the current collector. The negative electrode was a lithium sheet. The separator was a polyethylene separator, and the electrolyte was a lithium hexafluorophosphate organic electrolyte system. The lithium-ion batteries corresponding to Examples 1-3 and Comparative Examples 1-3 were prepared respectively, and then the following electrochemical performance tests were carried out on the lithium-ion batteries corresponding to Examples 1-3 and Comparative Examples 1-3.

[0052] (1) Charge and Discharge Performance The charge and discharge performance of the batteries corresponding to Example 1 and Comparative Example 1 was tested using a battery tester (model CT2001A, China LAND Company) at a current density of 0.2C, and Figure 4 the first and second charge and discharge curves shown in Figure 4 were obtained. Among them, (a) is the charge and discharge curve of Comparative Example 1, and (b) is the charge and discharge curve of Example 1. As can be seen from Figure 4As can be seen from (a) of Comparative Example 1, the initial charge specific capacity is 201.2 mAh / g, and the initial discharge specific capacity is 176.7 mAh / g. After that, in the second charge-discharge cycle, the charge specific capacity of the material is 178 mAh / g, and the discharge specific capacity is 177.7 mAh / g. From Figure 4 As can be seen from (b) of Example 1, the initial charge specific capacity is 277.4 mAh / g, and the initial discharge specific capacity is 216.2 mAh / g. In the second charge-discharge cycle, the charge specific capacity of the material is 220.2 mAh / g, and the discharge specific capacity is 210.7 mAh / g. Compared with Comparative Example 1, the initial charge-discharge specific capacities of Example 1 are significantly improved. The reason is that the doped F element will replace the O atom, forming more oxygen vacancies, promoting the oxidation-reduction reaction of oxygen, and thus increasing the specific capacity.

[0053] (2)Rate performance, cycle performance The rate performance and long-term cycling electrochemical performance of the batteries corresponding to Examples 1-3 and Comparative Examples 1-3 were tested using a battery tester (model CT2001A, China Blue Electric Co., Ltd.). Specifically: in the voltage range of 2.8 V to 4.3 V, the discharge specific capacities of the batteries were tested at current densities of 0.2C, 0.5 C, 1 C, 2 C, and 5 C in sequence, and the Figure 5 resulting rate curves are shown. As can be seen from Figure 5 it that as the current density increases, the discharge specific capacity of the material gradually decreases. At a current density of 5C, the discharge specific capacity of Comparative Example 1 is approximately 80 mAh / g, while that of Example 1 is 120 mAh / g, indicating that doping with Al and F can significantly improve the rate performance of the material at high-rate current densities. After the current density is restored to 0.5C again, the discharge specific capacities of Examples 1-3 all increase to the initial capacity, indicating that the batteries have excellent rate performance and good reversibility. And at the same time, LiAl 0.3 Ni 0.5 Co 0.1 Mn 0.1 O 1.5 F 0.5 corresponding Al and F doping amounts are the most preferred, and the rate performance of the material is the best. The main reasons for the significant improvement of the rate performance of the NCM cathode material by doping with Al and F mainly include: after Al 3+ replaces the transition metal site, it stabilizes the crystal structure by strengthening the Al-O bond, inhibits lattice distortion and phase transformation at high rates, and at the same time reduces Li + / Ni 2+ mixing and maintains the smoothness of the lithium-ion diffusion channel; while F -Doping or surface modification forms a stable lithium fluoride or transition metal fluoride layer, which not only inhibits electrolyte decomposition and hydrofluoric acid corrosion, but also optimizes the ionic conductivity of the cathode electrolyte interface (CEI) film and reduces the interfacial impedance. In addition, F may slightly broaden the Li + diffusion channels, cooperate with the improvement of electron conductivity by Al doping, and jointly reduce the electrode polarization, thereby significantly improving the capacity performance and cycle stability at high rates.

[0054] Long-term cycling at a certain current density can characterize the electrochemical cycling stability of the material. As Figure 6 shown, it can be seen that at 25 °C, in the voltage range of 2.8 V to 4.3 V, the discharge specific capacities of different samples are compared for 300 cycles at a current density of 1C. From the experimental results, it can be seen that after 300 charge-discharge cycles, the capacity retention rate of Comparative Example 1 is 72.6%, that of Comparative Example 2 is 72.5%, that of Comparative Example 3 is 74.6%, that of Example 1 is 78.3%, that of Example 2 is 73.2%, and that of Example 3 is 75.4%. Compared with Comparative Example 1, the capacity retention rates of Examples 1 to 3 have all increased significantly, and the increase in the capacity retention rate represents an improvement in the cycling stability. The improvement in the cycling stability of Examples 1 to 3 is due to: Al 3+ doping inhibits the phase transformation of H2 (medium delithiation state) → H3 (deep delithiation state) and the loss of lattice oxygen during charge and discharge through strong Al-O bonds, reduces structural collapse and volume strain, and at the same time reduces the Li + / Ni 2+ mixing and maintains the structural integrity; while F - doping forms a stable lithium fluoride or transition metal fluoride layer on the material surface, effectively blocking electrolyte corrosion and inhibiting the dissolution of transition metals, while optimizing the uniformity and stability of the CEI film. The synergistic effect of the two greatly slows down the particle cracks and interfacial side reactions during cycling, thereby significantly improving the long-cycle capacity retention rate. And among Examples 1 to 3, the capacity retention rate of Example 1 is the best.

[0055] (3) Impedance test The impedances of Examples 1 to 3 and Comparative Examples 1 to 3 were tested, and Figure 7The impedance spectrum shown. In the electrochemical impedance spectrum, different frequency ranges from high frequency to low frequency correspond to different physical and electrochemical processes in the electrode system, and the impedance components are usually analyzed in the following order: the high-frequency region (10 kHz ~ 100 Hz) represents ohmic impedance, which represents the electrolyte ion resistance, the electrode material body electronic resistance, the collector contact resistance, etc. At the same time, it also symbolizes the solid electrolyte interface film (SEI film / CEI film) impedance, which represents the migration resistance of Li⁺ through the negative electrode film (SEI film) or the positive electrode film (CEI film) on the electrode surface; the medium-frequency region (100 Hz ~ 1 Hz) is the charge transfer impedance, which represents the electrochemical reaction (such as Li + The kinetic resistance of the electrolyte (insertion / deinsertion) is related to the activation energy of the electrode / electrolyte interface. The larger the diameter of the semicircular arc in the mid-frequency region, the slower the reaction kinetics (such as the increase in charge transfer resistance after cyclic aging); the low-frequency region (1 Hz ~ 0.01 Hz) represents Li + The diffusion impedance in the bulk phase of the electrode material or the electrolyte is controlled by the concentration gradient. The low-frequency region is a 45° oblique line (limited diffusion) or a straight line perpendicular to the real axis (infinite diffusion). Figure 7 It can be seen that the impedance of the solid electrolyte interface film (SEI film / CEI film) of Examples 1 to 3 does not change significantly compared with Comparative Examples 1 to 3. However, compared with Comparative Example 1, the diameter of the semicircular arc in the mid-frequency region of Examples 1 to 3 is smaller and the charge transfer resistance is lower, indicating that doping Al and F can reduce Li + Kinetic resistance to embedding / de-embedding increases the activation energy at the electrode / electrolyte interface.

[0056] The morphology of the positive electrode materials in Example 1 and Comparative Example 1 after cycling for 300 cycles at a current density of 1C was characterized using a scanning electron microscope (model SU8010, Hitachi, Japan). Figure 8 SEM images shown. Figure 8 (a) is the morphology of the positive electrode material of Comparative Example 1 after 300 cycles. Figure 8 (b) shows the morphology of the positive electrode material of Example 1 after 300 cycles. Figure 8 (c) in the equation is Figure 8 The enlarged view of (a) in Figure 8 (d) in Figure 8 The enlarged view of (b) in Figure 2 is shown in Figure 2. Figure 2 Compared with (a) and (c), Figure 8 From (a), it can be seen that the surface roughness of the positive electrode material of Comparative Example 1 increases, that is, a large amount of SEI film appears on its surface after cycling, indicating that a violent side reaction occurs between the electrode and the electrolyte. Figure 8 In (c), we can see the structural collapse and defects of a single secondary particle. Figure 8The positive electrode material of Example 1 characterized by (b) and (d) in [reference] has no obvious SEI film, and at the same time, the particle surface remains intact without structural defects, and the secondary particle structure is stable.

[0057] The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An aluminum-fluorine doped cathode material, characterized in that, The molecular formula of the aluminum- and fluorine-doped cathode material is LiAl x Ni 0.8-x Co 0.1 Mn 0.1 O 2-y F y , where 0.01 ≤ x ≤ 0.05 and 0.025 ≤ y ≤ 0.

075.

2. The aluminum- and fluorine-doped cathode material according to claim 1, wherein The molecular formula of the aluminum- and fluorine-doped cathode material is LiAl 0.03 Ni 0.77 Co 0.1 Mn 0.1 O 1.95 F 0.05 .

3. The aluminum- and fluorine-doped cathode material according to claim 1, characterized in that, The average particle size of the aluminum- and fluorine-doped cathode material is 180 μm to 250 μm.

4. A method for preparing the aluminum-fluorine-doped cathode material according to any one of claims 1-3, characterized in that, It includes the following steps: Mix LiNi 0.8 Co 0.1 Mn 0.1 O2, a lithium source, an aluminum source, and a fluorine source according to the stoichiometric ratio of the aluminum-fluorine doped cathode material to obtain a mixture; Calcine the mixture.

5. The preparation method of the aluminum- and fluorine-doped cathode material according to claim 4, wherein The aluminum source includes at least one of aluminum oxide or aluminum hydroxide, and / or the fluorine source includes at least one of ammonium fluoride or lithium fluoride.

6. The preparation method of the aluminum-fluorine doped cathode material according to claim 4, characterized in that, The lithium source includes at least one of lithium hydroxide, lithium oxide, lithium fluoride, or lithium carbonate.

7. The preparation method of the aluminum- and fluorine-doped cathode material according to claim 4, characterized in that, The temperature of the calcination is 750 °C to 850 °C.

8. The preparation method of the aluminum-fluorine-doped cathode material according to claim 7, wherein The step of the calcination specifically includes: heating the mixture to the calcination temperature at a rate of 2 °C / min to 5 °C / min and holding for 5 h to 8 h.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes the aluminum- and fluorine-doped cathode material according to any one of claims 1-3.

10. A battery, characterized in that, The battery includes the positive electrode sheet according to claim 9.

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