Semi-solid fluid cathode based on magnetic modification and preparation method and application thereof

Abstract

The present invention discloses a semi-solid fluid positive electrode based on magnetic modification, and a preparation method and application thereof. A semi-solid fluid positive electrode based on magnetic modification comprises a composite material, a conductive agent and an electrolyte. The composite material, the conductive agent and the electrolyte are mixed in a certain proportion to obtain a semi-solid fluid positive electrode; the composite material is composited by a positive electrode active material, a superparamagnetic nanomaterial and a carbon material, and is mixed with a conductive agent and an electrolyte in a certain proportion to prepare a slurry, which has good magnetic responsiveness and high conductivity. The slurry is used as a semi-solid fluid positive electrode for lithium-ion batteries. Under a magnetic field, by regulating the internal microstructure of the electrode, the solid active particles are in close contact, the electron transmission path is shortened, and the specific capacity of the semi-solid fluid battery is improved. The design and control method of the semi-solid fluid positive electrode based on magnetic modification provided by the present invention can provide guidance and theoretical basis for the design of new semi-solid slurry electrodes, and can be extended to other battery systems.

Description

Technical Field

[0001] The invention belongs to the field of battery electrodes, and in particular relates to a semi-solid fluid positive electrode based on magnetic modification and a preparation method and application thereof. Background Art

[0002] Semi-solid flow batteries (SSFB) have attracted attention in recent years because they combine the advantages of high energy density of secondary batteries and flexible design of flow batteries. They are expected to be applied in the field of large-scale energy storage. The core of this battery is a semi-solid electrode slurry composed of solid active materials, conductive agents and electrolytes, among which the composition and ratio are the key factors affecting the electrochemical performance of the battery. The development of semi-solid batteries has made great progress in recent years, but there is still a problem that the energy storage capacity and conductivity of the electrode slurry cannot be improved at the same time as reducing the viscosity, which limits the further development of semi-solid flow batteries.

[0003] The core of semi-solid electrode slurry is active material, conductive agent and electrolyte. The insoluble solid components cause the viscosity of semi-solid slurry electrode to be much higher than the viscosity of traditional flow battery energy storage electrolyte, which increases the energy loss when pumping the slurry. In order to improve the storage energy of the battery, the content of active material needs to be increased. However, most active materials have poor conductivity themselves, so the content of conductive agent needs to be increased to enhance the conductivity of slurry electrode. However, with the increase of solid content of active material and conductive agent, the carbon network on which active material and conductivity depend will increase the viscosity of slurry, making its fluidity worse, resulting in mutual restriction of slurry conductivity, specific capacity and viscosity, which are related to the microstructure of particles inside electrode slurry.

[0004] In order to increase the specific capacity of the system, it is necessary to improve the conductivity and particle dispersion uniformity of the electrode slurry while ensuring fluidity. Therefore, it is crucial to find a suitable method to prepare an electrode slurry that takes into account both conductivity and fluidity. Summary of the invention

[0005] In order to solve the problem that it is impossible to simultaneously increase the energy storage capacity and conductivity of the electrode slurry and reduce the viscosity, the inventors have conducted intensive research and designed a semi-solid fluid positive electrode based on magnetic modification and its preparation method and application, which can effectively improve the conductivity of the slurry electrode and improve the electrochemical performance of the semi-solid fluid battery.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] On one hand, the present invention provides a semi-solid fluid cathode based on magnetic modification, which comprises a composite material, a conductive agent and an electrolyte, wherein the composite material, the conductive agent and the electrolyte are mixed in a certain proportion to obtain a semi-solid fluid cathode;

[0008] The composite material is prepared by compounding a positive electrode active material, a superparamagnetic material and a carbon material.

[0009] The present invention loads superparamagnetic materials on active materials so that active particles obtain reversible magnetism under the control of a magnetic field, thereby achieving the design and regulation of the microstructure of the slurry electrode. When a magnetic field is applied, the active material particles are rearranged so that the active material is in full contact with the current collector, shortening the electron transmission distance and improving the conductivity of the entire electrode. After the magnetic field is removed, the active material has zero remanence and no magnetism, so it is dispersed in the slurry, restoring the fluidity of the slurry. The electrochemical performance of the semi-solid flow battery is improved by independently adjusting the conductivity and viscosity of the slurry electrode.

[0010] The magnetically modified electrode composite material of the present invention is obtained by mixing and vacuum drying an active material, a superparamagnetic nanomaterial and a carbon material, and then the composite material is mixed with a conductive agent and an electrolyte in a certain proportion to obtain a semi-solid fluid electrode. The preparation process of the composite material is simple and the production cost is low. The composite material is used as a battery material to prepare a slurry electrode with the advantages of good magnetic response effect, high conductivity and high specific capacity, thereby completing the present invention.

[0011] Furthermore, the positive electrode active material in the composite material is selected from one or more of lithium manganese oxide, lithium cobalt oxide, nickel cobalt lithium manganese oxide (ternary), and lithium iron phosphate. Preferably, the positive electrode active material is lithium manganese oxide (LiMn 2 O 4 ,LMO).

[0012] Furthermore, the superparamagnetic material is selected from one or more of iron, cobalt, nickel, ferroferric oxide or ferrous oxide. Preferably, the superparamagnetic material is ferroferric oxide (Fe 3 O 4 , FEO).

[0013] Furthermore, the carbon material is selected from one or more of carbon nanotubes, nitrogen-doped graphene, carbon fiber and graphene oxide. Preferably, the carbon material is carbon nanotubes (CNT).

[0014] Furthermore, the conductive agent is selected from one or more of Ketjen black, acetylene black, carbon fiber or carbon nanotubes. Preferably, the conductive agent is Ketjen black.

[0015] Furthermore, the electrolyte is lithium hexafluorophosphate dissolved in ethylene carbonate / diethyl carbonate / dimethyl carbonate (LiPF 6 +EC / DMC / DEC).

[0016] Furthermore, the magnetically modified semi-solid fluid electrode is a composite material mixed with a conductive agent and an electrolyte in a volume ratio of 3-5:5-20:30-50, preferably uniformly mixed in a volume ratio of 3:10:37.5.

[0017] The second aspect of the present invention provides a method for preparing a semi-solid fluid cathode based on magnetic modification, wherein the semi-solid fluid cathode based on magnetic modification includes the aforementioned semi-solid fluid cathode based on magnetic modification, and the preparation method includes:

[0018] A composite material is prepared, the composite material preparation method comprising the following steps:

[0019] Step 1, preparing a superparamagnetic material suspension;

[0020] Step 2, loading the superparamagnetic material onto the surface of the positive electrode active material;

[0021] Step 3, loading the carbon material onto the surface of the positive electrode active material / superparamagnetic material composite material;

[0022] Step 4, vacuum drying the sample obtained in step 3 for later use.

[0023] Furthermore, in step 1, the superparamagnetic material suspension includes a ferroferric oxide suspension, and the volume ratio of the ferroferric oxide in the ferroferric oxide suspension to the solvent is 30-50 mg:1-5 ml, more preferably 30-40 mg:1 ml, and more preferably 35 mg:1 ml.

[0024] Furthermore, in step 2, the mass ratio of the positive electrode active material to the superparamagnetic material such as ferrosoferric oxide is 13-15:1, preferably 15:1.

[0025] Furthermore, in step 3, the carbon material includes carbon nanotubes, and the carbon nanotubes are first prepared into a suspension, and the volume ratio of the carbon nanotubes to the solvent is 1-5 mg:1 ml, preferably 1 mg:1 ml, wherein the solvent is a mixture of ethanol and deionized water in a volume ratio of 1:1.

[0026] Furthermore, the mass ratio of the positive electrode active material / superparamagnetic material (ferroferric oxide) composite material to the carbon nanotubes is 90-99:10-1, preferably 95:5.

[0027] Furthermore, in step 4, the sample is first evacuated in a vacuum drying oven, and then dried at 20-60° C. for 10-16 h, preferably at 25° C. for 10 h.

[0028] The third aspect of the present invention provides an application of a magnetically modified semi-solid fluid positive electrode or the preparation method described in the first aspect of the present invention. Under the regulation of a magnetic field, the magnetically modified semi-solid fluid positive electrode is used to improve battery performance.

[0029] The beneficial effects of the present invention include:

[0030] 1) The electrode composite material provided by the present invention uses micron-level positive electrode active materials, which can be directly purchased without pretreatment; nanomaterials with superparamagnetism are used to composite with carbon materials and active materials with good conductivity, so as to obtain a composite material based on magnetic modification with good magnetic response effect and good conductivity;

[0031] 2) The method for preparing a composite material based on magnetic modification provided by the present invention adopts a simple electrostatic adsorption method to load superparamagnetic particles on the active material. The superparamagnetic particles are nano-sized and can be stably and evenly coated on the surface of the active material, which is conducive to the active material to obtain uniform magnetism and has a good magnetic response effect;

[0032] 3) The magnetically modified composite material provided by the present invention is prepared into a semi-solid fluid positive electrode, which has the advantages of high conductivity, good stability and high specific capacity;

[0033] 4) The magnetically modified semi-solid fluid positive electrode provided by the present invention has a good magnetic response effect under the control of the magnetic field, and the active particles are neatly arranged and in close contact, which is conducive to shortening the electron transmission path and enhancing the conductivity of the electrode slurry. After the external magnetic field is removed, the active particles are non-magnetic due to zero remanence, so they are dispersed and restored to fluidity, obtaining an electrode slurry with both high conductivity and low viscosity;

[0034] 5) The design and control method of the magnetically modified semi-solid fluid positive electrode provided by the present invention can obtain an electrode slurry with both high conductivity and low viscosity, thereby improving the electrochemical performance of the battery. This dual-functional semi-solid electrode with fluidity and superparamagnetism can provide guidance and theoretical basis for the design of new semi-solid slurry electrodes, and can be extended to other battery systems, and is expected to be applied to the field of large-scale energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The XRD pattern of the ferrosoferric oxide prepared in Example 1 is shown;

[0036] Figure 2 The SEM image of the ferrosoferric oxide prepared in Example 1 is shown;

[0037] Figure 3 The XRD pattern of the lithium manganese oxide-iron oxide-carbon nanotube composite material prepared in Example 1 is shown;

[0038] Figure 4 The SEM and mapping images of the lithium manganate-ferroferric oxide-carbon nanotube composite material prepared in Example 1 are shown;

[0039] Figure 5 The magnetic response effect diagram of the lithium manganate-ferroferric oxide-carbon nanotube composite material in Example 1 is shown;

[0040] Figure 6 The conductivity diagram of the semi-solid slurry prepared from the lithium manganese oxide-ferroferric oxide-carbon nanotube composite material in Example 2 is shown;

[0041] Figure 7 The constant current charge and discharge curves of the semi-solid battery assembled with the lithium manganese oxide-iron oxide-carbon nanotube composite material in Example 2 are shown in the presence (M) and absence of a magnetic field. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present invention will become more clear and distinct.

[0043] In some embodiments, a semi-solid fluid positive electrode based on magnetic modification is provided, which includes a composite material, a conductive agent and an electrolyte. The composite material, the conductive agent and the electrolyte are mixed in a certain proportion to obtain a semi-solid fluid electrode; wherein the composite material is prepared by compounding a positive electrode active material, a superparamagnetic material and a carbon material.

[0044] The embodiment of the present invention provides a composite material based on magnetic modification, and the composite material is prepared by compounding a positive electrode active material, a superparamagnetic material and a carbon material. For example, the composite material is obtained by mixing and vacuum drying a positive electrode active material, a superparamagnetic nanomaterial and a carbon material, and then the composite material is mixed with a conductive agent and an electrolyte in a certain proportion to obtain a semi-solid fluid electrode. The composite material provided by the embodiment of the present invention has a simple preparation process and a low production cost. It is used as a battery material to prepare a slurry electrode, which has the advantages of good magnetic response effect, high conductivity and high specific capacity.

[0045] In a preferred embodiment, the positive electrode active material is selected from lithium manganese oxide, lithium cobalt oxide, nickel cobalt lithium manganese oxide (ternary), lithium iron phosphate, and further the positive electrode active material is preferably lithium manganese oxide (LiMn 2 O 4 ,LMO).

[0046] The positive electrode active material is preferably lithium manganate, because spinel lithium manganate (LiMn 2 O 4) has the advantages of abundant raw materials, low cost, and environmental friendliness. Its three-dimensional tunnel structure allows lithium ions to be reversibly deintercalated from the spinel lattice without causing structural collapse, thus having excellent rate performance and stability.

[0047] In a preferred embodiment, the superparamagnetic material is selected from one or more of iron, cobalt, nickel, ferroferric oxide or ferrous oxide, more preferably ferroferric oxide (Fe 3 O 4 , FEO).

[0048] The superparamagnetic material is preferably ferroferric oxide, because Fe 3 O 4 The ferromagnetism is strong, and when Fe 3 O 4 When the applied voltage is lower than 1.5 V, Fe 3 O 4 The positive electrode active material LiMn used in the embodiment of the present invention is 2 O 4 The working potential of Fe is higher than 3V. 3 O 4 At this potential, no electrochemical reaction occurs and only magnetism is provided, which is in line with experimental expectations, so it is used as the positive electrode active material.

[0049] In a preferred embodiment, the carbon material is selected from one or more of carbon nanotubes, nitrogen-doped graphene, carbon fiber and graphene oxide, and more preferably carbon nanotubes (CNT).

[0050] In the embodiments of the present invention, the addition of superparamagnetic materials and carbon materials is crucial to the preparation of magnetically modified composite materials and the improvement of their magnetic response effects and electrochemical properties. On the one hand, pure active materials do not have magnetism, and the addition of superparamagnetic materials gives the composite material a good magnetic response effect. On the other hand, most active materials have poor electrical conductivity themselves, and their electrochemical properties as lithium-ion battery electrode materials are not good. Composite with carbon materials can enhance their electrical conductivity and improve the electrochemical properties of the composite material.

[0051] In a preferred embodiment, the conductive agent is selected from one or more of Ketjen black, acetylene black, carbon fiber or carbon nanotube, and Ketjen black is more preferred.

[0052] In a preferred embodiment, the positive electrode electrolyte is lithium hexafluorophosphate dissolved in ethylene carbonate / diethyl carbonate / dimethyl carbonate (LiPF 6 +EC / DMC / DEC).

[0053] In a preferred embodiment, the electrode composite material, the conductive agent and the electrolyte are mixed in a volume ratio of 3-5:5-20:30-50, preferably in a volume ratio of 3:10:37.5.

[0054] In some embodiments, a method for preparing the magnetically modified semi-solid fluid cathode according to the first aspect of the present invention is also provided, the preparation method comprising:

[0055] A composite material based on magnetic modification is prepared, and the composite material preparation method comprises the following steps:

[0056] Step 1: preparing a superparamagnetic material suspension, illustratively, preparing a ferroferric oxide suspension;

[0057] The coprecipitation method was used to synthesize ferroferric oxide nanoparticles. First, 0.4 g FeCl 2 •4H 2 O, 1.08 gFeCl 3 •6H 2 O (the molar ratio of the two is 1:2) in a three-necked flask, 32 mL of deionized water was added, stirred for 10 min, and then 20 mL of NH 4 OH (mass fraction of 25%) was slowly dripped into the above three-necked flask and stirred for 5 minutes. Then the three-necked flask was removed from the device and ultrasonicated for 5 minutes. Then, it was centrifuged once at 12000 rpm for 10 minutes. The supernatant was poured out and washed once with deionized water. The obtained precipitate was placed in 10 mL of deionized water to obtain a ferroferric oxide suspension for later use.

[0058] Step 2: Loading superparamagnetic materials such as ferroferric oxide onto the surface of the positive electrode active material;

[0059] First, LiMn was prepared by electrostatic adsorption method. 2 O 4 -Fe 3 O 4(LMO-FEO) composite material. First, the surface of FEO was modified with PDDA solution to make its surface positively charged. 75.25 mg PDDA was weighed in a glass bottle and dissolved in 20 mL deionized water. The PDDA was magnetically stirred until the PDDA was completely dissolved, and then the PDDA solution was adjusted to pH = 8.5 with NaOH solution. The concentration of FEO solution was 35 mg / mL. 0.86 mL FEO solution was taken and added to the above PDDA solution (the mass ratio of FEO to PDDA was 1:2.5), ultrasonicated in an ultrasonic tank for 1 h, washed with deionized water once, 50 mL deionized water was added, mixed with LMO with negative surface charge, 200 mL deionized water was added, and stirred at 500 rpm for 90 min under mechanical stirring. After the suspension was allowed to stand overnight, it was centrifuged once at 5000 rpm for 5 min, the supernatant was poured off, and the sample was dried in a vacuum drying oven at 25 ° C for 12 h to obtain a LMO-FEO composite material.

[0060] Step 3, loading a carbon material such as carbon nanotubes onto the surface of the positive electrode active material / ferroferric oxide composite material;

[0061] Dissolve 15 mg of CNT in a mixture of 15 mL of ethanol and deionized water (volume ratio of ethanol to deionized water is 1:1), and sonicate in an ultrasonic bath for 30 min to disperse the CNT evenly. Mix 285 mg of LMO-FEO with the CNT suspension in step 5 at a mass ratio of 95:5 of LMO-FEO to CNT, shake for 20 min, and then centrifuge the suspension at 10,000 rpm for 5 min, and discard the supernatant.

[0062] Step 4, vacuum drying the sample for later use;

[0063] The centrifuged sample was dried in a vacuum drying oven at 25° C. for 10 h to obtain a LMO-FEO-CNT composite material.

[0064] It should be understood that when other types of superparamagnetic materials, positive active materials or carbon materials are used, the composite material preparation method has the same or similar principles and operating methods, which will not be described in detail here.

[0065] In an embodiment of the present invention, in the preparation method of a semi-solid fluid positive electrode based on magnetic modification, a composite material can be prepared first, and then the prepared composite material is mixed with a conductive agent and an electrolyte in a certain proportion to obtain a semi-solid fluid electrode.

[0066] In some embodiments, the use of a magnetically modified semi-solid fluid electrode or a preparation method thereof is also provided. Under the control of a magnetic field, the magnetically modified semi-solid fluid positive electrode can be used to improve battery performance. The magnetically modified semi-solid fluid positive electrode has good magnetic response effect and high conductivity. When applied to batteries, it has the advantage of high specific capacity under magnetic field control. For example, a semi-solid lithium-ion half-battery obtained by mixing an LMO-FEO-CNT composite material with a conductive agent and an electrolyte in a volume ratio of 3:10:37.5, under magnetic field control, when the current density is 0.5 mA / cm 2 The specific capacity is significantly improved.

[0067] In order to fully illustrate the relevant performance of the magnetically modified semi-solid fluid positive electrode provided by the present application and facilitate the understanding of the present invention, the present application has conducted multiple groups of experimental verifications. The present invention will be further described below in conjunction with specific embodiments.

[0068] Example 1

[0069] The coprecipitation method was used to synthesize ferroferric oxide nanoparticles. First, 0.4 g FeCl 2 •4H 2 O, 1.08 gFeCl 3 •6H 2 O (the molar ratio of the two is 1:2) in a three-necked flask, 32 mL of deionized water was added, stirred for 10 min, and then 20 mL of NH 4 OH (mass fraction of 25%) was slowly dripped into the above three-necked flask and stirred for 5 minutes. Then the three-necked flask was removed from the device and ultrasonicated for 5 minutes. Then, it was centrifuged once at 12000 rpm for 10 minutes. The supernatant was poured out and washed once with deionized water. The obtained precipitate was placed in 10 mL of deionized water to obtain a ferrosoferric oxide suspension.

[0070] refer to Figure 1 and Figure 2 As shown in the XRD pattern of the obtained ferroferric oxide sample, the diffraction peaks are consistent with the standard card, indicating that pure phase spherical FEO nanoparticles ( Figure 1 ). Further through its SEM image, it can be observed that the synthesized FEO nanoparticles have a uniform particle size of about 15nm ( Figure 2 ).

[0071] Preparation of LiMn by electrostatic adsorption 2 O 4 -Fe 3 O 4(LMO-FEO) composite material. First, the surface of FEO was modified with PDDA solution to make its surface positively charged. 75.25 mg PDDA was weighed in a glass bottle and dissolved in 20 mL deionized water. The PDDA was magnetically stirred until the PDDA was completely dissolved, and then the PDDA solution was adjusted to pH = 8.5 with NaOH solution. The concentration of FEO solution was 35 mg / mL. 0.86 mL FEO solution was taken and added to the above PDDA solution (the mass ratio of FEO to PDDA was 1:2.5), ultrasonicated in an ultrasonic tank for 1 h, washed with deionized water once, 50 mL deionized water was added, and mixed with LMO with negative surface charge, 200 mL deionized water was added, and the mixture was stirred at 500 rpm for 90 min under mechanical stirring. The liquid was left to stand overnight, and then centrifuged once at 5000 rpm for 5 min, and finally dried in a vacuum drying oven at 25 ° C for 12 h to obtain LMO-FEO composite material.

[0072] 15 mg of CNT was dissolved in a mixture of 15 mL of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:1), and ultrasonicated in an ultrasonic bath for 30 min to make the CNT dispersed evenly.

[0073] 285 mg of LMO-FEO was mixed with the above CNT suspension at a LMO-FEO to CNT mass ratio of 95:5, shaken for 20 min, then centrifuged once at 10000 rpm for 5 min, and dried in a vacuum drying oven at 25°C for 10 h to obtain a LMO-FEO-CNT composite material.

[0074] Figure 3 The XRD pattern of the LMO-FEO-CNT composite material prepared in Example 1 shows that the LMO-FEO-CNT composite material and LiMn 2 O 4 (PDF#35-0782) standard card, indicating that it has a complete spinel structure and no impurities are generated. The lack of FEO diffraction peaks in the XRD spectrum may be due to the small amount of added oxides, and CNTs are amorphous carbon, so the diffraction peaks are flat and weak, and are not obvious in the XRD spectrum.

[0075] Figure 4The SEM image and mapping image of the LMO-FEO-CNT composite material further prove the existence of FEO and CNT. It can be seen that the LMO particles still retain the angular structure of the cubic crystal system, the fine spherical particles coated on its surface are FEO, and the slender tubular objects wrapped around the LMO surface are CNT. In the mapping image, Mn and O elements come from LMO, Fe and O elements come from FEO, and C element comes from CNT. From the mapping image, it can be seen that Mn, O, Fe and C elements are evenly distributed on the composite material, that is, FEO and CNT are evenly coated on the LMO surface, indicating that the expected LMO-FEO-CNT composite material was prepared.

[0076] Figure 5 This is a diagram of the magnetic response effect of the LMO-FEO-CNT composite material. Under the condition of no magnetic field, the LMO-FEO-CNT composite material is freely dispersed in the aqueous solution, and the solution is black. After the magnetic field is applied on one side, the LMO-FEO-CNT composite material particles quickly gather to the side with the magnetic field, separate from the water, and the suspension becomes clear, indicating that it has a good magnetic response effect.

[0077] Example 2

[0078] from Figure 6 It can be seen that the electronic conductivity of LMO-FEO-CNT slurry is significantly greater than that of LMO slurry. The former (2.14 mS / cm) is about 4.3 times that of the latter (0.49 mS / cm). This is because the CNTs therein, as a material with good conductivity, improve the electronic conductivity of the composite material.

[0079] The semi-solid lithium-ion half-cell assembled in Example 2 was tested for rate performance. The test conditions were: the test voltage was 3.00-4.50V, and the tests were performed at 0.1C, 0.2C, 0.5C, 1C and 2C, respectively. The test results are shown in the figure. Figure 7 shown.

[0080] from Figure 7 It can be seen that at 0.5 mA / cm 2 Under current density, the specific capacity of LMO, LMO-FEO-CNT and LMO-FEO-CNT (M) fluid batteries increases successively, that is, the specific capacity of LMO-FEO-CNT (M) fluid battery is the highest when an external magnetic field is applied, indicating that the addition of FEO and CNT can effectively increase the specific capacity of the battery, and under the action of the external magnetic field, the magnetic active materials are in close contact, shortening the transmission path of electrons, thereby improving the electrochemical performance of the battery.

[0081] The present invention is described in detail above in combination with preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are only illustrative explanations of the present invention and do not constitute any limitation on the protection scope of the present invention. Without exceeding the spirit and protection scope of the present invention, various improvements, equivalent substitutions or modifications may be made to the technical content of the present invention and its embodiments, which all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. Application of a semi-solid fluid cathode based on magnetic modification, Features: The semi-solid fluid positive electrode comprises a composite material, a conductive agent and an electrolyte, wherein the composite material, the conductive agent and the electrolyte are mixed in a certain proportion to obtain a semi-solid fluid positive electrode; wherein the composite material is composited by a positive electrode active material, a superparamagnetic material and a carbon material; When a magnetic field is applied, the active material particles are rearranged, allowing the active material to fully contact the current collector; after the magnetic field is removed, the active material has zero remanence and is dispersed in the slurry, restoring the fluidity of the slurry; The positive electrode active material is lithium manganate; The preparation of the composite material comprises the following steps: Step 1, preparing a superparamagnetic material suspension, wherein the superparamagnetic material suspension comprises a ferroferric oxide suspension; Step 2, loading the superparamagnetic material onto the surface of the positive electrode active material, firstly modifying the surface of ferroferric oxide with a PDDA solution to make its surface positively charged, adding deionized water, mixing with lithium manganese oxide with a negative charge on the surface, stirring, and drying; Step 3, loading the carbon material onto the surface of the positive electrode active material / superparamagnetic material composite material; Step 4, vacuum drying the sample obtained in step 3 for later use.

2. The use of a magnetically modified semi-solid fluid cathode according to claim 1, Features: The superparamagnetic material is ferroferric oxide.

3. The use of a magnetically modified semi-solid fluid cathode according to claim 1, Features: The conductive agent is Ketjen black.

4. The use of a magnetically modified semi-solid fluid cathode according to claim 1, Features: The composite material, the conductive agent and the electrolyte are mixed in a volume ratio of 3:10:37.

5.

5. The use of a magnetically modified semi-solid fluid cathode according to claim 1, Features: In step 1, the volume ratio of the superparamagnetic material to the solvent in the ferroferric oxide suspension is 35 mg: 1 ml; In step 2, the mass ratio of the positive electrode active material to the superparamagnetic material is 15:

1.

6. The use of a magnetically modified semi-solid fluid cathode according to claim 1, Features: In step 3, the carbon material includes carbon nanotubes, and the carbon nanotubes are first prepared into a suspension, wherein the mass ratio of the carbon nanotubes to the volume ratio of the solvent is 1 mg:1 ml; the solvent includes a mixture of ethanol and deionized water in a volume ratio of 1:1; The mass ratio of the positive electrode active material / superparamagnetic material composite material to the carbon material is 95:5; In step 4, the sample is first evacuated in a vacuum drying oven and then dried at 25° C. for 10 h.

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