A manganese-based material, a preparation method and application thereof

Abstract

This invention discloses a manganese-based material, its preparation method, and its applications. The crystal structure of the manganese-based material includes an alkali metal layer, an oxygen element, and a transition metal layer. The alkali metal layer includes a lithium element; the transition metal layer includes a mn element and mn vacancies, or a mn element, a mn vacancy, and a lithium element. In the manganese-based material with a specific structure of this invention, the unique mn vacancies in the transition metal layer can activate the redox activity of oxygen anions, providing additional capacity during charge and discharge, and enriching the existing crystal structure configuration of this material. Furthermore, the structure is reverse-engineered to address the lithium deficiency of the material, with in-situ lithium replenishment, optimizing the application of this structure in lithium-ion batteries. The addition of extra lithium atoms leads to the rearrangement of the mn vacancy superstructure in the transition metal layer. The more dispersed vacancy configuration can better suppress the irreversible loss of lattice oxygen and the structural phase transition and capacity loss caused by intralayer / interlayer migration of manganese.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology, and in particular relates to a manganese-based material, its preparation method, and its application. Background Technology

[0002] With the booming development of portable mobile electronic devices, electric vehicles, and large-scale energy storage grids, the demand for high-performance lithium-ion batteries is constantly expanding. However, the actual capacity of currently commercially available cathode materials greatly restricts the further improvement of the energy density of lithium-ion batteries, necessitating the development of new cathode materials with higher capacity. O3-phase lithium-rich manganese-based cathode materials have a unique "Li-O-Li" configuration, which can activate lattice oxygen to participate in redox reactions. This anion / cation synergistic charge compensation mechanism enables these materials to exhibit ultra-high specific capacity, making them a relatively ideal next-generation cathode replacement material. However, uncontrolled oxygen loss leads to intralayer and interlayer migration of Mn ions, and the accumulation of oxygen vacancies leaves nanopores inside the material. This results in problems such as low initial coulombic efficiency, severe capacity and voltage decay in the practical application of lithium-ion batteries. The slow reaction kinetics of Mn also lead to poor rate performance, which seriously hinders its commercial application.

[0003] Currently, various modification methods, such as doping and coating, are used to address the aforementioned problems with the basic materials. However, the introduction of impurity atoms or coating layers cannot fundamentally solve the intrinsic problems of the material. Sodium-ion batteries often exhibit electrochemical behavior similar to lithium-ion batteries, and sodium-rich manganese-based cathode materials also face the same issues. The difference lies in their structural diversity (P2 / P3 structures, vacancy / Li / other element substitution™), which provides more options for solving the intrinsic problems of the material. For example, Na2Mn3O7 (Na 4 / 7 [□ 1 / 7 Mn 6 / 7 In sodium-based cathode oxides (CNOOCs), 1 / 7 of the Mn in the transition metal layer is replaced by vacancies, forming a regular mesh-like vacancy structure. The presence of these dispersed Mn vacancies can activate lattice oxygen while improving its redox reversibility and inhibiting intralayer migration of Mn and the formation of oxygen molecules. Direct structural design can fundamentally solve the problems of this type of material without introducing impurity atoms, effectively alleviating the release of lattice oxygen under high voltage, reducing irreversible capacity loss in the first cycle, improving the battery's long cycle life, and mitigating voltage decay. However, similar structures are lacking in lithium-based cathode oxide materials, and traditional solid-state sintering methods are difficult to synthesize. Therefore, developing a novel and readily achievable high-energy-density lithium-ion cathode material remains a worthy research topic. Summary of the Invention

[0004] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a manganese-based material, wherein the transition metal layer of the manganese-based material contains a dispersed Mn vacancy structure, the presence of which can improve the redox reversibility of the material while activating lattice oxygen, and inhibit the intralayer migration of Mn and the formation of oxygen molecules.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned manganese-based material.

[0006] The third objective of this invention is to provide a positive electrode material.

[0007] The fourth objective of this invention is to provide a lithium-ion battery.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A first aspect of the present invention provides a manganese-based material, the crystal structure of which includes an alkali metal layer, an oxygen element, and a transition metal layer; the oxygen element is located between the alkali metal layer and the transition metal layer, and is bonded to both the alkali metal layer and the transition metal layer; the alkali metal layer includes a lithium element; the transition metal layer includes a mn element and a mn vacancy, or a mn element, a mn vacancy, and a lithium element.

[0010] The molar ratio of the O element to the Li element in the alkali metal layer is 1:(0.2~0.4);

[0011] The molar ratio of O to Mn is 1:(0.3-0.6);

[0012] The molar ratio of the Mn vacancy to the Mn element is greater than 0 and less than or equal to 1 / 6;

[0013] The molar ratio of Li to Mn in the transition metal layer is 0 to 0.16.

[0014] The manganese-based material of this invention contains a specific proportion of Mn vacancy structures. The presence of this special structure alters the Mn-O electronic coordination environment around the Mn vacancies, allowing the 2p orbital electrons of lattice oxygen to interact more effectively with conduction band electrons. This provides an electron transfer pathway for the activation of lattice oxygen, enabling it to participate in charge compensation behavior during lithium-ion insertion / extraction, thereby improving the actual operating capacity of the lithium-ion battery. The dispersed Mn vacancy structure increases the intra- and inter-layer migration barrier of Mn during long-term cycling, suppressing the further oxidation and recombination of adjacent lattice oxygen ions to form oxygen gas, thus improving the redox reversibility of lattice oxygen. The suppression of Mn migration behavior improves the stability of the material structure, solving the capacity and voltage decay problems caused by phase transformation or layered structure collapse due to Mn intra- and inter-layer migration in traditional anion redox lithium-rich manganese materials. This material provides high charge / discharge capacity while improving the redox reversibility of oxygen anions, mitigating material structure collapse caused by Mn migration, and improving cycle stability and cycle life.

[0015] Specifically, when the molar ratio of Mn vacancies to Mn elements is 1:6, a mesh network vacancy structure is formed. This structure is a superstructure that exists in the transition metal layer and is synthesized by adjusting the Li / Mn stoichiometric ratio. As the proportion of Mn elements increases, the vacancy structure undergoes the following transformation: honeycomb-like → banded → mesh network structure.

[0016] In this invention, when the molar ratio of Li to Mn in the transition metal layer is 0:1, it means that the transition metal layer is not doped with Li; while when the molar ratio of Li to Mn in the transition metal layer is greater than 0:1, it means that the transition metal layer is doped with Li, and the doped Li will replace the Mn vacancies in the transition metal layer, further reducing the proportion of Mn vacancies.

[0017] In some specific embodiments of the present invention, the crystal structure of the manganese-based material includes an O2 phase structure, an O3 phase structure, or a combination thereof; more preferably, the manganese-based material is selected from the O3 phase structure.

[0018] The O3 phase is a face-centered cubic crystal structure with stacked layers in an ABCABC periodic pattern. "O (Octahedron) represents the octahedral coordination environment of the basic cation, and in this invention, it represents lithium. The number "3" represents the number of TMO2 plates (TM: transition metal element Mn) in a single unit cell. The lithium layer and transition metal layer of the O2 phase are stacked along the c-axis in the order ABAB..., and the number of TMO2 plates in a single unit cell is 2.

[0019] In some specific embodiments of the present invention, the transition metal layer of the manganese-based material includes a Li-O-□ structure, a Li-O-Li structure, or a combination thereof. “□” represents a Mn vacancy.

[0020] In this invention, when the transition metal layer is not doped with Li, oxygen, as the central atom, combines with Li in the alkali metal layer and vacancies in the transition metal layer to form a special internal structure of Li-O-□; while when the transition metal layer is doped with Li to replace some vacancies, an internal structure of Li-O-Li appears.

[0021] Preferably, the transition metal layer comprises Mn element, Mn vacancy and Li element; the molar ratio of Li element to Mn element in the transition metal layer is greater than 0 and less than or equal to 0.16; more preferably (0.03~0.16):1; even more preferably (0.05~0.12):1; more preferably (0.07~0.1):1.

[0022] When the transition metal layer is doped with Li, it helps to improve the lithium-deficient intrinsic properties of the undoped material in the transition metal layer. Partial Li occupancy of Mn vacancies can increase the initial charge capacity. Furthermore, the lithium in the transition metal layer does not participate in lithium insertion / extraction during charge / discharge, further improving structural stability and the material's long cycle life. Preferably, the molar ratio of the Mn vacancy to the Mn element is greater than 0 and less than 1 / 6; more preferably, it is 0.03 to 0.1; non-limiting examples include 0.03, 0.05, 0.08, or 0.1.

[0023] With the increase of the proportion of Mn element or the occupation of Li element in the transition metal layer, the content of Mn vacancy structure decreases, and the special structure formed has better electrochemical performance.

[0024] Preferably, the molar ratio of the O element to the Li element in the alkali metal layer is 1:(0.25-0.36); more preferably, it is 1:(0.27-0.34).

[0025] Preferably, the molar ratio of O to Mn is 1:(0.35-0.55); more preferably, it is 1:(0.4-0.5).

[0026] In some specific embodiments of the present invention, the structural formula of the manganese-based material is Li. 0.64 [□ 0.14 Mn 0.86 O2, Li 0.57 [□ 0.14 Mn 0.86 O2, Li 0.64 [Li 0.11 □0.03 Mn 0.86 O2 or Li 0.64 [Li 0.09 □ 0.05 Mn 0.86 O2.

[0027] The second aspect of the present invention provides a method for preparing the manganese-based material described in the first aspect of the present invention, comprising the following steps: subjecting a mixture containing sodium carbonate and manganese carbonate, or a mixture containing sodium carbonate, manganese carbonate and a first lithium source, to a first calcination to obtain a precursor; then mixing the precursor with a second lithium source and performing an ion exchange reaction through a second calcination to obtain the manganese-based material; wherein the first lithium source and the second lithium source may be the same or different.

[0028] In the preparation method of the present invention, a precursor material with an ordered structure of Mn vacancies (such as Na2Mn3O7) or a precursor material of NaLiMnO (NLMO) doped with lithium sources is first prepared by solid-state sintering; then, the sodium ions in the precursor material are replaced by lithium ions through ion exchange to synthesize a manganese-based material with a specific structure.

[0029] Specifically, this invention employs an ion exchange method to synthesize desired specific structures, solving the problem that traditional solid-state sintering methods cannot prepare lithium-ion Mn vacancy materials. From a material structure design perspective, lithium ions can only accept octahedral structures, while sodium ions can adapt to both prismatic and octahedral structures. When vacancies exist in the transition metal layer, the crystal structure is distorted, reducing material symmetry. Sodium ions, with their larger ionic radius, can move relatively freely within the crystal lattice during sintering. Their greater ion diffusion characteristics and diffusion channels help fill the spaces around vacancies or adjust their own distribution, alleviating local structural stress caused by Mn vacancies and allowing the material to maintain a certain degree of structural integrity even with Mn vacancies. Therefore, the mild preparation conditions of the ion exchange method reduce the occurrence of side reactions, achieving the goal of maintaining the structure of the sodium-based precursor and obtaining electrochemically active products. This is of great significance for developing high-performance lithium-based cathode materials, especially for some lithium-based cathode materials with specific structures that are difficult to synthesize using traditional methods. Furthermore, the vacancy order of the precursor material can be adjusted by doping it with Li or Mn, and after ion exchange, it can meet the needs of different application scenarios of lithium-ion cathode materials.

[0030] Preferably, the calcination temperature for the first calcination is 500–700°C; more preferably, it is 550–650°C; and even more preferably, it is 580–620°C.

[0031] Preferably, the holding time for the first calcination is 12-18 hours; more preferably, it is 14-16 hours.

[0032] Preferably, the calcination temperature of the second calcination is 200–300°C; more preferably, it is 250–290°C; and even more preferably, it is 270–280°C.

[0033] Preferably, the holding time for the second calcination is 2 to 10 hours; more preferably 4 to 8 hours; and even more preferably 5 to 7 hours.

[0034] Preferably, the first lithium source includes at least one of lithium carbonate, lithium sulfate, lithium chloride, or lithium nitrate; more preferably, the first lithium source is selected from lithium carbonate.

[0035] Preferably, the second lithium source includes at least one of lithium carbonate, lithium sulfate, lithium chloride, or lithium nitrate; more preferably, the second lithium source is selected from lithium chloride and lithium nitrate.

[0036] In the ion exchange process, lithium chloride and lithium nitrate, which are chemically active and stable, are selected as the second lithium source to achieve better energy efficiency and cost-effectiveness. These two lithium sources have a low eutectic temperature (280℃), which ensures sufficient ion exchange without damaging the original structure of the material and avoids unnecessary side reactions. Furthermore, both lithium sources are readily soluble in water, facilitating the washing of excess lithium from the ion-exchanged material.

[0037] Preferably, in the second lithium source, the mass ratio of lithium chloride to lithium nitrate is 1:(7-8); more preferably, it is 1:(7.2-7.5).

[0038] According to the binary phase diagram, the mass ratio of lithium chloride to lithium nitrate at the lowest eutectic temperature is 12:88. Therefore, a lower ion exchange temperature can be obtained near this mass ratio.

[0039] Preferably, in the mixture containing sodium carbonate and manganese carbonate, the molar ratio of sodium carbonate to manganese carbonate is 1:(2-4); more preferably 1:(2.5-3.5); and even more preferably 1:(2.8-3.2).

[0040] Preferably, in the mixture containing sodium carbonate, manganese carbonate and a first lithium source, the molar ratio of sodium carbonate to manganese carbonate is 1:(2-4); more preferably 1:(2.5-3.5); and even more preferably 1:(2.8-3.2).

[0041] Preferably, in the mixture containing sodium carbonate, manganese carbonate and a first lithium source, the molar ratio of manganese in the manganese carbonate to lithium in the first lithium source is (0.03-0.16):1; more preferably (0.05-0.12):1; and even more preferably (0.07-0.1):1.

[0042] The first calcination is performed using a mixture containing sodium carbonate, manganese carbonate, and a primary lithium source. This primarily involves adding the primary lithium source during the precursor preparation process as an in-situ lithium supplement to synthesize NaLiMnO material, followed by ion exchange. The precursor material obtained without the primary lithium source has the chemical formula Na₂Mn₃O₇, which can also be written as Na. 0.57 [□ 0.14 Mn 0.86 Since O2 is present, there are 0.14 mol of Mn vacancies in the transition metal layer of 1 mol of material. This invention achieves in-situ lithium replenishment by occupying these vacancies with lithium ions in different proportions. When the ratio of lithium atoms to manganese atoms in the transition metal layer is (0.03~0.16):1, it has a good lithium replenishment effect.

[0043] A third aspect of the present invention provides a positive electrode material, wherein the raw materials for preparing the positive electrode material include the manganese-based material described in the first aspect of the present invention, or the manganese-based material prepared by the preparation method described in the second aspect of the present invention.

[0044] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the third aspect of the present invention.

[0045] The beneficial effects of this invention are as follows: In the manganese-based material with a specific structure, the unique Mn vacancies in the transition metal layer can activate the redox activity of oxygen anions, providing additional capacity during charging and discharging, and enriching the existing crystal structure configuration of this material; furthermore, the structure is reverse-engineered to address the lithium deficiency of the material, and lithium is added in situ, optimizing the application of this structure in lithium-ion batteries. The addition of extra lithium atoms leads to the rearrangement of the Mn vacancy superstructure in the transition metal layer, and the more dispersed vacancy configuration can better suppress the irreversible loss of lattice oxygen and the structural phase transition and capacity loss caused by intralayer / interlayer migration of manganese. Attached Figure Description

[0046] Figure 1 The XRD patterns are those of samples from Examples 1 to 3 of this invention.

[0047] Figure 2 The XRD patterns are those of samples 2, 4, and 5 of this invention.

[0048] Figure 3 The XRD patterns are those of samples 4, 6, and 7 of this invention.

[0049] Figure 4 The XRD patterns are those of samples from Examples 8-11 and Example 4 of this invention.

[0050] Figure 5 These are SEM images of samples from Examples 4 and 10 of the present invention.

[0051] Figure 6 This is the EDS elemental spectrum of the sample in Example 4 of the present invention.

[0052] Figure 7 This is the EDS elemental spectrum of the sample in Example 10 of the present invention.

[0053] Figure 8 The graphs show the electrochemical performance test results of the batteries assembled from the samples of Examples 4 and 10 of this invention. Detailed Implementation

[0054] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments can be obtained from conventional commercial channels or by existing known methods.

[0055] Example 1

[0056] A manganese-based material, prepared by the following method:

[0057] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0058] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 500°C at a heating rate of 3°C / min and hold it for 12 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0059] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 6 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0060] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (LMO-500℃). After grinding, the material was sealed and dried for storage.

[0061] Example 2

[0062] A manganese-based material, prepared by the following method:

[0063] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0064] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 600°C at a heating rate of 3°C / min and hold it for 12 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0065] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 6 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0066] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (LMO-600℃). After grinding, the material was sealed and dried for storage.

[0067] Example 3

[0068] A manganese-based material, prepared by the following method:

[0069] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0070] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 700°C at a heating rate of 3°C / min and hold it for 12 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0071] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 6 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0072] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (LMO-700℃). After grinding the material finely, it was sealed and dried for storage.

[0073] The only difference between Examples 1-3 is the sintering temperature of the precursor, which is 500, 600, and 700℃ respectively. The phase composition of the prepared materials was confirmed by X-ray diffraction, with a scanning range of 10-90°. The obtained XRD patterns are shown below. Figure 1 As shown, the material prepared at 500℃ has poor crystallinity, and at 700℃, the material is a mixed phase of O2 and O3, with reduced structural symmetry and lower stability than the pure O3 phase cathode oxide material obtained by sintering at 600℃. Therefore, the sintering temperature of the subsequent precursors is 600℃.

[0074] Example 4

[0075] A manganese-based material, prepared by the following method:

[0076] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0077] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 600°C at a heating rate of 3°C / min and hold it for 15 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0078] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 6 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0079] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (600℃-15h). After grinding, the material was sealed and dried for storage.

[0080] Example 5

[0081] A manganese-based material, prepared by the following method:

[0082] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0083] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 600°C at a heating rate of 3°C / min and hold it for 18 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0084] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 6 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0085] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (600℃-18h). After grinding, the material was sealed and dried for storage.

[0086] The precursors in Examples 2, 4, and 5 were sintered at the same temperature of 600℃, differing only in the holding time during sintering: 12, 15, and 18 hours, respectively. The prepared materials were subjected to X-ray diffraction (XRD) with a scanning range of 10–90°. The resulting XRD patterns are shown below. Figure 2 As shown, when the holding time is increased to 15h, the (003) peak of the material is the sharpest, and the crystallinity is the best; after the holding time is extended to 18h, the (104) peak splits, and the symmetry of the layered structure decreases. Therefore, the precursor sintering temperature is 600℃ and the holding time is 15h, which has better structure and performance.

[0087] Example 6

[0088] A manganese-based material, prepared by the following method:

[0089] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0090] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 600°C at a heating rate of 3°C / min and hold it for 15 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0091] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 2 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0092] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (600℃-15h-2h). After grinding, the material was sealed and dried for storage.

[0093] Example 7

[0094] A manganese-based material, prepared by the following method:

[0095] 1) First, weigh out sodium carbonate and manganese carbonate powders in a molar ratio of 1:3 and put them into a ball mill. Mix them in a ball mill for 24 hours at a speed of 400 rpm to obtain a mixture.

[0096] 2) Spread the obtained mixture in a square ceramic boat, place it in a tube furnace and introduce oxygen. Under pure oxygen atmosphere and room temperature of 25°C, heat it to 450°C at a heating rate of 5°C / min and hold it for 5 hours. Then heat it to 600°C at a heating rate of 3°C / min and hold it for 15 hours. After that, keep the gas ventilated and cool it naturally to room temperature to obtain the Na2Mn3O7 precursor.

[0097] 3) The Na2Mn3O7 precursor, lithium chloride, and lithium nitrate were weighed in a molar ratio of 1:2.4:17.6 and ground in a mortar for 30 min to make the materials uniformly mixed. The mixture was transferred to a nickel crucible and placed in a muffle furnace. It was heated to 250°C at a heating rate of 4°C / min under air atmosphere at room temperature and held for 15 min. Then it was heated to 280°C at a heating rate of 2°C / min and held for 10 h. After that, it was naturally cooled to room temperature to obtain the calcined product.

[0098] 4) The calcined product was washed and filtered three times with deionized water and anhydrous ethanol to remove excess lithium and sodium salts. The cleaned material was then transferred to a glass dish and dried in an oven for 24 hours to remove excess moisture, resulting in Li2Mn3O7 material (600℃-15h-10h). After grinding, the material was sealed and dried for storage.

[0099] The difference between Examples 2, 6, and 7 lies in the ion exchange times: 2 h, 6 h, and 10 h, respectively. The materials prepared were analyzed by X-ray diffraction (XRD) with a scanning range of 10–90°, and the resulting XRD patterns are shown below. Figure 3 As shown in the figure, the main peak of (003) in the material with an ion exchange time of 10 h becomes wider, and some peaks in the 55-90° range merge, indicating that the material structure exhibits disordered stacking, lattice distortion, and reduced structural symmetry. However, the XRD diffraction curves for ion exchange times of 2 h and 6 h show that the I(003) / I(104) ratio is larger for the 6 h exchange time, indicating a more ordered atomic arrangement.

[0100] In summary, among Examples 1 to 7, the better preparation conditions for the Li2Mn3O7 sample are those of Example 4. The Li2Mn3O7 sample obtained in Example 4 will be referred to as P-LMO below.

[0101] Example 8

[0102] A manganese-based material, differing from Example 4 in that step 1) of this example involves weighing sodium carbonate, manganese carbonate, and lithium carbonate powders in a molar ratio of 1:3:0.045, placing them in a ball mill, and ball milling them for 24 hours at a speed of 400 rpm until homogeneous; other steps and raw materials are the same as in Example 4. The sample obtained in this example is denoted as D-LMO-0.045.

[0103] Example 9

[0104] A manganese-based material, differing from Example 4 in that step 1) of this example involves weighing sodium carbonate, manganese carbonate, and lithium carbonate powders in a molar ratio of 1:3:0.09, placing them in a ball mill, and ball milling them for 24 hours at a speed of 400 rpm until homogeneous; other steps and raw materials are the same as in Example 4. The sample obtained in this example is denoted as D-LMO-0.09.

[0105] Example 10

[0106] A manganese-based material, differing from Example 4 in that step 1) of this example is as follows: sodium carbonate, manganese carbonate, and lithium carbonate powders are weighed in a molar ratio of 1:3:0.14 and placed in a ball mill. The mixture is ball-milled for 24 hours at a speed of 400 rpm until homogeneous. Other steps and raw materials are the same as in Example 4. The sample obtained in this example is denoted as D-LMO-0.14.

[0107] Example 11

[0108] A manganese-based material, differing from Example 4 in that step 1) of this example is as follows: sodium carbonate, manganese carbonate, and lithium carbonate powders are weighed in a molar ratio of 1:3:0.24 and placed in a ball mill. The mixture is ball-milled for 24 hours at a speed of 400 rpm until homogeneous. Other steps and raw materials are the same as in Example 4. The sample obtained in this example is denoted as D-LMO-0.24.

[0109] The four samples obtained in Examples 8-11 were subjected to X-ray diffraction for phase identification, with a scanning range of 10-90°. The resulting XRD patterns are shown below. Figure 4As shown, the positions and patterns of the superlattice diffraction peaks in the 22-28° range of the four lithium-doped samples changed, possibly because the addition of extra lithium altered the arrangement of Mn vacancies in the material. Compared with P-LMO, the lithium-doped samples with ratios of D-LMO-0.045, D-LMO-0.09, and D-LMO-0.24 showed shoulder peaks or blunted peak shapes and broadened peaks at the (104) peak, indicating that the structural symmetry of the crystal and the ordered distribution of the spatial superstructure were reduced to varying degrees in these three lithium-doped modified samples. The D-LMO-0.14 sample had a complete crystal structure, and the superstructure diffraction peaks shifted to lower angles relative to the original sample, indicating that the occupation of Mn vacancies by lithium led to a reduction in the proportion of Mn vacancies and their reordering, resulting in a more dispersed distribution of Mn vacancies.

[0110] The preparation conditions for the solid sintering and ion exchange processes of the NaLiMnO (NLMO) precursors obtained in Examples 8-11 were consistent with the optimal preparation conditions for LMO in Examples 1-7.

[0111] In summary, among Examples 8 to 11, the superior lithium doping strategy is Example 10. The lithium-doped Li2Mn3O7 sample obtained in Example 10 will be referred to as D-LMO.

[0112] The morphology of samples from Example 4 (P-LMO) and Example 10 (D-LMO) was observed using scanning electron microscopy, and the SEM images are shown below. Figure 5 As shown in the figure, (a) is P-LMO and (b) is D-LMO. From the figure, we can see that P-LMO ( Figure 5 (a) consists of irregular single-crystal particles with a size of approximately 200–400 nm. The nanostructuring of the material is more conducive to the rapid insertion and extraction of lithium ions, providing good rate performance in practical lithium-ion battery applications. For the lithium-doped modified sample D-LMO (… Figure 5 (b) The morphology was not significantly different from that of P-LMO, and the particle surface was smooth and free of foreign matter.

[0113] EDS energy dispersive spectroscopy was performed on the two samples, and the results are as follows: Figures 6-7 As shown, Figure 6 The image shows the EDS elemental spectrum of the sample from Example 4. Figure 7 The image shows the EDS elemental spectrum of the sample from Example 10. The figure shows that manganese is uniformly distributed in both samples, and a small amount of sodium remains on the sample surface. Further ICP elemental analysis was performed, and the results are shown in Table 1. It is evident that the sodium content is extremely low, indicating that the ion exchange reaction was complete. The actual obtained material, P-LMO, has the molecular formula Li. 0.64 [□ 0.14 Mn 0.86O2, D-LMO has the molecular formula Li 0.64 [Li 0.11 □ 0.03 Mn 0.86 O2; The actual chemical composition of the two materials mentioned above differs from the target chemical composition Li 0.57 [□ 0.14 Mn 0.86 O2, Li 0.64 [Li 0.09 □ 0.05 Mn 0.86 The results for O2 are very close, so it can be considered that the target product has been obtained.

[0114] Table 1. ICP test results for P-LMO and D-LMO

[0115] P-LMO Quality percentage (%) Moor ratio D-LMO Quality percentage (%) Moor ratio Li 5.0435 0.7541 Li 6.0803 0.8761 Na 0.1604 0.0072 Na 0.0527 0.0023 Mn 52.9696 1 Mn 54.6763 1

[0116] The manganese-based materials from Examples 4 and 10 were used to make electrodes, and half-cells were assembled for electrochemical testing. The specific steps are as follows:

[0117] P-LMO and D-LMO cathode materials were weighed separately with polyvinylidene fluoride (PVDF) and conductive carbon black in a ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone solvent (NMP) was added, and the mixture was ground uniformly. The resulting material was then coated onto aluminum foil using a 200 μm thick scraper, dried at 60°C, and then vacuum-dried at 100°C for 10 hours. The coated material was then cut into 12 mm diameter discs, which were used as the cathode. Lithium metal was used as the anode, glass fiber as the separator, and an electrolyte solution with a ratio of 1.2 M LiPF6 and EC:EMC = 3:7 Vol%. A 2032 coin cell was assembled and electrochemical tests were performed. The test results are as follows: Figure 8 As shown, (a) is a graph of the long-cycle performance test of the D-LMO and P-LMO assembled batteries after 5 cycles of activation at 2-4.8V and 0.1C current, and at 0.2C current; (b) is a graph of the charge-discharge curve of the P-LMO assembled battery in the first two cycles; and (c) is a graph of the charge-discharge curve of the D-LMO assembled battery in the first two cycles.

[0118] like Figure 8(a) The P-LMO-assembled battery exhibited a discharge specific capacity of 241 mAh / g after five cycles of low-current activation, and 230 mAh / g in the first cycle at 0.2C. After 100 cycles, the discharge specific capacity was 190 mAh / g, with a capacity retention of 82.6%. In contrast, D-LMO showed a discharge capacity of 251.42 mAh / g after five cycles of 0.1C activation, and still retained a capacity of 243 mAh / g after 100 cycles at 0.2C. This demonstrates that the addition of Li significantly improves the material's cycle stability and cycle life, and also enhances its actual capacity. The reason for this is that Li doping occupies some Mn vacancies, leading to a change in the Mn atom arrangement in the transition metal layer. Combined with the phenomenon of the superlattice diffraction peak shifting to a lower angle in the XRD pattern, it can be seen that the mesh-like vacancy distribution structure in the original material is rearranged in D-LMO, and the vacancy distribution is more dispersed. This result leads to a higher Mn migration barrier in the transition metal layer, making it more difficult for adjacent peroxides around vacancies to combine and form oxygen. Intra- and inter-layer migration of manganese is suppressed, which is more conducive to maintaining the structural stability of the material and reversible capacity release. Figure 8 (b)~(c) Comparing the charge-discharge curves of P-LMO and D-LMO for the first two cycles, it can be seen that the first-cycle charge specific capacity of P-LMO is 54 mAh / g, while the Li-doped D-LMO shows a significant improvement, exhibiting a first-cycle charge specific capacity of 94 mAh / g. The higher capacity is reflected in the reaction at the 4.6V high-voltage plateau, which is attributed to the Li occupation of Mn vacancies activating more lattice oxygen to participate in the redox reaction. The additional Li occupation of Mn vacancies in the transition metal layer results in the classic "Li-O-Li" configuration in the material. In many lithium-rich manganese materials, this is the source of additional capacity provided by activating lattice oxygen redox. However, in traditional lithium-rich materials, lattice oxygen is easily irreversibly oxidized to oxygen during the first-cycle charge-discharge process and lost, causing the high-voltage reaction plateau to disappear in the second cycle, resulting in severe capacity loss in the first cycle. In the materials of this patent, it is evident that the irreversible capacity loss in the first cycle of both materials is minimal, and the high-voltage reaction plateau is reproduced in the second cycle, proving that the irreversible reaction of lattice oxygen is suppressed. This is attributed to the application of the Mn vacancy structure.

[0119] For the layered all-manganese-based lithium-ion cathode oxide with a specific Mn vacancy structure (e.g., mesh structure) in the transition metal layer synthesized in the embodiments of this invention, traditional solid-state sintering methods are difficult to use due to the special atomic arrangement. The embodiments of this invention fill this technical gap by using an ion exchange method, preparing a novel lithium-ion cathode oxide material with a Mn vacancy structure. XRD results show that it retains the superlattice structure of the transition metal layer of the sodium precursor and exhibits ultra-high capacity during lithium-ion battery testing. In embodiments 1-7 of this invention, the optimal preparation conditions for the precursor Na2Mn3O7 (sodium carbonate and manganese carbonate as precursor materials, oxygen atmosphere, high temperature 600℃ for 15 hours) and the optimal preparation conditions for ion exchange (using lithium chloride and lithium nitrate as lithium salts, with a mixing ratio of 12:88, and ion exchange performed at 280℃ for 6 hours) were determined. In embodiments 8-11 of this invention, the original material Li2Mn3O7 (Li 0.57 [□ 0.14 Mn 0.86 In-situ lithium supplementation modification was performed using O2 to partially occupy the Mn vacancies in the transition metal layer with Li. Anhydrous lithium carbonate was selected as the lithium source for doping, and the additional lithium atoms accounted for 63% of the Mn vacancies. The manganese-based materials prepared in Examples 1 to 11 of this invention were assembled into half-cells, which showed good electrochemical performance.

[0120] In summary, in the manganese-based material with a specific structure of this invention, the unique Mn vacancies in the transition metal layer can activate the redox activity of oxygen anions, providing additional capacity during charge and discharge and enriching the existing crystal structure configuration of this material. Furthermore, the structure is reverse-engineered to address the lithium deficiency of the material, and lithium is added in situ, optimizing the application of this structure in lithium-ion batteries. The addition of extra lithium atoms leads to the rearrangement of the Mn vacancy superstructure in the transition metal layer. The more dispersed vacancy configuration can better suppress the irreversible loss of lattice oxygen and the structural phase transition and capacity loss caused by intralayer / interlayer migration of manganese.

Claims

1. A manganese-based material, characterized in that, The crystal structure of the manganese-based material includes an alkali metal layer, an oxygen element, and a transition metal layer; the oxygen element is located between the alkali metal layer and the transition metal layer, and is bonded to both the alkali metal layer and the transition metal layer; the alkali metal layer includes a lithium element; the transition metal layer includes a mn element, a mn vacancy, and a lithium element. The molar ratio of the O element to the Li element in the alkali metal layer is 1:(0.2~0.4). The molar ratio of O to Mn is 1:(0.3~0.6). The molar ratio of the Mn vacancy to the Mn element is 0.03~0.1; The molar ratio of Li to Mn in the transition metal layer is (0.03~0.16):

1.

2. The manganese-based material according to claim 1, characterized in that, The crystal structure of the manganese-based material includes an O2 phase structure, an O3 phase structure, or a combination thereof.

3. A method for preparing a manganese-based material as described in any one of claims 1 to 2, characterized in that, Includes the following steps: A mixture containing sodium carbonate, manganese carbonate, and a first lithium source is calcined for the first time to obtain a precursor; the precursor is then mixed with a second lithium source and subjected to an ion exchange reaction through a second calcination to obtain the manganese-based material; the first lithium source and the second lithium source may be the same or different.

4. The preparation method according to claim 3, characterized in that, The calcination temperature for the first calcination is 500~700℃; And / or, the holding time for the first calcination is 12~18h.

5. The preparation method according to claim 3, characterized in that, The calcination temperature for the second calcination is 200~300℃; And / or, the holding time for the second calcination is 2 to 10 hours.

6. The preparation method according to claim 3, characterized in that, The first lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium chloride, or lithium nitrate; And / or, the second lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium chloride, or lithium nitrate.

7. The preparation method according to claim 6, characterized in that, The first lithium source is selected from lithium carbonate; And / or, the second lithium source is selected from lithium chloride and lithium nitrate; the mass ratio of the lithium chloride to the lithium nitrate is 1:(7~8).

8. A positive electrode material, characterized in that, The raw materials for preparing the cathode material include the manganese-based material as described in any one of claims 1 to 2, or the manganese-based material prepared by the preparation method described in any one of claims 3 to 7.

9. A lithium-ion battery, characterized in that, Includes the cathode material as described in claim 8.

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