Preparation method of lithium iron phosphate positive electrode material, lithium iron phosphate positive electrode material, positive electrode sheet and lithium ion battery

Abstract

The application relates to the field of lithium battery materials, and particularly discloses a preparation method of a lithium iron phosphate positive electrode material, the lithium iron phosphate positive electrode material, a positive electrode sheet and a lithium ion battery. In the preparation process of the lithium iron phosphate positive electrode material, a composite carbon source is added, so that the prepared lithium iron phosphate positive electrode material can form an excellent conductive network structure, and the prepared lithium ion battery has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium battery materials, in particular to a preparation method of lithium iron phosphate positive electrode material, the lithium iron phosphate positive electrode material, the positive electrode sheet and the lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have high volume energy density and mass energy density, excellent cycle performance, are internationally recognized as ideal energy sources, and are a new generation of green high-energy batteries. They are widely used in portable device fields such as mobile phones, digital cameras, large mobile energy fields such as plug-in hybrid electric vehicles, pure electric vehicles, and fixed energy fields such as energy storage power stations and UPS.

[0003] The positive electrode materials used in lithium ion batteries are mainly ternary materials and lithium iron phosphate. Among them, lithium iron phosphate has been widely used in the field of lithium batteries due to its excellent cycle performance, structural stability, safety and low cost. However, the low working voltage and energy density of lithium iron phosphate seriously limit the development of lithium iron phosphate in positive electrode materials.

[0004] In the prior art, the lithium iron phosphate material is often modified to obtain a positive electrode material with excellent electrochemical performance. For example, patent CN115775886A discloses a preparation method of lithium iron phosphate / carbon fiber composite material. The patent solves the problems of easy agglomeration of material particles and poor compactness during the preparation of battery materials by modifying lithium iron phosphate with carbon fiber material, thereby making the lithium battery have excellent electrochemical performance. For another example, patent CN118851128A discloses a modified lithium iron phosphate, a preparation method thereof, a positive electrode sheet and a secondary battery. The patent uses carbon source and nitrogen source to make the lithium iron phosphate still have excellent electrochemical performance at low temperature. However, the preparation method of lithium iron phosphate in the prior art still has problems such as complex operation, expensive raw materials, inability to popularize, and the prepared lithium iron phosphate cannot simultaneously have excellent cycle performance, working voltage and energy density. SUMMARY

[0005] The purpose of the present application is to overcome the problems in the prior art that lithium iron phosphate cannot simultaneously have excellent cycle performance and energy density, and to provide a preparation method of lithium iron phosphate. The lithium iron phosphate positive electrode material prepared by the method can simultaneously have excellent cycle performance and energy density, and the method is simple to operate, cost-effective and easy to popularize.

[0006] In order to achieve the above-mentioned purpose, one aspect of the present application provides a preparation method of lithium iron phosphate positive electrode material, which comprises:

[0007] S1: a first slurry containing lithium iron phosphate raw material and a first carbon source is prepared, the first slurry is placed in a hydrothermal reaction kettle for a first reaction, and then the first slurry is subjected to a first drying treatment to prepare a lithium iron phosphate precursor;

[0008] S2: a second slurry containing the lithium iron phosphate precursor and a second carbon source is prepared, and then the second slurry is sequentially subjected to a second drying treatment and a calcination treatment to prepare the lithium iron phosphate material positive electrode material;

[0009] The first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acid, salicylic acid, tartaric acid, oxalic acid and polysorbate.

[0010] The mass ratio of the amount of the first carbon source to the amount of the second carbon source is 1:1-2.

[0011] The second aspect of the present application provides a lithium iron phosphate positive electrode material prepared by the preparation method of the first aspect of the present application.

[0012] The third aspect of the present application provides a positive electrode sheet coated with the lithium iron phosphate positive electrode material of the second aspect of the present application.

[0013] The fourth aspect of the present application provides a lithium battery, wherein the positive electrode sheet of the lithium battery is the positive electrode sheet of the third aspect of the present application.

[0014] The above technical solution is adopted, the composite carbon source is added in the preparation process of the lithium iron phosphate positive electrode material, the prepared lithium iron phosphate positive electrode material can form an excellent conductive network structure, and the prepared lithium ion battery has excellent electrochemical performance. DETAILED DESCRIPTION

[0015] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The endpoints of the ranges of values and the values thereof can be combined with other endpoints to form new ranges and new values not expressly disclosed herein, but which are included in the scope of the present application. Moreover, any numerical values include any and all rounded-off values, and any ranges of values include any and all ranges therebetween.

[0016] The first aspect of the present application provides a preparation method of a lithium iron phosphate positive electrode material, which comprises:

[0017] S1: a first slurry containing lithium iron phosphate raw material and a first carbon source is prepared, the first slurry is placed in a hydrothermal reaction kettle for a first reaction, and then the first slurry is subjected to a first drying treatment to prepare a lithium iron phosphate precursor;

[0018] S2: preparing a second slurry containing lithium iron phosphate precursor and a second carbon source, and then sequentially performing a second drying treatment and a calcination treatment on the second slurry to prepare the lithium iron phosphate material positive electrode material;

[0019] wherein the first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acid, salicylic acid, tartaric acid, oxalic acid and polysorbate;

[0020] The mass ratio of the use amount of the first carbon source to the second carbon source is 1:1-2.

[0021] In the present application, preferably, the method for preparing the first slurry comprises: placing lithium iron phosphate raw material and a first carbon source in deionized water for first mixing treatment. Preferably, the conditions of the first mixing treatment comprise: temperature of 20-40℃, time of 1-3h. More preferably, in the first mixing treatment, the use amount of the deionized water is 80-120wt%, preferably 90-110wt%, based on the mass of the lithium iron phosphate raw material.

[0022] In the present application, preferably, the addition amount of the first carbon source is 1-5wt%, preferably 1.5-4wt%, for example, it can be 1.5wt%, 2wt%, 2.5wt%, 2.7wt%, 3.0wt%, 3.2wt%, 3.5wt%, 4wt% and the like, and the range between any two of them.

[0023] In the present application, preferably, the method for preparing the second slurry comprises: placing lithium iron phosphate precursor and a second carbon source in deionized water for second mixing treatment. Preferably, the conditions of the second mixing treatment comprise: temperature of 25-45℃, time of 2-4h. More preferably, in the second mixing treatment, the use amount of the deionized water is 85-125wt%, preferably 95-110wt%, based on the mass of the lithium iron phosphate raw material.

[0024] In the present application, by improving the cooperation of the first carbon source and the second carbon source, the lithium iron phosphate positive electrode material prepared has excellent electrochemical performance. Preferably, the mass ratio of the use amount of the first carbon source to the second carbon source is 1:1.2-1.8, for example, it can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8 and the like, and the range between any two of them.

[0025] In the present application, preferably, the lithium iron phosphate raw material comprises a lithium source, an iron source and a phosphorus source.

[0026] In the present application, in order to further improve the electrochemical performance of the lithium iron phosphate positive electrode material, preferably, the lithium source is selected from at least one of Li2CO3, LiOH and LiH2PO4. Preferably, the iron source is selected from at least one of FeSO4, FeC6H5O7 and FeC2O4. Preferably, the phosphorus source is selected from at least one of H3PO4, (NH4)2HPO4 and (NH4)3PO4.

[0027] In the present application, by reasonably adjusting the amount of lithium iron phosphate raw materials including lithium source, iron source and phosphorus source, the electrochemical performance of the subsequent lithium iron phosphate positive electrode material can be improved. Preferably, the molar ratio of lithium, iron and phosphorus in the lithium iron phosphate raw material is 1:0.1-1:0.1-1, preferably 1:0.2-0.8:0.2-0.8, for example, it can be 1:0.2:0.2, 1:0.2:0.8, 1:0.8:0.2, 1:0.8:0.8 and the like, and any ratio therebetween.

[0028] In the present application, preferably, the conditions of the first reaction include a temperature of 140-250°C and a time of 5-12h. More preferably, the conditions of the first reaction include a temperature of 150-200°C and a time of 8-10h.

[0029] In the present application, in order to enable the first carbon source to be better coated on the lithium iron phosphate raw material, preferably, the conditions of the first drying treatment include a temperature of 40-80°C, preferably 45-75°C, and a time of 2-5h, preferably 2.5-4.5h.

[0030] In the present application, in order to enable the second carbon source to be better coated on the lithium iron phosphate precursor, preferably, the conditions of the second drying treatment include a temperature of 50-100°C, preferably 55-85°C, and a time of 3-6h, preferably 4.5-5.5h.

[0031] In the present application, preferably, the conditions of the calcination treatment include a temperature of 500-800°C, preferably 600-700°C, and a time of 1-6h, preferably 2-3h.

[0032] According to a preferred embodiment, the preparation method of the lithium iron phosphate positive electrode material further comprises: performing a first grinding treatment on the first slurry; the conditions of the first grinding treatment include a rotation speed of 200-300r / min and a time of 6-10h.

[0033] According to another preferred embodiment, the preparation method of the lithium iron phosphate positive electrode material further comprises: performing a second grinding treatment on the second slurry; the conditions of the second grinding treatment include a rotation speed of 500-1000r / min and a time of 3-8h.

[0034] The second aspect of the present application provides a lithium iron phosphate cathode material prepared by the preparation method of the first aspect of the present application.

[0035] According to the present application, preferably, the compaction density of the lithium iron phosphate cathode material is 2.6-2.7 g / cm 3 .

[0036] The third aspect of the present application provides a cathode sheet coated with the lithium iron phosphate cathode material of the second aspect of the present application.

[0037] According to the present application, the preparation method of the cathode can adopt various methods commonly used in the art, for example, can include mixing the lithium iron phosphate cathode material provided by the present application, a cathode binder and a cathode solvent, coating and / or filling on a cathode current collector, forming a cathode material layer on the surface of the cathode current collector, drying, calendering or not, to obtain the cathode. Preferably, in the cathode material layer of the battery, the content of the lithium iron phosphate cathode material provided by the present application is 85-95 wt%.

[0038] In the present application, the type of the cathode binder can be one or more of polypropylene, polyethylene, polyvinylidene fluoride, polyvinylidene fluoride, vinylidene fluoride hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene. Preferably, the amount of the cathode binder can be 0.01-5 wt% based on the lithium iron phosphate cathode material provided by the present application.

[0039] In the present application, the cathode material layer preferably further contains a cathode conductive agent, and the type of the cathode conductive agent can be one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene. Preferably, the amount of the cathode conductive agent can be 0.01-5 wt% based on the lithium iron phosphate cathode material provided by the present application.

[0040] The fourth aspect of the present application provides a lithium battery, and the cathode sheet of the lithium battery is the cathode sheet of the third aspect of the present application.

[0041] According to the present application, the negative electrode, the separator and the non-aqueous electrolyte solution of the battery are not particularly limited, and various types of negative electrodes, separators and non-aqueous electrolyte solutions used in the field of battery preparation (for example, the field of lithium ion battery preparation) can be used, as long as the cathode used by the battery contains the lithium iron phosphate cathode material provided by the present application.

[0042] The preparation method of the negative electrode can adopt various methods commonly used in the art, for example, can include mixing a negative electrode active material, a negative electrode binder and a negative electrode solvent, coating and / or filling on a negative electrode current collector, forming a negative electrode material layer on the surface of the negative electrode current collector, drying, calendering or not, to obtain the negative electrode.

[0043] In the present application, the negative active material can be selected from artificial graphite and / or natural graphite. Preferably, the content of the negative active material in the negative material layer of the battery is 80-100wt%.

[0044] According to the present application, the negative binder can be selected from one or more of polypropylene, polyethylene, polyvinylidene fluoride, fluorochloroethylene-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene. Preferably, the amount of the negative binder can be 0.01-5wt% based on the negative active material.

[0045] According to the present application, the negative material layer preferably further contains a negative conductive agent, which can be one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene and carbon nanotube. Preferably, the amount of the negative conductive agent can be 0.01-5wt% based on the negative active material.

[0046] The type of the current collector in the positive and negative electrodes is known to those skilled in the art, which can be selected from any one of aluminum foil, copper foil and punched steel belt.

[0047] The separator is arranged between the positive and negative electrodes and has electrically insulating and liquid retaining properties. The separator can be selected from various separators used in lithium ion batteries, such as PP / PE separator, polyolefin microporous membrane, polyethylene felt and the like.

[0048] The non-aqueous electrolyte is a mixed solution of electrolytic lithium salt and non-aqueous solvent, and a conventional non-aqueous electrolyte in the art can be used.

[0049] The preparation method of the battery is a conventional preparation method in the art. In general, the positive and negative electrodes are wound apart by a separator layer to form an electrode group, and the obtained electrode group and non-aqueous electrolyte are sealed in a battery case to obtain the battery provided by the present application.

[0050] According to the present application, the lithium ion battery prepared by using the foregoing technical solution has excellent energy density and battery cycle performance. According to some preferred embodiments of the present application, the lithium ion battery prepared by using the lithium iron phosphate positive material provided by the present application has an energy density of not less than 170wh / kg and a capacity retention rate of more than 85% after 1C cycle for 300 cycles.

[0051] The present application will be described in detail by way of examples below.

[0052] Example 1

[0053] The following examples are used to illustrate the preparation of the lithium iron phosphate positive material.

[0054] S1: at room temperature (25℃, same below), lithium: iron: phosphorus = 1:0.8:0.8 according to the molar ratio of lithium iron phosphate raw material: 740g of Li2CO3, 576g of FeC2O4 and 528g of (NH4)2HPO4, and then the lithium iron phosphate raw material and 50g of glucose were mixed in 2000g of deionized water for the first mixing treatment for 2h, to prepare a first slurry, and then the first slurry was ground at 200r / min for 6h and then placed in a 180℃ hydrothermal reactor for the first reaction for 8h, and then the first drying treatment was carried out at 45℃ for 3h, to prepare a lithium iron phosphate precursor;

[0055] S2: the lithium iron phosphate precursor prepared in S1 and 80g of citric acid were placed in 2200g of deionized water, and then the second mixing treatment was carried out at 30℃ for 3.5h to obtain a second slurry, and then the second slurry was ground at 500r / min for 5h, and then the second drying treatment was carried out at 50℃ for 5h and the calcination treatment was carried out at 600℃ for 2h, to prepare a lithium iron phosphate material positive electrode material A1.

[0056] Example 2

[0057] The following examples are used to illustrate the preparation of lithium iron phosphate positive electrode materials.

[0058] S1: at room temperature, lithium: iron: phosphorus = 1:0.7:0.7 according to the molar ratio of lithium iron phosphate raw material: 740g of Li2CO3, 504g of FeC2O4 and 462g of (NH4)2HPO4, and then the lithium iron phosphate raw material and 55g of glucose were mixed in 1800g of deionized water for the first mixing treatment for 2.5h, to prepare a first slurry, and then the first slurry was ground at 300r / min for 8h and then placed in a 190℃ hydrothermal reactor for the first reaction for 2h, and then the first drying treatment was carried out at 50℃ for 2.5h, to prepare a lithium iron phosphate precursor;

[0059] S2: the lithium iron phosphate precursor prepared in S1 and 70g of citric acid were placed in 1900g of deionized water, and then the second mixing treatment was carried out at 35℃ for 3.5h to obtain a second slurry, and then the second slurry was ground at 600r / min for 3.5h, and then the second drying treatment was carried out at 55℃ for 4.5h and the calcination treatment was carried out at 650℃ for 2.5h, to prepare a lithium iron phosphate material positive electrode material A2.

[0060] Example 3

[0061] According to the similar method of Example 1, except that the same weight parts of polyethylene glycol were used instead of glucose, to prepare a lithium iron phosphate material positive electrode material A3.

[0062] Example 4

[0063] According to the similar method of Example 1, except that 50 g of citric acid was used instead of 80 g of citric acid, lithium iron phosphate material cathode material A5 was prepared.

[0064] Example 5

[0065] According to the similar method of Example 1, except that 50 g of citric acid was used instead of 80 g of citric acid, lithium iron phosphate material cathode material A5 was prepared.

[0066] Example 6

[0067] According to the similar method of Example 1, except that 100 g of citric acid was used instead of 80 g of citric acid, lithium iron phosphate material cathode material A6 was prepared.

[0068] Comparative Example 1

[0069] According to the similar method of Example 1, except that in step S2, the lithium iron phosphate precursor prepared in S1 was calcined at 200 °C for 2 h, lithium iron phosphate material cathode material B1 was prepared.

[0070] Comparative Example 2

[0071] According to the similar method of Example 1, except that 25 g of citric acid was used instead of 80 g of citric acid, lithium iron phosphate material cathode material B2 was prepared.

[0072] Comparative Example 3

[0073] According to the similar method of Example 1, except that 250 g of citric acid was used instead of 80 g of citric acid, lithium iron phosphate material cathode material B3 was prepared.

[0074] Test Example 1

[0075] The above lithium iron phosphate material cathode material was prepared into a lithium ion battery according to the following steps, and the electrochemical performance of the battery was tested, and the test results are shown in Table 1.

[0076] Preparation steps of lithium ion battery:

[0077] (1) Preparation of the positive electrode sheet: 25 g of the lithium iron phosphate cathode material prepared in the above examples and comparative examples, 0.6 g of conductive carbon black and 0.8 g of polyvinylidene fluoride were mixed and then placed in a solvent, and then ball milled at a speed of 360 rpm for 4 h to obtain a slurry, and the slurry was coated on an aluminum foil and dried to obtain a positive electrode sheet;

[0078] (2) Preparation of the negative electrode sheet: 30 g of natural graphite, 0.2 g of conductive carbon black and 0.5 g of polyvinylidene fluoride were mixed and then placed in a solvent, followed by ball milling at a speed of 400 rpm for 5 h to prepare a slurry, and the slurry was coated on an aluminum foil and dried to obtain the negative electrode sheet;

[0079] (3) Assembly of the lithium ion battery: in a glove box, the negative electrode sheet, PP / PE separator and positive electrode sheet were assembled, and a lithium salt electrolyte was injected during the process, followed by sealing the button cell using a sealing machine, and the assembled button cell was used for subsequent electrochemical performance test.

[0080] Test method:

[0081] (1) Energy density test method: the mass of the prepared battery (unit: g) was accurately weighed; the actual discharge capacity of the battery (unit: Ah) was measured by 1C charge-discharge cycle; the rated voltage of the battery (unit: volt, V) was recorded; the energy of the battery was calculated using the measured capacity and voltage, and then the mass energy density (unit: Wh / kg) was obtained by dividing the energy by the mass of the battery.

[0082] (2) Cycle performance test method: constant current-constant voltage charging was carried out at 1C rate, and after 10 min of standing, constant current discharging was carried out at 1C rate, and the cycle number and the discharge capacity corresponding to each cycle were recorded and compared with the discharge capacity of the first cycle.

[0083] Table 1

[0084] Example No. Energy density wh / kg 1C cycle / capacity retention rate Example 1 193 300 weeks, 92.2% Example 2 188 300 weeks, 91.4% Example 3 189 300 weeks, 91.6% Example 4 190 300 weeks, 91.8% Example 5 175 300 weeks, 89.2% Example 6 173 300 weeks, 88.4% Comparative Example 1 122 300 weeks, 70.2% Comparative Example 2 146 300 weeks, 79.4% Comparative Example 3 148 300 weeks, 78.2%

[0085] As can be seen from the results in Table 1, compared with Comparative Examples 1-3, the lithium ion battery prepared by the preparation method of the present application has excellent energy density and cycle performance, and in particular, the lithium ion battery prepared in Example 1-4 has an energy density of not less than 185 Wh / kg and a capacity retention rate of not less than 90% after 300 cycles.

[0086] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a lithium iron phosphate cathode material, characterized in that, The method comprises: S1: preparing a first slurry containing a lithium iron phosphate raw material and a first carbon source, placing the first slurry in a hydrothermal reaction kettle for a first reaction, and then performing a first drying treatment on the first slurry to prepare a lithium iron phosphate precursor; S2: preparing a second slurry containing the lithium iron phosphate precursor and a second carbon source, and then sequentially performing a second drying treatment and a calcination treatment on the second slurry to prepare the lithium iron phosphate material positive electrode material; The first carbon source and the second carbon source are each independently selected from at least one of citric acid, glucose, polyethylene glycol, amino acid, salicylic acid, tartaric acid, oxalic acid, and polysorbate; The mass ratio of the use amount of the first carbon source to the second carbon source is 1:1-2; The molar ratio of lithium, iron, and phosphorus in the lithium iron phosphate raw material is 1:0.1-1:0.1-1; The conditions of the first reaction include a temperature of 140-250°C and a time of 5-12h; The conditions of the calcination treatment include a temperature of 500-800°C and a time of 1-6h; The dosage of the first carbon source is 1-5wt% based on the mass of the lithium iron phosphate raw material.

2. The production method according to claim 1, wherein The mass ratio of the use amount of the first carbon source to the second carbon source is 1:1.2-1.

8.

3. The production method according to claim 1, wherein The lithium iron phosphate raw material comprises a lithium source, an iron source, and a phosphorus source.

4. The production method according to claim 3, wherein The lithium source is selected from at least one of Li2CO3, LiOH, and LiH2PO4.

5. The production method according to claim 3, wherein, The iron source is selected from at least one of FeSO4, FeC6H5O7, and FeC2O4.

6. The production method according to claim 3, wherein The phosphorus source is selected from at least one of H3PO4, (NH4)2HPO4, and (NH4)3PO4.

7. The production method according to claim 1, wherein The molar ratio of lithium, iron, and phosphorus in the lithium iron phosphate raw material is 1:0.2-0.8:0.2-0.

8.

8. The production method according to claim 1, wherein The conditions of the first reaction include a temperature of 150-200°C and a time of 8-10h.

9. The production method according to claim 1, wherein The conditions of the first drying treatment include a temperature of 40-80°C and a time of 2-5h.

10. The production method according to claim 1, wherein The conditions of the first drying treatment include a temperature of 45-75°C and a time of 2.5-4.5h.

11. The method of producing according to claim 1, wherein, The conditions of the second drying treatment include a temperature of 50-100°C and a time of 3-6h.

12. The method of producing according to claim 1, wherein, The conditions of the second drying treatment include a temperature of 55-85°C and a time of 4.5-5.5h.

13. The method of producing according to claim 1, wherein, The conditions of the calcination treatment include a temperature of 600-700°C and a time of 2-3h.

14. The method of making according to any one of claims 1-13, wherein, The method further comprises: performing a first grinding treatment on the first slurry; the conditions of the first grinding treatment include a rotation speed of 200-300r / min and a time of 6-10h; and / or, performing a second grinding treatment on the second slurry; the conditions of the second grinding treatment include a rotation speed of 500-1000r / min and a time of 3-8h.

15. A lithium iron phosphate material positive electrode material prepared by the preparation method in any one of claims 1-14.

16. The lithium iron phosphate cathode material of claim 15, wherein, The compaction density of the lithium iron phosphate positive electrode material is 2.6-2.7 g / cm 3 .

17. A positive electrode sheet characterized by comprising: The positive electrode sheet is coated with the lithium iron phosphate material positive electrode material in claim 15 or 16.

18. A lithium battery, characterized by, The positive electrode sheet of the lithium battery is the positive electrode sheet in claim 17.