Lithium iron phosphate with high compaction density and high rate capability
By controlling morphology and particle size distribution through boron and titanium doping, the method addresses thermal stability issues and reduces PTFE usage, achieving high packing density and rate performance in lithium iron phosphate.
Patent Information
- Application Number
- CN202510397402.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-01
- Publication Date
- 2025-07-15
AI Technical Summary
The prior art is difficult to simultaneously improve the compaction density and electrochemical performance of lithium iron phosphate, and excessive amount of binder used in the dry electrode process leads to low conductivity and poor rate performance.
Boron and titanium doping are used to prepare controllable morphology and controllable gradation primary sintered lithium iron phosphate. By forming large and small gradations, the binding energy on the surface of the powder is improved, the amount of binder is reduced, and the electrochemical performance is improved.
Lithium iron phosphate with high compaction density and high rate performance has been achieved, which improves the adhesion in the dry electrode process and improves the applicability of the material in the battery.
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Figure CN120308933A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of lithium iron phosphate preparation, and particularly relates to a lithium iron phosphate with high tap density and high rate performance. Background Art
[0002] With the rapid development of the electric vehicle market, users have put forward higher requirements for the charging speed and cruising range of electric vehicles. For lithium iron phosphate cathode materials, in order to achieve this application scenario, it is necessary to develop lithium iron phosphate materials with higher tap density and better electrochemical performance.
[0003] However, most of the traditional methods for improving the tap density of lithium iron phosphate are to increase the sintering temperature and extend the holding time. However, there are differences in the burn resistance between large and small particles. The burn resistance of large particles is relatively strong, while that of small particles is weak. Some side reactions will occur at higher temperatures and longer holding times, producing some by-products such as iron phosphide, iron pyrophosphate, and other magnetic substances. Since magnetic substances seriously affect the safety performance of the battery, it is particularly important to strictly control the content of magnetic substances in the material.
[0004] In addition, with the development of solid-state batteries, the powder extrusion molding technology route, as one of the routes expected to be mass-produced in the dry electrode process, has great application prospects. Its principle is to dry-mix active particles, conductive agents evenly and then add a binder (PTFE). Under the fibrillation effect of the binder, a self-supporting film is formed, and finally it is roll-pressed and covered on the surface of the current collector. However, the addition amount of PTFE is large (mass fraction exceeds 5%), and it is usually used to prepare thick electrodes, resulting in low conductivity and poor rate performance of the final battery.
[0005] Based on this, a low-magnetic lithium iron phosphate with controllable morphology, controllable particle size distribution, and one-time sintering is developed, and the binding energy on the surface of the lithium iron phosphate powder is increased, and the amount of binder used in the dry electrode process is reduced. Summary of the Invention
[0006] Object of the Invention: The technical problem to be solved by the present invention is to provide a low-magnetic lithium iron phosphate with controllable morphology, controllable particle size distribution, and one-time sintering, and to increase the binding energy on the surface of the lithium iron phosphate powder, and reduce the amount of binder used in the dry electrode process.
[0007] Technical Solution: The lithium iron phosphate with high tap density and high rate performance of the present invention is prepared by the following steps:
[0008] (1) Add the lithium source to boiling deionized water according to a solid-liquid ratio of 1:(5-10), add a boron source accounting for 0.05-0.5% of the mass of the iron phosphate precursor, mix evenly to obtain a lithium boron compound solution;
[0009] (2) Dissolve the iron phosphate precursor, lithium source, and carbon source in deionized water, adjust the solid content to 30 - 50%, and after stirring evenly, add the lithium boron compound solution cooled in step (1), and stir evenly to obtain the first mixed solution; subject the first mixed solution to grinding and spray drying to obtain material A;
[0010] (3) Dissolve the iron phosphate precursor, lithium source, carbon source, and titanium source in deionized water, adjust the solid content to 30% - 50%, and stir evenly to obtain the second mixed solution; subject the second mixed solution to grinding and spray drying to obtain material B; wherein, the addition amount of the titanium source is 0.1% - 1% of the mass of the iron phosphate precursor;
[0011] (4) Mix materials A and B according to the mass ratio of (0.1 - 0.9):(0.1 - 0.9), and sinter to obtain lithium iron phosphate.
[0012] When preparing lithium iron phosphate in the present invention, boron and titanium are respectively used for doping to prepare different materials. And when performing boron doping, first react it with the lithium source to prepare the lithium boron compound LiBO3, and add it to the mixed solution prepared from the iron phosphate precursor, lithium source, and carbon source. The addition of this lithium boron compound solution, on the one hand, realizes the mechanism of boron element doping, reduces the surface energy of particles, slows down the nucleation rate, promotes particle coarsening during the sintering process, and finally forms larger-sized particles, regulates the sphericity of lithium iron phosphate, significantly improves the binding energy on the surface of the lithium iron phosphate powder, and then is compounded with the small-particle material formed by titanium doping to form a size grading, balance the compaction density and electrochemical performance of the powder, and finally obtain lithium iron phosphate with high compaction density and high rate performance; and on the other hand, this LiBO3, as a cosolvent, can form a solid solution with other substances in the system during the sintering process, promote the growth of grains, make part of the LFP structure more stable, have fewer lattice defects, and increase the relative density, thereby further improving the density of the prepared lithium iron phosphate.
[0013] And based on forming a size grading, that is, controlling the particle size distribution, it can further improve the binding energy on the surface of the lithium iron phosphate powder, effectively improve the adhesiveness of PTFE during dry process mixing, and improve the applicability of the lithium iron phosphate material in the dry electrode process system.
[0014] Furthermore, in step (1) of the preparation of iron phosphate in the present invention, the boron source is boron oxide or boric acid.
[0015] Furthermore, in steps (1) to (2) of the preparation of iron phosphate in the present invention, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide, or lithium acetate.
[0016] Furthermore, in the preparation steps (2) and (3) of the iron phosphate of the present invention, the iron phosphate precursor is selected as an iron phosphate precursor with a phosphorus-iron ratio of 0.96 - 0.97 and a specific surface area of 7 - 9.
[0017] Furthermore, in the preparation steps (2) and (3) of the iron phosphate of the present invention, the carbon source includes a small molecule carbon source accounting for 0 - 4% of the mass of the iron phosphate precursor and a macromolecule carbon source accounting for 8 - 13% of the mass of the iron phosphate precursor; wherein, the small molecule carbon source is glucose or sucrose, and the macromolecule carbon source is PEG, PVP or starch.
[0018] Furthermore, in the preparation steps (2) and (3) of the iron phosphate of the present invention, the titanium source is titanium dioxide or titanium oxalate.
[0019] Furthermore, in the preparation steps (2) and (3) of the iron phosphate of the present invention, the inlet air temperature for spray drying is 240 - 280 °C, and the outlet air temperature is 80 - 90 °C.
[0020] Furthermore, in the preparation step (4) of the iron phosphate of the present invention, the sintering is carried out in an inert atmosphere at 650 - 770 °C for 5 - 15 h.
[0021] Furthermore, in step (2) of the iron phosphate of the present invention, the Li:P ratio in the material A is (1.0 - 1.03):1.
[0022] Furthermore, in step (3) of the iron phosphate of the present invention, the Li:P ratio in the material B is (1.0 - 1.03):1.
[0023] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: During the preparation of the lithium iron phosphate, by first synthesizing a lithium boron compound and then incorporating the lithium boron compound into the preparation process of the lithium iron phosphate slurry, a lithium iron phosphate slurry A with large particle size is obtained, and it is blended with a titanium-doped lithium iron phosphate slurry B with excellent electrochemical performance and small particle size, thereby enabling the preparation of lithium iron phosphate with high tap density and high rate performance; and by controlling the particle size distribution, the binding energy on the surface of the lithium iron phosphate powder is improved, effectively enhancing the adhesiveness of PTFE during dry mixing process, and improving the applicability of the lithium iron phosphate material in the dry electrode process system. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 It is a scanning electron microscope image of the lithium iron phosphate prepared in Example 1 of the present invention;
[0025] Figure 2 It is a scanning electron microscope image of the lithium iron phosphate prepared in the blank group of the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0027] Example 1
[0028] The lithium iron phosphate of this Example 1 is prepared by the following steps:
[0029] (1) Lithium carbonate is added to boiling deionized water at a solid-liquid ratio of 1:8, boron oxide is weighed according to 0.1% of the mass of the iron phosphate precursor, boron oxide is slowly added and mixed evenly to obtain a lithium boron compound solution, and it is left to stand and cool.
[0030] (2) An iron phosphate precursor with a phosphorus-iron ratio of 0.964 and a specific surface area of 7.45 is selected. Glucose is weighed according to 4% of the mass of the iron phosphate precursor, and PEG is weighed according to 13% of the mass of the iron phosphate precursor. The weighed materials and lithium carbonate are dissolved in deionized water, stirred evenly and the solid content is adjusted to 40%, then the lithium boron compound suspension cooled in step (1) is added, and stirred evenly to obtain a first mixed solution; the first mixed solution is pumped into a sand mill equipped with 0.6 mm zirconium beads and sanded until the D50 of the slurry is 0.5 um, and then finely ground to 0.35 ± 0.01 um with a sand mill equipped with 0.4 mm zirconium beads to obtain a first slurry; subsequently, the second slurry is dried under the conditions of a spray drying inlet temperature of 240 °C, an outlet temperature of 90 °C, and an atomizer rotation speed of 21,000 rpm to obtain a dried material A, and the Li, P ratio in this material A is 1.01:1.
[0031] (3) An iron phosphate precursor with a phosphorus-iron ratio of 0.964 and a specific surface area of 7.45 is selected. Glucose is weighed according to 4% of the mass of the iron phosphate precursor, PEG is weighed according to 13% of the mass of the iron phosphate precursor, and titanium dioxide is weighed according to 0.6% of the mass of the iron phosphate. The weighed materials and lithium carbonate are dissolved in deionized water, stirred evenly and the solid content is adjusted to 40% to obtain a second mixed solution; the second mixed solution is pumped into a sand mill equipped with 0.6 mm zirconium beads and sanded until the D50 of the slurry is 0.5 um, and then finely ground to 0.35 ± 0.01 um with a sand mill equipped with 0.4 mm zirconium beads to obtain a second slurry; subsequently, the second slurry is dried under the conditions of a spray drying inlet temperature of 240 °C, an outlet temperature of 90 °C, and an atomizer rotation speed of 21,000 rpm to obtain a dried material B, and the Li, P ratio in this material B is 1.01:1.
[0032] (4) The dried material A and the dried material B are mixed in a mass ratio of 0.6:0.4, and the mixed material is sintered at 760 °C for 6 h under a nitrogen atmosphere, and after cooling and pulverizing, a boron and titanium co-doped lithium iron phosphate cathode material is obtained.
[0033] Example 2
[0034] The basic steps are the same as those in Example 1, except that the mass ratio of dried material A to dried material B is 0.7:0.3.
[0035] Example 3
[0036] The basic steps are the same as those in Example 1, except that the mass ratio of dried material A to dried material B is 0.8:0.2.
[0037] Example 4
[0038] The basic steps are the same as those in Example 1, except that the mass ratio of dried material A to dried material B is 0.4:0.6.
[0039] Example 5
[0040] The basic steps are the same as those in Example 1, except that the mass ratio of dried material A to dried material B is 0.5:0.5.
[0041] Comparative Example 1
[0042] The basic steps are the same as those in Example 1, except that material A is directly sintered.
[0043] Comparative Example 2
[0044] The basic steps are the same as those in Example 1, except that material B is directly sintered.
[0045] Comparative Example 3: Blank group
[0046] Compared with Example 1, the blank group does not contain lithium boride compound and titanium, and the specific steps are as follows:
[0047] (1) Select a ferrophosphate precursor with a phosphorus-iron ratio of 0.964 and a specific surface area of 7.45. Weigh glucose according to 4% of the mass of the ferrophosphate precursor, and weigh PEG according to 13% of the mass of the ferrophosphate precursor. Dissolve the weighed materials and lithium carbonate in deionized water, stir evenly and adjust the solid content to 40% to obtain a first mixed solution; pump the first mixed solution into a sand mill equipped with 0.6 mm zirconium beads, grind until the D50 of the slurry is 0.5 um, and then finely grind it to 0.35 ± 0.01 um with a sand mill equipped with 0.4 mm zirconium beads to obtain a first slurry; then dry the second material under the conditions of an inlet air temperature of 240 °C, an outlet air temperature of 90 °C, and an atomizer rotation speed of 21,000 rpm in spray drying to obtain a dried material, and the Li:P ratio in this material is 1.01:1.
[0048] (2) Place the dried material in a nitrogen atmosphere at 760 °C and sinter for 6 h, and then cool and crush to obtain a lithium iron phosphate cathode material co-doped with boron and titanium.
[0049] Structural Characterization
[0050] The lithium iron phosphate cathode materials prepared in Example 1 and the blank group were subjected to structural analysis, and the obtained results are as follows Figure 1 and Figure 2 As shown. By comparing these two figures, it can be seen that the lithium iron phosphate cathode material prepared in the present invention forms a size gradation, while the particle size of the lithium iron phosphate cathode material prepared in the blank group is relatively uniform.
[0051] Performance Detection
[0052] The cathode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to compaction degree and electrochemical performance detection, and the obtained results are shown in Table 1 below.
[0053] Table 1 Cathode Material Performance of Examples and Comparative Examples
[0054]
[0055]
[0056] It can be seen from Table 1 that in the present invention, during the preparation process, a lithium boron compound is first prepared. By first synthesizing the lithium boron compound and then incorporating the lithium boron compound into the preparation process of the lithium iron phosphate slurry, a lithium iron phosphate slurry A with large particle size is obtained, and it is blended with a lithium iron phosphate slurry B with excellent electrochemical performance and small particle size doped with titanium, so as to be able to simultaneously prepare lithium iron phosphate with high compaction density and high rate performance, taking both into account and balancing.
[0057] Application Performance Characterization
[0058] At room temperature, the lithium iron phosphate in Example 1, conductive agent, and PTFE were mixed evenly according to a mass ratio of 95:3:2, and then roll-pressed multiple times until a dense self-supporting film was formed. Finally, a self-supporting electrode film with a uniform thickness of 116 μm was obtained. The electrode film was placed on the surface of a carbon-coated aluminum foil, and heat-rolled and cured using a hot roll mill to obtain a solvent-free dry electrode sheet. The peel strength of the electrode sheet was measured to be 0.0152 N / cm.
[0059] Similarly, the lithium iron phosphate in the blank group, conductive agent, and PTFE were mixed evenly according to a mass ratio of 95:3:2, and then roll-pressed multiple times until a dense self-supporting film was formed. Finally, a self-supporting electrode film with a uniform thickness of 103 μm was obtained. The electrode film was placed on the surface of a carbon-coated aluminum foil, and heat-rolled and cured using a hot roll mill to obtain a solvent-free dry electrode sheet. The peel strength of the electrode sheet was measured to be 0.0084 N / cm.
[0060] Through this performance detection, it can be seen that the present invention is based on forming a size gradation, that is, controlling the particle size distribution, and thus can improve the binding energy on the surface of the lithium iron phosphate powder, effectively improve the adhesiveness of PTFE during dry mixing, and improve the applicability of the lithium iron phosphate material in the dry electrode process system.
[0061] In addition to the above embodiments, it should be noted that the preparation steps and the defined process parameters adopted in the present invention can achieve the above-mentioned claimed technical effects according to the verification of Examples 1 to 5 and in combination with the theoretical basis, and thus there is no need to conduct experiments one by one for verification. Among them, for the mass ratio of Material A and Material B, the preferred value can be (0.4 - 0.8):(0.2 - 0.6).
[0062] It should be noted that when preparing the lithium boron compound solution, the addition amount of the lithium source can be determined first according to the Li:P ratio of (1.0 - 1.03):1, and then a part of the addition amount is selected to react with the boron source to form the lithium boron compound LiBO3 (the two satisfy the stoichiometric ratio). When preparing Material A, the addition amount of the lithium source, including lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide or lithium acetate, can be adjusted adaptively according to the final Li:P ratio.
Claims
1. A lithium iron phosphate with high tap density and high rate performance, characterized in that, The lithium iron phosphate is prepared by the following steps: (1) Add a lithium source to boiling deionized water at a solid-liquid ratio of 1:(5-10), and add a boron source accounting for 0.05-0.5% of the mass of the iron phosphate precursor, and mix evenly to obtain a lithium boron compound solution; (2) Dissolve the iron phosphate precursor, lithium source and carbon source in deionized water, adjust the solid content to 30-50%, stir evenly, and then add the lithium boron compound solution cooled in step (1), and stir evenly to obtain a first mixed solution; The first mixed solution is obtained as material A after grinding and spray drying; (3) Dissolve the iron phosphate precursor, lithium source, carbon source and titanium source in deionized water, adjust the solid content to 30-50%, and stir evenly to obtain a second mixed solution; The second mixed solution is obtained as material B after grinding and spray drying; wherein, the addition amount of the titanium source is 0.1%-1% of the mass of the iron phosphate precursor; (4) Mix materials A and B according to a mass ratio of (0.1-0.9):(0.1-0.9), and sinter to obtain lithium iron phosphate.
2. The lithium iron phosphate with high tap density and high rate performance according to claim 1, characterized in that, In step (1), the boron source is boron oxide or boric acid.
3. The lithium iron phosphate with high tap density and high rate performance according to claim 1, characterized in that, In steps (1) to (2), the lithium source at least includes one of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide or lithium acetate.
4. The lithium iron phosphate with high compaction density and high rate performance according to claim 1, wherein, In steps (2) and (3), the iron phosphate precursor selected has a phosphorus-iron ratio of 0.96-0.97 and a specific surface area of 7-9.
5. The lithium iron phosphate with high tap density and high rate performance according to claim 1, characterized in that, In steps (2) and (3), the carbon source includes a small molecule carbon source accounting for 0-4% of the mass of the iron phosphate precursor and a macromolecule carbon source accounting for 8-13% of the mass of the iron phosphate precursor; wherein, the small molecule carbon source is glucose or sucrose, and the macromolecule carbon source is PEG, PVP or starch.
6. The lithium iron phosphate with high compaction density and high rate performance according to claim 1, characterized in that In steps (2) and (3), the titanium source is titanium dioxide or titanium oxalate.
7. The lithium iron phosphate with high compaction density and high rate performance according to claim 1, characterized in that, In steps (2) and (3), the inlet air temperature for spray drying is 240-280°C, and the outlet air temperature is 80-90°C.
8. The lithium iron phosphate with high compaction density and high rate performance according to claim 1, characterized in that, In step (4), the sintering is carried out in an inert atmosphere at 650-770°C for 5-15 h.
9. The lithium iron phosphate with high tap density and high rate performance according to claim 1, characterized in that, In step (2), the Li:P ratio in material A is (1.0-1.03):
1.
10. The lithium iron phosphate with high tap density and high rate performance according to claim 1, characterized in that, In step (3), the Li:P ratio in material B is (1.0-1.03):1.