Positive electrode active material and preparation method, and electrochemical device

Abstract

A positive electrode active material. The positive electrode active material comprises a lithium manganese oxide. 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 from 17° to 20°. A peak position difference Δθ1 between the first diffraction peak and the second diffraction peak satisfies 0<Δθ1<2, and the peak intensity IB of the second diffraction peak and the peak intensity IA of the first diffraction peak satisfy 0<IB / IA≤0.15.

Description

Positive electrode active material and preparation method, and electrochemical device TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium batteries, and particularly relates to a positive electrode active material, a preparation method thereof and an electrochemical device. BACKGROUND

[0002] In order to solve the severe problems such as energy crisis, environmental pollution, climate change and low-carbon economy, the research and application of electric vehicles, large power sources and power storage field power sources have become inevitable. Lithium ion batteries have become an indispensable part of people's lives.

[0003] During the first charging process of a lithium ion battery, an organic electrolyte is reduced and decomposed on the surface of a negative electrode material such as graphite to form a solid electrolyte interface film (SEI). The SEI film consumes lithium in the positive electrode, and the process of consuming lithium is irreversible. At the same time, the formation and consumption of the SEI film consume lithium in the positive electrode, resulting in a low first cycle coulombic efficiency of the battery and reducing the capacity and energy density of the lithium ion battery.

[0004] In order to make up for the consumption of lithium, the positive electrode or the negative electrode is usually pre-lithiated. The pre-lithiation technology can greatly solve the problems of first irreversible consumption and lithium loss in the cycle process of the lithium ion battery. Compared with the negative electrode process, the positive electrode pre-lithiation is simple and economical, and has become the preferred solution for battery enterprises to pre-lithiate. Currently, the positive electrode pre-lithiation materials mainly include lithium ferrite and lithium-rich lithium nickelate, but these two materials have high residual alkali and poor stability in air, and are difficult to produce and use, which greatly limits the development of the pre-lithiation technology in lithium ion batteries. SUMMARY

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

[0006] To achieve the above-mentioned purpose, the present application proposes the following solutions:

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

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

[0009] As preferable, the third peak diffraction peak intensity is I C , the second peak diffraction peak intensity is I D , and 0 < I C / I D ≤ 0.2 is satisfied.

[0010] As preferable, 0.3 ≤ I D / I A ≤ 0.6 is satisfied.

[0011] As preferable, the positive electrode active material has a layered structure, and the positive electrode active material includes 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 includes one or two or more kinds of mixture 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 two or more kinds of mixture of S, N, F, Cl, or Br.

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

[0013] (1) The mole percentage content of M1 elements in the positive electrode material is a1 based on the mole amount of Mn elements in the positive electrode material, and 0.1% ≤ a1 ≤ 10% is satisfied, where 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) The mole percentage content of M2 elements in the positive electrode material is b1 based on the mole amount of Mn elements in the positive electrode material, and 0.1% ≤ b1 ≤ 5% is satisfied, where M2 includes at least one of S, N, F, Cl, or Br;

[0015] (3) The mole ratio of Li elements and Mn elements in the positive electrode material 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 content on the surface of the positive electrode active material is not greater 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 mixture is obtained by thoroughly mixing a Mn-containing compound, a lithium source, an optional M1 element source, an optional M2 element source, and an organic compound; the mixture is then heat-treated at 450–700°C for 2–8 hours under an inert atmosphere, followed by heat treatment at 800–1150°C for 5–25 hours to obtain lithium manganese oxide; wherein the manganese-containing compound and the lithium source are mixed in a lithium-manganese molar ratio (Li / Mn) of 0.9–1.1.

[0020] Preferably, the organic compound 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 organic matter used is 0.01 to 0.2 in the ratio of the mass of organic matter to the mass of lithium manganese oxide.

[0022] As a preferred option, at least one of the following conditions must be 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 source of the M1 element 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 in a molar ratio of M1 to Mn 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 in a molar ratio of M2 to Mn of 0.001 to 0.05.

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

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

[0033] The positive electrode active material of this application has high charge capacity and low residual alkali, thus exhibiting excellent air stability. It can be used as a positive electrode pre-lithiation material to improve the energy density of electrochemical devices, enhance the cycle performance of electrochemical devices, and promote the development of pre-lithiation technology in lithium-ion batteries. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the 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 based on these drawings without creative effort.

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

[0036] Figure 2 shows the XRD pattern of the product prepared in Comparative Example 2. Detailed Implementation

[0037] Some embodiments of the present invention provide a positive electrode active material comprising lithium manganese oxide. The X-ray diffraction pattern 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 Peak intensity I of the first diffraction peak A , satisfying 0 < I B / I A ≤0.15.

[0038] The first diffraction peak is a characteristic diffraction peak of lithium manganese oxide. The second diffraction peak is a new characteristic diffraction peak formed by solid solution treatment of lithium manganese oxide under certain process conditions after modification with the addition of certain modifying elements. The presence of the second diffraction peak can stabilize the structure of lithium manganese oxide and reduce lattice distortion, thereby improving the stability of the crystal structure of lithium manganese oxide in the high delithiation state, thus inhibiting the dissolution of manganese and improving the cycle performance of the electrochemical device. The new characteristic peak of the solid solution formed can increase the specific charge capacity of lithium manganese oxide within a certain range, but will decrease the specific charge capacity of lithium manganese oxide when there is an excess.

[0039] In some preferred embodiments, the X-ray diffraction pattern of the positive electrode active material has a third diffraction peak and a fourth diffraction peak in the range of 44° to 47°. The peak position difference Δθ2 between the third and fourth diffraction peaks satisfies 0 < |Δθ2| < 2°, and more preferably 0 < |Δθ2| < 1°. The third diffraction peak is a characteristic diffraction peak of lithium manganese oxide, and the fourth diffraction peak is a new characteristic diffraction peak generated by solid solution treatment of lithium manganese oxide after the addition of modifying elements. 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 lithium manganese oxide and increasing the effective lithium replenishment.

[0040] In a partially preferred embodiment, the peak intensity of the third diffraction peak is I. C The peak intensity of the second diffraction peak is I. D , satisfying 0 < I C / I D ≤0.2. The new characteristic peaks of the solid solution formed can reduce the discharge specific capacity of lithium manganese oxide within a certain range, while an excess will increase the discharge specific capacity of lithium manganese oxide.

[0041] In some preferred embodiments, 0.3 ≤ I D / I A ≤0.6. The reduction of crystal defects in lithium manganese oxide and the improvement of its stability promote the extraction of lithium ions from lithium manganese oxide, thereby further improving the specific charging 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 zWhere 0.9≤x≤1.1, 0<y≤0.1, 0<z≤0.05, M1 includes one 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 more of S, N, F, Cl, or Br. The presence of elements M1 and M2 forms a solid solution with a second characteristic diffraction peak and a fourth diffraction peak, thus possessing a stable structure and improving the specific charging capacity of lithium manganese oxide.

[0044] In some preferred embodiments, based on the molar amount of Mn element in the cathode material, the molar percentage content of M1 element in the cathode 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 Mn element in the cathode material, the molar percentage content of M2 element in the cathode 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, the molar ratio of Li to Mn in the cathode material is c1, where 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 content on the surface of the positive electrode active material is no more 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 the requirements of the operating environment, and thus increases its usage.

[0048] In some preferred embodiments, the average particle size Dv50 of the positive electrode active material is 1–20 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, decreases the amount of manganese leached, and thus improves cycle performance.

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

[0050] A mixture is prepared by thoroughly mixing a Mn-containing compound, a lithium source, optional M1 element sources, optional M2 element sources, and an organic compound. The mixture is then heat-treated at 450–700°C for 2–8 hours under an inert atmosphere, followed by heat treatment at 800–1150°C for 5–25 hours to obtain lithium manganese oxide. The manganese-containing compound and the lithium source are mixed with a lithium / Mn molar ratio of 0.9–1.1. The first stage of heat treatment at 450–600°C effectively 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 with the structure described in this application. Research has shown that organic matter can induce the formation of highly crystalline, pure monoclinic phase-doped modified LiMnO2 during heat treatment, thereby achieving a higher charging capacity. Doping elements promote stronger Mn-O bond bonding and reduce Mn dissolution during charge and discharge processes; at the same time, Li re-intercalation is restricted, resulting in a decrease in discharge capacity, thus exhibiting 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 in a lithium-manganese molar ratio (Li / Mn) ranging from 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 compound 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 organic matter used is 0.01 to 0.2 in ratio of the mass of organic matter to the mass of lithium manganese oxide, more preferably 0.05 to 0.2. In some preferred embodiments, the inert atmosphere includes 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 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 source of element M1 includes one 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 M1 to Mn of 0.001 to 0.1, and more preferably in a molar ratio of 0.005 to 0.1.

[0060] In some preferred embodiments, the M2 element includes one 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 M2 to Mn ranging from 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 including a positive electrode, wherein the positive electrode includes the positive electrode active material described in the first aspect of this application or the positive electrode material prepared according to the second aspect of this 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 more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

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

[0065] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this 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 Li:Mn molar ratio of 1.03:1. Then, an M1 element source was added at a M1:Mn molar ratio of 0.02:1, and an M2 element source was added at a M2:Mn molar ratio of 0.01:1. Organic matter was added at a mass ratio of glucose to ethylene glycol to the theoretical mass of lithium manganese oxide of (0.05+0.05):1. The mixture was mixed for 8 hours to obtain a final mixture. In this mixture, M1 element was Cr, and the M1 element source was nano-Cr2O3. M2 element was F, and the M2 element source was nano-LiF. The final Li:Mn molar ratio in the mixture was 1.04:1.

[0069] (2) Place the above mixture in a corundum porcelain boat, at a depth of 1.5m 3 Nitrogen gas was introduced at a rate of 5 °C / min, and the temperature was increased to 650 °C. Sintering was then carried out at 650 °C for 6 hours. The temperature was then increased to 960 °C at a rate of 5 °C / min, and sintering was carried out at 960 °C for 15 hours. The mixture was then allowed to cool naturally 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 the positive electrode

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

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

[0073] The obtained positive electrode, polypropylene separator and lithium metal sheet were placed in sequence in the steel shell of the coin cell, and an appropriate amount of 1mol / L LiPF6 electrolyte was added. After sealing, a lithium-ion coin cell was obtained.

[0074] 4. Testing Methods

[0075] 1) XRD test

[0076] The positive electrode active material powder was placed in the sample stage of an XRD instrument. An X-ray pathograph was obtained using a scanning rate of 2° / min and a scanning angle range of 10° to 90°. The position and intensity of each peak were then recorded.

[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 refers to the particle size that reaches 50% of the total volumetric size in a volumetric particle size distribution, starting from the smallest particle size.

[0080] 3) Element content testing methods

[0081] The positive electrode active material was dissolved in a mixed solvent (e.g., 0.4 g of positive electrode active material was dissolved in a mixed solvent of 10 mL aqua regia (nitric acid and hydrochloric acid mixed in a 1:1 ratio) and 2 mL HF), and the volume was adjusted to 100 mL. The content of elements such as M1, Mn, and Li in the positive electrode active material was then determined using an ICP analyzer. The content of M2 was determined using an atomic absorption analyzer after adjusting the volume.

[0082] 4) Test of residual lithium content in cathode materials

[0083] The lithium carbonate and lithium hydroxide in the cathode material were titrated using an acid-base titration method with a standard hydrochloric acid solution.

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

[0085] The LAND series battery testing system was used to conduct charge and discharge tests on lithium-ion coin cells to assess their charge and discharge performance. The cells were charged at 45°C with a constant current at a rate of 0.1C until the voltage reached 4.3V. They were then further charged at a constant voltage of 4.3V until the current decreased to 0.05C, bringing them to a fully charged state at 4.3V. The resulting charge specific capacity was recorded as the first charge specific capacity. Subsequently, the cells were discharged at a constant current at a rate of 0.1C until the voltage reached 3V. The resulting discharge specific capacity was recorded as the first discharge specific capacity. The ratio of the first discharge specific capacity to the first charge specific capacity was recorded as the initial efficiency at 45°C.

[0086] 6) Test of Mn dissolution

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

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

[0089] The difference between the preparation methods of the positive electrode active materials in Examples 2-27 and Example 1 lies in the parameters in Table 1.

[0090] Examples 16-25 contain two or more M1 elements and two or more M2 elements. Taking Example 16 as an example, the element source in Example 16 is Cr2O3+Nb2O3, representing that the M1 elements in this example are Cr and Nb, and the molar ratio of M1 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, totaling 0.02:1. Examples 17-25 follow the same pattern.

[0091] Table 1

[0092] Comparative Example 1

[0093] Mn3O4 and Na2CO3 were mixed evenly at a Na:Mn molar ratio of 1.05:1. The mixture was then heated to 800℃ at a rate of 5℃ / min and held at this temperature for 24 hours under a nitrogen atmosphere to obtain NaMnO2. A 5 mol / L LiBr ethanol solution was added at a LiBr:NaMnO2 molar ratio of 10:1, and the mixture was exchanged under an air atmosphere for 8 hours. After the exchange was completed, the powder was washed with ethanol and then dried in a 120℃ oven for 5 hours to obtain lithium manganese oxide produced by the conventional method.

[0094] Comparative Example 2

[0095] MnO2 and lithium hydroxide were mixed at a Li:Mn molar ratio of 1.03:1. Then, an M1 element source was added at a M1:Mn molar ratio of 0.02:1, and an M2 element source was added at a M2:Mn molar ratio of 0.01:1. The mixture was stirred for 8 hours to obtain a final mixture. In this mixture, M1 element was Cr, and the M1 element source was nano-Cr2O3; M2 element was F, and the M2 element source was nano-LiF. The final Li:Mn molar ratio in the mixture was 1.04:1.

[0096] The above mixture was placed in a corundum porcelain boat at a depth of 1.5m. 3 Nitrogen gas was introduced at a rate of 1 h, and the temperature was increased to 960 °C at a rate of 5 °C / min. The mixture was then sintered at 960 °C for 15 h and allowed to cool naturally to room temperature to obtain layered LiMn. 0.98 Al 0.02 O 1.99 F 0.01 Positive electrode active material.

[0097] The XRD pattern of the positive electrode active material obtained in Comparative Example 2 is shown in Figure 2. The characteristic diffraction peak at 15.4° corresponds to the characteristic diffraction peak of the cubic phase (o phase) of LiMnO2, and 18.30° corresponds to the characteristic diffraction peak of the monoclinic phase (m phase) of LiMnO2. Therefore, the obtained LiMnO2 material is a layered composite of orthorhombic and cubic phases. By comparing Figure 1 and Figure 2 and conducting analysis, it was found that simply doping at Mn and O sites will cause the monoclinic phase of LiMnO2 to transform into the cubic phase. However, by reasonably controlling the sintering conditions and adding organic matter during the sintering process, it is possible to induce a pure monoclinic phase LiMnO2 with excellent crystallinity and a new phase formed by the dopant.

[0098] Comparing the charge-discharge capacity and Mn dissolution data of Example 1 and Comparative Example 2 in Table 2, it was found that doping a single LiMnO2 monoclinic phase can improve the stability of the Mn-O bond, thereby reducing manganese dissolution, and can also improve the specific charge capacity of the material.

[0099] In the XRD patterns of the products obtained in each embodiment and comparative example, the peak positions of the first diffraction peak (θ1), the second diffraction peak (θ2), the peak position difference between the second and first diffraction peaks (Δθ1), and the peak intensity I of the second diffraction peak are shown. B With the peak intensity I of the first diffraction peak A The ratio I B / I A The peak positions of the third and fourth diffraction peaks (θ3 and θ4), the peak position difference between the fourth and third diffraction peaks (Δθ2), and the peak intensity I of the third diffraction peak. C With the peak intensity I of the fourth diffraction peak D The ratio I C / I D The peak intensity of the fourth diffraction peak I D With the peak intensity I of the first diffraction peak A The ratio I D / I A As shown in Table 2.

[0100] In Examples 1 to 7, the crystal structures formed due to the changes in sintering conditions are different, which in turn leads to differences in diffraction peak intensities and surface residual alkali, resulting in differences in charging specific capacity and Mn dissolution amount.

[0101] In Examples 1 and 8-9, when the molar ratio of Li / Mn in the mixture changes, the higher the molar ratio, the higher the charging specific capacity and the slightly increased discharge specific capacity, thus resulting in a higher effective lithium replenishment. At the same time, due to the increase in the amount of Li added, the surface residual alkali increases, and the amount of Mn dissolved increases slightly.

[0102] In Examples 1 and 10-23, changes in the content and type of M1 dopant lead to changes in the peak intensity ratio of the diffraction peaks. Higher M1 content results in a more stable material structure, reduced surface alkali residue, and a significant decrease in Mn dissolution. However, this reduces Li extraction during charging, leading to a decrease in charging specific capacity. Despite this, increased structural stability results in a slight increase in discharge specific capacity, but a decrease in effective lithium replenishment. Changes in the type of M1 dopant do not affect the overall crystal structure of the material, but they do influence the effective lithium replenishment and Mn dissolution to some extent.

[0103] In Examples 1 and 24-25, changes in the content and type of M2 doping element also lead to changes in the peak intensity ratio of the diffraction peaks. The higher the content of M2 element, the lower the specific charge capacity. When the content of M2 element is very small, a high specific charge capacity can still be obtained. Compared with M1, it has a smaller impact on the specific charge capacity, but it will significantly affect the surface residual alkali content, and the content will increase significantly, thereby increasing the amount of Mn dissolved.

[0104] In Examples 1, 26-27, and Comparative Example 2, when no organic matter was added during the synthesis process, the synthesized LiMnO2 simultaneously possessed cubic and monoclinic phase structures. After adding organic matter, a pure monoclinic phase LiMnO2 was generated. During heat treatment, the organic matter could induce the formation of a pure monoclinic doped LiMnO2 with excellent crystallinity. When the organic matter content was low, the crystal integrity decreased, resulting in a significant reduction in the charge specific capacity, and an increase in surface residual alkali, thus increasing Mn dissolution. As the organic matter content increased, the crystal integrity of the material improved, the charge specific capacity increased, and trace amounts of conductive carbon remained on the surface, further reducing surface residual alkali and thus decreasing Mn dissolution.

[0105] Table 2

[0106] Table 2 (continued)

[0107] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A positive electrode active material comprising a 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 of the first diffraction peak and the second diffraction peak satisfies 0 < Δθ1 = θ2 - θ1 < 2, and the peak intensity I B of the second diffraction peak satisfies 0 < I A / I B ≤ 0.

15. A ≤ 0.

15.

2. The positive electrode active material according to claim 1, wherein The X-ray diffraction spectrum of the positive electrode active material has third and fourth diffraction peaks in the range of 44° to 47°, and the peak position difference Δθ2 of the third and fourth diffraction peaks satisfies 0 < |Δθ2| < 2°; Preferably, the third peak diffraction peak has a peak intensity I C , the second peak diffraction peak has a peak intensity I D , and satisfies 0 C / I D ≤0.

2.

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

6.

4. The positive electrode active material according to any one of claims 1 to 3, characterized by The positive electrode active material has a layered structure, and the positive electrode active material includes Li x M1 y Mn 1-y O 2-z M2 z wherein 0.9≤x≤1.1, 0 y≤0.1, 0 5. The positive electrode active material according to claim 4, wherein The positive electrode active material satisfies at least one of conditions (1) to (3): (1) The mole percentage content of M1 elements in the positive electrode material is a1 based on the mole amount of Mn elements in the positive electrode material, and 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; (2) The mole percentage content of M2 elements in the positive electrode material is b1 based on the mole amount of Mn elements in the positive electrode material, and satisfies 0.1% ≤ b1 ≤ 5%, wherein M2 includes at least one of S, N, F, Cl or Br; (3) The mole ratio of Li elements and Mn elements in the positive electrode material is c1, and c1 satisfies 0.9 ≤ c1 ≤ 1.

1.

6. The positive electrode active material according to any one of claims 1 to 5, characterized by The sum of the surface residual lithium hydroxide and lithium carbonate content of the positive electrode active material is not more than 1% based on the mass of the positive electrode active material; and the average particle size Dv50 of the positive electrode active material is 1-20 μm.

7. A method for producing a positive electrode active material, characterized by, Comprising: The Mn-containing compound, the lithium source and the optional M1 element source, the optional M2 element source and the organic compound are sufficiently mixed to obtain a mixture; after the mixture is heat-treated at 450-700 ℃ for 2-8 h under an inert atmosphere, and then heat-treated at 800-1150 ℃ for 5-25 h, a lithium manganese oxide is obtained; wherein the Mn-containing compound and the lithium source are mixed in a lithium manganese mole ratio Li / Mn of 0.9-1.

1.

8. The method for producing a positive electrode active material according to Claim 7, wherein The organic matter is one or a mixture of two or more of glucose, citric acid, ethylene glycol, polyethylene glycol, polypropylene, polyacrylamide and sucrose; The amount of the organic matter is 0.01-0.2 in terms of the mass ratio of the organic matter to the lithium manganese oxide.

9. The method for producing a positive electrode active material according to claim 7, wherein At least one of the following conditions is satisfied: (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 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; (5) The M1 element source includes one or a mixture of two or more of Cr2O3, Al2O3, MgO, TiO2, Nb2O5, ZrO2, Y2O3 or CeO2; (6) the Mn-containing compound and the source of the M1 element are mixed at a molar ratio of the M1 element to the Mn element of 0.001 to 0.1; (7) the M2 element includes one or two or more of S, N, F, Cl, or Br; (8) the Mn-containing compound and the source of the M2 element are mixed at a molar ratio of the M2 element to the Mn element of 0.001 to 0.05; 10. An electrochemical device comprising a positive electrode, the positive electrode comprising the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material produced according to the production method of the positive electrode material according to any one of claims 7 to 9.

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