Conductive polymer coated Prussian blue composite material as well as preparation method and application thereof

Abstract

The invention discloses a conductive polymer coated Prussian blue composite material as well as a preparation method and application thereof. The conductive polymer coated Prussian blue composite material has a core-shell structure, the core-shell structure comprises an inner core and an outer shell coating the inner core, the inner core comprises Prussian blue, the outer shell comprises a plurality of periodic units which are arranged in a layer-by-layer coating manner, and the periodic units are arranged in the core-shell structure. Each periodic unit comprises a polyelectrolyte layer and a conductive polymer layer coating the polyelectrolyte layer; the polyelectrolyte layer in the periodic unit adjacent to the surface of the inner core coats the surface of the inner core, and the outermost layer of the shell is a conductive polymer layer. According to the conductive polymer coated Prussian blue composite material provided by the invention, accurate regulation and control and interface optimization of a coating layer are realized through a layer-by-layer self-assembly technology, the electrochemical performance of the conductive polymer coated Prussian blue composite material is improved, the preparation process is high in universality, and the conductive polymer coated Prussian blue composite material can be widely applied to the field of positive electrode materials or secondary batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material technology, specifically relating to a conductive polymer-coated Prussian blue composite material and its preparation method and application. Background Technology

[0002] Prussian blue materials, due to their three-dimensional open framework structure and high theoretical specific capacity (approximately 170 mAh / g), are considered ideal cathode materials for secondary batteries (such as sodium / potassium ion batteries). Currently, coating techniques are commonly used to modify Prussian blue materials to improve their processing performance and cycle stability. However, existing technologies suffer from the following core problems: First, there are intrinsic performance defects. Prussian blue has a low intrinsic conductivity (approximately 1). S / cm), structural deformation (volume expansion rate of about 15%) and dissolution of transition metals (such as Mn) are prone to occur during charging and discharging. The dissolution rate is approximately 1.2 mg / L, resulting in poor rate performance (capacity retention at 10C <50%) and cycling stability (capacity decay >30% after 100 cycles).

[0003] Second, the coating process has limitations. Traditional coating methods (such as physical mixing and chemical deposition) can only form randomly thick coating layers (thickness deviation ±20nm), making it impossible to precisely control the thickness and uniformity of the coating layer. This can easily lead to obstructed electron conduction (conductivity improvement of only 1-2 orders of magnitude) or excessively long ion diffusion paths (ionic conductivity <10). -9 S / cm).

[0004] Third, there is a lack of functional diversity. Existing conductive polymer coatings (such as polypyrrole and polyaniline) only focus on improving electronic conduction, without addressing the interfacial compatibility issue (interfacial binding energy < 15mJ / m²). The coating layer is prone to detachment during charge and discharge (peel strength < 5N / cm), making it impossible to simultaneously improve cycle stability and rate performance.

[0005] For example, the one-step coating method used in the existing technology can only form a random thick coating layer with large thickness deviation and cannot achieve layer control; direct coating without polyelectrolytes has weak interfacial bonding with Prussian blue, peel strength <5N / cm, and the coating layer is easy to fall off; chemical vapor deposition (CVD) is expensive, requiring more than 30% more equipment investment, and cannot control the coating layer thickness to the nanometer level.

[0006] Currently, although patents such as CN110224130A and CN113206224A have proposed conductive polymer coating schemes, they all adopt a "one-step method" or "simple repeated coating", which fails to achieve hierarchical precise control of the coating layer and does not introduce a polyelectrolyte medium layer to optimize the interface bonding. As a result, the coating effect and performance improvement are limited and cannot fully meet the requirements of high-performance batteries for cathode materials. Summary of the Invention

[0007] The main objective of this invention is to provide a conductive polymer-coated Prussian blue composite material, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: A first aspect of the present invention provides a conductive polymer-coated Prussian blue composite material having a core-shell structure, the core-shell structure comprising a core and an outer shell (coating layer) covering the core, the core comprising Prussian blue, the outer shell comprising a plurality of periodic units layered together, each periodic unit comprising a polyelectrolyte layer and a conductive polymer layer covering the polyelectrolyte layer; the polyelectrolyte layer in the periodic unit adjacent to the surface of the core covers the surface of the core, and the outermost layer of the outer shell is a conductive polymer layer.

[0009] A second aspect of the present invention provides a method for preparing a conductive polymer-coated Prussian blue composite material, comprising: Prussian blue is mixed evenly with a positively charged polyelectrolyte solution, resulting in electrostatic adsorption and the formation of a polyelectrolyte layer on the surface of Prussian blue. Under an inert atmosphere, Prussian blue with a polyelectrolyte layer is mixed evenly with a conductive polymer solution, and the polymer adsorption forms a conductive polymer layer to obtain a periodic unit. Periodic units were repeatedly prepared using a layer-by-layer self-assembly technique, followed by heat treatment, to obtain a conductive polymer-coated Prussian blue composite material.

[0010] A third aspect of the present invention provides a conductive polymer-coated Prussian blue composite material prepared by the above method.

[0011] A fourth aspect of the present invention provides a positive electrode material comprising the above-described conductive polymer-coated Prussian blue composite material.

[0012] A fifth aspect of the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the aforementioned positive electrode material.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The conductive polymer-coated Prussian blue composite material provided by the present invention can achieve precise control of the coating layer. By adopting the layer-by-layer self-assembly technology, the polyelectrolyte layer and the conductive polymer layer are assembled alternately, which realizes the precise control of the number of coating layers and the thickness of a single layer. The total coating layer thickness deviation is ≤ ±3nm, while the deviation of the traditional process is ±20nm, which breaks through the limitation of the traditional process that can only control the total coating layer thickness. Moreover, by controlling the type of polyelectrolyte layer and adjusting the polymerization time of the conductive polymer layer, the present invention can customize the conductive polymer-coated Prussian blue composite material of “3 layers × 10nm” (high power structure) or “10 layers × 5nm” (high energy structure) according to the needs, taking into account both ion diffusion and electron conduction.

[0014] (2) The conductive polymer-coated Prussian blue composite material provided by the present invention has an interfacial synergistic effect. The polyelectrolyte layer (such as polydiallyldimethylammonium chloride) fills the surface defects of Prussian blue through electrostatic adsorption, reduces the porosity of the Prussian blue surface, and combines with the conductive polymer layer (such as polypyrrole) through quaternary ammonium-pyrrole ring hydrogen bonds to form a "flexible buffer layer + rigid conductive layer" composite interface. In secondary batteries, it can suppress the volume expansion during charging and discharging and greatly reduce the shedding rate of the coating layer.

[0015] (3) The conductive polymer-coated Prussian blue composite material provided by the present invention can achieve a leap in electrochemical performance. The synergistic design of the dual-conducting interface enables the ionic conductivity of the polyelectrolyte layer to couple with the electronic conductivity of the conductive polymer layer, forming an "ion-electron dual-conducting" interface, which improves electronic conductivity and ionic conductivity. In secondary batteries, it can improve capacity retention, while suppressing transition metal dissolution and reducing volume expansion, thus achieving simultaneous improvement in cycle stability and rate performance.

[0016] (4) The present invention provides a conductive polymer coated Prussian blue composite material with a polyelectrolyte layer as a medium layer. The polyelectrolyte activates the surface of Prussian blue through electrostatic adsorption, thereby increasing the density of its active sites and acting as a "molecular bridge" to enhance the interfacial bonding with the conductive polymer. At the same time, it provides ion conduction channels and significantly improves ion conductivity.

[0017] (5) The present invention provides a method for preparing a conductive polymer-coated Prussian blue composite material, which has strong process versatility: it can flexibly replace conductive polymers or polyelectrolytes to meet the needs of multiple scenarios such as sodium / potassium ion batteries; and the preparation parameters (such as the number of layers, temperature, and time) are adjustable, making it compatible with large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a conductive polymer-coated Prussian blue composite material in a typical embodiment of the present invention. Detailed Implementation

[0020] In view of the problems of poor controllability of Prussian blue coating, weak interfacial bonding and insufficient performance improvement in the above-mentioned prior art, the inventors of this invention have conducted extensive and in-depth research and provided a conductive polymer-coated Prussian blue composite material, its preparation method and application. It mainly achieves precise control and interface optimization of the coating layer through the alternating assembly of "polyelectrolyte medium layer - conductive polymer functional layer" to construct a "dual-conducting ion-electron" core-shell structure.

[0021] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0022] A first aspect of the present invention provides a conductive polymer-coated Prussian blue composite material having a core-shell structure, the core-shell structure comprising a core and a shell covering the core, the core comprising Prussian blue, the shell comprising a plurality of periodic units layered together, each periodic unit comprising a polyelectrolyte layer and a conductive polymer layer covering the polyelectrolyte layer; the polyelectrolyte layer in the periodic unit adjacent to the surface of the core covering the surface of the core, and the outermost layer of the shell being a conductive polymer layer.

[0023] In this invention, the outer shell can also be referred to as a covering layer.

[0024] In some embodiments, the polyelectrolyte layer and the conductive polymer layer are bonded to form an ion-electron biconducting interface. Specifically, the conductive polymer layer bonds to the side groups of the polyelectrolyte layer through π-π stacking, forming an ion-electron biconducting interface.

[0025] In some embodiments, the conductive polymer-coated Prussian blue composite material has an ionic conductivity of 1 × 10⁻⁶. -7 ~5×10 -7 S / cm, electronic conductivity 1×10 -5 ~5×10 -5 S / cm; In some embodiments, the total number of periodic units is 3 to 10, the thickness of each periodic unit is 5 to 20 nm, and the total thickness deviation of the outer shell is ≤ ±3 nm. In this invention, fewer than three layers may result in poor coverage, while more than 10 layers may lead to insufficient material performance.

[0026] In some implementations, the thickness of each of the polyelectrolyte layers is 2 to 5 nm.

[0027] In some embodiments, the thickness of each of the conductive polymer layers is 5 to 20 nm.

[0028] In some implementations, the core includes Prussian blue particles.

[0029] Furthermore, the size of the Prussian blue particles is 100~500 nm.

[0030] Furthermore, the Prussian blue particles have a cubic crystal structure.

[0031] Furthermore, the Prussian blue particles include, but are not limited to, any one of cubic ferrocyanide and cubic nickel ferrocyanide.

[0032] In some implementations, the polyelectrolyte layer includes, but is not limited to, a positively charged polyelectrolyte.

[0033] Furthermore, the positively charged polyelectrolyte is a positively charged linear polymer.

[0034] Furthermore, the positively charged polyelectrolyte includes either polydiallyldimethylammonium chloride (PDDA) or polylysine.

[0035] Furthermore, the molecular weight of the positively charged polyelectrolyte is 1×1 ~1×1 .

[0036] In some embodiments, the conductive polymer layer is formed by polymerizing conductive polymer monomers.

[0037] Furthermore, the conductive polymer monomer includes at least one of polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), etc., but is not limited to this.

[0038] In some embodiments, the peel strength between the conductive polymer-coated Prussian blue composite material and the current collector is 8~12 N / cm.

[0039] In some implementations, the polyelectrolyte layer activates the Prussian blue surface through electrostatic adsorption.

[0040] Furthermore, the density of active sites on the surface of the Prussian blue is 5~10×1 / cm². In a typical embodiment of the invention, the density of active sites on the surface of unactivated Prussian blue is from 1. / cm² increased to 5×1 / cm².

[0041] Specifically, a schematic diagram of the structure of the conductive polymer-coated Prussian blue composite material in a typical embodiment of the present invention is shown below. Figure 1 As shown, the conductive polymer-coated Prussian blue composite material has a core-shell structure, which includes a core and an outer shell covering the core. The core includes Prussian blue, and the outer shell includes three periodic units arranged in layers. Each periodic unit includes a polyelectrolyte layer and a conductive polymer layer covering the polyelectrolyte layer. The polyelectrolyte layer in the periodic unit adjacent to the core surface covers the core surface, and the outermost layer of the outer shell is a conductive polymer layer.

[0042] In this invention, the polyelectrolyte layer is the key "medium layer," and its core functions can be summarized in the following three points: (1) Surface activation: Due to the chemical inertness of the cyano group, the Prussian blue particle surface has a weak binding force directly with the conductive polymer (interfacial binding energy of about 10~15 mJ / m²). The polyelectrolyte transforms the particle surface from an "inert surface" to an "active interface" through electrostatic adsorption, thereby increasing the density of conductive polymer deposition sites from 1 / cm² increased to 5×1 / cm², significantly improving coating uniformity.

[0043] (2) Thickness control: The molecular weight of the polyelectrolyte (e.g., the molecular weight of PDDA is 1) ~1 The thickness of the monolayer (2-5 nm) can be precisely controlled by adjusting the solution concentration (0.5-2 g / L). Combined with the subsequent polymerization time (60-180 min) and monomer concentration (0.01-0.05 mol / L), the thickness of the conductive polymer monolayer (5-20 nm) can be precisely controlled (deviation ≤ ±5%). In contrast, traditional chemical deposition methods, lacking a mediator layer, result in conductive polymer thickness deviations of up to ±30%. This application, through the "template effect" of the polyelectrolyte, allows the total coating layer thickness deviation to be controlled within ±3 nm.

[0044] (3) Enhanced functionality: The polyelectrolyte layer itself has ion conductivity (e.g., the quaternary ammonium groups of PDDA can conduct N). This forms an "ion-electron dual conduction channel" with the electronic conductivity of the conductive polymer.

[0045] In a typical implementation, when the polyelectrolyte layer is 2 nm thick and the conductive polymer layer is 10 nm thick, the ionic conductivity of the composite material increases from 1 nm for pure Prussian blue. S / cm increased to 1 S / cm, electronic conductivity from 1 S / cm increased to 1 The synergistic effect of the dual conductivity (S / cm) improves the capacity retention of the conductive polymer-coated Prussian blue composite material in secondary batteries by more than 25% at a high rate of 10C compared to the direct coating material without a polyelectrolyte layer.

[0046] Furthermore, in this invention, the polyelectrolyte layer and the conductive polymer layer have a synergistic effect. They are not simply physical superpositions, but rather achieve significant synergistic enhancement through charge matching and interfacial coupling, specifically in the following two aspects: (1) Charge-directed synergy: Polyelectrolytes (such as PDDA), as positively charged linear polymers, can be electrostatically attracted and adsorbed onto the surface of negatively charged Prussian blue particles (ζ potential approximately -25 mV), forming a uniform positively charged interface (ζ potential increased to +15 mV). This interface provides directional deposition sites for subsequent conductive polymer monomers (such as polypyrrole, which are usually negatively charged or contain polar groups in solution), avoiding self-aggregation and ensuring that the conductive polymer grows uniformly only on the particle surface, significantly improving the uniformity of the coating layer.

[0047] (2) Interfacial reinforcement synergy: The long-chain structure of the polyelectrolyte can embed into the microscopic defects (such as vacancies and grain boundaries) on the surface of Prussian blue particles, filling the voids on the core surface (the porosity can be reduced from 8% to 3%); while the conductive polymer is tightly bonded to the side groups of the polyelectrolyte (such as the quaternary ammonium groups of PDDA) through π-π stacking or hydrogen bonding, forming a composite interface of "polyelectrolyte bridging layer - conductive polymer functional layer". This interface not only increases the bonding force between the core and the outer layer to 8~12 N / cm (compared to less than 5 N / cm for traditional direct coating), but also buffers the volume expansion of the Prussian blue core during the charging and discharging process of the secondary battery through the flexible chain segments of the polyelectrolyte (the volume expansion rate can be reduced from 15% to 8%), effectively suppressing the cracking and shedding of the coating layer (the shedding rate is <5% after 300 cycles).

[0048] A second aspect of the present invention provides a method for preparing a conductive polymer-coated Prussian blue composite material, comprising: Prussian blue is mixed evenly with a positively charged polyelectrolyte solution, resulting in electrostatic adsorption and the formation of a polyelectrolyte layer on the surface of Prussian blue. Under an inert atmosphere, Prussian blue with a polyelectrolyte layer is mixed evenly with a conductive polymer solution, and the polymer adsorption forms a conductive polymer layer to obtain a periodic unit. Periodic units were repeatedly prepared using a layer-by-layer self-assembly technique, followed by heat treatment, to obtain a conductive polymer-coated Prussian blue composite material.

[0049] In some embodiments, the method for preparing the conductive polymer-coated Prussian blue composite material specifically includes: The Prussian blue is dispersed in a positively charged polyelectrolyte solution and mixed evenly. The mixture is stirred at 20-40°C for 30-120 minutes to induce electrostatic adsorption, forming a polyelectrolyte layer on the surface of the Prussian blue.

[0050] Furthermore, the mass concentration of the positively charged polyelectrolyte solution is 0.5~2 g / L.

[0051] Furthermore, the polyelectrolyte in the positively charged polyelectrolyte solution includes, but is not limited to, any one of polydiallyldimethylammonium chloride or polylysine.

[0052] Furthermore, the mass ratio of Prussian blue to the positively charged polyelectrolyte is 10:1 to 20:1.

[0053] Furthermore, the zeta potential between the Prussian blue surface and the polyelectrolyte layer is -25 mV to +15 mV.

[0054] In some embodiments, the method for preparing the conductive polymer-coated Prussian blue composite material specifically includes: Under an inert atmosphere, Prussian blue with a polyelectrolyte layer is uniformly dispersed in a conductive polymer mixture solution, and polymerized and adsorbed at 10~30℃ for 60~180 min to form the conductive polymer layer, thus obtaining the periodic unit.

[0055] Furthermore, the conductive polymer mixture solution comprises a conductive polymer monomer and an initiator.

[0056] Furthermore, the concentration of the conductive polymer monomer is 0.01~0.05 mol / L.

[0057] Furthermore, the mass ratio of Prussian blue with the polyelectrolyte layer to the conductive polymer monomer is 5:1 to 10:1.

[0058] Furthermore, the initiator includes, but is not limited to, ammonium persulfate, and the concentration of the initiator is 0.01~0.03 mol / L.

[0059] In some embodiments, the method for preparing the conductive polymer-coated Prussian blue composite material specifically includes: The layer-by-layer self-assembly technology is used to alternately adsorb polyelectrolytes and conductive polymers to prepare 3 to 10 cycle units, which are then heat-treated at 60 to 100°C for 2 to 4 hours to obtain the conductive polymer-coated Prussian blue composite material.

[0060] In some more specific embodiments, the preparation of the conductive polymer-coated Prussian blue composite material may include the following steps: S1. Disperse Prussian blue particles in a positively charged polyelectrolyte solution and stir at 20-40°C for 30-120 min to form a polyelectrolyte layer of 2-5 nm thickness through electrostatic adsorption; S2. Prussian blue particles with a polyelectrolyte layer are uniformly dispersed in a mixed solution containing conductive polymer monomers and an initiator. Polymerization and adsorption are carried out at 10-30°C under inert gas protection for 60-180 min to allow sufficient time for subsequent full coating and form a conductive polymer layer with a thickness of 5-20 nm. S3. Using the layer-by-layer self-assembly technology, polyelectrolyte adsorption and conductive polymer adsorption are alternately performed to prepare 3 to 10 cycle units. Then, the units are heat-treated at 60 to 100°C for 2 to 4 hours to enhance the interlayer bonding force, thereby obtaining the conductive polymer-coated Prussian blue composite material.

[0061] In step S1, the mass concentration of the positively charged polyelectrolyte solution is 0.5~2 g / L, wherein the positively charged polyelectrolyte includes either polydiallyldimethylammonium chloride or polylysine, the mass ratio of Prussian blue to the positively charged polyelectrolyte is 10:1~20:1, and the zeta potential between the surface of Prussian blue and the polyelectrolyte layer is -25 mV~+15 mV.

[0062] In a typical implementation, the positively charged polyelectrolyte is polydiallyldimethylammonium chloride.

[0063] In step S2, the conductive polymer mixture solution comprises a conductive polymer monomer and an initiator. The concentration of the conductive polymer monomer is 0.01~0.05 mol / L, and the concentration of the initiator is 0.01~0.03 mol / L. The conductive polymer monomer includes, but is not limited to, at least one of polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene), and the type of conductive polymer can be flexibly replaced. The initiator includes, but is not limited to, ammonium persulfate. The mass ratio of Prussian blue with the polyelectrolyte layer to the conductive polymer monomer is 5:1~10:1.

[0064] In a typical implementation, the conductive polymer monomer is polypyrrole, and the initiator is ammonium persulfate.

[0065] In step S3, the peel strength can be increased to 8~12 N / cm by enhancing the interlayer bonding force.

[0066] Furthermore, in this invention, Prussian blue particles are mainly synthesized via a co-precipitation method to obtain particles with specific crystal structures (e.g., cubic crystal system) and chemical compositions (e.g., Na₂Fe). 0.5 Mn 0. Prussian blue particles of 5[Fe(CN)6].

[0067] Specifically, this invention differs from the mechanical repetition of "simple layer-by-layer coating." It achieves the following innovative technical effects through layer-by-layer self-assembly technology, employing "alternating adsorption-precise control-interface optimization": (1) Breakthrough in structural precision: Traditional coating process can only control the total coating layer thickness (deviation ±20nm), while this application can independently control the thickness of each layer and the total number of layers (3~10 layers) by alternating assembly of "polyelectrolyte layer (2~5nm) + conductive polymer layer (5~20nm)", with a total thickness deviation ≤±3nm.

[0068] For example, in a typical implementation case, when the target total thickness is 50nm, it can be achieved by a combination of 5 layers × 10nm (polyelectrolyte 2nm + conductive polymer 8nm), while traditional processes cannot achieve single-layer-level thickness control, resulting in coatings that are too thick (>60nm, ion diffusion is hindered) or too thin (<40nm, electron conduction is insufficient).

[0069] (2) Improved cycle stability: The "gradient interface" formed by the multilayer structure can effectively inhibit the erosion of the Prussian blue core by the electrolyte.

[0070] For example, in a typical three-layer structure, the inner layer (closer to the Prussian blue core) is a thinner conductive polymer (5nm) providing high electronic conductivity; the outer layer is a thicker conductive polymer (20nm) acting as a physical barrier to reduce Mn. / Fe The dissolution rate of transition metals decreased from 1.2 mg / L in traditional coating to 0.3 mg / L. After 300 cycles at 1C rate, the capacity retention of the secondary battery increased from 75% in traditional coating to 92%, which is significantly better than the effect of simple layer-by-layer coating in the prior art.

[0071] (3) Improved process universality: The "modular" characteristics of layer-by-layer self-assembly allow for flexible adjustment of the material system.

[0072] For example, this invention can improve electron conduction by increasing the number of layers (10 layers) and the thickness of each conductive polymer layer for high energy density requirements (such as electric vehicles); and optimize ion diffusion by reducing the number of layers (3 layers) and the thickness of each conductive polymer layer for high power density requirements (such as energy storage power stations). In contrast, existing technologies using simple layer-by-layer coating cannot control the hierarchical structure and can only achieve performance adjustments by changing the type of coating material (such as replacing the conductive polymer), thus limiting their applicability.

[0073] Therefore, the layer-by-layer self-assembly technology of this invention forms an innovative technical solution that differs from simple layer-by-layer coating through precise structural control, interface synergy and functional enhancement, effectively solving the problems of "uncontrollable thickness, weak interface bonding and single performance" in traditional processes.

[0074] In addition, the method for preparing the conductive polymer-coated Prussian blue composite material provided by the present invention can be mass-produced. In a typical embodiment, the single batch production capacity of the conductive polymer-coated Prussian blue composite material is ≥50kg.

[0075] A third aspect of the present invention provides a conductive polymer-coated Prussian blue composite material prepared by the above method.

[0076] A fourth aspect of the present invention provides a positive electrode material comprising the above-described conductive polymer-coated Prussian blue composite material.

[0077] A fifth aspect of the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the aforementioned positive electrode material.

[0078] In some implementations, the secondary battery retains ≥92% capacity after 300 cycles at 1C and ≥75% capacity at 10C. In contrast, in conventional technologies, secondary batteries made with coating materials retain only about 75% capacity after 300 cycles at 1C and less than 50% capacity at 10C.

[0079] In some embodiments, the volume expansion rate of Prussian blue in the secondary battery is no higher than 8%. In conventional technologies, the volume expansion rate of Prussian blue is around 15%. In a typical embodiment, the volume expansion rate of Prussian blue in the secondary battery is 8%, representing a 47% reduction in volume expansion rate.

[0080] In some embodiments, the conductive polymer-coated Prussian blue composite shell of the secondary battery exhibits a shedding rate of less than 5% after 300 2C cycles. In conventional technologies, the shedding rate of the shell after 300 cycles is greater than 30%.

[0081] In some embodiments, the amount of transition metal dissolved in the secondary battery is no more than 0.32 mg / L, wherein the transition metal includes Mn. Or Fe Any one of them.

[0082] For example, in conventional technology, the transition metal Mn in the secondary battery The leaching amount is around 1.2 mg / L. In a typical embodiment of this invention, the transition metal Mn in the secondary battery... The dissolution amount is 0.3 mg / L, and its dissolution rate is reduced by 75%.

[0083] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0084] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0085] Example 1

[0086] This embodiment provides a method for preparing a Prussian blue-based cathode material, including the following steps: S1. Prepare a precipitant solution and a metal salt solution separately. The precipitant solution is one of the reaction raw materials, used to provide sufficient cyano ligands. In this embodiment, the precipitant solution is one or more of sodium ferrocyanide, sodium ferricyanide, and sodium manganese cyanide. Specifically: Deionized water is selected, the water temperature is raised to 35±2℃ and maintained at this temperature. The measured amount of precipitant is continuously dissolved under stirring until it is close to saturation. Then the temperature is stabilized at 35℃. If necessary, a small amount of deionized water is added to adjust the solution concentration to 1.5mol / L. Prepare fresh for later use. The metal salt solution is one of the reaction raw materials, used to provide metal ions. In this embodiment, the metal salt solution is ferrous nitrate. Specifically: Deionized water is selected, the water temperature is raised to 35℃ and maintained at this temperature. The measured amount of metal salt solution is continuously dissolved under stirring. If necessary, a small amount of deionized water is added to control the total metal ion concentration of the solution to 1.8mol / L. Prepare fresh for later use (to be used within 12 hours).

[0087] S2. Take a 50L reactor and directly prepare 15L of a base solution containing a complexing agent, namely citric acid, in the reactor. The concentration of the complexing agent is approximately 1.5mol / L. Control the temperature of the base solution at 40℃. S3. Simultaneously add 20L of the precipitant solution and 15L of the metal salt solution prepared in S1 into the reactor. Stir at low speed at a temperature of 40±1℃ for about 8 hours for co-precipitation reaction. S4. The Prussian blue obtained from the reaction in S3 is separated, washed with deionized water, filtered, and dried under an inert atmosphere to obtain Prussian blue cathode material, weighing approximately 4000g; wherein the drying temperature is controlled at 180℃ and the drying time is approximately 12h.

[0088] S5. Layer-by-layer self-assembly conductive polymer coating step

[0089] (1) Formation of polyelectrolyte layer

[0090] The Prussian blue particles (approximately 4000 g) obtained in S4 were dispersed in a positively charged polyelectrolyte solution, and the mass concentration of the polyelectrolyte solution was controlled to be 0.8 g / L. The positively charged polyelectrolyte was polydiallyldimethylammonium chloride (PDDA).

[0091] Stirring at 35°C for 70 minutes allows the polyelectrolyte to be uniformly coated onto the Prussian blue surface through electrostatic adsorption, forming a polyelectrolyte layer with a thickness of approximately 3 nm.

[0092] By controlling the mass ratio of Prussian blue to polyelectrolyte within the range of 10:1, the surface zeta potential was increased from approximately -25 mV to +15 mV.

[0093] (2) Formation of conductive polymer layer

[0094] The Prussian blue coated with the polyelectrolyte layer was dispersed in a conductive polymer mixture solution, the mixture solution containing the conductive polymer monomer pyrrole and the initiator ammonium persulfate.

[0095] Under an inert atmosphere (such as nitrogen), the reaction temperature is controlled at 25°C, and the polymerization adsorption is carried out for 80 minutes to form a conductive polymer layer with a thickness of about 10 nm.

[0096] The monomer concentration was controlled at 0.03 mol / L, the initiator concentration was 0.03 mol / L, and the mass ratio of Prussian blue to monomer was 10:1.

[0097] (3) Repeated assembly and heat treatment

[0098] Using the layer-by-layer self-assembly technique, the above steps (1) and (2) were repeated, and polyelectrolyte layer and conductive polymer layer were deposited alternately to prepare a total of 3 periodic units.

[0099] The multilayer coated material was heat-treated at 70℃ for 2 hours to enhance interlayer bonding, resulting in a conductive polymer-coated Prussian blue composite material with a core-shell structure. The total coating thickness deviation of the final material can be controlled within ≤±3 nm.

[0100] Example 2

[0101] The key difference from Example 1 is that the number of periodic units is 3 (optimized ion diffusion) and the thickness of the conductive polymer layer is 8 nm.

[0102] S1. Synthesis of Prussian blue particles: Same as in Example 1, obtaining cubic N... Mn[Fe(CN Particles (500±50nm).

[0103] S2, Polyelectrolyte layer formation: Disperse 4000g of Prussian blue in 1L of PDDA solution with a mass concentration of 1g / L (molecular weight 1×1). Stirred at 30°C for 60 min to form a 2 nm thick PDDA layer (ζ potential +15 mV).

[0104] S3. Formation of conductive polymer layer: Under nitrogen protection, disperse in a mixture containing 0.03 mol / L pyrrole and 0.015 mol / L ammonium persulfate, stir at 20°C for 90 min, and polymerize to form an 8 nm thick polypyrrole layer (1 periodic unit).

[0105] S4. Repeated assembly and heat treatment: Repeat steps S2 and S3 a total of 3 times (cycle unit = 3), heat treatment at 80℃ for 3h, to obtain a conductive polymer-coated Prussian blue composite material with a total coating thickness of 3×(2+8)=30nm (deviation ±2nm).

[0106] Example 3

[0107] The method for preparing a conductive polymer-coated Prussian blue composite material provided in this embodiment differs from that in Example 1 in that the number of periodic units is 10 (to improve capacity retention) and the thickness of the conductive polymer layer is 5 nm.

[0108] S1. Synthesis of Prussian blue particles: Same as in Example 1.

[0109] S2, Polyelectrolyte layer formation: Same as in Example 1 (2nm thick PDDA layer).

[0110] S3. Formation of conductive polymer layer: Under nitrogen protection, disperse in a mixture containing 0.03 mol / L pyrrole and 0.015 mol / L ammonium persulfate, stir at 20°C for 60 min, and polymerize to form a 5 nm thick polypyrrole layer (1 periodic unit).

[0111] S4. Repeated assembly and heat treatment: Repeat steps 2-3 a total of 10 times (cycle unit = 10), heat treatment at 80℃ for 3 hours, to obtain a composite material with a total coating thickness of 10×(2+5)=70nm (deviation ±2nm).

[0112] Example 4

[0113] The method for preparing a conductive polymer-coated Prussian blue composite material in this embodiment differs from that in Example 1 in that: S5. Layer-by-layer self-assembly conductive polymer coating step: The positively charged polyelectrolyte is polylysine, and the conductive polymer monomer is polyaniline; The mass ratio of Prussian blue to polyelectrolyte is 20:1; the concentration of initiator is 0.01 mol / L; and the mass ratio of Prussian blue to conductive polymer monomer is 5:1.

[0114] Example 5

[0115] The method for preparing a conductive polymer-coated Prussian blue composite material in this embodiment differs from that in Example 1 in that: S5. Layer-by-layer self-assembly conductive polymer coating step: The conductive polymer monomer is poly(3,4-ethylenedioxythiophene). The mass ratio of Prussian blue to polyelectrolyte is 15:1; the concentration of initiator is 0.02 mol / L; and the mass ratio of Prussian blue to conductive polymer monomer is 8:1.

[0116] Example 6

[0117] The method for preparing a conductive polymer-coated Prussian blue composite material in this embodiment differs from that in Example 2 in that: S2, Polyelectrolyte layer formation: Disperse 4000g of Prussian blue in 1L of PDDA solution with a mass concentration of 1g / L (molecular weight 1×1). In a 2nm thick PDDA layer (ζ potential +15mV), the mixture was stirred at 20℃ for 120min to form a PDDA layer.

[0118] S3. Formation of conductive polymer layer: Under nitrogen protection, disperse in a mixture containing 0.03 mol / L pyrrole and 0.015 mol / L ammonium persulfate, stir at 10°C for 180 min, and polymerize to form an 8 nm thick polypyrrole layer (1 periodic unit).

[0119] S4. Repeated assembly and heat treatment: Repeat steps S2 and S3 a total of 3 times (cycle unit = 3), heat treatment at 60℃ for 4h, to obtain a conductive polymer-coated Prussian blue composite material with a total coating thickness of 3×(2+8)=30nm (deviation ±2nm).

[0120] Example 7

[0121] The method for preparing a conductive polymer-coated Prussian blue composite material in this embodiment differs from that in Example 2 in that: S2, Polyelectrolyte layer formation: Disperse 4000g of Prussian blue in 1L of PDDA solution with a mass concentration of 1g / L (molecular weight 1×1). In a 40°C environment, the mixture was stirred for 30 minutes to form a 2nm thick PDDA layer (ζ potential +15mV).

[0122] S3. Formation of conductive polymer layer: Under nitrogen protection, disperse in a mixture containing 0.03 mol / L pyrrole and 0.015 mol / L ammonium persulfate, stir at 30°C for 60 min, and polymerize to form an 8 nm thick polypyrrole layer (1 periodic unit).

[0123] S4. Repeated assembly and heat treatment: Repeat steps S2 and S3 a total of 3 times (cycle unit = 3), heat treatment at 100℃ for 2h, to obtain a conductive polymer-coated Prussian blue composite material with a total coating thickness of 3×(2+8)=30nm (deviation ±2nm).

[0124] Comparative Example 1

[0125] The key difference from Example 1 is that the polyelectrolyte layer is omitted, and polypyrrole is directly coated.

[0126] The specific preparation steps are as follows: S1. Synthesis of Prussian blue particles: Same as in Example 1.

[0127] S2. Direct coating: 4000g of Prussian blue is dispersed in a mixed solution containing 0.03mol / L pyrrole and 0.015mol / L ammonium persulfate. The mixture is stirred at 20°C for 120min under nitrogen protection to form a 20nm thick polypyrrole layer. The mixture is then heat-treated at 80°C for 3h.

[0128] Technical effect: Electronic conductivity 1×1 S / cm, 15% coating peeling rate after 300 cycles, Mn 2+ Dissolution rate: 1.1 mg / L.

[0129] Comparative Example 2

[0130] The key difference from Example 1 is that it uses conventional chemical deposition and does not involve layer-by-layer self-assembly.

[0131] The specific preparation steps are as follows: S1. Synthesis of Prussian blue particles: Same as in Example 1.

[0132] S2, Conventional Deposition: 4000g of Prussian blue was dispersed in a mixed solution containing 0.05mol / L pyrrole and 0.025mol / L ammonium persulfate, stirred at room temperature for 240min, and naturally deposited to form a 50nm thick polypyrrole layer (deviation ±20nm) without heat treatment.

[0133] The performance data of the secondary batteries prepared by the conductive polymer-coated Prussian blue composite material of the embodiments and comparative examples of the present invention are shown in Table 1.

[0134] Table 1. Performance data of secondary batteries prepared from conductive polymer-coated Prussian blue composite materials of the examples and comparative examples.

[0135] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0136] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0137] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. An electrically conductive polymer-coated Prussian blue composite material, characterized by: The conductive polymer-coated Prussian blue composite has a core-shell structure, the core-shell structure comprises an inner core and an outer shell covering the inner core, the inner core comprises Prussian blue, and the outer shell comprises a plurality of period units arranged in layers, each of the period units comprises a polyelectrolyte layer and a conductive polymer layer covering the polyelectrolyte layer; The polyelectrolyte layer in the period unit adjacent to the surface of the inner core covers the surface of the inner core, and the outermost layer of the outer shell is the conductive polymer layer.

2. The electrically conductive polymer-coated Prussian blue composite of claim 1, wherein: The polyelectrolyte layer and the conductive polymer layer combine to form an ion-electron double-conducting interface; and / or the ion conductivity of the electrically conductive polymer-coated Prussian blue composite material is 1 x 10 -7 ~5 x 10 -7 S / cm, and the electronic conductivity is 1 x 10 -5 ~5 x 10 -5 S / cm; And / or, the total number of the period units is 3-10, the thickness of each period unit is 5-20 nm, and the total thickness deviation of the outer shell is ≤±3 nm; And / or, the thickness of each polyelectrolyte layer is 2-5 nm; And / or, the thickness of each conductive polymer layer is 5-20 nm; And / or, the inner core comprises Prussian blue particles; Preferably, the size of the Prussian blue particles is 100-500 nm; Preferably, the Prussian blue particles are of cubic crystal structure; Especially preferably, the Prussian blue particles comprise any one of cubic crystal ferric ferrocyanide and cubic crystal nickel ferrocyanide; And / or, the polyelectrolyte layer comprises a positively charged polyelectrolyte, preferably a positively charged linear polymer; Preferably, the positively charged polyelectrolyte comprises any one of poly diallyl dimethyl ammonium chloride or polylysine; Preferably, the positively charged polyelectrolyte has a molecular weight of 1 x 10 ~1 x 10 ; And / or, the conductive polymer layer is formed by polymerization of a conductive polymer monomer; Preferably, the conductive polymer monomer comprises at least any one of polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene); And / or, the peeling strength between the conductive polymer-coated Prussian blue composite and the current collector is 8-12 N / cm; And / or, the polyelectrolyte layer is activated by electrostatic adsorption on the surface of Prussian blue; Preferably, the active site density of the Prussian blue surface is 5 to 10 x 1 / cm2.

3. A method for preparing an electrically conductive polymer-coated Prussian blue composite material, characterized by, Comprise: uniformly mixing Prussian blue with a positively charged polyelectrolyte solution to occur electrostatic adsorption, forming a polyelectrolyte layer on the surface of Prussian blue; uniformly mixing Prussian blue with a polyelectrolyte layer with a conductive polymer mixed solution under an inert atmosphere, polymerizing and adsorbing to form a conductive polymer layer, and preparing a period unit; repeating the preparation of the period unit by using a layer-by-layer self-assembly technique, and then performing heat treatment to prepare the conductive polymer-coated Prussian blue composite.

4. The manufacturing method according to claim 3, characterized in that, Specifically comprise: uniformly mixing the Prussian blue dispersed in the positively charged polyelectrolyte solution, stirring at 20-40℃ for 30-120 min to occur electrostatic adsorption, and forming a polyelectrolyte layer on the surface of Prussian blue; Preferably, the mass concentration of the positively charged polyelectrolyte solution is 0.5-2 g / L; Preferably, the polyelectrolyte in the positively charged polyelectrolyte solution comprises any one of poly diallyl dimethyl ammonium chloride or polylysine; Especially preferably, the mass ratio of Prussian blue to positively charged polyelectrolyte is 10:1-20:1; Preferably, the zeta potential between the surface of Prussian blue and the polyelectrolyte layer is -25 mV to +15 mV.

5. The manufacturing method according to claim 3, characterized in that, Specifically comprise: The Prussian blue with the polyelectrolyte layer is uniformly dispersed in a conductive polymer mixed solution under an inert atmosphere, and the conductive polymer layer is formed by polymerization adsorption at 10-30℃ for 60-180 min, so as to prepare the period unit; Preferably, the conductive polymer mixed solution comprises a conductive polymer monomer and an initiator; Especially preferably, the concentration of the conductive polymer monomer is 0.01-0.05 mol / L; Especially preferably, the mass ratio of the Prussian blue with the polyelectrolyte layer to the conductive polymer monomer is 5:1-10:

1. Especially preferably, the initiator comprises ammonium persulfate, and the concentration of the initiator is 0.01-0.03 mol / L.

6. The manufacturing method according to claim 3, characterized in that, Specifically comprising: The period unit is repeatedly prepared for 3-10 times by alternately performing polyelectrolyte adsorption and conductive polymer adsorption by using the layer-by-layer self-assembly technology, and then the conductive polymer coated Prussian blue composite material is prepared by heat treatment at 60-100℃ for 2-4 h.

7. The conductive polymer coated Prussian blue composite material prepared by the method of any one of claims 3-6.

8. A positive electrode material, characterized by, The conductive polymer coated Prussian blue composite material of claim 1, 2 or 7.

9. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte, characterized by: The positive electrode comprises the positive electrode material of claim 8.

10. The secondary battery according to claim 9, characterized by: The capacity retention rate of the secondary battery is ≥92% after 1C cycle for 300 times, and the capacity retention rate is ≥75% under 10C rate; And / or, the volume expansion rate of the Prussian blue in the secondary battery is not higher than 8%; And / or, the shedding rate of the shell of the conductive polymer coated Prussian blue composite material in the secondary battery is less than 5% after 2C cycle for 300 times. and / or, the amount of transition metal elution from the secondary battery is not greater than 0.32 mg / L, wherein the transition metal includes Mn or Fe 2 .

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