HIGH-COMPACTION LITHIUM IRON PHOSPHATE POSITIVE ELECTRODE MATERIAL, PREPARATION METHOD THEREOF, POSITIVE ELECTRODE AND BATTERY INCLUDING THE SAME

Abstract

A high-compaction lithium iron phosphate positive electrode material, a preparation method thereof, a positive electrode and a battery including the same. The high-compaction lithium iron phosphate positive electrode material comprises lithium iron phosphate of formula LiFe.sub.1-x-yV.sub.xTi.sub.y(BO.sub.3).sub.z(PO.sub.4).sub.1-z, and carbon coated on a surface of the lithium iron phosphate, wherein, 0.001x0.01, 0.001y0.01, and 0.05z0.2. The high-compaction lithium iron phosphate positive electrode material has a high compacted density, a high specific capacity, and excellent rate performance and cycle performance, and is useful for preparing batteries having a high compacted density, a high capacity, good rate performance and cycle performance, which are suitable for high-end pure electric vehicles having a long driving mileage.

Claims

1. A high-compaction lithium iron phosphate positive electrode material, comprising: lithium iron phosphate of formula (I), and carbon coated on a surface of the lithium iron phosphate, $\begin{array}{cc}LiF{e}_{1-x-y}{V}_{x}T{i_y\left(B{O}_3\right)}_z{\left(P{O}_4\right)}_{1-z},& \left(I\right)\end{array}$ wherein, 0.001?x?0.01, 0.001?y?0.01, and 0.05?z?0.2.

2. The high-compaction lithium iron phosphate positive electrode material according to claim 1, wherein the lithium iron phosphate comprises a first-size particle of a particle size of 2-4 ?m and a second-size particle of a particle size of 0.2-0.4 ?m.

3. The high-compaction lithium iron phosphate positive electrode material according to claim 2, wherein, the proportion of the first-size particles is 10-30%, and the proportion of the second-size particles is 70-90%.

4. The high-compaction lithium iron phosphate positive electrode material according to claim 1, wherein a compacted density of the material is 2.5-3 g/mL, and a specific capacity of the material is 100-200 mAh/g.

5. A method for preparing a high-compaction lithium iron phosphate positive electrode material, comprising steps of: step A): mixing a phosphorus source, an iron source, a lithium source, a carbon source and water to obtain a mixture, to which spray drying and sintering are sequentially applied to obtain a precursor material; and step B): mixing a lithium source, a carbon source, a boron source, a vanadium source, a titanium source, water and the precursor material obtained from step A) to obtain a mixture, to which spray drying and sintering are sequentially applied to obtain the high-compaction lithium iron phosphate positive electrode material.

6. The method according to claim 5, wherein the phosphorus source is one or more selected from iron phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; the iron source is one or more selected from ferric phosphate, ferrous oxalate, ferric nitrate, ferrous chloride, and ferrous sulfate; the lithium source is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium bicarbonate; the carbon source is one or more selected from glucose, sucrose, polyethylene glycol, acetylene black, citric acid, and soluble starch; the boron source is one or more selected from boric acid, trimethyl borate, lithium metaborate, lithium borate, and diboron trioxide; the vanadium source is one or more selected from vanadium carbonate, vanadium pentoxide, and ammonium metavanadate; and the titanium source is one or more selected from tetrabutyl titanate and tetraisopropyl titanate.

7. The method according to claim 5, wherein, a carbon content of the precursor material in step A) is 0.1-0.3 wt %; and a molar ratio of Li, Fe, V, Ti, B, P, which are mixed in step B), is 1:1-x-y:x:y:z: 1-z, wherein, 0.001?x?0.01, 0.01?y?0.1, and 0.05?z?0.2.

8. The method according to claim 5, wherein, in step A), the sintering is carried out at a temperature of 700-900? C. for 10-15 hours; and in step B), the sintering is carried out at a temperature of 600-700? C. for 4-8 hours.

9. A positive electrode comprising the high-compaction lithium iron phosphate positive electrode material according to claim 1.

10. A battery comprising the positive electrode according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is the scanning electron microscope image of the anhydrous ferric phosphate of the present disclosure;

[0024] FIG. 2 is the scanning electron microscope image of the high-compaction lithium iron phosphate positive electrode material of the present disclosure;

[0025] FIG. 3 is the XRD spectrum of the high-compaction lithium iron phosphate positive electrode material of the present disclosure;

[0026] FIG. 4 is the charge-discharge graph of the high-compaction lithium iron phosphate positive electrode material of the present disclosure; and

[0027] FIG. 5 is the cycle performance graph of the high-compaction lithium iron phosphate positive electrode material of the present disclosure.

DETAILED DESCRIPTION

[0028] The present disclosure discloses a high-compaction lithium iron phosphate positive electrode material, a preparation method thereof, a positive electrode and a battery including the same. Those skilled in the art can refer to the content herein to appropriately improve the process parameters to achieve this. In particular, it should be noted that all similar substitutions and modifications will be apparent to those skilled in the art, and they are all considered to be encompassed in the present disclosure. The methods and applications of the present disclosure have been described by means of preferred embodiments, and it is apparent that the person concerned can implement and apply the techniques of present disclosure by making modifications or appropriate changes and combinations to the methods and applications herein without departing from the content, spirit and scope of the present disclosure.

[0029] The present disclosure is further described below in conjunction with examples:

Example 1

[0030] An appropriate amount of iron powder was added in a hydrochloric acid solution, and reaction was carried out to reach an end-point pH of 3.5, then the solution was filtered to obtain a ferrous chloride solution with a concentration of 1.8 mol/L, and then EDTA was added thereto, so that the concentration of EDTA in the solution was 0.015 mol/L, the above solution was put in a sealed reaction kettle, heated up to a temperature of 90? C., then a phosphoric acid solution with a concentration of 4 mol/L and hydrogen peroxide with a mass concentration of 29% were added while the solution was being stirred, so that the molar ratio of the ferrous chloride, phosphoric acid, and hydrogen peroxide was 1:1.03:0.65, meanwhile the sealed reaction kettle was evacuated to reach a vacuum degree of ?0.08 MPa, and the gas generated was drawn out and absorbed by being sprayed with pure water to obtain a hydrochloric acid solution which was recycled; the remaining material after the evaporation was added with pure water and was stirred and slurried to obtain a slurry, and then the slurry was filtered and washed with pure water to obtain ferric phosphate dihydrate; the water generated from the washing may be mixed with pure water for the spray absorption; and the obtained ferric phosphate dihydrate was calcined in a rotary kiln to obtain anhydrous ferric phosphate.

[0031] The morphology of the anhydrous ferric phosphate was characterized by a scanning electron microscope, and the results are shown in FIG. 1, which is a scanning electron microscope image of the anhydrous ferric phosphate of the present disclosure.

[0032] It can be seen from FIG. 1 that the anhydrous ferric phosphate has relatively high compactness and larger particles, which is suitable for preparing lithium iron phosphate with a high compacted density.

[0033] The physical and chemical indicators of the anhydrous ferric phosphate were characterized, and the results are shown in Table 1.

TABLE-US-00001 TABLE 1 Items Units Results Elemental Fe wt % 36.31 composition P 20.28 Ca ppm 12.5 Mg 18.5 Na 15.7 Iron to phosphorus / 0.991 molar ratio Specific surface area m.sup.2/g 3 Particle size D50 ?m 5.9 Tap density g/mL 1.03 Apparent density g/mL 0.57 Moisture % 0.18 Magnetic substance ppm 0.25

[0034] It can be seen from Table 1 that the anhydrous ferric phosphate has a very low impurity content, a small specific surface area as measured by BET method, and a relatively large D50, which correspond to the results shown in FIG. 1.

Example 2

[0035] Lithium carbonate and the anhydrous ferric phosphate obtained from Example 1 were mixed at a mass ratio of 0.235:1, and polyethylene glycol (PEG) and water were added simultaneously and the mixture was slurried, the material obtained after slurrying was ground by a sand mill to have a particle size of 700 nm to obtain a slurry, the mass fraction of the solids in the slurry was 35%; and then the slurry was spray-dried to have a particle size of 6 ?m.

[0036] The above spray-dried material was put into a roller furnace into which nitrogen was introduced, the furnace pressure in the roller furnace was adjusted to 100 Pa, and the spray-dried material was calcinated at 820? C. for 15 hours to obtain a precursor material, the carbon content of the precursor material was maintained at 0.1 wt %, the entire calcination cycle was 30 hours, and the cooling time was 6 hours.

[0037] The above precursor material was pulverized to have a particle size of 1.9 ?m by a pulverizer, then pure water was added, then a mixture of glucose and PEG was added, and the solution was stirred and slurried, and then lithium hydroxide, ammonium metavanadate and boric acid were added, and stirred at a speed of 300 r/min to be dissolved; then the material obtained after stirring was put into a sand mill and ground to have a particle size of 600 nm, then tetrabutyl titanate was added with a metering pump while the material was being stirred over a period of 60 min, and then the material was continued to be stirred at a speed of 300 r/min for 20 min; where, the mass ratio of the precursor material obtained after the pulverization, pure water, glucose, PEG, lithium hydroxide, ammonium metavanadate, boric acid, and tetrabutyl titanate was 1:4:0.05:0.05:0.015:0.005:0.05:0.01.

[0038] The above material obtained after mixing was spray-dried to obtain a spray-dried material having a particle size of 18 ?m, a tap density of 1.9 g/mL, and a water mass fraction of less than 0.5%. Then the spray-dried material was put into a roller furnace, the furnace pressure in the roller furnace was adjusted to 50 Pa, the humidity in the roller furnace was kept at 3% or less, and calcination was carried out at 700? C. for 8 hours, then cooling was carried out for 8 hours, and the material was discharged after being cooled to a temperature80? C. to obtain the high-compaction lithium iron phosphate positive electrode material of the present disclosure.

[0039] After the above high-compaction lithium iron phosphate positive electrode material was discharged, it went through air jet pulverization to have a particle size D50 of 1.3 ?m, and then it underwent screening, iron-removal and packaging. The iron removal removed iron with an electromagnetic iron remover until the magnetic substance in the material was ?0.5 ppm; and the packaging was carried out in a constant temperature and humidity room.

[0040] The morphology and structure of the high-compaction lithium iron phosphate positive electrode material were characterized by scanning electron microscopy and XRD, and the results are shown in FIG. 2 and FIG. 3. FIG. 2 is the scanning electron microscope image of the high-compaction lithium iron phosphate positive electrode material of the present disclosure, and FIG. 3 is the XRD spectrum of the high-compaction lithium iron phosphate positive electrode material of the present disclosure.

[0041] It can be seen from FIG. 2 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure comprises large single-crystal particles and small single-crystal particles, which achieves the blending of large and small particles; where the particle size of the large single crystal particle is about 2 to 4 ?m, and the particle size of the small single-crystal particle is about 0.2-0.4 ?m; the proportion of the large single-crystal particles is 10-30%, and the proportion of the small single-crystal particles is 70-90%; and both the large single-crystal particle and the small single-crystal particle are near spherical in morphology. It can be seen from FIG. 3 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure has a high crystallinity, and its diffraction peak coincides with the standard diffraction peak of lithium iron phosphate.

[0042] The physical and chemical indicators of the high-compaction lithium iron phosphate positive electrode material were characterized, where the powder resistivity was the data tested under the pressure of 8 MPa, the compacted density was the data tested under the pressure of 3 T, and the specific surface area was measured by BET method. The analysis results are shown in the Table 2.

TABLE-US-00002 TABLE 2 Items Units Results Elemental Li wt % 4.46 composition Fe 34.3 P 19.08 C 1.55 B ppm 8953.7 Ti 1185.4 V 1615.3 Sum up of 32.9 Ni, Cr, Cu and Zn Particle size D50 ?m 1.3 Specific surface area m.sup.2/g 10.9 Compacted density g/mL 2.67 Magnetic substance ppm 0.21 Moisture ppm 438 Powder resistivity ? .Math. cm 12.5

[0043] It can be seen from Table 2 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure has a major elemental composition of Li, Fe and P, doped with B, Ti and V, has a carbon coating, and a very low impurity content; its compacted density is 2.67 g/mL, which is higher than the lithium iron phosphate commonly seen on the market; it has an excellent powder resistivity, indicating that it has good electrical conductivity, which is beneficial to achieve better rate performance.

[0044] The high-compaction lithium iron phosphate positive electrode material was assembled according to the following method into a button battery and was tested for charge-discharge performance and cycle performance:

(1) Battery Assembly

[0045] The high-compaction lithium iron phosphate positive electrode material of the present disclosure, a conductive carbon black (SP) conductive agent, polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were mixed uniformly through a high-speed mixer, where the mass ratio of the high-compaction lithium iron phosphate positive electrode material of the present disclosure, the SP conductive agent, and PVDF was 90:5:5. Then the mixture was coated on an aluminum foil by an automatic coating machine, the coated aluminum foil was dried in an oven, rolled to have a required compacted density, cut into small discs of a required size, weighed, and then dried again to obtain a positive electrode plate; and lithium plate was used as a negative electrode plate, and a positive electrode case, a negative electrode case, the positive electrode plate, the lithium plate, a separator, and an electrolyte were assembled into a button battery as required; and the button battery was hung on the battery test system to rest before testing.

(2) Charge and Discharge Performance Test

[0046] The above assembled button battery was put on LAND battery test system for testing at a test temperature of 24-26? C., the battery was charged to 3.75 V at 0.1 C rate to obtain a specific charge capacity, and then the battery was discharged at 0.1 C, 0.2 C, 0.5 C and 1 C rate to 2.0 V to obtain a specific discharge capacity. The test results are shown in Table 3 and FIG. 4. FIG. 4 is the charge-discharge graph of the high-compaction lithium iron phosphate positive electrode material of the present disclosure. In FIG. 4, a, b, c, d and e are the charge-discharge curves at 0.1 C, 0.2 C, 0.5 C, 1 C and 3 C, respectively.

TABLE-US-00003 TABLE 3 Items Results First specific charge capacity at 0.1 C 162.3 mAh/g First specific discharge capacity at 0.1 C 159.5 mAh/g First discharge efficiency 98.30% Constant-voltage charge capacity 3.1 mAh/g Discharge capacity at 2.95 V 154.1 mAh/g

[0047] It can be seen from Table 3 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure has a relatively high specific capacity. It can be seen from FIG. 4 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure has excellent rate performance, less polarization, and no significant polarization caused by large particles, indicating that the doping of the present disclosure is effective.

(3) Cycle Performance Test

[0048] The above assembled button battery was subjected to cycle performance test at 1 C at ambient temperature, the test temperature was 24-26? C., the test rate was 1 C, and the test results are shown in FIG. 5, which is the cycle performance graph of the high-compaction lithium iron phosphate positive electrode material of the present disclosure. It can be seen from FIG. 5 that the high-compaction lithium iron phosphate positive electrode material of the present disclosure was cycled 1500 times at 1 C at ambient temperature, and its capacity retention rate remained above 95%, so the material has excellent cycle performance.

Example 3

[0049] Lithium carbonate and the anhydrous ferric phosphate obtained from Example 1 were mixed at a mass ratio of 0.3:1, and polyethylene glycol (PEG) and water were added simultaneously and the mixture was slurried, the material obtained after slurrying was ground by a sand mill to have a particle size of 700 nm to obtain a slurry, the mass fraction of the solids in the slurry was 35%; and then the slurry was spray-dried to have a particle size of 6 ?m.

[0050] The above spray-dried material was put into a roller furnace into which nitrogen was introduced, the furnace pressure in the roller furnace was adjusted to 100 Pa, and the spray-dried material was calcinated at 850? C. for 12 hours to obtain a precursor material, the carbon content of the precursor material was maintained at 0.15 wt %, the entire calcination cycle was 30 hours, and the cooling time was 6 hours.

[0051] The above precursor material was pulverized to have a particle size of 1.9 ?m by a pulverizer, then pure water was added, then a mixture of glucose and PEG was added, and the solution was stirred and slurried, and then lithium hydroxide, ammonium metavanadate and boric acid were added, and stirred at a speed of 300 r/min to be dissolved; then the material obtained after stirring was put into a sand mill and ground to have a particle size of 600 nm, then tetrabutyl titanate was added with a metering pump while the material was being stirred over a period of 60 min, and then the material was continued to be stirred at a speed of 300 r/min for 20 min; where, the mass ratio of the precursor material obtained after the pulverization, pure water, glucose, PEG, lithium hydroxide, ammonium metavanadate, boric acid, and tetrabutyl titanate was 1:4:0.05:0.05:0.015:0.005:0.05:0.01.

[0052] The above material obtained after mixing was spray-dried to obtain a spray-dried material having a particle size of 20 ?m, a tap density of 1.95 g/mL, and a water mass fraction of less than 0.5%. Then the spray-dried material was put into a roller furnace, the furnace pressure in the roller furnace was adjusted to 50 Pa, the humidity in the roller furnace was kept at 3% or less, and calcination was carried out at 750? C. for 7 hours, then cooling was carried out for 8 hours, and the material was discharged after being cooled to a temperature80? C. to obtain the high-compaction lithium iron phosphate positive electrode material of the present disclosure.

[0053] After the above high-compaction lithium iron phosphate positive electrode material was discharged, it went through air jet pulverization to have a particle size D50 of 1.3 ?m, and then it underwent screening, iron-removal and packaging. The iron removal removed iron with an electromagnetic iron remover until the magnetic substance in the material was 0.5 ppm; and the packaging was carried out in a constant temperature and humidity room.

Example 4

[0054] Lithium carbonate and the anhydrous ferric phosphate obtained from Example 1 were mixed at a mass ratio of 0.25:1, and polyethylene glycol (PEG) and water were added simultaneously and the mixture was slurried, the material obtained after slurrying was ground by a sand mill to have a particle size of 700 nm to obtain a slurry, the mass fraction of the solids in the slurry was 35%; and then the slurry was spray-dried to have a particle size of 6 ?m.

[0055] The above spray-dried material was put into a roller furnace into which nitrogen was introduced, the furnace pressure in the roller furnace was adjusted to 100 Pa, and the spray-dried material was calcinated at 800? C. for 18 hours to obtain a precursor material, the carbon content of the precursor material was maintained at 0.12 wt %, the entire calcination cycle was 30 hours, and the cooling time was 6 hours.

[0056] The above precursor material was pulverized to have a particle size of 1.9 ?m by a pulverizer, then pure water was added, then a mixture of glucose and PEG was added, and the solution was stirred and slurried, and then lithium hydroxide, ammonium metavanadate and boric acid were added, and stirred at a speed of 300 r/min to be dissolved; then the material obtained after stirring was put into a sand mill and ground to have a particle size of 600 nm, then tetrabutyl titanate was added with a metering pump while the material was being stirred over a period of 60 min, and then the material was continued to be stirred at a speed of 300 r/min for 20 min; where, the mass ratio of the precursor material obtained after the pulverization, pure water, glucose, PEG, lithium hydroxide, ammonium metavanadate, boric acid, and tetrabutyl titanate was 1:4:0.05:0.05:0.015:0.005:0.05:0.01.

[0057] The above material obtained after mixing was spray-dried to obtain a spray-dried material having a particle size of 17 ?m, a tap density of 1.89 g/mL, and a water mass fraction of less than 0.5%. Then the spray-dried material was put into a roller furnace, the furnace pressure in the roller furnace was adjusted to 50 Pa, the humidity in the roller furnace was kept at 3% or less, and calcination was carried out at 700? C. for 8 hours, then cooling was carried out for 8 hours, and the material was discharged after being cooled to a temperature80? C. to obtain the high-compaction lithium iron phosphate positive electrode material of the present disclosure.

[0058] After the above high-compaction lithium iron phosphate positive electrode material was discharged, it went through air jet pulverization to have a particle size D50 of 1.3 ?m, and then it underwent screening, iron-removal and packaging. The iron removal removed iron with an electromagnetic iron remover until the magnetic substance in the material was 0.5 ppm; and the packaging was carried out in a constant temperature and humidity room.

[0059] The above embodiments are only preferred embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto, and the equivalents or modifications made by any technical person familiar with the technical field according to the technical solution and the inventive concept of the present disclosure within the technical scope disclosed in the present disclosure, should be encompassed by the present disclosure.