Preparation method of positive electrode sheet, battery cell, battery device, energy storage device

Abstract

This application relates to a method for preparing a positive electrode sheet, a battery cell, a battery device, and an energy storage device. The preparation method includes: simultaneously mixing and photocatalyzing recovered lithium iron phosphate, a conductive agent, a binder, and a photocatalyst dispersion under first light radiation to obtain a positive electrode slurry; placing the positive electrode slurry on a current collector and performing in-situ reduction treatment under second light radiation to obtain an initial electrode sheet; and drying the initial electrode sheet under third light radiation to obtain a positive electrode sheet. The drying process includes sequentially performed first, second, and third stages, with the light wavelength decreasing and the drying temperature increasing sequentially in each stage. The positive electrode sheet prepared by the method provided in this application can improve surface defects, enhance interfacial structural stability, and improve the conductivity of lithium iron phosphate within the positive electrode sheet, resulting in a positive electrode sheet with both excellent rate performance and cycle stability.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to methods for preparing positive electrode sheets, battery cells, battery devices, and energy storage devices. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage, and other fields, the market has placed increasingly stringent technical requirements on the energy density, cycle life, rate performance, and batch consistency of lithium-ion batteries. Lithium iron phosphate (LiFePO4, LFP) cathode materials, with their excellent safety and stability, extremely low manufacturing costs, good environmental compatibility, and long cycle life, have become the mainstream cathode material for power batteries and grid energy storage batteries, and their industrial application scale continues to expand.

[0003] Currently, the preparation process of traditional lithium iron phosphate cathode slurry has limited maturity. In the preparation of high areal density thick electrodes and mass production of high-performance batteries, it has exposed many unavoidable technical defects, such as lithium iron phosphate particle agglomeration, which seriously restricts the further improvement of lithium iron phosphate battery performance. Summary of the Invention

[0004] This application provides a method for preparing a positive electrode sheet, a battery cell, a battery device, and an energy storage device. The preparation method of this application can improve the uniformity of the distribution of lithium iron phosphate particles in the slurry, while reducing particle agglomeration and microbubbles in the slurry, improving the surface defects of the positive electrode sheet, improving the interfacial structure stability of the positive electrode sheet, and improving the rate performance and cycle stability of the battery.

[0005] In a first aspect, this application provides a method for preparing a positive electrode sheet, the method comprising: The recovered lithium iron phosphate, conductive agent, binder and photocatalyst dispersion were simultaneously mixed and photocatalytically treated under the first light radiation to obtain the positive electrode slurry; The positive electrode slurry is placed on the current collector and then subjected to in-situ reduction treatment under second light radiation to obtain the initial electrode sheet. The initial electrode is placed under third light radiation for drying to obtain a positive electrode; wherein the drying process includes a first stage, a second stage and a third stage performed sequentially, wherein the light wavelength of the first stage, the second stage and the third stage decreases sequentially, and the drying temperature of the first stage, the second stage and the third stage increases sequentially.

[0006] In some possible implementations, the preparation steps of the positive electrode slurry include: The light intensity of the first light radiation is controlled to be 180 mW / cm²~220 mW / cm², and the light wavelength of the first light radiation is 450nm~480nm. Under the first light radiation, the recovered lithium iron phosphate and the photocatalyst dispersion are mixed and photocatalyzed simultaneously. During the treatment, the stirring rate is controlled to be 700rpm~1000rpm, and the stirring time is 20 minutes~30 minutes.

[0007] In some possible implementations, the solid content of the positive electrode slurry is 55% to 65%.

[0008] In some possible implementations, the mass ratio of the recovered lithium iron phosphate, the conductive agent, and the binder is (92~95): (1~3): (2~5).

[0009] In some possible implementations, the conductive agent includes at least one of carbon nanotubes, graphene, carbon black, and graphite.

[0010] In some possible implementations, the adhesive comprises polyvinylidene fluoride.

[0011] In some possible implementations, the photocatalyst dispersion comprises a sulfur-based semiconductor photocatalyst with Pt particles loaded on its surface.

[0012] In some possible embodiments, the sulfur-based semiconductor photocatalyst comprises NaFeS2 particles and a conductive material located on at least a portion of the surface of the NaFeS2 particles, the conductive material comprising at least one of carbon nanotubes, graphene, carbon black, and graphite; the Pt particles are located on the surface of the NaFeS2 particles and / or the conductive material.

[0013] In some possible implementations, the light wavelength of the first stage is 600nm~680nm, the drying temperature is 75℃~85℃, and the heat preservation time is 1 minute~2 minutes.

[0014] In some possible implementations, the light wavelength of the second stage is 400nm~480nm, the drying temperature is 95℃~110℃, and the heat preservation time is 3 minutes~5 minutes.

[0015] In some possible implementations, the light wavelength of the third stage is 300nm~380nm, the drying temperature is 115℃~130℃, and the heat preservation time is 1 minute~2 minutes.

[0016] In some possible implementations, the step of placing the positive electrode slurry on the current collector and performing in-situ reduction treatment under second light radiation includes: The light intensity of the second light radiation is controlled to be 130 mW / cm²~150 mW / cm², the light wavelength of the second light radiation is 400nm~410nm, and the in-situ reduction treatment time is 30 seconds~60 seconds to obtain the initial electrode.

[0017] In some possible implementations, the exposure side of the initial electrode has a conductive layer, the conductive layer comprising Li 1.1 FePO4; and / or, the thickness of the conductive layer is 3nm~5nm.

[0018] In some possible embodiments, the preparation method further includes the preparation of a photocatalyst dispersion, the steps of which include: Under xenon lamp irradiation, sulfur-based semiconductor photocatalyst was mixed with H2PtCl6 solution, and solid-liquid separation was performed to obtain sulfur-based semiconductor photocatalyst with Pt particles loaded on the surface. A sulfur-based semiconductor photocatalyst with Pt particles loaded on its surface was added to a solvent to obtain a photocatalyst dispersion.

[0019] In some possible embodiments, the preparation method further includes preparing the sulfur-based semiconductor photocatalyst, the steps of which include: The recovered lithium iron phosphate, thioacetamide and sodium source were reacted under hydrothermal conditions to obtain NaFeS2; The NaFeS2 is mixed with a conductive material to obtain a sulfur-based semiconductor photocatalyst; wherein the conductive material includes at least one of carbon nanotubes, graphene, carbon black, and graphite.

[0020] Secondly, this application provides a positive electrode sheet, which is prepared according to the preparation method provided in the first aspect above; the positive electrode sheet satisfies at least one of the following characteristics: The areal density of the positive electrode sheet is 390 g / m³. 2 ~410g / m 2 ; The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 ~2.7 g / cm 3 ; The peel strength of the positive electrode sheet is 25 N / m ~ 35 N / m.

[0021] Thirdly, this application provides a battery cell including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode is prepared according to the preparation method described in the first aspect above, or the positive electrode includes the positive electrode of the second aspect above.

[0022] Fourthly, this application provides a battery device, the battery device comprising a positive electrode sheet prepared by the preparation method described in the first aspect or as described in the second aspect, or comprising a battery cell as described in the third aspect, the battery device comprising one or more of a battery module and a battery pack.

[0023] Fifthly, this application provides an energy storage device, which includes the aforementioned battery device for storing electrical energy.

[0024] Sixthly, this application provides an electrical device, which includes the battery device described above, or includes the energy storage device described above.

[0025] The technical solution of this application has at least the following beneficial effects: The method for preparing the positive electrode sheet provided in this application firstly involves photocatalytic treatment during the mixing process of the positive electrode slurry. Some of the recovered lithium iron phosphate particles form agglomerates due to van der Waals forces or electrostatic attraction. Holes and high-energy photons generated by the photocatalyst can impact these agglomerates, decomposing the organic matter on the surface of the waste lithium iron phosphate particles, weakening the adsorption forces between particles, and facilitating the decomposition of agglomerates into individual particles. The energy generated by the photocatalyst can also disrupt the bubble nucleus structure generated during mixing, reducing microbubbles. After the positive electrode slurry is placed on the current collector, the recovered lithium iron phosphate is prone to iron ion valence state shifts. Under second photocatalytic radiation, the trivalent iron ions in the lithium iron phosphate are reduced to divalent iron ions, restoring electrochemical activity. Furthermore, residual microbubbles in the initial electrode sheet can also be heated and dissipated under light irradiation, improving the uniformity of the initial electrode sheet thickness. Finally, the initial electrode is dried under light radiation. In the first stage, due to the relatively long wavelength and low energy of the light source, the drying temperature is low, which gently removes free moisture and low-boiling-point solvents from the electrode surface. This promotes the bonding of the conductive agent distributed among the lithium iron phosphate molecules, forming a cross-linked conductive network and improving the electrode's conductivity. It also reduces phenomena such as electrode surface peeling and active material cracking caused by rapid heating. In the second stage, the shortened wavelength, increased light energy, and higher drying temperature help to deeply remove residual solvents from the electrode, reducing electrode bulging caused by solvent retention. Furthermore, deep drying facilitates the formation of microporous channels within the electrode, improving the electrolyte wetting ability of the positive electrode and enhancing its cycle stability. The third stage uses the shortest wavelength and highest energy light, combined with the highest drying temperature, to further stabilize the interface between the lithium iron phosphate, conductive agent, and binder within the electrode. This promotes the cross-linking and solidification of the binder molecular chains, resulting in a compact electrode structure that is less prone to detachment, improving the overall structural stability and mechanical strength of the positive electrode.

[0026] In summary, the positive electrode prepared according to the method of this application has a high compaction density, reduced surface defects, improved interfacial structure stability, and improved conductive network of lithium iron phosphate in the positive electrode, thus enabling the positive electrode to have both excellent rate performance and cycle stability.

[0027] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process flow for preparing the positive electrode sheet provided in the embodiments of this application.

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. Detailed Implementation

[0030] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0031] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0032] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0034] It should be noted that the directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this application are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this application. Furthermore, in the context, it should be understood that when referring to an element being connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected through an intermediate element.

[0035] With the increasing penetration of intermittent renewable energy sources such as wind and solar power into the power grid, long-duration energy storage technology has become crucial for ensuring grid stability and enabling energy regulation across time periods. Storage durations of 4 to 8 hours or even longer can effectively achieve energy regulation across time periods (such as shifting midday photovoltaic power generation to nighttime peak electricity consumption), which is of great significance for ensuring grid security and improving energy efficiency.

[0036] As the basic building block of energy storage systems, battery cells can convert electrical energy into chemical energy, enabling the storage and release of energy. In the field of electrochemical cells, the core advantage of batteries lies in their reversible electrochemical performance. This allows them to receive electrical energy through external charging, convert it into chemical energy for storage, and then convert that chemical energy back into electrical energy for release when needed, thus achieving efficient energy recycling. This characteristic not only significantly reduces long-term operating costs and minimizes resource consumption and waste generation, but also provides a flexible, portable, and stable energy storage solution, becoming a key foundational technology supporting modern portable electronic devices, electric vehicles, and renewable energy storage systems.

[0037] Lithium iron phosphate (LiFePO4, LFP) cathode materials have become the mainstream cathode materials for power batteries and grid energy storage batteries due to their excellent safety and stability, extremely low preparation cost, good environmental compatibility, and long cycle characteristics, and their industrial application scale continues to expand. However, due to the poor conductivity of lithium iron phosphate materials, particles are prone to agglomeration during conventional slurry stirring preparation, leading to the breakage and discontinuous distribution of the conductive network inside the electrode. Furthermore, a large number of microbubbles with a diameter of less than 100 μm are easily generated inside the slurry. Conventional degassing processes can only remove free bubbles on the surface of the slurry, resulting in low degassing efficiency. The residual microbubbles can easily cause surface defects such as pinholes and cracks on the electrode surface during electrode coating and drying, leading to a decrease in the interfacial structural stability of the cathode electrode, an aggravation of interfacial side reactions, and consequently affecting the battery's service life.

[0038] To improve the uniformity of lithium iron phosphate dispersion in the positive electrode slurry, reduce microbubbles in the slurry, and thus improve the interfacial stability and lithium-ion transport efficiency of the positive electrode sheet, this application provides a method for preparing a positive electrode sheet, such as... Figure 1 As shown, the preparation method includes: S10, the recovered lithium iron phosphate, conductive agent, binder and photocatalyst dispersion are simultaneously mixed and photocatalyzed under the first light radiation to obtain positive electrode slurry; S20, the positive electrode slurry is placed on the current collector and then subjected to in-situ reduction treatment under the second light radiation to obtain the initial electrode sheet; S30, the initial electrode is placed under the third light radiation for drying treatment to obtain the positive electrode; wherein, the drying treatment includes a first stage, a second stage and a third stage performed in sequence, the light wavelength of the first stage, the second stage and the third stage decreases in sequence, and the drying temperature of the first stage, the second stage and the third stage increases in sequence.

[0039] The method for preparing the positive electrode sheet provided in this application firstly involves photocatalytic treatment during the mixing process of the positive electrode slurry. Some of the recovered lithium iron phosphate particles form agglomerates due to van der Waals forces or electrostatic attraction. Holes and high-energy photons generated by the photocatalyst can impact these agglomerates, decomposing the organic matter on the surface of the waste lithium iron phosphate particles, weakening the adsorption forces between particles, and facilitating the decomposition of agglomerates into individual particles. The energy generated by the photocatalyst can also disrupt the bubble nucleus structure generated during mixing, reducing microbubbles. After the positive electrode slurry is placed on the current collector, the recovered lithium iron phosphate is prone to iron ion valence state shifts. Under second photocatalytic radiation, the trivalent iron ions in the lithium iron phosphate are reduced to divalent iron ions, restoring electrochemical activity. Furthermore, residual microbubbles in the initial electrode sheet can also be heated and dissipated under light irradiation, improving the uniformity of the initial electrode sheet thickness. Finally, the initial electrode is dried under light radiation. In the first stage, due to the relatively long wavelength and low energy of the light source, the drying temperature is low, which gently removes free moisture and low-boiling-point solvents from the electrode surface. This promotes the bonding of the conductive agent distributed among the lithium iron phosphate molecules, forming a cross-linked conductive network and improving the electrode's conductivity. It also reduces phenomena such as electrode surface peeling and active material cracking caused by rapid heating. In the second stage, the shortened wavelength, increased light energy, and higher drying temperature help to deeply remove residual solvents from the electrode, reducing electrode bulging caused by solvent retention. Furthermore, deep drying facilitates the formation of microporous channels within the electrode, improving the electrolyte wetting ability of the positive electrode and enhancing its cycle stability. The third stage uses the shortest wavelength and highest energy light, combined with the highest drying temperature, to further stabilize the interface between the lithium iron phosphate, conductive agent, and binder within the electrode. This promotes the cross-linking and solidification of the binder molecular chains, resulting in a compact electrode structure that is less prone to detachment, improving the overall structural stability and mechanical strength of the positive electrode.

[0040] In summary, the positive electrode prepared according to the method of this application has a high compaction density, reduced surface defects, improved interfacial structure stability, and improved conductive network of lithium iron phosphate in the positive electrode, thus enabling the positive electrode to have both excellent rate performance and cycle stability.

[0041] The technical solution of this application will be described in detail below with reference to specific embodiments.

[0042] Prior to step S10, the preparation method further includes the preparation of a sulfur-based semiconductor photocatalyst, the steps of which include: The recovered lithium iron phosphate material, thioacetamide and sodium source were reacted under hydrothermal conditions to obtain NaFeS2; By mixing NaFeS2 with a conductive material, a sulfur-based semiconductor photocatalyst is obtained; wherein the conductive material includes at least one of carbon nanotubes, graphene, carbon black, and graphite.

[0043] In some embodiments, the mass ratio of the recovered lithium iron phosphate material, thioacetamide, and sodium source is 1:2:(1~1.2), specifically 1:2:1, 1:2:1.1, 1:2:1.15, 1:2:1.2, or other values ​​within the above range. Controlling the mass ratio of the raw materials helps ensure the reaction proceeds fully to generate NaFeS2. The hydrothermal reaction temperature is 180℃~220℃, specifically 180℃, 190℃, 200℃, 210℃, 220℃, or other values ​​within the above range, and the hydrothermal reaction time is 16h~24h, specifically 16h, 18h, 20h, 22h, 24h, or other values ​​within the above range.

[0044] The product after the hydrothermal reaction was centrifuged, washed, and vacuum dried to obtain NaFeS2.

[0045] In some embodiments, the mass ratio of NaFeS2 to the conductive material is (7~9):(3:1), specifically 7:3, 8:2, 8.5:1.5, or 9:1, etc., which are not limited here. The conductive material can be selected from multi-walled carbon nanotubes and / or single-walled carbon nanotubes, preferably multi-walled carbon nanotubes with a diameter of 20nm~50nm.

[0046] The mixing method of NaFeS2 and conductive materials can be at least one of mechanical stirring and ultrasonic dispersion. The mixture can be stirred to dryness at 60°C to obtain a sulfur-based semiconductor photocatalyst. In some embodiments of this application, on the one hand, NaFeS2 is generated by hydrothermal reaction of recycled lithium iron phosphate material, thioacetamide, and sodium source, which can realize the reuse of recycled lithium iron phosphate and reduce the production cost. On the other hand, the combination of NaFeS2 and conductive materials can compensate for the conductivity deficiency of NaFeS2. The conductive materials can also rapidly conduct photogenerated electrons and holes, so that the sulfur-based semiconductor photocatalyst has both photocatalytic activity and electron transport performance.

[0047] In other embodiments of this application, the photocatalyst may also be a commercially available photocatalyst, such as titanium dioxide, zinc oxide, graphitic carbon nitride, etc., which are not limited here.

[0048] Furthermore, the method also includes preparing a photocatalyst dispersion, the steps of which include: Under xenon lamp irradiation, sulfur-based semiconductor photocatalyst was mixed with H2PtCl6 solution and stirred for 30 to 60 minutes. After solid-liquid separation, sulfur-based semiconductor photocatalyst with Pt particles loaded on the surface was obtained. A sulfur-based semiconductor photocatalyst with Pt particles loaded on its surface was added to a solvent to obtain a photocatalyst dispersion.

[0049] In some embodiments, the Pt content in the H2PtCl6 solution is 1wt%~2wt%. When the sulfur-based semiconductor photocatalyst is mixed with the H2PtCl6 solution and irradiated with a xenon lamp, the tetravalent Pt in the H2PtCl6 solution is reduced to Pt nanoparticles. These Pt nanoparticles adhere to the surface of the sulfur-based semiconductor photocatalyst under stirring. The Pt nanoparticles exhibit strong catalytic activity, providing more active sites within the in-situ reduction range of the subsequent step S20, thereby increasing the reduction reaction rate.

[0050] In some embodiments, the solvent may be N-methylpyrrolidone. To improve the dispersion of the photocatalyst dispersion, it can be dispersed by stirring or ultrasonication for about 10 minutes.

[0051] In some embodiments, the solid content of the photocatalyst dispersion is controlled to be 40wt%~55wt%, specifically 40wt%, 42wt%, 45wt%, 48wt%, 50wt%, 52wt%, 55wt% or other values ​​within the above range, which are not limited here.

[0052] In some embodiments, Pt particles are located on the surface of NaFeS2 particles and / or conductive materials.

[0053] In some preferred embodiments, a conductive material layer is formed on the surface of NaFeS2 particles, and Pt particles are embedded within the conductive material layer. This gives the sulfur-based semiconductor photocatalyst loaded with Pt particles a core-shell-island structure. The core, NaFeS2, is responsible for absorbing photons and generating photogenerated electron-hole pairs, providing the basis for the catalytic reaction. The shell is a conductive material layer (carbon nanotube layer) used to form a continuous conductive network, significantly accelerating electron transport. The islands are Pt particles, further enhancing the reduction catalytic ability. The above-mentioned composite with a core-shell-island structure can comprehensively improve photocatalytic ability, further reduce residual organic impurities on the surface of lithium iron phosphate, and improve the dispersion uniformity of lithium iron phosphate in the cathode material.

[0054] In step S10, the recovered lithium iron phosphate, conductive agent, binder and photocatalyst dispersion are simultaneously mixed and photocatalyzed under the first light radiation to obtain positive electrode slurry.

[0055] The aforementioned conductive agent may include at least one of carbon nanotubes, graphene, carbon black, and graphite. Specifically, carbon nanotubes may be multi-walled carbon nanotubes or single-walled carbon nanotubes. Carbon black may be conductive carbon black SP, acetylene black, Ketjen black, etc. Graphite may be artificial graphite or natural graphite, and is not limited thereto.

[0056] The adhesive can be selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid, preferably, the adhesive includes polyvinylidene fluoride.

[0057] The lithium iron phosphate used in this application is recovered from the positive electrode sheet of spent lithium iron phosphate batteries. In other embodiments, purchased lithium iron phosphate may also be used, and this is not a limitation. When recycled lithium iron phosphate is used, its surface is prone to residual organic matter such as binders. Photocatalytic treatment can effectively reduce the organic impurities on the surface of lithium iron phosphate.

[0058] In some embodiments, the mass ratio of the recovered lithium iron phosphate, conductive agent, and binder is (92~95):(1~3):(2~5). Exemplarily, the mass ratio can be 92:3:5, 93:2:5, 94:1:5, 94:2:4, 95:1:4, 95:2:3, 95:3:2, or other values ​​within the above range, and is not limited herein. Controlling the mass ratio of the recovered lithium iron phosphate, conductive agent, and binder within the above range helps to control the viscosity of the positive electrode slurry within a suitable range, thereby improving the adhesion between the slurry-formed coating and the current collector; it also helps to improve the conductivity and electrochemical performance of the electrode.

[0059] In order to improve the uniformity and stability of the slurry and thus improve the consistency of the positive electrode, in one embodiment of this application, the above mixing is carried out under stirring, and the stirring rate is controlled at 700 rpm to 1000 rpm and the stirring time is 20 minutes to 30 minutes.

[0060] In some embodiments, the photocatalytic treatment is illuminated by blue LEDs with a light intensity of up to 180 mW / cm². 2 ~220 mW / cm 2 Blue light has a wavelength of 450nm to 480nm. The specific light intensity can be 180 mW / cm². 2 190 mW / cm 2 200 mW / cm 2 220 mW / cm 2 Or other values ​​within the above range, without limitation. The wavelength of blue light can be 450nm, 460nm, 470nm, 475nm, 480nm or other values ​​within the above range, without limitation.

[0061] Under the combined action of stirring shear force, holes generated by the photocatalyst, and high-energy photons, agglomerates can be effectively impacted, weakening the adsorption forces between particles and helping to break down agglomerates into individual particles. The photocatalyst also helps to decompose organic matter on the surface of waste lithium iron phosphate particles, and the energy generated by the photocatalyst can also destroy the bubble nucleus structure generated during the mixing process, reducing microbubbles.

[0062] In some embodiments, the positive electrode slurry is further subjected to vacuum degassing treatment for a period of 5 to 10 minutes, specifically 5, 6, 7, 8, 9, or 10 minutes, or other values ​​within the above range, which are not limited here. After vacuum degassing treatment, the slurry becomes finer and more uniform.

[0063] In some embodiments, the viscosity of the positive electrode slurry is 9000 mPa·s to 18000 mPa·s. Controlling the viscosity of the positive electrode slurry within the above range helps to enhance the adhesion between the positive electrode slurry and the current collector, forming a strong positive electrode active material layer.

[0064] S20, the positive electrode slurry is placed on the current collector and then subjected to in-situ reduction treatment under the second light radiation to obtain the initial electrode sheet.

[0065] This application does not impose any particular limitation on the type of current collector; it can be any known material suitable for use as a positive electrode current collector. Materials for the positive electrode current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. Furthermore, to reduce the electronic contact resistance between the current collector and the active material layer, conductive additives or conductive coatings can be applied to the surface of the current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture of inorganic oxides, conductive agents, and positive electrode binders.

[0066] This application does not impose any particular restrictions on the coating process. The thickness of the wet film after coating can be 200±50μm, and the coating speed can be 2±0.5 m / min.

[0067] In some embodiments, in step S20, the light intensity of the second light radiation is controlled to be 130 mW / cm². 2 ~150mW / cm 2 The light wavelength is 400nm~410nm. The light intensity can specifically be 130 mW / cm². 2 135 mW / cm 2 138 mW / cm 2 140 mW / cm 2 143 mW / cm 2 145 mW / cm2 148 mW / cm 2 150 mW / cm 2 Or other values ​​within the above range, which are not limited here. The specific wavelength can be 400nm, 402nm, 405nm, 408nm, 410nm, or any combination of two values ​​within the above range, which are not limited here.

[0068] In step S20, the in-situ reduction treatment time is 30 to 60 seconds, specifically 30, 40, 45, 50, 55, or 60 seconds, or other values ​​within the above range, and is not limited here. Since the recovered lithium iron phosphate is prone to iron ion valence state shifts, the second photo-radiation catalysis helps to reduce the trivalent iron ions in the lithium iron phosphate to divalent iron ions, restoring electrochemical activity; furthermore, under light irradiation, residual microbubbles in the initial electrode can also be heated and dissipated, improving the uniformity of the initial electrode thickness.

[0069] In some embodiments of this application, the exposure side of the initial electrode has a conductive layer, the conductive layer including Li 1.1 FePO4. Li 1.1 FePO4 is the initial electrode surface where lithium iron phosphate is intercalated under light energy, forming a lithium-rich solid solution phase. An appropriate amount of Li... 1.1 The formation of the FePO4 conductive layer can reduce the interfacial impedance of the positive electrode and reduce the direct contact between the electrolyte and the lithium iron phosphate matrix inside the positive electrode, thereby improving the interfacial stability of the positive electrode, enhancing lithium-ion transport capability, reducing battery impedance, and further improving rate performance and cycle stability.

[0070] In some embodiments, the thickness of the conductive layer is 3nm to 5nm, specifically 3nm, 3.5nm, 4nm, 4.5nm, 5nm or other values ​​within the above range, which are not limited here.

[0071] Furthermore, the drying process in step S30 includes a first stage, a second stage, and a third stage performed sequentially, specifically including: The wavelength of light in the first stage is controlled to be 600nm~680nm, the drying temperature is 75℃~85℃, and the holding time is 1 minute~2 minutes; The wavelength of light in the second stage is controlled to be 400nm~480nm, the drying temperature is 95℃~110℃, and the holding time is 3 minutes~5 minutes. The wavelength of light in the third stage is controlled to be 300nm~380nm, the drying temperature is 115℃~130℃, and the holding time is 1 minute~2 minutes.

[0072] In some embodiments, the wavelength of light in the first stage can be 600nm, 620nm, 640nm, 650nm, 670nm, 680nm, or other values ​​within the above range, and is not limited herein. The drying temperature can be 75℃, 78℃, 79℃, 80℃, 82℃, or 85℃, and the holding time can be 1 minute, 1.5 minutes, or 2 minutes. This stage of long-wavelength red light combines mild photocatalysis with a low-heat effect. The lower drying temperature allows for the gentle removal of free moisture and low-boiling-point solvents from the electrode surface, promoting the formation of a cross-linked conductive network by the conductive agents distributed between the lithium iron phosphate electrodes, thus improving the conductivity of the electrode. It can also reduce phenomena such as electrode surface peeling and active material cracking caused by rapid heating.

[0073] In some embodiments, the wavelength of light in the second stage can be 400nm, 420nm, 440nm, 450nm, 460nm, 480nm, or any value within this range, and is not limited herein. The drying temperature can be 95℃, 98℃, 100℃, 103℃, 105℃, or 110℃, and the holding time can be 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, or 5 minutes. The shortened wavelength of light in the second stage, the increased light energy, and the increased drying temperature help to deeply remove residual solvent from the electrode, reducing electrode bulging caused by solvent retention. Furthermore, deep drying facilitates the formation of microporous channels inside the electrode, improving the electrolyte wetting ability of the positive electrode and enhancing the cycle stability of the positive electrode.

[0074] In some embodiments, the wavelength of the light in the third stage can be 300nm, 320nm, 340nm, 360nm, 380nm, or any value within this range, and is not limited here. The drying temperature can be 115℃, 120℃, 122℃, 125℃, 128℃, or 130℃, and the holding time can be 1 minute, 1.5 minutes, or 2 minutes. The third stage uses the shortest wavelength light with the highest energy, combined with the highest drying temperature, which can further stabilize the bonding interface between lithium iron phosphate, conductive agent, and binder within the electrode, promote the cross-linking and curing of binder molecular chains, make the electrode structure compact and less prone to detachment, and improve the overall structural stability and mechanical strength of the positive electrode.

[0075] In some embodiments, the positive electrode sheet prepared by the above preparation method has a smooth surface with very few defects such as pinholes, bubbles and cracks, and the stability of the interface structure is effectively improved.

[0076] In some embodiments, the areal density of the positive electrode is 390 g / m². 2 ~410g / m 2 Specifically, it could be 390 g / m 2 392g / m 2 395g / m2 398 g / m 2 400 g / m 2 402 g / m 2 405 g / m 2 408g / m 2 410 g / m 2 The range and any value within this range are not limited here. The areal density of the positive electrode sheet in this application is within the above range, which can increase the active material loading per unit area and effectively improve the volumetric energy density of the battery. Controlling the areal density within this range can improve the insufficient energy density caused by excessively low loading, while preventing problems such as excessively thick electrode sheets, uneven slurry coating, and incomplete drying caused by excessively high loading, thus ensuring the uniformity of the coating process.

[0077] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm³. 3 ~2.7 g / cm 3 Specifically, it could be 2.5g / cm³. 3 2.55 g / cm 3 2.6g / cm 3 2.65 g / cm 3 2.7 g / cm 3 The values ​​within this range are not limited here. Controlling the compaction density of the positive electrode sheet within the above range ensures the formation of a stable and continuous conductive network between the active material, conductive agent, and binder, reducing the internal resistance of the electrode sheet. If the compaction density is too low, the electrode sheet porosity will be too large, making it difficult to increase the cell's energy density; if the compaction density is too high, it can easily cause damage to the crystal structure of the active material and breakage of the conductive pathway, exacerbating the increase in internal resistance and deteriorating the battery's electrochemical performance.

[0078] In some embodiments, the peel strength of the positive electrode sheet is 25 N / m to 35 N / m, specifically 25 N / m, 27 N / m, 29 N / m, 31 N / m, 33 N / m, 35 N / m, and any value within this range, without limitation. Controlling the peel strength of the positive electrode sheet within this range allows it to resist interfacial stress caused by the volume expansion and contraction of the active material during battery charge-discharge cycles, delaying electrode interface failure and improving battery cycle stability and long-term reliability. If the peel strength is too low, the electrode sheet is prone to powder shedding and foil detachment, severely affecting production and use; if the strength is too high, it indicates excessive binder usage, which increases the internal resistance of the electrode sheet, affecting battery rate and discharge performance.

[0079] After the positive electrode sheet is prepared, it is used to prepare battery cells. During the production of battery cells, the positive electrode sheet, separator, and negative electrode sheet are stacked sequentially, and then formed into a cell assembly using winding, stacking, folding, or a combination thereof. The cell assembly is then installed in a casing and electrolyte is injected. Finally, a formation process is performed to form a usable battery cell.

[0080] The casing of the battery cell can be made of aluminum-plastic composite film flexible packaging, aluminum alloy hard casing, steel casing, polymer hard casing, etc., depending on the application requirements. This application does not impose any particular restrictions on this. In addition, this application does not impose any particular restrictions on the preparation methods of components such as separator, negative electrode sheet, and electrolyte, as long as they can meet the purpose of this application.

[0081] This application also provides a battery device, including the above-mentioned battery cell. The battery device in this application includes at least one of a battery module, a battery pack, and an energy storage battery. Since the battery cell in this application has good stability and excellent rate performance and cycle stability, the battery device in this application also has good performance.

[0082] This application also provides an electrical device, including the aforementioned battery device, which provides electrical energy. Electrical devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0083] This application also provides an energy storage device, including the aforementioned battery device, which is used to store electrical energy. Energy storage devices include, but are not limited to, residential energy storage cabinets, commercial energy storage cabinets, energy storage containers, energy storage racks, energy storage power stations, energy storage battery packs, or portable energy storage systems. Energy storage devices may also include energy management systems (EMS), battery management systems (BMS), and power conversion systems (PCS).

[0084] The technical solution of this application will be described in more detail below with reference to embodiments and comparative examples.

[0085] Test methods and equipment (1) Peel strength test of positive electrode sheet Equipment: Computerized adhesive tape release force tester Test method: Take the rolled positive electrode sheet and cut it to the specified size (400mm in length and 30mm in width) using a custom cutter; then, take a flat thin steel plate, apply double-sided tape, and stick the electrode sheet onto the steel plate, ensuring that the double-sided tape and the electrode sheet are of equal width and tightly adhered; next, clamp the steel plate and the free end of the electrode sheet onto the upper and lower clamps of the testing machine respectively; after setting the tensile speed (100mm / min) and other test parameters, start the testing machine to perform the peel test and record the force value change during the peel process; finally, calculate the average peel force per unit width based on the recorded data.

[0086] (2) Surface density test of the positive electrode sheet; Using a sampler, take 4 to 6 small round pieces of positive electrode plates, then place them on a pan balance and weigh them. Subtract the mass of the empty foil (uncoated aluminum foil) from the weighed mass, and then divide by the area of ​​the small round pieces to get the areal density.

[0087] (3) Compacted density test of the positive electrode sheet: The compacted density R of the positive electrode sheet is calculated using the formula: R = m / v. Where m is the mass of the positive electrode active material layer (g), and v is the volume of the positive electrode active material layer (cm³). 3 Where, the volume v is the product of the area Ar of the positive electrode active material layer and the thickness of the positive electrode active material layer.

[0088] (4) Resistivity test of the positive electrode: The electrode resistance was measured using a four-probe resistance meter (probe spacing 1 mm). The electrode was cut into 20 mm × 20 mm samples and dried under vacuum at 120℃ for 2 h. The electrode thickness was then measured using a micrometer (average of 5 points). During testing, the probes were pressed perpendicularly to the electrode coating surface, a constant pressure of 0.5 N was applied, and the test current was set to 1 mA. The data acquisition system should be able to simultaneously record the resistance value, test pressure, and electrode thickness.

[0089] (5) Electrochemical performance testing of the battery: Initial Coulombic Efficiency: The initial charge-discharge performance of the square-shell battery after formation was tested using a battery charge-discharge testing system at 25℃±2℃. The charging method was constant current-constant voltage (CC-CV) mode: first, the battery was charged at a constant current of 0.1C to the upper voltage limit of 3.65V, then switched to constant voltage charging until the current dropped to 0.02C; after resting for 30 minutes, it was discharged at a constant current of 0.1C to the lower voltage limit of 2.5V. The initial charge capacity and initial discharge capacity were recorded. Initial Coulombic Efficiency = Initial Discharge Capacity / Initial Charge Capacity.

[0090] 45℃ 0.5P Cycle: The prismatic battery was placed in a constant temperature chamber at 45℃±2℃, and cycle life was tested using a battery charge-discharge test system. The charge-discharge regime was as follows: charging at a constant power of 0.5P to the upper voltage limit of 3.65V, and resting for 10 minutes; discharging at a constant power of 0.5P to the lower voltage limit of 2.5V, and resting for 10 minutes. The above charge-discharge cycle was repeated, and the charging energy and discharging energy were recorded at each charge-discharge point. The energy retention rate was calculated using the following formula: Energy retention rate = Discharge energy / Charging energy.

[0091] Rate performance: Under constant temperature conditions of 25℃±2℃, the rate performance of the square-shell battery was tested using a battery charge-discharge test system. The test procedure is as follows: Standard charging: The battery was charged at a constant current and constant voltage of 0.5C (I1) to 3.65V (cutoff current 0.02C), and then left to rest for 30 minutes. Rate discharging: The battery was discharged at a constant current of 0.5C and 2.0C to 2.5V respectively, and the discharge capacity at this rate was recorded. Rate capacity retention rate = 2.0C discharge capacity / 0.5C discharge capacity.

[0092] Example 1 Step 1: Take the positive electrode sheet of a waste lithium iron phosphate battery, dissolve it with N-methylpyrrolidone, and peel off the aluminum foil to obtain lithium iron phosphate powder. Mix the lithium iron phosphate powder with thioacetamide (TAA) and sodium sulfide (Na2S·9H2O) at a mass ratio of 1:2:1, add ethylene glycol solvent, transfer to a hydrothermal reactor, react at 200℃ for 18 hours, cool, centrifuge, wash, and vacuum dry (80℃, 12 hours) to obtain black NaFeS2 powder.

[0093] NaFeS2 powder and acid-treated multi-walled carbon nanotubes (MWCNTs, 20 nm in diameter) were mixed at a mass ratio of 7:3. An ethanol / water (1:1) mixed solvent was added, and the mixture was ultrasonically dispersed for 30 minutes. The mixture was then stirred at 60°C until dry to obtain the NaFeS2 / CNT composite, which is a sulfur-based semiconductor photocatalyst.

[0094] 100 mg of the NaFeS2 / CNT complex was dispersed in 100 mL of methanol, and H2PtCl6 solution (Pt content 1 wt%) was added. The mixture was then irradiated with a xenon lamp (λ > 420 nm) for 2 hours. 4+ Photoreduction yielded Pt nanoparticles (average particle size 3 nm, confirmed by TEM), which were then loaded onto the surface of NaFeS2. Solid-liquid separation was performed to obtain a sulfur-based semiconductor photocatalyst with Pt particles on the surface. 100 g of the sulfur-based semiconductor photocatalyst with Pt particles on the surface was added to 3 L of N-methylpyrrolidone and ultrasonically dispersed for 10 min to obtain a photocatalyst dispersion.

[0095] Step 2: Add the recycled lithium iron phosphate, conductive carbon black SP, and binder (polyvinylidene fluoride) to the photocatalyst dispersion at a mass ratio of 95:2:3, transfer to a photoresponse stirring vessel, turn on the blue LED (455 nm, 200 mW / cm²), stir at 800 rpm and 25°C for 20 minutes, and then continue stirring. The resulting slurry is then subjected to vacuum degassing for 5 minutes to obtain the positive electrode slurry.

[0096] Step 3: Transfer the above positive electrode slurry to a coating machine and coat it onto an aluminum foil (12 μm thick). The wet film thickness is 200 μm, and the coating speed is 2 m / min. A 405 nm LED light source (150 mW / cm²) is placed at the oven inlet, with an irradiation length of 1 m and a wet film passage time of 30 seconds. Photogenerated electrons in situ reduce the LFP surface to obtain the initial electrode. The exposed side of the initial electrode has a 5 nm thick Li₂ layer. 1.1 FePO4 conductive layer.

[0097] Step four: The initial electrode is placed under light radiation for drying to obtain a positive electrode. The drying process includes the following steps: a first stage with a light wavelength of 620 nm, a drying temperature of 80 °C, and a holding time of 2 min; a second stage with a light wavelength of 455 nm, a drying temperature of 100 °C, and a holding time of 3 min; and a third stage with a light wavelength of 365 nm, a drying temperature of 120 °C, and a holding time of 2 min; thus obtaining the positive electrode.

[0098] Example 2 Unlike Example 1, in step four, the drying process includes a first stage performed sequentially, with a light wavelength of 650 nm, a drying temperature of 80 °C, and a holding time of 2 min; a second stage performed, with a light wavelength of 420 nm, a drying temperature of 100 °C, and a holding time of 5 min; and a third stage performed, with a light wavelength of 365 nm, a drying temperature of 120 °C, and a holding time of 2 min; thus obtaining the positive electrode sheet.

[0099] Example 3 Unlike Example 1, in step four, the drying process includes a first stage performed sequentially, with a light wavelength of 680nm, a drying temperature of 75°C, and a holding time of 2 minutes; a second stage performed, with a light wavelength of 400nm, a drying temperature of 100°C, and a holding time of 5 minutes; and a third stage performed, with a light wavelength of 365nm, a drying temperature of 120°C, and a holding time of 2 minutes; thus obtaining the positive electrode sheet.

[0100] Example 4 Unlike Example 1, in step two, a blue LED (480 nm, 180 mW / cm²) is turned on, the stirring rate is 800 rpm, the temperature is 25°C, and the stirring is continued for 20 minutes. The resulting slurry is then subjected to vacuum degassing treatment for 5 minutes to obtain the positive electrode slurry.

[0101] Example 5 Unlike Example 1, in step two, a blue LED (450 nm, 220 mW / cm²) is turned on, the stirring rate is 800 rpm, the temperature is 25°C, and the stirring is continued for 20 minutes. The resulting slurry is then subjected to vacuum degassing treatment for 5 minutes to obtain the positive electrode slurry.

[0102] Example 6 Unlike Example 1, in step three, a 405 nm LED light source (130 mW / cm²) is set at the oven inlet, with an irradiation length of 1 m and a wet film passage time of 30 seconds.

[0103] Example 7 Unlike Example 1, in step three, a 410 nm LED light source (150 mW / cm²) is set at the oven inlet, with an irradiation length of 1 m and a wet film passage time of 30 seconds.

[0104] Example 8 Unlike Example 1, in step three, a 400 nm LED light source (150 mW / cm²) is set at the oven inlet, with an irradiation length of 1 m and a wet film passage time of 60 seconds.

[0105] Example 9 Unlike Example 1, in step one, NaFeS2 powder and acid-treated graphene are mixed at a mass ratio of 7:3.

[0106] Example 10 The difference from Example 1 is: Step 1: Titanium dioxide powder and acid-treated multi-walled carbon nanotubes (MWCNTs, 20 nm in diameter) are mixed at a mass ratio of 7:3. An ethanol / water (1:1) mixed solvent is added, and the mixture is ultrasonically dispersed for 30 minutes. The mixture is then stirred at 60°C until dry to obtain the photocatalyst.

[0107] Add 100g of photocatalyst to 3L of N-methylpyrrolidone and ultrasonically disperse for 10min to obtain a photocatalyst dispersion.

[0108] Comparative Example 1 Unlike Example 1, in step four, the initial electrode sheet is placed in an oven for drying at 120°C for 30 minutes to obtain the positive electrode sheet.

[0109] Comparative Example 2 Unlike Example 1, in step three, the above positive electrode slurry is transferred to a coating machine and coated on an aluminum foil (12 μm thick) with a wet film thickness of 200 μm and a coating speed of 2 m / min to obtain the initial electrode sheet.

[0110] Comparative Example 3 Unlike Example 1, in step one, recycled lithium iron phosphate, conductive carbon black SP, and binder (polyvinylidene fluoride) are added to N-methylpyrrolidone in a mass ratio of 95:2:3. The stirring speed is controlled at 800 rpm and the temperature is 25°C. The mixture is stirred continuously for 20 minutes. The resulting slurry is then subjected to vacuum degassing treatment for 5 minutes to obtain the positive electrode slurry.

[0111] Comparative Example 4 Unlike Example 1, in step four, the initial electrode is placed under light radiation for drying to obtain a positive electrode. The drying process includes a first stage with a light wavelength of 365 nm, a drying temperature of 120 °C, and a holding time of 2 min; a second stage with a light wavelength of 455 nm, a drying temperature of 100 °C, and a holding time of 3 min; and a third stage with a light wavelength of 620 nm, a drying temperature of 80 °C, and a holding time of 2 min, to obtain the positive electrode.

[0112] Table 1. Physicochemical parameters of the positive electrode and electrochemical performance parameters of the battery

[0113] According to the data in Table 1, in Examples 1-10, using the preparation process of this application, the microbubbles in the positive electrode slurry are reduced. After the positive electrode slurry is coated onto the current collector, the residual microbubbles in the initial electrode sheet can also be dissipated by heat under light irradiation. The surface density and compaction density of the prepared positive electrode sheet are increased. This is because the photocatalytic treatment and the three-stage drying process reduce the microbubbles in the positive electrode slurry, make the particle dispersion more uniform, and improve the uniformity of the coating thickness. After the three-stage drying process, the residual solvent in the electrode sheet is reduced, and the combination of lithium iron phosphate, conductive agent and binder is more stable. The conductive agent distributed between the lithium iron phosphates forms a cross-linked conductive network, which improves the first-efficiency and rate performance of the battery. In addition, the peel strength of the positive electrode sheet is also improved, the electrode structure is more compact and not easy to fall off, the electrode surface is flat, and the surface pinholes and blistering defects are significantly reduced. The stability of the interface structure is effectively improved, and the cycle capacity retention rate of the battery is also improved.

[0114] According to the test data of Example 1 and Comparative Example 1, Comparative Example 1 did not use the three-stage drying process, the interface structure stability of the positive electrode decreased, the peel strength decreased compared with Example 1, the 500-cycle retention rate decreased, and due to the breakage of some conductive networks in the electrode, the conductive networks between lithium iron phosphates were discontinuous, and the first efficiency and rate performance of the battery also decreased compared with Example 1.

[0115] Based on the test data from Example 1 and Comparative Example 2, it can be seen that the initial electrode prepared in Comparative Example 2 was not subjected to in-situ reduction treatment under the second light radiation, resulting in an increase in microbubbles within the electrode. The initial coulombic efficiency of the battery decreased compared to Example 1, and the compaction density, areal density, and peel strength of the positive electrode all decreased. Furthermore, no lithium-rich Li phase was formed on the surface of the positive electrode. 1.1 FePO4 reduces the lithium-ion diffusion capacity of the positive electrode, decreases interface stability, and significantly reduces the battery's cycle capacity retention.

[0116] According to the test data of Example 1 and Comparative Example 3, during the preparation process of Comparative Example 3, the positive electrode slurry was not subjected to photocatalytic treatment during the mixing process. The number of lithium iron phosphate particles agglomerates in the positive electrode slurry increased, and a small portion of lithium iron phosphate was deactivated by residual organic matter. The compaction density and areal density of the positive electrode sheet decreased, and the initial coulombic efficiency of the battery decreased compared to Example 1. The compaction density, areal density, and peel strength of the positive electrode sheet also decreased.

[0117] According to the test data of Example 1 and Comparative Example 4, during the preparation process of Comparative Example 4, the wavelength of the irradiation light in the first, second, and third stages of the electrode drying process increases sequentially, that is, the light radiation energy gradually decreases, and the drying temperature in the first, second, and third stages decreases sequentially. Therefore, in the first stage, under the high drying temperature and light radiation, the electrode surface dries rapidly, making it difficult for the residual moisture and solvent inside the electrode to fully evaporate. Due to the rapid temperature rise, the electrode surface peels and cracks, the compaction density and areal density of the positive electrode decrease, the peel strength of the electrode also decreases significantly, the rate performance and first efficiency of the battery decrease, and during the repeated cycling process, the electrode swells locally, and the cycle stability of the battery decreases.

[0118] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a positive electrode sheet, characterized in that, The preparation method includes: The recovered lithium iron phosphate, conductive agent, binder and photocatalyst dispersion were simultaneously mixed and photocatalytically treated under the first light radiation to obtain the positive electrode slurry; The positive electrode slurry is placed on the current collector and then subjected to in-situ reduction treatment under second light radiation to obtain the initial electrode sheet. The initial electrode is placed under third light radiation for drying to obtain a positive electrode; wherein the drying process includes a first stage, a second stage and a third stage performed sequentially, wherein the light wavelength of the first stage, the second stage and the third stage decreases sequentially, and the drying temperature of the first stage, the second stage and the third stage increases sequentially.

2. The method for preparing the positive electrode sheet according to claim 1, characterized in that, The preparation steps of the positive electrode slurry include: The light intensity of the first light radiation is controlled to be 180 mW / cm²~220 mW / cm², and the light wavelength of the first light radiation is 450nm~480nm. Under the first light radiation, the recovered lithium iron phosphate and the photocatalyst dispersion are mixed and photocatalyzed simultaneously. During the treatment, the stirring rate is controlled to be 700rpm~1000rpm, and the stirring time is 20 minutes~30 minutes.

3. The method for preparing the positive electrode sheet according to claim 1 or 2, characterized in that, The method satisfies at least one of the following characteristics: (1) The solid content of the positive electrode slurry is 55%~65%; (2) The mass ratio of the recovered lithium iron phosphate, the conductive agent and the binder is (92~95): (1~3): (2~5); (3) The conductive agent includes at least one of carbon nanotubes, graphene, carbon black, and graphite; (4) The adhesive includes polyvinylidene fluoride.

4. The method for preparing the positive electrode sheet according to claim 1 or 2, characterized in that, The photocatalyst dispersion includes a sulfur-based semiconductor photocatalyst, wherein Pt particles are loaded on the surface of the sulfur-based semiconductor photocatalyst.

5. The method for preparing the positive electrode sheet according to claim 4, characterized in that, The sulfur-based semiconductor photocatalyst comprises NaFeS2 particles and a conductive material located on at least a portion of the surface of the NaFeS2 particles. The conductive material includes at least one of carbon nanotubes, graphene, carbon black, and graphite. The Pt particles are located on the surface of the NaFeS2 particles and / or the conductive material.

6. The method for preparing the positive electrode sheet according to claim 1 or 2, characterized in that, The drying process step satisfies at least one of the following characteristics: (1) The wavelength of light in the first stage is 600nm~680nm, the drying temperature is 75℃~85℃, and the heat preservation time is 1 minute~2 minutes; (2) The wavelength of light in the second stage is 400nm~480nm, the drying temperature is 95℃~110℃, and the heat preservation time is 3 minutes~5 minutes; (3) The wavelength of light in the third stage is 300nm~380nm, the drying temperature is 115℃~130℃, and the heat preservation time is 1 minute~2 minutes.

7. The method for preparing the positive electrode sheet according to claim 1 or 2, characterized in that, The step of placing the positive electrode slurry on the current collector and performing in-situ reduction treatment under second light radiation includes: The light intensity of the second light radiation is controlled to be 130 mW / cm²~150 mW / cm², the light wavelength of the second light radiation is 400nm~410nm, and the in-situ reduction treatment time is 30 seconds~60 seconds to obtain the initial electrode.

8. The method for preparing the positive electrode sheet according to claim 7, characterized in that, The initial electrode has a conductive layer on its exposure side, the conductive layer comprising Li 1.1 FePO4; and / or, the thickness of the conductive layer is 3nm~5nm.

9. The method for preparing the positive electrode sheet according to claim 1, characterized in that, The preparation method further includes preparing a photocatalyst dispersion, the steps of which include: Under xenon lamp irradiation, sulfur-based semiconductor photocatalyst was mixed with H2PtCl6 solution, and solid-liquid separation was performed to obtain sulfur-based semiconductor photocatalyst with Pt particles loaded on the surface. A sulfur-based semiconductor photocatalyst with Pt particles loaded on its surface was added to a solvent to obtain a photocatalyst dispersion.

10. The method for preparing the positive electrode sheet according to claim 9, characterized in that, The preparation method further includes preparing the sulfur-based semiconductor photocatalyst, the steps of which include: The recovered lithium iron phosphate, thioacetamide and sodium source were reacted under hydrothermal conditions to obtain NaFeS2; The NaFeS2 is mixed with a conductive material to obtain a sulfur-based semiconductor photocatalyst; wherein the conductive material includes at least one of carbon nanotubes, graphene, carbon black, and graphite.

11. A positive electrode plate, characterized in that, The positive electrode sheet is prepared by the preparation method according to any one of claims 1 to 10; the positive electrode sheet satisfies at least one of the following characteristics: The areal density of the positive electrode sheet is 390 g / m³. 2 ~410g / m 2 ; The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 ~2.7 g / cm 3 ; The peel strength of the positive electrode sheet is 25 N / m ~ 35 N / m.

12. A battery cell, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The positive electrode sheet is prepared by the preparation method according to any one of claims 1-10, or the positive electrode sheet includes the positive electrode sheet according to claim 11.

13. A battery device, characterized in that, The battery device includes a positive electrode sheet prepared by the preparation method according to any one of claims 1-10 or the positive electrode sheet according to claim 11, or includes a battery cell according to claim 12. The battery device includes one or more of the following: battery module and battery pack.

14. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 13, the battery device being used to store electrical energy.

15. An electrical appliance, characterized in that, The electrical device includes the battery device as described in claim 13, or the energy storage device as described in claim 14.

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