Microsphere additive, preparation method thereof, negative electrode electrolyte and all-vanadium redox flow battery

Abstract

The invention belongs to the field of flow batteries, and particularly relates to a microsphere additive, a preparation method thereof, a negative electrode electrolyte and an all-vanadium flow battery. The microsphere additive disclosed by the invention comprises a core substance and a double-crosslinking hydrogel shell layer coating the core substance, the core material comprises a polyhydroxy carbohydrate having a functionality greater than or equal to 4; the double-crosslinking hydrogel shell layer comprises a reaction product of a hydroxyl-containing acid-resistant hydrophilic polymer, an amino-containing acid-resistant hydrophilic polymer and an aldehyde crosslinking agent. The microsphere additive disclosed by the invention can effectively delay the capacity fading of the all-vanadium redox flow battery.

Description

Technical Field

[0001] This invention belongs to the field of flow batteries, specifically relating to a microsphere additive, its preparation method, a negative electrode electrolyte, and an all-vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries (VRFBs), as a large-scale flow energy storage system, occupy an extremely important position in the energy storage field because their positive and negative electrode electrolytes are composed entirely of vanadium ions. This eliminates the problem of cross-membrane contamination caused by different ions, resulting in excellent reversibility, extremely high cycle stability, and safety. Furthermore, VRFBs, with their high safety, long cycle life, and fully reusable electrolyte, are suitable for grid-connected regulation and grid load balancing scenarios for renewable energy sources such as wind and solar power. However, during actual long-term operation, the difference in osmotic pressure between the two electrolytes can cause vanadium ion migration across the membrane, leading to an imbalance between the two half-cells. This results in a decrease in stack discharge capacity, reduced cycle efficiency, and even electrolyte deposition or crystallization, causing severe capacity decay in VRFBs.

[0003] Existing technologies mainly suppress the transmembrane migration of vanadium ions, thereby reducing the capacity decay of vanadium redox flow batteries, through the following methods: First, using highly selective membrane materials, such as sulfonated polyimide (SPI) membranes and sulfonated polyether ether ketone (SPEEK) membranes, to enhance the membrane's shielding ability against vanadium ions; second, introducing inorganic particles into conventional ion exchange membranes to reduce the size of water channels in the membrane, further suppressing the co-migration of water and vanadium ions; and third, establishing numerical simulation models to precisely control the operating parameters of vanadium redox flow batteries, strategically mitigating the transmembrane diffusion of vanadium ions.

[0004] Although highly selective membrane materials possess better vanadium blocking capabilities, they are often accompanied by problems such as decreased proton conductivity and reduced energy efficiency, limiting their performance in high power density operation or long-term applications. Furthermore, introducing inorganic particles into conventional ion exchange membranes results in poor stack performance, and establishing numerical simulation models increases the complexity of system design and makes it difficult to dynamically respond to real-time changes in complex electrolyte environments. None of these approaches can fundamentally solve the capacity decay problem caused by electrolyte composition imbalance.

[0005] Therefore, there is an urgent need to develop a capacity decay suppression strategy that can meet the dual requirements of high stability and low cost of vanadium redox flow batteries under actual operating conditions. Summary of the Invention

[0006] To address the problems of existing technologies, the microsphere additive of this invention can gradually release the core components in the electrolyte. By adjusting the local osmotic pressure of the negative electrode electrolyte, it reduces the migration imbalance of vanadium ions and water molecules caused by the osmotic pressure difference between the positive and negative electrodes during charging and discharging, thereby effectively delaying the battery capacity decay.

[0007] This invention provides a microsphere additive comprising a core material and a double-crosslinked hydrogel shell coating the core material; the core material comprises a polyhydroxy carbohydrate with a functionality ≥4; the double-crosslinked hydrogel shell comprises a reaction product of a hydroxyl-containing acid-resistant hydrophilic polymer, an amino-containing acid-resistant hydrophilic polymer, and an aldehyde crosslinking agent.

[0008] In one or more embodiments, the density of the microsphere additive is less than 1.00 g / cm³. 3 .

[0009] In one or more embodiments, the polyhydroxy carbohydrate with a functionality of ≥4 is selected from one or more of α-lactose, sucrose, and xylooligosaccharides.

[0010] In one or more embodiments, the double crosslinked hydrogel shell has pores of 50-2000 nm.

[0011] In one or more embodiments, the core material has a diameter of 1 to 20 μm.

[0012] In one or more embodiments, the radius of the microsphere additive is 50~500 μm.

[0013] In one or more embodiments, the hydroxyl-containing acid-resistant hydrophilic polymer is selected from one or more of gelatin, hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol.

[0014] In one or more embodiments, the amino-containing acid-resistant hydrophilic polymer is selected from one or more of sericin, polyethyleneimine, and chitosan oligosaccharides.

[0015] In one or more embodiments, the molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to amino groups in the amino-containing acid-resistant polymer is 1:(2~5).

[0016] In one or more embodiments, the dual crosslinked hydrogel shell comprises silica nanoparticles.

[0017] In one or more embodiments, the molar ratio of the polyhydroxy carbohydrate with a functionality of ≥4 to the hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer is (5-80):1.

[0018] In one or more embodiments, the aldehyde crosslinking agent is glutaraldehyde and / or polyglutaraldehyde.

[0019] In one or more embodiments, the molar ratio of the aldehyde group in the aldehyde crosslinker to the amino group in the amino-containing acid-resistant hydrophilic polymer is 1:(0.5~0.8).

[0020] In one or more embodiments, the silica nanoparticles have a particle size of 50-200 nm.

[0021] In one or more embodiments, the molar ratio of the hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to the molar ratio of the silica nanoparticles is 1:(1-5).

[0022] In one or more embodiments, the hydroxyl-containing acid-resistant hydrophilic polymer is selected from one or more of hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol.

[0023] In one or more embodiments, the amino-containing acid-resistant hydrophilic polymer is polyethyleneimine and / or chitosan oligosaccharide.

[0024] The present invention provides a method for preparing the microsphere additive described herein, the method comprising the following steps:

[0025] (1) Preparation of a shell liquid comprising an acid-resistant hydrophilic polymer containing hydroxyl groups and an acid-resistant hydrophilic polymer containing amino groups;

[0026] (2) First add the core liquid to the shell liquid, then add an aldehyde crosslinking agent to mix and crosslink, to obtain a suspension containing microsphere precursors; filter, wash, centrifuge, freeze dry to obtain microsphere additives; the core liquid includes polyhydroxy carbohydrates with a functionality ≥4.

[0027] In one or more embodiments, step (1) includes: preparing a shell liquid precursor 1 of a hydroxyl-containing acid-resistant hydrophilic polymer and preparing a shell liquid precursor 2 of an amino-containing acid-resistant polymer.

[0028] In one or more embodiments, in step (1), the shell liquid further comprises silica nanoparticles.

[0029] In one or more embodiments, in step (2), the solvent of the core fluid is water.

[0030] In one or more embodiments, in step (2), the concentration of polyhydroxy carbohydrates with a functionality ≥4 in the core fluid is 0.2~1.0 mol / L.

[0031] In one or more embodiments, in step (2), the core fluid is added at a rate of 0.1 to 0.5 mL / min.

[0032] In one or more embodiments, in step (2), the rotation speed of the crosslinking is 500-1000 rpm.

[0033] In one or more embodiments, in step (2), the mixing and crosslinking time is 6 to 18 hours.

[0034] In one or more embodiments, in step (2), the centrifugation time is 5 to 15 minutes.

[0035] In one or more embodiments, in step (2), the centrifugation speed is 200~2000 rpm.

[0036] In one or more embodiments, in step (2), the freeze-drying temperature is -40 to -50°C.

[0037] In one or more embodiments, in step (2), the vacuum degree of freeze drying is 10~20 Pa.

[0038] In one or more embodiments, in step (2), the freeze-drying time is 24 to 72 hours.

[0039] In one or more embodiments, in step (2), the preparation of the core fluid includes: dissolving a polyhydroxy carbohydrate with a functionality ≥4 in a solvent at 40-60°C.

[0040] In one or more embodiments, in step (1), the concentration of hydroxyl groups in the shell liquid precursor 1 is 0.1-2 mmol / g.

[0041] In one or more embodiments, in step (1), the solvent of the shell liquid precursor 1 is water.

[0042] In one or more embodiments, during step (1), the heating temperature is 80~90°C during the preparation of the shell liquid precursor 1.

[0043] In one or more embodiments, in step (1), the concentration of amino group in the shell liquid precursor 2 is 0.1-2 mmol / g.

[0044] In one or more embodiments, in step (1), the solvent of the shell liquid precursor 2 is water.

[0045] In one or more embodiments, in step (1), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 is (1-2):1.

[0046] In one or more embodiments, in step (1), the mass of the silica nanoparticles accounts for 0.5 to 2 wt% of the total mass of the shell liquid.

[0047] In one or more embodiments, in step (2), the centrifugation speed is 500~2000 rpm.

[0048] The method for preparing the shell liquid of the present invention includes:

[0049] (a) The shell liquid precursor 1 and shell liquid precursor 2 are mixed for the first time, and silica nanoparticles are added for the second mixing to obtain the shell liquid; or

[0050] (b) Mix shell liquid precursor 1, shell liquid precursor 2, and silica nanoparticles to obtain a shell liquid; or

[0051] (c) Mix shell liquid precursor 1 and shell liquid precursor 2 to obtain shell liquid.

[0052] In one or more embodiments, in step (a), the mass of the silica nanoparticles accounts for 0.5 to 2 wt% of the total mass of the shell liquid.

[0053] In one or more embodiments, in step (a), the concentration of hydroxyl groups in the shell liquid precursor 1 is 0.1-2 mmol / g.

[0054] In one or more embodiments, in step (a), the solvent of the shell liquid precursor 1 is water.

[0055] In one or more embodiments, during step (a), the heating temperature is 80~90°C during the preparation of the shell liquid precursor 1.

[0056] In one or more embodiments, in step (a), the concentration of amino group in the shell liquid precursor 2 is 0.1-2 mmol / g.

[0057] In one or more embodiments, in step (a), the solvent of shell liquid precursor 2 is water; in step (a), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 is (1-2):1.

[0058] In one or more embodiments, in step (a), the first mixing is performed using ultrasound.

[0059] In one or more embodiments, in step (a), the first mixing time is 5-30 min.

[0060] In one or more embodiments, in step (a), the second mixing is performed using ultrasound.

[0061] In one or more embodiments, in step (a), the second mixing time is 15 to 30 minutes.

[0062] In one or more embodiments, in step (b), the mass of the silica nanoparticles accounts for 0.5 to 2 wt% of the total mass of the shell liquid.

[0063] In one or more embodiments, in step (b), the concentration of hydroxyl groups in the shell liquid precursor 1 is 0.1-2 mmol / g.

[0064] In one or more embodiments, in step (b), the solvent of the shell liquid precursor 1 is water.

[0065] In one or more embodiments, during step (b), the heating temperature during the preparation of the shell liquid precursor 1 is 80~90°C.

[0066] In one or more embodiments, in step (b), the concentration of amino groups in the shell liquid precursor 2 is 0.1-2 mmol / g.

[0067] In one or more embodiments, in step (b), the solvent of the shell liquid precursor 2 is water.

[0068] In one or more embodiments, in step (b), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 is (1-2):1.

[0069] In one or more embodiments, in step (b), the mixture is made using ultrasound.

[0070] In one or more embodiments, in step (b), the mixing time is 15 to 30 minutes.

[0071] In one or more embodiments, in step (c), ultrasound is used for mixing.

[0072] In one or more embodiments, in step (c), the mixing time is 5-30 min.

[0073] The present invention provides a negative electrode electrolyte containing the microsphere additive of the present invention.

[0074] This invention provides an all-vanadium redox flow battery comprising the negative electrode electrolyte of this invention.

[0075] Compared with the prior art, the present invention has the following beneficial technical effects:

[0076] (1) The microspheres of the present invention adopt a core-shell structure design, wherein the shell layer restricts the rapid release of the core components, allowing them to enter the electrolyte in a slow-release manner; compared with the one-time feeding method, the present invention can avoid the rapid increase in electrolyte viscosity and local thermal effect caused by the instantaneous excessive introduction of core components, thereby ensuring the stability of the physicochemical properties of the electrolyte; (2) The slow-release process of the present invention can continuously adjust the negative electrode osmotic pressure during battery operation, dynamically suppressing the cross-migration of vanadium ions caused by the osmotic pressure difference; (3) The microsphere additive of the present invention, through the core-shell structure design, enables the core components to be continuously and slowly released in the electrolyte, thereby maintaining a stable and lasting adjustment effect during long-term battery operation, effectively slowing down capacity decay and improving capacity retention rate. (4) The microsphere additive of the present invention can realize a dynamic capacity decay suppression strategy to actively deal with the electrolyte composition imbalance problem and effectively delay the capacity decay caused by it; (5) The microsphere additive of the present invention has a lower density than the electrolyte and can float naturally on the surface of the negative electrode tank (when stacked, it is suspended near or below the surface of the liquid (close to the surface of the liquid)), without interfering with the flow path of the electrolyte and the internal reaction process of the stack. It can be directly dispersed and added to the negative electrode electrolyte without changing the existing system structure, without additional energy consumption, and can play a stable role for a long time, with significant practicality and innovative value; In summary, the microsphere additive of the present invention takes into account the dual requirements of high stability and low cost of vanadium redox flow batteries under actual working conditions. Attached Figure Description

[0077] Figure 1 This is a process flow diagram for preparing microsphere additives according to some embodiments of the present invention. Detailed Implementation

[0078] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0079] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0080] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0081] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0082] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0083] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0084] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0085] In this invention, the stability of the microsphere additive refers to its stable existence during the main slow-release process. In acidic electrolyte, the main slow-release process of the microsphere additive core component occurs within 5-6 days. The shell layer of the microsphere additive undergoes a slow dissolution process in the acidic environment, but the dissolution rate is relatively slow. The microsphere additive structure begins to deteriorate approximately after 10 days of continuous contact with the acidic electrolyte; prior to this, it floats or floats on the surface of the liquid. The degradation of the microsphere additive occurs after the main slow-release process is completed. During this period, filtering the electrolyte ensures that the settled components do not negatively impact battery performance and operation, achieving the stability (i.e., stability during the slow-release process) desired by this invention.

[0086] The microsphere additive provided by this invention comprises a core material and a double-crosslinked hydrogel shell coating the core material. When the microsphere additive prepared by this invention is dispersed in a negative electrode electrolyte, the external electrolyte tends to penetrate into the interior of the microsphere additive. Due to the presence of the core material, the internal osmotic pressure of the microsphere is slightly higher than that of the external electrolyte, prompting the core material to be released into the external electrolyte, thus achieving the function of osmotic pressure response. At the same time, the moisture fluctuation inside the microsphere additive causes the microsphere volume to expand slightly or the structure to loosen, prompting the expansion of the pore structure or the enhancement of permeability of some shell layers, achieving the slow release of the core material, thereby achieving the purpose of slow release according to the osmotic pressure response, and thus improving the performance of the vanadium redox flow battery.

[0087] The microsphere additive of this invention has a three-dimensional network structure, and the double-crosslinked hydrogel shell has pores of 50-2000 nm, preferably 200-700 nm, such as 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, and 700 nm. In this invention, the micro-nano pores of the double-crosslinked hydrogel shell can be connected to the internal core. When the microsphere additive dissolves in the electrolyte, the dissolved core material consists of single molecules at the nanometer level, which can flow out from the micro-nano pores. In this invention, the diameter of the core material can be 1-20 μm. The diameter of the core material is the same as that of the core material in the freeze-dried microsphere additive. Since the dissolved core material consists of single molecules at the nanometer level, it can be released from the micro-nano pores of the double-crosslinked hydrogel shell.

[0088] The core material of this invention comprises a polyhydroxy carbohydrate with a functionality ≥4; the polyhydroxy carbohydrate with a functionality ≥4 can be one or more selected from α-lactose, sucrose, and xylooligosaccharides, preferably α-lactose. The core material of this invention can be released and dissolved in the negative electrode electrolyte, which is beneficial for dynamically adjusting the osmotic pressure of the negative electrode electrolyte during the operation of the vanadium redox flow battery, slowing down the transmembrane migration of vanadium ions, and thus ensuring that the vanadium redox flow battery exhibits higher capacity retention after long-cycle charge-discharge operation.

[0089] The double-crosslinked hydrogel shell of this invention comprises the reaction product of a hydroxyl-containing acid-resistant hydrophilic polymer, an amino-containing acid-resistant hydrophilic polymer, and an aldehyde crosslinking agent. In this invention, the hydroxyl-containing acid-resistant hydrophilic polymer, the amino-containing acid-resistant hydrophilic polymer, and the aldehyde crosslinking agent synergistically construct a double-crosslinked hydrogel network structure through a reversible Schiff base reaction and an irreversible aldehyde-alcohol condensation reaction. That is, the double-crosslinked hydrogel shell includes a Schiff base gel and an aldol condensation gel. This dense and stable three-dimensional shell network structure exhibits good stability and dynamic response capabilities, enhancing the stability of microsphere additives, effectively encapsulating the core material, and effectively controlling the release rate of the core material. In this invention, using the aforementioned acid-resistant raw materials is beneficial for obtaining an acid-resistant microsphere additive shell, thereby improving the sustained-release effect. The degree of crosslinking of the double-crosslinked hydrogel shell obtained by this invention is beneficial for improving the sustained-release effect.

[0090] In this invention, the hydroxyl-containing acid-resistant hydrophilic polymer can be one or more selected from gelatin, hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol, preferably one or more selected from hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol. Using the above-mentioned preferred hydroxyl-containing acid-resistant hydrophilic polymer in this invention is beneficial to improving the acid resistance of the microsphere additive, thereby further improving the performance of the vanadium redox flow battery. In this invention, the amino-containing acid-resistant hydrophilic polymer can be one or more selected from sericin, polyethyleneimine, and chitosan oligosaccharides, preferably polyethyleneimine and / or chitosan. Using the above-mentioned preferred hydroxyl-containing acid-resistant hydrophilic polymer in this invention is beneficial to improving the acid resistance of the microsphere additive, thereby further improving the performance of the vanadium redox flow battery. In this invention, using a combination of the above-mentioned preferred hydroxyl-containing acid-resistant hydrophilic polymer and the preferred amino-containing acid-resistant hydrophilic polymer is beneficial to obtaining a highly stable vanadium redox flow battery.

[0091] In this invention, the molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to amino groups in the amino-containing acid-resistant hydrophilic polymer can be 1:(2~5), for example 1:1, 1:2, 1:3, 1:4, 1:5. Controlling the molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to amino groups in the amino-containing acid-resistant hydrophilic polymer within the above range is beneficial for delaying capacity decay and obtaining a highly stable vanadium redox flow battery.

[0092] In this invention, the molar ratio of hydroxyl groups in the polyhydroxy carbohydrate with a functionality ≥4 to the hydroxyl-containing acid-resistant hydrophilic polymer can be (5-80):1, for example, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, or 80:1. Controlling the ratio of the polyhydroxy carbohydrate with a functionality ≥4 to the hydroxyl-containing acid-resistant hydrophilic polymer within the above range is beneficial for delaying capacity decay and obtaining a highly stable vanadium redox flow battery.

[0093] In this invention, the aldehyde crosslinking agent can be glutaraldehyde or polyglutaraldehyde. In this invention, the molar ratio of the aldehyde group in the aldehyde crosslinking agent to the amino group in the amino-containing acid-resistant hydrophilic polymer can be 1:(0.5~0.8), for example 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8. In this invention, controlling the molar ratio of the aldehyde group in the aldehyde crosslinking agent to the amino group in the amino-containing acid-resistant hydrophilic polymer within the above range is beneficial for delaying capacity decay and obtaining a highly stable vanadium redox flow battery.

[0094] In this invention, the double-crosslinked hydrogel shell may contain silica nanoparticles. The silica nanoparticles in the double-crosslinked hydrogel shell of this invention can improve the mechanical strength and acid resistance of the microsphere additive, enabling the microsphere additive to be immersed in acidic electrolyte environments for extended periods. This effectively resists structural collapse or rapid breakage, prolonging the sustained-release cycle. Simultaneously, it improves the porous structure of the microsphere additive, thereby achieving a long-lasting and controllable sustained-release function, ultimately enhancing the performance of the vanadium redox flow battery.

[0095] In this invention, the particle size of the silica nanoparticles can be 50~200nm, for example 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, and 200nm. In this invention, silica can improve the strength of the microsphere additive and make the microsphere additive size more uniform. It can be added according to the mass ratio; the amount of microsphere additive varies depending on the content of different synthetic groups. In this invention, the molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to the silica nanoparticles can be 1:(1-5), for example 1:1, 1:2, 1:3, 1:4, and 1:5. In this invention, controlling the molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to the silica nanoparticles within the above range is beneficial for delaying the release of core components, suppressing capacity decay, and obtaining a highly stable vanadium redox flow battery.

[0096] In this invention, the radius of the microsphere additive can be 50~500μm, for example 50μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm.

[0097] In this invention, the density of the microsphere additive can be less than 1.00 g / cm³. 3 The main advantage of this invention is that the microsphere additive has a low density and floats or suspends on the surface of the electrolyte. The double cross-linked hydrogel shell has a certain thickness, so only a small amount of electrolyte can penetrate into the interior of the microsphere and carry out the core material. The core material inside needs a period of time (e.g., 100 hours) to dissolve safely and be slowly released.

[0098] The present invention provides a method for preparing the microsphere additive of the present invention, comprising the following steps:

[0099] (1) Preparation of a shell liquid comprising an acid-resistant hydrophilic polymer containing hydroxyl groups and an acid-resistant hydrophilic polymer containing amino groups;

[0100] (2) First add the core liquid to the shell liquid, then add an aldehyde crosslinking agent to mix and crosslink, to obtain a suspension containing microsphere precursors; filter, wash, centrifuge, freeze dry to obtain microsphere additives.

[0101] The core electrolyte of this invention may contain polyhydroxy carbohydrates with a functionality ≥4. The solute in the core electrolyte of this invention is the core material. By introducing microsphere additives containing the core material into the electrolyte, the core material can be released and dissolved in the negative electrode electrolyte. This is beneficial for dynamically adjusting the osmotic pressure of the negative electrode electrolyte during the operation of the vanadium redox flow battery, slowing down the transmembrane migration of vanadium ions, and thus ensuring that the vanadium redox flow battery exhibits higher capacity retention after long-cycle charge-discharge operation.

[0102] In this invention, the shell liquid and the aldehyde crosslinking agent synergistically construct a double crosslinked hydrogel network structure through a reversible Schiff base reaction and an irreversible aldehyde-alcohol condensation reaction. The dense and stable three-dimensional shell network structure has good stability and dynamic response capability, which can enhance the stability of microsphere additives, effectively encapsulate the core material, and effectively control the release rate of the core material.

[0103] Step (1) includes: preparing a shell liquid precursor 1 containing a hydroxyl-containing acid-resistant hydrophilic polymer and preparing a shell liquid precursor 2 containing an amino-containing acid-resistant polymer. In step (1), the concentration of hydroxyl groups in shell liquid precursor 1 can be 0.1~2 mmol / g, for example 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (1), the solvent for shell liquid precursor 1 can be water, preferably deionized water. In step (1), during the preparation of shell liquid precursor 1, the heating temperature can be 80~90℃, for example 80℃, 82℃, 84℃, 86℃, 88℃, or 90℃. In step (1), the concentration of amino groups in shell liquid precursor 2 can be 0.1~2 mmol / g, for example 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (1), the solvent for shell liquid precursor 2 is water, preferably deionized water. In step (1), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 can be (1-2):1, for example 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1.

[0104] In step (1), the shell liquid may also contain silica nanoparticles; at this time, the mass of silica nanoparticles may account for 0.5 to 2 wt% of the total mass of the shell liquid, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%.

[0105] In this invention, the method for preparing a shell liquid comprising a hydroxyl-containing acid-resistant hydrophilic polymer, an amino-containing acid-resistant hydrophilic polymer, and silica nanoparticles can be as follows: (a) the shell liquid precursor 1 and the shell liquid precursor 2 are mixed for the first time, and silica nanoparticles are added for the second mixing to obtain the shell liquid.

[0106] In step (a), the concentration of hydroxyl groups in shell liquid precursor 1 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (a), the solvent for shell liquid precursor 1 can be water, preferably deionized water. In step (a), the heating temperature during the preparation of shell liquid precursor 1 can be 80~90℃, for example, 80℃, 82℃, 84℃, 86℃, 88℃, or 90℃. In step (a), the concentration of amino groups in shell liquid precursor 2 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (a), the solvent for shell liquid precursor 2 is water, preferably deionized water. In step (a), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 can be (1-2):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, or 2:1. In step (a), the mass of silica nanoparticles can account for 0.5~2wt% of the total mass of the shell liquid, for example, 0.5wt%, 1wt%, 1.5wt%, or 2wt%. In step (a), the first mixing can be performed using ultrasound. In step (a), the first mixing time can be 5-30 min, for example, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. In step (a), the second mixing can be performed using ultrasound. In step (a), the second mixing time can be 15-30 min, for example, 15 min, 20 min, 25 min, or 30 min.

[0107] In this invention, the shell liquid comprising a hydroxyl-containing acid-resistant hydrophilic polymer, an amino-containing acid-resistant hydrophilic polymer and silica nanoparticles can be prepared by: (b) mixing shell liquid precursor 1, shell liquid precursor 2 and silica nanoparticles to obtain a shell liquid.

[0108] In step (b), the concentration of hydroxyl groups in shell liquid precursor 1 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (b), the solvent for shell liquid precursor 1 can be water, preferably deionized water. In step (b), the heating temperature during the preparation of shell liquid precursor 1 can be 80~90℃, for example, 80℃, 82℃, 84℃, 86℃, 88℃, or 90℃. In step (b), the concentration of amino groups in shell liquid precursor 2 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (b), the solvent for shell liquid precursor 2 can be water, preferably deionized water. In step (b), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 can be (1-2):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, or 2:1. In step (b), the mass of silica nanoparticles can account for 0.5~2wt% of the total mass of the shell liquid, for example, 0.5wt%, 1wt%, 1.5wt%, or 2wt%. In step (b), mixing can be performed using ultrasound. In step (b), the mixing time can be 15~30 min, for example, 15 min, 20 min, 25 min, or 30 min.

[0109] In this invention, the shell liquid comprising a hydroxyl-containing acid-resistant hydrophilic polymer and an amino-containing acid-resistant hydrophilic polymer can be prepared by: (c) mixing shell liquid precursor 1 and shell liquid precursor 2 to obtain a shell liquid.

[0110] In step (c), the concentration of hydroxyl groups in shell liquid precursor 1 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (c), the solvent for shell liquid precursor 1 can be water, preferably deionized water. In step (c), the heating temperature during the preparation of shell liquid precursor 1 can be 80~90℃, for example, 80℃, 82℃, 84℃, 86℃, 88℃, or 90℃. In step (c), the concentration of amino groups in shell liquid precursor 2 can be 0.1~2 mmol / g, for example, 0.5 mmol / g, 1 mmol / g, 1.5 mmol / g, or 2 mmol / g. In step (c), the solvent for shell liquid precursor 2 can be water, preferably deionized water. In step (c), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 can be (1-2):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, or 2:1. In step (c), mixing can be performed using ultrasound. The mixing time in step (c) can be 5-30 minutes, for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0111] In this invention, the preparation of the core fluid includes dissolving a polyhydroxy carbohydrate with a functionality ≥4 in a solvent at 40-60°C, and in some embodiments, heating in a water bath environment.

[0112] In step (2), the solvent for the core electrolyte can be water, preferably deionized water. The concentration of the core electrolyte in step (2) can be 0.2~1.0 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1.0 mol / L. In this invention, controlling the concentration of the core electrolyte within the above range is beneficial for adjusting the osmotic pressure of the negative electrode electrolyte and controlling the subsequent slow-release rate. In step (2), the addition rate of the core electrolyte can be 0.1~0.5 mL / min, for example, 0.1 mL / min, 0.2 mL / min, 0.3 mL / min, 0.4 mL / min, or 0.5 mL / min. In step (2), the mixing and crosslinking speed can be 500-1000 rpm, for example, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm. In step (2), the mixing and crosslinking time can be 6-18 hours, for example, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, or 18 hours.

[0113] In step (2), a low-speed centrifuge can be used for the centrifugation process. The centrifugation time in step (2) can be 5~15 min, for example, 5 min, 7 min, 9 min, 11 min, 13 min, or 15 min. The centrifugation speed in step (2) can be 200~2000 rpm, preferably 500~2000 rpm, for example, 500 rpm, 100 rpm, 1500 rpm, or 2000 rpm. In this invention, controlling the centrifugation speed within the above-mentioned preferred range is beneficial for delaying capacity decay and obtaining a highly stable vanadium redox flow battery. In step (2), a freeze dryer can be used for the freeze-drying process. The freeze-drying temperature in step (2) can be -40~-50℃, for example, -40℃, -42℃, -44℃, -46℃, -48℃, or -50℃. In step (2), the vacuum degree of freeze drying can be 10~20 Pa, for example 10 Pa, 12 Pa, 14 Pa, 16 Pa, 18 Pa, 20 Pa. In step (2), the freeze drying time can be 24~72 h, for example 24 h, 30 h, 36 h, 42 h, 48 h, 54 h, 60 h, 66 h, 72 h.

[0114] This invention provides a negative electrode electrolyte containing the microsphere additive of this invention. In the negative electrode electrolyte of this invention, the content of the microsphere additive can be 0.5~5 wt% of the mass of the negative electrode electrolyte, for example 0.5 wt%, 1.0 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt%. By controlling the content of the microsphere additive within the above range, this invention effectively slows down the capacity decay of vanadium redox flow batteries.

[0115] This invention provides an all-vanadium redox flow battery comprising the negative electrode electrolyte of this invention.

[0116] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0117] In this invention, hydroxypropyl methylcellulose was purchased from Aladdin, brand name H434480-100g, with a number-average molecular weight of ~86000.

[0118] In this invention, the chitosan oligosaccharide was purchased from Aladdin, brand name C406214-100g.

[0119] In this invention, xylooligosaccharides were purchased from the exploration platform, with exploration number 041444224 and original number: Yuanye#S11137-25g.

[0120] In this invention, polyvinyl alcohol was purchased from Aladdin, brand name P139533-500g.

[0121] In this invention, the gelatin was purchased from Aladdin, brand name G108394-100g.

[0122] In this invention, the sericin was purchased from Aladdin, brand name S488097-25g.

[0123] In this invention, polyvinylpyrrolidone was purchased from Aladdin, brand name P110607-25g.

[0124] In this invention, α-monohydrated lactose was purchased from the exploration platform, exploration number 01093702.

[0125] In this invention, glutaraldehyde was purchased from the exploration platform, with exploration number 01008336.

[0126] In this invention, the silica nanoparticles were purchased from the exploration platform, exploration number 04904345, with an average particle size of approximately 100 nm.

[0127] Preparation Example 1

[0128] This preparation example follows... Figure 1 The process for preparing microsphere additives is as follows:

[0129] 1. Dissolve 10g of α-lactose hydrate in 50mL of deionized water, heat in a water bath at 50℃, and stir until homogeneous to obtain the core solution.

[0130] 2. Add 0.5g of hydroxypropyl methylcellulose (about 3mmol of hydroxyl groups) to 20mL of deionized water, heat in a water bath at 80℃, stir and dissolve to obtain shell liquid precursor 1, wherein the concentration of hydroxyl groups is about 0.15mmol / g.

[0131] 3. Add 2g of chitosan oligosaccharide (12mmol amino) to 20mL of deionized water and stir magnetically for 30min to obtain shell liquid precursor 2, in which the concentration of amino is approximately 0.55mmol / g.

[0132] 4. Take 20 mL of shell liquid precursor 1 and 20 mL of shell liquid precursor 2, mix them, add 0.5 g of 100 nm silica nanoparticles and sonicate for 20 min to obtain a uniform shell dispersion.

[0133] 5. Using a syringe pump, 50 mL of core solution was added dropwise to the shell solution at a rate of 0.2 mL / min. Then, 4.0 mL of 25 wt% glutaraldehyde solution (aldehyde content approximately 21.3 mmol) was added, and the mixture was magnetically stirred at a speed of 600 rpm for 12 h to obtain a suspension containing the microsphere precursor.

[0134] 6. The suspension was filtered to obtain the microsphere precursor. The microsphere precursor was then washed with deionized water, centrifuged, and freeze-dried to obtain the finished microsphere additive. The centrifugation process was carried out using a low-speed centrifuge at a speed of 1000 rpm for 10 min. The freeze-drying process was carried out using a freeze dryer with the cold trap temperature set at -50℃, the vacuum degree set at 20 Pa, and the freeze-drying time at 48 h.

[0135] Preparation Example 2

[0136] The other conditions in this preparation example are the same as those in Preparation Example 1, except that the 10g of α-lactose hydrate in Preparation Example 1 is replaced with 4.2g of xylooligosaccharide (the amount of substance is the same).

[0137] Preparation Example 3

[0138] The other conditions in this preparation example are the same as in Preparation Example 1, except that the 0.5 g hydroxypropyl methylcellulose (3 mmol hydroxyl) in Preparation Example 1 is replaced with 0.13 g polyvinyl alcohol (related to the degree of alcoholysis, here the degree of alcoholysis is 99%, approximately 3 mmol hydroxyl).

[0139] Preparation Example 4

[0140] The other conditions in this preparation example are the same as in Preparation Example 1, except that in this preparation example, 0.5 g of hydroxypropyl methylcellulose (3 mmol hydroxyl) is replaced with 0.7 g of hydroxypropyl methylcellulose (4.2 mmol hydroxyl), 2 g of chitosan oligosaccharide (12 mmol amino) is replaced with 2.8 g of chitosan oligosaccharide (16.8 mmol amino), and 4 mL of 25 wt% glutaraldehyde solution (aldehyde content of approximately 21.3 mmol) is replaced with 5.6 mL of 25 wt% glutaraldehyde solution (aldehyde content of approximately 29.8 mmol).

[0141] Preparation Example 5

[0142] The other conditions in this preparation example are the same as in Preparation Example 1, except that the 0.5 g hydroxypropyl methylcellulose (3 mmol hydroxyl) in Preparation Example 1 is replaced with 0.23 g gelatin, wherein the concentration of hydroxyl is approximately 0.15 mmol / g.

[0143] Preparation Example 6

[0144] The other conditions in this preparation example are the same as in Preparation Example 1, except that the 2g chitosan oligosaccharide (12mmol amino group) in Preparation Example 1 is replaced with 1.54g sericin, wherein the concentration of amino group is approximately 0.55mmol / g.

[0145] Preparation Example 7

[0146] The preparation conditions in this example are the same as those in Preparation Example 1, except that silica nanoparticles are not added in this example.

[0147] Preparation Example 8

[0148] The other conditions in this preparation example are the same as those in Preparation Example 1, except that the stirring speed in step (5) of this preparation example is 200 rpm.

[0149] Preparation of Comparative Example 1

[0150] The preparation comparative example is prepared under the same conditions as Preparation Example 1, except that the 10g α-lactose hydrate in Preparation Example 1 is replaced with 3.1g polyvinylpyrrolidone.

[0151] Preparation of Comparative Example 2

[0152] The preparation comparative example has the same other conditions as preparation example 1. The only difference is that step (4) of the preparation comparative example is: take 10 mL of shell liquid precursor 1 and 20 mL of shell liquid precursor 2, mix them, add 0.5 g of silica nanoparticles and sonicate for 20 min to obtain a uniform shell dispersion.

[0153] Preparation of Comparative Example 3

[0154] 1. Add 0.5g of hydroxypropyl methylcellulose (about 3mmol of hydroxyl groups) to 20mL of deionized water, heat in a water bath at 80℃, stir and dissolve to obtain shell liquid precursor 1, wherein the concentration of hydroxyl groups is about 0.15mmol / g.

[0155] 2. Add 2g of chitosan oligosaccharide (12mmol amino) to 20mL of deionized water and stir magnetically for 30min to obtain shell liquid precursor 2, in which the concentration of amino is approximately 0.55mmol / g.

[0156] 3. Take 20 mL of shell liquid precursor 1 and 20 mL of shell liquid precursor 2, mix them, add 0.5 g of 100 nm silica nanoparticles and sonicate for 20 min to obtain a uniform shell dispersion.

[0157] 4. Using a syringe pump, add 50 mL of water dropwise to the shell liquid at a rate of 0.2 mL / min. Then, add 4.0 mL of 25 wt% glutaraldehyde solution (aldehyde content is approximately 21.3 mmol) and perform magnetic stirring at a speed of 600 rpm. The crosslinking reaction is carried out for 12 h to obtain a suspension containing microsphere precursors.

[0158] 5. The suspension was filtered to obtain the microsphere precursor. The microsphere precursor was then washed with deionized water, centrifuged, and freeze-dried to obtain the finished microsphere additive. The centrifugation process was carried out using a low-speed centrifuge at a speed of 1000 rpm for 10 min. The freeze-drying process was carried out using a freeze dryer with a cold trap temperature of -50℃, a vacuum degree of 20 Pa, and a freeze-drying time of 48 h.

[0159] Test Example 1

[0160] Density test of microsphere additives: 200 mL of solution with a density of 1.00 g / cm³ was used. 3 1g of the microsphere additives prepared in Preparation Examples 1-8 and Comparative Examples 1-3 were added to deionized water, and the mixtures were added to 200mL of water with a density of 1.37g / cm³. 3 1g of the microsphere additive prepared in Preparation Examples 1-8 and Comparative Examples 1-3 was added to the electrolyte. The total vanadium concentration of the active material in the electrolyte was 1.7mol / L. 3+ / V 4+With a concentration ratio of 1, and supporting electrolyte of 4 mol / L sulfuric acid, the floating and sinking of the microsphere additives were observed, and the test results are shown in Table 1.

[0161] Table 1: Floating and sinking of the microsphere additives prepared in preparation examples 1-8 and comparative examples 1-3 in deionized water and electrolyte, respectively.

[0162] As shown in Table 1, the microsphere additives prepared in Preparation Examples 1-8 and Comparative Examples 1-3 all floated or suspended near the surface of the electrolyte in both deionized water and electrolyte. Therefore, the density of the microsphere additives prepared in Preparation Examples 1-8 is less than the density of water, i.e., the density of the microsphere additives is less than 1.00 g / cm³. 3 The electrolyte pumping pipeline of the vanadium redox flow battery system is located at the bottom of the storage tank, so the stack is not affected by the microsphere additives and can operate normally.

[0163] Test Example 2

[0164] Microsphere additive particle size test: Using an electron microscope and with the aid of a scale, the microsphere additives prepared in Examples 1-8 and Comparative Examples 1-3 were observed, and the size distribution range of the microspheres in each group of examples / comparative examples was recorded. The results are shown in Table 2.

[0165] Table 2: Particle size of microsphere additives prepared in Preparation Examples 1-8 and Comparative Examples 1-3

[0166] Test Example 3

[0167] Pore ​​size range test of microsphere additives: The microsphere additives were observed using a scanning electron microscope. The pore size of the microsphere additives prepared in Examples 1-8 and Comparative Examples 1-3 was measured using software tools. The size distribution range of the microspheres in each group of examples / comparative examples was recorded. The results are shown in Table 3.

[0168] Table 3: Pore sizes of microsphere additives prepared in Preparation Examples 1-8 and Comparative Examples 1-3

[0169] Example 1

[0170] In this embodiment, a single cell was prepared using the microsphere additive obtained in Preparation Example 1. The specific steps are as follows:

[0171] (1) Take 60 mL of electrolyte (the total vanadium concentration of the active material in the electrolyte is 1.7 mol / L, V 3+ / V 4+With a concentration ratio of 1 (supporting electrolyte of 4 mol / L sulfuric acid), 2.05 g (2.5 wt%) of the microsphere additive prepared in Preparation Example 1 was added to obtain the negative electrode electrolyte.

[0172] (2) Take 60 mL of electrolyte (the total vanadium concentration of the active material in the electrolyte is 1.7 mol / L, V 3+ / V 4+ The concentration ratio is 1, and the supporting electrolyte is 4 mol / L sulfuric acid) as the positive electrode electrolyte. The positive electrode electrolyte, the negative electrode electrolyte prepared in step (1), the perfluorosulfonic acid proton exchange membrane produced by Suzhou Kerun, and the effective area of ​​48 cm² are used. 2 A single cell was assembled from a carbon felt electrode with a compression ratio of 20% and a flat graphite plate.

[0173] Example 2

[0174] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 2 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0175] Example 3

[0176] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 3 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0177] Example 4

[0178] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 4 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0179] Example 5

[0180] This embodiment is the same as Embodiment 1 in all other conditions, except that the mass of the microsphere additive in step (1) of this embodiment is 0.82g (1wt%).

[0181] Example 6

[0182] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 5 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0183] Example 7

[0184] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 6 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0185] Example 8

[0186] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 7 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0187] Example 9

[0188] This embodiment is the same as Embodiment 1 in all other conditions, except that the microsphere additive prepared in Preparation Example 8 is used instead of the microsphere additive prepared in Preparation Example 1 in step (1) of this embodiment.

[0189] Comparative Example 1

[0190] The conditions for this comparative example are the same as those for Example 1, except that the microsphere additive prepared in Comparative Example 1 is used instead of the microsphere additive prepared in Example 1 in step (1) of this comparative example.

[0191] Comparative Example 2

[0192] The conditions for this comparative example are the same as those for Example 1, except that the microsphere additive prepared in Comparative Example 2 is used instead of the microsphere additive prepared in Example 1 in step (1) of this comparative example.

[0193] Comparative Example 3

[0194] The conditions for this comparative example are the same as those for Example 1, except that the microsphere additive prepared in Comparative Example 3 is used instead of the microsphere additive prepared in Example 1 in step (1) of this comparative example.

[0195] Comparative Example 4

[0196] The comparative example is the same as Example 1 under the same conditions, except that in step (1) of this comparative example, 2.05 g of α-monohydrated lactose is used instead of the microsphere additive prepared in Example 1.

[0197] Comparative Example 5

[0198] This comparative example is the same as Example 1 in all other conditions, except that no microsphere additive is added in step (1) of this comparative example.

[0199] Test Example 4

[0200] Cyclic stability test: using 160mA / cm 2 Constant current testing was conducted with a charging upper limit of 1.55V and a discharging lower limit of 1.00V, for 200 cycles. The coulombic efficiency, voltage efficiency, energy efficiency, discharge capacity, and capacity retention of the single cells prepared in Examples 1-9 and Comparative Examples 1-5 were tested. The data from the 5th, 50th, 100th, and 200th cycles were used as the results, and the discharge capacity data from the 5th cycle was used as the initial discharge capacity (reference value for capacity retention). The test results are shown in Tables 4 and 5.

[0201] Table 4: Coulombic efficiency, voltage efficiency, energy efficiency, discharge capacity, and capacity retention of the single cells prepared in Examples 1-7

[0202] Table 5: Coulombic efficiency, voltage efficiency, energy efficiency, discharge capacity, and capacity retention of the single cells prepared in Examples 8-9 and Comparative Examples 1-5

[0203] As shown in Tables 4 and 5, the microsphere additive obtained in Preparation Example 1 of this application can improve the three major efficiencies of the battery and effectively delay the discharge capacity decay compared with Comparative Example 4, which directly adds core material, thus achieving the purpose of suppressing capacity decay and providing a foundation for the long-term operation performance of the battery.

[0204] Test Example 5

[0205] Slow-release test of microsphere additive in water: 2.05 g of the microsphere additive prepared in Preparation Example 1 was added to 60 mL of deionized water and stirred magnetically at a speed of 200 rpm. Seven sets of experiments were conducted, and the microsphere additive was left for 6 h, 12 h, 24 h, 48 h, 96 h, 120 h, and 144 h, respectively. The floating, sinking, and dissolution of the microsphere additive were observed. The solution was then filtered using rapid filter paper (10-12 μm). After filtration, the filtrate was subjected to rotary evaporation under reduced pressure (70 °C) to obtain the substance after rotary evaporation. The weight of the substance was recorded in Table 6.

[0206] Table 6: Changes in the state of the microsphere additive prepared in Example 1 in water over time and the mass record after filtration and rotary evaporation.

[0207] The shell of the microsphere additive in deionized water is almost insoluble, with only the core material dissolving. As shown in Table 6, the microsphere additive of this invention can undergo slow release at the liquid surface, and the main slow release process occurs within 120 hours. Due to the low overall density of the microspheres, they are partially distributed above the liquid surface and partially located near the surface in deionized water, thus exhibiting a floating or suspended state. The stirring operation is used to simulate the flow state of the electrolyte in actual applications, causing the microspheres to continuously exchange fluids at the liquid surface due to the liquid flow. Because the environments of the electrolyte and water are different, the slow release time and slow release efficiency of the microsphere additive in water and electrolyte are different; the experiment here only demonstrates that slow release can occur.

[0208] Test Example 6

[0209] Sustained-release test of microsphere additive in electrolyte: in 60 mL of electrolyte with a density of 1.37 g / cm³ 32.05 g of the microsphere additive prepared in Preparation Example 1 was added to the electrolyte. The total vanadium concentration of the active material in the electrolyte was 1.7 mol / L. 3+ / V 4+ The concentration ratio was 1, the electrolyte was 4 mol / L sulfuric acid, magnetic stirring was used, the stirring speed was 200 rpm, 8 groups of experiments were carried out, and the microsphere additives were observed to float, sink and dissolve after 0 days, 2 days, 4 days, 6 days, 8 days, 10 days, 12 days and 14 days respectively. The test results are shown in Table 7.

[0210] Table 7: Changes in the state of the microsphere additive prepared in Example 1 over time in the electrolyte

[0211] As shown in Tables 6 and 7, the microsphere additive prepared in Preparation Example 1 floats on the surface of water or electrolyte due to its low density, while some microspheres remain suspended below the surface due to aggregation. The microspheres exist stably and perform the main sustained-release function. During the release of the core component, the microsphere structure remains stable, achieving the stability (i.e., stability during the sustained-release process) desired in this application.

Claims

1. A microsphere additive, characterized in that, The microsphere additive comprises a core material and a double-crosslinked hydrogel shell coating the core material; the core material comprises a polyhydroxy carbohydrate with a functionality ≥4; the double-crosslinked hydrogel shell comprises a reaction product of an acid-resistant hydrophilic polymer containing hydroxyl groups, an acid-resistant hydrophilic polymer containing amino groups, and an aldehyde crosslinking agent.

2. The microsphere additive as described in claim 1, characterized in that, The microsphere additive has one or more of the following characteristics: The density of the microsphere additive is less than 1.00 g / cm³. 3 ; The polyhydroxy carbohydrates with a functionality of ≥4 are selected from one or more of α-lactose, sucrose, and xylooligosaccharides. The double cross-linked hydrogel shell has pores of 50~2000nm; The core material has a diameter of 1~20μm; The radius of the microsphere additive is 50~500μm; The hydroxyl-containing acid-resistant hydrophilic polymer is selected from one or more of gelatin, hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol; The amino-containing acid-resistant hydrophilic polymer is selected from one or more of sericin, polyethyleneimine, and chitosan oligosaccharide; The molar ratio of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to amino groups in the amino-containing acid-resistant polymer is 1:(2~5); The dual cross-linked hydrogel shell contains silica nanoparticles; The molar ratio of the hydroxyl groups in the polyhydroxy carbohydrate with a functionality of ≥4 to the hydroxyl groups in the acid-resistant hydrophilic polymer is (5-80):

1. The aldehyde crosslinking agent is glutaraldehyde and / or polyglutaraldehyde; The molar ratio of the aldehyde group in the aldehyde crosslinking agent to the amino group in the amino-containing acid-resistant hydrophilic polymer is 1:(0.5~0.8).

3. The microsphere additive as described in claim 1, characterized in that, The microsphere additive has one or more of the following characteristics: The particle size of the silica nanoparticles is 50~200nm; The molar ratio of the amount of hydroxyl groups in the hydroxyl-containing acid-resistant hydrophilic polymer to the amount of silica nanoparticles is 1:(1-5). The hydroxyl-containing acid-resistant hydrophilic polymer is selected from one or more of hydroxypropyl methylcellulose, polyvinyl alcohol, and polyglycerol; The amino-containing acid-resistant hydrophilic polymer is polyethyleneimine and / or chitosan oligosaccharide.

4. A method for preparing the microsphere additive according to any one of claims 1-3, characterized in that, The method includes the following steps: (1) Preparation of a shell liquid comprising an acid-resistant hydrophilic polymer containing hydroxyl groups and an acid-resistant hydrophilic polymer containing amino groups; (2) First add the core liquid to the shell liquid, then add an aldehyde crosslinking agent to mix and crosslink, to obtain a suspension containing microsphere precursors; filter, wash, centrifuge, freeze dry to obtain microsphere additives; the core liquid includes polyhydroxy carbohydrates with a functionality ≥4.

5. The method as described in claim 4, characterized in that, The method has one or more of the following characteristics: Step (1) includes: preparing a shell liquid precursor 1 comprising an acid-resistant hydrophilic polymer containing hydroxyl groups, and preparing a shell liquid precursor 2 comprising an acid-resistant hydrophilic polymer containing amino groups. In step (1), the shell liquid further comprises silica nanoparticles; In step (2), the solvent for the core fluid is water; In step (2), the concentration of polyhydroxy carbohydrates with a functionality ≥4 in the core fluid is 0.2~1.0 mol / L; In step (2), the core fluid is added at a rate of 0.1~0.5 mL / min; In step (2), the rotation speed for mixing and crosslinking is 500-1000 rpm; In step (2), the mixing and cross-linking time is 6~18h; In step (2), the centrifugation time is 5~15 min; In step (2), the centrifugation speed is 200~2000 rpm; In step (2), the freeze-drying temperature is -40~-50℃; In step (2), the vacuum degree of freeze drying is 10~20 Pa; In step (2), the freeze-drying time is 24~72h; In step (2), the preparation of the core fluid includes: dissolving a polyhydroxy carbohydrate with a functionality of ≥4 in a solvent at 40-60°C.

6. The method as described in claim 5, characterized in that, The method has one or more of the following features: In step (1), the concentration of hydroxyl groups in shell liquid precursor 1 is 0.1-2 mmol / g; In step (1), the solvent of the shell liquid precursor 1 is water; In step (1), during the preparation of the shell liquid precursor 1, the heating temperature is 80~90℃; In step (1), the concentration of amino groups in shell liquid precursor 2 is 0.1-2 mmol / g; In step (1), the solvent for the shell liquid precursor 2 is water; In step (1), the volume ratio of shell liquid precursor 1 to shell liquid precursor 2 is (1-2):1; In step (1), the mass of the silica nanoparticles accounts for 0.5~2wt% of the total mass of the shell liquid; In step (2), the centrifugation speed is 500~2000 rpm.

7. The method as described in claim 5, characterized in that, The preparation of the shell fluid includes: (a) The shell liquid precursor 1 and shell liquid precursor 2 are mixed for the first time, and silica nanoparticles are added for the second mixing to obtain the shell liquid; or (b) Mix shell liquid precursor 1, shell liquid precursor 2, and silica nanoparticles to obtain a shell liquid; or (c) Mix shell liquid precursor 1 and shell liquid precursor 2 to obtain shell liquid.

8. The method as described in claim 7, characterized in that, The method has one or more of the following features: in step (a), the first mixing is performed using ultrasound; In step (a), the first mixing time is 5-30 min; In step (a), the second mixing is performed using ultrasound; In step (a), the second mixing time is 15-30 minutes; In step (b), the mixing is performed using ultrasound; In step (b), the mixing time is 15-30 minutes; In step (c), the mixing is performed using ultrasound; In step (c), the mixing time is 5-30 minutes.

9. A negative electrode electrolyte comprising the microsphere additive according to any one of claims 1-3.

10. A vanadium redox flow battery comprising the negative electrode electrolyte of claim 9.

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