Lithium manganese iron phosphate positive electrode material coated with oxide solid electrolyte and preparation method of lithium manganese iron phosphate positive electrode material

Abstract

The invention discloses an oxide solid electrolyte coated lithium manganese iron phosphate positive electrode material and a preparation method thereof, and relates to the technical field of lithium manganese iron phosphate preparation. The lithium manganese iron phosphate battery comprises a lithium manganese iron phosphate core and an oxide solid electrolyte coating layer, the oxide solid electrolyte coating layer comprises Li < 7 > La < 3 > Zr < 2 > O < 12 > (LLZO), Li < 6.75 > La < 3 > Zr < 1.75 > Ta < 0.25 > O < 12 > (LLZTO, Li < 3 > x La < 2 / 3-x > TiO < 3 > (LLTO), Li < 3 > BO < 3 > (LBO) and Li < 1 + x > Al < x > Ti < 2-x > (PO4) < 3 > (LATP); the lithium manganese iron phosphate core is LiMnxFe1-xPO4, wherein x is more than or equal to 0.5 and less than or equal to 0.8; the existing main problem of lithium manganese iron phosphate is solved, the comprehensive performance is improved, and the commercial application is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of lithium manganese iron phosphate preparation, and in particular to a lithium manganese iron phosphate positive electrode material coated with an oxide solid electrolyte and a preparation method thereof. Background Art

[0002] With the rapid development of portable electronic devices and electric vehicles, the demand for efficient, safe and environmentally friendly energy storage systems is growing. Among the many candidate cathode materials, lithium manganese iron phosphate (LiMnFePO 4 ) has become a research hotspot due to its excellent performance. 4 (LFP) has been widely used in the field of lithium batteries due to its excellent cycle performance, structural stability, safety and low cost. However, the low operating voltage (3.4V) and energy density (580Wh / kg) of LFP have severely restricted the development of LFP.

[0003] Compared with LFP, LiMnPO also has an olivine structure. 4 (LMP) has a higher working voltage (4.1V) and energy density (701Wh / kg). However, LMP has extremely low conductivity (<10-10S / cm) and Li + Diffusion coefficient (<10-16cm 2 / S). At the same time, during the charge and discharge process, Mn 3+ The resulting Jahn-Teller effect also has a great impact on the structural stability of LMP, thereby reducing the electrochemical performance of LMP.

[0004] Combining the above two materials, the researchers synthesized LiMn with Fe-doped LMP. 1-x Fe x PO 4 (LMFP) material, the study found that Fe doping replaced part of Mn, which not only improved the conductivity of the material, but also suppressed the 3+ The Jahn-Teller effect enables LMFP to have the advantages of both the high energy density of LMP and the good kinetic performance of LFP. Therefore, it is considered to be an ideal upgraded product of the cathode material LFP in the future.

[0005] Lithium manganese iron phosphate (LiMnFePO 4) is a lithium-ion battery cathode material with high energy density and good thermal stability, but its main disadvantages include low electronic conductivity and lithium ion diffusion coefficient, which seriously restricts its rate performance; the structural Jahn-Teller effect may cause structural distortion during the charge and discharge process, affecting the cycle stability; manganese dissolution will occur during the charge and discharge process of lithium manganese iron phosphate batteries, especially under the existing technical conditions, manganese dissolution is a problem that cannot be ignored, which directly affects the voltage platform, energy density, cycle life and safety of the battery. The present invention proposes a lithium manganese iron phosphate cathode material coated with an oxide solid electrolyte and a preparation method thereof to solve the existing main problems of lithium manganese iron phosphate, improve its comprehensive performance and promote its commercial application. Summary of the invention

[0006] The purpose of the present invention is to provide a lithium manganese iron phosphate positive electrode material coated with an oxide solid electrolyte and a preparation method thereof, so as to solve the main existing problems of lithium manganese iron phosphate, improve its comprehensive performance and promote its commercial application.

[0007] In order to solve the above problems, the present invention adopts the following technical means: A lithium iron manganese phosphate positive electrode material coated with an oxide solid electrolyte, comprising a lithium iron manganese phosphate core and an oxide solid electrolyte coating layer; The oxide solid electrolyte coating layer includes Li 7 La 3 Zr 2 O 12 (LLZO), Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZTO), Li 3x La 2 / 3-x TiO 3 (LLTO), Li 3 BO 3 (LBO), Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP); The lithium iron manganese phosphate core is LiMn x Fe 1-x PO 4 , where 0.5≤x≤0.8.

[0008] Preferably, the thickness of the oxide solid electrolyte coating layer is 2-10 nm.

[0009] In addition, a method for preparing the aforementioned oxide solid electrolyte-coated lithium manganese iron phosphate positive electrode material comprises the following steps: S1. Preparing oxide solid electrolyte precursor slurry; S2. adding the lithium manganese iron phosphate cathode powder to the precursor slurry to form a mixed slurry, and drying the mixed slurry to obtain a powder; S3. Sinter the powder, and then perform air flow crushing after sintering.

[0010] Preferably, in step S1, the oxide solid electrolyte comprises an oxide raw material, a soluble salt and a dispersant; The oxide raw material includes LiCO 3 、TiO 2 ,La 2 O 3 、Al 2 O 3 、ZrO 2 、 2 O 5 One of; The soluble salts include LiOH, LiNO 3 、Al(NO 3 ) 3 、TiCl 4 , H 3 PO 4 、Zr(NO 3 ) 4 、La(NO 3 ) 3 One of; The dispersant includes one or more of polyethylene glycol, cetyltrimethylammonium bromide and polyvinyl pyrrolidone.

[0011] Furthermore, the particle size D50 of the precursor slurry is 200-400 nm.

[0012] Furthermore, the solid content of the mixed slurry is 38-42%, and the mixed slurry is ball-milled before drying, and D50 is controlled at 25-50 μm.

[0013] Furthermore, the mixed slurry is spray dried.

[0014] Furthermore, in step S3, the sintering temperature is 780-850° C., and the sintering time is 3-10 hours.

[0015] Furthermore, in step S3, the air pressure of the air flow milling is 0.4-0.6 MPa, and the target particle size D50 of the milling is 1.5-4 μm.

[0016] The present invention has the following beneficial effects during application: The oxide solid electrolyte coating layer suppresses the John-Teller effect, so that the positive electrode active material maintains structural stability during the cycle; The in-situ produced solid electrolyte coating can significantly inhibit the dissolution of manganese in the lithium manganese iron phosphate during the charge and discharge process, thus improving its electrochemical performance. The solid electrolyte with high ionic conductivity improves the lithium ion migration at the interface and improves the rate performance of lithium manganese iron phosphate; The solid electrolyte coating also increases the excess active lithium, which is equivalent to replenishing lithium in the positive electrode, thereby increasing the capacity; This coating layer can also improve the interface contact between the oxide solid electrolyte system and the lithium manganese iron phosphate positive electrode material in the solid-state battery.

[0017] In summary, the in-situ generated oxide solid electrolyte coating layer can significantly improve the cycle stability and electrochemical performance of lithium iron manganese phosphate materials at high voltages, reduce side reactions with the electrolyte, and is suitable for high energy density lithium ion batteries. In addition, this coating layer can also improve the interface contact between the oxide solid electrolyte system and the lithium iron manganese phosphate positive electrode material in the solid-state battery. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0019] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0021] A lithium iron manganese phosphate positive electrode material coated with an oxide solid electrolyte, comprising a lithium iron manganese phosphate core and an oxide solid electrolyte coating layer; The oxide solid electrolyte coating layer includes Li 7 La 3 Zr 2 O 12 (LLZO), Li 6.75 La 3 Zr 1.75 Ta 0.25O 12 (LLZTO), Li 3x La 2 / 3-x TiO 3 (LLTO), Li 3 BO 3 (LBO), Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP); The lithium iron manganese phosphate core is LiMn x Fe 1-x PO 4 , where 0.5≤x≤0.8.

[0022] Preferably, the thickness of the oxide solid electrolyte coating layer is 2-10 nm.

[0023] In addition, a method for preparing the aforementioned oxide solid electrolyte-coated lithium manganese iron phosphate positive electrode material comprises the following steps: S1. Prepare oxide solid electrolyte precursor slurry.

[0024] The oxide solid electrolyte comprises an oxide raw material, a soluble salt and a dispersant; The oxide raw material includes LiCO 3 、TiO 2 ,La 2 O 3 、Al 2 O 3 、ZrO 2 、 2 O 5 One of; The soluble salts include LiOH, LiNO 3 、Al(NO 3 ) 3 、TiCl 4 , H 3 PO 4 、Zr(NO 3 ) 4 、La(NO 3 ) 3 One of; The dispersant includes one or more of polyethylene glycol, cetyltrimethylammonium bromide and polyvinyl pyrrolidone.

[0025] And the particle size D50 of the precursor slurry is 200~400nm.

[0026] S2. Adding lithium manganese iron phosphate positive electrode powder to the precursor slurry to form a mixed slurry, and drying the mixed slurry to obtain powder.

[0027] The solid content of the mixed slurry here is 38-42%. The mixed slurry is ball-milled before drying, and D50 is controlled at 25-50 μm.

[0028] And the mixed slurry here is spray dried.

[0029] S3. Sinter the powder, and then perform air flow crushing after sintering.

[0030] Specifically, during sintering, the sintering temperature is 780-850°C, the sintering time is 3-10 hours, the air pressure of the air flow milling is 0.4-0.6 MPa, and the target particle size D50 of the milling is 1.5-4 μm.

[0031] A more detailed description is given below in conjunction with the specific preparation process.

[0032] Example 1 a. Weigh 1kg of LiMnFePO 4 , 15.86 g of Li 2 CO 3 , 30g of La 2 O 3 and 15.13 g of ZrO 2 stand-by; b. Weigh the Li 2 CO 3 ,La 2 O 3 、ZrO 2 Add 100 ml of deionized water and grind until the particle size D50 reaches less than 400 nm; c. Add the ground slurry to 1600g of deionized water, pour into an ultrasonic stirring device, add 50g of hexadecyltrimethylammonium bromide, and continue to add the weighed LiMnFePO 4 , ultrasonic stirring for 2h; d. Spray dry the stirred slurry, the atomizer frequency is 265±10Hz (GL-5 spray dryer), and the spray particle size D50 is adjusted to control 30±10μm; e. Load the spray material into a graphite sagger and place it in a box-type atmosphere furnace for sintering (nitrogen protection). Control the oxygen content to ≤30ppm, the sintering temperature to 800℃, and keep it warm for 10 hours. After the temperature drops, take out the sintered material for inspection.

[0033] Example 2 a. Weigh 1kg of LiMnFePO 4 , 7.71 g of Li 2CO 3 , 21.72 g of TiO 2 , 56.19 g of (NH 4 ) 2 HPO 4 , 5.85 g of AlPO 4 And 50g of polyvinyl pyrrolidone for standby use; b. Weigh the Li 2 CO 3 、TiO 2 NH 4 ) 2 HPO 4 、AlPO 4 Add 120 ml of ethanol and grind until the particle size D50 reaches less than 400 nm; c. Add the ground slurry to 2750g deionized water, pour into an ultrasonic stirring device, add 50g polyvinyl pyrrolidone, and continue to add the weighed LiMnFePO 4 , ultrasonic stirring for 2h; d. Spray dry the stirred slurry, the atomizer frequency is 265±10Hz (GL-5 spray dryer), and the spray particle size D50 is adjusted to control 30±10μm; e. Load the spray material into a graphite sagger and place it into a box-type atmosphere furnace for sintering (nitrogen protection). Control the oxygen content to ≤30ppm, the sintering temperature to 820℃, and keep it warm for 10 hours. After the temperature drops, take out the sintered material for inspection.

[0034] Example 3 a. Weigh 1kg of LiMnFePO 4 , 30.54 g of Li 2 CO 3 , 50g of La 2 O 3 , 20.56 g of LiNO 3 and 30.26g of Ta 2 O 5 stand-by; b. Weigh the Li 2 CO 3 ,La 2 O 3 、 2 O 5 and LiNO 3 Add 100 ml of deionized water and grind until the particle size D50 reaches less than 400 nm; c. Add the ground slurry to 3025g of deionized water, pour into an ultrasonic stirring device, add 50g of polyethylene glycol, and continue to add the weighed LiMnFePO 4, ultrasonic stirring for 2h; d. Spray dry the stirred slurry, the atomizer frequency is 265±10Hz (GL-5 spray dryer), and the spray particle size D50 is adjusted to control 30±10μm; e. Load the spray material into a graphite sagger and place it in a box-type atmosphere furnace for sintering (nitrogen protection). Control the oxygen content to ≤30ppm, the sintering temperature to 800℃, and keep it warm for 10 hours. After the temperature drops, take out the sintered material for inspection.

[0035] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium manganese iron phosphate positive electrode material coated with an oxide solid electrolyte, characterized in that: It includes a lithium manganese iron phosphate core and an oxide solid electrolyte coating; The oxide solid electrolyte coating layer includes Li7La3Zr2O 12 (LLZO), Li 6.75 LqCy 1.75 Ta 0.25 O 12 (LLZTO), Li 3x La 2 / 3-x TiO3(LLTO), Li3BO3(LBO), Li 1+x Al x Ti 2-x (PO4)3(LATP); The lithium iron manganese phosphate core is LiMn x Fe 1-x PO4, where 0.5≤x≤0.

8.

2. The lithium iron manganese phosphate positive electrode material coated with an oxide solid electrolyte according to claim 1, characterized in that: The thickness of the oxide solid electrolyte coating layer is 2-10 nm.

3. A method for preparing a lithium manganese iron phosphate positive electrode material coated with an oxide solid electrolyte according to any one of claims 1 or 2, characterized in that: The following steps are involved: S1. Preparing oxide solid electrolyte precursor slurry; S2. adding the lithium manganese iron phosphate cathode powder to the precursor slurry to form a mixed slurry, and drying the mixed slurry to obtain a powder; S3. Sinter the powder, and then perform air flow crushing after sintering.

4. The preparation method according to claim 3, characterized in that: In the step S1, the oxide solid electrolyte includes an oxide raw material, a soluble salt and a dispersant; The oxide raw material includes one of LiCO3, TiO2, La2O3, Al2O3, ZrO2, and Ta2O5; The soluble salt includes one of LiOH, LiNO3, Al(NO3)3, TiCl4, H3PO4, Zr(NO3)4, and La(NO3)3; The dispersant includes one or more of polyethylene glycol, cetyltrimethylammonium bromide and polyvinyl pyrrolidone.

5. The preparation method according to claim 3 or 4, characterized in that: The particle size D50 of the precursor slurry is 200-400 nm.

6. The preparation method according to claim 3, characterized in that: The solid content of the mixed slurry is 38-42%. The mixed slurry is ball-milled before drying, and D50 is controlled at 25-50 μm.

7. The preparation method according to claim 3 or 6, characterized in that: The mixed slurry is spray dried.

8. The preparation method according to claim 3, characterized in that: In step S3, the sintering temperature is 780-850° C., and the sintering time is 3-10 hours.

9. The preparation method according to claim 3 or 8, characterized in that: In the step S3, the air pressure of the air flow milling is 0.4-0.6 MPa, and the target particle size D50 of the milling is 1.5-4 μm.