Preparation method of polyanion positive electrode material sodium ferric pyrophosphate NFPP without physical sanding process

Abstract

The invention discloses a preparation method of a polyanion positive electrode material ferric sodium pyrophosphate (NFPP, chemical formula: Na4Fe3 (PO4) 2P2O7) without a physical sanding process, and relates to the technical field of synthesis of inorganic functional materials. According to the method, dependence of a traditional process on physical sanding is broken through, common industrial raw materials are adopted, an iron source is limited to be a mixed system of water-insoluble iron phosphate and ferrous oxalate (the molar ratio is 1: (0.005-0.5)), and the water-insoluble iron phosphate and the ferrous oxalate form a specific proportion and can generate a synergistic effect in a solution to accelerate reaction and dissolution; the molar ratio of sodium to iron to phosphorus is accurately controlled to be (4-4.04): (2.9-3): 4, the self-adaption of pH and raw material ratio (the pH is stabilized at 4-6) is synergistically realized by utilizing the characteristics of the raw materials, and the particle refining and dispersing effects of sanding are replaced by combining chemical complexing, step-by-step feeding and multi-parameter coordinated regulation. The process is highly compatible with an existing mass production process, rapid adaptation can be achieved without modifying a production line, the investment and energy consumption of sanding equipment are omitted, the energy consumption of a unit product is reduced by about 20%, and the comprehensive production cost is reduced by 10% or above; the product is pure-phase NFPP, the particle size D50 is 2-10 microns, the first specific discharge capacity is greater than or equal to 105mAh / g, the capacity retention rate after 500 cycles is greater than 95%, and the product is suitable for the fields of energy storage batteries, power batteries and the like and has huge industrial potential.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of inorganic functional material synthesis, in particular to a preparation method of a polyanion positive electrode material sodium iron phosphate pyrophosphate (NFPP, chemical formula: Na4Fe3(PO4)2P2O7) without a physical sanding process, which is mainly applied to the field of sodium ion battery positive electrode materials. BACKGROUND

[0002] The polyanion positive electrode material sodium iron phosphate pyrophosphate (NFPP, chemical formula: Na4Fe3(PO4)2P2O7) is an inorganic functional material with high specific capacity, good cycle stability and ion conductivity. As a sodium ion battery positive electrode material, it is rich in resources, environmentally friendly and cost controllable, and meets the development needs of the new energy battery industry. It has broad application prospects in the fields of energy storage batteries and power batteries. With the rapid development of the sodium ion battery industry, higher requirements are put forward for the particle size distribution and electrochemical performance of the NFPP positive electrode material. At the same time, strict standards are put forward for the production process capacity, cost control and process simplification.

[0003] Currently, the mass production process of NFPP generally has a core technical bottleneck - it must rely on a physical sanding process to nanometerize the raw materials. This process has become a key pain point restricting the development of the industry. First of all, the sanding process requires high-energy sanding equipment, which not only requires a huge investment in equipment, but also requires regular replacement of grinding media, significantly increasing fixed asset investment and maintenance costs. Secondly, the sanding process has very high energy consumption. In order to achieve the required nanoscale particle size, the grinding time usually lasts for several hours or even tens of hours, resulting in high unit product energy consumption. Thirdly, the sanding process prolongs the process flow, and additional steps such as grading screening and particle size monitoring are required, significantly lengthening the production cycle. At the same time, the wear of the grinding medium in the sanding process easily introduces impurities, and the particle size uniformity is difficult to accurately control, increasing the difficulty of production control and directly affecting the product quality stability.

[0004] In addition, the existing mass production process also has the following defects: ① The selection of iron source is single or the proportioning is not accurately controlled, and the synergistic effect between iron sources is not utilized to improve the reaction efficiency; ② The selection of phosphorus source is limited, the phosphorus content adjustment precision is low, and it is difficult to adapt to different process requirements; ③ The pH adjustment is disconnected with the raw material proportioning, and it is simply dependent on acid-base reagents for forced adjustment, which easily leads to system fluctuations and further aggravates the product consistency problem; ④ Some sanding-free processes rely on special reaction methods or contain water-soluble iron sources containing sulfur, chlorine and other elements that are not friendly to batteries, which have poor compatibility with existing mass production raw material systems and production lines, and are difficult to realize large-scale promotion.

[0005] It is worth noting that while some existing related technologies attempt to circumvent the sand milling process, such as CN120081353A which uses iron black as a single iron source and leverages its ability to generate low-particle-size iron-containing compounds under acidic conditions for dispersion, these solutions rely heavily on the inherent reactivity of a specific iron source. The iron source type is singular and lacks proportional control, failing to address in-depth optimization of the process system and mass production compatibility. Raw material replacement may require adjustments to the supply chain and reaction parameters, leading to uncertainty in mass production adaptability. The core difference between this patent and such technologies lies in its systematic innovation: it does not rely on the characteristics of a single raw material. Instead, it fundamentally eliminates dependence on a specific raw material through a systematic innovation of "synergistic use of mixed iron sources + adaptation of process parameters + self-adjustment of raw material characteristics." Simultaneously, it ensures high compatibility with existing mass production lines and raw material systems, requiring no additional equipment investment or modification.

[0006] The aforementioned traditional mass production process centered on sand milling, along with the compatibility defects of existing sand-mill-free processes, results in high production costs, limited capacity release, and insufficient quality stability for NFPP products, severely restricting their large-scale application in the new energy battery field. Therefore, developing an NFPP preparation method that eliminates the need for physical sand milling, employs non-sol-gel and hydrothermal reaction methods, uses commonly used industrial raw materials, limits the iron source to a mixture of insoluble iron phosphate and ferrous oxalate (with precise and controllable proportions and synergistic effects), and leverages the inherent properties of the raw materials to achieve pH-adaptive mixing with the raw material ratio, is a crucial technological challenge urgently needing to be addressed in the sodium-ion battery materials field. This method would fundamentally solve the pain points of high fixed asset investment, high energy consumption, long processes, and difficult control in mass production processes. Summary of the Invention

[0007] The core objective of this invention is to overcome the reliance on physical milling in traditional processes and provide a method for preparing sodium iron pyrophosphate pyrophosphate (NFPP, chemical formula: Na4Fe3(PO4)2P2O7), a polyanionic cathode material, without the need for physical milling. The core innovations are as follows:

[0008] (1) Unique process route: This invention uses a non-sol-gel method and a non-hydrothermal reaction method, abandoning the physical sand milling process required by traditional processes. It replaces the particle refinement and dispersion effect of sand milling with "chemical complexation + step-by-step feeding + multi-parameter synergy", which is fundamentally different from the conventional sand-mill-free NFPP synthesis process. Figure 1 This is a process flow diagram of the present invention;

[0009] (2) Raw materials are suitable for mass production and have synergistic effects: The raw materials used are all common types commonly used in industrialization. Among them, the iron source is clearly limited to a mixture of non-water-soluble iron phosphate (FePO4) and ferrous oxalate (FeC2O4·2H2O), rather than water-soluble iron sources such as ferrous sulfate, ferric chloride, and ferric nitrate. When the two are mixed in a certain proportion, they can produce a significant synergistic effect in a specific solution, accelerating the complexation reaction and dissolution, which is in line with the existing mass production raw material system.

[0010] (3) Precise iron source ratio: The mixing ratio of ferric phosphate and ferrous oxalate is strictly controlled at 1:0.005 to 0.5, while ensuring that the synergistic effect is fully utilized;

[0011] (4) Strong process compatibility: The overall process is very similar to the current NFPP mass production process. Only the sand grinding process is omitted. It can be quickly adapted without major modifications to the existing production line, reducing the cost of industrial transformation. This is the biggest highlight of the present invention.

[0012] Meanwhile, this invention achieves efficient dissolution and full reaction of raw materials and stable product quality by precisely controlling the weighing of raw materials (specifying the molar ratio of sodium, iron, and phosphorus to 4-4.04:2.9-3:4, and the molar ratio of ferric phosphate to ferrous oxalate to 1:0.005-0.5, utilizing the acidic properties of the raw materials themselves to synergistically regulate the acidic environment), optimizing step-by-step feeding, precisely controlling multiple parameters (adaptive control of temperature, pH and raw material ratio, stirring speed, time, etc.), specifying the range and form of raw material selection (sodium dihydrogen phosphate and disodium hydrogen phosphate are in anhydrous form, citric acid is in monohydrate form), optimizing the carbon source ratio (10-45%), and precisely controlling the sintering process, thus meeting the needs of large-scale production and practical applications.

[0013] 1. Raw material selection and proportioning design

[0014] Based on the NFPP chemical formula Na4Fe3(PO4)2P2O7, the molar ratio of sodium, iron, and phosphorus is strictly controlled at 4–4.04:2.9–3:4 (sodium excess 0–1%, iron fluctuation -3.3%–0%, ensuring sufficient reaction and avoiding impurity formation). Raw material selection focuses on commonly used industrial types, clearly defined forms, and flexible proportions, as detailed below:

[0015] Iron source: Limited to a mixture of non-water-soluble ferric phosphate and ferrous oxalate, with the molar ratio strictly controlled at 1:0.005–0.5; the two iron sources produce a significant synergistic effect after mixing. The reducing properties of ferrous oxalate complement the structural stability of ferric phosphate, which can accelerate the complexation reaction process and increase the dissolution rate of raw materials. At the same time, ferrous oxalate provides a sufficient reducing atmosphere, significantly inhibiting the oxidation of iron and optimizing electrochemical performance; the total molar number of iron meets the requirement of 2.9–3 mol, eliminating water-soluble iron sources such as ferrous sulfate, ferric chloride, and ferric nitrate, which is suitable for mass production raw material system;

[0016] Its synergistic mechanism lies in the fact that, in a pre-set weakly acidic reaction environment (pH 4–6), ferrous oxalate transforms the physical dissolution of ferric phosphate into a highly efficient chemical process through a triple action:

[0017] (1) Reduction start-up: Fe provided by ferrous oxalate 2+ Interfacial reduction occurs on the surface of iron phosphate particles, rapidly initiating Fe... 3 + Dissociation;

[0018] (2) Complexation-driven: The dissociated iron ions are rapidly complexed and removed by citrate ions in the system, continuously pulling the dissolution equilibrium and forming a self-reinforcing cycle. The sodium source and carbon source must contain one or both of sodium citrate dihydrate and citric acid monohydrate to ensure a stable supply of citrate ions and guarantee the complexation-driven effect.

[0019] (3) Stable atmosphere: Fe 2+ The constructed reducing atmosphere protects the valence state of iron ions and prevents harmful side reactions.

[0020] This "chemical dissociation and dispersion" mechanism replaces the "mechanical crushing and dispersion" function of traditional sand milling at the microscopic level, and is the key to realizing sand-free milling process.

[0021] Sodium source: limited to one or more combinations of anhydrous sodium dihydrogen phosphate, anhydrous disodium hydrogen phosphate, sodium citrate dihydrate (which functions as both a sodium and carbon source and is weakly alkaline to adjust pH), sodium carbonate (stronger alkalinity to meet the needs of pH fine-tuning), and sodium oxalate (to assist in adjusting the reducing properties of the system). All of these are common raw materials used in industrial production. The total molar amount of sodium element meets the requirement of 4 to 4.04 mol, and a slight excess can compensate for sodium loss during the sintering process.

[0022] Phosphorus source: limited to one or more combinations of ferric phosphate (containing phosphorus), anhydrous sodium dihydrogen phosphate (containing phosphorus), anhydrous disodium hydrogen phosphate (containing phosphorus), and phosphoric acid (purity ≥85%, liquid raw material, pH adjustable, high precision in phosphorus content adjustment), all of which are commonly used phosphorus source types for mass production; the total molar amount of phosphorus is strictly controlled to 4 mol, and is used in the ratio calculation after being converted according to the concentration, so as to improve the flexibility of phosphorus source ratio and the synergy of pH control;

[0023] Carbon source: limited to one or more combinations of glucose (to optimize carbon layer coating effect), citric acid monohydrate (to stabilize crystal water, enhance complexation effect, and participate in acid environment regulation due to its weak acidity), and PEG2000 (to improve material dispersibility), all of which are industrially mature carbon sources; the amount of carbon source added is 10-45% of the total mass of iron source, which can be flexibly adjusted according to the product's conductivity requirements and pH adjustment requirements.

[0024] Sodium citrate dihydrate and citric acid monohydrate must be included in the sodium and carbon sources, and can be used alone or in combination.

[0025] Deionized water: The ratio of the total mass of raw materials to the mass of deionized water is 1:1 to 4. This wide range of liquid-to-solid ratios can be adapted to the dissolution requirements of different combinations of raw materials, thus improving process flexibility.

[0026] 2. Detailed process steps

[0027] (1) Raw material pretreatment

[0028] The non-water-soluble solid raw materials from the iron source (ferric phosphate, ferrous oxalate), sodium source, and phosphorus source were screened through a 200-mesh standard sieve using a vibrating sieve to thoroughly remove lumps, mechanical impurities, and large particles (particle size > 75 μm). The liquid phosphorus source was directly tested for purity and then used for later use without screening. The screened solid raw materials were sealed and stored in a dry environment (relative humidity ≤ 60%) to prevent moisture absorption, contamination, or cross-contamination, ensuring the accuracy of subsequent weighing and reaction.

[0029] (2) Weighing raw materials

[0030] Based on the requirements of a sodium, iron, and phosphorus molar ratio of 4–4.04:2.9–3:4 and a ferric phosphate to ferrous oxalate molar ratio of 1:0.005–0.5, and considering the purity of the raw materials, the dosage of each raw material is calculated as follows:

[0031] Calculation logic: First, allocate the molar amounts of ferric phosphate and ferrous oxalate according to the set molar ratio (the total number of moles meets the requirement of 2.9-3 mol of iron element, ensuring that the synergistic effect of the two is fully utilized); then, calculate the amount of various phosphorus sources based on the phosphorus content introduced in the iron source and the target number of phosphorus moles; at the same time, predict the pH of the system based on the characteristics of the raw materials, and ensure that the pH of the system naturally falls in the range of 4-6 after the raw materials are added by adjusting the proportion of alkaline sodium source or acidic component; the amount of carbon source is calculated as 10-45% of the total mass of iron source, of which the amount of citric acid monohydrate can be flexibly allocated according to the pH adjustment requirements;

[0032] Weighing equipment: Raw materials are weighed using an electronic balance with an accuracy of ≥0.01g. After weighing, each raw material is placed into a clean container and labeled to avoid confusion.

[0033] (3) Raw material dissolution and homogenization (the core optimization step that replaces physical sand milling, with raw material characteristics synergistically adapting to pH-raw material ratio and iron source synergistically enhancing the effect)

[0034] Equipment selection: The volume of the stirred reactor is ≥ 1.5 times the total mass of raw materials + the mass of deionized water, equipped with a paddle agitator (paddle diameter is 1 / 3 to 1 / 2 of the reactor body diameter) and a temperature control and heating device (temperature control accuracy ±1℃), consistent with the type of mass production equipment;

[0035] Adding water and heating: Add the preset amount of deionized water to the reactor, ensuring that the mass ratio of the total raw material to the deionized water is strictly controlled at 1:1 to 4; start stirring (initial speed 150 to 200 r / min) and heating, and maintain the system temperature stably at 25 to 55℃ (the low temperature end of 25 to 35℃ is suitable for easily soluble raw materials and reduces energy consumption; the high temperature end of 45 to 55℃ is suitable for difficult-to-dissolve raw materials, increases the reaction rate, and avoids thermal decomposition of raw materials due to high temperature).

[0036] Step-by-step feeding: Add the weighed raw materials in a fixed order of “carbon source → sodium source → solid phosphorus source → liquid phosphorus source (if applicable, add slowly dropwise) → iron source (mixed ferric phosphate and ferrous oxalate)”, every 30±5 minutes. The liquid phosphorus source is added slowly dropwise to avoid violent local reactions that could lead to precipitation. Adding the carbon source first can help form a complex system in advance, and citric acid monohydrate can play a weak acidity regulating role in advance. Adding the sodium source and solid phosphorus source in sequence can initially adapt the pH through their acid-base properties. Adding the iron source after mixing can accelerate the complexation reaction and dissolution with the help of the synergistic effect of the two, and prevent agglomeration.

[0037] Mixing and homogenization: After all raw materials have been added, the mixing speed is precisely adjusted to 200-1000 r / min and mixed for 10-48 hours. Through the synergistic effect of "stable temperature + flexible mixing + carbon source complexation + iron source synergy", even if a non-water-soluble mixed iron source is used, the raw materials can be completely dissolved without physical sand milling, and the dissolution efficiency is significantly improved, without the need for additional impurity removal process.

[0038] pH Adaptive Adjustment (Core Optimization): Utilizing the synergistic effect of the inherent acidity of the raw materials, pH is naturally adjusted according to the proportion of raw materials input, without the need for forced addition of additional acid or alkali reagents: ① When the system is insufficiently acidic (natural pH > 6), the acidity can be doubled by increasing the proportion of acidic components, stabilizing the system pH below 6; ② When the system is too acidic (natural pH < 4), the excess acidity can be neutralized by increasing the proportion of alkaline sodium source, stabilizing the system pH above 4; ③ If a small deviation occurs (pH < 4 or > 6), only a small amount of the corresponding reagent needs to be added or the amount of acidic components adjusted to ensure that the system pH value is stable between 4 and 6 until stirring is completed, resulting in a uniform, transparent, dark green aqueous solution; This pH range avoids hydrogen ion corrosion of equipment, inhibits the hydrolysis of iron ions to form ferric hydroxide precipitate, and simultaneously meets the requirements of the iron source synergistic complexation reaction.

[0039] (4) Spray drying granulation

[0040] Equipment parameters: Centrifugal or pressure spray dryer, compatible with mass production equipment. Parameters are set according to the moisture content (50-80%) of the homogenized aqueous solution: inlet air temperature 180-350℃ (180-250℃ for low moisture content 50-60%, 250-300℃ for medium moisture content 60-70%, and 300-350℃ for high moisture content 70-80%), outlet air temperature 90-110℃, atomization pressure 0.3-0.5MPa, and feed rate 20-30mL / min.

[0041] Product collection: The aqueous solution is pumped into the atomizer by a high-pressure pump to form micron-sized droplets of 5-50 μm. These droplets are rapidly dehydrated upon contact with hot air, forming dry particles with a sphericity ≥0.85 μm and uniform particle size. The powder is collected by a cyclone separator and tested by a Karl Fischer moisture analyzer to ensure that the moisture content is ≤2.0% (too high a moisture content can easily lead to sintering and agglomeration, while too low a moisture content can easily cause powder to fly away and be lost).

[0042] (5) Loading into saggers and sintering

[0043] Loading: The dry powder is evenly loaded into the graphite sagger, with the loading amount being 1 / 2 to 2 / 3 of the sagger volume. This avoids excessive powder accumulation, which can lead to uneven heat transfer. This process is consistent with the mass production loading process.

[0044] Furnace layout: The graphite saggers are placed into the atmosphere furnace (temperature control accuracy ±1℃, volume 10~100L), with a 5~10cm gap between the saggers to ensure uniform airflow inside the furnace;

[0045] Atmosphere replacement: Introduce high-purity nitrogen gas with a purity of ≥99.99% for 10±2 minutes each time, replacing the air in the furnace 3 times to ensure that the oxygen content in the furnace is ≤100ppm and to avoid oxidation of iron.

[0046] Heating and sintering: Heating to 550-630℃ at a precise heating rate of 5±0.5℃ / min, and holding at the set temperature for 6-12 hours;

[0047] Atmosphere control: Nitrogen gas is continuously introduced during the sintering process, and the flow rate is matched with the furnace volume and material loading to prevent outside air from entering.

[0048] (6) Airflow pulverization and classification

[0049] Cooling: The sintered material is allowed to cool naturally to room temperature;

[0050] Crushing and Classification: The sintered lumpy material (particle size 1-5mm) is fed into an air jet mill. The crushing pressure is set to 0.6-0.8MPa and the feeding speed is 5-8kg / h. Precise crushing is achieved by high-speed airflow impact at 300-500m / s. The crushed material enters an air classifier. The classifier wheel speed is adjusted to 3500-4500r / min. The intermediate product with particle size D50=2-10μm is collected by laser particle size analyzer.

[0051] (7) Sieving and finished product packaging

[0052] Sieving: The graded intermediate product is passed through a 100-mesh standard sieve (150μm aperture) to remove a small amount of large particulate impurities that are not completely crushed;

[0053] Testing: Comprehensive performance testing of the finished product, including particle size distribution (laser particle size analyzer), XRD characterization, and half-cell electrochemical testing;

[0054] Packaging: After passing the inspection, the products are packed into aluminum-plastic composite sealed bags under dry gas protection, with each bag weighing 25kg or 50kg. They are stored in an environment with a temperature of 20-25℃ and a relative humidity of ≤60%, protected from light and moisture, in accordance with the mass production packaging and storage standards.

[0055] (8) Performance characterization and testing

[0056] XRD characterization: An X-ray diffractometer (model: Rigaku D / max-2500) was used with Cu Kα rays (λ=1.5406Å) as the radiation source. The scanning range was 10°~80°, the scanning speed was 5° / min, the tube voltage was 40kV, and the tube current was 100mA. The finished product showed clear NFPP characteristic diffraction peaks at 2θ=9.8°±0.2°, 16°±0.2°, 16.7°±0.2°, 32.2°±0.2°, and 33.7°±0.2°, and there were no obvious impurity diffraction peaks (impurity peak intensity <1%), proving that the product is pure phase NFPP.

[0057] Half-cell fabrication and testing: Using the finished product as the positive electrode active material, it was mixed with conductive carbon black (SuperP) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added to prepare a uniform slurry with a solid content of 50-60%. This slurry was coated onto a 12μm thick aluminum foil with a coating surface density of 110±1 mg / cm². After vacuum drying at 80℃ for 12 hours, a positive electrode sheet was formed. A 0.5mm thick sodium metal sheet was used as the counter electrode, Celgard 2400 as the separator, and propylene carbonate (PC) / ethylene carbonate (EC) in 1mol / L NaClO4 solution (volume ratio 1:1) was used as the electrolyte. CR2032 button cells were assembled in an argon glove box (water and oxygen content ≤0.1ppm). A battery testing system (model: LAND) was used. The CT2001A was tested for charge and discharge at a rate of 0.1C (1C=120mAh / g) and a voltage range of 2.0 to 4.0V. The initial discharge specific capacity of the finished product was ≥105mAh / g, and the capacity retention rate was >95% after 500 cycles.

[0058] 3. The present invention has at least the following beneficial effects:

[0059] (1) Synergistic effect of iron source and significant improvement in dissolution efficiency: The mixture of iron phosphate and ferrous oxalate produces a significant synergistic effect, which replaces the "mechanical crushing and dispersing" function of traditional sand milling at the micro level. It realizes the key complementary characteristics of sand-free process, accelerates the complexation reaction process and raw material dissolution rate, greatly improves production efficiency, and the raw material is a mass-produced raw material, so there is no need to change the existing raw material supply chain, reducing production costs and transformation risks.

[0060] (2) The characteristics of raw materials work together to adjust pH, resulting in stronger process stability: The acidity of the raw materials themselves naturally adapts to the pH range of 4 to 6, eliminating the need to add additional acid or base reagents, reducing system fluctuations and the introduction of impurity elements, adapting to the complexation requirements of different raw material combinations, and increasing the process tolerance.

[0061] (3) The process is compatible with the existing mass production system and the transformation cost is extremely low: The overall process is highly similar to the current NFPP mass production process, only the sand grinding process is omitted. There is no need to make major modifications to the existing production line, and industrialization can be achieved quickly. This is the core advantage of the present invention.

[0062] (4) Abandon physical sand milling, significantly reduce costs and increase efficiency: save investment in sand milling equipment, reduce energy consumption per unit product by about 20%, reduce overall production cost by 10%, and avoid the risk of impurities introduced by sand milling media wear, fundamentally solving the problems of high fixed investment, high energy consumption, long process and difficult management in traditional mass production process. Attached Figure Description

[0063] Figure 1The process flow diagram for preparing sodium iron pyrophosphate (NFPP) of the present invention is as follows: 1 Raw material pretreatment unit; 2 Precision weighing unit; 3 Stepwise feeding, dissolving and homogenizing unit; 4 Spray drying and granulation unit; 5 Nitrogen atmosphere sintering unit; 6 Airflow pulverization and classification unit; 7 Sieving and packaging unit. Each unit is connected sequentially through a unidirectional conveying path to form a continuous single main line preparation process.

[0064] Figure 2 The XRD pattern of the finished product in Example 2 (showing characteristic diffraction peaks such as 2θ=9.8°±0.2°, with no impurity peaks);

[0065] Figure 3 The first charge-discharge curves (0.1C rate, 2.0-4.0V) of Example 2 and Comparative Example 1 are shown. Detailed Implementation

[0066] To further clarify the technical solution and implementation effect of the present invention, the following detailed description is provided in conjunction with three specific embodiments with different iron source mixing ratios (covering extremely low ratio, low ratio, and medium-high ratio). Those skilled in the art can adjust the raw material ratio and process parameters according to actual needs, all of which fall within the protection scope of the present invention.

[0067] Example 1: Ferric phosphate-ferrous oxalate molar ratio 1:0.005 (extremely low proportion of mixed iron source)

[0068] (1) Raw material pretreatment

[0069] Ferric phosphate and ferrous oxalate were passed through a 200-mesh vibrating sieve to remove lumps and impurities, and then sealed and stored in a dry environment. The concentration of the liquid phosphorus source (85% purity) was directly measured before use.

[0070] (2) Weighing of raw materials (calculated based on sodium:iron:phosphorus = 4.01:2.92:4)

[0071] Iron source: 44.24g ferric phosphate (0.293mol, Fe 0.293mol, P 0.293mol) + 0.26g ferrous oxalate (0.00146mol, Fe 0.00146mol); the molar ratio of the two is 1:0.005, and the total number of moles of iron is 0.29446mol. Both are non-water-soluble iron sources. After mixing, they exert a synergistic effect, accelerating complexation and dissolution.

[0072] Sodium source: 6.00g anhydrous sodium dihydrogen phosphate (0.05mol, Na element 0.05mol, P element 0.05mol) + 7.10g anhydrous disodium hydrogen phosphate (0.05mol, Na element 0.1mol, P element 0.05mol) + 24.87g sodium citrate dihydrate (0.0846mol, Na element 0.2538mol, used to adjust pH); total sodium element moles 0.404mol (meets the requirements after scaling down the NFPP chemical formula molar ratio Na:Fe=4.01:2.92, with an excess of 0.25%).

[0073] Phosphorus source: Iron phosphate (0.293 mol P) + Anhydrous sodium dihydrogen phosphate (0.05 mol P) + Anhydrous disodium hydrogen phosphate (0.05 mol P) + Liquid phosphorus source (0.01 mol P, for pH adjustment); Total molar amount of P: 0.403 mol (meets the requirements after scaling down the molar ratio P:Fe = 4:2.92 in the NFPP chemical formula); Calculation of liquid phosphorus source usage: 0.01 mol × 98 g / mol ÷ 85% ≈ 1.15 g;

[0074] Carbon source: 17.50g citric acid monohydrate (39% of the total iron source mass, involved in acidity adjustment);

[0075] Deionized water: 250g (total raw material mass to deionized water mass ratio 1:2.5).

[0076] (3) Process steps

[0077] a. Dissolution and homogenization: Add 250g of deionized water to a 1L reactor, stir (150r / min) and heat to 48℃; add citric acid monohydrate (adjust acidity beforehand) at 0 minutes, and add anhydrous sodium dihydrogen phosphate, anhydrous disodium hydrogen phosphate, and sodium carbonate after 30 minutes, stirring for 30 minutes until completely dissolved; slowly add liquid phosphorus source, and add a mixture of ferric phosphate and ferrous oxalate after 60 minutes; taking advantage of the synergistic effect of the two iron sources, increase the stirring speed to 600r / min after the addition is complete, and continue stirring for 30 hours; through the synergistic adaptation of raw material characteristics, the pH of the system is stabilized at 4.9 (within the range of 4 to 6), and a homogeneous and transparent dark green aqueous solution is obtained without the need for sand milling;

[0078] b. Spray drying: inlet air temperature 270℃, outlet air temperature 103℃, atomization pressure 0.38MPa, feed rate 23mL / min, collect dried powder, moisture content 1.3%;

[0079] c. Sintering: Load into a graphite sagger (loading capacity 2.5kg) and send it into a 20L atmosphere furnace; purge with nitrogen 3 times (9 minutes each time); heat to 560℃ at 5℃ / min and hold for 11 hours; nitrogen flow rate 2.5L / min, positive pressure inside the furnace 0.028MPa;

[0080] d. Grinding and classification: After cooling to room temperature, the air jet mill is used with a grinding pressure of 0.72 MPa, a feeding speed of 5.5 kg / h, and a classifying wheel speed of 4100 r / min;

[0081] e. Sieving and Packaging: Pass the product through a 100-mesh sieve to obtain the finished product.

[0082] (4) Performance test results

[0083] Particle size: D50 = 6.5 μm (measured by laser particle size analyzer);

[0084] XRD characterization: NFPP characteristic diffraction peaks appeared at 2θ = 9.8°, 16°, 16.7°, 32.2°, and 33.7°, with no impurity peaks;

[0085] Half-cell test: First discharge specific capacity at 0.1C rate is 106.3mAh / g, and capacity retention rate is 96.4% after 500 cycles.

[0086] Example 2: Ferric phosphate-ferrous oxalate molar ratio 1:0.1 (low-proportion mixed iron source)

[0087] (1) Raw material pretreatment

[0088] Ferric phosphate and ferrous oxalate were passed through a 200-mesh vibrating sieve to remove lumps and impurities, and then sealed and stored in a dry environment.

[0089] (2) Weighing of raw materials (calculated based on sodium:iron:phosphorus = 4.02:2.95:4)

[0090] Iron source: 40.77g ferric phosphate (0.27mol, Fe 0.27mol, P 0.27mol) + 4.86g ferrous oxalate (0.027mol, Fe 0.027mol); the molar ratio of the two is 1:0.1, and the total number of moles of iron is 0.297mol. Both are non-water-soluble iron sources. The synergistic effect after mixing is significant, greatly improving the complexation reaction and dissolution efficiency.

[0091] Sodium source: 15.96g anhydrous sodium dihydrogen phosphate (0.133mol, Na element 0.133mol, P element 0.133mol) + 26.55g sodium citrate dihydrate (0.0903mol, Na element 0.2709mol, weakly alkaline to adjust pH); total molar amount of sodium element 0.405mol (meets the requirements after scaling down the molar ratio of Na:Fe = 4.02:2.95 in the NFPP chemical formula, with an excess of 0.5%).

[0092] Phosphorus source: Iron phosphate (0.27 mol P) + anhydrous sodium dihydrogen phosphate (0.133 mol P); total molar P content: 0.403 mol (meets the requirements of the NFPP chemical formula molar ratio P:Fe = 4:2.95 after scaling).

[0093] Carbon source: 12.00g citric acid monohydrate (26% of the total iron source mass, used for acidity adjustment);

[0094] Deionized water: 300g (total mass of raw materials to mass of deionized water ratio 1:3).

[0095] (3) Process steps

[0096] a. Dissolution and homogenization: Add 300g of deionized water to a 1L stirred reactor, start stirring (180r / min) and heating, and stabilize the temperature at 42℃; add citric acid monohydrate at 0 minutes (adjust acidity beforehand), and add anhydrous sodium dihydrogen phosphate and sodium citrate dihydrate after 30 minutes, stirring for 30 minutes until completely dissolved; add a mixture of ferric phosphate and ferrous oxalate after 60 minutes; relying on the synergistic effect of the two iron sources, increase the stirring speed to 650r / min after the addition, and continue stirring for 22 hours; through the synergistic adaptation of the raw material characteristics, the pH of the system is stabilized at 4.2 (within the range of 4 to 6), and a homogeneous, transparent, dark green aqueous solution is obtained without the need for sand milling;

[0097] b. Spray drying: inlet air temperature 250℃, outlet air temperature 101℃, atomization pressure 0.4MPa, feed rate 25mL / min, collect dried powder, moisture content 1.2%;

[0098] c. Sintering: The powder is loaded into a graphite sagger (loading capacity 3kg) and sent into a 30L atmosphere furnace; nitrogen is purged 3 times (10 minutes each time); the temperature is increased to 600℃ at 5℃ / min and held for 9 hours; nitrogen flow rate is 3L / min and positive pressure inside the furnace is 0.03MPa;

[0099] d. Grinding and classification: After cooling to room temperature, the air jet mill is used with a grinding pressure of 0.7 MPa, a feeding speed of 6 kg / h, and a classifying wheel speed of 4200 r / min;

[0100] e. Sieving and Packaging: Pass the product through a 100-mesh sieve to obtain the finished product.

[0101] (4) Performance test results

[0102] Particle size: D50 = 5.8 μm (measured by laser particle size analyzer);

[0103] XRD characterization: Characteristic NFPP diffraction peaks appeared at 2θ = 9.8°, 16°, 16.7°, 32.2°, and 33.7°, with no impurity peaks. See the detailed spectrum for details. Figure 2 ;

[0104] Half-cell test: Initial discharge specific capacity at 0.1C rate is 107.3 mAh / g (charge-discharge curves are shown below). Figure 3 After 500 cycles, the capacity retention rate was 97.0%.

[0105] Example 3: Ferric phosphate-ferrous oxalate molar ratio 1:0.45 (medium to high proportion of mixed iron source)

[0106] (1) Raw material pretreatment

[0107] Ferric phosphate and ferrous oxalate were passed through a 200-mesh vibrating sieve to remove lumps and impurities, and then sealed and stored in a dry environment. The concentration of the liquid phosphorus source (85% purity) was directly measured before use.

[0108] (2) Weighing of raw materials (calculated based on sodium:iron:phosphorus = 4.03:2.98:4)

[0109] Iron source: 33.22g ferric phosphate (0.22mol, Fe 0.22mol, P 0.22mol) + 17.82g ferrous oxalate (0.099mol, Fe 0.099mol); the molar ratio of the two is 1:0.45, and the total number of moles of iron is 0.319mol. Both are non-water-soluble iron sources, and their mixture has a synergistic effect, accelerating the dissolution of raw materials.

[0110] Sodium source: 28.14g anhydrous disodium hydrogen phosphate (0.198mol, Na element 0.396mol, P element 0.198mol) + 2.35g sodium oxalate (0.018mol, Na element 0.36mol); total molar amount of sodium element 0.431mol (meets the requirements after scaling down the molar ratio of Na:Fe = 4.03:2.98 in the NFPP chemical formula, with an excess of 0.75%).

[0111] Phosphorus source: Iron phosphate (0.22 mol P) + Anhydrous disodium hydrogen phosphate (0.198 mol P) + Liquid phosphorus source (0.01 mol P, for pH adjustment); Total molar amount of P: 0.428 mol (meets the requirements after scaling down the molar ratio P:Fe = 4:2.98 in the NFPP chemical formula); Calculation of liquid phosphorus source usage: 0.01 mol × 98 g / mol ÷ 85% ≈ 1.15 g;

[0112] Carbon source: 5.4g glucose + 3.1g PEG2000 + 10g citric acid monohydrate (19.6% of the total iron source mass, involved in acidity adjustment); total carbon source mass 19.0g (37% of the total iron source mass, containing acidity adjustment components).

[0113] Deionized water: 350g (total raw material mass to deionized water mass ratio 1:3.5).

[0114] (3) Process steps

[0115] a. Dissolution and homogenization: Add 350g of deionized water to a 1L reactor, stir (200r / min) and heat to 38℃; add glucose, PEG2000 and citric acid monohydrate (to adjust the weak acidity) at 0 minutes; add anhydrous disodium hydrogen phosphate and sodium oxalate after 30 minutes, and stir for 30 minutes until completely dissolved; slowly add liquid phosphorus source, and add a mixture of ferric phosphate and ferrous oxalate after 60 minutes; with the synergistic effect of the two iron sources, increase the stirring speed to 700r / min after the addition is complete, and continue stirring for 48 hours; through the synergistic adaptation of the raw material characteristics, the pH of the system is stabilized at 4.8 (within the range of 4 to 6), and a homogeneous and transparent dark green aqueous solution is obtained without the need for sand milling;

[0116] b. Spray drying: inlet air temperature 230℃, outlet air temperature 99℃, atomization pressure 0.42MPa, feed rate 26mL / min, collect dried powder with a moisture content of 1.1%;

[0117] c. Sintering: Load into a graphite sagger (4kg) and place in a 50L atmosphere furnace; purge with nitrogen 3 times (11 minutes each time); heat to 620℃ at 5℃ / min and hold for 7 hours; nitrogen flow rate 4L / min, positive pressure inside the furnace 0.035MPa;

[0118] d. Grinding and classification: After cooling to room temperature, the air jet mill is used with a grinding pressure of 0.68 MPa, a feeding speed of 6.5 kg / h, and a classifying wheel speed of 4300 r / min;

[0119] e. Sieving and Packaging: Pass the product through a 100-mesh sieve to obtain the finished product.

[0120] (4) Performance test results

[0121] Particle size: D50 = 4.5 μm (measured by laser particle size analyzer);

[0122] XRD characterization: NFPP characteristic diffraction peaks appeared at 2θ=9.7°, 15.9°, 16.6°, 32.1°, and 33.6°, with no impurity peaks;

[0123] Half-cell test: First discharge specific capacity at 0.1C rate is 107.8mAh / g, and capacity retention rate is 97.8% after 500 cycles.

[0124] Comparative Example (Comparison with Traditional Sand Milling Process): To more realistically simulate the extreme operation of the traditional sand milling process and verify the core advantages of this invention—namely, eliminating the need for a physical sand milling step, using a non-water-soluble mixed iron source (ratio 1:0.005–0.5, with synergistic effect), and synergistic pH adjustment based on raw material characteristics—the raw material formulation of Example 2 was used as a benchmark. The raw material was then nano-milled using a traditional sand milling process and directly spray-dried. All other process parameters (pretreatment, weighing, sintering, pulverization and classification, etc.) were completely consistent with Example 2, as detailed below:

[0125] Comparative Example 1: NFPP Preparation Method Including Traditional Sand Milling Process

[0126] (1) Raw material pretreatment and weighing

[0127] It is completely consistent with Example 2 (the types of raw materials, proportions, pretreatment methods, and weighing accuracy are all the same, and the iron source is non-water-soluble ferric phosphate and ferrous oxalate, with a molar ratio of 1:0.1).

[0128] (2) Traditional sanding process

[0129] All pretreated and weighed solid raw materials were mixed with 300g of deionized water and added to a 1L horizontal sand mill (the grinding media were zirconia beads with a particle size of 0.3mm and a filling rate of 70%). The sand mill speed was set to 2500r / min and the grinding was continued for 6 hours. During this period, samples were taken every hour to test the particle size. The final particle size of the material was controlled to be <0.5μm (the ultimate fineness requirement of traditional processes).

[0130] (3) Subsequent process steps

[0131] a. Spray drying: The slurry after sand milling was directly fed into a spray dryer, and the spray drying parameters were exactly the same as in Example 2; the dried powder was collected, with a moisture content of 1.5%;

[0132] b. Sintering, crushing and grading, sieving and packaging: completely consistent with Example 2.

[0133] (4) Performance test results

[0134] Particle size: D50 = 6.1 μm (measured by laser particle size analyzer);

[0135] XRD characterization: NFPP characteristic diffraction peaks appeared at 2θ = 9.8°, 16°, 16.7°, 32.2°, and 33.7°, with no impurity peaks;

[0136] Half-cell test: First discharge specific capacity at 0.1C rate is 106.9 mAh / g (charge-discharge curves are shown below). Figure 3 After 500 cycles, the capacity retention rate was 96.7%.

[0137] Table 1 shows a comparative analysis of the performance and process of the comparative example and Example 2.

[0138] Table 1

[0139]

[0140] Example and Comparative Example Verification Description

[0141] The above three sets of examples cover the full range of iron source mixing ratios (1:0.005 extremely low ratio, 1:0.1 low ratio, and 1:0.45 medium to high ratio). All of them use a non-water-soluble iron phosphate and ferrous oxalate mixed system as the iron source. The two iron sources produce a significant synergistic effect, effectively accelerating the complexation reaction and dissolution process. The complete reaction of raw materials is achieved through the process of "synergistic pH of raw material characteristics-adaptive raw material ratio + sandless milling + process compatible mass production". The sintering temperature can be flexibly adjusted within the range of 550 to 630°C. The initial discharge specific capacity of the products is stable at over 105 mAh / g, and the cycle performance meets the standards.

[0142] The comparison results between Comparative Example 1 and Example 2 show that:

[0143] (1) No obvious performance advantage: Even if the traditional sand milling process reaches 6 hours and the particle size is refined to <0.5μm, the initial discharge specific capacity of the product is 106.9mAh / g, but it is slightly inferior to Example 2 (107.3mAh / g), and the core performance is not significantly improved.

[0144] (2) The disadvantages of traditional processes are prominent: Comparative Example 1 requires the addition of sand milling equipment. Sand milling for 6 hours leads to an increase in total energy consumption of about 20%, and the process complexity increases (it is necessary to monitor particle size and maintain sand milling media). There is also a potential risk of impurities being introduced due to the wear of sand milling media, resulting in high costs for industrial transformation.

[0145] (3) The process of this invention has significant advantages: no sand milling equipment is required, and a commonly used non-water-soluble mixed iron source (with precise and controllable proportions and synergistic effects) is adopted in industrial production. The process is highly compatible with existing production lines and can be adapted without modification. Through "step feeding + chemical complexation + gentle stirring + pH adjustment synergistic with raw material characteristics + synergistic enhancement of iron source", the raw materials are completely dissolved and the system is stable. The specific capacity of the product is stable at more than 105mAh / g, and the sintering temperature is suitable for a wide range of 550 to 630℃. The process is more flexible, energy consumption is lower, cost is more controllable, the batch stability of the product is better, and the industrialization potential is huge.

[0146] The above description is merely a typical embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made based on the scope of the present invention and the content of the specification are within the protection scope of the present invention.

Claims

1. A method for preparing sodium iron pyrophosphate pyrophosphate (NFPP, chemical formula: Na4Fe3(PO4)2P2O7), a polyanionic cathode material that does not require a physical milling process, characterized in that, This method eliminates the need for physical grinding, non-sol-gel methods, and hydrothermal reactions. It utilizes commonly used industrial raw materials, with the iron source being a mixture of insoluble ferric phosphate (FePO4) and ferrous oxalate (FeC2O4·2H2O). It achieves pH-raw material ratio self-adaptation through synergistic raw material characteristics (utilizing the acidic properties of the raw materials to maintain pH stability between 4 and 6), and efficient raw material reaction through stepwise feeding and multi-parameter synergistic control. The sodium and carbon sources must contain one or both of sodium citrate dihydrate and citric acid monohydrate. The specific steps include: (1) Raw material pretreatment: The non-water-soluble solid raw materials in the iron source, sodium source and phosphorus source are screened through a 200-mesh standard sieve. The liquid phosphorus source is tested for purity and then used for later use. The screened solid raw materials are sealed and stored in a dry environment with relative humidity ≤60%. (2) Weighing of raw materials: Calculate the amount of each raw material according to the molar ratio of sodium, iron and phosphorus elements of 4-4.04:2.9-3:4 and the molar ratio of ferric phosphate to ferrous oxalate of 1:0.005-0.5; (3) Raw material dissolution and homogenization: Add deionized water to the stirred reactor. The total mass of raw materials to the mass ratio of deionized water is 1:1 to 4. Start stirring (initial speed 150 to 200 r / min) and heating to stabilize the system temperature at 25 to 55℃. Add materials in the order of "carbon source → sodium source → solid phosphorus source → liquid phosphorus source (if present, add slowly) → iron source" every 30 ± 5 minutes. After all raw materials have been added, adjust the stirring speed to 200 to 1000 r / min and stir for 10 to 48 hours. The pH of the system will naturally stabilize in the range of 4 to 6, and a uniform and transparent dark green aqueous solution will be obtained. (4) Spray drying granulation: Centrifugal or pressure spray dryer is used, with the inlet air temperature set to 180-350℃, the outlet air temperature to 90-110℃, the atomization pressure to 0.3-0.5MPa, and the feeding speed to 20-30mL / min. Dry granules with a moisture content of ≤2.0% are collected. (5) Loading the sagger and sintering: Load the dry powder into the graphite sagger (the loading amount is 1 / 2 to 2 / 3 of the sagger volume), send it into the atmosphere furnace, and purge it with nitrogen gas of ≥99.99% purity 3 times (10±2 minutes each time) to make the oxygen content in the furnace ≤100ppm; raise the temperature to 550 to 630℃ at 5±0.5℃ / min, hold for 6 to 12 hours, and continuously purge with nitrogen gas (flow rate 1 to 10L / min) during the sintering process to maintain a positive pressure of 0.02 to 0.05MPa in the furnace; (6) Airflow milling and classification: After sintering, the material is naturally cooled to room temperature and then fed into an airflow mill (milling pressure 0.6-0.8MPa, feeding speed 5-8kg / h) for milling. The material is then screened by an airflow classifier (classifying wheel speed 3500-4500r / min) to collect intermediate products with particle size D50=2-10μm. (7) Sieving and packaging of finished products: The intermediate product passes through a 100-mesh standard sieve. After passing the test, it is sealed and packaged under dry gas protection and stored in an environment with a temperature of 20-25℃ and a relative humidity of ≤60%.

2. The preparation method according to claim 1, characterized in that, The molar ratio of ferric phosphate to ferrous oxalate in the iron source is 1:0.005 to 0.5, and the total number of moles of iron element meets the requirement of 2.9 to 3 mol.

3. The preparation method according to claim 1, characterized in that, The sodium source is one or a combination of anhydrous sodium dihydrogen phosphate (NaH2PO4), anhydrous disodium hydrogen phosphate (Na2HPO4), sodium citrate dihydrate (Na3C6H5O7·2H2O), sodium carbonate (Na2CO3), and sodium oxalate (Na2C2O4), and the total number of moles of sodium element meets the requirement of 4 to 4.04 mol.

4. The preparation method according to claim 1, characterized in that, The phosphorus source is one or a combination of iron phosphate (FePO4), anhydrous sodium dihydrogen phosphate (NaH2PO4), anhydrous disodium hydrogen phosphate (Na2HPO4), and phosphoric acid (H3PO4, purity ≥85%), and the total number of moles of phosphorus is strictly controlled to be 4 mol.

5. The preparation method according to claim 1, characterized in that, The carbon source is glucose (C6H4O). 12 One or more combinations of O6), citric acid monohydrate (C6H8O7·H2O), and PEG2000 are used, with the amount of carbon source added being 10-45% of the total mass of the iron source.

6. The preparation method according to claim 1, characterized in that, The sodium source and carbon source must contain one or both of sodium citrate dihydrate and citric acid monohydrate.

7. The preparation method according to claim 1, characterized in that, In the raw material dissolution and homogenization step, the volume of the stirred reaction vessel is ≥ 1.5 times the total mass of the raw materials plus the mass of deionized water, and it is equipped with a paddle stirrer (the diameter of the paddle is 1 / 3 to 1 / 2 of the diameter of the vessel body) and a heating device with a temperature control accuracy of ±1℃.

8. The preparation method according to claim 1, characterized in that, The pH-raw material ratio adaptive adjustment is achieved through the synergistic effect of the acidic properties of the raw materials themselves: when the natural pH of the system is >6, the proportion of acidic components is increased; When pH < 4, increase the proportion of alkaline sodium source; if there is a small deviation, add a small amount of the corresponding reagent to ensure that the pH is stable between 4 and 6.

9. The preparation method according to claim 1, characterized in that, During the saggar loading and sintering process, a nitrogen atmosphere is maintained throughout the atmosphere furnace sintering process. The nitrogen flow rate of 1 to 10 L / min is flexibly matched according to the furnace volume (10 to 100 L) and the material loading (1 to 20 kg) to avoid iron oxidation and ensure the electrochemical performance of the product.

10. The preparation method according to claim 1, characterized in that, The resulting product, sodium iron pyrophosphate (Na4Fe(PO4)2P2O7), has a particle size of D50 of 2–10 μm and is suitable for use as a cathode material in sodium-ion batteries.

11. The preparation method according to claim 1, characterized in that, XRD characterization of the finished product: Using Cu Kα rays (λ=1.5406Å), with a scanning range of 10° to 80° and a scanning speed of 5° / min, clear NFPP characteristic diffraction peaks appeared at 2θ=9.8°±0.2°, 16°±0.2°, 16.7°±0.2°, 32.2°±0.2°, and 33.7°±0.2°, and there were no obvious impurity diffraction peaks, proving that the product is pure phase NFPP.

12. The preparation method according to claim 1, characterized in that, The testing method for using the finished product to manufacture sodium-ion half-cells is as follows: using the finished product as the positive electrode active material, it is mixed with conductive carbon black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) is added to prepare a uniform slurry. This slurry is then coated onto aluminum foil and vacuum dried at 80°C for 12 hours to form a positive electrode sheet. Using metallic sodium as the counter electrode, Celgard 2400 as the separator, and propylene carbonate / ethylene carbonate (volume ratio 1:1) in 1 mol / L NaClO4 solution as the electrolyte, CR2032 type button cells are assembled in an argon glove box (water and oxygen content ≤0.1ppm). Charge-discharge tests are conducted at a rate of 0.1C and a voltage range of 2.0–4.0V. The initial discharge specific capacity is ≥105mAh / g, and the capacity retention rate after 500 cycles is >95%.

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