CN115676814A - Preparation method of titanium-doped graphene-coated lithium iron phosphate positive electrode material - Google Patents
Preparation method of titanium-doped graphene-coated lithium iron phosphate positive electrode material Download PDFInfo
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 69
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 43
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 41
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 239000007774 positive electrode material Substances 0.000 title abstract description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 20
- 239000010406 cathode material Substances 0.000 claims abstract description 16
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 14
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 14
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 12
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 12
- 229910052742 iron Inorganic materials 0.000 claims abstract description 12
- 239000011574 phosphorus Substances 0.000 claims abstract description 12
- 238000002156 mixing Methods 0.000 claims abstract description 10
- 238000000034 method Methods 0.000 claims description 15
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 238000006243 chemical reaction Methods 0.000 claims description 11
- 239000000203 mixture Substances 0.000 claims description 9
- 238000005245 sintering Methods 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical group [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 8
- 239000002904 solvent Substances 0.000 claims description 8
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 8
- VDPLLINNMXFNQX-UHFFFAOYSA-N (1-aminocyclohexyl)methanol Chemical compound OCC1(N)CCCCC1 VDPLLINNMXFNQX-UHFFFAOYSA-N 0.000 claims description 7
- 239000006185 dispersion Substances 0.000 claims description 7
- 238000001035 drying Methods 0.000 claims description 7
- 239000007788 liquid Substances 0.000 claims description 7
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical group CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 6
- 239000004964 aerogel Substances 0.000 claims description 6
- 239000002243 precursor Substances 0.000 claims description 6
- 230000001681 protective effect Effects 0.000 claims description 6
- 238000004108 freeze drying Methods 0.000 claims description 5
- 238000004140 cleaning Methods 0.000 claims description 4
- 239000008367 deionised water Substances 0.000 claims description 4
- 229910021641 deionized water Inorganic materials 0.000 claims description 4
- -1 polytetrafluoroethylene Polymers 0.000 claims description 4
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 4
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 4
- 238000003756 stirring Methods 0.000 claims description 4
- GIAFURWZWWWBQT-UHFFFAOYSA-N 2-(2-aminoethoxy)ethanol Chemical compound NCCOCCO GIAFURWZWWWBQT-UHFFFAOYSA-N 0.000 claims description 3
- BFSVOASYOCHEOV-UHFFFAOYSA-N 2-diethylaminoethanol Chemical compound CCN(CC)CCO BFSVOASYOCHEOV-UHFFFAOYSA-N 0.000 claims description 3
- 238000005530 etching Methods 0.000 claims description 3
- 239000002994 raw material Substances 0.000 claims description 3
- IWSZDQRGNFLMJS-UHFFFAOYSA-N 2-(dibutylamino)ethanol Chemical compound CCCCN(CCO)CCCC IWSZDQRGNFLMJS-UHFFFAOYSA-N 0.000 claims description 2
- 229910018119 Li 3 PO 4 Inorganic materials 0.000 claims description 2
- 238000004321 preservation Methods 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims description 2
- 239000010936 titanium Substances 0.000 abstract description 15
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 abstract description 7
- 229910052719 titanium Inorganic materials 0.000 abstract description 7
- 238000009792 diffusion process Methods 0.000 abstract description 6
- 239000004966 Carbon aerogel Substances 0.000 abstract description 5
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- 150000002500 ions Chemical class 0.000 abstract description 4
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 5
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- 229910001416 lithium ion Inorganic materials 0.000 description 5
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
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- 102000020897 Formins Human genes 0.000 description 1
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- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
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- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a preparation method of a titanium-doped graphene-coated lithium iron phosphate positive electrode material, which comprises the following steps: mixing Ti 3 C 2 Self-assembling MXene, graphene oxide, a lithium source, an iron source and phosphorus source mixed solution into the titanium-doped lithium iron phosphate graphene carbon aerogel by a one-step hydrothermal method; then self-assembled graphene carbon aerogelAnd obtaining the target cathode material titanium-doped graphene-coated lithium iron phosphate through simple heat treatment and crushing. The invention is based on Ti 3 C 2 Unstable and easily oxidized-MXene to nano TiO 2 The intermediate is used as a doped titanium source and Ti 3 C 2 The titanium doping and graphene coating of the lithium iron phosphate are realized by a one-step hydrothermal method with the self-assembly characteristic of the crosslinking esterification reaction between MXene and graphene oxide. The modification strategy of the invention is simple and effective, and is very effective for improving the intrinsic conductivity of the lithium iron phosphate and the ion diffusion kinetics.
Description
Technical Field
The invention relates to a lithium ion battery anode material and a preparation method thereof in the field of electrochemical energy storage, in particular to a titanium-doped graphene-coated lithium iron phosphate anode material.
Background
Polyanionic type positive electrode material lithium iron phosphate (LiFePO) 4 ) The method has the characteristics of rich resources, good circulation stability, high safety coefficient and the like, and is applied to the fields of electric automobiles and the like on a large scale. With the increasing demand of people for energy density of lithium ion batteries, it is important to develop a positive electrode material with high specific capacity, good rate capability and stability. However, the further development and application of the lithium iron phosphate are seriously hindered by the defects of low intrinsic conductivity of the lithium iron phosphate, slow kinetics caused by one-dimensional diffusion of lithium ions and the like. In addition, lithium iron phosphate has a relatively low electrode potential (3.4V vs. Li/Li) compared to ternary materials + ) And low specific capacity (170 mAh g) -1 ) The competitive advantage in the aspect of the anode material is slightly insufficient. Thus, it is possible to provideIt is necessary to develop a lithium iron phosphate positive electrode material with high capacity, good conductivity and rapid ion transmission.
Disclosure of Invention
The invention aims to solve the problems of low intrinsic conductivity of lithium iron phosphate, slow diffusion mass transfer kinetics of lithium ions and the like, and provides a titanium-doped graphene-coated lithium iron phosphate cathode material and a preparation method thereof. The lithium iron phosphate modified coating strategy provided by the invention has a good effect on solving the problems of poor conductivity, slow kinetics and the like of lithium iron phosphate. The method utilizes the fact that graphene oxide and MXene are dissolved in water to generate esterification reaction and the MXene is easily oxidized into nano TiO in the hydrothermal process 2 The method has the characteristics that the self-assembly preparation of the graphene-coated titanium-doped lithium iron phosphate is realized by a one-step hydrothermal method, the process flow is simple, and the industrial development is easy.
The method for solving the problems is realized by the following technical scheme:
step (1): mixing graphene oxide and Ti 3 C 2 Carrying out ice-bath mixing and dispersing on the MXene etching dispersion liquid in a solvent, and uniformly dispersing by ultrasonic;
step (2): sequentially adding a lithium source, an iron source and a phosphorus source into the dispersion liquid obtained in the step (1), adding water to dilute, stirring, and performing ice-bath ultrasonic dispersion again;
and (3): transferring the mixture solution obtained in the step (2) into a polytetrafluoroethylene reaction kettle for hydrothermal reaction to obtain a mixture aerogel;
and (4): alternately cleaning the mixture aerogel obtained in the step (3) by using deionized water and ethanol, and then freezing and drying to obtain a precursor;
and (5): and (5) placing the dried precursor in the step (4) in a tubular furnace with a protective atmosphere, sintering and crushing to obtain the titanium-doped graphene-coated lithium iron phosphate cathode material.
The solvent in the step (1) is selected from one or more of isopropanol, or (1-aminocyclohexyl) methanol, 2- (2-aminoethoxy) ethanol, diethylaminoethanol and dibutylethanol.
In the step (2), the lithium source is calculated by Li, the iron source is calculated by Fe, the phosphorus source is calculated by P, and the molar ratio of Li, fe and P formed in the raw materials is 1.0-2.0:1.0-1.5:1.0-1.5.
The iron source used in the step (2) is FeSO 4 、Fe(NO 3 ) 2 、FeC 2 O 4 With FeCl 2 The lithium source is LiOH or Li 3 PO 4 、Li 2 CO 3 、LiHCO 3 Wherein the phosphorus source is H 3 PO 4 、NH 4 H 2 PO 4 、(NH 4 ) 2 HPO 4 One of (a) and (b); the ultrasonic dispersion time is 1-5 h.
The hydrothermal reaction temperature in the step (3) is 120-200 ℃, and the hydrothermal reaction time is 10-24 h.
The freeze-drying condition in the step (4) is that the drying temperature is-40 ℃ to-60 ℃, and the drying time is 12-24 h.
In the step (5), the sintering temperature is 400-900 ℃, the heating rate is 5-10 ℃ per minute -1 The heat preservation time is 2-10 h, and the protective atmosphere is N 2 、Ar、CO 2 To (3) is provided.
In the technical scheme of the invention, step 1 illustrates that: the MXene can be effectively prevented from being oxidized in advance by ice bath mixing and dispersing in the organic alcohol solvent, and the mutual mixing mass transfer of the graphene oxide and the MXene is strengthened; in addition, the existence of the organic alcohol solvent can control the morphology of the lithium iron phosphate in the hydrothermal synthesis process, so that more active site crystal faces are exposed; the mass transfer of the graphene oxide and MXene in the organic alcohol solvent is further enhanced by ultrasonic waves, so that the graphene oxide and MXene are dispersed and dissolved more uniformly; the other purpose of the ultrasonic wave is to prevent the layered graphene oxide and the layered MXene from agglomerating into a plurality of layers, so that the subsequent coating process is facilitated.
Step 2 illustrates that: the stirring and the ultrasonic action are the same to ensure that substances in the solution are dispersed more uniformly; the ultrasonic time is controlled by considering the characteristic that MXene is unstable and easy to oxidize, and the MXene is oxidized into TiO in advance before hydrothermal reaction due to the fact that the ultrasonic time exceeds 5 h 2 And is not beneficial to the doping of the lithium iron phosphate and the titanium by the subsequent hydrothermal reaction.
Step 3 illustrates: the hydrothermal reaction temperature and time are controlled in consideration of the reaction characteristics of the reduction of graphene oxide, the oxidation doping of MXene and the generation of lithium iron phosphate: the generation of the lithium iron phosphate crystalline phase at the temperature lower than 120 ℃ and the reduction process of the graphene oxide are not easy to occur, the lithium iron phosphate crystal grows at the temperature higher than 200 ℃ to be not beneficial to the processing performance of the electrode material, and TiO is used for improving the processing performance of the electrode material 2 The particles can be agglomerated and grown to be not beneficial to doping; on the other hand, too high reaction temperature and time increase energy consumption and destroy the structure of the polytetrafluoroethylene reaction kettle.
Step 4 illustrates that: the purpose of cleaning with ethanol and deionized water is to remove soluble and insoluble impurities, so that the graphene carbon aerogel and the lithium iron phosphate are purer, and the performance is better exerted; the purpose of freezing and freeze-drying in liquid nitrogen is to maintain the structure of the carbon aerogel, and the step of using thermal drying can collapse the structure of the carbon aerogel, so that graphene is stacked.
Step 5 illustrates that: the high-temperature sintering mainly has three functions: (1) The crystal form of the lithium iron phosphate obtained by the hydrothermal reaction is more compact; (2) The reduction process of the redox graphene is strengthened at high temperature, the content of heteroatoms of the redox graphene is reduced, and the conductivity of the redox graphene is improved; (3) Simultaneously, partial MXene not participating in the doping in the hydrothermal reaction process is oxidized into nano TiO at high temperature 2 And the lithium iron phosphate is more thoroughly doped. In addition, the sintering temperature and the sintering time are regulated and controlled to control the particle size of the lithium iron phosphate, the temperature of less than 400 ℃ is not favorable for the reaction process, and the particle size of the lithium iron phosphate at the temperature of more than 900 ℃ is not favorable for the diffusion mass transfer, the rate capability and the processing performance of lithium ions. Finally, the sintered titanium-doped lithium iron phosphate sample is still a carbon aerogel whole and needs to be crushed to a target particle size distribution by a powder grinding machine; the crushing time is controlled to control the particle size distribution of a target sample, the crushing time is less than 5min, the particle size of the sample is too coarse, the capacity is not exerted, and when the crushing time exceeds 60 min, the sample has a powder passing condition, so that the processing performance is poor.
Compared with the existing lithium iron phosphate preparation technology, the invention has the beneficial effects that:
1. the synthesis, graphene carbon coating and titanium doping of lithium iron phosphate are realized by a one-step hydrothermal method, and the method is simple and easy to implement.
2. Most titanium sources used in the existing titanium-doped lithium iron phosphate technology are complex in preparation process and thick in particles, and cannot be doped in situ, and the lithium iron phosphate needs to be doped by complex ball milling and sand milling processes with high energy consumption. The titanium source used by the technology is derived from MXene oxidation and is nano-particles, and in-situ doping of lithium iron phosphate can be realized in the hydrothermal generation process. In addition, the use and performance of MXene materials require protection from oxidative deterioration, and usually require protection from oxidation by introducing a protective gas. The invention skillfully applies MXene in the air, and widens the use condition.
3. In the technology, the organic alcohol has the functions of oxidation resistance and diffusion mass transfer acceleration in the reinforced mixing process in the early reaction stage, and plays a role in controlling the appearance in the subsequent hydrothermal synthesis process, so that more active crystal faces and sites of the synthesized lithium iron phosphate are exposed, and the performance of the lithium iron phosphate is better played.
4. The intrinsic conductivity of the lithium iron phosphate is improved through a titanium doping and graphene coating mode realized by a one-step method, and the intrinsic conductivity is very obvious for improving the ion electron transmission rate, the rate capability and the capacity capability.
Drawings
Fig. 1 is a charge and discharge curve of the titanium-doped lithium iron phosphate prepared in example 2 at different magnifications.
Fig. 2 is a charge and discharge curve of the titanium-doped lithium iron phosphate prepared in example 3 at different magnifications.
Fig. 3 is a charge-discharge curve of the titanium-doped lithium iron phosphate prepared in example 4 at different rates.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
The invention discloses a titanium-doped graphene-coated lithium iron phosphate positive electrode material and a preparation method thereofA method. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. For example, ti is added to the raw material portion 3 C 2 Conversion of-MXene to Nb 2 C-MXene or V 2 The C-MXene can also realize the doping of niobium and vanadium in the lithium iron phosphate anode material, or Ti 3 C 2 Conversion of-MXene to Ti 2 The effect of the invention can be realized by C-MXene. All falling within the scope of the present invention.
Example 1
Step (1): mixing graphene oxide and Ti 3 C 2 Carrying out ice-bath mixing and dispersing on MXene etching dispersion liquid in a solvent, and carrying out ultrasonic dispersing uniformly;
step (2): sequentially adding a lithium source, an iron source and a phosphorus source into the dispersion liquid obtained in the step (1), adding water to dilute, stirring, and performing ice-bath ultrasonic dispersion again;
and (3): transferring the mixture solution obtained in the step (2) into a polytetrafluoroethylene reaction kettle for hydrothermal reaction to obtain a mixture aerogel;
and (4): alternately cleaning the mixture aerogel obtained in the step (3) by using deionized water and ethanol, and then freezing and drying to obtain a precursor;
and (5): and (5) placing the dried precursor in the step (4) in a tubular furnace with a protective atmosphere, sintering and crushing to obtain the titanium-doped graphene-coated lithium iron phosphate cathode material.
Example 2
This example is essentially the same as example 1 except that: in step 1, 230 mg of graphene oxide and 10 mg of Ti are mixed 3 C 2 -MXene dispersion was dissolved in 350 ml of (1-aminocyclohexyl) methanol and sonicated for 60 min; the lithium source, the iron source and the phosphorus source used in the step 2 respectively have the dosages of 35.92 mg LiOH and 154.95 mg FeSO 4 117.33 mg of NH 4 H 2 PO 4 (i.e., liOH, feSO) 4 、NH 4 H 2 PO 4 In a molar ratio of 1.5:1.02:1.02 The ultrasonic dispersion time of the mixed solution is 2 hours; in step 3, the stepTransferring the mixed solution in the step 2 into a 400 ml reaction kettle and carrying out hydrothermal reaction for 12 h at 180 ℃; step 4, freeze-drying at-40 ℃ for 12 h; the sintering temperature in the step 5 is 650 ℃, and the heating rate is 5 ℃ for min -1 And keeping the temperature for 12 h.
As shown in fig. 1, the modified lithium iron phosphate cathode material prepared in example 2 exhibits good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under C multiplying power can reach 161.38 mAh g -1 Discharge capacity of 155.96 mAh g at 0.3C multiplying power -1 And the discharge specific capacity can reach 152.98 mAh g at 0.5C multiplying power -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 97.20% after 2000 cycles of long cycling.
Example 3
This example is substantially the same as example 2 except that: the lithium source, the iron source and the phosphorus source used in the step 2 and the LiHCO with the dosage of 101.94 mg respectively 3 154.95 mg of FeSO 4 117.33 mg of NH 4 H 2 PO 4 (i.e., liHCO) 3 、FeSO 4 、NH 4 H 2 PO 4 In a molar ratio of 1.5:1.02:1.02 And the ultrasonic dispersion time of the mixed solution is 2 hours.
As shown in fig. 2, the modified lithium iron phosphate cathode material prepared in example 3 exhibits good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under the C multiplying power can reach 157.13 mAh g -1 Discharge capacity of 153.21 mAh g at 0.3C multiplying power -1 The discharge specific capacity at 0.5C multiplying power can reach 150.79 mAh g -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 95.48% after 2000 cycles of long cycling.
Example 4
This example is substantially the same as example 2 except that: the lithium source, the iron source and the phosphorus source used in the step 2 and the amounts of LiOH and FeCl are respectively 35.92 mg and 129.29 mg 2 117.33 mg of NH 4 H 2 PO 4 (i.e., liOH, feSO) 4 、NH 4 H 2 PO 4 In a molar ratio of 1.5:1.02:1.02 The ultrasonic dispersion time of the mixed solution is 2 hours;
as shown in fig. 3, the modified lithium iron phosphate cathode material prepared in example 4 exhibits good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under the C multiplying power can reach 157.02 mAh g -1 Discharge capacity of 151.42 mAh g at 0.3C multiplying power -1 The discharge specific capacity at 0.5C multiplying power can reach 149.08 mAh g -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 96.74% after 2000 cycles of long cycling.
Example 5
This example is substantially the same as example 2 except that: (1-aminocyclohexyl) methanol was replaced with 2- (2-aminoethoxy) ethanol. The modified lithium iron phosphate cathode material prepared in example 5 exhibits good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under C multiplying power can reach 154.38 mAh g -1 Discharge capacity of 150.26 mAh g at 0.3C multiplying power -1 The discharge specific capacity at 0.5C multiplying power can reach 147.75 mAh g -1 。
Example 6
This example is substantially the same as example 2 except that: (1-aminocyclohexyl) methanol was replaced with diethylaminoethanol. The modified lithium iron phosphate positive electrode material prepared in example 6 shows good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under the C multiplying power can reach 155.24 mAh g -1 Discharge capacity of 151.39 mAh g at 0.3C multiplying power -1 The discharge specific capacity at 0.5C multiplying power can reach 149.33 mAh g -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 97.83% after 2000 cycles of long cycling.
Example 7
This example is substantially the same as example 2 except that: (1-aminocyclohexyl) methanol was replaced with dibutylaminoethanol. The modified lithium iron phosphate positive electrode material prepared in example 7 exhibits good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under the C multiplying power can reach 156.65 mAh g -1 Discharge capacity of 152.44 mAh g can be achieved at 0.3C multiplying power -1 And the discharge specific capacity can reach 147.49 mAh g at 0.5C multiplying power -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 95.73% after 2000 cycles of long cycling.
Example 8
This example is substantially the same as example 2 except that: (1-aminocyclohexyl) methanol was replaced with isopropanol. The modified lithium iron phosphate positive electrode material prepared in example 8 shows good electrochemical performance in a half-cell test: 0.1 The specific discharge capacity under the C multiplying power can reach 146.86 mAh g -1 Discharge capacity of 143.33 mAh g at 0.3C multiplying power -1 The discharge specific capacity at 0.5C multiplying power can reach 141.78 mAh g -1 . In addition, the capacity retention rate of the lithium iron phosphate prepared in the embodiment can be maintained at 85.49% after 2000 cycles of long circulation.
The electrochemical performance of the modified lithium iron phosphate in the specific embodiment shows that the invention has good effects on improving the intrinsic conductivity and the ion diffusion mass transfer rate of the lithium iron phosphate, and the energy storage performance of the lithium iron phosphate is obviously improved; in addition, the modified lithium iron phosphate obtained by the preparation method under the combination of different lithium sources, iron sources and phosphorus sources has slightly different electrochemical properties but good overall performance, and the preparation method has good universality and is beneficial to large-scale use.
Claims (7)
1. The preparation method of the titanium-doped graphene-coated lithium iron phosphate cathode material is characterized by comprising the following steps of:
step (1): mixing graphene oxide and Ti 3 C 2 Carrying out ice-bath mixing and dispersing on the MXene etching dispersion liquid in a solvent, and uniformly dispersing by ultrasonic;
step (2): sequentially adding a lithium source, an iron source and a phosphorus source into the dispersion liquid obtained in the step (1), adding water to dilute, stirring, and performing ice-bath ultrasonic dispersion again;
and (3): transferring the mixture solution obtained in the step (2) into a polytetrafluoroethylene reaction kettle for hydrothermal reaction to obtain a mixture aerogel;
and (4): alternately cleaning the mixture aerogel obtained in the step (3) by using deionized water and ethanol, and then freeze-drying to obtain a precursor;
and (5): and (4) placing the dried precursor in the step (4) in a tubular furnace with a protective atmosphere, sintering and crushing to obtain the titanium-doped graphene-coated lithium iron phosphate cathode material.
2. The preparation method of the titanium-doped graphene-coated lithium iron phosphate cathode material according to claim 1, wherein the solvent is selected from isopropanol, or one or more of (1-aminocyclohexyl) methanol, 2- (2-aminoethoxy) ethanol, diethylaminoethanol and dibutylaminoethanol.
3. The preparation method of the titanium-doped graphene-coated lithium iron phosphate cathode material according to claim 1, wherein in the step (2), the lithium source is calculated as Li, the iron source is calculated as Fe, and the phosphorus source is calculated as P, and the molar ratio of Li, fe and P formed in the raw materials is 1.0-2.0:1.0-1.5:1.0-1.5.
4. The method for preparing the titanium-doped graphene-coated lithium iron phosphate cathode material as claimed in claim 3, wherein the iron source used in the step (2) is FeSO 4 、Fe(NO 3 ) 2 、FeC 2 O 4 With FeCl 2 Wherein the lithium source is LiOH or Li 3 PO 4 、Li 2 CO 3 、LiHCO 3 Wherein the phosphorus source is H 3 PO 4 、NH 4 H 2 PO 4 、(NH 4 ) 2 HPO 4 One of (1); the ultrasonic dispersion time is 1-5 h.
5. The preparation method of the titanium-doped graphene-coated lithium iron phosphate cathode material according to claim 1, wherein the hydrothermal reaction temperature in the step (3) is 120-200 ℃, and the hydrothermal reaction time is 10-24 h.
6. The preparation method of the titanium-doped graphene-coated lithium iron phosphate cathode material according to claim 1, wherein the freeze-drying conditions in the step (4) are drying temperature of-40 ℃ to-60 ℃ and drying time of 12-24 h.
7. The method for preparing the titanium-doped graphene-coated lithium iron phosphate cathode material according to claim 1, wherein the sintering temperature in the step (5) is 400-900 ℃, and the temperature rise rate is 5-10 ℃ per minute -1 The heat preservation time is 2-10 h, and the protective atmosphere is N 2 、Ar、CO 2 To (3) is provided.
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