A method for synthesizing a carbon-coated lithium iron manganese phosphate material by discontinuous vapor deposition
By employing a two-stage sintering method involving low-temperature pre-sintering and rotary kiln CVD vapor deposition, the problems of uneven carbon coating and poor conductivity in lithium manganese iron phosphate materials were solved, achieving dense and uniform carbon coating and improved electrochemical performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2024-01-04
- Publication Date
- 2026-06-09
AI Technical Summary
In the existing technology, the carbon coating method for lithium manganese iron phosphate materials has problems such as uneven and loose carbon layers, poor electronic conductivity, harsh reaction conditions, and low deposition rate.
A two-stage sintering method, consisting of low-temperature short-term pre-sintering organic carbon coating and rotary kiln CVD vapor deposition, is employed. This method utilizes a porous carbon network to restrict crystal growth and the formation of a conductive network, combined with reducing gas to fill the voids, thereby generating a dense carbon coating layer.
This study achieved a dense and uniform carbon coating layer for lithium manganese iron phosphate materials, resulting in good electronic conductivity, small particle size, shortened lithium-ion migration path, and improved electrochemical performance and compaction density.
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Figure CN118176162B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of lithium battery preparation, and in particular to a method for synthesizing a carbon-coated lithium manganese iron phosphate material by discontinuous vapor deposition. Background Technology
[0002] Olivine-type phosphate LiMPO4 (M=Fe,Mn) is considered the most promising cathode material for lithium-ion power batteries. Among them, lithium iron phosphate (LiFePO4) has been widely used in the lithium battery field due to its excellent cycle performance, structural stability, safety, and low cost. However, the energy density of lithium iron phosphate (LiFePO4) is approaching the theoretical limit for mass production (175~185Wh / kg).
[0003] Lithium manganese iron phosphate (LMP) combines the safety of lithium iron phosphate with the high energy density of ternary materials, making it one of the upgrade directions for cathode materials. LMP has a higher voltage plateau of 4.1V compared to lithium iron phosphate, which is 0.7V higher, resulting in a theoretical energy density that is approximately 15% higher.
[0004] LiMn manganese iron phosphate material with olivine-type structure 1-x Fe x PO4 has inherent defects, one of which is due to the lithium manganese iron phosphate material LiMn 1-x Fe x The strong PO bonds in PO4 restrict the free movement of electrons, resulting in low electronic conductivity; another reason is the low electronic conductivity of lithium manganese iron phosphate material LiMn. 1-x Fe x The olivine-type structure of PO4 causes its Li + The diffusion channel is one-dimensional, Li + The transmission rate is relatively low. Therefore, techniques such as carbon coating, nano-sizing, and metal ion doping are needed to improve the performance of lithium manganese iron phosphate (LiMn) materials. 1- x Fe x PO4 material was modified.
[0005] Existing coating methods typically involve high-temperature carbonization coating with organic carbon sources or carbon vapor deposition (CVD). High-temperature carbonization coating with organic carbon sources has a low carbonization temperature, and the resulting carbon layer can inhibit particle growth, but the coating layer is loose and uneven. Carbon vapor deposition (CVD) coating produces a uniform and dense coating layer, but it has disadvantages such as very high reaction temperature, harsh reaction conditions, and very low deposition rate.
[0006] Chinese patent application CN116230932A discloses a method for preparing a carbon- and lithium-phosphate dual-coated lithium manganese iron phosphate material. This method utilizes organic and inorganic carbon sources as primary carbon coating materials, sintering, pulverizing, and sieving them with iron, manganese, and lithium sources under an inert gas atmosphere to obtain a primary carbon-coated lithium manganese iron phosphate. Then, a vapor deposition coating method is used to further carbon-coate the primary carbon-coated lithium iron phosphate material. Finally, lithium phosphate coating is performed to obtain a carbon- and lithium-phosphate dual-coated lithium manganese iron phosphate material. However, during the synthesis of the primary carbon-coated lithium iron phosphate material, the lithium manganese iron phosphate crystals have already grown completely. Subsequent secondary carbon coating and lithium phosphate coating processes can easily lead to discontinuous conductive networks and loose coating layers. Summary of the Invention
[0007] Based on this, the purpose of this disclosure is to provide a method for synthesizing lithium manganese iron phosphate material with discontinuous vapor deposition carbon coating. This method improves the material properties of lithium manganese iron phosphate by obtaining a dense and uniform carbon coating layer through a two-stage sintering method of low-temperature and short-term pre-sintering organic carbon coating and rotary kiln CVD vapor deposition coating.
[0008] To achieve the above objectives, the present disclosure adopts the following technical solution:
[0009] A method for synthesizing a carbon-coated lithium manganese iron phosphate material by discontinuous vapor deposition includes the following steps:
[0010] (1) Preparation of precursor: Lithium source, manganese source, iron source, phosphorus source and organic carbon source are added to a grinding mill, and water is added. After grinding, a precursor slurry is obtained. The molar ratio of each element in the precursor slurry is Li:Mn:Fe:P=1.05:x:1-x:1, where x=0.3~0.7. The amount of organic carbon source added is 4~10wt% of the theoretical yield of lithium manganese iron phosphate. The precursor slurry is spray-dried to obtain the precursor.
[0011] (2) Pre-sintered organic carbon coating: The precursor is placed in a kiln with a protective atmosphere, heated to 530~570℃, and held for 1~3h; after the holding period, heating is stopped and the material is cooled to obtain the pre-sintered material.
[0012] (3) Rotary kiln vapor deposition (CVD) carbon coating: The pre-sintered material is placed in a rotary kiln with a protective atmosphere, heated to 680~780℃, and held for 5~7h. After holding for 4~5h, a reducing gas is introduced. The reducing gas is one or a combination of at least two of acetylene, methane, ethanol vapor, and benzene vapor. The gas is introduced for 1~2h. After the holding period, heating is stopped, and the material is cooled to obtain the sintered material.
[0013] (4) Crushing and sieving: The sintered material is crushed and sieved to obtain a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material.
[0014] The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material disclosed herein involves selecting raw materials to prepare a precursor, followed by a two-stage sintering process of pre-sintering organic carbon coating and rotary kiln vapor deposition (CVD) carbon coating on the precursor, and then crushing and sieving to obtain the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material. The carbon coating layer of the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material prepared by this method is dense and uniform, exhibiting good electronic conductivity.
[0015] In step (2), the precursor is pretreated by pre-sintering organic carbon coating. This involves a short-term, low-temperature pre-sintering process at 530-570°C for 1-3 hours, which carbonizes the organic carbon source to form a porous carbon network and removes volatile substances from the precursor. This process also prevents the formation and growth of lithium manganese iron phosphate (LMFP) nuclei (i.e., no LMFP is generated during this process), effectively avoiding the problems of discontinuous conductive network and loose coating caused by simultaneous carbonization of the organic carbon source and formation of LMFP. The porous carbon network formed by the carbonization of the organic carbon source uses amorphous carbon as a framework to confine the precursor particles within nanoscale pores. This porous carbon network serves both to limit crystal size and improve conductivity. Pre-sintering removes volatile components from the precursor, preventing the coating from becoming loose and porous due to subsequent volatilization of these volatile components.
[0016] In step (3), the pre-sintered material is sintered in a rotary kiln for 5-7 hours after reaching the nucleation temperature of 680-780°C. During the 4-5 hour holding period at the nucleation temperature of 680-780°C, lithium manganese iron phosphate (LMFP) crystals nucleate and grow within the nanoscale pores of the porous carbon network. After 4-5 hours, the growth of the LMFP crystals is nearly complete, and the LMFP crystals adhere tightly to the porous carbon network without damaging its conductivity. Then, a reducing gas is introduced at 680-780°C for 1-2 hours. The reducing gas can be adsorbed onto the surface of the material and directly carbonized, filling the gaps in the porous carbon network and generating a complete and dense highly graphitized carbon coating layer, which significantly improves the electronic conductivity of the material. In this step, the use of a rotary kiln allows the material to be continuously turned over, increasing the contact area between the material and the reducing gas, improving production efficiency, and making the carbon coating layer tighter, thereby generating lithium manganese iron phosphate-carbon composite material.
[0017] In one embodiment, in step (1), the lithium source is one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium oxalate, and lithium acetate. The above-mentioned lithium source is suitable for conversion into lithium manganese iron phosphate.
[0018] In one embodiment, in step (1), the manganese source is one or a combination of at least two of manganese ferric phosphate, manganese nitrate, manganese carbonate, and manganese oxalate. The above-mentioned manganese source is suitable for conversion into lithium manganese ferric phosphate.
[0019] In one embodiment, in step (1), the iron source is one or a combination of at least two of the following: ferric manganese phosphate, ferric hydroxide, ferric phosphate, ferric nitrate, and ferrous oxalate. The above-mentioned iron source is suitable for conversion into lithium manganese iron phosphate.
[0020] In one embodiment, in step (1), the phosphorus source is one or a combination of at least two of the following: iron phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate. The above-mentioned phosphorus source is suitable for conversion into lithium manganese iron phosphate.
[0021] By selecting the lithium, manganese, iron, and phosphorus sources mentioned above, the nucleation and growth of lithium manganese iron phosphate (LMFP) crystals is avoided during the short-term pre-sintering process at low temperature; while during the high-temperature process of 680~780℃ in the rotary kiln, lithium manganese iron phosphate crystals can nucleate and grow.
[0022] In one embodiment, in step (1), the organic carbon source is one or a combination of at least two of glucose, sucrose, citric acid, and polyethylene glycol. Using the above-mentioned organic carbon source, a porous carbon network can be formed by carbonization during a low-temperature and short-term pre-sintering process, i.e., holding at 530~570℃ for 1~3 hours.
[0023] In one embodiment, in step (1), the solid content of the mixture obtained after adding water is 20-35 wt%. By controlling the solid content of the mixture after adding water, the raw materials can be better mixed and the particle size can be better controlled during grinding in the grinder, thereby controlling the particle size of the final product.
[0024] In one embodiment, in step (1), the particle size D50 of the precursor slurry is 0.4~0.45μm. After grinding, a precursor slurry with a particle size D50 of 0.4~0.45μm is obtained. If the particle size is too small after grinding, the grinding efficiency will be low and the production capacity will be affected; if the particle size is too large after grinding, there will be particle residue, which will make the solid phase reaction difficult in the subsequent reaction process and affect the performance of the finished product.
[0025] In one embodiment, in step (2), the protective atmosphere is either nitrogen or argon; in step (3), the protective atmosphere is either nitrogen or argon. It should be understood that the protective atmospheres in steps (2) and (3) may be the same or different.
[0026] In one embodiment, the kiln is one of a tube kiln, muffle kiln, rotary kiln, or roller kiln. Using the above-mentioned kiln facilitates low-temperature, short-term pre-sintering treatment of the precursor.
[0027] In one embodiment, in step (2), the temperature is increased to 530-570°C at a heating rate of 2-5°C / min; in step (3), the temperature is increased to 680-780°C at a heating rate of 2-5°C / min. The selection of the heating rate ensures that the material is heated uniformly to reach a specific temperature. In other embodiments, other heating rates may also be selected. It should be understood that the heating rates in steps (2) and (3) may be the same or different.
[0028] In one embodiment, in step (2), the pre-sintered material is naturally cooled to below 80°C before being removed; in step (3), the sintered material is naturally cooled to below 80°C before being removed. In other embodiments, other cooling technologies can be selected to cool the material to other temperatures so that the processed material can be removed.
[0029] In one embodiment, in step (3), the flow rate of the reducing gas is 0.02~0.2 L / min. Introducing a suitable flow rate of reducing gas enables the reducing gas to be adsorbed onto the surface of the material and directly carbonized, filling the gaps in the porous carbon network and generating a complete and dense highly graphitized carbon coating layer.
[0030] In one embodiment, in step (4), the sintered material is crushed by air jet milling or mechanical grinding. In other embodiments, other crushing methods may also be selected to crush the sintered material.
[0031] In one embodiment, in step (4), a 200-mesh sieve is used for sieving. The material on the sieve is then crushed and sieved again, and the material under the sieve is the discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material. In other embodiments, other sieves can be selected for sieving according to actual needs.
[0032] This disclosure also provides a discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material, characterized in that it is obtained by the synthesis method of any of the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate materials described above.
[0033] This disclosure discloses a lithium manganese iron phosphate material prepared by discontinuous vapor deposition carbon coating, namely, the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material. This material features a continuous conductive network coating, primary particles concentrated in the 150-200 nm range, and a spherical structure, reducing the specific surface area and improving the actual processing performance of lithium manganese iron phosphate. The discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material of this disclosure has a dense and uniform carbon coating layer, resulting in good electronic conductivity. The primary particle size is less than 200 nm; this smaller size shortens the lithium-ion migration path, leading to improved electrochemical performance. The low free carbon content facilitates close particle contact, thereby increasing the compaction density.
[0034] To better understand and implement this disclosure, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description
[0035] Figure 1 This is a charge-discharge curve of the discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material from Example 1;
[0036] Figure 2 The charge-discharge curves of lithium manganese iron phosphate material in Comparative Example 1 are shown.
[0037] Figure 3 SEM images of lithium manganese iron phosphate materials from Examples 1, 1, 3 and 6. Detailed Implementation
[0038] The present disclosure is further illustrated below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from conventional markets.
[0039] Example 1
[0040] This embodiment provides a method for synthesizing a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material, including the following specific steps:
[0041] (1) Preparation of precursors;
[0042] ①Ingredients:
[0043] Lithium carbonate, manganese carbonate, ferrous oxalate, ammonium dihydrogen phosphate, and glucose were weighed according to the stoichiometric ratio, with the molar ratio of each element being Li:Mn:Fe:P = 1.05:0.6:0.4:1. The amount of glucose added was 6% of the theoretical mass of pure phase lithium manganese iron phosphate.
[0044] ② Sand milling: The lithium source, manganese source, iron source, phosphorus source and glucose weighed in the "ingredients" step are slowly added to the sand mill in sequence. An appropriate amount of deionized water is added as a dispersion medium to make the solid content 25wt%. After grinding, a precursor slurry with a particle size D50 of 0.4μm is obtained.
[0045] ③ Spray drying. The precursor slurry is spray dried. The inlet temperature of the spray tower is set to 180℃, the outlet air temperature is set to 80℃, and the compressed air pressure is 0.4 MPa. After spray drying, the precursor is obtained.
[0046] (2) Pre-sintered organic carbon coating:
[0047] The precursor was placed in a tube furnace with nitrogen as a protective atmosphere for sintering. The temperature was increased to 570°C at a rate of 5°C / min and held at this temperature for 2 hours. After the holding period, the heating was stopped and the material was naturally cooled to below 80°C before being removed to obtain the pre-sintered material. Nitrogen gas was used as a protective gas throughout the entire process from the start of heating to the end of cooling.
[0048] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0049] The pre-sintered material was placed in a rotary kiln with nitrogen as the protective atmosphere for sintering. The temperature was increased to 720°C at a heating rate of 5°C / min and held at this temperature for 7 hours. After holding for 5 hours, acetylene gas was introduced at a flow rate of 0.05 L / min for 2 hours. After the holding period, heating was stopped and the material was allowed to cool naturally to below 80°C before being removed to obtain the sintered material. Nitrogen gas was used as the protective gas throughout the entire process from the start of heating to the end of cooling.
[0050] (4) Crushing and sieving:
[0051] The sintered material is crushed by mechanical grinding. The crushed material is then screened through a 200-mesh sieve. The material that passes through the sieve is crushed again, and the material that passes through the sieve is lithium manganese iron phosphate material, which is a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material.
[0052] Example 2
[0053] This embodiment provides a method for synthesizing a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material, including the following specific steps:
[0054] (1) Preparation of precursors;
[0055] ①Ingredients: Weigh lithium carbonate, manganese carbonate, ferrous oxalate, ammonium dihydrogen phosphate and glucose according to the stoichiometric ratio, where the molar ratio of each element is Li:Mn:Fe:P = 1.05:0.6:0.4:1, and the amount of glucose added is 4% of the theoretical mass of pure phase lithium manganese iron phosphate.
[0056] ②Grinding: Same as in Example 1.
[0057] ③ Spray drying: Same as in Example 1.
[0058] (2) Pre-sintered organic carbon coating:
[0059] The precursor was placed in a tube furnace with nitrogen as a protective atmosphere for sintering. The temperature was increased to 530°C at a rate of 5°C / min and held at this temperature for 3 hours. After the holding period, the heating was stopped and the material was naturally cooled to below 80°C before being removed to obtain the pre-sintered material. Nitrogen gas was used as a protective gas throughout the entire process from the start of heating to the end of cooling.
[0060] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0061] The pre-sintered material was placed in a rotary kiln with nitrogen as the protective atmosphere for sintering. The temperature was increased to 780°C at a heating rate of 5°C / min and held at this temperature for 7 hours. After holding for 5 hours, methane gas was introduced at a flow rate of 0.2 L / min for 2 hours. After holding for 2 hours, heating was stopped and the material was allowed to cool naturally to below 80°C before being removed to obtain the sintered material. Nitrogen gas was used as the protective gas throughout the entire process from the start of heating to the end of cooling.
[0062] (4) Crushing and sieving:
[0063] Same as Example 1.
[0064] Example 3
[0065] This embodiment provides a method for synthesizing a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material, including the following specific steps:
[0066] (1) Preparation of precursors;
[0067] ①Ingredients: Same as in Example 1.
[0068] ②Grinding: Same as in Example 1.
[0069] ③ Spray drying: Same as in Example 1.
[0070] (2) Pre-sintered organic carbon coating:
[0071] The precursor was placed in a tube furnace with nitrogen as a protective atmosphere for sintering. The temperature was increased to 550°C at a rate of 5°C / min and held at this temperature for 1 hour. After the holding period, the heating was stopped and the material was naturally cooled to below 80°C before being removed to obtain the pre-sintered material. Nitrogen gas was used as a protective gas throughout the entire process from the start of heating to the end of cooling.
[0072] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0073] The pre-sintered material was placed in a rotary kiln with nitrogen as the protective atmosphere for sintering. The temperature was increased to 680°C at a heating rate of 5°C / min and held at this temperature for 7 hours. After holding for 5 hours, acetylene gas was introduced at a flow rate of 0.05 L / min for 2 hours. After the holding period, heating was stopped and the material was allowed to cool naturally to below 80°C before being removed to obtain the sintered material. Nitrogen gas was used as the protective gas throughout the entire process from the start of heating to the end of cooling.
[0074] (4) Crushing and sieving:
[0075] Same as Example 1.
[0076] Comparative Example 1
[0077] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0078] (1) Preparation of precursors;
[0079] ①Ingredients: Same as in Example 1.
[0080] ②Grinding: Same as in Example 1.
[0081] ③ Spray drying: Same as in Example 1.
[0082] (2) Rotary kiln vapor deposition (CVD) carbon coating:
[0083] The precursor was sintered in a rotary kiln with nitrogen as the protective atmosphere. The temperature was increased to 720°C at a rate of 5°C / min and held at this temperature for 7 hours. After 5 hours of holding, acetylene gas was introduced at a flow rate of 0.05 L / min for 2 hours. After the holding period, heating was stopped and the material was allowed to cool naturally to below 80°C before being removed to obtain the sintered material. Nitrogen gas was used as the protective gas throughout the entire heating process from start to finish.
[0084] (3) Crushing and sieving:
[0085] The sintered material is crushed by mechanical grinding. The crushed material is then screened through a 200-mesh sieve. The material that passes through the sieve is crushed again, and the material that passes through the sieve is lithium manganese iron phosphate material.
[0086] Comparative Example 2
[0087] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0088] (1) Preparation of precursors;
[0089] ①Ingredients: Same as in Example 1.
[0090] ②Grinding: Same as in Example 1.
[0091] ③ Spray drying: Same as in Example 1.
[0092] (2) Pre-sintered organic carbon coating:
[0093] The precursor was placed in a tube furnace with nitrogen as a protective atmosphere for sintering. The temperature was increased to 570°C at a rate of 5°C / min and held at this temperature for 2 hours. After the holding period, the heating was stopped and the material was naturally cooled to below 80°C before being removed to obtain the pre-sintered material. Nitrogen gas was used as a protective gas throughout the entire process from the start of heating to the end of cooling.
[0094] (3) Crushing and sieving:
[0095] The pre-sintered material is crushed by mechanical grinding. The crushed material is then screened through a 200-mesh sieve. The material that passes through the sieve is crushed again, and the material that passes through the sieve is lithium manganese iron phosphate material.
[0096] Comparative Example 3
[0097] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0098] (1) Preparation of precursors:
[0099] ①Ingredients: Weigh lithium carbonate, manganese carbonate, ferrous oxalate, and ammonium dihydrogen phosphate according to the stoichiometric ratio, where the molar ratio of each element is Li:Mn:Fe:P = 1.05:0.6:0.4:1.
[0100] ② Sand milling: The lithium source, manganese source, iron source and phosphorus source weighed in the "ingredients" step are slowly added to the sand mill in sequence. An appropriate amount of deionized water is added as a dispersion medium to make the solid content 25wt%. After grinding, a precursor slurry with a particle size D50 of 0.4μm is obtained.
[0101] ③ Spray drying: Same as in Example 1.
[0102] (2) Pre-sintered organic carbon coating:
[0103] Same as Example 1.
[0104] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0105] The pre-sintered material was placed in a rotary kiln with nitrogen as the protective atmosphere for sintering. The temperature was increased to 720°C at a heating rate of 5°C / min and held at this temperature for 7 hours. After 5 hours of holding, acetylene gas was introduced at a flow rate of 0.05 L / min for 2 hours. After the holding period, heating was stopped, and the material was allowed to cool naturally to below 80°C before being removed to obtain the sintered material. Throughout the entire process, nitrogen gas was used as the protective gas from the start of heating to the end of cooling.
[0106] (4) Crushing and sieving:
[0107] Same as in Example 1.
[0108] Comparative Example 4
[0109] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0110] (1) Preparation of precursors:
[0111] ①Ingredients: Same as in Example 1.
[0112] ②Grinding: Same as in Example 1.
[0113] ③ Spray drying: Same as in Example 1.
[0114] (2) Pre-sintered organic carbon coating:
[0115] Same as Example 1.
[0116] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0117] The pre-sintered material is placed in a rotary kiln with nitrogen as the protective atmosphere for sintering. The temperature is raised to 720°C at a rate of 5°C / min and held at this temperature for 7 hours. After the holding period, heating is stopped and the material is naturally cooled to below 80°C before being removed. Nitrogen gas is used as the protective gas throughout the entire process from the start of heating to the end of cooling.
[0118] (4) Crushing and sieving:
[0119] Same as in Example 1.
[0120] Comparative Example 5
[0121] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0122] (1) Preparation of precursors:
[0123] ①Ingredients: Same as in Example 1.
[0124] ②Grinding: Same as in Example 1.
[0125] ③ Spray drying: Same as in Example 1.
[0126] (2) Pre-sintered organic carbon coating:
[0127] Same as Example 1.
[0128] (3) Carbon coating by tubular furnace chemical vapor deposition (CVD):
[0129] The pre-sintered material was placed in a tube furnace with nitrogen as the protective atmosphere for sintering. The temperature was increased to 720°C at a heating rate of 5°C / min and held at this temperature for 7 hours. After holding for 5 hours, acetylene gas was introduced at a flow rate of 0.05 L / min for 2 hours. After holding for 2 hours, heating was stopped and the material was allowed to cool naturally to below 80°C before being removed. Nitrogen gas was used as the protective gas throughout the entire heating process.
[0130] (4) Crushing and sieving:
[0131] Same as in Example 1.
[0132] Comparative Example 6
[0133] This comparative example provides a method for synthesizing lithium manganese iron phosphate material, including the following specific steps:
[0134] (1) Preparation of precursors:
[0135] ①Ingredients: Same as in Example 1.
[0136] ②Grinding: Same as in Example 1.
[0137] ③ Spray drying: Same as in Example 1.
[0138] (2) Pre-sintered organic carbon coating:
[0139] The precursor was placed in a rotary kiln with nitrogen as a protective atmosphere for sintering. The temperature was increased to 600°C at a rate of 5°C / min and held at this temperature for 2 hours. After the holding period, the heating was stopped and the material was naturally cooled to below 80°C before being removed to obtain the pre-sintered material. Nitrogen gas was used as a protective gas throughout the entire process from the start of heating to the end of cooling.
[0140] (3) Rotary kiln vapor deposition (CVD) carbon coating:
[0141] Same as Example 1.
[0142] (4) Crushing and sieving:
[0143] Same as in Example 1.
[0144] Performance testing
[0145] The following tests were performed on the discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate materials prepared in Examples 1-3 and the lithium manganese iron phosphate materials prepared in Comparative Examples 1-6, respectively:
[0146] Carbon content test: conducted in accordance with GB / T 223.69.
[0147] Volume resistivity test: conducted in accordance with Appendix D of GB / T 33822-2017.
[0148] Tap density test: Performed in accordance with GB / T 5162.
[0149] First discharge specific capacity and coulombic efficiency tests: conducted according to Appendix G of GB / T 33822-2017, with the battery charge and discharge voltage range of 2.0V~4.3V.
[0150] Please refer to Table 1 for the test results:
[0151] Table 1 Test results of lithium manganese iron phosphate materials
[0152]
[0153] In Comparative Example 1, the low-temperature and brief pre-sintering organic carbon coating step was skipped compared to Example 1; in Comparative Example 2, the rotary kiln vapor deposition (CVD) carbon coating was skipped compared to Example 1; in Comparative Example 3, no organic carbon source was added during the preparation of the precursor compared to Example 1; in Comparative Example 4, no reducing gas was introduced during the rotary kiln vapor deposition (CVD) carbon coating compared to Example 1; in Comparative Example 5, a tube furnace was used for vapor deposition (CVD) carbon coating compared to Example 1; in Comparative Example 6, the temperature was raised to 600°C during the pre-sintering organic carbon coating compared to Example 1.
[0154] As can be seen from Examples 1-3 and Comparative Examples 1 and 2, the performance of lithium manganese iron phosphate materials obtained by single sintering is inferior to that of lithium manganese iron phosphate materials obtained by organic carbon coating and discontinuous vapor deposition carbon coating obtained by rotary kiln vapor deposition (CVD). This is because the organic carbon coating of the present invention, through low-temperature short-term pre-sintering, can carbonize the organic carbon source to form a porous carbon network and avoid the generation and growth of lithium manganese iron phosphate (LMFP) crystal nuclei, effectively limiting particle growth. Furthermore, by performing rotary kiln vapor deposition (CVD) carbon coating on the pre-sintered material, the lithium manganese iron phosphate (LMFP) crystals nucleate and grow within the nanoscale pores of the porous carbon network after reaching the nucleation temperature. The lithium manganese iron phosphate (LMFP) crystals adhere tightly to the carbon layer without damaging the conductive network. The vapor deposition (CVD) carbon coating fills the gaps in the porous carbon network, generating a complete and dense highly graphitized carbon coating layer, which significantly improves the electronic conductivity of the material.
[0155] As can be seen from Examples 1-3 and Comparative Examples 3 and 4, only the addition of carbon sources and reducing atmospheres within the appropriate range of this disclosure will improve the material properties. Using only organic carbon sources or reducing gases for carbon coating will result in increased resistivity and decreased electrochemical performance. Comparative Example 3 did not add an organic carbon source, but only used acetylene, the reducing gas in rotary kiln vapor deposition (CVD), for carbon coating, resulting in increased resistivity and decreased electrochemical performance. Comparative Example 4 only used an organic carbon source for carbon coating, without using acetylene in rotary kiln vapor deposition (CVD), which also resulted in increased resistivity and decreased electrochemical performance. Comparative Example 3, using only rotary kiln vapor deposition (CVD) for carbon coating, had the worst effect. This is because the addition of organic carbon sources not only reduces particle size but also inhibits the oxidation of ferrous iron during ball milling.
[0156] As can be seen from Examples 1-3 and Comparative Example 5, the rotary kiln used in Examples 1-3 can continuously rotate during the chemical vapor deposition (CVD) process, increasing the contact area between the material and the reducing gas, resulting in a more uniform carbon layer deposition and thus better electrochemical performance of the material. Comparative Example 5, which uses a tube furnace for CVD carbon coating, exhibits high volume resistivity but relatively poor initial discharge specific capacity and coulombic efficiency.
[0157] By comparing Examples 1-3 with Comparative Example 6, it can be seen that adjusting the sintering regime within a reasonable range has little impact on the performance of the finished product. In Comparative Example 6, the temperature during the pre-sintering organic carbon coating process is 600°C, which exceeds the temperature range of this disclosure. In Comparative Example 6, lithium manganese iron phosphate is directly synthesized in the pre-sintering organic carbon coating step. Since the growth of lithium manganese iron phosphate (LMFP) and the formation of the carbon coating layer are carried out simultaneously, a continuous coating layer cannot be obtained. Moreover, the loose carbon coating layer formed on the material surface has a weaker effect on limiting particle size than in Examples 1-3. The subsequent rotary kiln vapor deposition (CVD) carbon coating only plays a role in improving conductivity.
[0158] This disclosure also provides charge-discharge curves for the lithium manganese iron phosphate materials of Example 1 and Comparative Example 1. Please refer to... Figure 1 In Example 1, the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material exhibits a first-cycle discharge specific capacity of 153.2 mAh / g and a coulombic efficiency of 97.2%. Please refer to Comparative Example 1, where the lithium manganese iron phosphate material has a first-cycle discharge specific capacity of only 122.2 mAh / g and a relatively low coulombic efficiency of only 91.3%.
[0159] This disclosure also includes SEM analysis of the lithium manganese iron phosphate materials prepared in Examples 1, 1, 3, and 6. Please refer to [link to relevant documentation]. Figure 3From the perspective of morphology, the morphology of the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material in Example 1 is that of a spherical lithium manganese iron phosphate material with a continuous conductive network coating and primary particles concentrated in the range of 150~200nm. The morphology of the lithium manganese iron phosphate materials in Comparative Examples 1, 3 and 6 does not have an obvious conductive network. In terms of particle size, Example 1 < Comparative Example 6 < Comparative Example 1 < Comparative Example 3. The reduced particle size of the discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material in Example 1 is beneficial to improving ionic conductivity, which also corresponds to the charge-discharge test results.
[0160] Compared to existing technologies, the method for synthesizing lithium manganese iron phosphate (LFP) materials with discontinuous vapor deposition carbon coating as described in this disclosure improves the material properties of LFP by obtaining a dense and uniform carbon coating layer through a two-stage sintering method of low-temperature and short-duration pre-sintering organic carbon coating and rotary kiln CVD vapor deposition coating. The LFP material prepared by discontinuous vapor deposition carbon coating as described in this disclosure has a continuous conductive network coating, primary particles concentrated in the 150-200 nm range, and a spherical material structure, reducing the specific surface area and improving the actual processing performance of LFP. The LFP material with discontinuous vapor deposition carbon coating as described in this disclosure has a dense and uniform carbon coating layer, exhibiting good electronic conductivity; the primary particle size is less than 200 nm, which shortens the lithium-ion migration path and improves electrochemical performance; the low free carbon content facilitates close particle contact, thereby increasing compaction density.
[0161] The embodiments described above are merely examples of several implementations of this disclosure, and while the descriptions are 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 this disclosure, and this disclosure also intends to include these modifications and variations.
Claims
1. A method for synthesizing a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material, characterized in that: Includes the following steps: (1) Preparation of precursor: Lithium source, manganese source, iron source, phosphorus source and organic carbon source are added to a grinding mill, and water is added. After grinding, a precursor slurry is obtained. The particle size D50 of the precursor slurry is 0.4~0.45μm. The molar ratio of each element in the precursor slurry is Li:Mn:Fe:P=1.05:x:1-x:1, where x=0.3~0.
7. The amount of organic carbon source added is 4~10wt% of the theoretical yield of lithium manganese iron phosphate. The precursor slurry is spray-dried to obtain the precursor. (2) Pre-sintered organic carbon coating: The precursor is placed in a kiln with a protective atmosphere, heated to 530~570℃, and held for 1~3h; after the holding period, heating is stopped and the material is cooled to obtain the pre-sintered material. (3) Rotary kiln vapor deposition carbon coating: The pre-sintered material is placed in a rotary kiln with a protective atmosphere, heated to 680~780℃, and held for 5~7h. After holding for 4~5h, a reducing gas is introduced. The reducing gas is one or a combination of at least two of acetylene, methane, ethanol vapor, and benzene vapor. The gas is introduced for 1~2h and the gas flow rate is 0.02~0.2L / min. After the holding period, heating is stopped and the material is cooled to obtain the sintered material. (4) Crushing and sieving: The sintered material is crushed and sieved to obtain a discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material.
2. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: The lithium source is one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium oxalate, and lithium acetate.
3. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (1), the manganese source is one or a combination of at least two of manganese iron phosphate, manganese nitrate, manganese carbonate, and manganese oxalate.
4. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (1), the iron source is one or a combination of at least two of the following: ferric manganese phosphate, ferric hydroxide, ferric phosphate, ferric nitrate, and ferrous oxalate.
5. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (1), the phosphorus source is one or a combination of at least two of the following: iron phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.
6. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (1), the organic carbon source is one or a combination of at least two of glucose, sucrose, citric acid, and polyethylene glycol.
7. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (1), the solid content of the mixture obtained after adding water is 20~35wt%.
8. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (2), the protective atmosphere is either nitrogen or argon; in step (3), the protective atmosphere is either nitrogen or argon.
9. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (2), the kiln is one of the following: tube kiln, muffle kiln, rotary kiln, and roller kiln.
10. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (2), the temperature is increased to 530-570℃ at a heating rate of 2-5℃ / min; in step (3), the temperature is increased to 680-780℃ at a heating rate of 2-5℃ / min.
11. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (2), the pre-sintered material is naturally cooled to below 80°C before being taken out; in step (3), the sintered material is naturally cooled to below 80°C before being taken out.
12. The method for synthesizing discontinuous vapor deposition carbon-coated lithium manganese iron phosphate material according to claim 1, characterized in that: In step (4), the sintered material is crushed by air jet milling or mechanical grinding; in step (4), a 200-mesh sieve is used for sieving, the material on the sieve is crushed and sieved again, and the material under the sieve is the discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material.
13. A discontinuous vapor-deposited carbon-coated lithium manganese iron phosphate material, characterized in that: The material was obtained by the method for synthesizing carbon-coated manganese iron lithium phosphate material by discontinuous vapor deposition as described in any one of claims 1 to 12.