Method for continuous microwave-assisted hydrothermal synthesis of LiFe1-xMnxPO4 nanocrystals

Abstract

The invention relates to the field of lithium ion batteries, in particular to a method for continuous microwave-assisted hydrothermal synthesis of LiFe < 1-x > Mn < x > PO4 nanocrystals. The method comprises the following steps: (1) synthesizing Li3PO4 turbid liquid by using a micro-channel reactor; and (2) taking the Li3PO4 suspension as a precursor, adding FeSO4. 7H2O and MnSO4.H2O into the suspension, introducing the suspension into a tubular delay reactor, and carrying out microwave-assisted heating to realize rapid and continuous synthesis of the LiFe1-xMnxPO4 solid solution with small size and uniform particle size distribution. The microchannel reactor is used for synthesizing Li3PO4 particles, micromixing can provide a uniform supersaturated environment for nucleation of the Li3PO4 particles, so that the particles with small size and uniform particle size distribution are more favorably generated, and finally, the tubular delay reactor and microwave-assisted heating are combined to quickly and continuously synthesize the LiFe1-xMnxPO4 solid solution with uniform and fine grain size. Meanwhile, continuous feeding can be achieved, so that continuous synthesis of LiFe < 1-x > MnxPO4 is achieved, and the problem that continuous synthesis is difficult to achieve through traditional hydrothermal synthesis can be solved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystals method. Background Art

[0002] In response to global warming, countries around the world have successively issued a timetable for banning the sale of fuel vehicles (Nature, 2016, 534 (7609): 631-639.). As an alternative, hybrid electric vehicles and pure electric vehicles urgently need safe, reliable, high-performance lithium-ion batteries (Angewandte Chemie International Edition, 2018, 57 (19): 5301-5305; Nature Chemistry, 2015, 7 (1): 19-29.). Lithium-ion batteries are mainly composed of four parts: positive electrode, negative electrode, electrolyte and diaphragm. Among them, the positive electrode is the most important component, and its performance determines the performance of lithium-ion batteries. LiFePO4 with olivine structure is currently recognized as the safest positive electrode material (Energy & Environmental Science, 2011, 4: 805). Not long ago, BYD released a blade battery based on LiFePO4 positive electrode material. In the puncture test, there was no open flame or smoke on the surface of the battery, and the surface temperature of the battery was only 30℃~60℃, which shows that LiFePO4 has unparalleled safety as a positive electrode material for lithium-ion batteries. In addition, the domestic market lithium iron phosphate battery installation volume has surpassed ternary lithium batteries for three consecutive years. However, the theoretical energy density of LiFePO4 is relatively low (586Wh kg -1 ), which is difficult to meet the needs of current high-end electric vehicles. LiMnPO4 with olivine structure has a higher theoretical energy density (701Wh kg -1 ), but the Jahn-Taylor effect leads to very poor electrochemical performance. Therefore, the synthesis of LiFe 1-x Mn x PO4 solid solution is the fundamental way to achieve high energy density.

[0003] At present, the penetration rate of new energy electric vehicles in northern my country is relatively low, mainly because commercial lithium iron phosphate is mainly synthesized by solid phase method, with coarse grains and small active area, resulting in unsatisfactory low-temperature electrochemical performance. The key to solving this problem is to develop LiFe 1-x Mn xPO4 electrode material, thereby increasing the active area at low temperatures. Microwave-assisted hydrothermal method is an important method for preparing ultrafine materials in liquid phase reactions. This method uses water as a solvent in a closed reactor to heat the reaction system to create a high temperature and high pressure reaction environment, so that the usually insoluble or insoluble substances dissolve and react chemically. The operation is simple, and the prepared material has stable performance. The prepared LiFe 1-x Mn x The PO4 solid solution has uniform phase, high purity, small particle size and uniform distribution.

[0004] As a low-cost synthesis process, continuous microwave-assisted hydrothermal method has attracted more and more attention from the world. However, there is no continuous microwave hydrothermal method for producing LiFe in China. 1-x Mn x According to reports on PO4 solid solution, the domestic method used is the intermittent operation of a conventional hydrothermal reactor. However, this production method has many disadvantages: low wall heat transfer coefficient and long heating time; the slurry is easy to stick to the wall, further reducing the heat transfer efficiency; under high temperature and high pressure, the local temperature in the reactor may be uneven, and the safety is low; large-scale production equipment and small and pilot test equipment have large product performance differences. It is difficult for current high-pressure reactors to achieve continuous reaction and continuous feeding and discharging, and it is difficult to achieve large-scale industrial production. Therefore, the present invention proposes a continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x The new method of PO4 solid solution solves the above problems. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystals, using a microchannel reactor, a tubular delayed reactor and microwave-assisted heating during the synthesis process, can achieve continuous synthesis of small-sized and uniformly distributed LiFe 1-x Mn x PO4 solid solution, microwave heating makes the reactants heated more evenly, making the reaction rate of the material dozens or even thousands of times faster than conventional hydrothermal methods, and can synthesize substances that are difficult to produce by conventional methods.

[0006] The technical solution of the present invention is:

[0007] A continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x The method for producing PO4 nanocrystals is characterized by comprising the following steps:

[0008] Step 1: Prepare a lithium ion aqueous solution with a concentration of 0.1 to 5 mol·L -1 ;

[0009] Step 2: Prepare a phosphate ion aqueous solution with a concentration of 0.1 to 5 mol·L -1 ;

[0010] Step 3: The lithium ion-containing aqueous solution of step 1 and the phosphate ion-containing aqueous solution of step 2 are micro-mixed to obtain a uniform Li3PO4 suspension;

[0011] Step 4: Prepare an aqueous solution containing ferrous ions and / or divalent manganese ions, with a concentration of 0.1 to 5 mol·L -1 and 0.1~5.0mol·L -1 ;

[0012] Step 5: Use a feed pump to introduce the Li3PO4 suspension of step 3 into a buffer tank for stirring and then pump it into a collision mixer, use a feed pump to pump the aqueous solution containing ferrous ions and / or divalent manganese ions of step 4 into the collision mixer, and after being fully premixed in the collision mixer, enter the tubular delayed reactor, the temperature of the tubular delayed reactor is 50-300° C., the residence time of the material in the tubular delayed reactor is 5-120 minutes, and the heating method is microwave-assisted heating;

[0013] Step 6: The synthesized target product enters the solid-liquid separator, and then the precipitate is collected, washed and dried to obtain LiFe with uniform particle size distribution. 1-x Mn x PO4 nanocrystals.

[0014] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x The method for preparing PO4 nanocrystals, the lithium ion aqueous solution prepared in step 1 preferably has a concentration of 2.0 to 5.0 mol·L -1 The raw material containing lithium ions is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium sulfate and lithium chloride.

[0015] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, the phosphate ion aqueous solution prepared in step 2 preferably has a concentration of 0.5 to 3.0 mol·L -1 The raw material containing phosphate ions is one or more of phosphoric acid, ammonium phosphate, monoammonium hydrogen phosphate, and diammonium phosphate.

[0016] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, in step 1 and step 2, the molar ratio of the aqueous solution containing lithium ions to the aqueous solution containing phosphate ions is (2.5-3.5):1.

[0017] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystals, in step 3, a lithium ion aqueous solution and a phosphate ion aqueous solution are pumped into a microchannel reactor by a plunger pump, and the flow rates of the lithium ion aqueous solution and the phosphate ion aqueous solution are 30 to 90 mL min -1 and 10~60mL·min -1 .

[0018] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, step 4 prepares an aqueous solution containing ferrous ions and / or divalent manganese ions, and the ferrous ion concentration is preferably 0.2 to 2.0 mol·L -1 The divalent manganese ion concentration is preferably 0.1 to 2.0 mol·L -1 The raw material containing ferrous ions is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous acetate, and the raw material containing divalent manganese ions is one or more of manganese sulfate, manganese dichloride, manganese nitrate and manganese acetate.

[0019] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, in step 3 and step 4, Li3PO4, Fe 2+ , Mn 2+ The molar ratio is (0.5~2.0):(0~3.0):(0~3.0).

[0020] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, in step 5, the flow rate of the Li3PO4 suspension pumped into the collision mixer is 10 to 90 mL min -1 The flow rate of the aqueous solution containing ferrous ions and / or divalent manganese ions pumped into the collision mixer is 10 to 90 mL min -1 .

[0021] The continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, LiFe 1-x Mn x In PO4 nanocrystals, x is 0 to 1.0.

[0022] The design concept of the present invention is:

[0023] The present invention introduces a microchannel reactor to synthesize Li3PO4 particles. Microscopic mixing can provide a uniform supersaturated environment for the nucleation of Li3PO4 particles, which is more conducive to the generation of particles with small size and uniform particle size distribution. 1-x Mn x The synthesis of PO4 follows a dissolution-recrystallization mechanism, with the dissolution of Li3PO4 and the 1-x Mn x The nucleation and growth process of PO4 is small in size and uniform in particle size distribution. Li3PO4 has a low dissolution temperature and a fast dissolution rate, which can significantly increase the nucleation rate and effectively inhibit the growth of grains. In addition, the use of microwave-assisted heating tubular delayed reactor can solve the problem of traditional hydrothermal inability to produce continuously, and finally achieve LiFe 1-x Mn x Continuous synthesis of PO4 nanocrystals.

[0024] The advantages and beneficial effects of the present invention are:

[0025] 1. The present invention uses a microchannel reactor to synthesize Li3PO4 precursors, and can prepare Li3PO4 with small size and uniform particle size distribution. Compared with traditional macroscopic equipment, microchannel reactors can provide a larger interphase contact area and higher mixing efficiency in a small space, and in particular can achieve controllable continuous operation.

[0026] 2. The present invention introduces a tubular delayed reactor and uses microwave-assisted heating to rapidly and continuously synthesize LiFe with small size and uniform particle size distribution. 1-x Mn x PO4 nanocrystals.

[0027] 3. The microchannel reactor and tubular delayed reactor of the present invention can solve the problems of traditional hydrothermal synthesis of LiFe 1-x Mn x PO4 has high cost and discontinuous production problems, and LiFe 1-x Mn x Continuous macro-synthesis of PO4 nanocrystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 LiFe 1-x Mn x Process flow chart of PO4 nanocrystal continuous production system. In the figure, 1 is the first feed pump, 2 is the second feed pump, 3 is the third feed pump, and 4 is the fourth feed pump.

[0029] Figure 2 This is a transmission electron microscope photo of Li3PO4 synthesized in Example 1.

[0030] Figure 3 Synthesis of LiFe for Example 1 0.5 Mn 0.5 Transmission electron microscope micrograph of PO4.

[0031] Figure 4 This is a transmission electron microscope photo of Li3PO4 synthesized in Example 2.

[0032] Figure 5 This is a transmission electron microscope photo of LiFePO4 synthesized in Example 2.

[0033] Figure 6 This is a transmission electron microscope photo of Li3PO4 synthesized in Example 3.

[0034] Figure 7 Synthesis of LiFe for Example 3 0.5 Mn 0.5 Transmission electron microscope micrograph of PO4. DETAILED DESCRIPTION

[0035] In the specific implementation process, the present invention proposes a continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystal method, comprising the following steps ( Figure 1 ):

[0036] First, prepare a certain concentration of lithium ions (Li + ) aqueous solution and a certain concentration of phosphate ions (PO4 3- ) aqueous solution, the aqueous solution containing lithium ions enters the microchannel reactor through the third feed pump 3, and the aqueous solution containing phosphate ions enters the microchannel reactor through the second feed pump 2. In the microchannel reactor (MISR-1, the channel size is 10 to 500 microns), they collide and undergo microscopic mixing to form a Li3PO4 precursor (suspension). By utilizing the impact flow (higher flow rate) to enhance mass transfer, Li3PO4 with small size and uniform particle size distribution can be synthesized.

[0037] Then, the Li3PO4 suspension is introduced into a buffer tank (BV, with stirring function) for stirring. The Li3PO4 suspension enters the collision mixer from the top outlet of the buffer tank through the fourth feed pump 4. 2+ and / or Mn 2+ The aqueous solution enters the collision mixer through the first feed pump 1, and after being fully premixed in the collision mixer (MISR-2), it enters the tubular delayed reactor (TDR), and after microwave-assisted heating, the outlet of the tubular delayed reactor is connected to the solid-liquid separator (SLS) through the back pressure valve (BPV). The whole system is in a high temperature and high pressure environment, and LiFe is continuously synthesized at a certain temperature and pressure. 1-x Mn xPO4 nanocrystals, the products are separated by a solid-liquid separator, and finally the target product is obtained.

[0038] In the present invention, the first feed pump 1, the second feed pump 2, the third feed pump 3, and the fourth feed pump 4 are all plunger pumps. In addition, the difference between the microchannel reactor (MISR-1) and the collision mixer (MISR-2) is that MISR-1 is a T-type microchannel reactor with a channel size of 10 to 500 microns; MISR-2 is a Y-type collision mixer with a channel size of 100 to 500 microns.

[0039] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0040] Below, the feasibility of the present invention is further verified by examples.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment continuously synthesizes LiFe by microwave-assisted hydrothermal 1-x Mn x The method of PO4 nanocrystals is as follows:

[0043] (1) Synthesis of Li3PO4: 201 g of LiOH·H2O powder was dissolved in 1000 mL of deionized water and stirred magnetically for 30 min to form a solution with a concentration of 4.8 mol·L -1 49.2 mL of 85 wt% concentrated H3PO4 was dispersed in 500 mL of deionized water and ultrasonically dispersed for 20 min to form a 1.6 mol·L -1 The LiOH solution passes through the third feed pump 3, and the flow rate of the third feed pump 3 is 30 mL min -1 , H3PO4 solution passes through the second feed pump 2, the flow rate of the second feed pump 2 is 30mL·min -1 LiOH solution and H3PO4 solution collide in MISR-1 to form Li3PO4 suspension. The microstructure of synthesized Li3PO4 is as follows: Figure 2 As shown, the particles are small and uniform, and their particle size is 20 to 200 nanometers.

[0044] (2) LiFe 0.5 Mn 0.5Synthesis of PO4 nanocrystals: 220.2 g of FeSO4·7H2O powder and 133.8 g of MnSO4·H2O powder were dissolved in 1500 mL of deionized water and stirred magnetically for 20 min to form FeSO4 and MnSO4 solutions; the FeSO4 and MnSO4 solutions entered MISR-2 through the first feed pump 1 at a flow rate of 20 mL·min -1 After being stirred in BV, the Li3PO4 suspension enters MISR-2 through the fourth feed pump 4. The flow rate of the fourth feed pump 4 is 20 mL min -1 After being fully premixed at MISR-2, the system enters TDR. The entire system is in a high temperature and high pressure environment, where the pressure is maintained at 2.0 MPa and the temperature is stabilized at 210 ° C to continuously synthesize LiFe 0.5 Mn 0.5 PO4 nanocrystals enter the cooling system, and the products are separated by SLS to finally obtain LiFe 0.5 Mn 0.5 PO4 nanocrystals, synthetic LiFe 0.5 Mn 0.5 The microstructure of PO4 nanocrystals is as follows Figure 3 As shown, it presents a uniform nanosheet structure.

[0045] Example 2

[0046] like Figure 1 As shown, this embodiment continuously synthesizes LiFe by microwave-assisted hydrothermal 1-x Mn x The method of PO4 nanocrystals is as follows:

[0047] (1) Synthesis of Li3PO4: 100.5 g of LiOH·H2O powder was dissolved in 1000 mL of deionized water and stirred magnetically for 30 min to form a solution with a concentration of 2.4 mol·L -1 49.2 mL of 85 wt% concentrated H3PO4 was dispersed in 500 mL of deionized water and ultrasonically dispersed for 20 min to form a 1.6 mol·L -1 The LiOH solution passes through the third feed pump 3, and the flow rate of the third feed pump 3 is 40 mL min -1 , H3PO4 solution passes through the second feed pump 2, the flow rate of the second feed pump 2 is 22.73mL·min -1 , LiOH solution and H3PO4 solution collide in MISR-1 to form Li3PO4 suspension, and the formed Li3PO4 is a uniform nano-shape, such as Figure 4 shown.

[0048] (2) Synthesis of LiFePO4 nanocrystals: 440.4 g of FeSO4·7H2O powder was dissolved in 1500 mL of deionized water and stirred magnetically for 20 min to form a FeSO4 solution. The FeSO4 solution entered MISR-2 through the first feed pump 1 at a flow rate of 20 mL·min -1 After being stirred in BV, the Li3PO4 suspension enters MISR-2 through the fourth feed pump 4. The flow rate of the fourth feed pump 4 is 20 mL min -1 After being fully premixed at MISR-2, it enters TDR. The entire system is in a high temperature and high pressure environment, where the pressure is maintained at 2.0 MPa and the temperature is stabilized at 210°C. LiFePO4 nanocrystals are continuously synthesized and enter the cooling system. The product is separated by SLS to finally obtain LiFePO4 nanocrystals. The synthesized LiFePO4 is a uniform nano-sized flake structure, such as Figure 5 shown.

[0049] Example 3

[0050] like Figure 1 As shown, this embodiment continuously synthesizes LiFe by microwave-assisted hydrothermal 1-x Mn x The method of PO4 nanocrystals is as follows:

[0051] (1) Synthesis of Li3PO4: 201 g of LiOH·H2O powder was dissolved in 1000 mL of deionized water and stirred magnetically for 30 min to form a solution with a concentration of 4.8 mol·L -1 98.4 mL of 85 wt% concentrated H3PO4 was dispersed in 500 mL of deionized water and ultrasonically dispersed for 20 min to form a 3.2 mol·L -1 The LiOH solution passes through the third feed pump 3, and the flow rate of the third feed pump 3 is 60 mL min -1 , H3PO4 solution passes through the second feed pump 2, the flow rate of the second feed pump 2 is 30mL·min -1 LiOH solution and H3PO4 solution collide in MISR-1 to form Li3PO4 suspension. The synthesized Li3PO4 particles are small and uniform, with a particle size of 20 to 50 nm.

[0052] (2) Synthesis of LiMnPO4 nanocrystals: 267.7 g of MnSO4·H2O powder was dissolved in 1500 mL of deionized water and stirred magnetically for 20 min to form a MnSO4 solution. The MnSO4 solution entered MISR-2 through the first feed pump 1 at a flow rate of 20 mL·min -1After being stirred in BV, the Li3PO4 suspension enters MISR-2 through the fourth feed pump 4. The flow rate of the fourth feed pump 4 is 20 mL min -1 After being fully premixed at MISR-2, it enters TDR. The entire system is in a high temperature and high pressure environment, where the pressure is maintained at 2.0 MPa and the temperature is stabilized at 210°C. LiMnPO4 nanocrystals are continuously synthesized and enter the cooling system. The product is separated by SLS to finally obtain LiMnPO4 nanocrystals.

[0053] Example 4

[0054] like Figure 1 As shown, this embodiment continuously synthesizes LiFe by microwave-assisted hydrothermal 1-x Mn x The method of PO4 nanocrystals is as follows:

[0055] (1) Synthesis of Li3PO4: 100.5 g of LiOH·H2O powder was dissolved in 1000 mL of deionized water and stirred magnetically for 30 min to form a solution with a concentration of 2.4 mol·L -1 49.2 mL of 85 wt% concentrated H3PO4 was dispersed in 500 mL of deionized water and ultrasonically dispersed for 20 min to form a 1.6 mol·L -1 The LiOH solution passes through the third feed pump 3, and the flow rate of the third feed pump 3 is 40 mL min -1 , H3PO4 solution passes through the second feed pump 2, the flow rate of the second feed pump 2 is 20mL·min -1 LiOH solution and H3PO4 solution collide in MISR-1 to form Li3PO4 suspension. The synthesized Li3PO4 is very small, with a particle size of 20 to 60 nanometers. Figure 6 shown.

[0056] (2) LiFe 0.5 Mn 0.5 Synthesis of PO4 nanocrystals: 110.1 g of FeSO4·7H2O powder and 66.9 g of MnSO4·H2O powder were dissolved in 1500 mL of deionized water and stirred magnetically for 20 min to form FeSO4 and MnSO4 solutions; the FeSO4 and MnSO4 solutions entered MISR-2 through the first feed pump 1, and the flow rate of the first feed pump 1 was 30 mL·min -1 After being stirred in BV, the Li3PO4 suspension enters MISR-2 through the fourth feed pump 4. The flow rate of the fourth feed pump 4 is 30 mL min -1After being fully premixed at MISR-2, the system enters TDR. The entire system is in a high temperature and high pressure environment, where the pressure is maintained at 2.0 MPa and the temperature is stabilized at 220°C to continuously synthesize LiFe 0.5 Mn 0.5 PO4 nanocrystals enter the cooling system, and the products are separated by SLS to finally obtain LiFe 0.5 Mn 0.5 PO4 nanocrystals, synthesis of LiFe 0.5 Mn 0.5 PO4 nanocrystals are very uniform and have a nanosheet structure, such as Figure 7 shown.

[0057] The results of the embodiment show that the method of the present invention can continuously feed and realize continuous hydrothermal synthesis of LiFe with small size and uniform particle size distribution. 1-x Mn x PO4 nanocrystals. This method is simple, fast and low-cost. It not only solves the problem that traditional hydrothermal synthesis is difficult to continuously synthesize, but also prepares LiFe 1-x Mn x The PO4 crystal grain size is uniform and small. The present invention is applicable to the preparation of various positive electrode materials, especially for the olivine type positive electrode materials that need to be synthesized with small size and uniform particle size distribution, and has broad application prospects.

[0058] The above description is only a preferred embodiment of the present invention, but the implementation of the present invention is not limited to the above embodiment. Any obvious improvement, replacement, or modification made by a person skilled in the art on the basis of the present invention shall fall within the protection scope of the present invention.

Claims

1. A continuous microwave-assisted hydrothermal synthesis of LiFe 1-x Mn x PO4 nanocrystals method, characterized in that, The steps include: Step 1: Prepare a lithium ion aqueous solution with a concentration of 0.1 to 5 mol·L -1 ; Step 2: Prepare a phosphate ion aqueous solution with a concentration of 0.1 to 5 mol·L -1 ; Step 3: The lithium ion-containing aqueous solution of step 1 and the phosphate ion-containing aqueous solution of step 2 are micro-mixed to obtain a uniform Li3PO4 suspension; Step 4: Prepare an aqueous solution containing ferrous ions and / or divalent manganese ions, with a concentration of 0.1 to 5 mol·L -1 and 0.1~5.0mol·L -1 ; Step 5: Use a feed pump to introduce the Li3PO4 suspension of step 3 into a buffer tank for stirring and then pump it into a collision mixer, use a feed pump to pump the aqueous solution containing ferrous ions and / or divalent manganese ions of step 4 into the collision mixer, and after being fully premixed in the collision mixer, enter the tubular delayed reactor, the temperature of the tubular delayed reactor is 50-300° C., the residence time of the material in the tubular delayed reactor is 5-120 minutes, and the heating method is microwave-assisted heating; Step 6: The synthesized target product enters the solid-liquid separator, and then the precipitate is collected, washed and dried to obtain LiFe with uniform particle size distribution. 1-x Mn x PO4 nanocrystals.

2. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, The lithium ion aqueous solution prepared in step 1 preferably has a concentration of 2.0 to 5.0 mol·L -1 The raw material containing lithium ions is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium sulfate and lithium chloride.

3. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, The phosphate ion aqueous solution prepared in step 2 preferably has a concentration of 0.5 to 3.0 mol·L -1 The raw material containing phosphate ions is one or more of phosphoric acid, ammonium phosphate, monoammonium hydrogen phosphate, and diammonium phosphate.

4. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, In step 1 and step 2, the molar ratio of the aqueous solution containing lithium ions to the aqueous solution containing phosphate ions is (2.5-3.5):

1.

5. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, In step 3, a lithium ion aqueous solution and a phosphate ion aqueous solution are pumped into the microchannel reactor by a plunger pump, and the flow rates of the lithium ion aqueous solution and the phosphate ion aqueous solution are 30 to 90 mL min -1 and 10~60mL·min -1 .

6. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, The aqueous solution containing ferrous ions and / or divalent manganese ions prepared in step 4 preferably has a ferrous ion concentration of 0.2 to 2.0 mol·L -1 The divalent manganese ion concentration is preferably 0.1 to 2.0 mol·L -1 The raw material containing ferrous ions is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous acetate, and the raw material containing divalent manganese ions is one or more of manganese sulfate, manganese dichloride, manganese nitrate and manganese acetate.

7. A continuous microwave-assisted hydrothermal synthesis of LiFe according to any one of claims 1 to 6 1-x Mn x PO4 nanocrystals method, characterized in that, In step 3 and step 4, Li3PO4, Fe 2+ , Mn 2+ The molar ratio is (0.5~2.0):(0~3.0):(0~3.0).

8. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, In step 5, the flow rate of the Li3PO4 suspension pumped into the collision mixer is 10-90 mL min -1 The flow rate of the aqueous solution containing ferrous ions and / or divalent manganese ions pumped into the collision mixer is 10 to 90 mL min -1 .

9. A continuous microwave-assisted hydrothermal synthesis of LiFe according to claim 1 1-x Mn x PO4 nanocrystals method, characterized in that, LiFe 1-x Mn x In PO4 nanocrystals, x is 0 to 1.0.

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