Positive electrode active material, preparation method, and electrochemical device

Abstract

The present invention provides a positive electrode active material, which includes lithium manganese oxide. The X-ray diffraction spectrum of the positive electrode active material has a first diffraction peak θ1 and a second diffraction peak θ2 in the range of 17° to 20°, and the peak position difference Δθ1 between the first diffraction peak and the second diffraction peak satisfies 0<Δθ1<2, and the peak intensity I of the second diffraction peak is B The peak intensity of the first diffraction peak I A Satisfy 0<I B / I A ≤0.15. This positive electrode active material has a high charge capacity and low residual alkali, resulting in excellent air stability. It can be used as a positive electrode pre-lithiation material to improve the energy density and cycle performance of electrochemical devices. Also provided are a method for preparing this positive electrode active material and an electrochemical device containing this positive electrode active material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a positive electrode active material and a preparation method thereof, and an electrochemical device. Background Art

[0002] To address the energy crisis, environmental pollution, climate change, and the need for a low-carbon economy, the development and application of power sources in electric vehicles, large-scale power supplies, and energy storage have become inevitable. Lithium-ion batteries have become an indispensable part of our lives.

[0003] During the initial charging of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the surface of negative electrode materials such as graphite, forming a solid electrolyte interface (SEI) film. This SEI film consumes lithium from the positive electrode, and this lithium consumption process is irreversible. Furthermore, the formation and consumption of the SEI film require lithium from the positive electrode, resulting in a low coulombic efficiency during the battery's initial cycle, reducing the capacity and energy density of the lithium-ion battery.

[0004] In order to compensate for the consumption of lithium, the positive or negative electrode is usually pre-lithiated. Pre-lithiation technology can greatly solve the problems of the first irreversible consumption of lithium-ion batteries and the loss of lithium during the cycle. Compared with the negative electrode process, positive electrode pre-lithiation is simpler and more economical, making it the preferred solution for battery companies for pre-lithiation. At present, the main positive electrode pre-lithiation materials are lithium ferrite and lithium-rich lithium nickel oxide, but these two materials have high residual alkalinity, poor stability in air, and are difficult to produce and use, which greatly limits the development of pre-lithiation technology in lithium-ion batteries. Summary of the Invention

[0005] In view of the above technical problems, the object of the present invention is to provide a positive electrode active material and a preparation method thereof, and an electrochemical device.

[0006] To achieve the above objectives, the present invention proposes the following solutions:

[0007] A positive electrode active material, comprising lithium manganese oxide, wherein an X-ray diffraction spectrum of the positive electrode active material has a first diffraction peak θ1 and a second diffraction peak θ2 within a range of 17° to 20°, and a peak position difference Δθ1 between the first diffraction peak and the second diffraction peak satisfies 0<Δθ1=θ2-θ1<2, and a peak intensity I of the second diffraction peak is B The peak intensity of the first diffraction peak I A , satisfying 0<I B / I A ≤0.15.

[0008] Preferably, the X-ray diffraction spectrum of the positive electrode active material has a third diffraction peak and a fourth diffraction peak in the range of 44° to 47°, and the peak position difference Δθ2 between the third diffraction peak and the fourth diffraction peak satisfies 0<︱Δθ2︱<2°.

[0009] Preferably, the third peak diffraction peak intensity is 1 C , the second peak diffraction peak intensity is 1 D , satisfying 0<I C / I D ≤0.2.

[0010] As a preference, satisfying 0.3≤I D / I A ≤0.6.

[0011] Preferably, the positive electrode active material has a layered structure, and the positive electrode active material comprises Li x M1 y Mn 1- y O 2-z M2 z , wherein 0.9≤x≤1.1, 0<y≤0.1, 0<z≤0.05, M1 includes one or a mixture of two or more of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca, and M2 includes one or a mixture of two or more of S, N, F, Cl or Br.

[0012] Preferably, the positive electrode active material satisfies at least one of the conditions (1) to (3):

[0013] (1) Based on the molar amount of the Mn element in the positive electrode material, the molar percentage of the M1 element in the positive electrode material is a1, which satisfies: 0.1%≤a1≤10%, wherein M1 includes at least one of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca;

[0014] (2) Based on the molar amount of the Mn element in the positive electrode material, the molar percentage of the M2 element in the positive electrode material is b1, satisfying: 0.1%≤b1≤5%, wherein M2 includes at least one of S, N, F, Cl or Br;

[0015] (3) In the positive electrode material, the molar ratio of the Li element to the Mn element is c1, and c1 satisfies: 0.9≤c1≤1.1.

[0016] Preferably, based on the mass of the positive electrode active material, the sum of the residual lithium hydroxide and lithium carbonate contents on the surface of the positive electrode active material is no more than 1%.

[0017] Preferably, the average particle size Dv50 of the positive electrode active material is 1-20 μm.

[0018] As a general inventive concept, the present invention also provides a method for preparing a positive electrode active material, comprising:

[0019] A Mn-containing compound, a lithium source, an optional M1 element source, an optional M2 element source, and an organic compound are fully mixed to obtain a mixture; the mixture is heat-treated at 450-700° C. under inert atmosphere conditions for 2-8 hours, and then heated to 800-1150° C. for 5-25 hours to obtain a lithium manganese oxide; wherein the manganese-containing compound and the lithium source are mixed according to a lithium-manganese molar ratio Li / Mn in the range of 0.9-1.1.

[0020] Preferably, the organic matter is one or a mixture of two or more of glucose, citric acid, ethylene glycol, polyethylene glycol, polypropylene, polyacrylamide, and sucrose.

[0021] Preferably, the amount of the organic matter used is in a ratio of 0.01 to 0.2 based on the mass of the organic matter to the mass of the lithium manganese oxide.

[0022] Preferably, at least one of the following conditions is met:

[0023] (1) The inert atmosphere includes at least one of nitrogen and argon;

[0024] (2) The manganese-containing compound includes at least one of Mn3O4, MnO2, MnO, MnCO3, Mn(OH)2, and MnOOH;

[0025] (3) The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium sulfate;

[0026] (4) The M1 element includes at least one of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca;

[0027] (5) The M1 element source includes at least one of Cr2O3, Al2O3, MgO, TiO2, Nb2O5, ZrO2, Y2O3 or CeO2;

[0028] (6) the Mn-containing compound and the M1 element source are mixed so that the molar ratio of the M1 element to the Mn element is in the range of 0.001 to 0.1;

[0029] (7) The M2 element includes at least one of S, N, F, Cl or Br.

[0030] (8) The Mn-containing compound and the M2 element source are mixed so that the molar ratio of the M2 element to the Mn element is in the range of 0.001 to 0.05.

[0031] As a general inventive concept, the present invention also provides an electrochemical device including a positive electrode, wherein the positive electrode includes the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned method for preparing the positive electrode material.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The positive electrode active material of the present application has a high charge capacity and low residual alkali, thus having excellent air stability. It can be used as a positive electrode pre-lithiation material to improve the cycle performance of the electrochemical device on the basis of improving the energy density of the electrochemical device and promote the development of pre-lithiation technology in lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is the XRD pattern of the product prepared in Example 1.

[0036] Figure 2 This is the XRD pattern of the product prepared in Comparative Example 2. DETAILED DESCRIPTION

[0037] Some embodiments of the present invention provide a positive electrode active material, the positive electrode active material comprising lithium manganese oxide, the positive electrode active material having an X-ray diffraction spectrum within the range of 17° to 20°, a first diffraction peak θ1 and a second diffraction peak θ2, and a peak position difference Δθ1 between the first diffraction peak and the second diffraction peak satisfying 0<Δθ1=θ2-θ1<2, and a peak intensity I of the second diffraction peak B The peak intensity of the first diffraction peak I A , satisfying 0<I B / I A ≤0.15.

[0038] The first diffraction peak is characteristic of lithium manganese oxide, while the second diffraction peak is a new characteristic diffraction peak generated by solid solution formation of lithium manganese oxide after modification with certain modifying elements under certain process conditions. The presence of the second diffraction peak stabilizes the structure of lithium manganese oxide and reduces lattice distortion, improving the stability of the crystal structure of lithium manganese oxide in a highly delithiated state, thereby inhibiting the dissolution of manganese and improving the cycling performance of electrochemical devices. The new characteristic peak of the solid solution can increase the charge capacity of lithium manganese oxide within a certain range, but can reduce it when excessive.

[0039] In some preferred embodiments, the X-ray diffraction spectrum of the positive electrode active material has a third diffraction peak and a fourth diffraction peak within the range of 44° to 47°, and the peak position difference Δθ2 between the third diffraction peak and the fourth diffraction peak satisfies 0<︱Δθ2︱<2°, and more preferably 0<︱Δθ2︱<1°. The third diffraction peak is a characteristic diffraction peak of the lithium manganese oxide, and the fourth diffraction peak is a new characteristic diffraction peak generated by solid solution of the lithium manganese oxide after adding a modifying element. The presence of the fourth diffraction peak can enhance the stability of the Mn-O bond after delithiation, thereby reducing the discharge specific capacity of the lithium manganese oxide and increasing the effective amount of lithium replenishment.

[0040] In some preferred embodiments, the third peak diffraction peak intensity is 1 C , the second peak diffraction peak intensity is 1 D , satisfying 0<I C / I D The new characteristic peak of the solid solution formed can reduce the discharge capacity of lithium manganese oxide within a certain range, and increase the discharge capacity of lithium manganese oxide when it is excessive.

[0041] In some preferred embodiments, 0.3≤I D / I A ≤0.6. The crystal defects of lithium manganese oxide are reduced, the stability is improved, and the release of lithium ions in lithium manganese oxide is promoted, thereby further improving the charge capacity of lithium manganese oxide.

[0042] In some preferred embodiments, the positive electrode active material has a layered structure.

[0043] In some preferred embodiments, the positive electrode active material comprises Li x M1 y Mn 1-y O 2-z M2 z, where 0.9≤x≤1.1, 0<y≤0.1, 0<z≤0.05, M1 comprises one or a mixture of two or more of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B, or Ca, and M2 comprises one or a mixture of two or more of S, N, F, Cl, or Br. The presence of M1 and M2 elements forms a solid solution having a second characteristic diffraction peak and a fourth characteristic diffraction peak, thereby having a stable structure and improving the charge capacity of the lithium manganese oxide.

[0044] In some preferred embodiments, based on the molar amount of the Mn element in the positive electrode material, the molar percentage of the M1 element in the positive electrode material is a1, satisfying: 0.1%≤a1≤10%, wherein M1 includes at least one of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca.

[0045] In some preferred embodiments, based on the molar amount of the Mn element in the positive electrode material, the molar percentage of the M2 element in the positive electrode material is b1, satisfying: 0.1%≤b1≤5%, wherein M2 includes at least one of S, N, F, Cl or Br.

[0046] In some preferred embodiments, in the positive electrode material, the molar ratio of Li element to Mn element is c1, and c1 satisfies: 0.9≤c1≤1.1.

[0047] In some preferred embodiments, based on the mass of the positive electrode active material, the sum of the residual lithium hydroxide and lithium carbonate contents on the surface of the positive electrode active material is no greater than 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc. Low residual alkali content improves the air stability of the material, reduces environmental requirements for use, and thus increases usage.

[0048] In some preferred embodiments, the average particle size Dv50 of the positive electrode active material is 1 to 20 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc. This reduces the contact area between the material and the electrolyte during use, reduces the amount of manganese dissolution, and thus improves the cycle performance.

[0049] Some embodiments of the present invention provide a method for preparing a positive electrode active material, comprising:

[0050] A mixture is obtained by thoroughly mixing a manganese-containing compound, a lithium source, an optional M1 element source, an optional M2 element source, and an organic compound; the mixture is heat-treated at 450-700°C under an inert atmosphere for 2-8 hours, and then heated to 800-1150°C for 5-25 hours to obtain a lithium manganese oxide. The manganese-containing compound and the lithium source are mixed so that the lithium-manganese molar ratio Li / Mn is in the range of 0.9-1.1. The first stage of heat treatment at 450-600°C fully removes carbon dioxide and water from the mixture, resulting in a material with low residual alkali. The second stage of heat treatment at 800-1150°C forms a positive electrode active material having the structure of the present application. Research has found that the organic compound can play an inductive role during heat treatment to obtain a doped-modified LiMnO2 with excellent crystallinity and a pure monoclinic phase, thereby having a higher charge capacity. Doping elements will make the Mn-O bond stronger and reduce the Mn dissolution during the charge and discharge process; at the same time, the Li back-intercalation is restricted, resulting in a decrease in discharge capacity, thus having a higher irreversible capacity.

[0051] In some preferred embodiments, the second heat treatment temperature is 900-1150° C., and the heat treatment time is 8-25 hours.

[0052] In some preferred embodiments, the manganese-containing compound and the lithium source are mixed at a lithium-manganese molar ratio Li / Mn in the range of 0.9 to 1.08, for example, 0.9, 0.92, 0.95, 0.98, 1.0, 1.02, 1.05, 1.08, etc.

[0053] In some preferred embodiments, the organic matter is one or a mixture of two or more of glucose, citric acid, ethylene glycol, polyethylene glycol, polypropylene, polyacrylamide, and sucrose.

[0054] In some preferred embodiments, the amount of the organic matter used is 0.01 to 0.2, more preferably 0.05 to 0.2, based on the mass of the organic matter to the mass of the lithium manganese oxide. In some preferred embodiments, the inert atmosphere comprises at least one of nitrogen and argon.

[0055] In some preferred embodiments, the manganese-containing compound includes at least one of Mn3O4, MnO2, MnO, MnCO3, Mn(OH)2, and MnOOH.

[0056] In some preferred embodiments, the lithium source includes one or a mixture of two or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium sulfate.

[0057] In some preferred embodiments, the M1 element includes one or a mixture of two or more of Al, Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca.

[0058] In some preferred embodiments, the M1 element source includes one or a mixture of two or more of Cr2O3, Al2O3, MgO, TiO2, Nb2O5, ZrO2, Y2O3 or CeO2.

[0059] In some preferred embodiments, the Mn-containing compound and the M1 element source are mixed in a molar ratio of the M1 element to the Mn element in the range of 0.001 to 0.1, and more preferably in the range of 0.005 to 0.1.

[0060] In some preferred embodiments, the M2 element includes one or a mixture of two or more of S, N, F, Cl or Br.

[0061] In some preferred embodiments, the Mn-containing compound and the M2 element source are mixed in a molar ratio of the M2 element to the Mn element in the range of 0.001 to 0.05, and more preferably in a molar ratio of 0.005 to 0.1.

[0062] Some embodiments of the present invention provide an electrochemical device comprising a positive electrode, wherein the positive electrode comprises the positive electrode active material described in the first aspect of the present application or the positive electrode material prepared according to the second aspect of the present application. In some embodiments, the electrochemical device is a lithium-ion battery.

[0063] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0064] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0065] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0066] Example 1

[0067] 1. Preparation of positive electrode active materials

[0068] (1) MnO2 and lithium hydroxide were mixed at a molar ratio of Li:Mn of 1.03:1, and then an M1 element source was added at a molar ratio of M1 element:Mn of 0.02:1, and an M2 element source was added at a molar ratio of M2 element:Mn of 0.01:1. Organic matter was added at a mass ratio of glucose and ethylene glycol to the theoretical mass of lithium manganese oxide of (0.05+0.05):1, and the mixture was mixed for 8 hours using a mixing device to obtain a mixture; wherein the M1 element was Cr, the M1 element source was nano-Cr2O3, the M2 element was F, and the M2 element source was nano-LiF. The final molar ratio of Li:Mn in the mixture was 1.04:1.

[0069] (2) Place the above mixture in a corundum boat at 1.5m 3 Nitrogen was introduced at a rate of 5°C / min, and the temperature was raised to 650°C at a heating rate of 5°C / min, and sintered at 650°C for 6h, and then raised to 960°C at a heating rate of 5°C / min, and sintered at 960°C for 15h, and naturally cooled to room temperature to obtain layered LiMn 0.98 Cr 0.02 O 1.99 F 0.01 Positive electrode active material.

[0070] 2. Preparation of positive electrode

[0071] The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a mass ratio of 80:10:10, N-methylpyrrolidone (NMP) was added, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 50wt%. The positive electrode slurry was evenly coated on one surface of the positive electrode current collector aluminum foil, dried at 80°C, and cold pressed to cut a disc with a diameter of 1 cm to obtain a positive electrode.

[0072] 3. Preparation of lithium-ion button batteries

[0073] The obtained positive electrode, polypropylene separator and metal lithium sheet were placed in a button battery steel shell in order, and an appropriate amount of 1 mol / L LiPF6 electrolyte was dropped into it. After sealing, a lithium-ion button battery was obtained.

[0074] 4. Test Method

[0075] 1) XRD test

[0076] Place the cathode active material powder on the sample stage of an XRD instrument. Use a scan rate of 2° / min and a scanning angle range of 10° to 90° to obtain an X-ray spectrum. Read the position and intensity of each peak.

[0077] 2) Average particle size test

[0078] The average particle size Dv50 of the positive electrode active material was measured using a particle size analyzer.

[0079] Dv50 is the particle size at which the volume accumulation reaches 50% from the smallest particle size side in the volume-based particle size distribution.

[0080] 3) Element content test method

[0081] Dissolve the positive electrode active material in a mixed solvent (for example, 0.4 g of positive electrode active material is dissolved in 10 mL of a mixture of aqua regia (nitric acid and hydrochloric acid, mixed in a ratio of 1:1) and 2 mL of HF). Dose to 100 mL and then analyze using an ICP analyzer to determine the contents of M1, Mn, and Li in the positive electrode active material. After dilution, analyze the M2 element using an atomic absorption analyzer.

[0082] 4) Residual lithium content test of positive electrode material

[0083] The acid-base titration method is used to titrate the lithium carbonate and lithium hydroxide in the positive electrode material with a standard hydrochloric acid solution.

[0084] 5) Lithium-ion button battery charge and discharge test

[0085] Lithium-ion button cells were charged and discharged using a LAND series battery testing system to test their charge and discharge performance. The cells were charged at a constant current rate of 0.1C at 45°C until the voltage reached 4.3V. The cells were then charged at a constant voltage of 4.3V to a current of 0.05C, bringing the cells to a full charge of 4.3V. The resulting charge capacity was recorded as the first charge capacity. The cells were then discharged at a constant current rate of 0.1C until the voltage reached 3V. The resulting discharge capacity was recorded as the first discharge capacity. The ratio of the first discharge capacity to the first charge capacity was recorded as the first efficiency at 45°C.

[0086] 6) Test of Mn dissolution

[0087] The lithium-ion button cell was charged to 4.3V at a constant current of 0.1C. After disassembly, the positive electrode was immersed in an electrolyte at 60°C for 7 days. The Mn content in the electrolyte was tested by ICP. The Mn dissolution amount = Mn content in the electrolyte / mass of the positive electrode active material.

[0088] The X-ray diffraction pattern (XRD) of the positive electrode active material obtained in Example 1 is as follows: Figure 1 As shown, from Figure 1 As can be seen from the graph, the synthesized lithium manganate is pure monoclinic LiMnO2 and a new phase formed by doping. The relevant properties are shown in Table 2.

[0089] The differences between the preparation methods of the positive electrode active materials of Examples 2 to 27 and Example 1 lie in the parameters in Table 1.

[0090] In Examples 16-25, there are two or more M1 elements and two or more M2 elements. For example, Example 16, where the element sources are Cr2O3+Nb2O3, represents an M1 element consisting of Cr and Nb. The molar ratio of M1 element to Mn is (0.01+0.01):1, meaning the molar ratios of Cr, Nb, and Mn are 0.01:1 and 0.01:1, respectively, for a total of 0.02:1. The same applies to Examples 17-25.

[0091] Table 1

[0092]

[0093] Comparative Example 1

[0094] After Mn3O4 and Na2CO3 are uniformly mixed at a Na:Mn molar ratio of 1.05:1, the temperature is raised to 800℃ at a heating rate of 5℃ / min in a nitrogen atmosphere and maintained at a constant temperature for 24 hours to obtain NaMnO2; LiBr ethanol solution with a concentration of 5 mol is added at a LiBr:NaMnO2 molar ratio of 10:1, and the mixture is exchanged under an air atmosphere for 8 hours. After completion, the powder is washed with ethanol and then placed in a 120℃ oven to dry for 5 hours to obtain lithium manganese oxide prepared by the traditional method.

[0095] Comparative Example 2

[0096] MnO2 and lithium hydroxide were mixed at a molar ratio of Li:Mn of 1.03:1. An M1 element source was then added at a molar ratio of M1 element:Mn of 0.02:1. An M2 element source was then added at a molar ratio of M2 element:Mn of 0.01:1. The mixture was mixed for 8 hours using a mixing device to obtain a mixture. The M1 element was Cr, the M1 element source was nano-Cr2O3, and the M2 element was F, the M2 element source was nano-LiF. The final mixture had a molar ratio of Li:Mn of 1.04:1.

[0097] The above mixture was placed in a corundum boat and 3 Nitrogen was introduced at a rate of 5°C / min and the temperature was raised to 960°C. The mixture was sintered at 960°C for 15 h and then cooled naturally to room temperature to obtain layered LiMn 0.98 Al 0.02 O 1.99 F 0.01 Positive electrode active material.

[0098] The XRD pattern of the positive electrode active material obtained in Comparative Example 2 is as follows: Figure 2As shown, the characteristic diffraction peak corresponding to 15.4° is the characteristic diffraction peak of LiMnO2 cubic phase (o phase), and 18.30 is the characteristic diffraction peak of LiMnO2 monoclinic phase (m phase). Therefore, the obtained LiMnO2 material is a layered composite of orthorhombic phase and cubic phase. By comparison Figure 1 and Figure 2 , and analysis found that simply doping with Mn and O sites will cause the monoclinic phase of LiMnO2 to partially transform into the cubic phase. By reasonably controlling the sintering conditions and adding organic matter during the sintering process, pure monoclinic LiMnO2 with excellent crystallinity and new phases formed by doping substances can be induced.

[0099] By comparing the charge-discharge capacity and Mn dissolution data of Example 1 and Comparative Example 2 in Table 2, it is found that doping the single monoclinic phase of LiMnO2 can improve the stability of the Mn-O bond, thereby reducing manganese dissolution and improving the charge capacity of the material.

[0100] In the XRD patterns of the products obtained in each embodiment and comparative example, the peak position of the first diffraction peak (θ1), the peak position of the second diffraction peak (θ2), the peak position difference between the second diffraction peak and the first diffraction peak (Δθ1), the peak intensity of the second diffraction peak I B The first diffraction peak intensity I A The ratio I B / I A , the third diffraction peak position (θ3), the fourth diffraction peak position (θ4), the peak position difference between the fourth diffraction peak and the third diffraction peak (Δθ2), the third diffraction peak peak intensity I C and the fourth diffraction peak intensity I D The ratio I C / I D , the fourth diffraction peak intensity I D The first diffraction peak intensity I A The ratio I D / I A As shown in Table 2.

[0101] In Examples 1 to 7, the sintering conditions varied, resulting in different crystal structures, which in turn led to different diffraction peak intensities and surface residual alkali, which in turn led to different charge capacity and Mn dissolution amounts.

[0102] In Examples 1 and 8-9, when the Li / Mn molar ratio of the mixture changes, the higher the molar ratio, the higher the charge specific capacity and the slightly increased discharge specific capacity, thereby having a higher effective lithium replenishment amount; at the same time, due to the increase in the amount of Li added, the surface residual alkali increases, and the amount of Mn dissolution increases slightly.

[0103] In Examples 1 and 10-23, variations in the content and type of the M1 doping element led to changes in the diffraction peak intensity ratio. A higher M1 content resulted in a more stable material structure, reduced surface residual alkali, and significantly lowered Mn dissolution. However, this reduced Li release during charging, resulting in a lower charge capacity. However, due to increased structural stability, the discharge capacity increased slightly, but the effective lithium replenishment decreased. Varying the M1 type does not affect the overall crystal structure of the material, but it does affect the effective lithium replenishment and Mn dissolution to some extent.

[0104] In Examples 1 and 24-25, changes in the content and type of the M2 doping element also lead to changes in the diffraction peak intensity ratio. The higher the M2 element content, the lower the charge capacity. When the M2 element content is very low, a high charge capacity can still be obtained. Compared with M1, the effect on the charge capacity is smaller, but it will significantly affect the surface residual alkali content. The content increases significantly, thereby increasing the amount of Mn dissolution.

[0105] In Example 1, Examples 26-27, and Comparative Example 2, when no organic matter was added during the synthesis process, the synthesized LiMnO2 had both cubic and monoclinic phase structures. After the addition of organic matter, the reaction generated pure monoclinic LiMnO2. The organic matter played an inductive role during heat treatment to obtain doped-modified LiMnO2 with excellent crystallinity and pure monoclinic phase. When the organic matter content was low, the integrity of the formed crystal decreased, thereby significantly reducing the charge capacity, and the surface residual alkali increased, thereby increasing the amount of Mn dissolution. When the organic matter content increased, the crystal integrity of the material was higher, the charge capacity was higher, and a trace amount of conductive carbon would remain on the surface, thereby further reducing the surface residual alkali, thereby reducing the amount of Mn dissolution.

[0106] Table 2

[0107]

[0108] Table 2 continued

[0109]

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A positive electrode active material comprising lithium manganese oxide, characterized in that: The X-ray diffraction spectrum of the positive electrode active material has a first diffraction peak θ1 and a second diffraction peak θ2 in the range of 17° to 20°, and the peak position difference Δθ1 between the first diffraction peak and the second diffraction peak satisfies 0<Δθ1=θ2-θ1<2°, and the peak intensity I of the second diffraction peak is B The peak intensity of the first diffraction peak I A Satisfy 0<I B / I A ≤0.15; the positive electrode active material has a layered structure, and the positive electrode active material contains Li x M1 y Mn 1-y O 2-z M2 z , wherein 0.9≤x≤1.1, 0<y≤0.1, 0<z≤0.05, M1 includes one or a mixture of two or more of Al, Nb, Mg, Ti, W, Ga, Zr, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B or Ca, and M2 includes one or a mixture of two or more of S, N, F, Cl or Br; the X-ray diffraction spectrum of the positive electrode active material has a third diffraction peak and a fourth diffraction peak in the range of 44° to 47°, and the peak position difference Δθ2 between the third diffraction peak and the fourth diffraction peak satisfies 0<︱Δθ2=θ4-θ3︱<2°; the peak intensity of the third diffraction peak is I C , the fourth diffraction peak intensity is 1 D , satisfying 0<I C / I D ≤0.

2.

2. The positive electrode active material according to claim 1, wherein Satisfy 0.3≤I D / I A ≤0.

6.

3. The positive electrode active material according to claim 1, wherein The positive electrode active material satisfies at least one of the conditions (1) to (3): (1) Based on the molar amount of the Mn element in the positive electrode active material, the molar percentage content of the M1 element in the positive electrode active material is a1, which satisfies: 0.1%≤a1≤10%; (2) Based on the molar amount of the Mn element in the positive electrode active material, the molar percentage content of the M2 element in the positive electrode active material is b1, which satisfies: 0.1%≤b1≤5%; (3) In the positive electrode active material, the molar ratio of Li element to Mn element is c1, and c1 satisfies: 0.9≤c1≤1.

1.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that Based on the mass of the positive electrode active material, the sum of the residual lithium hydroxide and lithium carbonate contents on the surface of the positive electrode active material is no more than 1%; and the average particle size Dv50 of the positive electrode active material is 1 to 20 μm.

5. The method for preparing a positive electrode active material according to any one of claims 1 to 4, wherein: include: A Mn-containing compound, a lithium source, an M1 element source, an M2 element source, and an organic compound are fully mixed to obtain a mixture; the mixture is heat-treated at 450-700° C. for 2-8 hours under inert atmosphere, and then heated to 800-1150° C. for 5-25 hours to obtain a lithium manganese oxide; wherein the Mn-containing compound and the lithium source are mixed according to a lithium-manganese molar ratio Li / Mn in the range of 0.9-1.1; the M1 element includes one or more of Al, Nb, Mg, Ti, W, Ga, Zr, Y, V, Sr, Mo, Ag, Sn, La, Ce, Cu, Na, Zn, Fe, Co, Ni, Cr, B, or Ca; the M2 element includes one or more of S, N, F, Cl, or Br; and the organic compound is one or more of glucose, citric acid, ethylene glycol, polyethylene glycol, polypropylene, polyacrylamide, and sucrose.

6. The method for preparing a positive electrode active material according to claim 5, wherein: The amount of the organic compound used is 0.01-0.2 according to the ratio of the mass of the organic compound to the mass of the lithium manganese oxide.

7. The method for preparing a positive electrode active material according to claim 5, wherein: At least one of the following conditions is met: (1) The inert atmosphere includes at least one of nitrogen and argon; (2) The Mn-containing compound includes one or a mixture of two or more of Mn3O4, MnO2, MnO, MnCO3, Mn(OH)2, and MnOOH; (3) The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium sulfate; (4) The M1 element source includes one or a mixture of two or more of Cr2O3, Al2O3, MgO, TiO2, Nb2O5, ZrO2, Y2O3 or CeO2; (5) The Mn-containing compound and the M1 element source are mixed in a molar ratio of the M1 element to the Mn element of 0.001 to 0.1; (6) The Mn-containing compound and the M2 element source are mixed in a molar ratio of the M2 element to the Mn element of 0.001 to 0.

05.

8. An electrochemical device comprising a positive electrode, wherein the positive electrode comprises the positive electrode active material according to any one of claims 1 to 4 or the positive electrode active material prepared by the method for preparing a positive electrode active material according to any one of claims 5 to 7.

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