Selective area patterned lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a selective patterned lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of batteries. The preparation method comprises the following steps: preparing an LMFP precursor, pre-sintering the LMFP precursor in an argon atmosphere, placing the LMFP precursor in an SLM-laser-microwave coupled cavity, regulating and controlling parameters such as oxygen partial pressure and laser power density, synchronously performing microwave heating, inducing plasma shock waves, spraying PTFE micro powder, performing He quenching, and finally annealing and screening to obtain a product. The positive electrode material has the advantages of zero carbon coating, deep oxygen vacancy, high electron conductivity, high pole piece density, and excellent high and low temperature performance and cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a selectively patterned lithium manganese iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) 0.6 Fe 0.4 PO4 (LMFP) is a cathode material for lithium-ion batteries. It combines the high safety and long cycle life of lithium iron phosphate (LFP) with the high voltage platform of lithium manganese phosphate (LMP). The theoretical discharge voltage can reach 3.8-4V and the theoretical capacity is 170mAh / g. It has broad application prospects in new energy vehicles, energy storage power stations and other fields.

[0003] However, the inherent defects of LMFP materials themselves severely restrict their commercialization process: on the one hand, the electronic conductivity of LMFP (approximately 10⁻⁶) is limited. -10 -10 -8 The extremely low S / cm ratio leads to significant polarization of the material during high-rate charge and discharge, resulting in insufficient capacity utilization. On the other hand, in order to improve conductivity, traditional preparation processes usually require the introduction of carbon sources (such as sucrose, acetylene black, graphene, etc.) for coating modification. However, the carbon coating layer increases the battery's internal resistance, reduces the electrode compaction density, and is prone to side reactions with the electrolyte during high-temperature storage or cycling, generating gas that causes the battery to bulge, affecting the battery's safety and cycle stability.

[0004] Therefore, developing a method for preparing LMFP cathode materials without the need for additional carbon sources, and improving properties such as electronic conductivity, has become a key technical problem that urgently needs to be solved for the industrial application of LMFP materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a selectively patterned lithium manganese iron phosphate cathode material and its preparation method, which has zero carbon coating and contains deep oxygen vacancies. The prepared cathode material has high electronic conductivity, high electrode density, and excellent high and low temperature performance and cycle stability of the battery.

[0006] The technical solution of this invention is as follows: On one hand, the present invention provides a method for preparing a selectively patterned lithium manganese iron phosphate cathode material, comprising the following steps: S1 preparation of LMFP precursor; S2 pre-calcination: Pre-calcined at 350℃ for 4 hours under argon atmosphere, then naturally cooled to obtain amorphous LMFP precursor; S3 Laser-Microwave Plasma Coupling Treatment: The pre-calcined material is placed in the SLM-laser-microwave coupling cavity, and the process parameters are adjusted as follows: oxygen partial pressure 8 × 10⁻⁶. -5atm, laser power density 5-8MW / cm² 2 The belt speed is 0.2 m / s, the single-point exposure is 0.5-2 ms, the spatial light modulator pixel is adjusted to 13 µm, and the grayscale is 180-220. After startup, the 2.45 GHz microwave bulk phase heating is synchronized, and a plasma shock wave is induced for 0.3 ms. ≤1 ms before the pulse ends, 0.1-0.5% of PTFE micro powder of the pre-calcined material mass is sprayed in, and He quenching jet is applied at 0.8 MPa. The surface temperature drops to <400℃ within 20 ms. S4 post-treatment: Anneal at 600℃ for 30 min under argon atmosphere, then sieve to obtain the final product.

[0007] Preferably, the specific process of step S1 is as follows: weigh Li2CO3, MnCO3, FeC2O4·2H2O and NH4H2PO4 in the molar ratio Li:Mn:Fe:P=(1-1.1):0.6:0.4:(1-1.03), ball mill and vacuum dry to obtain LMFP precursor dry powder.

[0008] Preferably, the ball milling speed is 400 rpm, the time is 4 h, and ethanol solvent is added.

[0009] Preferably, the vacuum drying temperature is 80°C.

[0010] Preferably, in step S2, during preheating, the heating rate is 5°C / min.

[0011] Preferably, in step S4, the sample is passed through a 200-mesh sieve.

[0012] On the other hand, the present invention provides a selectively patterned lithium manganese iron phosphate cathode material, which is prepared by the above-mentioned selectively patterned lithium manganese iron phosphate cathode material preparation method.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention is the first to simultaneously apply three methods—millisecond-level laser-microwave plasma coupling, SLM selective patterning, and laser-fluorine co-point injection—to LMFP. Under the premise of zero carbon coating, it greatly improves electronic conductivity, electrode compaction density, and capacity retention, significantly reduces high-temperature gas production, and eliminates three high-energy-consuming and high-polluting processes: carbonization, ALD, and NMP.

[0014] 2. This invention employs millisecond-level laser-microwave plasma dual-source coupling treatment on LMFP precursors. Long-pulse lasers induce plasma shock waves on the particle surface, simultaneously heating the bulk phase with microwaves, reducing the Vo formation energy by 0.3 eV and preventing grain growth. Simultaneously, this invention performs laser-fluorine co-point implantation, injecting PTFE micropowder ≤1 ms before the pulse ends, resulting in transient decomposition to form a LiF-rich self-limiting layer, replacing ALD fluorine implantation. Furthermore, in SLM selective patterning, this invention uses a spatial light modulator to directly write alternating patterns of 5µm conductive strips and 10µm insulating strips into the powder bed, realizing an "electronic highway." This invention achieves a zero-carbon coating high conductivity process, without adding any carbon source throughout the process, resulting in VOCs in the exhaust gas of approximately 0, achieving "decarbonized" conductivity. Detailed Implementation

[0015] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 The method for preparing the selectively patterned lithium manganese iron phosphate cathode material in this embodiment includes the following steps: S1 Preparation of LMFP precursor Weigh out 40.64g Li2CO3, 68.97g MnCO3, 71.95g FeC2O4·2H2O, and 115.03g NH4H2PO4 in a 500mL ball mill jar with a molar ratio of Li:Mn:Fe:P = 1.1:0.6:0.4:1. Add 200mL anhydrous ethanol and 500g Ø5mm zirconia balls. Run the planetary ball mill at 400rpm bidirectionally, reversing the direction every 30min, and mill for 4h. Then remove the jar and vacuum dry at 80℃ for 12h. Grind the powder to obtain a loose dry powder.

[0017] S2 preheating The dry powder was placed in an argon atmosphere box furnace and pre-calcined at 350°C for 4 hours with a heating rate of 5°C / min. After natural cooling, the amorphous LMFP precursor was obtained.

[0018] S3 laser-microwave plasma coupling treatment Equipment used: RFL-C6000M pulsed fiber laser (1070nm, peak 6kW, pulse width 1ms, frequency 200Hz); 2.45GHz microwave source (3kW, phase lag laser 40°); SLM (1024×768 pixels, conductive strip width 5µm, spacing 10µm).

[0019] Operation procedure: Place the pre-calcined material in the SLM-laser-microwave coupling cavity, and adjust the process parameters as follows: oxygen partial pressure 8×10. -5 ATM (oxygen probe closed loop), laser power density 6MW / cm² 2 (Spot size Ø 0.4mm), belt speed 0.2m / s, single-point exposure 1ms, spatial light modulator pixel adjusted to 13µm, grayscale 200. After startup, synchronous 2.45GHz microwave (3kW) bulk heating is applied, simultaneously inducing a plasma shock wave lasting 0.3ms; 0.8ms before the pulse ends, PTFE micro powder (D50=200nm, powder feeding rate 0.5g / min) accounting for 0.3% of the pre-calcined material mass is synchronously injected, He quenching jet at 0.8MPa, and the surface temperature drops to <400℃ within 20ms (infrared thermometer at 1kHz).

[0020] S4 Post-processing Under an argon atmosphere, the surface stress was eliminated by annealing at 600℃ for 30 min, and the product was passed through a 200-mesh sieve to obtain the final product, zero-carbon coated deep oxygen vacancy patterned LMFP (abbreviated as LMFP@Vo-F).

[0021] Example 2 The method for preparing the selectively patterned lithium manganese iron phosphate cathode material in this embodiment includes the following steps: S1 Preparation of LMFP precursor Weigh out 37.78g Li2CO3, 68.97g MnCO3, 71.95g FeC2O4·2H2O, and 115.03g NH4H2PO4 in a 500mL ball mill jar with a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Add 200mL anhydrous ethanol and 500g Ø5mm zirconia balls. Run the planetary ball mill at 380rpm bidirectionally, reversing the direction every 30min, and mill for 3h. Remove the jar and then vacuum dry at 75℃ for 12h. Grind the powder to obtain a loose dry powder.

[0022] S2 preheating The dry powder was placed in an argon atmosphere box furnace and pre-calcined at 320℃ for 5 hours with a heating rate of 6℃ / min. After natural cooling, the amorphous LMFP precursor was obtained.

[0023] S3 laser-microwave plasma coupling treatment The pre-calcined material was placed in an SLM-laser-microwave coupled cavity, and the process parameters were adjusted as follows: oxygen partial pressure 6 × 10⁻⁶. - 5 atm (oxygen probe closed loop), laser power density 5MW / cm² 2(Spot size Ø 0.4mm), belt speed 0.15m / s, single-point exposure 0.5ms, spatial light modulator pixel adjusted to 11µm, grayscale 180. After startup, synchronous 2.4GHz microwave (3kW) bulk heating is applied, simultaneously inducing a plasma shock wave lasting 0.4ms; 0.8ms before the pulse ends, PTFE micro powder (D50=200nm, powder feeding rate 0.5g / min) accounting for 0.2% of the pre-calcined material mass is synchronously injected, He quenching jet at 0.6MPa, and the surface temperature drops to <400℃ within 15ms (infrared thermometer at 1kHz).

[0024] S4 Post-processing Under an argon atmosphere, the surface stress was eliminated by annealing at 580℃ for 40 min, and the product was passed through a 200-mesh sieve to obtain the final product, zero-carbon coated deep oxygen vacancy patterned LMFP (abbreviated as LMFP@Vo-F).

[0025] Example 3 The method for preparing the selectively patterned lithium manganese iron phosphate cathode material in this embodiment includes the following steps: S1 Preparation of LMFP precursor Weigh out 36.95g Li2CO3, 38.97g MnCO3, 71.95g FeC2O4·2H2O, and 117.33g NH4H2PO4 in a 500mL ball mill jar with a molar ratio of Li:Mn:Fe:P=1:0.6:0.4:1.02. Add 200mL anhydrous ethanol and 500g Ø5mm zirconia balls. Run the planetary ball mill at 420rpm bidirectionally, reversing the direction every 30min, and mill for 5h. Then remove the jar and vacuum dry at 85℃ for 12h. Grind the powder to obtain a loose dry powder.

[0026] S2 preheating The dry powder was placed in an argon atmosphere box furnace and pre-calcined at 380 °C for 3 hours with a heating rate of 4 °C / min. After natural cooling, an amorphous LMFP precursor was obtained.

[0027] S3 laser-microwave plasma coupling treatment The pre-calcined material was placed in an SLM-laser-microwave coupled cavity, and the process parameters were adjusted as follows: oxygen partial pressure 7 × 10⁻⁶. - 5 ATM (oxygen probe closed loop), laser power density 8MW / cm² 2(Spot size Ø 0.4mm), belt speed 0.25m / s, single-point exposure 2ms, spatial light modulator pixel adjusted to 15µm, grayscale 220. After startup, synchronous 2.5GHz microwave (3kW) bulk heating is applied, simultaneously inducing a plasma shock wave lasting 0.4ms; 0.8ms before the pulse ends, PTFE micro powder (D50 = 200 nm, powder feeding rate 0.5 g / min) accounting for 0.5% of the pre-calcined material mass is synchronously injected, He quenching jet at 1MPa, and the surface temperature drops to <400℃ within 25ms (infrared thermometer at 1kHz).

[0028] S4 Post-processing Under an argon atmosphere, the surface stress was eliminated by annealing at 620℃ for 20 min, and the product was passed through a 200-mesh sieve to obtain the final product, zero-carbon coated deep oxygen vacancy patterned LMFP (abbreviated as LMFP@Vo-F).

[0029] Comparative Example 1 The traditional method for preparing carbon-coated lithium manganese iron phosphate cathode materials includes the following steps: S1 Preparation of LMFP precursor Weigh out 40.64g Li₂CO₃, 68.97g MnCO₃, 71.95g FeC₂O₄·2H₂O, and 115.03g NH₄H₂PO₄ in a 500mL ball mill jar, and add 14.58g C₆H₂O. (Li:Mn:Fe:P = 1.1:0.6:0.4:1) 12 O6·H2O, 200mL anhydrous ethanol, 500g Ø5mm zirconia balls, planetary ball mill running at 400rpm bidirectionally, reversing direction every 30min, ball milling for 4h and then removing; subsequently vacuum drying at 80℃ for 12h, and grinding to obtain loose dry powder.

[0030] S2 sintering The dry powder was placed in an argon atmosphere box furnace and sintered at 350℃ for 2 hours and 680℃ for 6 hours, with a heating rate of 5℃ / min. After natural cooling, carbon-coated LMFP was obtained.

[0031] The cathode materials prepared in Examples 1-3 and Comparative Example 1 were tested. The carbon content was detected using a high-frequency infrared carbon-sulfur analyzer; the surface resistance of the electrode sheet was detected using the four-probe method; and the areal density of the cathode material was 20 mg / cm³ when the surface resistance of the electrode sheet was tested. 2 The test results are shown in Table 1: Table 1. Test results of the cathode materials prepared in Examples 1-3 and Comparative Example 1 The cathode materials of Examples 1-3 and Comparative Example 1 were directly dry-formed into films, composited with aluminum foil current collectors, and assembled into 2032 coin cells for testing. Performance tests were then conducted, and the results are shown in Table 2. Table 2 Performance test results of the assembled batteries in Examples 1-3 and Comparative Example 1 As can be seen from Tables 1-2, the performance of the cathode material in Comparative Example 1 is inferior to that in Examples 1-3. The core reason lies in the defects in material structure and interface characteristics caused by differences in the preparation process, which are analyzed in detail below: (1) Carbon content and electronic conductivity Comparative Example 1 has a carbon content of 3.2 wt.%, which is much higher than the <0.05 wt.% of the Example. This is because traditional processes rely on carbon source coating to improve conductivity, but the carbon layer is an insulating / semiconductor phase and is prone to agglomeration to form an uneven coating layer, resulting in discontinuous electron transport channels.

[0032] The embodiment constructs a deep oxygen vacancy and selected area patterned structure through "laser-microwave plasma coupling processing": oxygen vacancies, as electronic defect sites, can significantly reduce the electronic transition energy barrier, while the SLM-controlled micro-patterned structure forms a directional electron transport channel, achieving a density of 1.1 × 10⁻⁶ without carbon coating. -7 -1.5×10 -7 Electronic conductivity in S / cm.

[0033] (2) Electrode surface resistance and compaction density The surface resistivity of the electrode in Comparative Example 1 was 0.85 Ω / sq, higher than that in the Example 1. This is because the porous nature of the carbon layer increases the resistance to electron transport within the electrode, making it difficult to form a highly efficient conductive network even with a high carbon content. After cold pressing at 300 MPa, the electrode density of Comparative Example 1 was only 2.35 g / cm³. 3 The density is lower than that of the example. This is because the carbon layer cannot be effectively densified during the pressing process and is prone to forming interfacial voids with the active material, which reduces the volumetric energy density of the electrode; while the zero-carbon design of the example group avoids the interference of the carbon layer, the contact between the active material particles is closer, and the compaction density is significantly improved.

[0034] (3) Charge / discharge capacity (0.1C / 10C) The 0.1C discharge capacity of Comparative Example 1 is only 152 mAh·g. -1 The efficiency is lower than that of the previous embodiment. This is because although traditional carbon coatings can improve electron conduction, they can hinder the adsorption and diffusion of lithium ions on the surface of the active material, resulting in some active sites being unable to participate in the electrochemical reaction; the deep oxygen vacancies of the previous embodiment can provide additional lithium ion adsorption sites, and the patterned structure constructs short-range ion diffusion channels, thereby increasing the utilization rate of the active material.

[0035] Comparative Example 1 has a 10C high-rate capacity of only 120 mAh·g -1 The capacity is significantly lower than that of the example. This is because at high magnification, the low electronic conductivity and slow ion diffusion rate of Comparative Example 1 lead to increased polarization and rapid capacity decay; while the "electron-ion dual transport channel" of the example significantly reduces polarization and maintains capacity at high magnification.

[0036] (4) Low-temperature discharge capacity (-40℃, 0.2C) Comparative Example 1: Low-temperature capacity is only 95 mAh·g -1 The efficiency is significantly lower than that of the example. This is because lithium-ion diffusion kinetics decrease sharply at low temperatures, and the carbon layer at the interface with the active material in Comparative Example 1 easily forms a lithium-ion deposition barrier, further hindering diffusion; the deep oxygen vacancies in the example can reduce the lithium-ion diffusion activation energy, and even at low temperatures, a high ion diffusion rate can still be maintained, ensuring effective capacity utilization.

[0037] (5) High temperature cycling stability (55℃, 1C cycle 1000 times) The capacity retention rate of Comparative Example 1 was only 83.6%, lower than that of the Example. This is because at high temperatures, the carbon layer of Comparative Example 1 is prone to oxidation side reactions with the electrolyte (such as carbon combustion and electrolyte decomposition), leading to SEI film thickening and destruction of the active material structure. The zero-carbon design of the Example avoids the side reactions between the carbon layer and the electrolyte from the root, and the surface protective layer formed by PTFE micropowder modification inhibits electrolyte erosion, the deep oxygen vacancies stabilize the crystal structure, and the loss of active material during cycling is significantly reduced.

[0038] (6) Gas production during high-temperature storage (60℃, 30 days) Comparative Example 1 produced 0.25 mL·Ah of gas. -1 The results are significantly better than those of the embodiments. This is because, under high temperature and full charge conditions, the carbon layer in Comparative Example 1 reacts violently with the electrolyte interface, producing gases such as CO and CO2; the zero-carbon surface of the embodiments reduces the interfacial reaction sites, and the hydrophobic protective layer formed by PTFE micropowder hinders the contact between the electrolyte and the surface of the active material, significantly suppressing gas production and improving battery storage safety.

Claims

1. A method for preparing a selectively patterned lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: S1 preparation of LMFP precursor; S2 pre-calcination: Pre-calcination at 320-380℃ for 3-5 hours under argon atmosphere, followed by natural cooling, to obtain amorphous LMFP precursor; S3 Laser-Microwave Plasma Coupling Treatment: The pre-calcined material is placed in the SLM-laser-microwave coupling cavity, and the process parameters are adjusted as follows: oxygen partial pressure 6 × 10⁻⁶. -5 -8×10 -5 atm, laser power density 5-8MW / cm² 2 The belt speed is 0.15-0.25 m / s, the single-point exposure is 0.5-2 ms, the spatial light modulator pixel is adjusted to 11-15 µm, and the grayscale is 180-220; after startup, the 2.4-2.5 GHz microwave bulk phase heating is synchronized, and a plasma shock wave is induced for 0.2-0.4 ms; ≤1 ms before the pulse ends, 0.1-0.5% of PTFE micro powder of the pre-calcined material mass is sprayed in, and He quenching jet is applied at 0.6-1 MPa, and the surface temperature drops to <400℃ within 15-25 ms; S4 post-treatment: Anneal at 580-620℃ for 20-40 min under argon atmosphere, then sieve to obtain the final product.

2. The method for preparing selectively patterned lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The specific process of step S1 is as follows: weigh Li2CO3, MnCO3, FeC2O4·2H2O and NH4H2PO4 in the molar ratio Li:Mn:Fe:P=(1-1.1):0.6:0.4:(1-1.03), ball mill and vacuum dry to obtain LMFP precursor dry powder.

3. The method for preparing selectively patterned lithium manganese iron phosphate cathode material as described in claim 2, characterized in that, The ball milling speed is 380-420 rpm, the time is 3-5 hours, and ethanol solvent is added.

4. The method for preparing selectively patterned lithium manganese iron phosphate cathode material as described in claim 2, characterized in that, The vacuum drying temperature is 75-85℃.

5. The method for preparing selectively patterned lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S2, during preheating, the heating rate is 4-6℃ / min.

6. The method for preparing selectively patterned lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S4, the sample is passed through a 200-mesh sieve.

7. A selectively patterned lithium manganese iron phosphate cathode material, characterized in that, It is prepared by the selective patterning lithium manganese iron phosphate cathode material as described in any one of claims 1-6.

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