Lithium-rich manganese-based positive electrode material, preparation method thereof and secondary battery

Abstract

The invention provides a lithium-rich manganese-based positive electrode material and a preparation method thereof, and a secondary battery, the positive electrode material comprises a spinel phase surface transition layer, the molecular formula of the lithium-rich manganese-based positive electrode material is LixMyAaBbO2, M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co, A is lithium ion vacancy, B is oxygen ion vacancy, 1lt; xlt; 1, 1.2, 0.8 lt; yt; Yt; 1, 0lt; a < lt >; 0.1, 0 lt; blt; and 0.05%. According to the lithium-rich manganese-based positive electrode material, the preparation method thereof and the secondary battery, the lithium-rich manganese-based positive electrode material is subjected to surface treatment, in-situ construction of a surface buffer layer is realized, the stability of combination with a matrix is improved, and stable material dynamics improvement is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium secondary battery technology, and more specifically, to a lithium-rich manganese-based cathode material, its preparation method, and a secondary battery. Background Technology

[0002] Lithium-rich manganese-based cathode materials have attracted widespread attention in the industry due to their high capacity, high energy density, low cost, and high safety. However, the unique anion redox charge compensation principle of lithium-rich manganese-based cathode materials results in poor kinetic performance during charge and discharge. Furthermore, the low electronic conductivity of lithium-rich manganese oxide further degrades the kinetic characteristics of lithium-rich manganese-based cathode materials.

[0003] To address the kinetic defects of lithium-rich manganese-based cathode materials, researchers have proposed several solutions. Currently, the industry typically employs methods such as grain boundary modification and surface coating to improve the kinetic performance of lithium-rich manganese-based materials. Filling the grain boundaries of lithium-rich manganese-based cathode materials with compounds possessing high ionic conductivity can reduce the charge transfer resistance and impedance of the material, thereby improving its kinetic performance. Surface coating methods utilize compounds with higher ionic / electronic conductivity to coat the surface, enhancing ion / electron transport and thus improving kinetic performance. For example, surface coating of lithium-rich manganese-based cathode materials using a co-coating method of manganese dioxide and aluminum fluoride reduces charge transfer resistance and increases lithium-ion active sites; molten SeO2 implantation improves grain boundary ionic conductivity and enhances kinetic performance.

[0004] However, all such surface coating methods involve the construction of heterogeneous interfaces, namely, the construction of a non-coherent interface between the bulk lithium-rich manganese-based cathode material and the surface coating layer (usually a spinel structure). In such interfaces, due to the different crystal structures, problems such as interface separation can occur during long-term cycling, affecting the electrochemical performance of the material.

[0005] Therefore, there is an urgent need for a dynamic improvement technique that can maintain stability during long-term cycles. In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to address the problems of poor kinetic performance and interface separation in existing lithium-rich manganese-based cathode materials, and to provide a lithium-rich manganese-based cathode material, its preparation method, and a secondary battery. By performing surface treatment on the lithium-rich manganese-based cathode material, an in-situ construction of a surface buffer layer is achieved, improving the stability of the bonding with the substrate and realizing stable material kinetic improvement.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A lithium-rich manganese-based cathode material includes a spinel phase surface transition layer, wherein the molecular formula of the lithium-rich manganese-based cathode material is Li. x M y A a B b O2, where M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co, A is a lithium ion vacancy, B is an oxygen ion vacancy, 1 <x<1.2,0.8<y<1,0<a<0.1,0<b<0.05。

[0008] Furthermore, the molecular formula of the lithium-rich manganese-based cathode material is Li. x M y A a B b O2 expands to hLiM'O2·kLi2MnO3·lLi2O, where M' is Ni / Co / Mn or Ni / Mn, 1<(h+2k+2l) / (h+k)≤1.5, and -0.05. <l<0.05。

[0009] The above-mentioned method for preparing lithium-rich manganese-based cathode material includes step S1, which involves thoroughly mixing the lithium-rich manganese-based cathode material precursor with a lithium-containing compound to obtain mixture A; Step S2: Heat-treat, cool, and crush the mixture A to obtain the sintered product B of the positive electrode material; Step S3: Dissolve the additive in a solvent in a certain proportion to obtain solution C; Step S4: Mix the sintered product B with the solution C in a certain proportion, stir for a specified time, filter and dry to obtain the dried material D; Step S5: Heat-treat the dried material D, cool it, and crush it to obtain the finished positive electrode material E.

[0010] Further, the general formula of the lithium-rich manganese-based cathode material precursor in step S1 is M(OH)2 or MCO3, where M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co.

[0011] Furthermore, the median particle size D of the lithium-rich manganese-based cathode material precursor described in step S1 50 The value is 2~13μm.

[0012] Furthermore, in step S1, the molar ratio of lithium in the lithium-containing compound to the lithium-rich manganese-based cathode material precursor is 1~1.55:1.

[0013] Further, in step S1, the lithium-containing compound is at least one of lithium hydroxide, lithium carbonate, lithium oxide, and lithium hydroxide monohydrate.

[0014] Furthermore, the mixing method used in step S1 is at least one of grinding, high-speed mixer, ball mill, and plow mixer.

[0015] Furthermore, the heat treatment in step S2 is a stepped sintering process performed on at least two isothermal platforms in an air or oxygen atmosphere.

[0016] Furthermore, in step S2, the sintering temperature of the first stage is 200~700℃, the heating rate is 1~10℃ / min, and the sintering time is 2~8h; the sintering temperature of the second stage is 800~1000℃, the heating rate is 2~10℃ / min, and the sintering time is 5~15h.

[0017] Furthermore, in step S3, the additive is one or both of a substance with strong oxidizing properties and an acidic substance; preferably, the additive is a substance with strong oxidizing properties and an acidic substance.

[0018] Furthermore, the substance with strong oxidizing properties is at least one of peroxide, permanganate, perchlorate, persulfate, hypochlorite, and dichromate.

[0019] Furthermore, the acidic substance is at least one of hydrochloric acid, sulfuric acid, oxalic acid, nitric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, persulfate, sulfate, and nitrate.

[0020] Further, in step S3, the proportion of the substance with strong oxidizing properties in solution C is 0.1~1 mol / L, and the proportion of the acidic substance is 0.1~1 mol / L; the solvent in step S3 is at least one of water.

[0021] Furthermore, in step S4, the mass ratio of sintered product B to solution C is: 0.5 < solution / material < 30.

[0022] Furthermore, in step S5, the heat treatment is carried out at a constant temperature of 200~500℃ for 3~10 hours in an air atmosphere.

[0023] A secondary battery using the above-mentioned lithium-rich manganese-based cathode material, or a lithium-rich manganese-based cathode material prepared by the above-mentioned preparation method.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention relates to a lithium-rich manganese-based cathode material, which improves the stability of bonding with the substrate and achieves stable material kinetic improvement by surface treatment of the lithium-rich manganese-based cathode material.

[0025] 2. The surface transition layer of the lithium-rich manganese-based cathode material of this invention directly degrades the surface structure into a buffer layer structure through surface reaction. Compared with traditional solid-phase coating processes, the resulting buffer layer bonds firmly to the substrate. Buffer layers coated by traditional solid-phase methods are difficult to bond well to the substrate due to differences in reactivity and crystal structure.

[0026] 3. The method for preparing lithium-rich manganese-based cathode material of the present invention can effectively remove lattice oxygen on the surface of lithium-rich manganese-based cathode material by using strong oxidizing substances. At the same time, under acidic environment, lithium-hydrogen exchange reaction occurs, effectively removing lithium ions on the lattice surface, thereby effectively constructing Li2O vacancies on the surface. The deoxygenation and delithiation can play a role in pre-activation of the material. The relatively stable spinel phase formed can maintain good kinetic performance in long-term cycling.

[0027] 4. The method for preparing lithium-rich manganese-based cathode material of the present invention uses a spinel phase pre-generated by a chemical method, which has better stability and can still maintain good ion transport performance after long cycling. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 Here is a scanning electron microscope (SEM) image of the finished cathode material E obtained in Example 1 of this invention; Figure 2 The XRD patterns of the finished cathode material E prepared in Example 5 of the present invention are compared with those of the sintered product B of the unmodified layered cathode material prepared in Comparative Example 1. Figure 3 The XPS O1s orbital spectrum of the finished cathode material E obtained in Example 5 of this invention; Figure 4 The XPS O1s orbital spectrum of the unmodified layered cathode material sintering product B prepared in Comparative Example 1 of this invention is shown. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For those reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] A lithium-rich manganese-based cathode material includes a surface transition layer of spinel phase. The molecular formula of the lithium-rich manganese-based cathode material is Li x M y A a B b O2, where M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co, A is a lithium ion vacancy, B is an oxygen ion vacancy, 1 < x < 1.2, 0.8 < y < 1, 0 < a < 0.1, 0 < b < 0.05, x is any value among 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.14, 1.16, 1.18 or any value between them, y is any value among 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, satisfying x + y = 2, a = 2b.

[0032] Preferably, the thickness of the surface transition layer is not higher than 10 nm.

[0033] [[ID=1​​​​​​​​​​​​Step S1: Thoroughly mix the lithium-rich manganese-based cathode material precursor with the lithium-containing compound to obtain mixture A; Step S2: Heat-treat, cool, and crush the mixture A to obtain the sintered product B of the positive electrode material.

[0035] Step S3: Dissolve the additive in a solvent in a certain proportion to obtain solution C; Step S4: Mix the sintered product B with the solution C in a certain proportion, stir for a specified time, filter and dry to obtain the dried material D; Step S5: Heat-treat the dried material D, cool it, and crush it to obtain the finished positive electrode material E.

[0036] This invention improves the stability of the bonding with the substrate by treating the surface of lithium-rich manganese-based cathode material and constructing a surface buffer layer in situ, thereby achieving stable material kinetic improvement.

[0037] Preferably, the general formula of the lithium-rich manganese-based cathode material precursor in step S1 is M(OH)2 or MCO3, wherein M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co.

[0038] Preferably, the median particle size D of the lithium-rich manganese-based cathode material precursor in step S1 is... 50 The micrometer diameter ranges from 2 to 13 μm, including but not limited to 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, and 13 μm, with a specific surface area of ​​3 to 40 m². 2 / g, including but not limited to 3m 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g. If the particle size of the lithium-rich manganese-based cathode precursor is too small, it will lead to a low precursor yield, an excessively high BET (Bite-Earning Threshold) in the cathode material, and a decrease in cycle performance. If the particle size of the lithium-rich manganese-based cathode precursor is too large, it will lead to an excessively long lithium-ion transport distance, decreased kinetic performance, and reduced capacity utilization.

[0039] Preferably, in step S1, the molar ratio of lithium in the lithium-containing compound to the lithium-rich manganese-based cathode material precursor is 1 to 1.55:1, including but not limited to 1.55:1, 1.5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1, and 1:1.

[0040] Preferably, the lithium-containing compound in step S1 is at least one of lithium hydroxide, lithium carbonate, lithium oxide, and lithium hydroxide monohydrate.

[0041] Preferably, the mixing method used in step S1 is at least one of grinding, high-speed mixer, ball mill, plow mixer, etc.

[0042] Preferably, the heat treatment in step S2 is a stepped sintering process with no less than two isothermal platforms in an air or oxygen atmosphere. The main purpose of the first sintering is to fully decompose the reacting raw materials, and the purpose of the second sintering is to synthesize the product components.

[0043] Preferably, in step S2, the sintering temperature of the first stage is 200~700℃, including but not limited to 200℃, 300℃, 400℃, 500℃, 600℃, and 700℃, the heating rate is 1~10℃ / min, including but not limited to 1℃ / min, 3℃ / min, 5℃ / min, 6℃ / min, 8℃ / min, and 10℃ / min, and the sintering time is 2~8h, including but not limited to 2h, 4h, 6h, and 8h. The sintering temperature of the second stage is 800~1000℃, including but not limited to 800℃, 850℃, 900℃, 950℃, and 1000℃, the heating rate is 2~10℃ / min, including but not limited to 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, and 10℃ / min, and the sintering time is 5~15h, including but not limited to 5h, 8h, 10h, 12h, and 15h.

[0044] Preferably, the additive in step S3 is one or both of a substance with strong oxidizing properties and an acidic substance.

[0045] Preferably, the substance with strong oxidizing properties is at least one of peroxide, permanganate, perchlorate, persulfate, hypochlorite, and dichromate. By using a substance with strong oxidizing properties, lattice oxygen on the surface of lithium-rich manganese-based cathode materials can be effectively removed.

[0046] Preferably, the acidic substance is at least one of the following: hydrochloric acid, sulfuric acid, oxalic acid, nitric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, persulfate, sulfate, nitrate, etc., whose solutions in water have a pH < 7. Under acidic conditions, a lithium-hydrogen exchange reaction occurs, effectively removing lithium ions from the crystal lattice surface, thereby effectively constructing Li₂O vacancies on the surface.

[0047] Preferably, the additives are substances with strong oxidizing properties and acidic substances. The present invention preferably uses additives with strong oxidizing properties and acidic substances, so that the simultaneous deoxygenation and delithiation during the reaction can act as a pre-activation of the material, forming a more stable spinel phase that can maintain good kinetic performance even during long cycles. In the separate delithiation / deoxygenation process, using acidic substances alone for delithiation cannot handle the excess lattice oxygen in the crystal lattice, and excessive anion redox during the electrochemical process will still cause deterioration in kinetic performance. Even in samples with only deoxygenation, higher anion redox is still required for charge compensation, and good kinetic performance cannot still be obtained.

[0048] For the lithium-rich manganese oxide phase, the equation is: Li₂MnO₃ = MnO₂ + Li₂O. The layered lithium-rich manganese oxide phase, after Li₂O removal and subsequent heat treatment, can effectively form a spinel-active manganese dioxide phase. During electrochemical processes, after lithium removal from the lithium-rich manganese oxide phase, layered manganese dioxide and highly reactive oxygen species are formed. Compared to the spinel phase, the layered phase exhibits poorer lithium-ion transport. For the electrochemically formed spinel phase, the spinel phase pre-generated by the chemical method in this invention has better stability and can maintain good ion transport performance even after long cycling.

[0049] Lithium-rich manganese-based cathode materials decay into a spinel phase during cycling. This invention uses a chemical method to construct a spinel phase on the surface of the material before electrochemical cycling, hence the term "pre-generated spinel phase".

[0050] Preferably, in step S3, the proportion of the strongly oxidizing substance in solution C is 0.1~1 mol / L (including but not limited to 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1 mol / L), and the proportion of the acidic substance is 0.1~1 mol / L (including but not limited to 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1 mol / L).

[0051] Preferably, the solvent in step S3 is at least one of water.

[0052] Preferably, in step S4, the mass ratio of sintered product B to solution C is: 0.5 < solution / material < 30.

[0053] Preferably, the heat treatment in step S5 is a constant temperature heat treatment at 200~500℃ (including but not limited to 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃) for 3~10 hours in an air atmosphere to repair the material surface.

[0054] A secondary battery using the above-mentioned lithium-rich manganese-based cathode material, or a lithium-rich manganese-based cathode material prepared by the above-mentioned preparation method.

[0055] Example 1 A method for preparing a lithium-rich manganese-based cathode material includes the following steps: a. Take 1000g Ni 0.36 Mn 0.64 (OH)2 and 500g of lithium carbonate were mixed evenly using a plow mixer to obtain mixture A, with a rotation speed of 1000r / min and a mixing time of 40min; b. Place mixture A in an air atmosphere furnace and calcine it in two steps. First, sinter at 500℃ for 4 hours with a heating rate of 3℃ / min. Then, heat it to 900℃ again and sinter for 15 hours with a heating rate of 3℃ / min. After sintering, cool it to room temperature and crush and sieve it to obtain unmodified layered cathode material sintered product B. c. Prepare solution C by mixing potassium permanganate at a concentration of 0.4 mol / L and nitric acid at a concentration of 0.4 mol / L. d. Thoroughly mix sintered product B and solution C in a 1:1 mass ratio, stir for 1 hour, filter, and dry to obtain dried material D; e. The dried material D is heat-treated at 300℃ for 12 hours in an air atmosphere furnace. After sintering and cooling to room temperature, it is crushed and sieved to obtain the finished cathode material E, i.e., Li. 1.11 Ni 0.315 Mn 0.575 O2 or 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3·-0.02Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0056] Example 2 The difference between this embodiment and Embodiment 1 is that in step c, potassium dichromate at a concentration of 0.4 mol / L and potassium dihydrogen phosphate at a concentration of 0.4 mol / L are used to prepare solution C; the rest is the same as in Embodiment 1, i.e., Li 1.11 Ni 0.315 Mn 0.575 O2 or 0.7LiNi 0.5 Mn 0.5O2·0.3Li2MnO3·-0.015Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0057] Example 3 The difference between this embodiment and Embodiment 1 is that in step a, 1000g Ni 0.163 Co 0.163 Mn 0.674 (OH)₂ and 620g of lithium carbonate were mixed uniformly using a plow mixer at a speed of 1000 r / min for 40 min to obtain mixture A; the sintering temperature in the second step of step b was 950℃, and the rest was the same as in Example 1, i.e., Li 1.18 Ni 0.132 Co 0.132 Mn 0.544 O2, or 0.4LiNi 0.33 Co 0.33 Mn 0.34 O2·0.4Li2MnO3·-0.02Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0058] Example 4 The difference between this embodiment and Embodiment 1 is that: in step a, 1000g Ni 0.30 Co 0.05 Mn 0.65 (OH)₂ and 570g of lithium carbonate were mixed uniformly using a plow mixer at a speed of 1000 r / min for 40 min to obtain mixture A; the rest was the same as in Example 1, i.e., Li 1.11 Ni 0.261 Co 0.041 Mn 0.554 O2, or 0.65LiNi 0.46 Co 0.08 Mn 0.46 O2·0.35Li2MnO3·-0.02Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0059] Example 5 The difference between this embodiment and Embodiment 1 is that in step a, 1000g Ni 0.163 Co 0.163 Mn 0.674 CO3 and 450g of lithium carbonate were mixed uniformly using a plow mixer at a speed of 1000 r / min for 40 min to obtain mixture A; the sintering temperature in the second step of step b was 850℃. The rest was the same as in Example 1, i.e., Li... 1.16 Ni 0.135 Co 0.135 Mn0.545 O2, or 0.4LiNi 0.33 Co 0.33 Mn 0.34 O2·0.4Li2MnO3·-0.03Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0060] Example 6 The difference between this embodiment and Embodiment 1 is that in step a, 1000g Ni 0.35 Mn 0.65 (OH)₂ and 610g of lithium hydroxide monohydrate were mixed uniformly using a plow mixer to obtain mixture A, with a rotation speed of 1000 r / min and a mixing time of 40 min; the rest was the same as in Example 1, i.e., Li 1.11 Ni 0.315 Mn 0.575 O2 or 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3·-0.02Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0061] Comparative Example 1 a. Take 1000g Ni 0.163 Co0.163Mn 0.74 CO3 and 450g of lithium carbonate were mixed evenly using a plow mixer to obtain mixture A, with a rotation speed of 1000r / min and a mixing time of 40min. b. The mixture A was placed in an air atmosphere furnace and calcined in two steps. First, it was sintered at 500℃ for 4 hours with a heating rate of 3℃ / min. Then, it was heated again to 850℃ and sintered for 15 hours with a heating rate of 3℃ / min. After sintering, it was cooled to room temperature, crushed, and sieved to obtain the unmodified layered cathode material sintered product B, i.e., Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, or 0.4LiNi 0.33 Co 0.33 Mn 0.34 O2·0.4Li2MnO3.

[0062] Comparative Example 2 The difference between this comparative example and Example 1 is that in step c, nitric acid is prepared into solution C at a ratio of 0.4 mol / L; the rest is the same as in Example 1, i.e., Li 1.11 Ni 0.31 Mn 0.57 O2 or 0.72LiNi 0.48 Mn 0.52O2·0.28Li2MnO3.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that in step c, sodium dihydrogen phosphate is prepared into solution C at a ratio of 0.4 mol / L; the rest is the same as in Example 1, i.e., Li 1.12 Ni 0.31 Mn 0.57 O2 or 0.71LiNi 0.48 Mn 0.52 O2·0.29Li2MnO3.

[0064] Comparative Example 4 The difference between this comparative example and Example 1 is that: mixture A was calcined in an air atmosphere furnace at 950°C for 15 hours with a heating rate of 3°C / min. After sintering, it was cooled to room temperature and then crushed and sieved to obtain unmodified layered cathode material sintered product B; the rest was the same as in Example 1, i.e., Li 1.125 Ni 0.317 Mn 0.577 O2 or 0.7LiNi 0.5 Mn 0.5 O2·0.3Li2MnO3·-0.005Li2O, where the coefficient is negative, representing lithium ion vacancies and oxygen ion vacancies.

[0065] Experimental example: 1. XRD tests were performed on the finished cathode material E obtained in Example 5 and the unmodified layered cathode material sintering product B obtained in Comparative Example 1. The XRD patterns of Example 5 and Comparative Example 1 were compared as follows: Figure 2 As shown, the XRD data of Example 5 and Comparative Example 1 are shown in Table 1.

[0066] Table 1. XRD data of Example 5 and Comparative Example 1

[0067] from Figure 2 A comparison of the XRD patterns of Example 5 and Comparative Example 1 with the XRD data of Example 5 and Comparative Example 1 in Table 1 shows that after surface treatment, the half-peak width of the diffraction peak of the 104 crystal plane of the cathode material in Example 5 becomes wider, indicating that the spinel component in the structure increases. This proves that after surface treatment, a better spinel phase is formed, and also indirectly proves the existence of surface delithiation.

[0068] II. XPS testing was performed on the finished cathode material E obtained in Example 5 and the unmodified layered cathode material sintering product B obtained in Comparative Example 1. The O1s orbital spectrum of the XPS test in Example 5 is shown below. Figure 3 As shown in the figure, the XPS test spectrum of the O1s orbital in Comparative Example 1 is as follows. Figure 4As shown.

[0069] from Figures 3-4 The XPS spectra of Example 5 and Comparative Example 1 show that the O1s orbital can be split into high binding energy peaks, medium binding energy peaks, and low binding energy peaks, representing the detected lattice oxygen, oxygen vacancies, and surface adsorbed oxygen signals, respectively. This allows us to determine the proportion of oxygen vacancies to surface oxygen. In Example 5, the oxygen vacancy ratio is 44.75%, while in Comparative Example 1 (the untreated material), the oxygen vacancy ratio is only 23.31%. The test results demonstrate the effectiveness of the oxygen vacancy structure constructed after surface treatment according to the present invention.

[0070] III. Electrochemical Performance Testing: The positive electrode materials from Examples 1-6 and Comparative Examples 1-4 were assembled into button cells for testing. A CR2032 button cell mold was used. The positive electrode sheet was composed of positive electrode material: conductive agent: PVDF in a mass ratio of 90:5:5. The cells were subjected to 50 cycles of 0.1C and 0.33C charge-discharge tests under test conditions of 2.3-4.52V (in practice, more than 500 cycles can represent long-cycle performance, but this method is difficult to use for material screening due to its excessive time consumption; therefore, 50-cycle data is usually used for rapid screening in practice). The test results are shown in Table 2. Table 2. Electrochemical performance test results of the cathode materials in Examples 1-6 and Comparative Examples 1-4

[0071] Comparing the data of Example 5 and Comparative Example 1 in Table 2, it can be seen that after surface treatment, the capacity utilization at 0.1C and 0.33C, as well as the cycle performance at 0.33C, are improved. Comparing Example 1 and Comparative Examples 2 and 3, it can be seen that without the use of strong oxidizing agents, the performance of the sample undergoing only delithiation is inferior to that of the sample undergoing simultaneous deoxygenation and delithiation. Comparing Example 1 and Comparative Example 4, it can be seen that sintering and temperature control using two isothermal platforms can effectively improve the capacity utilization and rate performance of the material, and also help improve the cycle life. This invention, through stepped sintering using no fewer than two isothermal platforms, significantly improves the capacity utilization at 0.1C and 0.33C.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that, A surface transition layer comprising a spinel phase, the lithium-rich manganese-based positive electrode material having a molecular formula of Li x M y A a B b O2, wherein M is Mn, Mn / Ni, Mn / Co, or Mn / Ni / Co, A is a lithium ion vacancy, B is an oxygen ion vacancy, 1 < x < 1.2, 0.8 < y < 1, 0 < a < 0.1, 0 < b < 0.

05.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that, The lithium-rich manganese-based positive electrode material has a molecular formula Li x M y A a B b O2 is expanded as hLiM'O2·kLi2MnO3·lLi2O, wherein M' is Ni / Co / Mn or Ni / Mn, 1<(h+2k+2l) / (h+k)≤1.5, and -0.05<l<0.

05.

3. The method of producing a lithium-rich manganese-based positive electrode material according to claim 1 or 2, characterized by, Step S1, mix the lithium-rich manganese-based positive electrode material precursor and the lithium-containing compound to obtain a mixture A; Step S2, heat-treat, cool and crush the mixture A to obtain a sintered product B of the positive electrode material; Step S3, dissolve the additive in the solvent to obtain a solution C; Step S4, mix the sintered product B and the solution C, stir for a specified time, and then perform suction filtration and drying to obtain a dried material D; Step S5, heat-treat the dried material D, cool and crush to obtain a finished product E of the positive electrode material.

4. The method for preparing lithium-rich manganese-based cathode material according to claim 3, characterized in that, At least one of the following technical features is included: (1) The general formula of the lithium-rich manganese-based positive electrode material precursor in step S1 is M(OH)2 or MCO3, wherein M is Mn, Mn / Ni, Mn / Co or Mn / Ni / Co; (2) The particle size median D50 of the lithium-rich manganese-based positive electrode material precursor in step S1 is 2-13 μm. 50 is 2-13 μm. (3) The molar ratio of lithium in the lithium-containing compound to the lithium-rich manganese-based positive electrode material precursor in step S1 is 1-1.55:1; (4) The lithium-containing compound in step S1 is at least one of lithium hydroxide, lithium carbonate, lithium oxide and lithium hydroxide monohydrate; (5) The mixing method used in step S1 is at least one of grinding, high-speed mixing, ball milling and plowshare mixer; (6) The heat treatment in step S2 is step sintering with not less than two constant temperature platforms in an air or oxygen atmosphere.

5. The method for preparing lithium-rich manganese-based cathode material according to claim 4, characterized in that, In step S2, the first-stage sintering temperature is 200-700℃, the heating rate is 1-10℃ / min, the sintering time is 2-8h, the second-stage sintering temperature is 800-1000℃, the heating rate is 2-10℃ / min, and the sintering time is 5-15h.

6. The method for preparing lithium-rich manganese-based cathode material according to claim 3, characterized in that, The additive in step S3 is one or both of a strong oxidizing substance and an acidic substance; preferably, the additive is a strong oxidizing substance and an acidic substance.

7. The method of claim 6, wherein the lithium-rich manganese-based cathode material is prepared by the steps of: mixing a lithium source, a manganese source, and a transition metal source to form a mixture; and heating the mixture at a temperature of 600-900 °C for 6-24 hours. At least one of the following technical features is included: (1) The strong oxidizing substance is at least one of a peroxide, a permanganate, a perchlorate, a persulfate, a hypochlorite and a dichromate; (2) The acidic substance is at least one of hydrochloric acid, sulfuric acid, oxalic acid, nitric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, persulfide, sulfate and nitrate.

8. The method for preparing lithium-rich manganese-based cathode material according to claim 7, characterized in that, In step S3, the strong oxidizing substance is configured at a proportion of 0.1-1mol / L, and the acidic substance is configured at a proportion of 0.1-1mol / L; and the solvent is water.

9. The method for preparing the lithium-rich manganese-based cathode material according to claim 8, characterized in that, At least one of the following technical features is included: (1) In step S4, the mass ratio of the sintered product B to the solution C is 0.5< solution / material <30; (2) In step S5, the heat treatment is constant-temperature heat treatment at 200-500℃ for 3-10h in an air atmosphere.

10. A secondary battery characterized by comprising: The lithium-rich manganese-based positive electrode material of claim 1 or 2, or the lithium-rich manganese-based positive electrode material prepared by the preparation method of any one of claims 3-9.

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