Lithium-rich manganese-based positive electrode material with combined action of surface heterojunction and bulk phase doping as well as preparation method and application of lithium-rich manganese-based positive electrode material

Abstract

The invention belongs to the technical field of lithium-rich manganese-based positive electrodes, and discloses a surface heterojunction and bulk phase doping combined lithium-rich manganese-based positive electrode material and a preparation method and application thereof, the method comprises the following steps: preparing a surface heterojunction Ma (TiO3) b (1 < = a < = 5, 1 < = b < = 5 and bulk phase Ti and M doped Li < 1.2 > MnxNi0. 2TiyMzO2 (0.3 lt) through a molten salt assisted solvothermal method; x is less than or equal to 1.5, 0.0001 lt; y is less than or equal to 0.001, 0.0001 lt; z is less than or equal to 0.001, and M is Na, K, Ba, Ca, Mg, Pb, Fe or Bi. The heterojunction inhibits interface reaction, reduces generation of Li vacancies on the surface, metal cations are introduced to stabilize lattice oxygen in the lithium-rich manganese material, crystal stability is improved, and under the combined action of the heterojunction and bulk phase doping, the positive electrode material has excellent electrochemical performance, improves battery capacity and cycling stability and can be applied to a lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-rich manganese-based positive electrodes, and more specifically, relates to a lithium-rich manganese-based positive electrode material with surface heterojunction and bulk doping as well as a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have gradually become the main way to power portable electronic devices and electric vehicles due to their high energy density, long cycle life and environmental friendliness. In these batteries, the cathode material is a key factor in determining battery performance, cost and safety. Currently, the main commercial cathode materials, such as LiCoO 2 , NCM and LiFePO 4 The specific capacity of lithium-ion batteries is low, making it difficult for lithium-ion batteries to be used in many fields. Therefore, lithium-rich manganese-based materials have become ideal candidates for the next generation of lithium-ion batteries due to their high theoretical capacity (>250 mAh / g) and low cost. The high capacity characteristics of this type of positive electrode material come from its Li 2 MnO 3 The components can be activated at high voltages above 4.5 V to trigger the oxygen anion charge compensation mechanism, thereby providing additional capacity. It is this unique mixed anion and cation redox mechanism that makes LMRO a promising candidate cathode material for the next generation of high-energy lithium-ion batteries.

[0003] However, lithium-rich manganese-based cathode materials under high voltage will have problems such as low first coulombic efficiency, severe capacity and voltage decay, poor rate performance and poor cycle stability. In order to deal with these phenomena, researchers have been actively exploring various strategies, including element doping, surface treatment and structural optimization. However, the capacity and cycle stability of lithium-rich manganese-based cathode materials still need to be further improved, and they have great potential for practical application. Summary of the invention

[0004] In order to solve the above-mentioned deficiencies and shortcomings of the prior art, the primary purpose of the present invention is to provide a method for preparing a lithium-rich manganese-based positive electrode material with the combined action of surface heterojunction and bulk doping. The method adopts a molten salt-assisted solvothermal method to prepare a surface heterojunction M by coordinated doping of Ti and metal cations M. a (TiO 3 ) b(1 ≤ a ≤ 5, 1 ≤ b ≤ 5) and the bulk-phase Ti and metal cation M-doped lithium-rich manganese-based cathode material, under the dual combined action of the surface heterojunction and bulk-phase doping mechanisms, effectively inhibits the occurrence of interfacial reactions, while reducing the generation of surface Li vacancies, thereby slowing down the migration rate of transition metals TM (Mn and Ni in lithium-rich) and the heterostructure evolution process. By introducing metal cations to stabilize the lattice oxygen in the lithium-rich manganese material, the crystal structure stability of the material is improved, endowing it with excellent cycling performance and structural stability, and enhancing the electrochemical performance of the battery.

[0005] Another object of the present invention is to provide a lithium-rich manganese-based cathode material with the combined action of surface heterojunction and bulk-phase doping prepared by the above method. The lithium-rich manganese-based cathode material under the dual mechanism of the heterojunction is Li 1.2 Mn x Ni 0.2 Ti y M z O 2 , 0.3 < x ≤ 1.5, 0.0001 < y ≤ 0.001, 0.0001 < z ≤ 0.001, M = Na, K, Ba, Ca, Mg, Pb, Fe or Bi, and is prepared by the coordinated doping of Ti and metal cation M to form a surface M a (TiO 3 ) b (1 ≤ a ≤ 5, 1 ≤ b ≤ 5) heterojunction and the bulk-phase Ti and metal cation-doped M lithium-rich manganese-based cathode material (Li 1.2 Mn 0.6 Ni 0.2 O 2 ), which has excellent voltage and capacity stability.

[0006] Another object of the present invention is to provide the application of the above lithium-rich manganese-based cathode material with the combined action of surface heterojunction and bulk-phase doping.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A preparation method of a lithium-rich manganese-based cathode material with the combined action of surface heterojunction and bulk-phase doping, comprising the following steps:

[0009] S1. Stir carbonate precursor Mn 0.75 Ni 0.25 CO 3 , absolute ethanol and tetrabutyl titanate at room temperature, perform a solvothermal reaction at 120 - 180 °C, and after filtration, washing and drying, obtain a Ti polymer-coated Mn 0.75 Ni 0.25 CO 3Precursor on the surface; calculated by Ti element, the tetrabutyl titanate is 0.1 - 1 mol% of carbonate precursor Mn 0.75 Ni 0.25 CO 3 ; the molar ratio of the carbonate precursor Mn 0.75 Ni 0.25 CO 3 to the volume of absolute ethanol is 0.008 mol:(50 - 100) mL;

[0010] S2. Uniformly grind the precursor on the surface of Mn 0.75 Ni 0.25 CO 3 covered by Ti polymer with a molar ratio of 1:(1 - 1.1):(2 - 4):(0.001 - 0.01), lithium salt, molten salt and metal compound, sinter the above mixed powder at 800 - 900 °C, cool to room temperature, and after washing, dry at 180 - 200 °C to obtain black powder;

[0011] S3. Dry the black powder at 300 - 400 °C, cool to room temperature, to obtain a lithium-rich manganese-based cathode material with the combined action of surface heterojunction and bulk doping, and its molecular formula is Li 1.2 Mn x Ni 0.2 Ti y M z O 2 , 0.3 < x ≤ 1.5, 0.0001 < y ≤ 0.001, 0.0001 < z ≤ 0.001, where the surface heterojunction is M a (TiO 3 ) b , 1 ≤ a ≤ 5, 1 ≤ b ≤ 5, and the bulk doping is Ti and M doping, and M is Na, K, Ba, Ca, Mg, Pb, Fe or Bi.

[0012] Preferably, in step S2, the lithium salt is one or more of lithium carbonate, lithium hydroxide, lithium nitrate or lithium chloride; the molten salt is sodium chloride or / and potassium chloride; the metal compound is carbonate or / and chloride of Na, K, Ba, Ca, Mg, Pb, Fe or Bi.

[0013] Preferably, in step S2, the heating rate of sintering at 800 - 900 °C is 2 - 4 °C / min, and the sintering time is 10 - 20 h.

[0014] A lithium-rich manganese-based cathode material with the combined action of surface heterojunction and bulk doping is prepared by the described method.

[0015] Application of the described lithium-rich cathode material with the combined action of surface heterojunction and bulk doping in the preparation of lithium-ion batteries.

[0016] The lithium-rich manganese-based positive electrode material of the present invention, which is a combination of surface heterojunction and bulk doping, is constructed by constructing a surface heterojunction M a (TiO 3 ) b (1≤a≤5, 1≤b≤5) effectively inhibits the occurrence of interfacial reactions and reduces the generation of surface Li vacancies, thereby slowing down the migration rate of transition metals Mn and Ni and the evolution of heterogeneous structures. Then, by introducing metal cations to form strong Ti-O bonds, MO bonds and stable valence states, the electrochemical properties and lithium ion diffusion rate of lithium-rich manganese-based cathode materials are improved. The synergistic effect of Ti and metal cations simultaneously enhances the crystal structure and oxygen anion redox stability of lithium-rich manganese-based layered cathode materials, significantly alleviating surface and interfacial reactions.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention adopts a molten salt-assisted solvothermal method to prepare a surface heterojunction M by coordinated doping of Ti and metal cation M. a (TiO 3 ) b (1≤a≤5, 1≤b≤5) and bulk Ti and metal cation-doped M Li 1.2 Mn 0.6 Ni 0.2 O 2 Among them, the heterojunction effectively inhibits the occurrence of interface reactions and reduces the generation of surface Li vacancies, thereby slowing down the migration rate of transition metals and the evolution of heterostructures. The doping of Ti and metal cations constructs Ti-O bonds and MO bonds. The stronger bond energy inhibits the Li-rich manganese-based material Li 1.2 Mn 0.6 Ni 0.2 O 2 The structural phase change during the charge and discharge process reduces the loss of lattice oxygen, thereby increasing the Li 1.2 Mn 0.6 Ni 0.2 O 2 In addition, the introduction of metals with larger ionic radius can play a "pillar" role and stabilize the lithium-rich manganese-based material Li 1.2 Mn 0.6 Ni 0.2 O 2 The layered structure inhibits the collapse and phase transition of the structure during charge and discharge, and improves the Li 1.2 Mn 0.6 Ni 0.2 O 2The cycle stability of the positive electrode material is guaranteed by the combined effect of surface heterojunction and bulk doping of Li 1.2 Mn 0.6 Ni 0.2 O 2 The positive electrode material has excellent electrochemical performance. The method is simple, and the molten salt-assisted solvothermal method can be used to prepare a lithium-rich manganese-based positive electrode material with a dual action mechanism in one step, that is, Li with the dual mechanism of surface heterojunction and bulk doping. 1.2 Mn 0.6 Ni 0.2 O 2 , creating good conditions for industrial application.

[0019] 2. Surface M prepared by the present invention a (TiO 3 ) b The electrochemical performance of the button half-cell assembled with lithium-rich manganese-based cathode materials with (1≤a≤5, 1≤b≤5) heterojunction and bulk Ti and metal cation doping was tested, and the maximum capacity reached 206.9 mAhg at 2~4.8V and 1C. -1 After 250 cycles, the capacity retention rate is still 98.8%. The lithium-rich manganese-based positive electrode material with the dual mechanism of surface heterojunction and bulk doping has excellent cycle performance and structural stability, improves the electrochemical performance, and can be used in lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The XRD refined images and local enlarged images of the lithium-rich manganese-based positive electrode material of Example 1 with the combined effect of surface heterojunction and bulk doping and the lithium-rich manganese-based positive electrode material of Comparative Example 1.

[0021] Figure 2 This is a comparison chart of voltage decay and discharge specific capacity cycle of the lithium-rich manganese-based positive electrode material prepared by the surface heterojunction and bulk doping in Example 1 and the lithium-rich manganese-based positive electrode material of Comparative Example 1 under 1C (200mA / g) and 4.8V cut-off voltage conditions.

[0022] Figure 3 TEM images of the lithium-rich manganese-based positive electrode material prepared in Example 1 with the combined action of surface heterojunction and bulk doping and the lithium-rich manganese-based positive electrode material of Comparative Example 1 after 100 cycles.

[0023] Figure 4 This is a SEM photograph of the lithium-rich manganese-based positive electrode material prepared in Example 1 with the combined effect of surface heterojunction and bulk doping before cycling. DETAILED DESCRIPTION

[0024] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0025] Example 1

[0026] 1. 0.927 g of carbonate precursor (Mn 0.75 Ni 0.25 CO 3 ) was placed in a polytetrafluoroethylene (PTFE) liner, and 50 mL of anhydrous ethanol and 19 μL of tetrabutyl titanate were added. After stirring at room temperature for 30 minutes, it was placed in a reactor for solvent thermal reaction at 150°C for 12 hours. After the reaction, the sample was taken out and filtered, washed with ethanol three times, and then dried at 180°C to obtain a uniformly covered Mn Ti polymer. 0.75 Ni 0.25 CO 3 Surface precursors;

[0027] 2. Ti polymer uniformly covers Mn 0.75 Ni 0.25 CO 3 Surface precursor, 0.4655gLi 2 CO 3 (Compared to the uniform coverage of Mn by Ti polymer 0.75 Ni 0.25 CO 3 The precursors on the surface were in excess of 5 mol %), 1.8701 g NaCl, 3.5784 g KCl and 0.01 g BaCO 3 The mixed powder was sintered in air at 850°C for 12 h, cooled to room temperature, the block solid was taken out, washed with deionized water for 3 times, filtered, and dried at 180°C to obtain a black powder.

[0028] 3. Dry the black powder at 400℃ for 3 h and cool it to room temperature to obtain surface heterojunction BaTiO 3 The lithium-rich manganese-based positive electrode material that works together with the bulk Ba and Ti doping is Li 1 .2 Mn 0.5925 Ni 0.2 Ti 0.005 Ba 0.005 O 2 Positive electrode material.

[0029] Example 2

[0030] The difference from Example 1 is that the temperature of the solvent thermal reaction in step 1 is 180°C.

[0031] Example 3

[0032] The difference from Example 1 is that the temperature of the solvent thermal reaction in step 1 is 120°C.

[0033] Example 4

[0034] The difference from Example 1 is that the content of tetrabutyl titanate and barium carbonate added in steps 1 and 2 is Mn 0.75 Ni 0.25 CO 3 0.24 mol% to obtain the surface heterojunction BaTiO 3 The lithium-rich manganese-based positive electrode material that works together with the bulk Ba and Ti doping is Li 1 .2 Mn 0.5955 Ni 0.2 Ti 0.003 Ba 0.003 O 2 .

[0035] Example 5

[0036] The difference from Example 1 is that the content of tetrabutyl titanate and barium carbonate added in steps 1 and 2 is Mn 0.75 Ni 0.25 CO 3 0.8 mol% to obtain the surface heterojunction BaTiO 3 The lithium-rich manganese-based positive electrode material that works together with the bulk Ba and Ti doping is Li 1 .2 Mn 0.585 Ni 0.2 Ti 0.01 Ba 0.01 O 2 .

[0037] Example 6

[0038] The difference from Example 1 is that the metal compound in step 2 is K 2 CO 3 .

[0039] Example 7

[0040] The difference from Example 1 is that the metal chemical in step 2 is CaCO 3 .

[0041] Example 8

[0042] The difference from Example 1 is that the metal chemical in step 2 is MgCO 3 .

[0043] Example 9

[0044] The difference from Example 1 is that the sintering temperature in step 2 is 830°C.

[0045] Example 10

[0046] The difference from Example 1 is that the sintering temperature in step 2 is 870°C.

[0047] Comparative Example 1

[0048] 1. 0.927 g of carbonate precursor (Mn 0.75 Ni 0.25 CO 3 )、0.4655g Li 2 CO 3 (relative to Mn 0.75 Ni 0.25 CO 3 Excess 5 mol%), 1.8701 g NaCl and 3.5784 g KCl were evenly ground, and the mixed powder was sintered at 850 °C in air for 12 h, cooled to room temperature, and the block solid was taken out, washed with deionized water for 3 times, filtered, and dried at 180 °C to obtain a black powder.

[0049] 2. Sinter the black powder at 400℃ in air for 3 h and cool to room temperature to obtain Li 1.2 Mn 0.6 Ni 0.2 O 2 Positive electrode material.

[0050] Comparative Example 2

[0051] 1. 0.927 g of carbonate precursor (Mn 0.75 Ni 0.25 CO 3 )、0.004g TiO 2 , 0.01g BaCO 3 、0.4655gLi 2 CO 3 (relative to Mn 0.75 Ni 0.25 CO 3 The mixed powder was sintered in air at 850℃ for 12 h, cooled to room temperature, the block solid was taken out, washed with deionized water for 3 times, filtered, and dried at 180℃ to obtain a black powder.

[0052] 2. Sinter the black powder at 400℃ in air for 3 h and cool to room temperature to obtain bulk Ba and Ti doped lithium-rich manganese-based cathode material, namely Li 1 .2 Mn 0.5925 Ni0.2 Ti 0.005 Ba 0.005 O 2 .

[0053] Comparative Example 3

[0054] The difference from Comparative Example 2 is that the TiO 2 and BaCO 3 The content is Mn 0.75 Ni 0.25 CO 3 0.24 mol% was used to prepare the bulk phase doped lithium-rich manganese-based positive electrode material, namely Li 1 .2 Mn 0.5955 Ni 0.2 Ti 0.003 Ba 0.003 O 2 .

[0055] Comparative Example 4

[0056] The difference from Comparative Example 2 is that the TiO 2 and BaCO 3 The content is Mn 0.75 Ni 0.25 CO 3 0.8 mol% of the bulk Ba and Ti doped lithium-rich manganese-based positive electrode material was obtained, namely Li 1 .2 Mn 0.585 Ni 0.2 Ti 0.01 Ba 0.01 O 2 .

[0057] Comparative Example 5

[0058] The difference from Comparative Example 2 is that the metal compound in step 1 is K 2 CO 3 .

[0059] Comparative Example 6

[0060] The difference from Comparative Example 2 is that the metal compound in step 1 is CaCO 3 .

[0061] Comparative Example 7

[0062] The difference from Comparative Example 2 is that the metal compound in step 1 is MgCO 3 .

[0063] Comparative Example 8

[0064] The difference from Comparative Example 2 is that the sintering temperature in step 1 is 830°C.

[0065] Comparative Example 9

[0066] The difference from Comparative Example 2 is that the sintering temperature in step 1 is 870°C.

[0067] The positive electrode materials prepared in Examples 1-10 and Comparative Examples 1-9 were added with polyvinylidene fluoride binder, acetylene black conductive agent and N-methylpyrrolidone cosolvent for homogenization, and the positive electrode materials were coated on a metal aluminum sheet to form a positive electrode sheet. The positive electrode sheet was then assembled with a polypropylene and polyethylene composite membrane, a 3036 electrolyte and a lithium sheet to form a battery. The assembled battery was connected to a charger and initially charged by constant current charging and constant voltage charging. After charging was completed, the battery was tested for capacity and cycle performance. The test parameters of the battery were as follows: 4.8V DCR for the first time; 4.8V DCR cycle (1C), and the results are shown in Table 1.

[0068] Table 1 Electrochemical performance of the positive electrode materials assembled into batteries of Examples 1-10 and Comparative Examples 1-9

[0069] Group <![CDATA[Initial discharge specific capacity (mAh g -1 ).]]> First Coulombic efficiency Capacity retention after 250 cycles (%) Example 1 206.9 81.81 98.80 Comparative Example 1 235.7 73.86 42 Comparative Example 2 208.51 80.05 80.26 Example 2 202.93 78.46 91.24 Example 3 204.57 79.01 88.82 Example 4 213.45 80.64 77.56 Comparative Example 3 203.45 78.64 74.74 Example 5 198.51 77.72 81.86 Comparative Example 4 194.88 76.47 78.48 Example 6 223.66 77.09 65.25 Comparative Example 5 218.69 75.63 62.95 Example 7 215.98 80.85 67.10 Comparative Example 6 205.37 77.69 65.47 Example 8 202.65 81.96 69.34 Comparative Example 7 195.86 81.96 65.85 Example 9 191.30 82.17 67.40 Comparative Example 8 185.76 80.74 64.45 Example 10 208.70 79.84 85.28 Comparative Example 9 204.57 76.84 78.85

[0070] Table 1 shows the electrochemical performance of lithium-ion batteries assembled with lithium-rich manganese-based positive electrode materials prepared by the dual mechanism of surface heterojunction and bulk doping in Examples 1-10 and batteries assembled with lithium-rich manganese-based positive electrode materials in Comparative Example 1 and bulk doped lithium-rich manganese-based positive electrode materials in Comparative Examples 2-9. As shown in Table 1, the surface heterojunction (BaTiO 3 ) and bulk Ba and Ti doping combined with Li 1 .2 Mn 0.5925 Ni 0.2 Ti 0.005 Ba 0.005 O 2 The optimal performance is achieved, indicating that this method forms a heterojunction M between Ti and metal cations on the surface. a (TiO 3 ) b (1≤a≤5, 1≤b≤5) effectively inhibits the occurrence of interfacial reactions and reduces the generation of surface Li vacancies, thereby slowing down the migration rate of transition metals Mn and Ni and the evolution of heterostructures. The doping of Ti and metal cations constructs Ti-O bonds and MO bonds. Stronger bonds can inhibit the Li-rich manganese-based materials Li 1.2 Mn 0.6 Ni 0.2 O 2 The structural phase change during the charge and discharge process reduces the loss of lattice oxygen, thereby increasing the Li 1.2 Mn 0.6 Ni 0.2 O2 The stability and electrochemical performance of the cathode material enhances the Li 1.2 Mn 0.6 Ni 0.2 O 2 The cycle stability and first coulombic efficiency of the positive electrode material at 4.8V. The lithium-ion battery assembled with the lithium-rich manganese-based positive electrode material prepared in Examples 1-10 by the combined action of surface heterojunction and bulk doping has higher charge and discharge capacity, first efficiency and capacity retention rate than the battery assembled with the lithium-rich manganese-based positive electrode material in Comparative Example 1. The surface heterojunction BaTiO prepared by the molten salt-assisted solvothermal method in Examples 1-10 3 Compared with the bulk Ba and Ti doped lithium-rich manganese-based positive electrode material, the bulk doped lithium-rich manganese-based positive electrode material prepared by the molten salt method in comparative example 2-9 has better cycle stability and first charge and discharge efficiency.

[0071] Figure 1 The surface heterojunction (BaTiO 3 ) and bulk Ba and Ti doping combined with Li-rich manganese-based cathode materials Li 1 .2 Mn 0.5925 Ni 0.2 Ti 0.005 Ba 0.005 O 2 Compared with the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.6 Ni 0.2 O 2 XRD pattern and its local magnification. Figure 1 It can be seen that the surface heterojunction and bulk doping of Example 1 work together to produce no impurity peaks in the lithium-rich manganese-based cathode material, proving that Ba and Ti are successfully doped into the cathode material Li 1.2 Mn 0.6 Ni 0.2 O 2 In the figure, it is shown that the surface heterojunction of BaTiO 3 The doping with Ba and Ti does not affect the crystal structure of the material. The local XRD pattern shows that after the surface heterojunction BaTiO 3 After the doping with Ba and Ti, the Li 1 .2 Mn 0.5925 Ni 0.2 Ti 0.005 Ba 0.005 O 2 The 003 and 104 peaks of the Ba 2+ The doping of has an impact on the lattice constant of the material, expands the unit cell parameters of the sample, and is more conducive to Li + diffusion. Figure 2 The voltage decay (a) and discharge specific capacity (b) of the lithium-rich manganese-based positive electrode material prepared in Example 1 with the combined action of surface heterojunction and bulk doping and the lithium-rich manganese-based positive electrode material of Comparative Example 1 under 1C (200mA / g) and 4.8V cut-off voltage conditions are compared. Figure 2 It can be seen that at 2~4.8V and 1C, the Li 1.2 Mn 0.6 Ni 0.2 O 2 The voltage decay within 50~250 cycles (1.01 mV / cycle) is much lower than that of Li 1.2 Mn 0.6 Ni 0.2 O 2 (2.22 mV / cycle), the voltage stability is more than doubled. Compared with the maximum specific capacity comparison example 1, the discharge capacity after 250 cycles dropped significantly to 95.84 mAhg −1 The capacity retention rate is 42%. The discharge capacity of the lithium-rich manganese-based positive electrode material in Example 1, which is a combination of surface heterojunction and bulk doping, is still as high as 204.4 mAh g after 250 cycles. −1 The capacity retention rate is 98.8%, indicating that the optimal sample of lithium-rich manganese-based positive electrode material with the combined effect of surface heterojunction and bulk doping has been greatly improved compared with the lithium-rich manganese-based positive electrode material. Figure 3 TEM images of the surface heterojunction and bulk doping-cooperated lithium-rich manganese-based positive electrode materials (a and b) prepared in Example 1 and the lithium-rich manganese-based positive electrode materials (c and d) of Comparative Example 1 after 100 cycles. Figure 3 It can be seen that the surface heterojunction and bulk doping of the lithium-rich manganese-based positive electrode material in Example 1 work together to make the material structure dense after 100 cycles without obvious corrosion; while the lithium-rich manganese-based positive electrode material in Comparative Example 1 has a loose structure and is severely corroded by the electrolyte, indicating that the surface heterojunction BaTiO 3 The lithium-rich manganese-based positive electrode material, together with Ba and Ti doping, greatly improves its stability. Figure 4 The SEM photograph of the lithium-rich manganese-based positive electrode material with the combined effect of surface heterojunction and bulk doping in Example 1 before cycling. (a) is the SEM photograph of the lithium-rich manganese-based positive electrode material with the combined effect of surface heterojunction and bulk doping before cycling, and (b) is the EDX mapping. Figure 4 It can be seen that the heterojunction BaTiO 3 The structure effectively inhibits the occurrence of interfacial reactions.

[0072] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based positive electrode material with the combined action of surface heterojunction and bulk doping, characterized in that: The following steps are involved: S1. The carbonate precursor Mn 0.75 Ni 0.25 CO3, anhydrous ethanol and tetrabutyl titanate were stirred at room temperature and reacted at 120-180℃ for solvent thermal reaction. After filtering, washing and drying, Ti polymer covered Mn 0.75 Ni 0.25 Precursors on the CO3 surface; According to the calculation of Ti element, the tetrabutyl titanate is a carbonate precursor Mn 0.75 Ni 0.25 0.1~1mol% of CO3; the carbonate precursor Mn 0.75 Ni 0.25 The volume ratio of the amount of CO3 to anhydrous ethanol is 0.008 mol: (50~100) mL; S2. Cover Mn with Ti polymer in a molar ratio of 1: (1~1.1): (2~4): (0.001~0.01) 0.75 Ni 0.25 The precursor, lithium salt, molten salt and metal compound on the surface of CO3 are uniformly ground, and the mixed powder is sintered at 800-900°C, cooled to room temperature, washed and dried at 180-200°C to obtain a black powder; S3. Dry the black powder at 300~400 °C and cool it to room temperature to obtain a lithium-rich manganese-based cathode material with the combined effect of surface heterojunction and bulk doping, whose molecular formula is Li 1.2 Mn x Ni 0.2 Ti y M z O2, where 0.3 < x ≤ 1.5, 0.0001 < y ≤ 0.001, 0.0001 < z ≤ 0.

001. Among them, the surface heterojunction is M a (TiO3) b , where 1 ≤ a ≤ 5, 1 ≤ b ≤ 5, and the bulk doping is Ti and M doping, and M is Na, K, Ba, Ca, Mg, Pb, Fe or Bi.

2. The method for preparing a lithium-rich manganese-based positive electrode material with the combined action of surface heterojunction and bulk doping according to claim 1, characterized in that: The lithium salt in step S2 is one or more of lithium carbonate, lithium hydroxide, lithium nitrate or lithium chloride; the molten salt is sodium chloride and / or potassium chloride; the metal compound is carbonate and / or chloride of Na, K, Ba, Ca, Mg, Pb, Fe or Bi.

3. The method for preparing a lithium-rich manganese-based positive electrode material with the combined action of surface heterojunction and bulk doping according to claim 1, characterized in that: The heating rate of the sintering at 800-900° C. in step S2 is 2-4° C. / min, and the sintering time is 10-20 h.

4. A lithium-rich manganese-based positive electrode material with a surface heterojunction and bulk doping, characterized in that: The lithium-rich manganese-based positive electrode material with the combined effect of surface heterojunction and bulk doping is prepared by the method described in any one of claims 1 to 3.

5. Use of the lithium-rich positive electrode material with the combined action of surface heterojunction and bulk doping as claimed in claim 4 in the preparation of lithium-ion batteries.

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