Cobalt-free lithium-rich manganese-based cathode material doped by anion and cation and preparation method thereof

Abstract

The present application relates to the technical field of lithium ion batteries, in particular to a kind of anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material and preparation method.The method uses metal salt solution, precipitant, fluorine source, complexing agent to prepare modified lithium-rich manganese-based precursor, using modified lithium-rich manganese-based precursor and lithium source to prepare the cobalt-free lithium-rich manganese-based positive electrode material of anion and cation co-doped type;Metal salt solution contains manganese salt, nickel salt, aluminium salt.The method effectively reduces voltage attenuation by doping Al and F, improves the long cycle performance of material, improves the rate performance of material, and effectively suppresses lithium-nickel cation mixing, thereby improving the cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a cathode and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for sustainable and clean energy worldwide, lithium ion batteries, as high-energy-density energy storage devices, play an increasingly important role in portable electronic devices, electric vehicles, and large-scale energy storage systems. Cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O2(LNMO) has become a hot research topic in the field of lithium ion batteries due to its high specific capacity, cost-effectiveness, and environmental friendliness. This material has a theoretical capacity of more than 250mAh g -1 and an energy density of more than 900Whkg -1 , and has a lower cost advantage compared to traditional LiCoO2, LiFePO4, etc. positive electrode materials, which is of great significance for promoting the cruising range of electric vehicles and reducing battery costs.

[0003] However, lithium-rich manganese-based positive electrode materials still have problems such as low first coulombic efficiency, poor high-rate performance, poor cycle stability, and severe capacity and voltage decay under long cycle, which seriously limit their commercialization. Therefore, how to further inhibit the average voltage decay of lithium-rich manganese-based positive electrode materials and improve the cycle stability of the materials is a research focus and difficulty in the field.

[0004] Currently, some modification methods have certain improvement on the performance of LNMO, but these modification methods have many types of doped metals, and the corresponding effects are uneven, the doping process is complex and the cost is high, which cannot meet the demand for LNMO. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a cathode and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material and a preparation method thereof.

[0006] The technical solution of the present application to solve the above technical problems is as follows:

[0007] The present application provides a preparation method of a cathode and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material, which uses a metal salt solution, a precipitating agent, a fluorine source, and a complexing agent to prepare a modified lithium-rich manganese-based precursor, and uses the modified lithium-rich manganese-based precursor and a lithium source to prepare the cathode and anion co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0008] The metal salt solution contains manganese salt, nickel salt and aluminum salt; wherein the molar ratio of manganese, nickel and aluminum is a:b:x, and the molar ratio of fluorine is y; the value range of a, b, x and y is: a>0.5, 0

[0009] Based on the above technical solution, the application can be further improved as follows.

[0010] Further, the precipitant includes lye, and the complexing agent includes one or more of ammonia and ammonium bicarbonate.

[0011] Further, the lithium source is one or more of lithium hydroxide, lithium sulfide and lithium carbonate; the aluminum salt is one or both of aluminum oxide and aluminum nitrate; and the fluorine source includes one or both of ammonium fluoride and lithium fluoride.

[0012] Further, the method comprises the following steps:

[0013] S1, after dissolving the complexing agent, the metal salt solution, the precipitant and the fluorine source are injected into the bottom liquid in parallel flow, stirring and co-precipitation reaction under heating, and after the reaction is completed, cooling, filtering and drying are performed to obtain the modified lithium-rich manganese-based precursor;

[0014] S2, the modified cobalt-free lithium-rich manganese-based precursor is mixed with the lithium source for ball milling treatment, and then sintering is performed.

[0015] Further, in step S1, the flow rate of the parallel injection is 30-80 ml / min.

[0016] Further, in step S1, the pH of the co-precipitation reaction is 8-9, the reaction temperature is 50-80 DEG C, and the reaction time is 8-16 h.

[0017] Further, in step S2, the sintering comprises one-stage sintering and two-stage sintering in sequence; the holding time of the one-stage sintering is 4-8 h, and the temperature is 400-600 DEG C; the holding time of the two-stage sintering is 8-16 h, and the temperature is 750-950 DEG C.

[0018] The application also provides a cathode material doped with anions and cations, which is prepared by the above method; the chemical formula of the cathode material is Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y .

[0019] The application also provides a lithium ion battery positive pole piece prepared by using the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material.

[0020] The application also provides a lithium ion battery comprising the lithium ion battery positive pole piece.

[0021] The application has the following beneficial effects:

[0022] (1) The preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material can simultaneously modify anions and cations by doping Al and F; Al doping can adjust the local electronic structure, increase the redox potential, improve the interaction with oxygen, further stabilize the lattice oxygen and inhibit the release of the lattice oxygen, so that the positive electrode material structure is stable and has good long cycle performance; F doping can induce the generation of initial spinel phases on the material surface and inhibit the transformation of the layered phases to the spinel phases during the cycle process, so that the ion and electronic conductivity of the material is improved, and the rate performance of the material is improved;

[0023] (2) The preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material can slow down the voltage attenuation of the modified positive electrode material and has excellent cycle performance, and solves the problems of serious voltage attenuation and poor cycle stability of the existing cobalt-free lithium-rich manganese-based materials;

[0024] (3) The preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material can synthesize the cobalt-free lithium-rich manganese-based positive electrode material doped with Al at the manganese site and F at the oxygen site by using the coprecipitation method-high temperature solid phase method, and the synthesis can follow the conventional preparation process of the lithium-rich manganese-based material; by jointly adding aluminum fluoride elements in the reaction solution, the lithium-rich manganese-based material with excellent electrochemical stability and performance can be obtained without a large-scale increase in the production process and links, and the method has a wide range of application;

[0025] (4) The preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material has simple preparation process and convenient process control, can control the particle size of the positive electrode material by controlling the pH value and holding time, the product particle size is uniform and the electrochemical performance is excellent, can meet the needs of various products, the whole production process has less pollution, is relatively simple, has strong controllability, does not need advanced instruments, has low cost, and is suitable for industrial production;

[0026] (5) The anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application realizes the reduction of lithium-nickel cation mixing, the improvement of the interlayer distance of the layered structure, the improvement of stability, the more convenient embedding and extraction of lithium ions, the faster electron transfer rate of the material, and thus the effective improvement of the first cycle coulombic efficiency and cycle stability of the material, and the improvement of the rate performance under 5C large current conditions after fluorine and aluminum doping, which is helpful for the application of the material in future fast charging batteries. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The PXRD graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 8, Example 3 and Example 7;

[0028] Figure 2 The SEM graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 8, Figure 2 The scale of a in FIG. 8 is 400 nm, Figure 2 The scale of b in FIG. 8 is 100 nm;

[0029] Figure 3 The SEM graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 3, Figure 3 The scale of a in FIG. 3 is 400 nm, Figure 3 The scale of b in FIG. 3 is 200 nm;

[0030] Figure 4 The SEM graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 7, Figure 4 The scale of a in FIG. 7 is 400 nm, Figure 4 The scale of b in FIG. 7 is 200 nm;

[0031] Figure 5 The cycle performance comparison graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 8, Example 3 and Example 7;

[0032] Figure 6 The first cycle charge-discharge comparison graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 8, Example 3 and Example 7;

[0033] Figure 7 The rate performance comparison graph of the material of the preparation method of the anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application, the material of Example 8, Example 3 and Example 7;

[0034] Figure 8For the preparation method of the cation and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material of the application, Figure 8 is a discharge curve diagram of Example 8 under different currents.

[0035] Figure 9 For the preparation method of the cation and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material of the application, Figure 7 is a discharge curve diagram of Example 7 under different currents. DETAILED DESCRIPTION

[0036] The principles and characteristics of the application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the application and are not used to limit the scope of the application.

[0037] The preparation method of the cation and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material of the application uses a metal salt solution, a precipitating agent, a fluorine source and a complexing agent to prepare a modified lithium-rich manganese-based precursor, and uses the modified lithium-rich manganese-based precursor and a lithium source to prepare a cation and anion co-doped cobalt-free lithium-rich manganese-based positive electrode material. The metal salt solution contains manganese, nickel and aluminum; the molar ratio of manganese, nickel and aluminum is a:b:x, and the molar ratio of fluorine is y; the values of a, b, x and y are in the range of a>0.5, 0

[0038] The preparation method of the cation and anion doped modified cobalt-free lithium-rich manganese-based positive electrode material of the application can realize cation and anion modification of the cobalt-free lithium-rich manganese (LNMO) through the aluminum salt in the metal salt solution and the fluorine source. Al doping can adjust the local electronic structure, increase the redox potential, improve the interaction with oxygen, further stabilize the lattice oxygen and inhibit the release of the lattice oxygen, make the positive electrode material structure stable, and have good long cycle performance; F doping can induce the generation of the initial spinel phase on the material surface, and inhibit the transformation of the layered structure to the spinel phase during the cycle process, improve the ion and electronic conductivity of the material, and further improve the rate performance of the material. Al and F simultaneously perform cation and anion modification, and through the combination of the two, not only improve the long cycle performance of the original material, but also modify the rate performance of the material, effectively inhibit the lithium-nickel cation mixing, improve the stability of the layered structure and the rate performance under the condition of 5C large current, and better improve the electrochemical performance of the lithium-rich layered oxide. Therefore, the simultaneous use of Al doping and F doping can slow down the voltage attenuation of the modified positive electrode material and improve the cycle performance, and solves the problems of serious voltage attenuation and poor cycle stability of the existing cobalt-free lithium-rich manganese-based materials.

[0039] Preferably, the molar ratio x of aluminum is 0.01-0.06; further preferably, x is 0.01, 0.02, 0.03, 0.04, 0.05 or 0.06.

[0040] Preferably, the molar ratio y of fluorine is 0.02, 0.04, 0.06, etc.

[0041] Since the material obtained by the preparation method of the present application is modified LNMO, the modified material necessarily contains oxygen elements, and for the addition of Li, various specific optional molar ratios can be set.

[0042] Preferably, in the preparation method of the present application, the precipitant includes one or more of lye, and the complexing agent includes one or more of ammonia, ammonium bicarbonate.

[0043] Further preferably, the lye is one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0044] Preferably, the lithium source is one or more of lithium hydroxide, lithium sulfide, and lithium carbonate; the aluminum source is one or both of aluminum oxide and aluminum nitrate; and the fluorine source includes one or both of ammonium fluoride and lithium fluoride.

[0045] The preparation method of the present application comprises the following steps:

[0046] S1, after dissolving the complexing agent, as a bottom liquid, the metal salt solution, the precipitant, and the fluorine source are injected into the bottom liquid in parallel flow, stirring and performing co-precipitation reaction under heating conditions, after the reaction is completed, cooling, filtering, and drying are performed to obtain a modified lithium-rich manganese-based precursor. The solvent for dissolving the complexing agent can be water.

[0047] The cobalt-free lithium-rich manganese-based positive electrode material doped with aluminum at the manganese site and fluorine at the oxygen site is synthesized by the co-precipitation method-high temperature solid phase method. The synthesis can follow the conventional preparation process of lithium-rich manganese-based materials. By jointly adding aluminum and fluorine elements in the reaction solution, a lithium-rich manganese-based material with excellent electrochemical stability and performance can be obtained without significantly increasing the production process and links. This method has a wide range of applications.

[0048] Preferably, the co-precipitation reaction is performed in a reaction kettle; specifically, the bottom liquid is added to the reaction kettle, and then the metal salt solution, the precipitant, and the fluorine source are injected into the reaction kettle in parallel flow. At this time, the peristaltic pump in the reaction kettle is stirred and continuously performs the co-precipitation reaction.

[0049] The flow rate of parallel injection is 30-80 ml / min, specifically referring to the metal salt solution, the precipitant, and the fluorine source being injected into the reaction kettle at the same speed and uniform parallel flow.

[0050] Preferably, the pH of the co-precipitation reaction is 8-9, the reaction temperature in the reaction kettle is 50-80℃, and the reaction time is 8-16h.

[0051] Further preferably, the reaction temperature in the reaction kettle is 50℃, 55℃, 60℃, 63℃, 70℃, 77℃, 80℃, etc.

[0052] Further preferably, the pH of the co-precipitation reaction is 8, 8.2, 8.5, 8.8 or 9, etc.

[0053] Further preferably, the reaction time is 8h, 9h, 9.5h, 10h, 12h or 16h, etc.

[0054] Preferably, after the completion of the co-precipitation reaction, the obtained precipitate is dissolved with deionized water, washed with deionized water and then washed with ethanol for 3-6 times by means of suction filtration or centrifugation, and dried in an oven at 60-120℃ for 12-24h.

[0055] S2, the modified cobalt-free lithium-rich manganese-based precursor is mixed with a lithium source for ball milling treatment, and then sintered.

[0056] Preferably, the mixing ball milling treatment is carried out by using a planetary ball mill, and the treatment time is 1-3h; further preferably, the treatment time is 1h, 2h, 3h, etc.

[0057] Preferably, the sintering comprises a first sintering and a second sintering in sequence; the holding time of the first sintering is 4-8h, and the temperature is 400-600℃; the holding time of the second sintering is 8-16h, and the temperature is 750-950℃.

[0058] Further preferably, the holding time of the first sintering is 4h, 4.5h, 5h, 6h, 6.5h, 7h or 8h, etc., and the temperature is 400℃, 450℃, 500℃, 520℃ or 600℃, etc.

[0059] Further preferably, the holding time of the second sintering is 8h, 8.5h, 10h, 12h, 14h or 16h, etc., and the temperature is 750℃, 800℃, 850℃, 900℃ or 950℃, etc.

[0060] The anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material of the present application is prepared by the above method, and the chemical formula of the positive electrode material is Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y .

[0061] The positive electrode material of the present application, after being modified by doping Al and F anions and cations, has slow voltage attenuation and excellent cycle performance, solving the problems of serious voltage attenuation and poor cycle stability of general cobalt-free lithium-rich manganese-based materials.

[0062] The lithium ion battery positive electrode sheet of the present application is prepared by using the above anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material.

[0063] When the positive electrode material of the application is used to prepare a positive electrode sheet, any optional conventional method can be used, and in one specific embodiment of the application, the preparation method comprises the following steps:

[0064] The active material, the conductive agent and the binder are mixed and then dissolved in a solvent to obtain a slurry, the slurry is uniformly coated on the surface of an aluminum foil as a current collector, and a lithium ion positive electrode sheet is obtained after drying.

[0065] The active material is a modified cobalt-free lithium-rich manganese-based material, the binder is one or more of polyvinylidene fluoride, polyacrylic acid and sodium alginate, the conductive agent is acetylene black, conductive carbon black, Super-P or Ketjen black, the solvent is N-methyl pyrrolidone, and the mass ratio of the cobalt-free lithium-rich manganese-based positive electrode material doped and modified by anions and cations, the conductive agent and the binder is 70-90:5-20:5-20.

[0066] The lithium ion battery of the application has a discharge specific capacity of 200-250 mAh.g -1 at the first circle in a voltage range of 2.0-4.8 V, the working voltage attenuation of the lithium ion battery before and after cycling is obviously slowed down, and the capacity retention rate is greater than 80% after 200 cycles at a current density of 0.5 C.

[0067] When the positive electrode sheet of the application is used to prepare a lithium battery, any optional conventional method can be used, and in one specific embodiment of the application, the preparation method comprises the following steps:

[0068] The lithium metal is pressed and cut to prepare a negative electrode sheet. Ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 are mixed to form a carbonate electrolyte with a concentration of 0.1-2 mol / L. A commercial polypropylene separator is used as a separator, and the support is foamed nickel and a gasket.

[0069] The positive electrode sheet, the separator, the electrolyte, the negative electrode sheet and the foamed nickel of the lithium ion battery are sequentially assembled in a glove box, and the lithium ion battery is prepared through a pressing and standing process.

[0070] The application is illustrated by specific examples as follows.

[0071] Example 1

[0072] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material doped and modified by anions and cations in this embodiment comprises the following steps:

[0073] First, manganese sulfate monohydrate, nickel sulfate hexahydrate and aluminum nitrate nonahydrate are weighed according to the stoichiometric ratio and dissolved in deionized water to obtain a mixed sulfate solution A with a total cation concentration of 2 mol / L.

[0074] Anhydrous sodium carbonate and ammonium fluoride were also weighed according to the stoichiometric ratio, dissolved in deionized water, and prepared into a basic solution with a concentration of 2 mol / L, to obtain solution B.

[0075] An ammonium bicarbonate solution with a concentration of 0.1 mol / L was prepared as a bottom solution, and was injected into a round-bottom flask, which was placed in a water bath at 55°C.

[0076] Then, solution A and solution B were injected into the round-bottom flask containing the ammonium bicarbonate at a rate of 20 ml / h using a syringe pump, and were continuously stirred at 55°C. During the reaction, the pH of the solution was maintained at 8-9. After the feeding was completed, the reaction was continued for 12 h. After the reaction was completed, the supernatant was discarded, and the precipitate was centrifuged three times with deionized water and ethanol at a speed of 7500 r / min to remove impurity ions such as sodium ions, sulfate ions, and ammonium ions. The precipitate was dried in a vacuum drying oven at 60°C for 12 h, to obtain a pink carbonate precursor powder.

[0077] Finally, the precursor powder was mixed with lithium carbonate in a molar ratio of 5% excess, and was ball-milled for 2 h. The mixed sample was calcined in a tube furnace at 500°C for 5 h and at 900°C for 12 h, at a heating rate of 5°C / min, to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y .

[0078] Example 2

[0079] The anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y , x = 0.01, y = 0.

[0080] The difference between the preparation process of this example and Example 1 is that, in step S1, the manganese sulfate salt, the nickel sulfate salt, the aluminum nitrate salt, and the ammonium fluoride need to be mixed according to the stoichiometric ratio of the required components determined according to the cobalt-free lithium-rich manganese-based chemical formula of Example 2.

[0081] Example 3

[0082] The anion and cation doped modified cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2O (2-y) F y , x = 0.02, y = 0.

[0083] The difference between the preparation process of this embodiment and Example 1 is that the manganese sulfate salt, nickel sulfate salt, aluminum nitrate salt, and ammonium fluoride in step S1 need to be mixed according to the stoichiometric ratio of the required components determined by the cobalt-free lithium-rich manganese-based chemical formula described in Example 3.

[0084] Example 4

[0085] The cathode and anode ion-doped modified cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y , x = 0.03, y = 0.

[0086] The difference between the preparation process of this embodiment and Example 1 is that the manganese sulfate salt, nickel sulfate salt, aluminum nitrate salt, and ammonium fluoride in step S1 need to be mixed according to the stoichiometric ratio of the required components determined by the cobalt-free lithium-rich manganese-based chemical formula described in Example 4.

[0087] Example 5

[0088] The cathode and anode ion-doped modified cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y , x = 0.02, y = 0.02.

[0089] The difference between the preparation process of this embodiment and Example 1 is that the manganese sulfate salt, nickel sulfate salt, aluminum nitrate salt, and ammonium fluoride in step S1 need to be mixed according to the stoichiometric ratio of the required components determined by the cobalt-free lithium-rich manganese-based chemical formula described in Example 5.

[0090] Example 6

[0091] The cathode and anode ion-doped modified cobalt-free lithium-rich manganese-based positive electrode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y , x = 0.02, y = 0.04.

[0092] The difference between the preparation process of this embodiment and example 1 is that in step S1, the manganese sulfate salt, nickel sulfate salt, aluminum nitrate salt, and ammonium fluoride need to be mixed according to the stoichiometric ratio of the required components determined by the cobalt-free lithium-rich manganese-based chemical formula described in example 6.

[0093] Example 7

[0094] The cathode material Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y , x = 0.02, y = 0.06.

[0095] The difference between the preparation process of this embodiment and example 1 is that in step S1, the manganese sulfate salt, nickel sulfate salt, aluminum nitrate salt, and ammonium fluoride need to be mixed according to the stoichiometric ratio of the required components determined by the cobalt-free lithium-rich manganese-based chemical formula described in example 7.

[0096] At the same time, the cathode material of this embodiment is used to prepare a cathode sheet. The mass ratio of the cathode material to the binder is 8:1, and the mass ratio of the cathode material to the conductive agent is 8:1.

[0097] The binder is polyvinylidene fluoride, the solvent is N-methyl pyrrolidone, and the conductive agent is Super-P; the support is foamed nickel. The electrolyte is a mixture of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7, and the concentration of the carbonate electrolyte is 1 mol / L.

[0098] Example 8

[0099] This embodiment uses the method of example 1 to prepare a cathode material, which does not contain Al and F, and the other steps are the same as example 1. The obtained material is Li 1.2 Mn 0.6 Ni 0.2 O2.

[0100] The performance of the cathode materials obtained in the above examples is tested and compared, and the following results are obtained:

[0101] (1) Figure 1 The PXRD patterns of the materials of example 8, example 3, and example 7. Example 8 is a Li 1.2 Mn 0.6 Ni 0.2 O2, example 3 is a Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) Fy (x = 0.02, y = 0), and example 7 is Al and F doped Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y (x = 0.02, y = 0.06).

[0102] According to Figure 1 It can be seen that all samples have obvious characteristics of layered structure, and no visible impurities. And the main diffraction peak belongs to the R-3m space group of layered LiMO2phase. This shows that whether or not to be doped, the LNMO material required can be prepared by the method of the application.

[0103] (2) Figures 2 to 4 The SEM images of the materials of example 8, example 3 and example 7 respectively. According to Figures 2 to 4 It can be found by comparison that the surface roughness of the unmodified example 8 material is obviously serious, which is caused by excessive oxygen loss during the secondary sintering process without the supplement of other anions, and after doping, the surface is smooth, which shows that F can replace the position of O, thereby inhibiting the material structure damage caused by O loss.

[0104] (3) Figure 5 The cycle performance comparison chart of the materials of example 8, example 3 and example 7. According to Figure 5 It can be seen that after doping, the cycle stability of the material is significantly improved.

[0105] (4) Figure 6 The first charge-discharge comparison chart of the materials of example 8, example 3 and example 7. According to Figure 6 It can be seen that all samples show the characteristics of lithium-rich positive electrode material, and the specific capacity of the first charge-discharge of the double modified material is obviously increased.

[0106] (5) Figure 7 The rate performance comparison chart of the materials of example 8, example 3 and example 7. According to Figure 7 It can be seen that the double modified sample shows good rate performance at different rates, and the capacity retention of the modified sample is more obvious at 2C and 5C high current, and the decay is slow.

[0107] (6) Figure 8 The discharge curve chart of example 8 at different currents, Figure 9 The discharge curve chart of example 7 at different currents.

[0108] Comparison Figure 8 and Figure 9It can be seen that the voltage attenuation of the modified sample is obviously alleviated.

[0109] In summary, by simple and effective fluorine-aluminum co-doping method, the discharge capacity and cycle stability of the cobalt-free lithium-rich manganese-based positive electrode material are improved, and the comparison results show that the modified material has better rate performance, higher cycle capacity retention rate and smaller voltage attenuation degree.

[0110] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0111] In addition, the terms "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0112] In the present application, unless otherwise explicitly specified and limited, the "on" or "under" of the first feature to the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the "over", "above" and "on" of the first feature to the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "under", "below" and "under" of the first feature to the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0113] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0114] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0115] The above is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing anion- and cation-doped modified cobalt-free lithium-rich manganese-based positive electrode material, characterized in that: A modified lithium-rich manganese-based precursor is prepared by using a metal salt solution, a precipitant, a fluorine source, and a complexing agent, and the modified lithium-rich manganese-based precursor and a lithium source are used to prepare the anion-cation co-doped cobalt-free lithium-rich manganese-based positive electrode material; the metal salt solution contains manganese salt, nickel salt, and aluminum salt; The molar ratio of manganese, nickel, aluminum and fluorine is a:b:x:y; the value ranges of a, b, x and y are: a>0.5, 0<b≤0.2, 0<x<0.1, and a+b+x=0.8; 0.01≤y≤0.06; S1, preparing the complexing agent into a base liquid, injecting the metal salt solution, the precipitant and the fluorine source into the base liquid in parallel, stirring and performing a co-precipitation reaction under heating conditions, and cooling, filtering and drying after the reaction is completed to obtain the modified lithium-rich manganese-based precursor; In step S1, the flow rate of the parallel injection is 30 to 80 ml / min; S2. Mixing the modified cobalt-free lithium-rich manganese-based precursor with the lithium source, subjecting the mixture to ball milling treatment, and then sintering.

2. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by anion and cation doping according to claim 1, characterized in that: The precipitant includes alkali solution, and the complexing agent includes one or more of ammonia water and ammonium bicarbonate.

3. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by anion and cation doping according to claim 1, characterized in that: The lithium source is one or more of lithium hydroxide, lithium sulfide, and lithium carbonate; the aluminum salt is one or both of aluminum oxide and aluminum nitrate; and the fluorine source includes one or both of ammonium fluoride and lithium fluoride.

4. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by anion and cation doping according to claim 1, characterized in that: In step S1, the pH of the coprecipitation reaction is 8-9, the reaction temperature is 50-80° C., and the reaction time is 8-16 hours.

5. The method for preparing a cobalt-free lithium-rich manganese-based cathode material modified by anion and cation doping according to claim 1, characterized in that: In step S2, the sintering includes a first stage sintering and a second stage sintering in sequence; the holding time of the first stage sintering is 4 to 8 hours at a temperature of 400 to 600°C, and the holding time of the second stage sintering is 8 to 16 hours at a temperature of 750 to 950°C.

6. A cobalt-free lithium-rich manganese-based cathode material modified by anion and cation doping, characterized in that: Prepared by the method according to any one of claims 1 to 5; the chemical formula of the positive electrode material is Li 1.2 Mn (0.6-x) Al x Ni 0.2 O (2-y) F y .

7. A positive electrode plate for a lithium-ion battery, characterized in that: It is prepared by using the anion-cation doped modified cobalt-free lithium-rich manganese-based positive electrode material as claimed in claim 6.

8. A lithium-ion battery, characterized in that: The invention comprises the lithium-ion battery positive electrode sheet as claimed in claim 7.

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