A low-manganese-dissolution lithium iron manganese phosphate cathode material, a cathode and a lithium ion battery

Abstract

The application relates to a low-manganese-dissolution lithium iron manganese phosphate positive electrode material, a positive electrode and a lithium ion battery; a preparation method of the positive electrode material comprises the following steps: (1) adding a lithium source, an iron source, a phosphorus source and a manganese source into water, then adding a carbon source, sand grinding, drying, calcining to obtain carbon-coated lithium iron manganese phosphate; (2) adding a lithium source, a phosphorus source and an iron source into water, then adding a carbon source, sand grinding, drying, calcining to obtain carbon-coated lithium iron phosphate; (3) adding carbon-coated lithium iron phosphate and carbon-coated lithium iron manganese phosphate into water according to a molar ratio of (0.14-0.45):1, then adding a carbon source, sand grinding, drying, calcining to obtain the lithium iron manganese phosphate positive electrode material. The positive electrode material can effectively prevent the direct contact between Mn ions and electrolyte, greatly inhibit the dissolution of manganese in the crystal lattice structure, significantly reduce the manganese ion dissolution amount, improve the 1C cycle performance of the battery, and ensure that the battery has a high 1C charging capacity.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and relates to lithium-ion batteries, specifically to a low-manganese-leaching lithium manganese iron phosphate cathode material, a cathode, and a lithium-ion battery. Background Technology

[0002] Lithium iron phosphate (LiFePO4), an olivine-type lithium iron phosphate, has become the mainstream cathode material for lithium-ion batteries due to its excellent structural stability and significant cost advantages. However, its relatively low operating voltage of 3.4 V (vs. Li+ / Li) severely limits the improvement of energy density. As a performance upgrade of lithium iron phosphate, lithium manganese iron phosphate (LiFePO4) partially replaces iron by introducing manganese, thus forming lithium manganese iron phosphate (LiFePO4). 1-x Mn x The PO4 (LFMP) system can raise the voltage platform to 4.1V, with a theoretical energy density increase of 20%, combining the high safety of lithium iron phosphate with the high voltage advantage of lithium manganese phosphate. However, the high voltage advantage of lithium manganese iron phosphate can only be achieved under conditions of high manganese content (Mn / Fe>1). While increasing the manganese content can enhance electrochemical performance, it will also exacerbate the Mn content deficiency. 3+ The Jahn-Teller effect causes lattice distortion, manganese ion dissolution, and structural collapse, leading to a significant decrease in cycle stability. Furthermore, the inherently low intrinsic conductivity of manganese materials severely restricts their high-rate performance; these two major technical bottlenecks have become key obstacles hindering their industrialization.

[0003] Appropriate ion doping and surface coating of LFMP crystals can effectively suppress the aforementioned reaction processes and significantly improve the electrochemical performance of the material. Ion doping stabilizes the crystal structure and reduces manganese dissolution by increasing the average valence state of manganese. For LFMP materials, Al is a commonly used doping element. 3+ It can effectively stabilize the LFMP structure and inhibit manganese ion dissolution, thereby improving its cycling performance. However, since the bond energy of the Al-O bond is significantly higher than that of the Mn-O bond, Li... + The expansion or contraction of the crystal structure during the insertion / extraction process is suppressed, which is the key mechanism for Al doping to stabilize the crystal structure. Unfortunately, Li + The migrating 8a-16c-8a channels will also shrink to some extent, leading to a decrease in material capacity—essentially sacrificing capacity for structural stability. Surface coating involves coating the surface of lithium manganese iron phosphate with oxides, phosphates, or carbon layers to reduce its direct contact with the electrolyte—on the one hand, reducing electrolyte corrosion of the material, and on the other hand, hindering Mn... 2+ It dissolves into the electrolyte, thereby inhibiting the dissolution of manganese. However, existing surface coatings have limited effectiveness in reducing the amount of manganese ions leached out. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a low-manganese-leaching lithium manganese iron phosphate cathode material, cathode, and lithium-ion battery, which can effectively reduce the amount of manganese ion leaching and improve 1C cycle stability while ensuring that the battery has a high 1C charging capacity.

[0005] The first aspect of this invention is to provide a method for preparing a lithium manganese iron phosphate cathode material, comprising the following steps:

[0006] (1) According to the stoichiometric ratio of lithium manganese iron phosphate, lithium source, iron source, phosphorus source and manganese source are added to water, and then carbon source is added at 1wt%~5wt% of the mass of the generated lithium manganese iron phosphate. The mixture is then sand-milled, dried and calcined to obtain carbon-coated lithium manganese iron phosphate.

[0007] The chemical formula of the lithium manganese iron phosphate is LiFe 1-x Mn x PO4, 0.55≤X≤0.80;

[0008] (2) Take lithium source, phosphorus source and iron source according to the stoichiometric ratio of lithium iron phosphate and add them to water. Then add carbon source according to 1wt%~5wt% of the mass of generated lithium iron phosphate, sand mill, dry, calcine to obtain carbon-coated lithium iron phosphate.

[0009] The chemical formula of the lithium iron phosphate is Li y FePO4, 1.00≤y≤1.05;

[0010] (3) Take carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate in a molar ratio of (0.14~0.45):1 and add them to water. Then add carbon source at 0.3wt%~1wt% of the total mass of carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate. Sand mill, dry and calcine to obtain the lithium manganese iron phosphate cathode material.

[0011] In some embodiments, in step (3), carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate are added to water at a molar ratio of (0.2~0.4):1.

[0012] In some embodiments, in step (3), the molar ratio is (0.23~0.33): 1. Carbon-coated lithium iron phosphate and carbon-coated manganese iron phosphate are added to water.

[0013] In some embodiments, the calcination temperature in step (1) is 500℃~650℃ and the time is 5h~10h.

[0014] In some embodiments, the calcination temperature in step (1) is 550℃~600℃ and the time is 5h~8h.

[0015] In some embodiments, the heating rate of calcination in step (1) is 2℃ / min to 5℃ / min, preferably 3℃ / min to 5℃ / min.

[0016] In some embodiments, the calcination temperature in step (2) is 500℃~650℃ and the time is 5h~10h.

[0017] In some embodiments, the calcination temperature in step (2) is 500℃~550℃ and the time is 5h~8h.

[0018] In some embodiments, the heating rate of calcination in step (2) is 2℃ / min to 5℃ / min, preferably 3℃ / min to 5℃ / min.

[0019] In some embodiments, the calcination temperature in step (3) is 700℃~800℃ and the time is 5h~10h.

[0020] In some embodiments, the calcination temperature in step (3) is 750℃~800℃ and the time is 5h~8h.

[0021] In some embodiments, the heating rate of calcination in step (3) is 2℃ / min to 5℃ / min, preferably 3℃ / min to 5℃ / min.

[0022] In some embodiments, the lithium source in steps (1) and (2) is independently selected from any one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide.

[0023] In some embodiments, the iron source in steps (1) and (2) is independently selected from any one of ferric phosphate, ferric oxide, and ferrous oxalate.

[0024] In some embodiments, the phosphorus source in steps (1) and (2) is independently selected from at least one of ammonium dihydrogen phosphate, iron phosphate and lithium dihydrogen phosphate.

[0025] In some embodiments, the manganese source is selected from manganese carbonate and manganese acetate.

[0026] In some embodiments, the carbon source in steps (1), (2) and (3) is independently selected from at least one of glucose, sucrose, and PEG.

[0027] A second aspect of the present invention is to provide a cathode material prepared by the preparation method described above.

[0028] A third aspect of the present invention is to provide a lithium-ion battery cathode, the cathode comprising the cathode material described above.

[0029] A fourth aspect of the present invention is to provide a lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrode solution, wherein the positive electrode comprises the positive electrode material as described above.

[0030] Through research and optimization, this invention constructs a three-layer protective barrier on the surface of lithium manganese iron phosphate, consisting of a carbon layer coating, a lithium iron phosphate coating, and a carbon layer coating. During the preparation process, the molar ratio of the surface-coated lithium iron phosphate to the coated lithium manganese iron phosphate is controlled within a suitable range. This effectively blocks the direct contact between Mn ions and the electrolyte, significantly suppresses the dissolution of manganese in the crystal structure, and significantly reduces the amount of manganese ions dissolved in high-manganese-ratio (Mn / Fe>1) lithium manganese iron phosphate cathode materials. Furthermore, it improves the 1C cycle performance of the battery while ensuring a high 1C charging capacity.

[0031] The preparation of the lithium manganese iron phosphate cathode material of this invention does not require the introduction of additional complex equipment and can be directly integrated into existing production lines. The operation is simple and reduces the cost and threshold for industrial application. Detailed Implementation

[0032] To facilitate understanding of the present invention, a more complete description will be provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0033] Unless otherwise specified, experimental methods in the following examples are generally performed under standard conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the examples are commercially available products.

[0034] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0035] The present invention will be further described in detail below with reference to specific embodiments.

[0036] In the following implementation, n / n refers to the molar ratio of the raw materials.

[0037] Lithium manganese iron phosphate is abbreviated as LFMP, and lithium iron phosphate is abbreviated as LFP.

[0038] Example 1

[0039] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0040] (1) According to LiFe0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0041] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0042] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0043] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0044] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0045] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0046] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.14, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0047] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0048] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate is obtained. After crushing and sieving, the finished lithium manganese iron phosphate product is obtained.

[0049] Example 2

[0050] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0051] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0052] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0053] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0054] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0055] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0056] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0057] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.23, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0058] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0059] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0060] Example 3

[0061] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0062] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0063] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0064] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0065] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0066] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0067] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0068] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.33, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0069] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0070] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0071] Example 4

[0072] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0073] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0074] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0075] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0076] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0077] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0078] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0079] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.45, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0080] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0081] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0082] Comparative Example 1

[0083] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0084] (1) According to LiFe 0.2 Mn 0.8The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0085] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0086] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0087] (4) Mix carbon-coated LFMP with deionized water, and add glucose at 0.38 wt% of the mass of carbon-coated LFMP. After stirring thoroughly, use a sand mill to sand mill the mixture.

[0088] (5) Spray drying: A spray drying device is used to implement the secondary granulation process of sand mill powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed. Glucose is added at 0.38 wt% of the powder obtained by spraying and mixed evenly. It is recorded as LFMP precursor 2 for later use.

[0089] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0090] Comparative Example 2

[0091] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0092] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0093] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0094] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0095] (4) Mix carbon-coated LFMP with deionized water, and add glucose at 0.38 wt% of the mass of carbon-coated LFMP. After stirring thoroughly, use a sand mill to sand mill the mixture.

[0096] (5) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and a uniform dry powder is finally formed. Glucose is added at 0.63wt% of the mass of the powder obtained by spraying and mixed evenly. It is recorded as LFMP precursor 2 for later use.

[0097] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0098] Comparative Example 3

[0099] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0100] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0101] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0102] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0103] (4) Mix carbon-coated LFMP with deionized water, and add glucose at 0.38 wt% of the mass of carbon-coated LFMP. After stirring thoroughly, use a sand mill to sand mill the mixture.

[0104] (5) Spray drying: A spray drying device is used to implement the secondary granulation process of sand mill powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and a uniform dry powder is finally formed. Glucose is added at 0.88wt% of the mass of the powder obtained by spraying and mixed evenly. It is recorded as LFMP precursor 2 for later use.

[0105] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0106] Comparative Example 4

[0107] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0108] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0109] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0110] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0111] (4) Mix with deionized water at a ratio of n(Al(OH)3) / n (carbon-coated LFMP) of 0.01, and add glucose at a ratio of 0.75wt% of the total mass of Al(OH)3 and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0112] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 2 for later use.

[0113] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0114] Comparative Example 5

[0115] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0116] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0117] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0118] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0119] (4) Mix with deionized water at a ratio of n(Al(OH)3) / n (carbon-coated LFMP) of 0.02, and add glucose at 0.75wt% of the total mass of Al(OH)3 and carbon-coated LFMP. After stirring thoroughly, use a sand mill to sand mill the mixed slurry.

[0120] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 2 for later use.

[0121] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0122] Comparative Example 6

[0123] This comparative example provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0124] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0125] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0126] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0127] (4) Mix with deionized water at a ratio of n(Al(OH)3) / n (carbon-coated LFMP) of 0.03, and add glucose at 0.75wt% of the total mass of Al(OH)3 and carbon-coated LFMP. After stirring thoroughly, use a sand mill to sand mill the mixed slurry.

[0128] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 2 for later use.

[0129] (6) The LFMP precursor 2 is heated to 750℃ at a rate of 5℃ / min and held for 5h. After natural cooling, the lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0130] Comparative Example 7

[0131] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0132] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0133] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0134] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0135] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0136] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0137] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0138] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.07, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0139] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0140] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0141] Comparative Example 8

[0142] This embodiment provides a lithium iron phosphate cathode material, which is prepared by the following method:

[0143] (1) According to LiFe 0.2 Mn 0.8 The PO4 molecular formula is obtained by mixing lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and manganese carbonate (MnCO3) with deionized water in a stoichiometric ratio of n(Li):n(Fe):n(Mn):n(P) of 1.02:0.2:0.8:1.02. Glucose is added at 2.53 wt% of the mass of the generated lithium manganese iron phosphate. After thorough stirring, the mixture is milled using a sand mill.

[0144] (2) Spray drying: The secondary granulation process of the sand-milled powder is carried out by spray drying device. During the spray drying process, the liquid raw material is converted into a mist dispersion system by the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFMP precursor 1 for later use.

[0145] (3) After calcination, the temperature was raised to 600℃ at a rate of 5℃ / min and held for 5h. Then, the temperature was naturally cooled to obtain carbon-coated lithium manganese iron phosphate, which was recorded as carbon-coated LFMP for later use.

[0146] (4) Lithium dihydrogen phosphate (LiH2PO4), ferrous oxalate (FeC2O4), and deionized water were mixed according to the molecular formula of LiFePO4 and the stoichiometric ratio of n(Li):n(Fe):n(P) was 1.02:1:1.02. Glucose was added at 2.53 wt% of the mass of the generated lithium iron phosphate. After stirring thoroughly, the mixture was sand-milled.

[0147] (5) Spray drying: A spray drying device is used to carry out the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as LFP precursor 1 for later use.

[0148] (6) After calcination, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 5h. Then, the temperature is naturally cooled to obtain carbon-coated lithium iron phosphate, which is recorded as carbon-coated LFP for later use.

[0149] (7) Mix with deionized water at a ratio of n(carbon-coated LFP) / n(carbon-coated LFMP) of 0.6, and add glucose at a ratio of 0.75wt% of the total mass of carbon-coated LFP and carbon-coated LFMP. After thorough mixing, use a sand mill to sand mill the mixed slurry.

[0150] (8) Spray drying: A spray drying device is used to implement the secondary granulation process of the sand-milled powder. During the spray drying process, the liquid raw material is converted into a mist dispersion system through the atomizer. Under the action of high temperature airflow, the moisture is removed and finally a uniform dry powder is formed, which is recorded as mixed precursor 1 for later use.

[0151] (9) After calcination, the temperature is raised to 750℃ at a rate of 5℃ / min and held for 5 hours. After natural cooling, lithium manganese iron phosphate cathode material is obtained. After crushing and sieving, the finished lithium manganese iron phosphate cathode material is obtained.

[0152] Experimental characterization data

[0153] Button cell fabrication

[0154] (1) Preparation of positive electrode sheet

[0155] First, the lithium manganese iron phosphate cathode material C / LFMP, Super-P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared in the above embodiments and comparative examples were mixed at a weight ratio of 90:5:5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent was added. These components were uniformly mixed using a mixer to form a slurry with good flowability. Subsequently, the slurry was uniformly coated onto a 12 μm thick aluminum foil substrate using an automatic coating machine. The coated electrode material was dried in a vacuum oven at a low temperature (60°C) for 10 h to ensure complete evaporation of the solvent in the slurry and uniform curing of the electrode material. The dried electrode film was cut into 15 mm diameter discs to prepare standard electrode samples. The final active material loading of the C / LFMP cathode material was 4.5-5 mg / cm².

[0156] (2) Battery assembly

[0157] To test the electrochemical performance of the prepared samples, a CR2032 coin cell was used as the test platform, with lithium metal as the negative electrode material. The electrolyte consisted of 1 mol / L LiPF6 salt, dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a 1:1:1 volume ratio. During assembly, a Celgard 2400 polypropylene film was used as the separator to effectively prevent short circuits between the positive and negative electrodes and maintain the stability and safety of the battery. All battery assembly was performed in a glove box filled with high-purity argon gas to ensure that the samples were not affected by moisture and oxygen, thereby avoiding hydrolysis or oxidation of the electrolyte and ensuring the high performance and long-term stability of the battery.

[0158] Button test

[0159] Constant current constant voltage (CC-CV) charge-discharge tests were performed on the LAND CT2001A battery testing system, with a voltage range of 2.00–4.35 V (vs. Li+ / Li). This test involves charging to 4.35 V under constant current and maintaining that voltage until the battery current drops to 0.05 C. It primarily evaluates the battery's capacity, efficiency, and voltage characteristics during charging. To further evaluate the battery's long-term stability, 100 cycles were performed at a test rate of 1.00 C.

[0160] 1C cycle capacity retention rate / % = (100-cycle discharge capacity / first-cycle discharge capacity) × 100%.

[0161] Water-soluble manganese leaching test

[0162] The determination was performed using ICP-OES according to the test method specified in GB / T46512-2025.

[0163] Carbon content test

[0164] The carbon and sulfur were determined using a carbon and sulfur analyzer according to the test methods specified in GB / T 20123.

[0165] The test results are shown in Table 1 below:

[0166] Table 1 Test Results

[0167]

[0168] As shown in Table 1 above, the lithium-ion batteries (Examples 1-4) prepared by this invention exhibit significantly reduced Mn ion dissolution content, while also possessing high 1C charging capacity and 1C cycle stability. This may be because the coating layer structure of the cathode material of this invention is dense and without obvious pores, effectively preventing direct contact between the electrolyte and the manganese element inside the LFMP, thus greatly reducing the amount of manganese ion dissolution; and the intrinsic conductivity of iron in the lithium iron phosphate coating layer is better than that of manganese, which helps to improve the conductivity of lithium manganese iron phosphate.

[0169] Compared to Example 3, the positive electrode material of Comparative Example 1 lithium-ion battery did not contain lithium iron phosphate during preparation. Instead, it was coated with a protective layer of "carbon layer coating-carbon layer coating-carbon layer coating" through three carbon coating processes (first milling, second milling, and second spray drying, respectively). This resulted in a significant increase in the Mn ion dissolution content and a marked deterioration in the 1C charging capacity and cycle stability. This may be because the electrolyte can still contact manganese through pores after carbon coating. Further increasing the carbon content (Comparative Examples 2 and 3) can reduce the amount of manganese ion dissolution, but the 1C charging capacity also deteriorates accordingly.

[0170] Compared to Example 3, Comparative Example 4 used Al(OH)3 instead of LFP as the coating material, resulting in a significant increase in Mn ion leaching content and a marked deterioration in 1C charging capacity and cycle stability. While the Mn ion leaching content decreased with increasing Al coating amount, the battery's 1C charging capacity significantly deteriorated, failing to balance cycle stability and 1C charging capacity. When n(Al(OH)3) / n(LFMP) was 0.03 (Comparative Example 6), the 1C charging capacity had already decreased to 145.89 mAh / g. Therefore, further reducing the Mn ion leaching content by increasing the Al coating amount was not feasible, as it would severely impair the battery's 1C charging capacity.

[0171] Compared with Example 1, the molar ratio of lithium iron phosphate coated on the surface to coated lithium manganese iron phosphate used in Comparative Example 7 was lower (less than 0.14:1) during the preparation of the cathode material, the content of Mn ion dissolution was higher, and the 1C charging capacity was not well improved.

[0172] Compared to Example 4, the molar ratio of the surface-coated lithium iron phosphate to the coated lithium manganese iron phosphate used in Comparative Example 8 was higher (above 0.45:1) during the preparation of the cathode material. This resulted in an excessively high Fe content in the material, which weakened the voltage boost brought by the Mn element. Furthermore, the excessively thick LFP coating layer hindered the diffusion of lithium ions from the internal high-manganese core, making it difficult to utilize the capacity in the high-voltage portion, thereby reducing the energy density of the material. Because an excessively thick LFP coating would form a thick shell that hinders the rapid transfer of lithium ions at the interface, the capacity utilization under high current would be limited, damaging the 1C charging capacity of the battery.

[0173] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: (1) According to the stoichiometric ratio of lithium manganese iron phosphate, lithium source, iron source, phosphorus source and manganese source are added to water, and then carbon source is added at 1wt%~5wt% of the mass of the generated lithium manganese iron phosphate. The mixture is then sand-milled, dried and calcined to obtain carbon-coated lithium manganese iron phosphate. The chemical formula of the lithium manganese iron phosphate is LiFe 1-x Mn x PO4, 0.55≤X≤0.80; (2) Take lithium source, phosphorus source and iron source according to the stoichiometric ratio of lithium iron phosphate and add them to water. Then add carbon source according to 1wt%~5wt% of the mass of generated lithium iron phosphate, sand mill, dry, calcine to obtain carbon-coated lithium iron phosphate. The chemical formula of the lithium iron phosphate is Li y FePO4, 1.00≤y≤1.05; (3) Take carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate in a molar ratio of (0.14~0.45):1 and add them to water. Then add carbon source at 0.3wt%~1wt% of the total mass of carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate. Sand mill, dry and calcine to obtain the lithium manganese iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, In step (3), carbon-coated lithium iron phosphate and carbon-coated lithium manganese iron phosphate are added to water at a molar ratio of (0.2~0.4):

1.

3. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio is (0.23~0.33):

1. Carbon-coated lithium iron phosphate and carbon-coated manganese iron phosphate are added to water.

4. The preparation method according to claim 1, characterized in that, In step (1), the calcination temperature is 500℃~650℃ and the time is 5h~10h.

5. The preparation method according to claim 1, characterized in that, In step (2), the calcination temperature is 500℃~650℃ and the time is 5h~10h.

6. The preparation method according to claim 1, characterized in that, In step (3), the calcination temperature is 700℃~800℃ and the time is 5h~10h.

7. The preparation method according to claim 1, characterized in that, The lithium source in steps (1) and (2) is independently selected from at least one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide; and / or, The iron source in steps (1) and (2) is independently selected from at least one of ferric phosphate, ferric oxide, and ferrous oxalate; and / or, The phosphorus source in steps (1) and (2) is independently selected from at least one of ammonium dihydrogen phosphate, iron phosphate, and lithium dihydrogen phosphate; and / or, The manganese source is selected from at least one of manganese carbonate and manganese acetate; and / or, The carbon source in steps (1), (2) and (3) is independently selected from at least one of glucose, sucrose and PEG.

8. The cathode material prepared by the preparation method according to any one of claims 1 to 7.

9. A lithium-ion battery positive electrode, characterized in that, The positive electrode comprises the positive electrode material as described in claim 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrode solution, characterized in that, The positive electrode comprises the positive electrode material as described in claim 8.

Images