Preparation method and application of light storage integrated graphene battery

Abstract

A method for preparing and applying an integrated photovoltaic and energy storage graphene battery, the graphene battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the method for preparing the graphene / lithium iron phosphate composite material of the positive electrode active material includes the following steps: Step 1, chelating lithium acetate, graphene oxide / EDTA-containing Fe... 3+ The precursor is obtained by dispersing ammonium dihydrogen phosphate and deionized water in stoichiometric ratio and undergoing hydrothermal reaction; step two: heat treatment of the precursor; to obtain sheet-like material loaded on the surface of graphene lithium iron phosphate nanoparticles; the present invention also discloses an integrated photovoltaic and energy storage system, including an electrically connected photovoltaic array, a DC / DC converter and a graphene battery for storing energy; the present invention utilizes graphene oxide and disodium ethylenediaminetetraacetate to chelate and position the iron source, effectively ensuring a uniform positional relationship between graphene oxide and the generated lithium iron phosphate, and effectively improving the electronic conductivity and ionic conductivity of the obtained lithium iron phosphate composite material.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic energy storage technology, and in particular to a method for preparing and applying an integrated photovoltaic and energy storage graphene battery. Background Technology

[0002] The grid connection of photovoltaic (PV) power generation is limited by the intermittent and uncertain nature of PV power generation. Therefore, it is necessary to store the electrical energy generated by the PV array in lithium-ion batteries using a DC / DC converter. Lithium-ion battery cathode materials mainly include lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and ternary materials. A PV energy storage power generation system disclosed in utility model patent CN206628883U allows operators to select either PV or AC mains power input via an AC / PV input distribution device. The PV input is converted into 48V low-voltage DC power by a PV charging device, while the 220V AC mains input is converted into 48V low-voltage DC power by an AC rectifier.

[0003] The energy storage battery charging method based on partial state of charge (SoC) cycling, which operates within a relatively narrow state of charge window (approximately 20% to 90%), ensures that the battery is neither deeply discharged nor deeply charged under normal charge and discharge conditions, maximizing the utilization of the battery's cycle life. However, after a period of use, the activity of the materials in the battery decreases, and its capacity will be lost. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing and applying an integrated photovoltaic and energy storage graphene battery, thereby reducing capacity loss.

[0005] This invention utilizes graphene oxide and disodium ethylenediaminetetraacetate to chelate and position the iron source, effectively ensuring a uniform positional relationship between the graphene oxide and the generated lithium iron phosphate. This effectively improves the electronic and ionic conductivity of the resulting lithium iron phosphate composite material, resulting in a stable structure suitable for stable cycling of partially charged batteries and reducing capacity loss.

[0006] To solve this technical problem, the technical solution of the present invention is as follows: A method for preparing an integrated photovoltaic and energy storage graphene battery, wherein the graphene battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte.

[0007] The positive electrode sheet is obtained by coating and drying a slurry, which is mainly composed of the following raw materials by weight percentage: The composition consists of 92%–95% graphene / lithium iron phosphate composite material, 3%–5% conductive carbon black, and 1%–5% polyvinylidene fluoride (PVDF).

[0008] The negative electrode sheet is obtained by coating and drying slurry two, which is mainly composed of the following raw materials by weight percentage: The composition consists of 90%–95% artificial graphite, 1%–3% carboxymethyl cellulose, 1%–3% styrene-butadiene rubber, and 1%–5% Ketjen black.

[0009] The preparation method of the graphene / lithium iron phosphate composite material includes the following steps: Step 1: chelate Fe with lithium acetate, graphene oxide / EDTA 3+ The ammonium dihydrogen phosphate and ammonium dihydrogen phosphate were dispersed in deionized water according to the stoichiometric ratio, mixed evenly, and the pH of the solution was adjusted to 6.8-7.2. The solution was then added to a reaction vessel for hydrothermal reaction to obtain the precursor. Furthermore, in step one of the preparation method of graphene / lithium iron phosphate composite material, the hydrothermal reaction process conditions are: 200℃~215℃, and holding for 5 hours~8 hours.

[0010] Step 2: Heat treat the precursor obtained in Step 1; Furthermore, in step two, the heat treatment process involves heating the material at room temperature to 700℃-800℃ at a heating rate of 5℃ / min-8℃ / min, holding it at that temperature for 5-8 hours, and then cooling it to room temperature in the furnace. This yields sheet-like materials loaded onto the surface of graphene, specifically lithium iron phosphate nanoparticles, i.e., graphene / lithium iron phosphate composite materials.

[0011] Furthermore, Fe chelated by graphene oxide / EDTA 3+ The preparation method includes the following steps: S1. Add graphene oxide (GO) to a solution of disodium ethylenediaminetetraacetate (EDTA-2Na), disperse by ultrasonication, mix evenly, add ethanol, and dry under an infrared lamp to obtain EDTA / graphene oxide linked by hydrogen bonds. Ethanol is added in step S1 to disperse the particles; it is sufficient to disperse them.

[0012] EDTA is linked to graphene oxide via hydrogen bonds, as follows: ; S2. Disperse the EDTA / graphene oxide obtained in step S1 in deionized water, add Fe(NO3)3 solution dropwise, stir until homogeneous, and let stand to obtain Fe oxide chelated with EDTA. 3+ Dispersion in which Fe 3+ As EDTA is distributed around EDTA.

[0013] This invention utilizes hydrogen bonding and chelation to achieve the relative positioning between graphene oxide and ferric ions, which is beneficial to the formation of the target product.

[0014] Furthermore, in step S2, the molar ratio of the solute Fe(NO3)3 in the Fe(NO3)3 solution to disodium ethylenediaminetetraacetate (i.e., EDTA-2Na) in step S1 is 1:(8-10). In this invention, the amount of EDTA-2Na used is sufficient, and its role as a complexing agent and reducing agent is effectively exerted.

[0015] Furthermore, in step one of the preparation method of the graphene / lithium iron phosphate composite material, the molar ratio of lithium, iron, and phosphate is (1.0–1.05):1.0:1.0. Based on the stoichiometric ratio, lithium can be added in slight excess, which is beneficial to the reaction.

[0016] Furthermore, Fe chelated by graphene oxide / EDTA 3+ In the preparation method, the mass percentage of graphene oxide in step S1 relative to the total mass of lithium acetate (lithium source) in step S1, Fe(NO3)3 (iron source) in step S2, and ammonium dihydrogen phosphate (phosphate) in step S1 is 5.0 wt% to 8.0 wt%. Graphene oxide effectively ensures the loading of lithium iron phosphate and promotes the dispersion of sheet-like lithium iron phosphate.

[0017] Furthermore, in step S1, the graphene oxide undergoes a pretreatment to achieve uniform dispersion. This pretreatment includes the following steps: A1. Microwave treatment of graphene oxide removes moisture and increases interlayer spacing; A2. The graphene oxide treated in A1 is dispersed in an oxidizing electrolyte. A constant voltage of 12V to 15V is applied between the cathode and the anode. Water molecules decompose to generate hydroxyl radicals, and the number of oxidized groups on the surface of the graphene oxide sheets increases. A3. Stop applying voltage, filter, wash, collect, and dry to obtain pretreated graphene oxide. This invention, through pretreatment, further strips and increases the oxide groups of graphene oxide, promotes the encapsulation of sheet-like graphene oxide by disodium ethylenediaminetetraacetate, and simultaneously improves the dispersibility of graphene oxide in water, resulting in a more complete loading.

[0018] Furthermore, in step A2, the electrolyte in the oxidizing electrolyte is hydrogen peroxide, sulfuric acid, or concentrated sulfuric acid, and the concentration of the electrolyte is 0.5 mol / L to 0.8 mol / L. This invention utilizes an oxidizing electrolyte to promote an increase in the number of oxygen-containing groups on the surface of graphene oxide.

[0019] Furthermore, in step A1, the microwave power is preferably 500W to 800W, and the microwave time is 3min to 6min.

[0020] The second objective of this invention is to provide an integrated photovoltaic and energy storage system. This invention uses graphene-loaded lithium iron phosphate, which is suitable for stable cycling of partially charged batteries and reduces capacity loss.

[0021] To solve this technical problem, the technical solution of the present invention is: an integrated photovoltaic and energy storage system, comprising an electrically connected photovoltaic array, a DC / DC converter, and a graphene battery prepared by any one of the preparation methods of the present invention for storing electrical energy.

[0022] Preferably, the photovoltaic array has a power generation layer material, which is one of amorphous silicon, cadmium telluride, copper indium gallium selenide, and gallium arsenide.

[0023] By adopting the above technical solution, the beneficial effects of the present invention are: Lithium iron phosphate (LFP) exhibits poor electrical conductivity in existing technologies. Due to its unique olivine-type structure, the tetrahedron formed by phosphorus (P) and oxygen (O) separates the octahedron formed by feium (Fe) and oxygen (O), resulting in an electronic conductivity of only 10⁻⁶. -10 S*m -1 The poor conductivity between lithium iron phosphate particles means that lithium ions can only be transported along specific axes on specific faces of the lithium iron phosphate crystal, severely restricting the diffusion of lithium ions from the interior into the electrolyte. This leads to a significant decrease in the rate of redox reactions. Even if electrons reach the reaction sites of the active material at an extremely high rate, the slow rate of lithium ion release prevents the entire reaction from proceeding. These technical problems limit the transport of electrons and lithium ions, thus limiting the application of lithium iron phosphate in integrated photovoltaic and energy storage systems. To address these issues, this invention utilizes the relatively good dispersibility of graphene oxide in water. Disodium ethylenediaminetetraacetate (EDTA-2Na) is grafted onto its circumferential direction using hydrogen bonds. Then, the chelation of ferric ions by EDTA-2Na achieves the pre-setting of the lithium iron phosphate particle formation position. In the hydrothermal reaction liquid environment, EDTA acts as a complexing agent. During precursor formation, EDTA-2Na effectively maintains the surrounding of graphene oxide particles, resulting in relatively uniform dispersion of lithium iron phosphate and graphene oxide.

[0024] The present invention forms a lithium iron phosphate precursor surrounding graphene oxide; accompanied by high-temperature calcination, EDTA acts as a reducing agent to form carbon and nitrogen during the calcination process, thereby reducing Fe... 3+ Reduced to Fe 2+ Furthermore, the reduced graphene combines with lithium ions and phosphate ions to form lithium iron phosphate, effectively creating a loading of lithium iron phosphate nanosheets with reduced graphene oxide. The composite material obtained by this invention has a uniform particle size distribution, good dispersibility, and stable structure. Under partial state of charge (PSoC), the ionic conductivity of nanoscale lithium iron phosphate is significantly improved, while the electronic conductivity of lithium iron phosphate is also significantly improved due to the loading of reduced graphene oxide.

[0025] Reduced graphene oxide / lithium iron phosphate cathode material exhibits structural stability during cycling. The lithium iron phosphate exhibits uniform morphology and size, with a particle size between 100 and 300 nm. The sheet-like structure of lithium iron phosphate nanoparticles effectively utilizes the increased specific surface area to reduce the one-dimensional limitation of lithium ion transport paths within LiFePO4, resulting in rapid electron and ion conduction. This suppresses capacity loss of Li caused by particle aggregation, structural collapse, or untimely lithium ion insertion / extraction. It is suitable as a graphene battery in integrated photovoltaic and energy storage systems for grid connection or energy storage, and can maintain stable cycling even under partial charge. Attached Figure Description

[0026] Figure 1 This is a SEM image of the graphene / lithium iron phosphate composite material prepared in Example 1 of this invention; Figure 2 This is the XRD pattern of the graphene / lithium iron phosphate composite material prepared in Example 1 of the present invention; Figure 3 This is the infrared spectrum of EDTA-2Na attached to the surface of graphene oxide in Example 1 of this invention; Figure 4 These are the cycle and rate performance curves of the batteries obtained in Examples 1, 3, and the comparative examples of this invention. Detailed Implementation

[0027] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0028] This invention utilizes the relatively good dispersibility of graphene oxide in water, and uses hydrogen bonds to graft disodium ethylenediaminetetraacetate (EDTA-2Na) onto its circumferential direction. Then, the chelation of trivalent iron ions by disodium ethylenediaminetetraacetate (EDTA-2Na) is used to achieve the pre-setting of the formation position of lithium iron phosphate particles. In the hydrothermal reaction liquid environment, EDTA acts as a complexing agent, and EDTA-2Na effectively maintains the surrounding of graphene oxide particles during the formation of the precursor, resulting in relatively uniform dispersion of lithium iron phosphate and graphene oxide.

[0029] The present invention forms a lithium iron phosphate precursor surrounding graphene oxide; accompanied by high-temperature calcination, EDTA acts as a reducing agent to form carbon and nitrogen during the calcination process, thereby reducing Fe... 3+ Reduced to Fe 2+ Furthermore, the reduced graphene combines with lithium ions and phosphate ions to form lithium iron phosphate, effectively creating a loading of lithium iron phosphate nanosheets with reduced graphene oxide. The composite material obtained by this invention has a uniform particle size distribution, good dispersibility, and stable structure. Under partial state of charge (PSoC), the ionic conductivity of nanoscale lithium iron phosphate is significantly improved, while the electronic conductivity of lithium iron phosphate is also significantly improved due to the loading of reduced graphene oxide.

[0030] Reduced graphene oxide / lithium iron phosphate cathode material exhibits structural stability during cycling. The lithium iron phosphate exhibits uniform morphology and size, with a particle size ranging from 100 to 300 nm. The sheet-like structure of lithium iron phosphate nanoparticles effectively utilizes the increased specific surface area to reduce the one-dimensional limitation of lithium ion transport pathways within LiFePO4, resulting in rapid electron and ion conduction and suppressing capacity loss of Li caused by particle aggregation, structural collapse, or untimely lithium ion insertion / extraction.

[0031] Example 1 The method for preparing a photovoltaic-storage integrated graphene battery in this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0032] The positive electrode sheet is obtained by coating and drying a slurry, which is made from the following raw materials by weight percentage: The composition consists of 92% graphene / lithium iron phosphate composite material, 3% conductive carbon black, and 5% PVDF. The negative electrode sheet is obtained by coating and drying a second slurry, which is made from the following raw materials by weight percentage: 92% artificial graphite, 3% carboxymethyl cellulose, 1% styrene-butadiene rubber, and 4% Ketjen Black.

[0033] The preparation method of the graphene / lithium iron phosphate composite material described in this embodiment includes the following steps: Step 1: chelate Fe with lithium acetate, graphene oxide / EDTA 3+ The ammonium dihydrogen phosphate and ammonium dihydrogen phosphate were dispersed in deionized water according to the stoichiometric ratio, mixed evenly, and the pH of the solution was adjusted to 6.8. The solution was then added to a reaction vessel for hydrothermal reaction to obtain the precursor. The process conditions for the hydrothermal reaction in step one of this embodiment are as follows: Keep warm at 200℃ for 8 hours.

[0034] Step 2: Heat treat the obtained precursor; The heat treatment process involves heating the material at room temperature to 700°C at a rate of 5–8°C / min, holding it at that temperature for 8 hours, and then cooling it to room temperature in the furnace. This yields sheet-like materials loaded onto the surface of graphene, forming lithium iron phosphate nanoparticles, i.e., graphene / lithium iron phosphate composite materials.

[0035] The scanning electron microscope image of the graphene / lithium iron phosphate composite material prepared in this embodiment is shown below. Figure 1 As shown, the XRD test is as follows Figure 2 As shown.

[0036] In this embodiment, Fe is chelated with graphene oxide / EDTA. 3+ The preparation method includes the following steps: S1. Add graphene oxide to a solution of disodium ethylenediaminetetraacetate, disperse by ultrasonication, mix evenly, add ethanol, and dry under an infrared lamp to obtain EDTA / graphene oxide linked by hydrogen bonds. EDTA is linked to graphene oxide via hydrogen bonds, as follows: ; S2. Disperse the EDTA / graphene oxide obtained in step S1 in deionized water, add Fe(NO3)3 solution dropwise, stir until homogeneous, and let stand to obtain Fe oxide chelated with EDTA. 3+ Dispersion in which Fe 3+ As EDTA is distributed around EDTA.

[0037] This invention utilizes hydrogen bonding and chelation to achieve the relative positioning between graphene oxide and ferric ions, which is beneficial to the formation of the target product. Figure 3 The image shows the infrared spectrum of EDTA-2Na / GO. From the image, we can see that GO reaches a wavelength of 3388 cm⁻¹. -1 A broad peak of the stretching vibration of -OH is formed at 1719 cm⁻¹. -1 There is a bending vibration peak at C=O; at 1631 cm⁻¹ -1 There is a C=C stretching vibration peak at 1402 cm⁻¹. -1 There is a C-OH stretching vibration peak at 1056 cm⁻¹; -1 The peaks at 3459 cm⁻¹ represent the stretching vibrations of COC. At 3459 cm⁻¹, the peaks at 1636 cm⁻¹ represent the stretching vibrations of C=O in the -NHCO- functional group, and at 1086 cm⁻¹, the peaks at 1086 cm⁻¹ represent the stretching vibrations of CO, indicating that EDTA is effectively bonded to the GO surface.

[0038] In step S2 of this embodiment, the molar ratio of the solute Fe(NO3)3 in the Fe(NO3)3 solution to disodium ethylenediaminetetraacetate (i.e., EDTA-2Na) in step S1 is 1:8. In this invention, the amount of EDTA-2Na used is sufficient, and its role as a complexing agent and reducing agent is effectively exerted.

[0039] In step one of the preparation method of the graphene / lithium iron phosphate composite material in this embodiment, the molar ratio of lithium, iron and phosphate is 1.05:1.0:1.0.

[0040] In the method for preparing Fe3+ chelated with graphene oxide / EDTA, the mass percentage of graphene oxide in step S1 is 5.0 wt% of the total mass of lithium acetate (lithium source) in step S1, Fe(NO3)3 (iron source) in step S2, and ammonium dihydrogen phosphate (phosphate) in step S1. Graphene oxide effectively ensures the loading of lithium iron phosphate and promotes the dispersion of sheet-like lithium iron phosphate.

[0041] Example 2 The method for preparing a photovoltaic-storage integrated graphene battery in this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode sheet is obtained by coating and drying a slurry, which is made from the following raw materials by weight percentage: Graphene / lithium iron phosphate composite material 95%, conductive carbon black 3%, and PVDF 2%; The negative electrode sheet is obtained by coating and drying a second slurry, which is made from the following raw materials by weight percentage: 94% artificial graphite, 1% carboxymethyl cellulose, 2% styrene-butadiene rubber, and 3% Ketjen black.

[0042] This embodiment discloses a method for preparing graphene / lithium iron phosphate composite material, including the following steps: Step 1: chelate Fe with lithium acetate, graphene oxide / EDTA 3+ Ammonium dihydrogen phosphate and ammonium dihydrogen phosphate are dispersed in deionized water according to stoichiometric ratio, mixed evenly, and the pH of the solution is adjusted to 7.2. The solution is then added to a reaction vessel for hydrothermal reaction to obtain the precursor. The process conditions for the hydrothermal reaction in step one of this embodiment are as follows: 215℃, keep warm for 5 hours.

[0043] Step 2: Heat treat the obtained precursor; The heat treatment process involves heating the material at room temperature to 800°C at a rate of 5–8°C / min, holding it at that temperature for 5 hours, and then cooling it to room temperature in the furnace. This yields sheet-like materials loaded onto the surface of graphene, forming lithium iron phosphate nanoparticles, i.e., graphene / lithium iron phosphate composite materials.

[0044] In this embodiment, Fe is chelated with graphene oxide / EDTA. 3+ The preparation method includes the following steps: S1. Add graphene oxide to a solution of disodium ethylenediaminetetraacetate, disperse by ultrasonication, mix evenly, add ethanol, and dry under an infrared lamp to obtain EDTA / graphene oxide linked by hydrogen bonds. EDTA is linked to graphene oxide via hydrogen bonds, as follows: ; S2. Disperse the EDTA / graphene oxide obtained in step S1 in deionized water, add Fe(NO3)3 solution dropwise, stir until homogeneous, and let stand to obtain Fe oxide chelated with EDTA. 3+ Dispersion in which Fe 3+ With EDTA distributed around EDTA, this invention utilizes hydrogen bonding and chelation to achieve the relative positioning between graphene oxide and ferric ions, which is beneficial for the formation of the target product.

[0045] In this embodiment, in step S2, the molar ratio of the solute Fe(NO3)3 in the Fe(NO3)3 solution to disodium ethylenediaminetetraacetate (i.e., EDTA-2Na) in step S1 is 1:10. In this invention, the amount of EDTA-2Na used is sufficient, and its role as a complexing agent and reducing agent is effectively exerted.

[0046] In step one of the preparation method of the graphene / lithium iron phosphate composite material described in this embodiment, the molar ratio of lithium, iron and phosphate is 1.05:1.0:1.0.

[0047] In the method for preparing Fe3+ chelated with graphene oxide / EDTA, the mass percentage of graphene oxide in step S1 is 8.0 wt% of the total mass of lithium acetate (lithium source) in step S1, Fe(NO3)3 (iron source) in step S2, and ammonium dihydrogen phosphate (phosphate) in step S1. Graphene oxide effectively ensures the loading of lithium iron phosphate and promotes the dispersion of sheet-like lithium iron phosphate.

[0048] Example 3 The main difference between this embodiment and the graphene / lithium iron phosphate composite material in Embodiment 1 is that in step S1 of this embodiment, the graphene oxide undergoes a pretreatment to achieve uniform dispersion. The pretreatment includes the following steps: A1. Microwave treatment of graphene oxide removes moisture and increases interlayer spacing; A2. The graphene oxide treated in A1 is dispersed in an oxidizing electrolyte. A constant voltage of 12V is applied between the cathode and the anode. Water molecules decompose to generate hydroxyl radicals, and the number of oxidized groups on the surface of the graphene oxide sheets increases. A3. Stop applying voltage, filter, wash, collect, and dry to obtain pretreated graphene oxide. This invention, through pretreatment, further strips and increases the oxide groups of graphene oxide, promotes the encapsulation of sheet-like graphene oxide by disodium ethylenediaminetetraacetate, and simultaneously improves the dispersibility of graphene oxide in water, resulting in a more complete loading.

[0049] In step A2 of this embodiment, the electrolyte in the oxidizing electrolyte is hydrogen peroxide, and the concentration of the electrolyte is 0.8 mol / L. This invention utilizes an oxidizing electrolyte to promote an increase in the number of oxygen-containing groups on the surface of graphene oxide.

[0050] In step A1 of this embodiment, the microwave power is 500W and the microwave time is 6min.

[0051] The graphene / lithium iron phosphate composite material prepared in this embodiment is used to prepare a battery, wherein the graphene battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode sheet is obtained by coating and drying a slurry, which is made from the following raw materials by weight percentage: The composition consists of 92% graphene / lithium iron phosphate composite material, 5% conductive carbon black, and 3% PVDF. The negative electrode sheet is obtained by coating and drying a second slurry, which is made from the following raw materials by weight percentage: 92% artificial graphite, 3% carboxymethyl cellulose, 1% styrene-butadiene rubber, and 4% Ketjen Black.

[0052] Except as otherwise specified above, the other operations and parameters in this embodiment 3 are the same as those in embodiment 1.

[0053] Example 4 The main difference between this embodiment and the graphene / lithium iron phosphate composite material in Embodiment 2 is that in step S1 of this embodiment, the graphene oxide undergoes a pretreatment to achieve uniform dispersion. This pretreatment includes the following steps: A1. Microwave treatment of graphene oxide removes moisture and increases interlayer spacing; A2. The graphene oxide treated in A1 is dispersed in an oxidizing electrolyte. A constant voltage of 15V is applied between the cathode and the anode. Water molecules decompose to generate hydroxyl radicals, and the number of oxidized groups on the surface of the graphene oxide sheets increases. A3. Stop applying voltage, filter, wash, collect, and dry to obtain pretreated graphene oxide. This invention, through pretreatment, further strips and increases the oxide groups of graphene oxide, promotes the encapsulation of sheet-like graphene oxide by disodium ethylenediaminetetraacetate, and simultaneously improves the dispersibility of graphene oxide in water, resulting in a more complete loading.

[0054] In step A2 of this embodiment, the electrolyte in the oxidizing electrolyte is sulfuric acid, and the concentration of the electrolyte is 0.5 mol / L. This invention utilizes an oxidizing electrolyte to promote an increase in the number of oxygen-containing groups on the surface of graphene oxide.

[0055] In step A1 of this embodiment, the microwave power is 800W and the microwave time is 3min.

[0056] The graphene / lithium iron phosphate composite material prepared in this embodiment is used to prepare a battery, wherein the graphene battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode sheet is obtained by coating and drying a slurry, which is made from the following raw materials by weight percentage: Graphene / lithium iron phosphate composite material 95%, conductive carbon black 3%, and PVDF 2%; The negative electrode sheet is obtained by coating and drying a second slurry, which is made from the following raw materials by weight percentage: 94% artificial graphite, 1% carboxymethyl cellulose, 2% styrene-butadiene rubber, and 3% Ketjen black.

[0057] Except as otherwise specified above, the other operations and parameters in this embodiment 4 are the same as those in embodiment 2.

[0058] Comparative Example Equal amounts of graphene oxide, lithium acetate, ferric nitrate, and ammonium dihydrogen phosphate, as in Example 1, were dispersed in deionized water according to stoichiometric ratio, mixed evenly, and added to a reaction vessel for hydrothermal reaction to obtain the precursor. The process conditions for the hydrothermal reaction in step one of this embodiment are as follows: Keep warm at 200℃ for 8 hours.

[0059] Step 2: Heat treat the obtained precursor; The heat treatment process involves heating the material to 700°C at a rate of 5–8°C / min from room temperature, holding it at that temperature for 8 hours, and then cooling it to room temperature in the furnace to obtain a graphene / lithium iron phosphate composite material.

[0060] The specific surface areas of the graphene / lithium iron phosphate composite materials obtained in Test Examples 1 to 4 and the comparative examples are shown in Table 1.

[0061] Table 1. Specific surface area of ​​graphene / lithium iron phosphate composite materials obtained in Examples 1 to 4 and comparative examples.

[0062] As shown in Table 1, the specific surface area of ​​the graphene / lithium iron phosphate composite materials obtained by the present invention in Examples 1-4 is much larger than that of the comparative examples; while the specific surface area of ​​the graphene / lithium iron phosphate composite materials obtained by Examples 3 and 4 after uniformly dispersing the graphene oxide is greater than that of Examples 1 and 2.

[0063] The electrochemical performance of the graphene lithium-ion batteries prepared in Examples 1 to 4 and the comparative examples was tested respectively. The increase rate of DC resistance is shown in Table 2. The increase rate of DC resistance R = (DCR) 500 -DCR1) / DCR1*100%; The specific testing method is as follows: At 25°C, the battery is charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After resting for 5 minutes, the voltage V1 is recorded. Then, the battery is discharged at 1 / 3C for 30 seconds, and the voltage V2 is recorded. The DC impedance of the battery after the first and 500th cycles is obtained by calculating (V2-V1) / 1 / 3C.

[0064] Table 2. DC impedance variations of the batteries obtained in Examples 1 to 4 and the comparative examples.

[0065] The batteries obtained in Examples 1 and 3, as well as the comparative examples, were tested for their 0.2C, 0.5C, 1C, 2C, and 5C cycle and rate performance curves, respectively, as shown below. Figure 4 As shown.

[0066] Combination Figures 1 to 4 As can be seen from the differences in the manufacturing process parameters of Tables 1 and 2, as well as the various examples and comparative examples, compared to the comparative examples where graphene oxide was directly mixed with lithium, iron, and phosphorus sources to prepare the precursor hydrothermally, the relative positions of the lithium iron phosphate precursor and graphene oxide were not pre-positioned. Combined with the specific surface area data, it can be seen that the relative dispersion of lithium iron phosphate and graphene oxide is uneven, and the dispersion of lithium iron phosphate by graphene oxide is insufficient. Correspondingly, the cycle performance and rate performance of the resulting lithium-ion battery are significantly different from those of the lithium-ion batteries obtained in Examples 1 to 4. In contrast, compared to the composite materials and lithium-ion batteries obtained in Examples 3 and 4 by increasing the oxide groups on the graphene surface, increasing the degree of graphene oxidation further strengthens the hydrogen bond connection between EDTA-2Na and graphene oxide. Furthermore, during the process of increasing the oxide groups in graphene oxide, further exfoliation and fragmentation occur. Therefore, compared to Examples 1 and 2, the relative dispersion of graphene and lithium iron phosphate precursor in Examples 3 and 4 is more uniform, and the reaction in the aqueous phase is also more complete. from Figure 1 and Figure 2 It can be seen that the LiFePO4 crystal particles obtained by this invention are uniform, the particle dispersion is stable, the structure is stable, and the DC impedance growth rate is small, which promotes the cycle performance of the battery.

[0067] The lithium-ion battery prepared in this invention is applied to a photovoltaic-energy storage integrated system, comprising an electrically connected photovoltaic array, a DC / DC converter, and a graphene battery prepared in this invention for storing energy. The photovoltaic array has a power-generating layer material, which is one of amorphous silicon, cadmium telluride, copper indium gallium selenide, and gallium arsenide. The reduced graphene oxide / lithium iron phosphate cathode material exhibits structural stability during cycling. The lithium iron phosphate has a uniform morphology and size, with a particle size between 100 and 300 nm. The sheet-like structure of the lithium iron phosphate nanoparticles effectively utilizes the increased specific surface area to reduce the one-dimensional limitation of the lithium-ion transport path within LiFePO4, resulting in rapid electron and ion conduction. This suppresses Li capacity loss caused by particle aggregation, structural collapse, or untimely lithium-ion insertion / extraction, making it suitable as a grid-connected or energy storage graphene battery in a photovoltaic-energy storage integrated system, capable of stable cycling even under partial charge.

Claims

1. A method for preparing an integrated photovoltaic and energy storage graphene battery, characterized in that: The graphene battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode sheet is obtained by coating and drying a slurry, which is made from the following raw materials by weight percentage: The composition consists of 92%–95% graphene / lithium iron phosphate composite material, 3%–5% conductive carbon black, and 1%–5% polyvinylidene fluoride. The negative electrode sheet is obtained by coating and drying a second slurry, which is made from the following raw materials by weight percentage: 90%–95% artificial graphite, 1%–3% carboxymethyl cellulose, 1%–3% styrene-butadiene rubber, and 1%–5% Ketjen Black; The preparation method of the graphene / lithium iron phosphate composite material includes the following steps: Step 1: chelate Fe with lithium acetate, graphene oxide / EDTA 3+ The ammonium dihydrogen phosphate and ammonium dihydrogen phosphate were dispersed in deionized water according to the stoichiometric ratio, mixed evenly, and the pH of the solution was adjusted to 6.8-7.

2. The solution was then added to a reaction vessel for hydrothermal reaction to obtain the precursor. Step 2: Heat treat the precursor obtained in Step 1; In step two, the heat treatment process involves heating the material at room temperature to 700℃-800℃ at a heating rate of 5℃ / min-8℃ / min, holding it at that temperature for 5h-8h, and then cooling it to room temperature in the furnace. This yields sheet-like material loaded onto the surface of graphene, which is a graphene / lithium iron phosphate composite material. Fe chelated with graphene oxide / EDTA 3+ The preparation method includes the following steps: S1. Add graphene oxide to a solution of disodium ethylenediaminetetraacetate, disperse by ultrasonication, mix evenly, add ethanol, and dry under an infrared lamp to obtain EDTA / graphene oxide linked by hydrogen bonds. EDTA is linked to graphene oxide via hydrogen bonds, as follows: ； S2. Disperse the EDTA / graphene oxide obtained in step S1 in deionized water, add Fe(NO3)3 solution dropwise, stir until homogeneous, and let stand to obtain Fe oxide chelated with EDTA. 3+ Dispersion in which Fe 3+ As EDTA is distributed around EDTA.

2. The method for preparing the integrated photovoltaic and energy storage graphene battery as described in claim 1, characterized in that: In step S2, the molar ratio of the solute Fe(NO3)3 in the Fe(NO3)3 solution to the disodium ethylenediaminetetraacetate in step S1 is 1:(8-10).

3. The method for preparing the integrated photovoltaic and energy storage graphene battery as described in claim 1, characterized in that: In step one of the preparation method of graphene / lithium iron phosphate composite material, the molar ratio of lithium, iron, and phosphate is (1.0–1.05):1.0:1.0; Fe chelated with graphene oxide / EDTA 3+ In the preparation method, the mass percentage of graphene oxide in step S1 to the total mass of lithium acetate in step S1, Fe(NO3)3 in step S2 and ammonium dihydrogen phosphate in step S1 is 5.0 wt% to 8.0 wt%.

4. The method for preparing the integrated photovoltaic and energy storage graphene battery as described in claim 1, characterized in that: In step one of the preparation method of graphene / lithium iron phosphate composite material, the hydrothermal reaction process conditions are: 200℃~215℃, heat preservation for 5 hours~8 hours.

5. The method for preparing the integrated photovoltaic and energy storage graphene battery as described in claim 1, characterized in that: In step S1, the graphene oxide undergoes a pretreatment process to achieve uniform dispersion. This pretreatment includes the following steps: A1. Microwave treatment of graphene oxide removes moisture and increases interlayer spacing; A2. The graphene oxide treated in A1 is dispersed in an oxidizing electrolyte. A constant voltage of 12V to 15V is applied between the cathode and the anode. Water molecules decompose to generate hydroxyl radicals, and the number of oxidized groups on the surface of the graphene oxide sheets increases. A3. Stop applying voltage, filter, wash, collect, and dry to obtain pretreated graphene oxide.

6. The method for preparing the integrated photovoltaic and energy storage graphene battery as described in claim 5, characterized in that: In step A2, the electrolyte in the oxidizing electrolyte is hydrogen peroxide or sulfuric acid, and the concentration of the electrolyte is 0.5 mol / L to 0.8 mol / L.

7. The method for preparing a photovoltaic-storage integrated graphene battery as described in claim 5 or 6, characterized in that: In step A1, the microwave power is 500W to 800W and the microwave time is 3min to 6min.

8. A photovoltaic-storage integrated system, characterized in that: The invention includes an electrically connected photovoltaic array, a DC / DC converter, and a graphene battery prepared according to any one of claims 1 to 7 for storing electrical energy.

9. The integrated photovoltaic and energy storage system according to claim 8, characterized in that: The photovoltaic array has a power generation layer material, which is one of amorphous silicon, cadmium telluride, copper indium gallium selenide, and gallium arsenide.

Images